So You Wanna Buy a Telescope...
Advice for Beginners
By Ed Ting
Updated 8/31/06
 Best Telescopes, telescope accessories, astronomy products from OpticsPlanet.com, Meade, Celestron, Bushnell, Tasco, Swift, Coronado, Galileo, Konus, Leica, Leupold, Zhumell, Oberwerk, Pentax, SolarScope, Steiner, Streamlight, Swarovski, TeleVue, Vixen, Nikon, Zeiss from OpticsPlanet w/ FREE UPS!
|
So, you've decided to take the plunge and buy a telescope -- congratulations!
Astronomy can be a life long pleasure, with the right equipment. But what to
buy? And how do you not wind up with a room that looks like the above? There's
more equipment out there than ever before. This article will attempt to make
some sense out of the seemingly huge selection of scopes and accessories.
Ready? Good. Let's begin. First of all, some words of advice:
1) Learn to spot a few constellations and maybe a planet or two with the
naked eye. If you can't point to M42, how do you expect to able to point a
telescope (which has a much narrower field of view) there?
2) Subscribe to one of the two major magazines, Sky and Telescope or
Astronomy. These will get you started not only with finding celestial objects,
it will also acquaint you with the variety of equipment out there. Don't buy
anything yet!
3) Join a club, or tag along on one of their observing sessions. This is
the single best piece of advice I can give you. There is no substitute for
spending time with real equipment out in the field. You may discover, for
example, that you like the portability of Schmidt-Cassegrains, or that you
enjoy the views through a good refractor, or that the big Dobsonian you saw
in the catalog is much more of a handful than you imagined. Or whatever.
There's no substitute for experience.
That said, your ideal first telescope may not be a telescope at all, but
a pair of binoculars. Perhaps you have a pair lying around the house
already. Most experienced astronomers keep a pair of binoculars close
by, for quick peeks or for scanning the field of view before using their
telescopes. The common recommendation is to get a pair of 7X50's, or
at least, 7X35's. The first number "7" is the magnification, the second
"50" is the aperture of each objective lens, in mm. You want the largest
lenses you can comfortably hold.
Many astronomers opt for 10X50's, although you should make sure in
advance that you can hold them steady at that power. It seems that
the current trend is towards 10X50's, but I still like the traditional
7X50 size.
Finally, there are new "giant" binoculars which can give stunning views
of the heavens, if you know how to use them. If someone offers you
a view through one of these, by all means oblige, but hold off buying a
pair for now. You'll know later if you want them.
OK, so binoculars aren't exciting the way telescopes are. Before I leave
the topic, allow me to make a final case for good binos:
1) Cheap binoculars are much, much more useful than cheap telescopes.
Trust me on this one.
2) Good binoculars can last you a lifetime. As you trade up (or down)
your telescopes, you'll still need a pair of binos for quick peeks and
scanning. As a result, binoculars tend to be something you buy only
once or twice.
Telescopes!
Ask a roomful of people what the purpose of a telescope is, and chances are
they will say something like, "to make distant objects look bigger." I'm a
frequent guest speaker at local schools, and I always get that answer (or
something close to it) when I ask that question.
Is the primary function of a telescope really to make things look bigger?
Take this test. Step outside on a clear night from a brightly lit room. See
anything? Probably not. But it gets better after a few minutes, doesn't it?
In fact, after a while, you'll wonder why you didn't see all those stars before.
What made it better? Did you change the magnification, or make the appar-
ent size of anything change? Of course not. What you DID change, was the
amount of light your eye gathered, when your pupils opened to compensate
for the darkness.
So, the primary function of a telescope is to gather light.
The more light a scope gathers, the more powerful it is. And remember,
telescope apertures are circles, and the areas of circles increase with
the square of the radius, so moving up in aperture, even modestly,
can yield big results. Our hypothetical 7X50 binoculars (above) gather
over twice the light of the 7X35's, even though they look about the same
size. Put another way, the owner of an 10" Schmidt-Cassegrain who
decides to upgrade to a 12" will see a 44% increase in light-gathering
ability. Not bad for a 2" increase, eh?
So, you should buy the biggest telescope you can afford, right?
The answer, is an unqualified MAYBE, and for some people, the answer
will be NO. But we're getting ahead of ourselves.
Types of Telescopes
Modern amateur telescopes can be divided into three classes:
1) The refractor is what most people think of when they hear the word
"telescope". Refractors gather light with an objective lens at one end and
focus the light at the eyepiece at the other end. Refractors were almost
extinct at one point, but modern glass elements (including an exciting new
artificially grown crystal known as fluorite) have brought the refractor
back to prominence.
