telescope | eyepieces

Understanding Binoculars

2011-04-01T23:57:00.001+08:00

Understanding binoculars is acute afore because affairs one. The -to-be client is faced with a countless of options and will be larboard added abashed if not accustomed with the abstruse aspects of binoculars. The purpose of this commodity is to accustom the amateur with the abstruse aspects of binoculars.

The concrete appearance of binoculars which bang you first, are basal design, axial absorption knob/wheel and diopter.

Basic design: There are two basal and clearly altered types of designs. All binoculars either use "porro prisms" or "roof prisms". The ones application porro prisms are the acceptable architecture area the eye pieces are askance to the barrels, admitting the ones application roof prisms the eye pieces are in band with the cold lenses and accept a glassy design. Porro prism binoculars are, about speaking, beneath big-ticket and accept greater three-dimensional examination effect, admitting roof prism binoculars are added bunched and lighter, but are usually added expensive. Making a roof prism architecture binocular weatherproof is additionally easier and added successful.

Central absorption knob/wheel: The bulge amid the two optical barrels by agency of which you change the focus back attractive at an object. Some binoculars accept a toggle about-face focus in account of a wheel/knob.

Diopter: This is a focus ascendancy bulge (usually at the appropriate eyepiece) that lets you focus one ancillary of the binoculars alone from the other, in acclimation to set the binoculars to board differences in the absorption of your two eyes. Some binoculars accept diopters for every eyepiece.

Technical features:

Magnification/power: A set of abstruse detail imprinted on any brace of binoculars could be article like this: 8x42, or 10x50. The aboriginal cardinal (8, 10) is the deepening number, the "power" of the binoculars. The article is abstract by 8 or 10 times, which agency that it appears to be 8 or 10 times afterpiece than apparent with the naked eye.

Objective lens: The additional cardinal (42, 50) is the bore of the cold lens (in millimeters), i.e. the two big lenses at the advanced of the two barrels. The bigger the cold lens, the added ablaze is captured, consistent in a clearer and brighter image, which is important back acclimated in crumbling ablaze or back absorption on article in the adumbration of a tree. Cold lens aperture is additionally alleged the "aperture" of the binocular.

Is added ability better? This amount is important for compassionate binoculars. It seems accessible that the bigger the magnification, the bigger the binoculars. This is not true. The added able a binocular, the beneath ablaze the angel - which will be a botheration back absorption on article in the adumbration of a timberline or in dim ablaze in general. Added ability additionally has an appulse on acreage of view.

Moreover, added ability is absolutely abortive unless the binoculars are kept altogether still, which is not accessible at all. Some binoculars do accept angel stabilization which electronically reduces movement for steadier viewing, but these are absolute expensive. A deepening of 8 xs is about admired as ideal for general, bold and bird viewing.

Field of appearance (FOV): Addition set of abstruse detail which is imprinted on the binoculars, could be article like this: 367 ft. at 1000 yds. This is the acreage of view, the amplitude of the appearance at the accurate distance. In this case 367 anxiety at 1000 yards. Could be appointed in meters or in degree. Field-of-view is primarily bent by the architecture of the eyepieces, but deepening additionally plays a role.

The avenue pupil: The avenue adherent can be apparent by captivation the binoculars at arm's breadth and attractive through the eyepieces. The pencil of ablaze you see is the avenue pupil. The absolute bore of the avenue adherent is computed by adding the bore of the advanced cold lens (in millimeters) by the deepening of the binocular. So, in the case of a 7x35 binoculars, the bore of the avenue adherent is 5 millimeters. The about accuracy basis (RBI) is an adumbration of angel brightness. It is computed by squaring the avenue pupil. So the RBI of our archetype is 25 (5x5=25). A RBI of 25 or greater is advised acceptable for use in dim light.

Eye relief: For every brace of binoculars, there is an optimal ambit amid your eyes and the eyepieces, which is alleged eye relief. If your eyes are too abutting to or too far from the eyepieces, you can't see the accomplished picture: allotment of it is blacked out. So, if you appear to abrasion eyeglasses, you accept to accomplish abiding the eye abatement is at atomic 15 mm. Except in the case of absolute big-ticket binoculars, acreage of appearance and eye abatement assignment adjoin one another. If the architect increases the one, it is at the amount of the other.

Coating of lenses: The lenses of all binoculars will be coated with anti-reflective coating, which is activated to enhance the affection of the image. Accomplish abiding you accept a "fully multi-coated" brace of binoculars. In the case of roof prism binoculars "phase correcting" blanket is additionally necessary.

Waterproofing: A waterproof archetypal will not alone be beneath acceptable to fog up internally, it will additionally be bigger closed adjoin dust and dirt.

Close focus: Absorption at a ambit is no botheration for any brace of binoculars; absorption at abutting range, however, is a absolutely altered matter. For watching birds or collywobbles you will accept to attending for a brace with a abutting focus ambit of beneath than 4 meters.

The focus speed: If you charge the binoculars for watching agrarian animals, in accurate birds, the acceleration of focus is important. While afterward a bird in flight, you charge to change the focus all the time and if your binoculars do not acquiesce for quick adjustment, you will attempt all the way.

Summary

You should now be accustomed with concepts like "porro prisms" and "roof prisms", "diopter", "magnification" and "objective lens" and "exit pupil" and able-bodied on your way to compassionate binoculars and accessible to buy an affordable and affection brace of binoculars.

Invention of Telescope

2011-03-28T22:44:00.002+08:00

The apparatus of the telescope was a above beforehand in the science of Astronomy, but who invented it? Maybe you anticipate you already apperceive the answer.

Well, what would you say if I told you that you're apparently wrong? After all, it was Galileo Galilei who invented it, right? You ability be afraid by the acknowledgment to that question. Although Galileo Galilei was a abundant astronomer, he didn't ad-lib the telescope.

If not Galileo, again who?

A man called Hans Lipperhey invented the telescope. He was built-in in Wesel, Germany and fabricated his home in Middleburg, allotment of the Zeeland arena in the Netherlands. He was affiliated there in 1594, and became a aborigine in 1602. He was a spectacle-maker by trade.

The Italians developed new glass-making techniques which were alien to the Netherlands in the 1590's. These new techniques helped to accompany about new account and innovations in the glass-making association and bodies started to agreement with altered means to amalgamate lenses.

Where is the proof?

Many added bodies affirmation to accept invented the telescope, but Hans Lipperhey is the alone being accurate to accept activated for a apparent for the device.

Child's play

Legend has it that it wasn't Hans himself, but his accouchement who absolutely invented the telescope while they were playing.

So now you apperceive the adventure of the telescope and how it came to be.

The History of Binoculars and Telescopes

2011-03-20T23:22:00.001+08:00

The conception of so abounding optical instruments nowadays had been traced to the conception of accustomed telescope and binoculars on the aboriginal centuries. Telescopes and binoculars are classified as optical instruments. The attendance of a telescope and a binocular are acutely benign in the assignment of abounding individual. Since both are advised to be optical instruments, they are both acclimated to aggrandize altar that are in a far breadth or location. Telescopes on the added hand, annal object, address and reflect them application arresting radiation. Although they are acclimated alternately, there are advantages of one apparatus from the other.

Before archetype bottomward the roots or history of these two admired optical instruments, let us see some of the aberration amid a telescope and a binocular. If you ask a lot of bodies about affluence of use, abounding of them will accept binoculars. This is because examination with the use of two eyes is added adequate compared to the use of a distinct eye in application a telescope. Bodies can use a binocular for a continued aeon compared to application a telescope. One of the aberration additionally amid the two is the perceived adverse and blush that is improved. For a nearer object, binoculars are actuality acclimated because of the 40% advantage that it allows the user aback it comes to blush and contrast.

There are so abounding optical instruments today that are actuality acclimated in abounding studies. Some of the instruments that scientist use includes camera testing, alignment telescope, telescopes, interferometers, camera analysis pattern, autocollimator and camera software. If we booty a afterpiece attending into the history of telescopes and binoculars, we can see that the aboriginal abstraction to actualize the aboriginal telescope came from the ablaze artist Hans Lippershey. Although his apparatus was not accustomed for a apparent because of poor quality, Galileo reinvented the concept, and he auspiciously acclimated the apparatus he alleged as "looking-glass" in celebratory adorable bodies.

Many bodies believed that the abstraction of a telescope originated from his ablaze cerebration adeptness because of the things that he apparent in application his "looking glass" instrument. With the use of the apparatus that Galileo created, he was able to ascertain the four moons in the planet Jupiter. In accession to his astronomic contribution, he was additionally the acumen why we apperceive that the planet Saturn has rings on it and additionally he apparent the sunspots. Galileo's abstraction of the telescope is aloof like a brace of opera glasses.

Since we accept able thinkers in history, abounding of them approved to actualize their own adaptation of the telescope. For example, the Prince Frederick Sesi of Venice, who bigger the arched and biconcave lenses of the telescope. Johannes Kepler added an added prism abaft the eyepiece. The acclaimed scientist Sir Isaac Newton, makes use of tin and mirrors to accomplish a greater deepening that will aftermath a cogitating telescope way aback 1668. Another arresting astronomer called William Herschel was able to actualize a forty-foot continued telescope that he uses in his work. The huge telescope that he was able to ascertain is additionally actuality acclimated in some observatories nowadays.

The conception of optical instruments anachronous on the aboriginal 1600 era but up to now, the abstraction that those affecting thinkers accept activated in their discoveries are still advised the basal of avant-garde eyes today. Their inventions and concepts account us today. The concepts of light, optics, celebratory far altar and optical-related instruments are now actuality acclimated in so abounding areas of abstraction that includes breakthrough mechanics, nuclear, physics, bio-molecular interactions, atom physics, seismology, claret physics, cilia optics, alien sensing, astronomy, oceanography and astronomy.

The abstraction of eyes and the conception of binoculars and telescopes resulted in the development of adult and high-precision optical instruments. There are abounding acclaimed scientists and inventors alike today that are able to advance optical instruments aloof like the microscope, autocollimator, camera, alignment telescopes and abounding added that are accurate accessible in abounding studies.

Telescopes – Principle Of Operation And Factors That Affect Its Properties

2010-08-26T14:26:00.001+08:00

Telescopes are devices that are used to view the distant objects. They find its use in astronomy and physics. It enables you to view the distant objects by magnifying them. There are many types of telescopes and their prices vary according to the specifications. Many accessories are also available that can be used in conjunction with the telescopes. Small telescopes that are used as toys are also capable of viewing some objects around 50 meters away.

Principle in which the telescope works

The principle in which the telescope works is very simple. There are two lenses that make up the task of viewing the objects that are at a distance. One of the lenses picks up the light from the object viewed and makes it available at a focus point. Another lens picks up the bright light from the focus point and spreads it out to your retina so that you can view. The lens that picks up the light from the object is called the objective lens or primary mirror. The lens that picks up the light from the focal point is called the eyepiece lens.

Factors that affect the viewing of the object

The capability of the telescope to collect the light from the object that is viewed and the capability to enlarge the image are the factors that affect the efficiency of the telescope. The capability to collect light from the object depends on the diameter of the lens or mirror, which is otherwise called the aperture. The larger the aperture the more the light it can collect. Enlarging of an image depends on the combination of the lenses that are used. The eyepiece in the telescope performs the magnification.

Some of the world's largest optical telescopes in operation

We say a telescope to be larger based on the aperture size. Based on this we can say that Keck and Keck II are the largest telescopes in operation with an aperture of 10 meters diameter. The Keck telescope is composed of 36 mirror segments. This is located at Mauna Kea, Hawaii. The next largest is Hobby-Eberly located at Mt. Fowlkes, Texas which has an aperture of 9.2 meters. You can get a list of the largest optical telescopes at here.

