Telescope Info/Buying FAQ for Beginners - Part 1

This is where you can read up the answers to some FAQs on astronomy and star-gazing in Singapore. Members' contributions are welcomed.
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Airconvent
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Telescope Info/Buying FAQ for Beginners - Part 1

Post by Airconvent »

With all the beginners joining Singastro, thought I might attach this useful FAQ by Mr Bishop. Be aware that he has some strong opinions and not everyone will agree with what he advocates. I found it very useful when I was reading up on scopes for the very first time...
Licence is free as long as you copy it whole sale with all the acknowledgements intact. Cheers!
rich
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Telescope Buyers FAQ

Purchasing Amateur Telescopes FAQ
Slc.Dennis Bishop
starlord@inreach.com
Last Updated: 06-29-02
Copyright (c) 2002 Slc.Dennis Bishop All rights reserved.

This FAQ is under construction. There may be some sections
that are not totally done yet.

Questions in this FAQ:

1. What is the single most important thing I should know before buying a
telescope?
2. Recommendations for Beginners.
3. What Does All the Jargon Mean?
4. What Are Some Good Introductions To Amateur Astronomy?
5. What Will I Be Able To See?
6. Buying A Telescope
6.1 What Company Makes the Best Telescopes?
6.2 What is the Best Telescope to Buy?
7. Where Do I Buy My Telescope?
7.1 What About Buying Used?
7.2 What About Building A Telescope?
7.3 What is the Best Mount?
7.4 Binocular Telescope
8. What Accessories Will I Need?
9. What are Digital Setting Circles?
10. Why Should I Start With Binoculars?
11. What Books and Star Charts Are Recommended?
11.1 What About Computer Programs?
11.2 E-mail Lists
12. About this FAQ

Contributors to this posting include:
Pierre&nbspAsselin, Dana&nbspBunner,
Doug&nbspCaprette, Mike&nbspCollins,
Kevin&nbspDeane, Jay&nbspFreeman,
Chuck&nbspGrant, Dyer&nbspLytle,
Christopher&nbspGunn, Doug&nbspMcDonald,
Andy&nbspMichael, Dave&nbspNash,
Jim&nbspVan&nbspNuland, Bill&nbspNelson,
Leigh&nbspPalmer, Alan&nbspPeterman,
Tom&nbspRandolph, David&nbspSmith,
Geoff&nbspSteer, Mario&nbspWolczko,
C.&nbspTaylor&nbspSutherland, Paul&nbspZander,
David&nbspKnisely

Frequently-Asked Questions

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 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.

Department stores always show little 2 1/4 inch refractors from 125+
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) Recommendations for Beginning Amateur Astronomers

Occasionally, amateur astronomers ask for recommendations about telescope
buying, learning the sky, and so on. Here are some thoughts.

(Let me state credentials. I am primarily a visual observer: Over 40 years
I have logged about 6000 observations of nearly 3000 objects, and used
perhaps thirty telescopes and binoculars enough to know them well. I have
made roughly ten optical surfaces to 16-inch diameter (a sphere -- my
biggest paraboloid was 8 inches). My forte is deep-sky work; observations I
am proud to include the Sculptor Dwarf Galaxy (10x70 binocular), Maffei I
and Leo II(Celestron 14), and S147 (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 maintain amateur status in visual
wavelengths -- my thesis work was in extreme ultraviolet.)

What to do First.
================

First, some meta-advice. Written words do not substitute for experience.
Join an astronomy club, go to observing sessions, and try other peoples'
telescopes. You will learn a lot, and will find people who like to discuss
equipment and observing.

To find clubs, ask at science stores, museums, planetariums, and the like.
Physics and astronomy departments of colleges may know, though clubs aren't
strictly their line. Two popular astronomy magazines, Astronomy and
Sky&Telescope, publish annual directories of clubs, stores, observatories,
and such. Look for them on newsstands, or go to a library and read back
issues, or try their web pages.

