What Will Telescope Cost?

Amateur telescopes come in a wide range of prices, from a low of under $200 to a high of $5,000 and more, much more. There really is no upper limit. Someone out there will be happy to take as much money as you’d care to spend. In fact, the Beck Telescope (a Cassegrain-focus telescope with a 30” diameter primary mirror) located in Bradley Observatory at Agnes Scott College was originally owned privately by one Henry Gibson, who had it housed in a dome near his house. He sold the telescope to the College in 1947 for $15,000—a lot of money back then! The beginner need not invest in the four-digit range; however, spending less than about $300 on a new telescope (except in the case of certain rich-field instruments, which we will get to shortly) is likely to result in disappointment.

If you’ve been hitting the malls and looking at telescopes in department stores, camera stores, hobby shops, and even some optical stores, you may be surprised that most of the instruments you’ve seen will not provide you with a satisfying observing experience. The market is full of telescopes in the $100 to sub-$300 range—and they sell! But they’re mostly not worth their “bargain” prices. That’s not a subjective judgment. It’s a cold, hard fact. Here are some typical attributes of cheap telescopes:

• A cheap, wobbly mount. If the view wiggles, you will have a very frustrating time looking at the sky, especially if there is the slightest breeze, or you bump the telescope trying to focus the image. We’ll discuss mounts in just a few minutes, but be aware that a shoddy equatorial mount is inferior to a simpler altazimuth mount—if that mount is steady and well made.
• A telescope that trumpets its magnification but makes little or no mention of its aperture. Aperture, the diameter of the telescope’s objective lens (if it’s a refractor) or primary mirror (if it’s a reflector), determines how much light you will be able to collect. After you get tired of looking at the moon, you’ll find yourself increasingly interested in the dimmer objects of the night sky. Buy the largest aperture you can afford; aperture size and component quality are far more important than magnification numbers. A 2.75-inch (70 mm) aperture is a very good minimum for a refractor, and a 4-inch (100 mm) aperture is a good minimum for a reflector. Excellent Maksutov-Cassegrain instruments start at 90 mm, but the entry-level Schmidt-Cassegrain is a 5-inch model.
• Poor optical quality. Stars should focus as bright, sharp points of light, not smears, blurs, or flares. Unfortunately, it is rarely possible to field test a telescope before you buy it, so purchase only an instrument that comes with a noquestions-asked return policy. Put the telescope through its paces by focusing on a reasonably bright star. You may want to find Altair, Betelgeuse or Arcturus, for example. On a night with good seeing, the star should focus to a clean point. Next, using the highest magnification, slightly unfocus the image by turning the focus knob first one way and then the other. With good optics that are properly collimated (the optical elements made perfectly parallel with one another), the out-of-focus image will look the same regardless of which way you turn the knob. If the two out-of-focus images are significantly different, the optical collimation is poor.
• Small eyepiece. The modern standard for an eyepiece barrel diameter is 1.25”. Two-inch diameter eyepieces are common on larger, more expensive telescopes (14” diameter mirrors and greater). A short-barrel eyepiece can restrict the field of view at low power and is generally a sign of an inferior telescope.
• A junk finderscope. The finderscope (or finder)—the small telescope attached to the side of the main telescope—is very important for locating the objects you wish to study, especially if your telescope lacks go-to capability. An inferior scope is of little use. Look for one with an aperture of at least 30 millimeters. Also make sure the bracket that mounts the finder is easily, firmly, and accurately adjustable. You’ll need to align the finderscope with the main instrument frequently. You may want to also replace the factory finderscope with a “bullseye” on the sky, powered typically by a small red LED.
• Obscure and/or skimpy instructions. Not only is a clear and ample manual an important aid to using and enjoying a telescope, it is a sign of the quality of thought that has gone into making the instrument.

Telescope shopping advice

Here are a few words of shopping advice—much of which applies to telescopes as well:

• Examine and feel the binoculars. They should strike you as a well-crafted precision instrument.
• Test the focusing mechanism. It should be smooth and offer steady resistance.
  