Choosing your telescope

The choice of the telescope largely depends on what you want to observe. You can choose compound telescopes and refractor type of telescope for viewing through the urban skies. For the rural skies, you can use compound telescopes and reflectors. They are better than the refractors type of telescopes. Each type has its own advantages and disadvantages. Hence, many people have different telescope for different purposes.

By: David Chandler
Article Source: Article City

The Timeline of the Telescope

2010-07-28T17:45:00.003+08:00

It is actually quite easy to make a timeline with regards to the invention of the telescope as well as how it has evolved over the years. Much has been written about the telescope and good records have been kept with regards to new technologies and inventions. Basically, the telescope timeline looks something like this:

1609 - Galileo first invented the telescope. Though it was crude, it still did the trick and allowed him to look into space for the very first time other than with the naked eye. Galileo's telescope was a reflecting one causing light to bounce off a mirror when looked at through a lens.

Mid-1600's - Johannes Keplar came up with the idea of a refracting telescope that would widen the field of view as well as improve the quality of the image. He did this by changing the shape and the placement of the lenses, but doing this caused little circles of color that would surround bright objects - chromatic aberration.

Late 1600's - As the century began to draw to a close, telescope makers were realizing that with a bigger lens, you could see much more. With a bigger lens, the telescope had to be bigger to accommodate it. Eventually, telescopes were being built that we as long as a hundred feet!

It was at this point in the telescope timeline that Sir Isaac Newton began to change telescope lenses so that there would be no chromatic aberration. He also found a way to add mirrors to improve images without having to make the telescope longer. This appealed to people as Newton's telescope was small but had the same power as the larger ones.

Mid-1800's - The first photographic telescope is introduced. John William Draper found a way to focus the Moon's image on a light-sensitive photographic plate. He used a clockwork device to keep the light in place even as the Earth rotated and the moon moved through the sky. After an exposure of 20 minutes, he had taken the first ever photograph of the moon! After the introduction of the photographic telescope came about, we were able to see the skies up close and personal. And what a great accomplishment!

The early timeline of telescopes shows that many advances were made even before we advanced into what we think of as modern times. Since the 1800's, so many advancements were made in the field of producing telescopes that documenting each and every one would be able to fill up pages and pages of text.

Suffice it to say that now we are graced with telescopes that can see even the minutest parts of Saturn's rings and even realize that Pluto is just a little too small to be a real planet. The timeline of telescopes will continue. All we have to do now is sit back, watch, and document the advancements.

You can visit here for more about telescopes and how this can be a fun and rewarding hobby for the whole family.

By: Elijah Kim
Article Source: Ezine Articles

History of Hubble Space Telescope

2010-04-20T14:08:00.003+08:00

Hubble Space Telescope launched in 1990 and has been an invaluable source of information to astronomers and scientists throughout the world. By it orbits its way around the earth once every 95 minutes, it continues to gather more knowledge about not only our galaxy but the ones beyond as well.

A timeline of Hubble Space Telescope History:

1924 - Edwin Hubble looked up into the night sky to disprove the theory of a single galaxy. He discovered that the universe was filled with other galaxies rather than just gasses and dust. He prove that our universe was continuing to grow and expand. However, he did not have the suitable of the tools to use, so his knowledge was still somewhat limited although his vision was far-reaching.

1924-1983 - the concept of a Large Space Telescope (LST) was conceived, designed, revised, developed and implemented. To honor the man who started it all, in 1985, the LST was renamed the Hubble Space Telescope.

1990 - The Hubble Space Telescope was sent into orbit, after delays with its launch, due to conflicts with the launch of the space shuttle.

1994 - the telescope took pictures of a comet collision, and detailed photos of Pluto, as well as giving us a greater knowledge of Neptune and Uranus.

1995 - the Hubble took pictures of the “birth” of a star as it developed from interstellar clouds.

1996 - Photos from the Hubble Space Telescope show that quasars are actually nuclei which illuminate when a black hole uses energies from surrounding gases and stars.

1997 - Black holes are bigger than the sun, proved by the picture taken by the Hubble.

1998 - The Hubble take the most detailed pictures of the planets in our solar system.

2004 - The Hubble Space Telescope was able to document in pictures how, when, and why stars die and using the Hubble Ultra Deep Field technology, to take pictures of the expanding universe unlike any that had previously been taken. It also took pictures of Mars when it was closer to Earth than it had been in 60,000 years.

2005 — Took pictures of a comet with a projected piece of equipment from the Hubble Space Telescope.

Future Developments—The Hubble Space Telescope’s mission is scheduled to end with this decade. Astronauts will go up, make repairs and assess the future usefulness of this tool in deep space discovery and a decision will be made about whether it should be discontinued or remain in service. But, no matter what decision is made, this telescope has been an amazing resource for a broader understanding of space and its limitless possibilities. Thank you, Mr. Hubble.

By: Guy Scott
Article Source: Article City

Telescope Making

2009-10-06T01:05:00.001+08:00

Let's learn how to make your telescope by yourself. Make it easier!

A description and demonstration of how to ake a refrractive telescope. Its 2009 , International Year of Astronomy (IYA 2009); lets be galileos today.

Let's discover the universe together..

History Of Telescopes - A Look At Galileo And The Galileo Galilei Telescope

2009-10-06T00:44:00.004+08:00

The first inhabitants of the world were compelled to accommodate their acts to the daily and annual alternations of light and darkness and of heat and cold. In history there are only a few distinguished men who made such a big contribution to astronomy, one of them was Galileo Galilei and his work with the telescope.

When we look at today's telescopes we mainly are working with either Galileo's telescope or Newton's telescope. These men made such a big impact in astronomy and telescopes, that we still use the same types of telescopes invented by these men!

Galileo or his full name Galileo Galilei was an Italian physicist and astronomer. Galileo was born in Pisa on 15 February 1564 and lived 78 years till 1642 when he passed away. In this time he made such advancement in astronomy, that we still know the name Galileo.

Galileo not only made advancements in astronomy, he is also noted with the invention of the thermometer! Galileo Galilei telescope was the first to make observations of the Moon and its crescents, the Sun, planets and stars.

Most of Galileo's time and energy was in mathematics and that is what he spent most of his time. In fact he became professor of mathematics at the University of Pisa in 1589. What made Galileo change from mathematics and physics to a big interest in astronomy was when he heard about the invention of the telescope in Holland in 1609.
From this date, Galileo immediately focused his attention on building his own telescope. Galileo Galilei telescope was put together and he immediately started viewing the heavens. He published his findings in Sidereus Nuncius. The Starry Messenger one year later in 1610. The book was such a sensation throughout Europe that it made Galileo and his telescope famous.

Galileo Galilei telescope and his findings did not always go so rosy however. At that time the common idea held by the church was that the universe revolved around the Earth! Copernicus had a new theory, the Copernican theory that said that the universe does not revolve around the Earth. Galileo held this belief as well, and it caused major outrage with the church. The church declared the view heretical and Galileo was instructed to abandon the Copernican theory.

In 1632 a book was published called Dialogue Concerning The Two Chief World Systems. In the book the Galileo Galilei telescope was used to make the evidence of how the view adopted by the church was wrong. It resulted to Galileo being sentenced to life imprisonment. The sentence was commuted to house arrest for the rest of his life.

Galileo was a great inventor and has given the world some of the greatest inventions. In a Galileo Galilei telescope, the light enters through a tube starting with a convex objective lens. The light focuses even more with a concave lens in the eyepiece, before meeting the eye with a magnified and upright image.

Galileo Galilei telescope is one which we can never forget. It was an invention which showed at his time a planet (Saturn), one which has ears! Within 2 years of the invention of Galileo's telescope, he gave us fairly accurate information on the orbits of 4 of Jupiter's satellites. Galileo also gave us great information on the Sunspots on the sun.

Article Source: EzineArticles
By: Koz Huseyin

Galileo's Telescope

2009-09-06T10:46:00.001+08:00

The narrative on Galileo's telescope is well known and retold many times. It was in the summer of 1609 that Galileo heard of news that some Dutch opticians had come up with some kind of optical instrument that can amplify objects and made them closer. The news was by then very well-known when Galileo was told of it.

The Venetian government was alert to it and was considering buying over the instrument from a foreigner until Galileo's friend Paolo Sarpi advised them to delay purchasing as he was positive that Galileo could match or even better it.

Galileo was a great experimentalist and then he devoted himself to improve the instrument and he came up with a more powerful instrument that had greater than before magnifying power. This was done through his understanding of improved magnification through a weak convex lens and a strong concave lens. At that time no optician was able to manufacture a much higher magnification than three and he has to grind the lenses himself.

It was then in the autumn of 1609 and as curiosity taken over him, he aimed the refined instrument towards the sky. He was then astounded by the power of the new device. From the observation, he figured out that the earth was not the center of the universe. It was opposite to what the bible was about at that times and the church stated publicly that Galileo was wrong. Galileo disputed that the interpreter of the bible might be wrong but he was accused of deviation. Though he was found innocent, he was banned from spreading the Copernican belief system.

Copernican belief system was the set of guidelines that Earth is not the center of the universe but revolve round the sun. Galileo went on to apply his knowledge of the refined instrument to other areas in particular the study on Jupiter and the ocean's tides. He persisted with the Copernican belief system even though he was not allowed to perpetuate. As a result he was placed on house arrest until his death.

It was from there that he unearthed even more sightings. The spots on the surface of the sun, rings that surround Saturn and the number of phases that Venus goes through were a result of his observations. All these were published in "The Starry Messenger" in 1610. That caused quite a stir back then just to imagine that the earth was round and not flat as thought earlier.

Galileo was the early contributor to the refined, contemporary telescope that we known today. Without his inquisitiveness and observations, our understanding and knowledge of the modern universe will not be as complete.

By: By Jhye Jhyiong
Article Source: EzineArticles

Homemade Telescope

2009-09-01T07:43:00.004+08:00

This video is about how to make your telescope. It's using home items. Pretty cool!
But it just basic..
Maybe you can make it for your family or want to know more about telescope..
Watch it!

Tag: homemade, telescope, homemade telescope

Choosing the Telescope Binoculars For Exceptional Stargazing

2009-08-04T10:47:00.003+08:00

Astronomy or telescope binoculars are quite different than those used for, say bird watching. There is not a "best" pair of binoculars, such as those rated by reviewers. But it is very important that you choose the best pair of binoculars for your specific needs. Binoculars automatically provide you with right-side-up representations as well as providing you with a wider field of scrutiny.

Aperture

When considering a pair of astronomy binoculars you should first understand aperture. It deals with the sizes of the front part of the lens on the binoculars. The bigger the lens, the more light will be collected, and since many astronomical subjects are murky, increased light will allow you to see them much better. You can tell what the aperture is when looking at binoculars since the numbers printed on the binoculars tell you exactly the aperture size.

Thus, when you see a pair of binoculars that proclaims that they are 7X50's means they have a 50mm size aperture. 25X100 size for handheld telescope binoculars would be more than ideal! Any binoculars larger than 25X100 will require a tripod, as they would be too cumbersome to be handheld. Aperture is also referred to as the objective lens diameter and is always the last number printed on the binoculars themselves.

Magnification

The first number printed on the binoculars tells you the magnification. For stargazing you should look for binoculars showing at least 7 times, but no more than 10 times, or again you'll need a tripod for ease of handling.

Exit Pupil

This refers to the width of the light beam that leaves or exits the eyepiece. Figuring this number is quite simple as you simply divide the aperture number by the magnification number. Hence, a 10X50 pair of binoculars would have an exit pupil size of 5 mm.

Because the human eye's average pupil size at night, which is when you'll be using them, is over 7mm, in order for your telescope binoculars to be comfortable when using them you should look for at least a 7mm exit pupil.

Prisms

Binoculars use prisms inside them to make the objects being viewed right side up. There are two different kinds available-roof and Porro. Roof prisms are more compact and may exhibit dimmer images. They are also more expensive. Porro prisms, on the other hand, use differently shaped prisms, are lower priced, but tend to be heavier and bulkier. For telescope binoculars weight and bulk need to be traded off for brighter images.

