I’ve Bought My Telescope, Now What?

Many subsequent chapters contain advice on observing various celestial objects, but for now, having bought your telescope (and having assembled it; typically, some assembly is required), what do you do with it?
In two words: Use it.
You don’t need a plan, but many first-time sky watchers christen their new telescope by looking at the moon. A more original inaugural journey begins by marking out an interesting-looking piece of sky for yourself and studying it. Find what you can. Later, we’ll talk about recording what you see.
Another good way to start is to go to your local library and check out Astronomy or Sky & Telescope magazine. Both of these periodicals (and their online equivalents) include a guide to the night sky in their center section every month, and you can check to see if there are any planets in the sky or which constellations are up. Also see Appendix E, “Sources for Astronomers,” for recommended guidebooks. An interesting second activity is to locate another piece of sky—one that looks almost empty—and try to find dim and distant objects. Test the limits of your new telescope and your own eyesight. Notice how many more stars you see with your finder telescope, which has a larger aperture than your eye, and then notice how many stars you see in your main telescope.

The Go-To Revolution

Books on amateur astronomy used to supply only two important pieces of advice about tripods and mounts.
First: Don’t cheap out. Invest in something sturdy and steady.
Second: Choose between an altazimuth mount and an equatorial mount. The simple altazimuth mount is adjustable on two axes: up and down (altitude) and left and right (movement parallel to the horizon, or azimuth). There is nothing automatic about most altazimuth mounts. If you are trying to follow an object, you must continually adjust both the altitude and the azimuth. The alternative equatorial mount is aligned with the earth’s rotational axis and, therefore, may be made to follow a celestial object by adjusting one axis only (to counteract the rotation of the earth).

These two pieces of advice used to be quite sufficient. In the late 1990s, however, popular manufactures started selling even some entry-level telescopes with go-to computer controllers that drive servo-motors built into the telescope mount. The handheld go-to controller stores a database of the locations of thousands of celestial objects. Select a object or punch it its coordinates, and (if properly trained and aligned) the telescope’s servos will point the telescope at your target object.

In addition to servo motors for go-to capability, equatorial and altazimuth mounts typically include a clock drive that synchronizes the telescope with the earth’s rotation so that a given object can be followed—“tracked”—without your having continually to re-aim the telescope.
Go-to capability can work on telescopes that have either altazimuth or equatorial mounts. For example, the go-to features on the Meade ETX 90EC telescope can be used in either equatorial or altazimuth mode. One just has to be careful that the computer has been informed of your choice (usually accomplished on the setup menu). The amazing thing is that go-to technology has become sufficiently affordable to be included in even entry-level telescopes. This feature has truly revolutionized amateur astronomy, greatly broadening its appeal. Keep in mind that the “go-to” hand paddle must typically be purchased as an accessory, and will cost several hundred dollars itself. If this capability is important to you, you should buy a telescope that can be updated at a later time.

Dobsonians: More for Your Money?

During the 1970s, an avid amateur astronomer named John Dobson began building large, standard Newtonian reflectors (10-inch mirrors were typical) and cutting costs by mounting them not on elaborate and expensive equatorial mounts but on inexpensive altazimuth mounts. Dollars were invested in optics and aperture—lightgathering ability—rather than in fancy mounting hardware and clock drives to aid in tracking objects. The result was a powerful reflecting telescope with a wide field of view.

Very nice Dobsonians can be purchased in the $300 to $1,000 range, or you could see if your local amateur astronomy club offers workshops in making your own telescope. Many astronomy club members make their own Dobsonians. Is there a Dobsonian downside? Some users find the simple altazimuth mount—which lacks the ability to track objects—too limiting.

Maksutov-Cassegrain: New Market Leader

Like the Schmidt-Cassegrain telescopes, the Maksutov-Cassegrain is a catadioptric design; however, these newer instruments optimize imaging performance by combining a special spherical meniscus (concave) lens with two mirrors. The secondary mirror multiplies the focal length of the telescope. The combined effect of the concave lens, the aspherical primary mirror, and the convex secondary mirror produces a telescope that is almost as well suited to lunar and planetary observation as a refractor, yet it has many of the reflector’s advantages for deep-space viewing. These qualities are similar to the conventional Schmidt-Cassegrain design, but the Maksutov-Cassegrain variation tends to yield images of greater contrast than one gets from telescopes of the earlier design.