Refractor advantages: Potential for the best images, no obstruction in
light path.
Refractor disadvantages: Some secondary color ("chromatic aberration")
still visible in all but the best units, large aperture instruments can be
massive, most expensive of the three designs (often by a large margin),
"Guilt By Association" with horrible department store refractors.
A typical 4" refractor
2) The Newtonian Reflector, invented by Sir Isaac Newton, uses a
parabolic mirror at the end of a tube and focuses the light back at the
front of the tube, where the eyepiece sits, after being deflected by a
smaller secondary mirror in the light path.
Reflector advantages: Cheapest of the three designs (especially those
on Dobsonian mounts), more portable than refractors of similar aperture,
inherently color free (no chromatic aberration).
Reflector disadvantages: Secondary obstruction results in some loss
of contrast, still quite large compared with Schmidt-Cassegrains, can
require frequent collimation (alignment) of optics.
An 8" Newtonian Reflector
3) The Schmidt-Cassegrain and its derivatives (Maksutov-Cassegrain,
Classical Cassegrain, etc.) use BOTH mirrors and lenses to fold the
optical path back onto itself, resulting in a compact tube. The technical
term for these scopes is catadioptrics, but since nobody seems to use
this term, I won't.
S-C Advantages: Most compact of the three designs, less expensive than
refractors, huge assortment of after-market accessories, can be totally
computer driven, very popular.
S-C disadvantages: More expensive than reflectors, images are potentially the
worst of the three designs (notice I said "potentially!"), most subject to dew
of the three designs.
Meade's ETX, a Maksutov-Cassegrain
So, which one should I buy?
Depends. The "right" telescope depends on you, your observing habits,
and your financial situation. Picking a telescope used to be a simple
matter. You started out with a 60 mm refractor (probably from a department
store), then you upgraded to a 6" f/8 reflector from either Criterion or
Meade, and if you stuck with it long enough, you eventually bought an 8"
Schmidt-Cassegrain from Celestron.
My, how things have changed. Throughout the 1960 and 1970's, the Newtonian
reflector ruled the amateur roost. From about the 1980's onward, astronomers
flocked to the portability of Schmidt-Cassegrains as both Meade and Celestron
duked it out to try and out-do one another on features. Then, the refractor,
long given up for dead, came roaring back with the advent of ED and fluorite
glass. Now, you see all three designs in use regularly.
The advantages/disadvantages of each design are well-documented elsewhere,
so I'll attempt to give you some "other" information which may be useful to you.
Despite the optical superiority of good refractors and the lower cost of
reflectors, most astronomers still wind up with Schmidt-Cassegrains as
their primary instruments. It's not hard to see why. A 10" S-C is relatively
affordable and portable. A 10" reflector is a handful, especially an equatorially-
mounted one. And a 10" refractor? Forget it -- you'll probably need a separate
observatory to house one.
4.5" or 6" reflectors make excellent beginner's instruments. For $300-$650,
you get a decent aperture and a scope that's relatively portable. On the
refractor side of the table, look for an 80 mm scope on a stable mount.
Avoid like the plague any cheap refractor sold on the basis of its magnification.
A "675X" 60 mm telescope is almost certainly a piece of junk. Maximum useful
magnification is usually given as 50X-60X per inch of aperture. Thus, the 60 mm
example given above is really only a 120X-144X telescope (and its images will
probably break down well before that point). You find these scopes all over
the place, in department stores, toy stores, etc. This is not just what Ed Ting
thinks you should do. This same important advice can be found in any responsible
text on telescopes.
Let me repeat that one again: Do NOT buy a telescope from your local depart-
ment store, toy store, or from a television commercial. Most scopes found
at the Nature/Science stores at your local mall also fall under this category.
These telescopes are little more than toys and will likely kill your budding
enthusiasm. Buy from a retailer who specializes in serious amateur telescopes.
Some of the better ones are linked off my "links" page. As a general rule, avoid
any telescope that costs less than $300. Please do not e-mail me with something
you have found in a dept store.
I'll say one thing for Newtonians. They're the most comfortable to use
of the three designs. The eyepiece is nearly always at a convenient height.
Refractors are the worst in this regard. Looking at anything near the zenith
with most any refractor is a less-than-appealing proposition.
Many astronomers give up trying to decide what's best for them and buy
more than one scope. While this may not be the best advice for beginners,
newcomers might want to keep this in mind when making a purchasing
decision. For example, if your first scope is an 80 mm refractor, you
might balance things out by getting a 12" Dobsonian in a year or two.