Conclusion

This article recommended that you purchase binoculars that you find comfortable to use for what you intend to use them for.

After you purchase your telescope binoculars enjoy not only the moon and its lunar mountains, but multiple stars, asteroids, comets, open star clusters, and wide binocular star fields.

By Arnold J. Tadjman
Article Source: EzineArticles.com

Tag: telescope, binocular, stargazing, astronomy, magnification, prism, aperture, moon, telescope binocular, open star cluster

Backyard Astronomy Without a Telescope

2009-05-09T00:46:00.002+08:00

Are you looking to do backyard astronomy? You maybe stuck in a problem. No telescope and you still want to do backyard astronomy! In this article, you will discover some astronomy experiments you can do without the need for a telescope.

The first thing we see, when we look up at the sky, is lots of shinning points of light. These points of light seem to make up patterns, and these patterns are what we call constellations.

There are 88 in total that are visible from the Earth. These constellations have such an old meaning to us, that we still have birth signs. Your birth sign is one of those 88 constellations.

Constellations are made up of a group of objects in space. This makes looking at constellations, one of the greatest things to do. Imagine, knowing where these 88 constellations are. You could literally take any rough coordinate for a star or object in the sky, and manage to navigate to it, much more easily. And all this because you learned about the constellations.

Many myths have been conjured up with the constellations. From the great hunter, to the story of the scorpion, looking at the constellations teaches us much more than simply knowing the layout of space!

Many early astronomers started with no tools at all, apart from using what they had - their own kind of telescope, their eyes! And still managed to invest a lifetime into astronomy.

A telescope still does help, and once you do have a telescope, you likely will prefer the telescope than simply looking up at constellations. However, there is always that fascination with constellations.

A group of astronomers all put in their life research into space to find those constellations which many today take for granted. These constellations have helped countless navigators at sea, be able to do their voyages.

Now you can partake in the same essence, by learning about the constellations. There is a lot to learn about the constellations. Such information that can be learned from constellations and backyard astronomy is the shape, the size, the amount of stars or objects that make up the constellation.

You could also look at when these objects appear in the sky, and when they are no longer there. It is easy to look up this information in a book, but when you start doing proper backyard astronomy, and find out these truths for yourself. Suddenly you have a strong sense of satisfaction, as you now know that you are really taking part in science.

A good idea is to keep a notebook. Draw pictures, write down your findings. Over time this can be a great way to see your progress in backyard astronomy.

Here are some telescope resources that can help you find and buy a telescope:
* backyard astronomy

By Koz Huseyin
Article Source: EzineArticles

Types of Telescopes and How to Buy One

2009-04-21T12:28:00.003+08:00

Telescopes are instruments used to observe distant objects. It makes distant object appear nearer and magnified.

Out of several hundred models of telescopes it is really a challenge to buy one that suits the need of a buyer. Here are few points that help one choose the one best fulfills the usage of a buyer.

There are two basic types of Telescopes:

1. The Reflector Telescope: This type is best suitable for sky based observation as it does not give distorted images. If you are an amateur astronomer choose a reflector telescope. Different price ranges are available and the costlier models allow us to observe the extreme reaches of the universe.

2. The Refractor Telescope: This type shows some distortion due to different colour bending into the lens (as two lenses concave and convex are used). Going in for costlier ones will put off this complaint. Due to this distortion reason it is best for earth based viewing. And if you are traveler who move around with your backpacks and telescope then choose a smaller, handy light weight one that is compact to carry.

In spite of any brand, model or pricing it is always important that you go in for a wider objective telescope for a clearer and better magnification. As in optics how much high you pay high results and features will be offered to you.

The other few guidelines of maintenance:

• Get maximum number of accessories that come along with a telescope.
• Learn all the features available in a model and try using them.
• Always keep the telescope in its case safely.
• Dust and clean the telescope after every use.
• Do not ever try to service or repair it on your own and always seek for a well trained technician's help for a good maintenance of your telescope.
• Always handle them with good care as rough handling will cause misalignment of the lens which leads to aberration of the images.

By Victor Thomas
Article Source: http://EzineArticles.com/?expert=Victor_Thomas

How To Use Your Telescope To Bring The Unseen Into View

2009-04-11T16:20:00.000+08:00

Telescopes can help you to see far off objects. The distance is determined by the type and quality of your telescope. Of course, a toy store telescope will not be able to put into view the same objects as the Hubble Telescope can. Somewhere in the middle is a modest, but good-working telescope for the amateur astronomer.

To see how this viewing tool works, you must understand something about the eye, particularly about the retina. There will always be things you cannot see from far away. You must ask yourself why you cannot see them. There are two main reasons.

One reason you have trouble seeing objects that are far from you is that not enough light from the object reaches your eye. When the item is shrouded in darkness, it is hard to make out. The other reason is that the object takes up so little space on your retina that it is impossible to get a clear picture of it.

Therefore, the goals of the telescope are to focus more light on the retina, and to make a larger image of the object strike the retina. That way, it will stand out in a way that will let you examine the item clearly. Two main types of telescopes have been made to accomplish these purposes.

The refractor telescope is one type, and it uses an objective lens. The other type is a reflector telescope, which uses a primary mirror. In either case, the lens or mirror brings together plenty of light from the faraway object you are trying to study. It further focuses that light and the image it creates into a sharp point.

That is just one part of the process. If that was all that the telescope did, you would not be able to see anything more than a piercing stream of light. However, an eyepiece lens will solve this problem by magnifying this point of light. It will then be spread out over a much larger portion of the retina than it originally had been. This is how the image goes from being difficult to spot to seeming big enough to study easily.

There are a couple of properties that a telescope has that can help you see into the distance. The aperture is one. This is the diameter of the lens or mirror. A lens or mirror with a larger aperture is likely to gather more light and give you a brighter, clearer image.

Magnification allows the telescope to take the focused image and enlarge it. You can use different eyepieces on any telescope to get more or less powerful magnification. This gives you the freedom to change your telescope to suit your needs. At the same time, it does not affect the basic usefulness of your telescope.

By knowing how a telescope works, you can be aware of what parts might need to be replaced on your telescope if the time comes. You can also make it a part of your study to learn the wonders of man's explorations of the night sky.

Gregg Hall is an author living with his 18 year old son in Jensen Beach, Florida. Find more about astronomy as well as telescopes at here.

By Gregg Hall
Article Source: http://EzineArticles.com/?expert=Gregg_Hall

Hubble Telescope

2009-04-07T00:29:00.000+08:00

Telescopes are instruments used for viewing the objects at a distance. They are mainly used for viewing the astronomical objects. They find application in non-astronomical areas also. The working is with the help of two lenses. These lenses will work in a co-ordinate manner to give the exact image in a magnified form. There are different types of telescopes greatly used for varied purposes.

These telescopes vary in the structure and also the working. The basic types of telescopes that are available is the optical telescope and the radio telescope. There are still different types like, the Galileo telescope and the Hubble telescope.

Hubble telescope is quite a familiar term. It is used to orbit round the earth. The telescope is used to get a more clear view of the external atmosphere of the earth.

This gives images that are not blurred. This makes it quite unique among the other types of telescopes. Because of this they have an important place in the astronomical area. The telescope has been serving the humanity with the clear images for a long time.

The Hubble telescope photographs have proved to be very useful to prove the mysteries that existed in the field of astronomy. It helped to prove many unsolved issues in the solar system. The pictures taken by the Hubble telescope was not that clear in the earlier stages. Now it has become clearer with the advent of the technology.

The distances between the stars were become more accurate after the Hubble started sending the pictures. The estimated calculation was replaced with a more proven data. The galaxies that were farther were viewed in a closer view with the help of the pictures from Hubble telescope.

The pictures taken by the telescope is first stored in an archive. Later it is being transmitted to the earth. This will help the users to use it in a clearer manner. The transmitted images are clearer and free of any issues. This can get a vivid picture of what all are happening in the world beyond the reach of human eyes.

The use of the telescope is open to anyone. There will be a ratio in the time available to the users. This can vary in a range also. There are no restrictions based on any barriers to use the telescope. This will help all types of users to view the astronomical objects at any time. The use is very simple and there will be instructions that can help a novice user to handle the vision properly.

The Hubble telescope finds great use in the scientific applications. They helped in proving various unsolved truths of the astronomy in a more reliable manner. The pictures are clearer and brighter than any other telescopes in the earth. There is no scattering of the light and there is no blurred image produced.

By Steve Hill
Article Source: http://EzineArticles.com/?expert=Steve_Hill

A Telescope Buying Guide For Beginners

2009-03-31T02:49:00.000+08:00

Buying a telescope is a daunting task for a newcomer. It all depends on your astronomy goals and careers. There is no perfect one which suits all observers in all conditions. You have to look for the features you want in your telescope and select the best one's according to your requirement.

Selecting the proper type

• The refractor type telescopes best suit for watching moon and major planets. Refractor telescopes are long & thin, and known for their sharp, detailed and contrasty images. They collect light through multi-element lenses. If you are just a starter then a small, quality achromatic refractor of 60 to 90 mm aperture would be a good one. The best thing about a refractor telescope is that they are inexpensive, portable and almost maintenance free. A refractor telescope is also useful when you will be mostly observing from city or the surrounding areas where the night skies are lightly polluted.

• Reflector telescopes are also known as Newtonian telescopes. They are good for planetary as well as deep-sky viewing. However Newtonian telescopes are more fragile and need more maintenance than others. These telescopes collect light with a curved, concave mirror and with the help of their large apertures, they show fine,
highly-resolved images. The reflector scopes are not suitable for terrestrial viewing because they produce an upside-down image.

• Catadioptrics use both lenses and mirrors to collect and focus the incoming light. They are also called compound telescopes. Catadioptrics scopes are considered the most versatile telescopes and gives great all-around performance. They use a large aperture in very compact tubes. They show magnificent images of the moon, planets and faint deep-sky objects, when viewed in dark skies away from urban areas. These scopes are best suited for astrophotography. Compared to other two, these scopes have a wide range of accessories available. They can be entirely computer controlled.

Factors affecting the performance of a telescope

• Aperture: Telescopes collect light from distant objects and focus it to produce images. The light collecting capacity of a telescope is the most important feature. It is the aperture of scope (diameter of mirror or lens) that is responsible for gathering light. Larger the aperture, the more light gathered, the more you'll see.

• Telescope Mounts: There are three basic mounts for telescopes altazimuth, Dobsonian, or equatorial. Altazimuth is the simplest type of mount, providing up-down, left-right motions. It is mainly recommended for terrestrial viewing and casual stargazing. The Dobsonian mount was basically designed for easy maneuvering of large reflectors of more than six inches. It is a boxy altaz-type mount sitting close to the ground. Equatorial mounts are designed for the purpose of astronomical viewing. These mounts are more expensive and complicated than the altazimuth mounts. With the help of these type of mounts users can track or follow the motion of celestial objects through the sky with a single manual hand control.

• Magnification: Magnification should never top the priority for buying a telescope. The quality if image degrades with magnification. Practically 300X is maximum magnification for good quality images. Telescope's magnification is also known as its power and it is adjusted by changing eyepieces. Ideally there should have been three eyepieces for the magnification of a scope: one low, one medium and one high. Lower powers of 30 - 50X are recommended for observing galaxies, star clusters and nebulae as they are spread over a wide area of sky. For observing the rings of Saturn, Jupiter, studying craters and valleys of the Moon's surface medium power of 80 - 100X are advised. Higher powers of 150 - 200X allow the astronomers to observe mountain peaks and fine lunar detail, the surface features of Mars.

