Amateur astronomers occasionally seek advice on telescope buying, learning the sky, observing skills, and so on. Here are some thoughts.
(My credentials? I do visual astronomy: I have logged over 20000 observations of more than 10000 objects, and used some thirty telescopes and binoculars enough to know them well. I have made about ten optical surfaces to 16-inch diameter. My forte is deep-sky work: I am especially proud of logging the Sculptor Dwarf Galaxy (10x70 binocular), Maffei I and Einstein's Cross (Celestron 14), and Simeis 147 (6-inch Maksutov). My interests led to a physics PhD, studying the interstellar medium from a spacecraft: By training I am an astrophysicist, but I have amateur status in the visual -- my thesis work used extreme ultraviolet light.)
What to do First.
To find clubs, ask at science stores, museums, and planetariums. College physics or astronomy departments may know, though clubs aren't their line. The magazines Sky & Telescope and Astronomy publish annual directories of clubs, stores, observatories, and such. Find them on newsstands, or in a library -- or try their respective web pages, www.skyandtelescope.com and www.astronomy.com.
Been to a club already? Honest? Okay, keep reading...
If you have a telescope, you might skip on to "What about observing skills?". Otherwise, here are some hints on telescope selection.
Hey! Just Tell Me What To Buy.
Some Basic Questions.
With these thoughts in mind, I can make some general comments.
There is one special case: For delicate planetary detail, a fine refractor may do 50 percent better than a fine example of any other common design.
One qualifier: Their portability comes from short tubes, but for small apertures -- four inches or less -- portability of all types is dominated by clumsiness of the tripod, so the advantage of Schmidt-Cassegrains and Maksutov-Cassegrains diminishes.
Let me regroup that information into three common questions:
Usually, a high-quality refractor.
Usually, a Schmidt-Cassegrain or Maksutov-Cassegrain.
Usually, a medium to large Dobson.
My Big Iron is Harvey, a white Celestron 14 that stands six feet, three and a half inches tall on its Losmandy G-11 mounting. Believe it or not, Harvey fits into a Geo Metro with room for me and plenty of luggage, too. A C-14 is a handful to set up -- the optical tube assembly of mine weighs 52 pounds, and that's a lot to lift shoulder-high over uncertain footing on a cold, dark night -- but the advantages of a compact, driven telescope with a convenient eyepiece position are worth a lot.
Buyers of Big Iron enjoy a diverse market. There are many manufacturers of Dobson-mounted Newtonians with apertures as much as a meter, there are amateur-type Newtonians with apertures up through at least 40 cm available on German equatorial mounts, and Celestron and Meade have Schmidt-Cassegrains of apertures 35 and 40 cm, respectively.
I have had several Largest Conveniently Portable Telescopes. Once I built an eight-inch Dobson designed so the tube just barely fit across the back seat of my car. I used it a lot till I bought a smaller car. Then I took to a Vixen 90 mm f/9 fluorite refractor, a handy size of telescope with absolutely wonderful optics, on an altazimuth fork or a Great Polaris German equatorial, and I have also put other telescopes on the same mounting. A faster Dobson than my 8-inch would do, with more performance for most purposes. Then I bought a Celestron NexStar 8, which I describe at greater length later herein. But my current favorite is an Astro-Physics 130 mm f/6.3 "Gran Turismo" triplet apochromat, which I mount on the same Losmandy G-11 that I use for Harvey.
Several manufacturers make decent 15 to 25 cm Dobson-mounted Newtonians, 12 to 25 cm Schmidt-Cassegrains and Maksutovs, and 9 to 13 cm refractors. Any of these will probably do for a Largest Conveniently Portable Telescope.
At present I am using my Astro-Physics "Gran Turismo" -- described in the last section -- for this purpose.
My current Quick Look 'Scope is a 70 mm f/8 Vixen fluorite refractor on a light altazimuth mounting that has slow motions.
