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Purchasing Amateur Telescopes FAQ by Ronnie B. Kon
Part I
- What is the single most important thing I should know before buying a
telescope?
- What is the single best piece of advice to give to someone thinking about
buying a first telescope?
- What Does All the Jargon Mean?
- What Are Some Good Introductions To Amateur Astronomy?
- What Will I Be Able To See?
- Buying A Telescope
- What Company Makes the Best Telescopes?
- How do Meade and Celestron Name Their Telescopes?
- Comparison of Schmidt-Cassegrains
- What is the Best Telescope to Buy?
1. What is the single most important thing I should know before buying a
telescope?
This is the single most important thing you should get out of this FAQ: DO
NOT BUY YOUR TELESCOPE FROM A DEPARTMENT STORE. Ignore everything any literature
tells you about magnification and such. Buy from a telescope store, where you
will get a telescope that makes as smaller claims, but will give you FAR better
performance. The reason is that as far as telescopes go, how much you can
magnify is a function of the amount of light the telescope receives, which is
almost entirely determined by the telescope's aperture (the size of the lens or
mirror that points at the sky). As far as magnification goes, you can expect 50x
per inch of aperture on a normal night, up to 62.5x on an exceptionally clear
night (this is the number Meade uses in calculating their magnifications).
Department stores always show little 2 1/4 inch refractors for up to 300+
dollars and say that the refractor can get up to a whopping 600x or so. Strictly
speaking, this is true. However, applying the 50x rule, it is easy to see that
125x would be pushing the optics, and that is assuming that they were high
quality ones. With the quality of the parts they usually give you are lucky to
get 100x with reasonable resolution.
2. What is the single best piece of advice to give to someone thinking
about buying a first telescope?
Find a local astronomy club and attend a star party. Find ways to look
through telescopes of different quality and prices so you can determine what you
want to buy. This FAQ can give you information, but cannot possibly compare to
actually going out and looking for yourself. Besides, it's the last chance
you'll get to look at the sky for free.
3. What Does All the Jargon Mean?
OK, by popular request, here is a glossary of common astronomy terms
encountered in amateur astronomy.
altazimuth mount
This is what you think of when you think of a tripod mount. It
allows movement in two directions: parallel to the ground
(azimuth), and at right angles to the ground (altitude). It is
very useful for terrestrial observations, as it is a very natural
way of observing. It is significantly less useful for astronomi-
cal use, where an equatorial mount is preferred.
aperture
The diameter of the objective.
Barlow
A Barlow lens is a device which has the effect of increasing the
magnification. It does this by lengthening the effective focal
length of the telescope you are using. Thus a 2x Barlow will
double the magnification, a 3x will triple it. Barlows used to
have a bad reputation, stemming largely from rather poor quality
ones being sold. Modern Barlows are high quality and a good
choice for expanding your collection of eyepieces. You should
keep the Barlow in mind when buying eyepieces--buying a 3mm, 6mm,
12mm, and a 24mm and a 2x Barlow is a very dumb idea. The only
use you get from the Barlow is changing the 3mm to a 1.5mm (which
is probably going to give you higher than usable magnification
anyway). On the other hand, a 6mm, 9mm, 15mm and 24mm would be
complemented very well by a 2x Barlow.
catadioptric
Any of a number of compromise telescope designs, using both a
lens and mirrors. Examples are the Schmidt-Cassegrain and
Maksutov-Cassegrain. Because the light path is folded twice, the
telescope is very compact. These are pretty expensive. Pictures
can be seen in the ads in any issue of a popular astronomy maga-
zine: the Meade 2080 and the Celestron C-8 are examples of
Schmidt-Cassegrain; the Celestron C-90 and Questar are examples
of Maksutov-Cassegrain.
chromatic aberration
In refractor telescopes, which use lenses to bend the light, dif-
ferent wavelengths of light bend at different angles. This means
that the stars you see will usually have a blue/violet ring
around them, as this light is bent more than the rest of the
spectrum. It is not present at all in reflectors, nor to any
significant degree in catadioptrics. Different glasses and cry-
stals (notably fluorite) are sometimes used to compensate for the
aberration. Such telescopes are termed "achromat," or "apo-
chromat" if the correction is is nearly perfect.
collimation
This refers to how correctly the optics are pointing towards each
other. If a telescope is out of collimation, you will not get as
clear an image as you should. Refractors generally haved fixed
optics, so you don't have to collimate them. Reflectors and
catadioptrics usually have screws that you turn to collimate.