By Mike Kirsten
Article Source: http://EzineArticles.com/?expert=Mike_Kirsten

The Vivitar 50x 100x Refractor Telescope

2009-03-25T18:39:00.000+08:00

The Vivitar 50x 100x Refractor Telescope makes a great companion at sporting events, under the night sky, or on a bird watching trek. This article will talk about the MPN, key features and some miscellaneous data.

The MPN (manufacturer's part number) is explained by first talking about what a part number is exactly. A part number is a unique identifier of a part used in a particular industry. Its purpose is to simplify referencing to that part. A part number unambiguously defines a part within a single manufacturer. This unambiguous definition is called the MPN. The Vivitar 50x 100x refractor telescope's MPN is 1607225.

The Vivitar 50x 100x refractor telescope's key features are the finderscope (optical), max useful magnification (x 100) and optical design (refractor).

The Vivitar telescope's finderscope is a small auxiliary telescope mounted atop the main astronomical telescope and pointed in the same direction. The finderscope usually has a much smaller magnification than the main telescope can provide and therefore can see more of the sky. This helps in locating the desired astronomical object in the night sky. Some finderscopes have cross hairs to mark exactly where the main telescope is looking. The vivitar's finderscope is optical vs digital with a 3x magnification.

The Vivitar telescope's max useful magnification is x100. What this actually means is far too complicated for this article but you can Google "What does "magnification" actually mean?" to find out more.

The Vivitar 50x 100x telescope's optical design is refractor. A refracting or refractor telescope is a dioptric telescope that uses a lens as its objective to form an image. The refracting telescope design was originally used in spy glasses and astronomical telescopes but is also used in other devices such as binoculars and long or telephoto camera lenses.

If you are interested in getting more info on the Vivitar telescopes, such as pictures, just click on vivitar telescope now.

By Olan Butler
Article Source: http://EzineArticles.com/?expert=Olan_Butler

Telescopes For Sale For Budding Astronomers

2009-03-10T16:59:00.000+08:00

Tips for Finding the Right Astronomy Telescope for You

Children and adults everywhere find the night sky fascinating and love to make wishes on the stars they see. As children get older, they begin to learn about what is in the night sky and many develop an interest in astronomy.

Astronomy is a word from the Greek language. Astro, the first part of the word, comes from the Greek word for the star shape and also refers to outer space. The last part of the word, onomy, is Greek for "the study of". So from the original Greek, astronomy means study of the star or outer space.

Novices and experienced astronomers need one main tool to learn about and enjoy the night sky: an astronomy telescope. There are many different kinds of astronomy telescopes. You need to choose carefully and consider some important aspects of the telescope, such as the size of the lens and the sturdiness of the telescope stand, when you are looking to buy your first telescope.

The Importance of the Lens Diameter

Certain aspects of your new astronomy telescope will either make it enjoyable or leave you frustrated. Lens diameter is one of these aspects. Forget about magnification; the size of the lens of the telescope is more important. The larger the lens diameter, the more light it lets into the telescope and that affects how well you can see the things you are trying to look at in the night sky. The brighter the light, the clearer the images will be.

Choosing a Good Astronomy Telescope Stand

You will want to give a lot of thought to the type of stand you mount your new telescope to so that you get the most efficient use out of your telescope. A good tripod stand is the way to go. You want to choose a stand that will keep the telescope still so you get the best views of the night sky. Any movement at all will make the images you see blurry and cause you frustration.

Where and How to Shop for an Astronomy Telescope

You need to find out what your options are and know what the different telescopes offer before choosing one. One of the easiest ways to gather information about telescopes is by looking online. You should try and find out what the features are that are offered on each kind of telescope, how much they cost and what reviewers think about the different brands of telescopes.

One way to choose a good astronomy telescope is to try some of your potential telescopes out. If there is an astronomy club in your local area, you might be able to join and meet people who share your hobby. Then, you can try a variety of different telescopes to see which ones work for you.

You can also get a lot of useful information to help you choose an astronomy telescope by talking to people who are in astronomy. Your friends and family members who have astronomy telescopes can tell you what they like and dislike about theirs.

If you have friends or family involved in astronomy, you might ask them to let you know when they are replacing their telescopes so you can possibly buy their old one from them.

If you are looking to take your astronomy to the next level and learn more about how to buy a telescope drop by the TelescopesCafe.

By Bo Collins
Article Source: http://EzineArticles.com/?expert=Bo_Collins

History of the Telescope

2009-03-02T19:07:00.000+08:00

When the Phoenicians were cooking on sand, they discovered glass around 3500 BC, but it took about 5,000 years more for glass to be moulded and shaped into lens to make the first telescope. A spectacle maker was probably associated to assemble the first telescope. Hans Lippershey (1570-1619) of Holland is credited with the invention, but there is an element of uncertainty lurking on the discoverer of Telescope. Lippershey though was the first to invent the new device now widely known as Telescope.

Historically, the telescope was introduced to astronomy in 1609 by the legendary Italian scientist Galileo Galilee, who became the first scientist to observe the craters of the moon.

Galileo went further to discover sunspots, the rings of Saturn and the four large moons of Jupiter through the telescope. Galileo's telescope was akin to a pair of opera glasses. In Galileo's telescope, an arrangement of glass lenses was used to magnify objects. This arrangement provided limited degree of magnification up to 30 times for Galileo and a highly narrow scope of view. Galileo was not able to see no more than a quarter of the moon's face without repositioning a part of telescope. In the year 1704, Sir Issac Newton propagated a new concept in telescope design whereby instead of glass lenses, a curved mirror was made use of to collect light and reflect it back to a point of focus.

This reflecting mirror functions like a light-collecting bucket, the larger the bucket, the more amount of light it can collect. The reflector telescope that Newton designed magnified objects millions of times far beyond what could ever be achieved with the help of a lens.
The notion of a segmented mirror dates back to the 19th century, but experiments with it had been fewer and insignificant. Many astronomers doubted its feasibility or in other words practicability of application. It was left for the Keck Telescope to take the technology forward and bring into existence this innovative form of design.

The Short Telescope, however, was designed by the Scottish Instrument maker James Short in the year 1740. An optician and astronomer, James Short invented the first ideal parabolic and elliptic, distortion less mirror perfect for reflecting telescopes.

Visit Telescope reviews exclusive telescope site for expert reviews on Tasco, Seben, Meade and Astronomical Telescopes. You can read unbaised reviews and find best selling telescopes in UK.

By Victor Thomas
Article Source: http://EzineArticles.com/?expert=Victor_Thomas

Refracting Telescope Compared With Reflecting Telescopes

2009-02-23T01:18:00.000+08:00

Are you thinking of buying a telescope? Perhaps you are wondering - what are the differences between refracting telescopes and reflecting telescopes, and which are better refracting telescopes or reflecting telescopes. As you read this article, you will discover more about which is the best telescope to purchase.

There are many different telescopes for sale. These different telescopes, however, fall into mainly 2 categories. The first is refracting telescopes, which is the one that reminds us most of Galileo's telescope. The other is reflecting telescopes, which is commonly attributed with Isaac Newton.

Both refracting telescopes and reflecting telescopes have benefits, advantages and disadvantages. The key element here is that your needs are the main focus, and as you read this article, you will discover which type of telescope is best for your needs in backyard astronomy.

- Information About Refracting Telescopes
The design of the refracting telescope is also the type you find on binoculars, though in pairs! How a refracting telescope works, is that there is a lens at the front of the optical tube assembly.

Light enters the optical tube assembly, and goes right to the lenses at the back of the telescope. And finally meets the eye, where an image of Saturn, perhaps can be seen.

A refracting telescope is good, in that it is enclosed. The simple design, allows it to be maintenance free, for a number of years. The simple design also makes it easy to use, which is great as a telescope for children.

- Information About Reflecting Telescopes
How reflecting telescopes work, is that light enters the optical tube assembly, and goes straight to the back of the telescope, where it meets a big mirror. This mirror then reflects the light back up the tube.

Now, the light meets a secondary mirror, which is near to the top of the telescope. As the light bounces, it enters the lenses, and finally meets the eye.

Reflector telescopes are great in that they offer good price verses performance ratio. Reflecting telescopes can be much larger than refracting telescopes.

- Refracting Telescopes Compared With Reflecting Telescopes
Realize however, that the refracting telescopes are not cheap. Compared with reflecting telescopes they can be more expensive for similar performance.

For viewing the planets, buying a refracting telescope may be the best way to go, however, if you desire to see more of the heavens, there is nothing that compares, as with a reflecting telescopes. Though you may be able to get similar performance with refracting telescopes, you would need to invest a much bigger investment, which brings back the question - couldn't the investment in a reflecting telescope be much better?

Here are some telescope resources that can help you find and buy a telescope:

- Meade refracting telescopes

- Refractor telescopes for sale

- Buying astronomy binoculars

By Koz Huseyin
Article Source: http://EzineArticles.com/?expert=Koz_Huseyin

What is a Refracting Telescope?

2009-02-02T01:04:00.000+08:00

A refracting telescope uses a lens as its objective to form an image. The refracting telescope was designed for used in a spy glass, but is also used in other devices such as binoculars and telephoto camera lenses.

There are two principles to a refracting telescope, an objective lens and an eyepiece. These two principles gather more light for the human eye and helps to focus and present it in a brighter, clearer, and magnified virtual image. A refractive telescope bends light to cause parallel light rays to converge at a focal point.

Galilean Telescopes are refracting telescopes. Galileo came up with the design in 1608 and uses a convex lens and a concave eyepiece lens. The Galilean telescope magnifies objects up to thirty times. The Galilean telescope was the first telescope to see the planet Jupiter and its moons.

The Keplerian Telescope, invent by Johannes Kepler in 1611 improves upon Galileo's design. The Keplerian Telescope uses a convex lens in opposition to Galileo's concave lens. This allows for a broader field of view and greater eye relief. However, the view is introverted.

An achromatic refractor is a refracting lens which was invented in 1733. The design over came the need for very long focal lengths and used two pieces of glass with different dispersion to limit the effects of chromatic and spherical aberration. Each side of each piece of glass is ground and polished, at which point the two pieces of glass are assembled together. Achromatic lenses bring two wavelengths together and focus them on the same plane.

Alex Sutton has worked in the telescopes profession for nearly 11 years. For more information please visit telescopes

By Alexander Sutton
Article Source: http://EzineArticles.com/?expert=Alexander_Sutton

Telescope Shopping Tips From an Experienced Astronomer

2009-01-13T12:57:00.000+08:00

Telescopes are popular gifts for Christmas, birthdays or other occasions... but buyer beware! Many people live to regret their telescope purchasing decisions, either because they bought a cheap telescope that under performs, or because they paid far too much for a telescope they rarely use. But armed with the right advice, smart shoppers can buy a good quality telescope for just a few hundred dollars.

First, whatever you do, don't buy a telescope from a department store or drug store! The telescopes you'll find there, while cheap, are typically of very low quality. They're appropriate for a child in elementary school: If the child breaks it, you're out only a modest amount of money. But if you're buying for a teenager or an adult, buy from a store that specializes in telescopes, or buy online. Good telescope brand names include Antares, Orion, Celestron, and Meade.

While there are several types of telescopes, most beginners would do well to purchase what is called a "Dobsonian" telescope. Dobsonian telescopes (or "Dobs") are relatively low-cost, yet high-quality telescopes. Generally speaking, they do not have any high-tech, computerized gadgets on them. Yet their optics are just as good as the overwhelming majority of computerized telescopes that cost thousands of dollars. Once you gain some experience using a Dob -- and should you eventually decide to make astronomy into a serious hobby -- you might one day purchase a more expensive "Schmidt-Cassegrain" or "apochromatic refracting telescope." But start with a Dob!

Astronomers compare telescopes primarily by the diameter of their main ("primary") mirrors. This is referred to as the "aperture" of the telescope. You'll want to get a Dob with an aperture of either 6 inches (150 mm), 8 inches (203 mm), or 10 inches (254 mm).