• Look for antireflection coating on all lenses. This thin coating will make the lenses appear blue, yellow, magenta, or purple when held at an angle to the light.
• Look through the binoculars. Try focusing on a point of light (a distant bulb, for example). It should be absolutely sharp, at least until the point of light gets very near the edge of the field of view.
• Focus on a vertical straight line such as the corner of a building. Even with very good binoculars, the straight line will bend at the extreme edges of your field of view. However, if the line remains bent a third of the way from the edge, the quality of the optics is poor.
• The twin barrels of binoculars must be perfectly parallel with one another. If they aren’t, you will see a double image. Your eyes will work hard to compensate and fuse that double image, but ideally, there should be no double image to fuse.

Do You Really Need a Telescope?

Few experiences with the night sky are more instantly rewarding than your first look at the moon, a nebula, or a planet through a telescope. Saturn, in particular, can look almost too perfect. One of us taught students (while in graduate school) who refused to believe that the planet that they were looking at through the telescope was real. This student insisted that Saturn was a sticker on the telescope lens. However, it is also true that such an experience can be singularly disappointing if that shiny new telescope you bought at the mall turns out to be a piece of wobbly, hard-to-use junk. If you are willing to invest in a good telescope (we’ll talk about the magnitude of the investment in just a moment), and if you are willing to invest the time to learn how to use it, a telescope can be a wonderful thing to have.
But will you use it?
If you are an urban dweller who never escapes the streetlights of the city and are hemmed in by tall buildings, you may be better advised to spend your money elsewhere. Then again, owning a sufficiently portable telescope gives you a good excuse to pack up every once in a while and head for the country, where the skies are darker and the seeing is better.
faint to see with the naked eye visible, all stars are so incredibly far away (the closest beyond our sun, Alpha Centauri, is about four light-years away) that a given star at higher magnification will still be nothing more than a point of light. Magnification is also largely wasted if what you look at is too dim to see well. Get binoculars with the largest aperture (the diameter of the objective, or main lens) you can afford. An aperture of 50 millimeters is a good choice. Couple this with a 7magnification, and you have a 7 50 pair of binoculars—a good allaround choice for handheld viewing.
If you want to successfully use binoculars with a magnification of more than 10or 12, you will need to mount them on a camera tripod equipped with a binocular adaptor clamp or a specially designed binocular tripod; otherwise, the sky will be a blur.
Binoculars have the advantage of being very portable, and whole guidebooks have been written about observing the sky with them (for example, Exploring the Night Sky with Binoculars, by Patrick Moore [3rd ed., Cambridge University Press, 1996]). However, at anywhere from $200 to $1,000 and more, binoculars with high quality optics are not cheap; if you’re thinking about buying a pair of big, expensive binoculars, there are other possibilities you may want to consider.

Little advice about telescope

At nearly $3 billion for the Chandra X-Ray Observatory, astronomy can be a dauntingly expensive pursuit. Fortunately, you don’t have to spend quite that much to get started. In fact, you don’t really have to spend anything. A lot of observation can be done with the naked eye, and many local communities have active amateur astronomers who would be happy to let you gaze at the heavens through their telescopes. Some veteran amateur astronomers even warn newcomers that they will be disappointed with a telescope unless they first obtain some star charts and guidebooks and make an effort to learn the major constellations, perceive differences in brightness, and learn to explain the phases of the moon. “Learn to use your eyes before you buy a telescope,” they say.

There’s some real value in this advice. You need at least a little working knowledge of the sky before you can locate much of anything with a telescope. In addition, the type of telescope you buy will depend in part on the type of observing that you want to do, and you won’t know that until you have a little experience. So our first piece of advice is to be patient: Don’t run out to a sale at your local Mega-Lo-Mart and buy a telescope just yet.

But let’s face it—part of the fun of astronomy is making faint objects look brighter and distant objects look closer. To many, a big part of the fun of astronomy is its tools.