(This only takes a few minutes to do--it is dead easy).
coma This refers to the blurring of objects at the edge of the field
of view, most common in short focal ratio Newtonian telescopes
(at f/10 and longer, Newtonians are very well corrected for
coma).
declination
All astronomical objects are located via a pair of coordinates:
Right Ascension and Declination. These are easily visualized by
imagining that the Earth is in the center of a hollow celestial
sphere, which has all the stars, nebulae and galaxies painted on
the shell, and the sun, moon and planets move around the shell's
inner surface. We can then project the Earth's lines of Latitude
and Longitude onto the sphere, and have a unique location for
each object (obviously, these will change rapidly for quickly
moving objects, very slowly for slower objects. See also preces-
sion). The Declination is the celestial latitude, the Right
Ascension is the celestial longitude. "The Ecliptic" is the path
the Sun travels over the course of the year. If it were pro-
jected onto the Earth it would form a sine wave bounded by the
Tropics of Cancer and Capricorn.
Dobsonian
Named for John Dobson of The San Francisco Sidewalk Astronomers
(who prefers to call these "Sidewalk Telescopes"), this is a
design which allows for very large apertures at very affordable
prices. The trade-off is that they are mounted on altazimuth
mounts, instead of equatorial ones, which makes them essentially
useless for astrophotography, but an inexpensive alternative if
you only plan to do visual work. These are light buckets. If
you are planning to build your own telescope, you might want to
consider a Dobsonian.
double star
A double star is a pair of stars which appear to be very close
together. There are two types of double stars: binary stars,
where the two stars are actually a part of a system and orbit
each other; and optical doubles, where the two stars are not
gravitationally bound at all, they just happen to lie on the same
line of sight from the Earth.
ephemeris
Plural, ephemerides. A table of the location of a celestial
object at regular intervals in time.
equatorial
An equatorial mount is set to the current latitude, and is polar
aligned (pointed at the North Pole in the Northern Hemisphere,
the South Pole in the Southern Hemisphere) and then moves only in
Right Ascension and in Declination. This take a while to get
used to, but offers the wonderful side effect of being able to
track the astronomical objects you are looking at as they move
across the sky (which is very visible motion at telescopic mag-
nifications) by moving in only one direction (Right Ascension).
Most equatorial mounts come with motor drives that take care of
this for you.
exit pupil
This refers to how wide the beam of light exiting the eyepiece
is, and is equal to the aperture divided by the magnification.
If it is bigger than the size of your pupil in the dark (7mm when
you are young, 5 or 6mm when you are over 40, as a general rule)
you will not be taking in all the light available--effectively,
you will be using a smaller aperture telescope than you have.
eyepiece
This is the thing you actually look into. Almost all telescopes
separate the Optical Tube (the telescope proper) from the eye-
piece. Essentially, the telescope makes a really tiny image of
what it's pointed at. The eyepiece acts as a magnifying glass to
allow you to see the image bigger than it would otherwise be.
The magnification is the focal length of the telescope divided by
the focal length of the eyepiece. Eyepieces are described by the
diameter of the barrel, always expressed in inches (.965", 1.25"
and 2" are the sizes in common use) and the focal length always
expressed in millimeters (4mm - 40mm is the usual range). Short
focal length eyepieces are also termed high power, long focal
length are low power.
Also significant with eyepieces is the apparent field of view
(expressed in degrees) and eye relief (expressed in millimeters).
The apparent field refers to how big the circle of space you see
in an eyepiece appears. Bigger is better. Eye relief is a meas-
ure of how far from the eyepiece you can have your eye and still
see. If you wear glasses to correct astigmatism, you will need
fairly long eye relief (the focus knob will correct for almost
all vision problems except astigmatism).
There are several types of eyepiece designs. The most popular
are Kellner (inexpensive, most popular for cheap telescopes,
short eye relief and narrow fields of view. Good to avoid if you
can afford better); Orthoscopic (good price/performance comprom-
ise); Erfle (wide field of view, expensive); Plossl (perhaps the
best all-around eyepiece. Some moderately expensive versions
available); and Ultra Wide (very expensive, almost double the
number of lenses as other designs makes for more light loss in
the eyepiece, large exit pupils. Can cost more than a small
telescope. Not a good place to spend your money when you are
just starting out).
You really don't want to buy many .965" eyepieces--they are gen-
erally not as well made as the 1.25" ones, and if you get a
bigger telescope it will probably not accept your .965" eye-
pieces. You can buy an adapter to let you use 1.25" in your
.965" focuser. This is probably worth the money.
f/10, f/6.3
See Focal Ratio
finder scope
The finder scope is a low power telescope attached to the tele-
scope you are using. Because most telescopes show such a small
portion of the sky, it is virtually impossible to locate anything
just by looking through them. So you look through the finder
scope to center the object you want (the finder has crosshairs)
and then you can use your real telescope on it. Note that you
can ignore all the claims about big finder scopes. You almost
certainly don't care. All you need is to be able to point your
main telescope at something in the sky. Finder scope size only
matters when you are starhopping through fairly dim stars (where
the larger aperture allows you to see dimmer stars). This will
not be an issue for you for quite a while (if ever). Many people
use a Telrad sight, which is simply a red LED you can sight on--
you get absolutely no more aperture than your naked eye. The
finder scopes are usually advertised as 8x50 (or such). The
eight refers to the magnification, the 50 to the aperture in
millimeters--just like binoculars.