If you can afford it, purchase either an 8 or 10 inch version: The larger the diameter of the mirror, the easier it is for you to see dim objects (like galaxies and nebulae) in the night sky. Prices range from roughly $230 USD for 6-inch apertures to $500 USD for 10-inch apertures. The telescope should come with two or three eyepieces: If it doesn't, shop somewhere else. You'll use the eyepieces to control the magnification of the telescope. For example, with one eyepiece in the telescope, you can see the entire surface of the Moon. But with another eyepiece, you can zoom in on a crater.

Also, consider purchasing the following accessories:

Nightwatch: A Practical Guide to Viewing the Universe -- a really good introductory book by author Terence Dickinson;
A subscription to Astronomy magazine -- a monthly publication with beautiful photos, a guide to the night sky, product reviews, and the latest astronomy news;
Some astronomy software -- such as Name A Star Live's Virtual Planetarium software;
A planisphere -- Use this simple, lightweight, handheld device to identify constellations and major stars in the night sky;
An inexpensive pair of binoculars -- These are good for helping you navigate around the night sky as you search for a galaxy, nebula, or star to observe through your telescope; and
A TELRAD -- Most telescopes come with a very small telescope, called a "finderscope," mounted on top of the main telescope. As the name implies, a finderscope helps you find the astronomical object you're looking for through your main telescope. But most astronomers prefer to use a TELRAD -- a battery-powered device that projects a red bullseye in the night sky. It's much easier to aim a telescope with a TELRAD than with a finderscope.

These tools will help you learn the constellations, and otherwise help you get started in astronomy. Also, consider joining a local astronomy club where you can gain experience using various types of telescopes, and get help learning the night sky.

Happy stargazing!

Richard Pickering is an astronomer for Name A Star Live, which lets you express your feelings in a romantic, meaningful way by 'naming a star' for a loved one. While no star-naming service can change the scientific designations of stars, only Name A Star Live makes it real by providing you: Virtual Planetarium astronomy software; an opportunity to view your star live using an online telescope; and the launch of your star name into space!

By Richard Pickering
Article Source: http://EzineArticles.com/?expert=Richard_Pickering

How Telescopes Work and the Different Types of Telescopes

2009-01-06T14:03:00.000+08:00

A telescope can help us in looking at far-away objects of the infinite space out there in our universe. Hubble telescope is one such huge telescope that offers us a look at diverse parts of the universe aside from ours. Telescopes are essentially of the reflecting and refracting types and the magnification make far off objects noticeable.

Astronomy as a hobby is delightful as the discovery of the unknown always bewilder men. The collection of stars in our vast outer space is enough to enthrall a child and how a telescopes work will set off the imagination of any knowledge's seekers. Binocular is a good way to arouse the curiosity of a child who might one day be the next Galileo.

If you will like to graduate away from binocular, the factors to look out for in buying a telescope are cost, maintenance, storage space and portability. Try to achieve a balance between prices and the best telescope out there to get one that observes the furthest. Living in countryside offers the infinite vastness of the sky but those living in city area can fiddle with their telescope to ensure maximum view. As well as, a portable telescope can secure into a car to journey to a location that better utilize your telescope but make sure that you know how to assemble in the dark.

Store and cover the telescope in a location free from moisture and dust and proper storage and maintenance will extend the life of the telescope. Other accessories for instant the eyepiece and the mount are equally essential to your viewing pleasure, so choose one that you are at ease with.

Eyepieces come in diverse designs and lenses for our viewing pleasure so do not get more than two to three pieces. Get the right one and it will add to your hobby. Mount takes the weight of the telescope while you focus. The two diverse kind of mount are the Alt-Azimuth and the Equatorial. Choose wisely to add more joy to astronomy.

Learning how telescopes work and understanding the various kind of telescopes not only make astronomy fascinating besides just exploring the mystery of the vast universe. Telescopes add a third eye and magnify the mysterious unidentified aside from broadening our knowledge. The mysterious universe will open up if we can see and discover, and telescopes make available the apparatus to satisfy our everlasting search for answer to decipher the vast and infinite universe.

Jhye is an author of numerous websites and astronomy and how telescopes work fascinate him. Take a tour at http://www.viewtelescopes.com

By Jhye Jhyiong
Article Source: http://EzineArticles.com/?expert=Jhye_Jhyiong

Astronomical Telescope Eyepieces: A Discussion for the Beginner

2008-11-12T04:31:00.000+08:00

Beginners sometimes wonder what eyepieces to get for a new telescope, and what eyepieces are all about in general. Eyepiece design and performance is fascinating, and many technical sources explain what's what, but I would like to give some simple, practical comments that might otherwise get lost in minutia.

Introduction:

Basic terminology, arithmetic, and how-does-it-work:

The magnification of a telescope is the ratio of its focal length to the focal length of the eyepiece in use.
Thus a telescope with a 1000 mm focal length, used with an eyepiece of 25 mm focal length, has a magnification of 1000 / 25, or 40. It makes things look 40 times wider, or if you prefer, 40 times closer. Put in an eyepiece with 4 mm focal length, and the same telescope now has magnification of 1000 / 4, or 250.

Focal lengths of commercially available telescope eyepieces range from 2.5 mm to 60 mm or more.

Magnification is sometimes symbolized by the letter "X", or "x". Thus we might speak of 40x, or 250x, and a 7x50 binocular magnifies seven times. (The "50" is the diameter of its front lenses, in millimeters.)

I have the eccentric habit of not using the word "power" to refer to the magnification of a telescope/eyepiece combination. "Power" conveys the impression that more magnification is always better, or that magnification is all that matters. Both of those notions are wrong, as we shall shortly see.

When you look into an eyepiece, the width of the apparent field of view is the angle through which you must turn your eyeball to transfer your gaze from one side of the field of view to the other. It varies with eyepiece design, from as little as 30 degrees to more than 80 degrees. The width of the actual field of view is the angular width of the patch of sky you are looking at, before it is magnified. It is more or less equal to the width of the apparent field of view divided by the magnification.
Thus if you are using an eyepiece with an apparent field of view of 50 degrees, in combination with a telescope such that its magnification is 100x, the width of the actual field of view will be about 50 degrees / 100, or 0.5 degree -- about the width of the full Moon.

Eyepieces come in many different designs, and they all have names -- Huygenian, Ramsden, Kellner, Orthoscopic, Erfle, Plossl, Koenig, Nagler, and many others. Don't worry about what the names mean, just remember that they do mean something. Some cost more than others, some work better than others. The ones that cost more aren't always the ones that work better.
Eyepieces come with different barrel diameters -- the diameter of the cylindrical part of the eyepiece, that fits into the telescope's eyepiece holder. There are three common sizes on the market today, and one less common one. The common barrel diameters are 2.00 inches, 1.25 inches, and 24.5 millimeters (0.965 inch). The less common one is 23 mm (0.917 inch).
Barrel diameter has nothing to do with magnification. But too small a barrel may restrict the apparent field of view of a long focal-length eyepiece.

A device called a Barlow lens, or sometimes a telextender, may be used with eyepieces to change their magnification. The best way to think of a Barlow lens is as a device which multiplies the telescope's focal length. Thus if you insert a 3x Barlow lens into the back of a telescope with 1000 mm focal length, the combined focal length of the telescope and Barlow lens becomes 3000 mm, and the magnification of any eyepiece used with the telescope will be tripled when it is used with the Barlow lens, compared to the magnification without.
Barlow lenses on the commercial market come in at least the three common barrel diameters, and have focal-length multiplication ratios from 1.75 to 5.00. Some have adjustable multiplication ratios.

Eye relief is the distance between the final glass surface of the eyepiece and the lens of your eye when you are looking through it. It is the space into which your glasses must fit, if you wear them when you observe, and is the clearance which keeps your eyelashes from smearing the outermost lens surface of the eyepiece, and your eyebrow ridges and cheekbones from jiggling the telescope.
Sufficient eye relief is a good thing. Too little is vexing. Too much can be vexing, too -- sometimes you can have trouble figuring out where to put your eye.

In general, for eyepieces of the same design, eye relief increases in proportion to focal length. But at constant focal length, it varies enormously from design to design. Several lines of eyepieces have been designed specifically to provide the same, ample, eye relief over a wide range of focal lengths.

Generalities about Eyepiece Selection:

Hands-on experience is more valuable than the printed word -- join an astronomy club, take your telescope to star parties, and ask to try out other people's eyepieces in it.
A small number of good eyepieces is better than a large number of bad eyepieces.
Not all Barlow lenses work well with all telescopes and eyepieces. You have to try the combinations you have in mind, and find out what works.
It is ultimately desirable, to have eyepieces that provide a nicely-spaced sequence of magnifications along a useful range for your telescope. Yet some magnifications are more useful than others. It makes sense to buy those first. I have an opinion on what they are:
I recommend starting with two eyepieces, one with magnification of about one-fifth the aperture of your telescope, expressed in millimeters, and the other with magnification about equal to the aperture in millimeters. That is, for a six-inch telescope -- 152 mm -- I recommend you start with magnifications of about 30 and about 150. I won't complain if they are 25 and 120, or 40 and 200.

The more powerful eyepiece gives a magnification most of us would call "medium". It will be the one you use in decent seeing, to look at the Moon, planets, and double stars. The other one will give brighter images of faint nebulae and galaxies, and so make them easier to see than if their limited light were spread wide, by high magnification.

The low-magnification eyepiece will also do double duty for finding things. Thus it should have a field of view as wide as possible, and that means that its front lens should be as big in diameter as possible, subject to two limits -- your budget (wide-field eyepieces are expensive), and the diameter of the focus tube of your telescope (wide lenses won't help if telescope parts get in the way). If you have a telescope with a long focal ratio (big "f" number), with a small-diameter focus tube, then you won't be able to get a wide-field view, but you will still want a low magnification for faint fuzzies.

If you have money left after buying these two eyepieces, and if you absolutely cannot wait until you have joined a club and tried things out, then the next two magnifications you will want will probably be one a little less than the half-way point between the first two -- say, 65x to 75x on a six-inch -- and one at not quite twice the magnification of the more powerful of the first two -- say, 250x on a six-inch.

Specific Recommendations:

Here are recommendations for the "first two", for common telecopes.

f/5 Dobson -- Get a 5 mm Orthoscopic for the "high" magnification. For the low one, if you are on a budget, get a 20 mm Erfle from Pocono, or find a used one with another label. If you are not on a budget, and if you have a two-inch focuser, you will probably look at Tele Vue Panoptics, Meade Super-Wides, and the Tele Vue 20 mm Nagler Type 2, but you will have to decide for yourself which one you like, because I don't like any of them -- I'd go with the Erfle. I hasten to add, that all these high-price eyepieces have advocates among experienced users. I'm just weird.
f/10 Schmidt-Cassegrain, Maksutov, or refractor -- Get a 10 mm Orthoscopic or Plossl. Then, if you have a 1.25-inch focuser, a 40 mm Plossl or Kellner in that diameter will do nicely -- several vendors carry them -- or maybe a 32 mm if you find the narrow field of the 40 mm aesthetically unappealing. With a two-inch focuser, Meade, Orion, Pentax and University Optics have suitable 40 mm eyepieces. Some of those eyepieces are expensive.
Many of these telescopes come with a decent 25 mm or 26 mm eyepiece as standard equipment. If so, keep it for a while, and just buy the 10 mm.