Been to a club already? Honest? Okay, you can keep reading...

Some Basic Questions.
====================

In buying a telescope, you face bewildering, expensive choices. To help
deal with the confusion, here are some questions to ask yourself.

1. How much effort are you willing to put into learning the sky? If you
know the constellations, and have practiced finding things by
"star-hopping" -- using charts instead of dial-in or punch-in
coordinates -- you will be able to use a telescope cheaper, smaller,
lighter, and easier to set up than one using precise alignment or
computer control to locate objects.
2. How much effort are you willing to spend on your observing skills?
Seeing fine detail in celestial objects, or just seeing faint ones at
all, requires practice and special knowledge. Yet the rewards are
enormous: An experienced observer may see things with a small
telescope that a beginner will miss with one five times larger, even
with objects and sky conditions that favor both telescopes equally.
3. How far will you have to lug your telescope to get it from where you
keep it to where you use it, by what means, and how much effort will
you put up with to do so? Differences in size and optical design
create vast differences in telescope portability, and any telescope
that you take out and use will be far better than one that sits in the
closet because it is too heavy or too cumbersome.
4. Some people are into technology for its own sake, without regard to
whether it is useful or cost effective. Are you willing to pay extra
for sophisticated features, even if you don't need them? If so, fine
-- lots of us like neat equipment. But if not, take care technology
enthusiasts don't sell you things you don't need.
5. Do you want to take photographs or CCD images of celestial objects?
"Astrophotography" is an expensive word. I am not into this side of
the hobby, but friends who are typically take several telescopes and
several years before they are satisfied, and spend lots more money
than visual observers do.

Some Realities.
==============

With these thoughts in mind, I can make some general comments.

(A) The most important thing in determining the optical performance of a
telescope is the diameter of the beam of light that goes into it -- its
"clear aperture". Obviously, the more light, the fainter the things you can
see, but less obviously, image detail is limited by clear aperture, via
physical optics. Bigger telescopes produce sharper images, just because
they are bigger.

There are important qualifiers. First, bad craftsmanship can make any
telescope perform poorly. Cheesy optics won't work. Fortunately, it is not
too hard to make optics of the sizes and types common in amateur
telescopes: most manufacturers routinely turn out units that are okay. Bad
ones turn up, but major manufacturers will often fix or replace a real
lemon, if you have wit to recognize that you have one, and will to
complain. (Most of us have neither; that's how some manufacturers make
money!)

Second, different optical designs perform differently. Schmidt-Cassegrains,
Newtonian reflectors, and refractors all have good and bad points. People
who love telescopes, or sell them, will be eager to debate the matter.
However, variations are relatively minor. It is usually adequate to assume
all telescopes of given clear aperture and given quality of optical
craftsmanship have the same optical performance: Real differences will
correspond to changes in aperture of usually no more than 10 to 20 percent.
Shabby optical work will increase that percentage enormously.

Third, atmospheric turbulence ("seeing") limits the ability of a telescope
to show detail, and sky brightness limits its ability to show faint
objects. Poor seeing usually hits large telescopes harder than small ones.
When seeing is poor, there may be no reason to take out and set up a big
telescope. If you always observe from such conditions, you may have no
reason to buy a big telescope. Yet, even in bright sky, a large-aperture
telescope will show fainter stuff than a small one. And many of us have
found dark-sky stable-seeing sites within a reasonable drive of home --
from sites near San Francisco Bay, sometimes I have to stare through the
eyepiece of my Celestron 14 for several minutes before I can tell that
there is any air between me and what I am looking at.

Notwithstanding these caveats, APERTURE WINS, and wins big. If you buy the
finest 90 mm fluorite refractor in the world, do not be chagrined if a
junior high school student shows up with a home-made 6-inch Newtonian that
blows it clean out of the water: The 6-inch I made at 13 puts my
world-class 90 mm fluorite to shame. There is no contest, and it's not
because I was a master optician at 13, it is because six inches is bigger
than 90 mm, hence intrinsically better.