The Hubble Space Telescope

There are other ways to escape the seeing caused by the earth’s atmosphere: You can get above and away from the atmosphere. In fact, for observing in some portions of the electromagnetic spectrum, it is absolutely required to get above the earth’s atmosphere. That is just what NASA, in conjunction with the European Space Agency, did with the Hubble Space Telescope. High above the earth’s atmosphere, the HST regularly achieves its theoretical resolution.
The HST was deployed from the cargo bay of the space shuttle Discovery in 1990. The telescope is equipped with a 94-inch (2.4-meter) reflecting telescope, capable of 10 times the angular resolution of the best Earthbased telescopes and approximately 30 times more sensitive to light, not because it is bigger than telescopes on the earth, but because it is above the earth’s atmosphere. Unfortunately, due to a manufacturing flaw, the curvature of the 2.4-meter mirror was off by literally less than a hair (it was too flat by 1/50 of the width of a human hair), which changed its focal length. The telescope still focused light, but not where it needed to, in the plane of the various detectors.

Astronauts aboard the shuttle Endeavour rendezvoused with the HST in space in 1993 and made repairs—primarily installing a system of small corrective mirrors. HST then began to transmit the spectacular images that scientists had hoped for and the world marveled at. Subsequent repair missions have installed the short-lived but productive infrared camera (NICMOS) and other instrumentation. A final servicing mission is planned for 2003, after which HST will be replaced by the Next Generation Space Telescope (NGST) near 2010.

New optical technology

The greatest limitation of ground-based observations is that Earth’s atmosphere gets in the way. The turbulence present in the upper atmosphere means that the best resolution attainable with a traditional telescope from the surface of Earth is about 1 arcsecond, or 1/1800 the size of the Moon. Now that might seem like a pretty sharp picture, but for the largest telescopes on the surface of Earth, it is only a fraction of the theoretical resolution, the resolution that a telescope should have, based on its size. It was thought to be a shame, for example, that the 10-m diameter Beck telescope, while it could collect more light, would have no better resolution than a 1-m diameter telescope.
A new technology has been developed to get around this limitation. Dubbed adaptive optics, it allows astronomers to counteract the distortions introduced by the atmosphere with distortions of their own. The distortions are made to another reflective surface inserted into the optical path, the path that light follows through the telescope. The idea is that if the distortions can be removed quickly enough, then large telescopes would have both of the advantages that they should have, namely more sensitivity and more resolution. This technology has produced stunning results recently on the Keck Telescope and the Gemini North Telescope located on Mauna Kea, Hawaii. What does this all mean? As the technology is perfected, ground-based telescopes will be able to make images as sharp as those made from space—in a more easily maintained and upgradeable package.
This technology is very dependent on fast computers and rapidly movable motors that can make tiny, precise adjustments to the surfaces of small mirrors.

Computer Assisted Telescope

Beginning in the late nineteenth century, most serious telescope viewing was done photographically. Astronomers (despite the popular cartoon image) didn’t peer through their telescopes in search of new and exciting information, but studied photographic plates instead. Photographic methods allowed astronomers to make longer observations, seeing many more faint details than could ever be distinguished with visual observing. In recent years, chemical-based photography has increasingly yielded to digital photography, which records images not on film but on CCDs (charge-coupled devices), in principle the same device at the focal plane of your camcorder lens. CCDs are much more sensitive than photographic film, which means they can record fainter objects in briefer exposure times; moreover, the image produced is digital and can be directly transferred to a computer.

Remember the sound of old-fashioned 12-inch, vinyl LP records? Even the best of them had a hiss audible during quiet musical passages, and the worst served up more snap, crackle, and pop than a popular breakfast cereal. CDs, recorded digitally, changed all that by electronically filtering out the nonmusical noise found at high frequencies. Analogous digital computer techniques can be used to filter out the “visual noise” in an image to improve its quality. The disadvantage of current CCDs is that they are relatively small. That is, CCD chips are much smaller than a photographic plate, so that only relatively small areas of the sky can be focused on a single CCD chip.