Truly excellent telescopes in very small sizes are mostly scarce, and mostly out of production. If you want a high-end Quick Look 'Scope, my advice is to wait until you know exactly what is right for you, then keep an eye on the used market until it shows up.
Many people mount binoculars on a tripod, but for me their primary advantage has been extremely quick setup -- just open the case -- and walk-around portability. If I am going to go to the trouble of putting something on a mount, I would rather have a more versatile instrument there -- a telescope.
There are binoculars of every shape and kind, and describing how not to pick a bad one takes a whole separate article. Be careful, because there are lots of junk binoculars on the market.
I have an Orion 120 mm f/5 refractor optical tube assembly, and I have built a simple home-made altazimuth mounting, with teflon bearings, for it. This combination works so well that I have all but retired my 25x100 binocular.
The name "rich-field telescope" stems from the vast number of stars that one can see in a Milky Way field with a low-magnification instrument about the size of my Orion 120.
The default High-Tech Conversation-Stopper these days is usually an apochromatic refractor, or something close. ("Apochromat" is a precise technical term; not all superb refractors are apochromats, and vice-versa.) If well made and well baffled, it will deliver outstanding performance for its size. Available sizes suffice for many amateurs who have recovered from aperture fever or not yet succumbed, or who have exhausted their supply of fullbacks and circus elephants to set up Big Iron. Few other telescopes types qualify -- you're not allowed to have a Schiefspiegler unless you can spell it, and nobody wants a Yolo because people expect you to walk the doggie. Some Maksutovs make the grade, particularly Maksutov-Newtonians with tiny diagonal mirrors.
My High-Tech Conversation-Stoppers are the 90 mm Vixen fluorite I mentioned earlier, a 1987 model Astro-Physics 6-inch refractor, a 10-inch Astro-Physics Maksutov-Cassegrain, and the 130 mm Astro-Physics "Gran Turismo". The Vixen is too small to be really impressive, and is short on knobs, but I talk fast enough to make up the difference. The Astro-Physics units are bigger, and do a vastly better job of inflating my ego.
There are at least four manufacturers of first-rate refractors whose wares are regularly sold in the United States, where I get to see them, and several more elsewhere in the world. High-end Maksutovs in both Cassegrain and Newtonian configurations are available from several manufacturers. They are somewhat less expensive for their size than refractors, hence show up in larger sizes.
CyberScopes do a decent job locating large numbers of objects from an internal database, and permit motorized tracking with a telescope lighter, less bulky, simpler to set up and align, and rather more expensive than if it were equatorially mounted. Low-quality mechanisms and sloppy construction often restrict their potential. Even so, those fond of technology may like them a lot, and folks with skill and equipment to program the control interface have a field day doing things most of us have never dreamed of.
It took me a long time to get around to buying a CyberScope. That's because I write computer programs for a living, and too many of them. In my hobbies, I avoid anything suspected to contain electrons.
Actually, I didn't really feel the need for one, because of personal history: I developed my star-hopping skills before CyberScopes became available, and I find myself good enough at it that a "go-to" interface couldn't help much. I spend enough time looking at things I find, that it wouldn't go a lot faster even if I could locate new ones instantly. Star-hopping isn't hard to learn, and I expect most amateur astronomers would find use for the knack if they had it. Yet not everyone chooses or bothers to learn it, and most beginners want to find things to look at right away.
What I bought, out of curiosity as much as anything else, was an early model Celestron NexStar 8. The version I got was the one with the single-arm fork, no built-in global-positioning system, and flimsy tripod. The software was buggy, the user interface uninspired, the pointing only marginally adequate for finding things with a low-magnification eyepiece (I added a real finder to help), it took a few trips to the hardware store to fix that tripod, and oh, yes, there were some errors in the database. Notwithstanding, the optics of the telescope are very good, it has proved extremely easy to find things with the unit, it is very portable, and also quick to set up and take down.