That way, you'd have both a light bucket and a planetary/double star scope.
Avoid any thoughts of astrophotography for now. You are going to
have your hands full dealing with the scope itself. Trust me. More astronomers
leave the hobby due to excessive involvement with astrophotography than for
any other reason, save the cheap department store telescopes.
Finally, avoid "paralysis-by-analysis." If you spend more than an hour
a day reading telescope catalogs, you are probably in this category. Just
get something; you'll feel a lot better.
OK, Ed -- You still haven't answered the question: Which one
would you buy, if you could only get one?
This is a tough one to answer, since everyone has their own priorities and
preferences. Still, knowing what I know, if I were starting out today, I
would probably get a 6" or 8" Dobsonian-mounted reflector. The fact that
I am something of a "refractor guy" says a lot about this choice.
A 6" Dobsonian is simple, cheap, and will teach you a lot. The simplicity part
is important, since you will spend your time aiming and observing with your
telescope, rather than playing around with the sometimes complicated controls
on an equatorial mount.
Beginners need early success, and the 6" or 8" aperture is big enough to throw
up a bright image of most common celestial objects.
A great beginner's scope: Orion's XT8,
an 8" Dobsonian reflector ($499)
I like all the 6" Dobsonians from Meade, Celestron, Orion, and Discovery.
I like the Orion the best, but you can just pick one; they're all good.
If you're feeling ambitious, get an 8" version. The differences between
the brands show up mainly in the quality of the accessories. Look for a
6X30 finder (or larger), Plossl instead of Kellner eyepieces, and Pyrex
instead of plate glass mirrors. If I were pressed to recommend one
telescope for beginners, it would be the Orion Skyquest XT8.
Avoiding "Aperture Fever"
Audiophiles have a saying that goes something like this: The stereo system
which reveals the most music to you is the one you use the most.
For most of us, that's our car stereo.
Astronomy is a lot like that. The probability that a telescope will be
used is inversely proportional to its size. This seems to apply to just
about everyone, regardless of experience.
I've carried on a correspondence with a fellow astronomer. He has an 18"
"Luxo-Dob", I have a tiny TeleVue Ranger. Our conversations tend to go
something like this:
Me: So, did you see Saturn last night?
Him: No, it was too cold out to go observing.
Me: Oh.
Him: But my 18" dob blows your puny little 2.7" refractor out of the water,
you teeny dweeb!
OK, so maybe it doesn't go exactly like that, but you get the idea. Sure,
he's got me whipped on aperture, but I got in 2.7" worth of observing that night,
and he got in zero.
Little scopes get used more often, and thus show you more. Your Luggability
Tolerance may be different from mine, however, and that's where visiting
public star parties becomes an invaluable experience.
The star parties also come in handy when I DO want to look through a big
scope. I just look through someone else's. This way, I get my share of
"big gun" observing time and I don't have to deal with the hassle of set up
and break down.
For balance, I should state that I have recently learned to dodge this
"bulk" issue with larger telescopes by placing them on rolling platforms
with lockable castors. Go to your local lumber yard/hardware store and
get 3/4"-1" thick plywood and four castors. Don't skimp on the quality
of the castors; get the best ones the store carries. Also remember to
use lock washers or the nuts will eventually work themselves loose.
I can leave the 20" Obsession fully assembled in my garage, and when I
want to use it I just roll the whole thing outside. I can be observing in less
than 5 minutes. There is something rather nice about kicking a 20" Dob
out the door and observing with it within a couple of minutes while your
friends are still assembling their small equatorial mounts. This works so
well, I built platforms for the rest of my scopes as well.
Eyepieces
The TeleVue Radians
Here's one area where beginners tend to go overboard. You don't really
NEED more than 3 or 4 carefully chosen eyepieces, a barlow, and perhaps
a filter or two, but most of us eventually wind up with collections, some
of them needlessly impressive. Still, the first accessory a newcomer
buys is usually a new eyepiece. Below is a guide to various designs.
Ramsden and Huygenian are 2-element eyepiece designs. While simple,
they exhibit narrow fields of view, have numerous aberrations, and terrible edge
correction. Generally supplied only with the least expensive telescopes. While
not of much use visually, they make good solar projection eyepieces (i.e. you
can risk 'em). About $25-$40.
The Kellner is a three element design that shows an acceptable 40-45
degree FOV, and good correction of spherical and chromatic aberration.