4.5-inch f/8 Newtonian -- 8mm Orthoscopic or Plossl, and 32 mm Plossl.
Small "beginner" refractor, f/10 to f/12, with 0.965-inch focuser -- The right answer for 0.965-inch focusers is a "hybrid" star diagonal that fits the focuser and accepts 1.25-inch eyepieces. The focuser restricts the field of view, but there are lots more eyepieces to choose from at 1.25-inch diameter than at 0.965. You can then go for a 10 or 12 mm Orthoscopic or Plossl, and a 40 mm Plossl or Kellner. But be careful, not all small refractors will come to focus with a hybrid diagonal in place, and a 40 mm Plossl may be too big and clumsy for such a small telescope. If the hybrid diagonal does not work for you, you will have to hunt down eyepieces with 0.965-inch barrels in appropriate focal lengths. 10 or 12 mm should be no problem, but you will be lucky to find a decent eyepiece of that barrel diameter with a focal length over 30 mm.
An Approach to Technical Minutia:

Switching eyepieces enables a tradeoff among three important, related quantities; namely

Magnification,
Image brightness of extended objects, like nebulae, and
Width of field of view.
Magnification:

Some folks think high magnification is what telescopes are all about, but there is a lot more to it. If an object is sufficiently bright to begin with, then increasing magnification up to certain a point will generally allow you to see more details. But, where is that "certain point"? There is no single answer. If you increase the magnification of your telescope in small increments, there are several reasons why you might want to stop after a while. They include:

Poor seeing. At sufficient magnification, images may look as if you were viewing through swirling water -- the effect of turbulence in the atmosphere. How much magnification it takes before the swirling gets objectionable will vary from night to night, and perhaps from minute to minute, from place to place, and from telescope to telescope -- large apertures are often bothered by poor seeing more than small apertures. And if you are patient and persistent, you may wish to try a high magnification even in poor seeing, in the hope that things may settle down for a second or so every now and then, so you can get a good look.
Jiggly mounting. Not only must the atmosphere be steady, but so also must be the mounting of your telescope, if the images are not to look wiggly.
Less than perfect telescope optics. Other things being equal, poor optics will give a blurrier image than good optics. There's no point magnifying detail that isn't there!
Even a telescope with good optics may temporarily misbehave when it is first set up, before all the parts have cooled to the temperature of the surrounding air. Large amateur telescopes may take hours to settle to temperature. The problem is worse in winter than in summer.

The wave nature of light itself. There is a limit to the amount of detail in the image of even a perfect telescope, and there is no point using more magnification than it takes to see all of it. The amount of detail present in the image formed by a perfect telescope, in perfect conditions, is proportional to its clear aperture -- doubling the aperture produces twice as sharp a view. Thus the maximum amount of magnification that is useful, is proportional to aperture: As a rule of thumb, it is extremely rare for an observer to have any use for a magnification much greater than approximately twice the telescope's clear aperture, in millimeters -- that would be 300x on a 150 mm telescope.
The actual upper limit for useful magnification depends on the visual acuity of the observer, which of course varies from person to person. People who have "sharp eyes" won't need as much magnification, to see all the detail that is present in the images of their telescopes.

This matter is rarely understood, so I repeat: There is a limit to the amount of detail in the image of even a perfect telescope, and there is no point in using more magnification than it takes to see all of it.

Not enough light. When you look at any particular object, the amount of its light entering the front of your telescope is fixed. If you are looking at an extended object, like the surface of the Moon, or a planet, or a galaxy or nebula, then as you increase magnification, that light is spread out over an ever-greater area of the retina of your eye, so the image looks dimmer and dimmer. Spread it out too much, and it will become too dim to see at all. What's more, various kinds of fine or low-contrast detail become hard to see before the object itself vanishes. If the object is dim to begin with, then the right magnification to see detail of a given size and contrast will be different, and almost certainly lower, than for a bright object. You will have to try many magnifications to see which one works best.
Image Brightness:

This discussion is closely related to the material in the paragraph about "not enough light", immediately above. The image brightness of an unresolved point of light -- like a star -- does not change as you change magnification, at least, not until the magnification is high enough so that you can begin to see the diffraction pattern of the star. The brightness of an extended object, however, declines as the square of magnification -- twice as much magnification reduces the image brightness by a factor of four. Reducing brightness will eventually make objects and their details harder to see, but on the other hand, increasing magnification does make those details larger. It is not always obvious which way the tradeoff works -- does increasing magnification gain more by enlarging details than it loses by making them fainter? You have to try it and see.

You might think that the best way to see faint extended objects is therefore to use a very low magnification, which makes their images as bright as possible. That doesn't always work, either. The eye behaves in a more complicated manner: Sometimes the tradeoff between image size and brightness favors a larger, dimmer image: I often have best luck looking at distant, faint galaxies at a magnification of about two-thirds the telescope clear aperture in millimeters (100x on a 150 mm telescope), which is a lot more magnification than many books say to use for deep-sky observation. Sometimes, also, it seems to help to have a magnification great enough that the background sky looks black -- at very low magnifications, it may look gray, and that seems to make faint things harder to see.

The tradeoff between image size and brightness often varies dramatically with only small changes in magnification. A change as little as ten percent can sometimes make a big difference.

At very low magnifications, another thing begins to happen. The diameter of the beam of light coming out of an eyepiece -- which is called the "exit pupil" -- is equal to the telescope clear aperture divided by the magnification. Thus a 150 mm telescope used at 100x has a 1.5 mm exit pupil. It turns out that the exit pupil can also be calculated as the eyepiece focal length divided by the focal ratio of the telescope. Thus any f/10 telescope used with a 15 mm eyepiece will have a 1.5 mm exit pupil. When the exit pupil is bigger than the pupil of the observer's eye, not all the light that comes out of the telescope can make it to the observer's retina -- some will be blocked by the iris of the eye. Once magnification has dropped so far that that has started to happen, then further reductions in magnification do not make the images of extended objects any brighter. Extended object surface brightnesses stay the same, and images of point sources, like stars, get dimmer, as magnification decreases further.

The diameter of the pupil of the dark-adapted human eye varies from person to person, but tends to decline with age. As a rule of thumb, persons younger than about 40 will likely have dark-adapted pupils of 7 mm diameter; older people will have smaller ones. But I do not generally recommend magnifications that produce exit pupils larger than four or five millimeters anyway.

There is a special case: If you have a fast (small f-number) telescope, and need a very wide field eyepiece to find things, or for spectacular views of very large objects, then perhaps you have cause to get a very low-magnification eyepiece, even if it has an over-large exit pupil. You will be throwing away light, but perhaps the wider field is worth it to you.

Field of View:

For eyepieces of a given design (Kellner, Orthoscopic, Plossl...) the width of the field of view is generally inversely proportional to the magnification -- doubling the magnification cuts the field width in half. But at the same magnification, different eyepiece types have dramatically different fields of view -- expensive modern designs, like Naglers, may have twice as wide a field as such old standbys as Kellners and Orthoscopics. So if you want a wide field of view, perhaps for finding things or for looking at some of your favorite large objects, you must either get a long focal-length, low-magnification eyepiece, or spend some money for a fancy design, or both.

There is a catch, too: There is no magic to getting a wide field of view in an eyepiece -- look down the barrel of a short focal-length, high-magnification eyepiece, and see how tiny the lenses are compared to those in a low-magnification eyepiece. Wide fields of view require wide lenses. But wide lenses won't do any good if the eyepiece barrel, or the focuser tube, or the baffle tube of a Schmidt-Cassegrain, prevents light from getting to their outer edges. For good use of a low-magnification, wide-field eyepiece design, it must be mounted in a large eyepiece barrel and used with a large-diameter focuser and baffle tube. A 40 mm eyepiece will give a nice low magnification in an f/10 refractor or in a Schmidt-Cassegrain, but it must be have a two-inch barrel and be used in a two-inch focuser, if it is to give a wide field of view, as well.

Eyepiece Errors of Color -- Some Basics:

Many people know that designers of the objective lenses of refracting telescopes have engaged in a centuries-long battle against longitudinal chromatic aberration, which is also called longitudinal color. The nature of that aberration is that different colors of light do not come to the same focal point. With too much error of this kind, the image seen through a refractor is not in sharp focus for all the colors of light that the human eye can see; rather, the image will likely be in pretty good focus for yellow and green light, but will have a violet blur composed of the out-of-focus red and blue images in combination.

You might think that eyepieces would have the same problem -- after all, they use lenses, too. You might conclude that the image seen through a poor eyepiece might not be in simultaneous focus for all colors, even if the main telescope were a reflector, or some other design that reduced longitudinal chromatic aberration to a minimum.

Surprisingly, that's not so. It's not that eyepieces lenses don't have longitudinal chromatic aberration -- they certainly do -- rather, it is that the amount is so small that it is generally far smaller than the focusing tolerance for the telescope. Other things being equal, the length of the region along the optical axis where the various colors of visible light come to focus, is proportional to the focal length of the lens in question. For a long focal-length lens, like a 1-meter focal-length refractor objective, that length is large enough to matter. For a short focal-length lens, like a 10 mm eyepiece, it's too tiny to make a difference.

The most common error of color introduced by eyepieces is a different one, called chromatic difference of magnification, or lateral chromatic aberration, or just lateral color. This problem also stems from the fact that lenses do not bring all colors of light to the same focal point, but lateral color involves a different consequence of that fact than does longitudinal color: If an eyepiece, used as a lens, does not bring all colors of light to the same focal point, it follows that the focal length of that eyepiece will vary with color, and consequently, that magnification will vary with color.

The image seen while looking through an otherwise perfect telescope, while using an eyepiece that has noticeable lateral color, will in effect comprise different-colored images of slightly different sizes, superimposed. Most eyepieces with this problem have images whose size increases from the red to the blue end of the spectrum. With such an eyepiece, if the object you are looking at is a white circle, or something like it -- perhaps a planet or the Moon -- then when it is nicely centered in the field, the edge of the circle will look blue, where the large blue image overlaps beyond the edge of the smaller images of other colors. If you are looking at a test pattern of black and white stripes, then the sides of the white stripes that are away from the center of the field will have blue edges, and the sides toward the center of the field will have red edges.

The width of the red and blue edges will increase in proportion to the distance of the edge from the center of the field. Lateral color, from the eyepiece, goes away when an small object is centered. Longitudinal color, from the objective, does not.

Lateral color is often particularly easy to see in binoculars. Try looking at a dark telephone pole silhouetted against the bright sky, or at a white picket fence against the dark interior of a garden. Colored edges will often be easy to see when the object is out at the edge of the field. Stars will be drawn out into short, radial spectral streaks, with the red ends pointing toward the center of the field.

It turns out that eyepieces don't need to be very fancy to correct pretty well for lateral color. The centuries-old Ramsden eyepiece, composed of two identical plano-convex lenses placed convex sides toward one another at a separation equal to their focal length, has essentially no lateral color. (Strictly, it is corrected for lateral color through first order in the longitudinal color of each of the lenses it is made from.) Good Ramsdens eyepieces are essentially color-free, even though they do not use achromatic lenses. That sounds like something that ought to be impossible, but it's not: Jesse Ramsden was a smart man.

Many people confuse lateral color with another color problem which doesn't have to do with the telescope at all. Dispersion of the different colors of light by the atmosphere causes stars and other objects near the horizon to be drawn out into very short spectra -- the atmosphere works like a big, weak prism. The spectra will all point in the same direction, no matter where they are in the field, but at a quick glance you might not notice that they were all the same. With high magnification, these effects are detectable surprisingly far above the horizon. So when you are testing an eyepiece for lateral color, be sure to look only for color variations in the horizontal direction, so that you will not be confused by atmospheric dispersion.

Good Eyepieces and Bad -- Generalities:

Whether an eyepiece is good or bad depends on what you want it to do. What observers want from eyepieces often includes the following:

Good images when used with telescopes with fast f numbers,
Wide apparent field of view, and
Ability to reveal low-contrast, fine detail, if there is any in the image in the first place.
Some warnings: First, you probably are not going to find any one eyepiece that delivers all these things. Second, some of these qualities are expensive.