focal length
This is the length of the light path, from the objective to the
focal plane. The magnification is the focal length of the tele-
scope divided by the focal length of the eyepiece. See also
focal ratio.
focal plane
The plane that the telescope (or eyepiece) focuses on. When you
turn the focus knob on the telescope, you are moving the eyepiece
back and forth until you make the two focal planes coincide.
focal ratio
Also referred to as the "speed" of the telescope, is the ratio of
focal length to aperture, and is always expressed as an f/
number. Thus an 8" telescope with a 2000mm focal length is f/10
(because 8" is 200mm, and 2000 / 200 = 10). An f/10 telescope is
"slower" than an f/4.
Fast telescopes give wider, brighter images with a given eyepiece
than slower ones (but note that at a given magnification, the
images are--assuming identical optics--exactly the same: what you
see through a f/6.3 telescope with a 12mm eyepiece is identical
in width and brightness to what you would see through a f/10
telescope with a 19mm eyepiece).
In general, the slower the telescope the more forgiving it is of
optical errors in the objective and eyepiece. A telescope of
f/10 is fairly forgiving, f/6.3 much less so.
focuser
This is the thing that holds the eyepiece. It moves in and out
so you can focus the telescope. It is always included with the
telescope when you buy one. The size, almost always .965", 1.25"
or 2" refers to the barrel diameter of the eyepieces it accepts.
fork mount
A fork mount is a type of mount where the telescope is held by
two arms, and swings between them. A fork mount can be either
alt-azimuth or equatorial (through the use of a wedge). Fork
mounts are most commonly used with Schmidt-Cassegrain telescopes,
and are almost always equatorial.
German Equatorial Mount
The first equatorial mount devised and still the most common for
small to moderate sized reflectors and refractors. Unlike the
equatorial fork, the german equatorial is suitable for telescopes
with either short or long tubes (although, if poorly designed, a
long tube may strike the tripod, preventing viewing at the zen-
ith). They usually are designed with movable counterweights,
which make them easy to balance, but heavy and bulky.
The tube of the telescope is joined to a shaft (the Declination
shaft or axis) which rotates in a housing that in turn is joined
at right angles to another shaft (The polar axis). The polar
axis is pointed at the celestial pole (just like any other equa-
torial mount). A counterweight, which is required for balance,
is placed on the other end of the decination shaft.
Tracking an object past the zenith requires that the telescope be
turned (both Right Ascension and Declination rotated through 180
degrees), which reverses the field of view. Not so much a prob-
lem for visual astronomy, but a limitation on astrophotography.
light bucket
A common slang term for a large aperture. The cure for "Aperture
Fever." Well, not really. After a month with the Keck tele-
scope, any amateur worth her salt would be bitching about how
much more she could see if only she could double the aperture.
Maksutov-Cassegrain
See catadioptric.
meridian
An imaginary north/south line passing through the zenith.
nebula
Plural nebulae. An unfortunate term which basically means "some-
thing up there which isn't a star or a planet." Until the early
years of this century nobody knew what the diffuse light sources
in the sky were, so they were all termed nebulae, from the Latin
for mist. They encompass galaxies, supernova remnants and space
dust. "Emission nebulae" are nebulae that emit light, thus you
can see them. "Dark nebulae" are things which don't emit light,
and hence can only be seen as a dark foreground against a
brighter light. The Horsehead Nebula is probably the most famous
dark nebula. Note that most astronomers will grimace loudly if
you refer to galaxies as nebulae.
Newtonian
See reflector.
nutation
Like precession, this is a term you really don't want to know
about. It turns out that not only does the sun make the Earth
wobble in her orbit (see precession), the moon does as well.
This wobble (about 10 arc seconds with a period of about 18
years) is termed nutation. You will never have to worry about
it.
objective
This is the thing that gathers light from the sky and folds the
light into a cone. In a refractor it is the big lens that points
at the sky, in a reflector it is the big mirror at the bottom of
the tube. The job of the objective is to create a light cone
which comes into tight focus at a single focal point.
optical tube
This is the telescope proper. It is the tube which holds the
objective. The rest of the stuff are accessories, such as the
mount, tripod, and eyepieces. When reading ads, note that some-
times optical tubes are sold by themselves. You will need to go
out and buy (or build) a mount for them before you can use them.
precession
This is a motion which you don't need to think about. It is the
drifting of the north pole, and all other celestial coordinates
with it, in a rough circle. This occurs over so long a timespan
(it is a 26,000 year cycle) that it will not affect you. It is,
however, one of the main reasons (proper motion being the other)
that star atlases are all prepared as of a specific date (January
1, 2000 is the current standard, the previous was January 1,
1950. Except they are really December 31 of the year before--
which makes a huge difference, as you can well imagine).
proper motion
Everything in the Universe is moving relative to the Earth. It
is convenient to divide this motion into two vectors: the motion
directly toward or away from the Earth (termed radial motion),
and the motion perpendicular to the former, termed proper motion.