Offshoots include the Meade MA, Celestron SMA, and Edumnd RKE. A
decent general-purpose eyepiece for the price. About $30-$50.
Orthoscopic eyepieces were once considered the best for general use, but
have lost some of their luster compared with newer Plossl designs. Using 4
elements, they are still popular for planetary work. They are well corrected
throughout their 45 degree FOV. About $40-100.
The Plossl seems to be the most popular eyepiece design today. Using 4 or
5 elements, they are very well-corrected and have a wider (50-52 degree) FOV
than Orthoscopics. However, some models have shorter eye relief than equivalent
Orthos. About $50-$150.
Erfles seem to have fallen out of favor these days. Using 6 elements, Erfles
throw up a wide 60-65 degree FOV, with increasing distortions near the edge.
Rapidly becoming extinct. About $75-$150.
Newer designs, primarily from the efforts of TeleVue, are gaining in popularity.
These include the 6 element, 67 degree FOV Panoptics (about $200-$400)
and the 7-8 element, 82 degree FOV Naglers (about $175-$425). Both
series are truly amazing. It is said that once you have looked through a
Nagler, nothing else will be good enough for you. As a Nagler owner, I think
they might have a point.
Sparked by the success of the TeleVue eyepieces, the Japanese have gotten
into the act. The Meade Super Wides ($140-$300) and Ultra Wides ($170-$300)
are virtual clones of the TeleVues. And Pentax's 6-7 element SMC-XL (about
$250 each) are thought by some to exceed the performance of the TeleVues,
especially at the lower focal lengths. Vixen's Lanthanums ($100-$200) and
TeleVue's Radians ($250) throw out a generous 20 mm of eye relief regardless
of focal length, and are a godsend to those who must wear glasses while observing.
Many observers find a barlow lens to be a valuable accessory. Inserted
between the focuser and your eyepiece, a barlow will typically double or triple
the magnification of any eyepiece. Thus, for $60-$100, you have effectively
doubled the size of your eyepiece collection. Also, a barlow preserves the eye
relief of your longer focal length eyepieces, thus reducing the amount of squinting
you have to do.
What can I expect to see?
Next to "What telescope should I buy?" this is the most common question I
usually get asked. This is a tougher question to answer than you may think.
What you can see depends on a lot of factors, including the type of telescope
you bought, the quality of your local seeing conditions, and your level of
skill.
Since the quality of your instrument and conditions are largely out of
your control, it would make sense to hone your observing skills. Sadly,
I don't see this happening much anymore. Observers, eager for instant
results, often upgrade to larger and larger telescopes without bothering
to learn how to "see" properly.
Seeing well is both an art and a skill. You need to spend lots of quality
time with your telescope. The more you look, the more you will see, and
the better you will get. As a result, an experienced observer might enjoy
deep sky objects in an 80 mm refractor, while a beginner with a light
bucket next door is still struggling to find the Orion Nebula.
Astronomy is a patient hobby. Don't be in too great a rush. The cosmos
will still be there tomorrow.
OK, now that the lecture is over, here's what you can see with a typical
6" reflector under reaonably good skies:
All 110 Messier objects, which includes nebulae, open and globular
clusters, and extended galaxies. Most of these will seem impossibly
dim to you at first. Later in your career, they will seem really bright.
All of the planets except Pluto. Saturn's rings are easy. Shadow
transits on Jupiter are easy. Detail on Mars is somewhat harder, but
gets a little easier once every two years. Venus, Mercury, Neptune,
and Uranus are pretty much featureless balls.
Hundreds of named craters on the moon.
Sunspots and other activity on the sun, with a proper filter.
Do not look at the sun without proper filtration!
Hundreds of other various objects.
Summing it up...
In summary, here are the prominent points given above:
1) Binoculars, even cheap ones, are sometimes a good substitute for a cheap
telescope. In addition, binoculars are almost always good companions to a
telescope.
2) Avoid department store, toy store, and "Nature/Science" store telescopes.
I cannot restate this strongly enough: STAY AWAY from department store
telescopes!
3) The primary purpose of a telescope is to gather light. Thus, all other
things being equal, beginners should buy the largest aperture telescope they
can afford. A 6" Dobsonian reflector is an excellent first telescope.
4) BUT, if the instrument is too large, you may never use it. Be realistic
about what you're willing to lug around.
5) You don't need more than 3 or 4 carefully chosen eyepieces in your collection
at first. The minimum quality you should consider are Kellners (and their offshoots).
A barlow is useful tool for doubling your collection at minimal cost.
End Beginner's Advice
Home Page