Fast F-Numbers:

It is harder to make eyepieces that work well at fast f-numbers (that is, at small f-numbers) than at slow ones. To see why, let's take an eyepiece with 10 mm focal length. Suppose you use it with an f/10 telescope -- perhaps a refractor or a Schmidt-Cassegrain. Consider the bundle of rays of light from a single star, as it passes through the telescope and then the eyepiece. The bundle comes to focus at a single point, or very nearly so, in the telescope's focal plane, then expands outward into the eyepiece.

A 10 mm eyepiece used with an f/10 telescope will have a 1 mm exit pupil diameter: The bundle of rays leaving the eyepiece will be 1 mm in diameter. Thus a chunk of eyepiece only about 1 mm wide will have been used to get the rays from that star set up to go into your eye. The eyepiece designer will only have had to worry about aberrations being small across a 1 mm wide hunk of glass. Of course, the bundles of rays from other stars in the field of view will go through different 1 mm hunks -- that's why the eyepiece has lenses that are more than 1 mm wide -- and for a good eyepiece, the aberrations in each individual 1 mm hunk must be small. But a slow variation in some optical property across the full width of the lenses will be okay, as long as 1 mm worth of it doesn't add up to too much aberration.

Now put the same eyepiece in an f/5 telescope -- perhaps a fast Newtonian. The bundle of rays from one star, leaving the eyepiece, is now 2 mm in diameter, and the designer has a correspondingly harder task -- the aberrations must be kept small over a 2 mm wide hunks of glass, instead of smaller, 1 mm hunks.

Thus it is no surprise that eyepieces that work well at fast f-numbers are fancier and more costly than ones that don't. There are inexpensive centuries-old eyepiece designs, like the Ramsden and Huygenian, that have only two pieces of simple glass, and work perfectly well at f/15 or more, as in classic refractors. But don't try them in fast Newtonians.

Wide Fields of View:

As I said before, there is no magic to getting a wide apparent field of view -- it takes wide pieces of glass. The labors of the eyepiece designer thus increase, for the task is to provide good images over a bigger area of the focal plane than with a narrow-field eyepiece. To do so may take lots of pieces of fancy glass, processed to tight tolerances.

Fast F-Numbers and Wide Fields:

If you want an eyepiece that works with a wide field at a fast f-number, then you are compounding the two previous problems. Only in the last decade or two have there begun to be wide-field eyepieces that work decently with f-numbers down around 5 -- as you find in many Dobsons and fast refractors. They cost an arm and a leg. The first was the Tele Vue Nagler; Tele Vue, Meade, and perhaps some of the Japanese manufacturers have produced others.

It is interesting, that many people who think they have seen the off-axis coma and astigmatism which we are all taught characterize a fast Newtonian, are wrong. What they have actually seen is the off-axis aberrations of some hapless eyepiece that can't hope to work well at -- say -- f/5. The coma and astigmatism of the eyepiece are greater than that of the mirror.

I said earlier that I don't much like the modern whizzy wide-field designs, that do work with fast f-numbers. That's because I am willing to fuss to keep an object centered, even in a big Dobson -- I need wide fields of view only for finding things, and that doesn't require pinpoint star images at the edges of the field. From that point of view, the likes of Tele Vue Naglers and Panoptics, or of Meade Super Wide Angles and Ultra Wide Angles, are all too big, too heavy, and too expensive. I don't like lugging them around, I don't like rebalancing the telescope every time I change eyepieces, and most of all, I don't like paying for them. But your preferences may vary: Many observers disagree with me. And if I had a Dobson too big to steer easily, or if I wanted to use one regularly at high magnification, I might well want the extremely wide well-corrected fields of some of these eyepieces.

Fine, Low-Contrast Detail:

Suppose you have many types of eyepieces, with many focal lengths of each type, all well enough corrected to work at the f number of your telescope. Which one will show the most low-contrast detail on Mars or Jupiter, or will have the best chance to find the close, faint companion of a double star? It should be clear from what I have said before, that selecting the right magnification has a lot to do with the answer, but suppose you still have a choice: For instance, suppose you think a 6 mm eyepiece is best for what you have in mind, but you have several different 6 mm eyepieces in your collection. Which will work best?

The likely problem here is scattered light -- light from the bright parts of the object itself, which is not getting to the point in the image where it is supposed to be, but instead ends up a little way away, on top of the image of some fainter part of the object. The image as a whole looks a little foggy, or seems to have extra glare. We've all seen this kind of effect in non-astronomical circumstances, perhaps looking through real fog, or through a dusty or dew-covered window or spectacle lens.

Scattering in the eyepiece generally comes from irregularities or defects at the surface of a lens, where light passes from air into glass, or vice-versa. Dust or dew may be present, but for purposes of comparison testing, let's assume the eyepieces are clean and dew-free. Other irregularities may come from incomplete or flawed polishing of the lens surface -- that is, from pits or scratches -- or from defects in the lens coatings. Places where one lens is cemented to another are less likely to cause problems -- these surfaces will not have coatings, and the lens cement itself does a pretty good job of filling surface irregularities in the glass and masking their effect. Thus what counts is the number of air/glass interfaces in the eyepiece.

Lest we not see the forest for the trees, let me stress one obvious fact: The fewer the air/glass interfaces, the fewer the places where scattering can occur. At any given level of quality of polish and quality of coating, simple eyepieces, with few air/glass interfaces, will have less scattering than fancy eyepieces, with lots of air/glass interfaces. Of course, lots of simple eyepieces are made to sell at low prices, and perhaps do not have as good polish and coatings as fancier types, but do not let the workings of the marketplace obscure what's going on: Other things being equal, more air/glass interfaces means more glare.

Many complicated eyepieces have six, eight, or even ten air/glass interfaces, but such simple designs as Orthoscopics, Kellners, Plossls, Ramsdens, and Huygenians have four. There are rarer designs with only two air/glass interfaces -- the optics are one solid or cemented piece of glass. They include the Coddington, Tolles, Hastings Triplet, and several different designs called Monocentric. Any of these simple designs will have a leg up over whizzy types with lots of air/glass interfaces, for fine, low-contrast detail. If the simple eyepiece has well-polished lenses, and if the coatings -- if any -- are first-rate, then the simple eyepiece will probably show more low-contrast fine detail.

This effect is significant. I have done a moderate amount of comparison testing of eyepieces, looking for scattered light, and eyepieces with few air/glass interfaces almost always have noticeably less scattering than eyepieces with many air/glass interfaces. I have some old Ramsden eyepieces -- four air/glass interfaces -- which don't work well at fast f-numbers. Yet at long focal ratios, they are embarrassingly good planetary eyepieces, and often put to shame more modern, fancier designs. The embarrassment is heightened by the fact that my Ramsdens cost only ten or twenty dollars each, when I bought them in about 1980.

Don't forget to count the air/glass interfaces in Barlow lenses, too. Every Barlow has at least two of them, and some have more.

Let's talk about polish. Good polish costs money: Not only must the lens spend extra time on the polishing machine, but also the manufacturer must more carefully control the quality of the polishing materials and the cleanliness of the polishing area. I suspect some manufacturers skimp on polishing. Some of the best polish seems to be on old military-surplus optics. I think the military has always had a no-nonsense attitude about contrast, hence about polishing -- when you are peering into the dark looking for someone coming to kill you, it is useful to be able to see clearly. My old Ramsdens were probably assembled from military-surplus lenses; that's a likely reason why they work well.

The effect of coatings requires more thought. The purpose of coatings is to increase transmission of light. An uncoated air/glass interface transmits only about 96 percent of the light that strikes it, and reflects essentially all the rest. The best modern coatings increase transmission to 99 percent or better. The older, magnesium fluoride coatings transmit about 98 percent. Transmissions multiply, so so the transmission through the ten air/glass interfaces of a Barlow and a fancy modern eyepiece combined will be something like 0.96 to the tenth power, or 66 percent, if they are uncoated. With magnesium fluoride coatings, it will be 82 percent, and with good modern coatings, 90 percent or more . That's quite a difference: Coatings are important for looking at faint objects.

Reducing reflected light is important for another reason: That light may return to haunt you. Some eyepiece types are noted for ghosts -- out-of-focus images of what you are looking at, caused by multiple, back-and-forth reflections from lens surfaces. Kellners and some of the Monocentric designs have notable ghosts. Even with no ghosts, light lost by reflection may scatter off the inside of the eyepiece barrel or focuser tube, and add glare to the image. Good coatings hit the heart of these problems, by reducing reflections. Yet not all eyepiece designs have ghosts, and it is possible to control scattering off the inside of the eyepiece barrel or focuser tube by means of black paint, threading, baffles, and so forth.

Coatings may have one undesired effect on the detection of fine low-contrast detail. I have heard it said that some coatings may increase scattering at the air/glass interface. I don't have any details. It is clear, however, that every time you put something on a lens surface, you have the opportunity to trap dust, or to create irregularities by imperfections in the coating process. Multi-layered coatings have many such opportunities. Yet I prefer coated eyepieces to uncoated ones, across the board, notwithstanding.

In any case, the effect of coatings upon scattering at the air/glass interface seems minimal. Some of my Ramsdens are uncoated, yet they exhibit neither more nor less glare than do other eyepieces with the same number of air/glass interfaces (four) and with coated lenses. The uncoated Ramsdens undoubtedly have less overall transmission than most coated eyepieces, but for bright stars and planets there is usually plenty of light, so the lower throughput is not a big deal.

I also have worked with some Monocentric eyepieces manufactured by the Russian firm, Intes, which have only two air/glass interfaces. Most of them have terrible coatings -- the lens surfaces reflect more light than does uncoated glass. Yet the best of these eyepieces produce less glare than the Ramsdens. I hope Intes gets its coatings together. The Monocentric designs make excellent planetary eyepieces. Well-made ones would be welcome.

I think the bottom line on detection of fine, low-contrast detail is to use an eyepiece with only a small number of well-polished air/glass interfaces, and not worry too much about coatings. But this subject is complicated, and there is probably more that should be said, that I do not know about.

What's in My Eyepiece Box:

We could discuss the pros and cons of various eyepiece types for a long time without coming to any conclusions, so I am just going to tell you what I have in the box of eyepieces that I bring to star parties, and leave it at that. I work with telescopes of various focal ratios from f/5 to f/12, so I need more eyepieces than for just one. Not all of my telescopes have 2.00-inch focusers, so there are duplications in longer focal lengths. I of course have a bushing to adapt 1.25-inch eyepieces to 2.00-inch focusers. What I carry at the moment is three sequences of eyepieces, plus some odds and ends. The first sequence is a run of high-definition eyepieces for use when image quality is paramount:

32.0 mm, 1.25-inch barrel, Brandon "Orthoscopic"
24.0 mm, 1.25-inch barrel, Brandon "Orthoscopic"
16.0 mm, 1.25-inch barrel, Brandon "Orthoscopic"
12.0 mm, 1.25-inch barrel, Brandon "Orthoscopic"
8.0 mm, 1.25-inch barrel, Brandon "Orthoscopic"
6.0 mm, 0.965-inch barrel, Pentax SMC ED Orthoscopic
5.0 mm, 0.965-inch barrel, Pentax SMC ED Orthoscopic
3.8 mm, 0.965-inch barrel, Pentax SMC XP Orthoscopic
2.8 mm, 0.965-inch barrel, Takahashi Orthoscopic
Brandons use two cemented doublets face to face, rather like Plossls -- they are not the kind of "Orthoscopic" most people think of, though I suspect the design is technically entitled to that name. They are excellent high-definition eyepieces, and not cheap, with apparent fields of view near 45 degrees. There are better eyepieces, but they are less cheap -- a lot less cheap -- and some brands are difficult to locate. I used to have some other old orthoscopics in the lineup, but I have replaced them.

I keep the Pentax and Takahashi eyepieces installed in 0.965-inch to 1.25-inch adapters, so it is easy to use them in my 1.25-inch focusers.