Motion directly towards or away from the Earth has no effect on
the body's position as seen from Earth. Proper motion, however,
does. This is one reason (along with precession) that star
charts are prepared as of a specific date.
reflector
A reflector is any telescope which uses a mirror as its objec-
tive. The most common type is the Newtonian reflector, which has
a mirror at the bottom of a tube, which focuses the light into a
cone which is deflected by a flat "secondary" mirror (which is
mounted near the top of the tube in something called a "spider")
out a hole in the side. This is where you put the eyepiece. The
advantages of the Newtonian design are numerous: there is only
one optical surface on a mirror, as opposed to two on a lens, so
it is cheaper to make; part of the light path is at right angles
to the length of the tube, so it can be somewhat shorter than a
similar refractor; you can get it in much larger apertures than a
refractor, and there is no chromatic aberration . The principle
disadvantage is that you do not get as good resolution as with a
refractor of equal aperture (all other factors being similar).
refractor
This is what you usually think of as a telescope--it has a lens
at one end, and you look straight through the other. This is
sometimes referred to as a "Galilean" telescope, as it is of the
same design that Galileo used (although strictly speaking, a
Galilean telescope is a specific kind of refractor--one with a
simple double-convex objective lens and a simple double-concave
eye lens. This will not be on the quiz, so you need not memorize
it). See reflector for a comparison of the two designs.
right ascension
See declination.
Schmidt-Cassegrain
See catadioptric.
spherical aberration
A problem where a lens or mirror in a telescope is not shaped
correctly, so the light from the center is focused at a different
location than the light from the edges. You should never have to
worry about this. This only shows up in really cheap telescopes,
like the Hubble Space Paperweight. [OK, this last comment is no
longer appropriate (if it ever was). But I am leaving it in
because it emphasizes the similarities between the telescopes
available to you, and the very best professional telescopes. The
optical laws governing them are identical.]
spotting scope
A small telescope, always a refractor or catadioptric, generally
used for terrestrial viewing. Of limited utility for astronomy,
though many are marketed as such. Probably the wrong choice
unless you want to use it also for birdwatching, or as a powerful
telephoto lens on a SLR camera.
The Starry Messenger
The Starry Messenger (or TSM) is a classified advertising monthly
for astronomy stuff. Lots of ads, so a must-have for anyone con-
sidering buying used. It has started charging the sellers a 4%
commission, though, which has prompted a new paper, "The Cosmic
Exchange" (TCE), to begin publishing without charging the commis-
sion. I expect only one of them to last. Currently TCE is about
half the size of TSM, but is growing. Subscriptions are $20/year
for TSM, $16/year for TCE.
wedge
This is the thing that a fork-mounted Schmidt-Cassegrain tele-
scope will attach to, to connect it to the tripod. You want it
to be sturdy.
worm drive
This is the sort of drive most telescopes come with, if they come
with a drive. It is a very accurate and smooth drive. However,
due to imperfections in the manufacturing process, there will be
periodic errors that occur at the same point in every worm cycle
(usually about 8 minutes). To deal with this, higher end tele-
scopes come with drives which compensate for the mechanical
defects. Celestron's is the PEC (Periodic Error Correction),
Meade's is the Smart Drive.
zenith
The sky directly overhead. An object "transits" when its line of
right ascension crosses the zenith.
4. What Are Some Good Introductions To Amateur Astronomy?
In the United States, there are two popular astronomy magazines: Sky
and Telescope (S&T), and Astronomy. Of the two, S&T is more techni-
cal, while Astronomy has more things like "artist's conception of
Jupiter-rise on Ganymede" which are very pretty. I consider S&T a
necessity, but getting both is not a bad idea.
In the U.K., there is a magazine called Astronomy Now which you prob-
ably want to subscribe to. It is rather like Astronomy in style, but
slightly less bulky. Also, fewer pretty pictures. There is also a
magazine called Popular Astronomy (which is not sold on newstands--you
have to join the Junior Astronomical Society).
There is also a U.K. monthly periodical The Astronomer (ISSN 0950-
138X). This is stapled A4 format with glossy front and back covers.
It is the journal of a group of observers of the same name and is
devoted to rapid publication of observations. Not for the absolute
beginner. Contact John Colls, 177 Thunder Lane, Norwich, NR7 0JF,
United Kingdom. (+44 603-36695). Subscriptions are 21 pounds (UK),
25 pounds (rest of Europe)>
There are many good introductory books. I can recommend The Light-
Hearted Astronomer by Ken Fulton as being an excellent introduction
for the complete neophyte. The writing style is a little irritating,
but it is full of practical information. It is more about observing
than astronomy, though. It has advice like "if you are in bear coun-
try, make a lot of noise so the bears don't bother you."