A 7-inch Maksutov is significantly more expensive than an 8-inch Schmidt-Cassegrain; however, Meade has marketed for some years now two extremely popular small Maksutov models, the ETX-90EC and ETX-125EC (90 mm and 125 mm, respectively), which trade aperture for price. The 90-mm model can be purchased for under $500, and the 125-mm model for less than $900.

Diagram of a Maksutov-Cassegrain telescope. Light enters the concave lens at the right and is reflected by the aspheric primary mirror at the left, which sends it back to the spherical secondary mirror on the right. This, in turn, focuses the image on the focal plane on the left.

Schmidt-Cassegrain: High-Performance Hybrid

Also called a catadioptric telescope, the Schmidt-Cassegrain design combines mirrors and lenses. Telescopes of this design are an increasingly popular choice for serious amateurs and introductory astronomy classes. The light passes through a corrector lens before it strikes the primary mirror, which reflects it to a secondary mirror. Since light bounces down the tube an extra time, the focal length of the telescope is effectively doubled, belying the very compact—wide but short and stubby—look of the instrument. A long effective focal length means that these telescopes can have a high magnification (remember that magnification is the ratio of objective focal length to eyepiece focal length) without a cumbersome long tube. Schmidt-Cassegrain telescopes are elegant instruments that offer some of the compactness of rich-field instruments but are much more powerful. The catch?


Diagram of a Schmidt-Cassegrain, or catadioptric, telescope. Light enters from the left and is focused by the primary mirror at the back of the telescope. Then it is refocused by a secondary mirror and sent out through an opening in the primary mirror to an eyepiece at the rear of the telescope.

These are usually more expensive amateur instruments, typically priced from $900 to much, much more, depending on aperture size and features. The portability of the Schmidt-Cassegrain design is a very big plus—not just because a compact telescope is easier to transport, but also because it is easier to keep a small scope stable during use.

Rich-Field Telescopes: Increasing in Popularity

Worth investigating is a relatively new category of telescope. Ultra compact and reasonably priced, rich-field reflectors are typically handheld with a Newtonian focus. What they have in common is a short-tube design that offers low degrees of magnification but a bright, wide field of view (typically a few degrees). They range in price from about $250 to $400 and can weigh as little as 4 or 5 pounds. Highly portable and relatively rugged, these telescopes nevertheless have the disadvantage that, since they are handheld, they do not track with objects in the sky, and are only as steady as you are. The great advantages of these telescopes, besides price, are their portability and the brightness of the image they deliver.

Refractor and Reflector

Refractor
Most astronomers agree that a good refractor is the instrument of choice for viewing the moon and the planets. Typically, the refractor’s field is narrow, which enhances the contrast offered by good optics and brings out the details of such things as the lunar surface and planetary detail.
Refractors, however, are not the best choice for deep-sky work—looking at dim galaxies, for example. They are great for bright objects, but a refracting telescope with the same light-collecting ability of a decent reflecting telescope would be prohibitively expensive.
Some of the cheapest, mass-market telescopes are refractors, but most of these will perform poorly. Most good refractors are long, heavy, and expensive—although the recently introduced Meade ETX-60AT and ETX-70AT are compact yet high-quality entry-level instruments. The disadvantage of expense is obvious, as is that of weight: You’ll be discouraged from taking the telescope with you on trips to the dark skies of the country. Length poses a less obvious problem. The longer the tube, the less inherently steady the telescope. A large refractor requires a very firm mount and tripod.

Reflectors
Traditionally, the Newtonian reflector has been the most popular telescope with experienced amateurs, although, in recent years, affordable Schmidt-Cassegrain and Maksutov-Cassegrain instruments have found increasing favor. Generally, a reflector gives you more aperture—and thus more light—for your dollar than a refractor, and the reflector’s mirror is not subject to chromatic aberration (the differences in the ways various colors, especially red and blue, are focused), which all but the most expensive refractor lenses suffer from. Although reflectors may be large, they are generally lighter than refractors; however, they tend not to be as robust, and unlike a good refracting telescope, they do require at least some minimal maintenance to realign optical components occasionally.