I have used the NexStar 8 a lot, and have modified the mount so I can remove the original optical tube assembly and attach others. This mount, with one or another tube assembly, has become a very useful small-telescope system. If it were lost or stolen I would probably buy another like it. That I am able to speak so well of such an ineptly implemented product probably says great things about the future of CyberScopes; I do hope Celestron gets its act together.
In any case, prices of electronic aids for finding objects, both as accessories and as part of the original telescope, have been declining. The ease of use of such equipment, and its advantages for people who do not know the sky well, has probably gotten many folks going in the hobby, who would otherwise have been intimidated or frustrated by inability to find things to look at.
Several manufacturers produce telescopes with computer-operated drive motors, like my NexStar 8. They can find objects on the user's behalf. Many more produce digital setting circles (DSCs), both as part of complete telescopes and as add-on accessories, that tell where a telescope is pointed. They even work for altazimuth-mounted telescopes, including the ubiquitous Dobson-mounted Newtonians.
At present, I can think of only two reasons to be cautious about purchasing this kind of equipment. First, its cost is not always negligible, particularly if you are contemplating adding the capability to a telescope that didn't come with it. Second, the fancier stuff -- in particular, the computer-operated drives -- is not available on all the kinds of telescopes that you might want to buy.
What are common beginner telescope-buying mistakes?
The tripods generally used with spotting 'scopes often do not allow the telescope to point very far above the horizon. That is a serious obstruction to doing astronomy. Parents often buy a little telescope on a table-top tripod of this sort, for a child who wants to look at the stars, without realizing that it won't point high enough to see them.
On the other hand, a spotting 'scope on a light tripod is often handy for quick looks at things. Just be sure you are willing to put up with its limitations before you buy one.
What about mountings?
A badly mounted telescope may jiggle too much, or move in jerks too big for finding things. Beginners often do not appreciate these problems, and many units advertised as first telescopes have mounts that are way too flimsy, particularly mass-market junk refractors.
Good mounts can be expensive. For equatorially mounted telescopes, a very rough rule of thumb is that a decent mounting will cost as much as the optical tube assembly. Good altazimuth mountings are generally less costly, but that does not mean cheap altazimuth mountings are good ones.
Carefully weigh the benefits of an equatorial mounting versus its added cost, weight, and bulk. Even without a sidereal drive, an equatorial mounting often makes it easier to find objects and track them across the sky, and it also helps figure out directions in the field of view. Yet if you mostly prefer to observe deep-sky objects at lower magnifications, these advantages may be minor.
A driven mounting, whether equatorial or altazimuth, also offers advantages. It helps when you are making precision observations at high magnification, or when you want to step away from the eyepiece to consult your charts or make notes, and it is invaluable for showing things to long lines of people at a star party.
Among altazimuth mountings, the style invented by John Dobson has special merits. Sturdy construction from materials that damp vibration well makes a good observing platform. Slippery plastic -- like DuPont's "Teflon" -- in the bearings lets you track stars by hand, without electrical or mechanical slow motions. Simplicity permits inexpensive Dobson mountings that are solid and durable. Unfortunately, some commercial manufacturers of Dobson-mounted Newtonians have cut too many corners, and produced units that are too flimsy.
What about accessories?
Yet if you are up against limits of telescope portability, or have lots of money, or like technology, go ahead and buy fancy accessories. I won't tell, provided you remember that APERTURE WINS.
In any case, I will mention some plain-vanilla accessories that you might want to have, and maybe a few chocolate ones, too:
The next magnification you will likely reach for is medium to medium high, to see details. Such an eyepiece might give magnification roughly equal to telescope clear aperture, in millimeters. On my C-14 I use a 12 mm eyepiece, and on my 8-inch Dobson, a 4 mm. The objects you look at with this magnification probably won't be very wide, so for economy, you might not want a super-wide-field type.
I also find lots of use for an eyepiee that gives a magnification of roughly two-thirds the telescope clear aperture in millimeters -- say, a 16 mm focal length on my C-14. I find that a very useful magnification for looking at galaxies.