P. Clay Sherrod's A Complete Guide to Amateur Astronomy, available
through Sky Publishing Company, is a more technical introduction.
Sidgewick's books are absolutely excellent books, probably the very
best ever written on amateur astronomy. They are also probably over a
beginner's head. Holding off on these for a while would not be a bad
idea.
Nightwatch by Terence Dickinson is a good introductory book on Astron-
omy. Great section on purchasing a telescope. Star charts are so-so.
The Backyard Astronomer's Guide by Terence Dickinson and Alan Dyer. A
comprehensive introduction to astronomy and the equipment amateurs
like to use. Written by and for amateur astronomers.
Also see below, the section on Books and Starcharts.
5. What Will I Be Able To See?
The best way to find out is to go observing with someone. Look for a
local astronomy club (S&T lists them periodically). This is also a
very good way to get a good price on a used telescope of proven qual-
ity.
In general, you will be able to see all planets except Pluto as disks.
You will be able to see the bands and Red Spot on Jupiter and the
rings around Saturn. You may be able to see the ice caps on Mars
(although Mars is probably the most disappointing object in the Solar
System). Venus and Mercury will show phases but not much else.
You will be able to see four of Jupiter's moons as points. Ditto
Saturn's moon Titan. You will be able to see comets.
Do not expect your images to be anywhere as nice as the ones you see
>from the Voyager spacecraft. If a $2000 telescope could get these,
nobody would have spent billions of dollars to send a spacecraft out
there.
As far as "deep sky" objects, you will be able to see all the Messier
objects in most any modern telescope. Galaxies will tend to look like
bright blobs. Look a while longer and you may find some spiral arms
or dust lanes (assuming it has them). Galaxies look nothing like
their pictures--you will not see the arms anywhere near as clearly.
You will also find that the colors you see are considerably more muted
than the pictures you see. This is because our retinas work by having
two different types of light sensitive organs, rods and cones. Rods
are very sensitive to dim light, but relatively useless for color
vision. Cones are the opposite. Thus when looking through a tele-
scope you are using your rods, and you aren't seeing a lot of color.
6. Buying A Telescope
6.1. What Company Makes the Best Telescopes?
Hard to say, actually. The two biggest sellers are Celestron and
Meade, both of which turn out good quality optics at fairly affordable
prices (Celestron's optics have the reputation of being better than
Meade's). Both do, however, occasionally turn out clunkers, which
they will repair for free (as long as you are the original buyer).
Televue has a very good reputation, at a somewhat higher price. Ques-
tar has an excellent reputation, at an astronomical price.
Coulter makes inexpensive Dobsonians, with acceptable optics. They
offer the most aperture for the money, with several drawbacks. First,
they are big. Think long and hard about how you are going to tran-
sport it before deciding on the 10 inch or bigger. Second, they are
basically deep-sky telescopes. All the Odyssey Dobsonians are short
focal-ratio, which means they're picky about alignment errors. They
all also have more than a trace of coma near the edge of the field
(minor to unimportant nuisance for clusters, nebulae, and galaxies; a
more serious one for planets and other small targets). Hence they're
not as suited for high power planetary work as your basic, medium-
sized refractor. The telescope is very basic; in particular no finder
scope and the focuser is a bit on the rudimentary side--a simple fric-
tion tube you pull in and out of the telescope's side. Third, they,
like all Dobsonians, are altazimuth mounts: very stable but unsuited
for astrophotography. Also, you usually have to order directly from
Coulter and they're back ordered for six months or more on most of
their telescopes. You can look for a dealer who could deliver
quicker, for a bit more money (like $100).
Tasco is sold at Toys R Us. Buy some Lego Blocks while you are there,
and you can build your own tripod, and have a mount of like quality to
your optics.
6.2. How do Meade and Celestron Name Their Telescopes?
Both in rather stupid ways, Celestron being stupider than Meade.
Essentially, every Celestron Telescope is C-#, where the # is the size
of the aperture in either inches or millimeters. Thus the C-90 is
Celestron's 90mm spotting scope (a Maksutov-Cassegrain), the C-8 is
their 8" Schmidt-Cassegrain, the C-6 is their 6" Newtonian. They will
prefix these with "Super Polaris" to indicate the the telescope comes
with their Super Polaris tripod and mount (a German Equatorial).
Powerstar or PEC (for Periodic Error Correction) means it has their
good drive (comparable to Meade's Smart Drive). Ultima means it comes
with a heavier wedge and fork.
Meade simply numbers everything. 2080 means an 8" Schmidt-Cassegrain.