(B) Hundreds of deep-sky objects are big and bright enough to show well
through apertures of two inches or so, at low magnifications. Thus, medium
sized binoculars -- 7x50 or 10x50, say ("7x50" means "7 power, 50-mm
aperture") make inexpensive, highly portable, easily operated beginner
instruments. Perhaps you have one already. To use them well, you must be
willing to learn the sky enough to find things with a hand-held instrument.
And don't get one that gets too heavy to hold steady before you are done
observing.

(C) Speaking broadly:

(C.1) The most optical performance per unit of clear aperture comes from
modern, high-quality refractors -- but they are outrageously expensive
compared to other designs of the same aperture. Also, in sizes much above
four-inch aperture, the tubes are generally long enough to make the whole
instrument cumbersome and heavy.

(C.2) The most optical performance per unit of portability comes from
Schmidt-Cassegrain and Maksutov designs -- but they are still pretty
expensive. There's a qualifier here: What makes them portable are short,
stubby tubes, but for small apertures -- say, four inches or less --
portability of all types is dominated by clumsiness of the tripod, so the
portability advantage of Schmidt-Cassegrains and Maksutovs diminishes.

(C.3) The most optical performance per unit of cost comes from Newtonians
-- particularly those with Dobson mountings. Compared to other telescopes
of the same aperture, they are clumsier than Schmidt-Cassegrains and
Maksutovs, but not nearly as clumsy as refractors.

Let me regroup that information into three questions telescope buyers often
ask:

(C.1) What gives most optical performance for a given aperture? Usually, a
high-quality refractor.

(C.2) What gives most optical performance for a given car to carry it?
Usually, a Schmidt-Cassegrain.

(C.3) What gives most optical performance for a given budget? Usually, a
big Dobson.

(D) Though costly and cumbersome, small refractors are durable and
difficult to get out of whack. Good ones make respectable beginner
instruments, particularly for beginners with extra thumbs. And a good small
refractor provides a wonderful way for an experienced observer to embarrass
folks with humongous Newtonians who lack observing skills to exploit them.
But BEWARE of mass-marketed junk refractors, advertised as high-power and
sold in department stores.

(E) Altazimuth mountings tend to be cheaper, lighter, less clumsy, and more
quickly set up than equatorial ones, but to use one you must be willing to
learn the sky well enough to find things without dialing in celestial
coordinates. (Computer-controlled altazimuth mounts allow use of celestial
coordinates to find things, or perhaps will look up the coordinates for
you, in an internal data base, but they are not cheap.)

(F) There's another way to look at this material. There are variety of
ecological niches for telescopes, corresponding to different uses and
requirements. I know of seven:

(F.1) Big Iron: This is the giant Dobson-mounted Newtonian, or humongous
Schmidt-Cassegrain, that fills your garage. To transport it requires a
small trailer, pickup truck, or panel van, and setting it up calls for the
concerted efforts of three used fullbacks and a circus elephant. The ladder
to climb to the eyepiece is so tall you need supplemental oxygen to deter
altitude sickness. This telescope is your galaxy-gazer and cluster-buster
supreme, and if it is well made, then when the seeing is good it will show
detail that those condescending high-tech dweebs with their confounded
itty-bitty seven-inch apochromatic refractors can only dream about.

My "Big Iron" is a Celestron 14, with a little tiny single-axle cargo
trailer to haul it.

(F.2) Largest Conveniently Portable Telescope: This is the most telescope
that will fit easily in your regular vehicle without hiring a bulldozer to
clean it out. What it is, depends on what your vehicle is -- with a
ten-speed, or a subway train, you have a problem. An eight- to eleven-inch
Schmidt-Cassegrain is the right size for many people; that is one reason
these telescopes are popular.