Your next choices will depend on what you like to look at. If you are not sure, hold off buying more eyepieces till you find out.
"Fast" f-numbers, typical in Dobson-mounted Newtonians, need fancy, expensive eyepieces to give good views, because the steeply converging light cones of these instruments are difficult for an eyepiece to cope with, particularly away from the center of the field. Slow instruments can use simpler eyepiece designs. A "Catch-22" of amateur astronomy is that cheap telescopes (fast Dobsons) need expensive eyepieces, but expensive telescopes (most refractors and Schmidt-Cassegrains, with slow f numbers) can use cheap eyepieces.
"Zoom" eyepieces change focal length at the twist of a knurled ring, but many of the ones around, particularly the older models, are not very good. Recently, however, several manufacturers have released units reported to be serviceable. The only ones that I have seen are by Vixen and Tele Vue, but there are said to be others. The range of focal length of the Vixen and Tele Vue units -- 8-24 mm -- neatly spans most of the range that many of us use for deep-sky observation. Visibility of faint features often varies dramatically with magnification, and is sometimes maximized only over a very narrow range, so a good zoom eyepiece may be a valuable addition to the deep-sky observer's kit. Yet do try one out before you buy, for they are not cheap.
Barlow lenses, also called telextenders, multiply the focal length of a telescope: It used to be that they generally worked well only with telescopes with large f-numbers, where they were not needed -- another "Catch-22". There are now Barlow lenses that work with fast telescopes, where they are needed, but I urge a try-before-you-buy approach to selecting one.
For over fifteen years I used an eyepiece set bought in 1980. It had no fancy designs, just a 55 mm Plossl, 32, 20, and 12.4 mm Erfles, and 7 and 4 mm Orthoscopics. The 55 and 32 mm eyepieces were in 2-inch barrels, the others in 1.25 inch barrels. All were good quality -- the 55 and 32 mm were from University Optics, and the others were Meade Research-Grade. All worked reasonably, even at f/5, and the 68-degree apparent field of the Erfles was enough so I was not tempted by wider-field types. Besides, a big Erfle is already so heavy that I must rebalance the telescope to use one. I did use the 4 mm eyepiece on the C-14, but only rarely.
In mid 1996 I bought some more. I found that decent Plossls are comparable to Orthoscopics. I also got some Vixen "Lanthanum" eyepieces, with built-in Barlow lenses to give 20 mm eye relief, even at such short focal lengths as 2.5 mm. Even without glasses, long eye relief makes viewing more relaxed: I don't worry about bumping the eyepiece. It also helps with public viewing: I focus with glasses on, and tell folks to leave theirs on and not refocus.
A year or so later, I started becoming more particular about eyepieces for viewing objects with lots of fine detail. I eventually bought several Brandons -- a design labeled "Orthoscopic" but which resembles a Plossl -- for that purpose. They are rather expensive, but I was willing to pay for increased performance.
Note what high-tech eyepieces can and cannot do. The best give wider fields, with fewer eyepiece aberrations near the edges, than older types, and work noticeably better at fast f numbers. If that matters to you, you might want some. But eyepieces are not aperture stretchers. They cannot increase image detail beyond the theoretical limit for the aperture, or increase the number of photons that make it to your eye. If you think otherwise, you are making the same mistake as the clueless beginner who buys a drug-store refractor because the box shouts "Magnifies 675 Times!!!". The best an eyepiece can do is not make things worse. A simple eyepiece, with good coatings and well-polished lenses, will show all the on-axis detail a telescope has, and absorb and scatter almost no light. That's what counts most for astronomical work.
In 1980, I bought several Ramsden eyepieces -- an old, simple, design -- for some ten dollars each. I use them at star parties without telling. They have only four air/glass surfaces, so simple coatings give good throughput, and there are few chances for bad polish to scatter light and ruin contrast. The field of view is narrow, but on axis, at slow f numbers, they give up nothing to new designs; images are superb.