2120 means a 10". Premier means sturdier wedge and tripod, and a
better drive (but the same optics). All Premiers manufactured in the
past coupld of years (but not necessarilly before) are equipped with
"Smart Drive," which is essentially the same as Celestron's PEC. The
Premier telescopes come with model numbers: 30 or 36 (no longer sold)
means no hand controller, 40 or 46 means you get the hand controller,
50 or 56 means you get a declination drive (so the N/S buttons on the
hand controller work) along with a slightly bigger finderscope and a
2" diagonal, 70 or 76 means you get a whole bunch of stuff. If the
number ends in a 0 (eg. 40) it is f/10. If the number ends in a 6
(eg. 46) it is f/6.3. If the number has an H postfixed to it (10"
models only) it comes with the "superwedge," a heavier wedge that is
more stable than the regular wedge, and is useful for astrophotogra-
phy. The rest of their stuff is pretty obvious, if you stop and
think: the DS-16 is a 16" reflector, for example.
Meade has recently introduced the LX100 and LX200 series of tele-
scopes. The LX refers to the drive (Meade has a very strange habit of
changing what LX means--it used to refer to the drive, then
(apparently) the focal ratio, now it's back to being the drive), which
are certainly the most wiz-bang on the market. The LX200 has a com-
puter driven declination drive, as well as the right ascension drive,
which permits it to be used without an equatorial wedge. It can slew
(move quickly across the sky) at the touch of a button on the hand
control, you can hit the GOTO button to go directly to one of the 747
objects in it's library. You cannot do astrophotography on the
Schmidt-Cassegrains without the equatorial wedge ($110 for the 8",
$395 for the 10"). The LX100 does not have the declination drive, and
so comes with a wedge, and doesn't seem to have most of the neat
features of the LX200.
6.3. Comparison of Schmidt-Cassegrains
One of the more frequent criticisms I have had on this FAQ is that it
is very biased towards Schmidt-Cassegrains, and this table doesn't
help that appearance. It is here largely because S-C's are packaged
in more funny ways than reflectors or refractors, so keeping track of
the different packagings is hard. Please bear in mind that the main
advantage of a S-C is the smaller length for the aperture. And you
pay dearly for that. For a beginner, especially one who will be doing
most of her observing from her back yard, it is probably not worth the
added expense.
To make selecting a Schmidt-Cassegrain somewhat easier, the following
table summarizes the features on different models. Under the
Make/Model column, a C indicates Celestron, a M is Meade. The tele-
scopes that come without tripods (eg. 2045D, Classic 8, PEC-14) are
priced with their recommended tripods. Fork is a fork mount, GEM is a
German Equatorial.
This table is very out of date. The prices are almost certainly
wrong, and some of the models may no longer be offered. But the
equipment is most likely correct.
smart hand DEC motor computer
Make/Model Speed Price Mount drive ctrlr drive focus control
-------------------------------------------------------------------------------
C SP-8 f/10 $1050 GEM no no no no no
M 2045D (4") f/10 $1050 fork no no no no no
M 2080A f/10 $1140 fork no no no no no
C SP-8 w/SB f/10 $1300 GEM no no no no no
C Classic 8 f/10 $1450 fork no no no no no
M 2120B 10" f/10 $1600 fork no no no no no
M LX100 8" either $1700 fork yes yes no no no
C PEC-8 f/10 $1800 fork yes yes no no no
M 2080 #40 f/10 $1850 fork yes yes no no no
M 2080 #50 f/10 $1850 fork yes yes yes no no
M LX200 8" either $2000 fork yes yes yes no yes
M 2080 #46 f/6.3 $2000 fork yes yes no no no
M LX200 10" either $2300 fork yes yes yes no yes
C Ultima 8 f/10 $2300 fork yes yes no no no
M 2080 #56 f/6.3 $2300 fork yes yes yes no no
M 2120 #40 f/10 $2300 fork yes yes no no no
M LX100 10" either $2400 fork yes yes no no no
M 2120 #46 f/6.3 $2400 fork yes yes no no no
C Compustar 8 f/10 $2800 fork ? yes yes ? yes
M 2120 #50 f/10 ? fork yes yes yes no no
M 2120 #56 f/6.3 ? fork yes yes yes no no
M 2120 #50H f/10 $2900 fork yes yes yes no no
M 2120 #56H f/6.3 $3000 fork yes yes yes no no
C Ultima 11 f/10 $3500 fork yes yes no no no
M 2080 #70 f/10 ? fork yes yes yes yes no
M 2080 #76 f/6.3 ? fork yes yes yes yes no
M 2120 #70 f/10 ? fork yes yes yes yes no
M 2120 #76 f/6.3 ? fork yes yes yes yes no
C PEC-14 f/11 $6500 fork yes yes yes ? no
C Compustar 14 f/11 $9700 fork ? yes yes ? yes
6.4. What Is The Best Telescope To Buy?
Well, Meade has a 16" Schmidt-Cassegrain which is beautiful. It is
portable (ie., you and a couple of friends can lug it), reasonably
compact, and readily available. You can pick one up for about
$10,000. If you are in a position to spend this kind of money on a
first telescope (hey Wozniak: this is the one for you. Buy me one
while you're at it) it would be a strong candidate. If money is an
object, you will have to compromise. My recommendations, by price
level, follow. Prices are given as a range, using the price from the
cheap New York mail order companies as a low, and Orion or Lumicon as
a high, where applicable. Bear in mind that you will need to have
some money left over for extra eyepieces if nothing else.