I have had several Largest Conveniently Portable Telescopes, over the last
few cars. Once I built an eight-inch Dobson whose key design parameter was
that the tube just barely fit crosswise across my back seat. I used it a
lot till I bought a smaller car. For a while, my Largest Conveniently
Portable Telescope was a Vixen 90 mm f/9 fluorite refractor on an
altazimuth fork or a Great Polaris German equatorial (I have hardware to
fit both), but at present I use a six-inch f/10 Intes Maksutov on the Great
Polaris. A somewhat faster Dobson than my 8-inch f/5 would work equally
well, and would have more performance for most purposes.

(F.3)Public Star Party 'Scope: You'll want something pretty portable, with
the added provisos that it's nice to have a sidereal drive so you won't
have to keep re-pointing it between viewers, and that it shouldn't be so
expensive you worry about kids and idiots. Your SCT will do nicely.

I put the Intes or the Vixen fluorite on the Great Polaris, but I set the
tripod legs to maximum length, so the expensive optics are out of reach. So
far, no one has slam-dunked a rock.

(F.4)Quick Look Scope: The idea here is to leave something all set up in
your entrance hall, or hidden under a stack of old Sky&Telescopes in the
back of your car, so you will have a telescope on two minutes notice if a
truly close comet comes whizzing by, or if you are too lazy to assemble one
of your real telescopes. Such an instrument can also double for nature
watching or spying on the neighbors, which may be the same thing -- just
don't tell your fellow amateur astronomers, or you will lose observer
points. Many people have a spotting 'scope on a light tripod, or perhaps a
90 mm Maksutov on one a bit heavier.

Lately, my Quick Look 'Scope has been a 102 mm f/9.8 Vixen refractor with a
conventional achromat, on a Vixen bent-fork altazimuth mount that has
clutches and slow motions on both axes. I have a couple of smaller
refractors that I sometimes use similarly, but since I have room to leave
the 102 mm set up in my living room, I benefit from the extra aperture.

(F.5)Binocular: A good binocular is very useful, and can do much of the
work of a 'Quick Look Scope. I have too many; ones I use for astronomy
include the 7x35 Tasco ($29.95 at Sears) that I keep in my car for
bird-watching (oops, lost observer points), an old Swift Commodore Mark II
7x50 (long out of production), which was one of the first binoculars I saw
with BAK-4 prisms, and an Orion 10x50 and 10x70 with BAK-4 prisms and fully
multicoated everything, up to but not including the case. At star parties I
tend to wander around with one dangling from my neck. I tried two, but
lacked sufficient eyes.

(F.6)High-Tech Conversation-Stopper: This is how you put to shame those
grass-chewing hillbilly clodstompers who have giant cardboard Dobinsons
with tubes so big that they echo. Odds are the seeing will never get good
enough for them to demonstrate that a half-meter shaving mirror will blow
eighteen centimeters of optical perfection clean out of the water, and if
they start talking about faint galaxies you can always change the subject
to diffraction rings and modulation transfer functions, and ask them to
compare internal baffles and background sky brightness. Besides, your
telescope has more knobs than all theirs put together, and it cost more
than all theirs put together, too.

The default choice for the High-Tech Conversation-Stopper these days is
typically an apochromatic refractor, or some close approximation
("apochromat" is a precise technical term; not all superb refractors are
apochromats, and vice-versa), which if well made and well baffled will
deliver outstanding performance for its size. The apertures available
suffice for many amateurs who have either recovered from aperture fever or
have not yet succumbed, or who have exhausted their supply of fullbacks and
circus elephants to set up the Big Iron. Few other kinds of telescopes
qualify -- you're not allowed to have a Schiefspiegler unless you can
remember how to spell it, and nobody wants a Yolo because people expect you
to walk the doggie. Some folks like Questars, but not me.

My present High-Tech Conversation-Stopper is the 90 mm Vixen fluorite
refractor I mentioned earlier. It is not big enough to be as impressive as
I might want, and is rather short on knobs, but I can talk fast enough to
make up the difference.