The second sequence has much wider fields of view, for deep-sky observation:

55.0 mm, 2.00-inch barrel, University Optics Plossl
40.0 mm, 2.00-inch barrel, Vernonscope Erfle
32.0 mm, 2.00-inch barrel, University Optics Erfle
20.0 mm, 1.25-inch barrel, Brandon Wide-Field
Erfles work fine at focal ratios of eight or more, but begin to show substantial aberrations of their own, at the edges of their fields, at faster f numbers. They have apparent fields of view close to 70 degrees.

Plossls do not have as wide an apparent field of view as Erfles, but the field of the 55 mm is limited by the inner diameter of the two-inch barrel, so who cares?

The Brandon Wide-Field appears to be a variant of the Erfle design, but I wouldn't want to say so for certain.

I used to have some shorter focal-length Erfle eyepieces in this sequence, 15.5 mm and 12.4 mm Meade "Research-Grade" Erfles that I liked a lot, but I found myself using the 16 and 12 mm Brandons in their place. The Brandons seem to give a bit less glare than the Meades, yet the Meades had a much wider field of view, which made it easier to find things with them. However, when I bought copy of Millennium Star Atlas, which has lots more stars than my previous observing atlases, I found that the extra stars made it easy to find things even with the narrower fields of view of the Brandons. Who would have thought that changing atlases would have caused me to change eyepieces?

I have a zoom eyepiece, which is very useful.

8.0-24.0 mm, 1.25-inch barrel, Vixen Lanthanum zoom eyepiece
The main advantage of zooming is that the range of magnifications at which an object shows best is sometimes very narrow, and zoom capability can help find it. Furthermore, the Vixen is one of the newer zoom units on the market, which have a wider actual field of view at low magnification than at high: Most older zoom units show the exact same patch of sky at all focal lengths, just stretched or shrunken. Thus when I use the Vixen, I can "zoom out" for a wide field to help find something, then "zoom in" for a better look. It is also fun to say "Quick, Chewie, the jump to lightspeed!" when the stars expand outward as I dial up the magnification. Furthermore, the zoom has enough eye relief to make it a good star-party eyepiece, when there are long lines of visitors and I don't want to have to keep refocusing the telescope when people to take off their glasses to get close to the eyepiece.
The Vixen zoom eyepiece delivers images about as good as a "generic" inexpensive Plossl.

I carry one of the regular Vixen Lanthanum LV eyepieces, too. It has a long eye relief, and serves as a star-party eyepiece when I need more magnification than the zoom provides.

5.0 mm, 1.25-inch barrel, Vixen Lanthanum LV
I also have a couple of Monocentrics, that I have been experimenting with:

12.0 mm, 1.25-inch barrel, Intes Micro Steinheil Monocentric
9.0 mm, 1.25-inch barrel, Intes Micro Steinheil Monocentric
6.0 mm, 1.25-inch barrel, Intes Micro Steinheil Monocentric
The Monocentrics are special-purpose planetary eyepieces, with the good and bad points that I discussed earlier.

With my 1.25-inch eyepieces I sometimes use a good Barlow lens:

2.0x, 1.25-inch barrel, Celestron Ultima Barlow
If I were going to work with a large, fast, Dobson-mounted Newtonian, I might well want Tele Vue Nagler or Panoptic, or a Speers-Waller, in a focal length of approximately 20 mm, as well as a Nagler or Speers-Waller at about 7 mm focal length. I might want a Tele Vue Paracorr Coma Corrector as well.

By Jay Reynolds Freeman (Jay.Freeman@Sun.COM)
Article Source: http://www.observers.org/beginner/eyepieces.freeman.html

How Do Telescopes Work - Telescope Lenses

2008-11-03T13:33:00.000+08:00

Lenses and mirrors are the elements used to collect and view focused light in telescopes. Mirrors are the medium for focusing in reflector telescopes, while lenses are the medium in refractors. Each type has its own distinct advantages and disadvantages. Refractor type telescopes use lenses. These lenses bend the light when it enters the telescope from the distant object being viewed through it. Because of this refraction it is possible to closely view a distant object. The telescope has two lenses, with one slightly larger.

The eyepiece in the telescope is generally a small lens. Some telescope however, may not use lenses for the eyepiece at all. The eyepiece, in any case, is the most important element of a telescope. It is the element which lets you see correctly whatever it is that you want to focus on. These eyepieces are adjustable and are of a low power. Adjusting the eyepiece allows you to change the magnification factor. What kind of lens you use for the eyepiece is a personal choice. In today's age, several different kinds of eyepieces are available in the market. Because of this motley available, choosing the correct eyepiece from your requirement may be a difficult task. As a result, you should concentrate on defining the criteria you think are important for your choice. The depth of field, optical quality, sharpness, clarity, brightness, market price, barrel size and how it affects your eyesight are some of the major points of concern. However these criteria always remain individual prerogatives.

Lens designs used in older telescopes go by the name of Huygens and Ramsden. Professional astronomers are advised to not use these lenses anymore as they are not of superior quality, even though they are comparatively less expensive than other market lenses. These lenses also do not provide correction for chromatic aberration or the light circles that form around brighter objects when they are viewed.

Professional astronomers use orthoscopic lenses that are designed specifically for professional stargazing. Even amateurs will find these lenses good for their telescopes. The orthoscopic telescopes use four lenses in the eyepiece, and have a 45 degree field of vision (FOV). Since the eyepiece is the element most important to the quality of a telescope, this design is a winner. The lenses do not strain the user's eyes, and can be used even for viewing closer objects like planets.

For a person with a moderate budget, a Barlow lens is a viable option. The design provides average quality but is a good bargain. It does not burn a hole in one's pocket, and yet is not of inferior quality because of its cost. The range at which this lens is available starts at a low $30 and goes up to $70. The magnification factor is generally not enough for professional use, however for amateurs it should be enough. For hobbyists, it is an ideal lens.

When you're looking for lenses for a telescope, it is important that you determine criteria that most comprehensively fulfill your needs from the lens. Adjustable lenses is a good option as it means you can view objects which are not too far, as well as distant stars with it, and thus obtain the best deal your money can buy you.

Download free hubble image space telescope as well as learning more about refractor vs reflector telescopes when you visit http://www.howdotelescopeswork.com, the online portal for free resource on telescopes making and usage.

By John B Mayall
Article Source: http://EzineArticles.com/?expert=John_B_Mayall

How Do Telescopes Work - Making a Telescope Purchase

2008-10-12T18:40:00.000+08:00

Before you make your purchase of a telescope, there are several factors you must take into consideration. One of these is the technical aspects of the telescope. When you walk into a store to inquire about the specifications of the instrument you're about to buy, you must know the difference hat exists between your want and you need. If you know all there is to know about your intended purchase, then you will be acutely aware of this difference. Making a telescope purchase is not a small matter. You will spend a good amount of money on this, and it is therefore imperative that you conduct a thorough research before you set out to buy one. Also decide on the budget you can afford for this purchase.

Once you have answered the above questions, your buy will not be too difficult and will be worth the effort. The answer to a question on budget is most important because it determines the kind of telescope you will be able to buy, no matter what your needs are. If you have a bigger budget, then you can look at the powerful telescopes, but if you have extremely limited finances, it is better to invest in a pair of binoculars. And no, even if you think they are child's play, they actually are not. You will marvel at how much of the sky you can explore with a simple pair binoculars.

In this modern era, there are several different types of telescopes available. Each telescope has its own special USP and offers something unique to the user in terns of quality and features. For someone who doesn't want his purchase to be a futile expenditure, it is best that they research as much as they can, Weight the advantages and disadvantages carefully before you make a choice about what is relevant to you. If you don't know what each aspect of the instrument entails, you will have trouble selecting one that meets your requirements completely. The element that carries most weight is the eyepiece. It is this little lens that is the window to the world for a telescope user. An adjustable eyepiece makes the telescope experience more fulfilling because then the magnification factor can be changed to suit your convenience. This eyepiece should be able to minimize the chromatic aberration and light circles for brighter objects.

You must also have an idea of where you are planning to use the telescope to go stargazing. Different light populations lead to difference in performance, and noise also affects the view. In case your intended location is heavily populated, you should be prepared to face a few difficulties because of excessive light.

Telescopes use either of lenses or mirrors. Reflectors, as the name suggests use mirrors and are the ones astronomers would recommend. Refractors use lenses. The main mirror or lens in a telescope is called its objective. This objective and its width should be an important part of your deliberations because the power is proportional to its surface area.

The main point of consideration when you buy a telescope is to make sure it matches your requirements. Do not just think about the power that the telescope has. All its parts have to work perfectly for the telescope to be a good instrument. Do not skimp and buy a low-price telescope as you will be severely disillusioned with the quality it will provide you with. The best bet is a moderately priced telescope that provides sufficient quality without being too heavy on your pocket.

For more information on lx200r meade telescope as well as tips and techniques on how to make simple telescope, visit http://www.howdotelescopeswork.com

By John B Mayall
Article Source: http://EzineArticles.com/?expert=John_B_Mayall

Telescopes Introduction

2008-09-24T03:51:00.004+08:00

The naked eye is clumsy to see altar that are too tiny or too far. But telescopes acquiesce the naked eye to get a acceptable appearance of abroad objects.

Telescopes are accessories that are able with magnifiers to acquiesce you to see things abstract with a bright view. Telescopes are frequently acclimated in science or its branches, decidedly astrochemistry and physics.

A telescope assignment with its two lenses are installed. This makes examination a abroad article possible. Each of the lenses has a function. The cold lens, or the primary mirror, collects the beam broadcast by the article beheld and makes it readily accessible in a assertive focus point. The eyepiece lens picks up the active ablaze from the focus point and spreads it to the retina so that examination becomes possible.

There are assorted determinants to acceptable article examination in the telescope. An able telescope care to acquire the competent affection of accession ablaze from the article that is beheld and the accommodation to aggrandize the image.

The bore of the lens or the mirror active in the telescope determines the accumulating of light. It is additionally termed aperture. Logically, the bigger the aperture, the added ablaze it is able to gather. Angel enlargement, however, is absolutely abased aloft the aggregate of lenses. It is the eyepiece of the telescope that does the magnification.

The prices of telescopes alter with the blueprint and capacities. You can additionally acquirement accessories that will adjure with your telescope’s image. Whether you base a telescope on your balustrade for a adorable conceiving experience, or you opt for a toy telescope, the action of the telescope charcoal the aforementioned -- to accredit you to booty a bright appearance of far abroad objects.

Tag: telescope, lenses, stargazing, Hubble Space Telescope, Mirror Telescope, Camera Telescope

How Choose Your Telescope Eyepieces?

2008-09-21T23:36:00.009+08:00

One of the understood aspects of telescope optical instruments when beginning astronomers start taking a look at telescopes is telescope eyepieces. The actual eyepiece itself can be confusing than lenses & mirrors & designs are simple to grasp.

Keep in mind, when you are taking a look at telescope eyepieces, you are fundamentally paying for the lenses in the eyepiece. The more an eyepiece costs, the better the lenses inside & the better the picture it creates.

Another aspect to think about when choosing telescope eyepieces is the apparent field of view. This is the apparent width of the picture, in degrees, which indicates how far a person needs to move their eye in order to look from one finish of the picture to the other. Fundamentally, it is a measure of the peripheral vision available to the person looking through the eyepiece. Depending on the design of the telescope eyepiece, the apparent field of view can range from 40 to 82 degrees.

Keep in mind also that picture quality of telescope eyepieces can be affected by the design of the eyepiece; Huygens eyepieces can generate chromatic aberrations, Erfle eyepieces can produce some ghost images, & Plossl eyepieces tend to have some astigmatism around the edges of the picture. That why it is better to understand the limits of each design & what kind of work each design is suited to.

Overall, telescope eyepieces are best judged through experience. It’s means that trying out several designs & models is the best way to figure out what works best. But, with a tiny trial & error, the right telescope eyepieces can make their way in to your telescope kit.