You will also find useful articles in the November 1991 issue of
Astronomy (specs on a wide range of telescopes, and answers to a lot
of the questions about technical jargon surrounding advertisers and
equipment. There is also an article in the November 1991 issue of
"Popular Astronomy." Both Astronomy and S&T (especially the former) do
review articles on telescopes, accessories, etc. on a fairly regular
basis. Also, no FAQ list is going to be truly definitive--we all have
our own opinions and interests, and one person's "piece-of-junk
optics" might be another person's dream telecope. This does not apply
to department store telescope, though. Really.
Note that this information is out of date. I'll revise it eventually.
Almost all the 'scopes are still available, the prices are just some-
what different. Also, there is a line of Dobsonians from Orion which
should definitely be included (the Deep Space Explorers).
Under $100
Get a pair of binoculars. The only telescopes in the double
digit range are pure junk. On the other hand, you can get a good
pair of binoculars. Orion sells a pair (the 7x50 or 10x50
Observer (17mm and 14mm eye relief respectively)) for $85 specif-
ically designed for astronomy. The Bushnell "SportView" are a
possibility as well. If you can spend a bit more, the Orion 8x56
Mini-Giant binoculars look like real winners ($150), with 18mm of
eye relief.
Around $250
Odyssey 8" ($275). An 8" Dobsonian from Coulter Optical. Use-
less for astrophotography, but far and away the most aperture for
the money.
The Orion 10x70 binoculars ($300). Personally, I would recommend
going with a telescope before an expensive pair of binoculars,
but enough people with a lot more observing experience than I
have have suggested listing a high end pair. These are good
ones.
Under $500
The Orion SpaceProbe 4.5" Reflector ($399). A straight-forward
Newtonian on a German Equatorial Mount, with cable controls so
tracking right ascension should be easy. Most aperture for the
money. Comes with a tripod and a couple of Kellner 1.25" eye-
pieces (a 25mm and a 9mm).
The Orion Sky Explorer 80 ($533). An 80mm equatorial refractor.
Fairly sturdy tripod, and cable controls for right ascension and
declination that should make it fairly easy to track stars
without a drive. It comes with the same eyepieces as the Spa-
ceProbe 4.5" mentioned above.
I don't know if I'd recommend the 60mm version of the above,
which sells for $344. An 80mm objective gathers 78% more light-
-a big difference.
Edmunds Astroscan 2001 ($290 - $340). It is a very portable 4"
Newtonian with the distinctive shape of a cylinder thrust into a
sphere. The sphere rests in an aluminum base and the telescope
can be pointed in any direction. Uses 1.25" diameter eyepieces.
Supplied with a 28mm eyepiece giving 16x and a 3-degree field of
view, wide enough to do without a finder scope. The drawbacks
are that it is not very good for planets; and that it's difficult
to track at high power. Also the "permanent collimation" the
Astroscan comes with probably isn't. One respondent's seems to
have come slightly out of alignment; this is unnoticeable at low
power (e.g., the 16x it gives with the eyepiece it comes with),
but is noticeable and rather objectionable at about 100x. Since
it's permanently sealed up you can't go in and tweak the mirrors
the way you can with most reflectors; you have to send it off to
Edmund so they can look at it. Even if you could tweak it your-
self, getting it all aligned would be tricky; short focal-length
reflectors (which the Astroscan is an example of) are much more
sensitive to minor alignment errors than longer ones. Accord-
ingly, your high power images may be on the fuzzy side.
Odyssey 10.1" ($345). A 10.1" Dobsonian from Coulter Optical.
Useless for astrophotography, but far and away the most aperture
for the money. Also the 13.1 inch ($575). Note that the 13.1
inch appears to be f/4.5, which means that the tube is almost 5
feet long. Think about how you will transport this before you
buy it.
The Celestron C-90 Spotting Scope with Multi-Coatings ($370 -
$500). This is a catadioptric telescope with a 90mm objective.
Note that due to the central obstruction, the C-90 has the
equivalent light grasp of an 83mm refractor. The principle
advantage is that it is compact and is very easy to carry around.