In dark sky, the 10x40 finder on my C-14 shows stars to beyond magnitude 10, which is a good match for my big charts. The 7x35 on my 6-inch Maksutov does almost as well. In suburbia, the 5x24 finder on my 8-inch Dobson goes to about magnitude 6.5, which would be the naked-eye limit in darker conditions, and thus matches many naked-eye star atlases.
Unit-magnification finders, like the Telrad, let you view the sky with both eyes, and see a pattern of light where your telescope is pointing. A cardboard and tape peep sight may work as well, and will be much cheaper, and any magnifying finder in which you face where the finder is pointing, can be used with both eyes open -- just let your brain fuse the images from both eyes. I tried a unit-magnification finder (Orion's) on my 90 mm refractor, but found it inferior to the original 6x30 finder.
My opinion on unit-magnification finders is in the minority. I suggest you practice with both magnifying and unit-magnification types, then decide which is for you. But do learn the trick I just mentioned for using straight-through finders; it's very useful.
Some folks run such a program on a laptop, at the telescope. Please put red cellophane over the screen, if you do.
I have little use for the popular oversize-format charts with lesser magnitude limits, like 7.5 to 8.5; they don't show enough stars to be useful with my finders, and are too cumbersome. The plastic-laminated versions make good place mats, though. Everyone should use the box of a Dobson as a picnic table at least once.
Even some experienced amateur astronomers think seeing things comes free and easy, with no more effort than opening your eyes: But as current popular slang so evocatively articulates,
Vision is an acquired skill. You must learn it, you must practice, and you must keep learning new things, and practicing them, too.
Buying a big telescope to see better is like buying a big pot to cook better, or a big computer to program better. It might help, but cooking and programming depend more on knowledge and experience than on hardware. So does visual astronomy. People with garages full of telescopes (I can't close the door to mine) are victims of materialism, marketeering, and hyperbole. Practice is cheaper, and works better. As I said before, an experienced observer may see things with a small telescope that a beginner will miss with one five times larger.
Canadian amateur astronomer Gary Seronik has said that telescopes are like musical instruments. It takes time to learn to play them well, and even an accomplished musician cannot necessarily make beautiful music with a new or unfamiliar instrument right away. And it certainly doesn't make sense to buy a bigger piano or guitar with the hope of thereby making better music.
What skills may you hope to cultivate? What techniques should you practice? Not all have names, but here are a few, in what I think is order of importance; what matters most comes first.
I am not kidding by putting patience and persistence first. There is a lot of stuff in my logbook that I did not see during the first five seconds, or the first five nights, or even the first five years. If you give up, you won't see a thing.
Many observers use averted vision on faint objects, but forget it for bright ones. Detecting something doesn't mean you've seen all of it. Don't let the dazzle of a galaxy's lens make you miss spiral arms that go beyond the field edge. How about increasing magnification, and using averted vision to seek more detail in the paler, larger, image?
Averted vision helps with double stars, when one star is much fainter than the other, even if the faint star is bright enough not to need averted vision if it were by itself. I don't know why.
My first view of the Sculptor Dwarf Galaxy was with my jacket collar pulled up over my binocular eyepieces. I looked like a cross between the Headless Horseman and the guns of Navaronne, but I saw the galaxy.
If you don't change magnifications, how can you be sure you are using the best one?
Clear sky, and enjoy your telescope.
-- Jay Freeman Jay_Reynolds_Freeman@mac.com
PS: Specific Recommendations For The Lazy.
If you simply must have a telescope right away...
The Orion Dobson-mounted Newtonians are not first-rate, but these telescopes are good values. The company has a web site, at www.telescope.com.
Cheaper Celestron 8-inch Schmidt-Cassegrains work just about as well, but without the whiz.
I say again, you will make a better decision and be happier with your purchases, if you join a club and do some homework first. I repeat: You will make a better decision and be happier with your purchases, if you join a club and do some homework first. Good luck!