The disadvantage is that it appears to be a telescope almost as
an afterthought--the finderscope is pretty feeble, and you have
to supply your own tripod. Probably the wrong choice unless you
want to use it as a spotting scope in the daytime, or as a camera
lens. Note that this last sentence is probably controversial--
many people that have the C-90 rave about it.
Around $1000
The Meade Star Finder ($760), a 10" Newtonian. See review in
January 1993 Sky & Telescope.
The Celestron C-6 ($720 - $900), a 6" Newtonian. Comes on a
solid German Equatorial Mount (the "Super Polaris"), and with an
18mm 1.25" Orthoscopic eyepiece (42x).
The Celestron Super Polaris C-8 with Starbright Coatings ($1150 -
$1300). This is an 8" Schmidt-Cassegrain system on the "Super
Polaris" mount. It comes with an equatorial mount, and a drive
which can track in right ascension. Note that you do not want
the "Classic 8," which is the same optics in a fork mount but no
tripod for $970 - $1250.
The Meade 2080A ($915 - $1150). An 8" Schmidt-Cassegrain in a
fork mount, with a decent tripod. Essentially comparable to the
Super Polaris C-8. I'd suggest buying whichever is less expen-
sive.
The Celestron SP-C102 ($1050 - $1250). A 4" f/9.8 refractor
(102mm) on the same "Super Polaris" mount as above. Takes 1.25"
eyepieces (comes with a 26mm orthoscopic).
Odyssey 17.5" ($1150). A 17.5" Dobsonian from Coulter Optical.
Useless for astrophotography, but far and away the most aperture
for the money. This appears to be f/4.5, which means that the
tube is over 6.5 feet long. This will not fit into many cars.
Make sure you will be able to transport this if you don't have a
great observing sight at your house.
Around $1500
The Meade 2120B (? - $1600). The cheapest 10" Schmidt-Cassegrain
I could find, except for the 2120A, which appears to be the same
'scope, but without the coatings. The 2120A sells for $1500 from
the discounters, so the B is almost certainly a better buy. The
2120B appears to be an f/10 scope with a fork mount. It comes
with a tripod and a motor drive in right ascension. Presumably,
no hand controller. (As you may have guessed, I've never seen
one). All in all, a stripped down 'scope, but you get the aper-
ture, which is the most important part of a telescope (after
quality of optics, of course).
Around $2000
The Meade 2120 model 40 ($2000 - $2150). A 10" f/10 Schmidt-
Cassegrain system with "Smart Drive" and a hand controller. The
motor works in the Right Ascension direction but not declination
(the declination motor costs extra). Do NOT opt for the super
wedge. It costs about $300 extra, and can be bought separately
(ie., later when you decide you actually could use it) for about
$300. The same logic applies to all the nice things you get with
the model 50--it costs as much to buy them packaged as to buy
them individually. The issue is that beginning astronomers do
not need all the fancy equipment. The big disadvantage, which I
did not appreciate until I bought this telescope, is that while
the optical tube weighs only 45 pounds, it is unwieldy as hell in
the case they give you. I find that I cannot maneuver it around
corners in my house, so I either have to get my wife to help me,
or I have to carry it by holding the forks, which do not give as
good a purchase as one would like, given that one is holding a
$2000 piece of very sensitive, and reasonably heavy, junk. It
also takes up enough room in the back of the car that it won't
fit if we are filling the car for a camping trip.
Around $2500
The TeleVue Genesis (? - $1600) and Systems Mount (? - $900). A
4" Fluorite Refractor, which many people rave about. The Genesis
II has been designed to fit into an airline overhead rack.
The Meade 10" LX200. Tons of wiz-bang features (see above), for
not a lot more than the Premier 2120s. The finder scope looks
like the feeble one that came with my 2120/40, but you can cer-
tainly live with that for a while.
Over $3000
This is well beyond my knowledge. I would recommend avoiding all
the fully loaded and computer controlled versions of cheaper
telescopes available at this price level. The fact is that you
are a beginning astronomer and don't need all the fancy junk (of
course, this applies to the Meade LX200 also). If you have the
money, you should at least look at a Star Fire refractor, a JMI
NGT reflector and a Questar. I have heard very good things about
all, but never seen through any.
David Smith contributes the following about the NGT (about $9000-
--not an inexpensive choice): I have spent a couple of evenings
with an acquaintance who has an NGT-18. It is a very good scope.
It's comparable in size to a Dobsonian, and I don't need a ladder
to see into the eyepiece. I could see dim stars among the Tra-
pezium which I couldn't see in other scopes nearby (4" refractors
and 8-10" Newtonians and SC's). The rotating nosepiece works
well, although it places increased demands on accuracy of physi-
cal and optical axes: the view was sharper from one rotation of
the nosepiece than from another. Disadvantages of the NGT-18 are
price, time to set up and take down, and lack of fine adjustments
for polar alignment.
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