What about accessories?
======================
I have already said most of what you need to know about accessories, which
is that (A) aperture wins. If you are planning a telescope budget, and
eyepieces, finders, and such account for the lion's share of your funds,
sit back and think carefully about what you are about to do -- it might be
better to get a bigger telescope instead of fancy accessories. A 10-inch
telescope with a hand magnifier as an eyepiece will give a better view of
most objects than an 8-inch telescope with the finest eyepieces in the
world. Why? Because (A) aperture wins.

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 (A) 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:

(a) Eyepieces. A small number of good ones is better than a large number of
bad ones. You will need a low-power, wide-field eyepiece, both for finding
things and for low-power views of big, diffuse objects. It might give a
magnification equal to five or six times the telescope clear aperture, in
inches. On my f/11 Celestron 14, the low-power eyepiece has a 55 mm focal
length, and is mounted in a two-inch barrel, so that the front lens --
which sets the field diameter -- can be as large as possible. (In little
f/10 or f/11 telescopes, internal baffles may mean that no light gets to
the edges of a two-inch wide eyepiece; if so, don't bother with the extra
cost of one.) On my f/5 8-inch Dobson, I use a 20 mm eyepiece, which
doesn't need a two-inch barrel.

The next power you will likely reach for is medium to medium high, for a
good look at detail in the object in view. Such an eyepiece might give a
magnification of 20 to 30 times the telescope clear aperture, in inches. On
my C-14 I use a 12.4 mm eyepiece, and on my 8-inch Dobson, a 4 mm. The
objects you look at with high power probably won't be very wide (though
they might be), so for economy, you might not want a super-wide-field type.

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, require 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. Slower instruments
can use simpler eyepiece designs. It is a "Catch-22" of amateur astronomy,
that cheap telescopes (fast Dobinsons) need expensive eyepieces, but
expensive telescopes (most refractors and Schmidt-Cassegrains, with slow f
numbers) can use cheap eyepieces.

"Zoom" eyepieces, which change focal length at the twist of a knurled ring,
tend not to be very good. Barlow lenses, also called telex tenders,
multiply the focal length of the telescope with which they are used: It
used to be that they generally worked well only with telescopes with large
f-numbers, where they were not needed -- another "Catch-22". Yet I have
heard that there are now Barlow lenses that work with fast telescopes,
where they are indeed needed, but I urge a try-before-you-buy approach to
selecting one.

For over fifteen years I used an eyepiece set bought in roughly 1980. It
featured no fancy designs, just a 55 mm Plossel, 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 very good quality
-- the 55 and 32 mm were from University Optics, and the others were Meade
Research-Grade. All worked reasonably well even at f/5, and the 68-degree
apparent field of the Erfles was enough that I was untempted to buy
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
now and then, but occasions where I want that much power are rare.

In mid 1996 I bought more eyepieces, mostly out of curiosity. I found that
decent Plossels are comparable to decent Orthoscopics. I bought several
Vixen "Lanthanum" eyepieces, which have built-in matched Barlow lenses to
give 20 mm eye relief, even at such short focal lengths as 2.5 mm. I don't
need glasses to observe, but even so, long eye relief makes viewing more
relaxed -- I'm not worrying about bumping the eyepiece. It also facilitates
public viewing -- I focus with my glasses on, and tell everyone to leave
theirs on and not refocus.

Note what high-tech eyepieces can and cannot do. The best give wider fields
of view, with fewer eyepiece aberrations near the edges, than older types.
The improvement is most noticeable at fast f numbers. If that's important
to you, you might want some. But eyepieces are not aperture stretchers.
They can neither increase image detail beyond the theoretical limit for the
aperture, nor increase the number of photons that make it to the focal
plane. If you think otherwise, you are making the same mistake as the
clueless beginner who buys a drug-store refractor because it says
"Magnifies 400 Times!!" on the box. 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 almost
no light. That's what counts most for astronomical work.

In 1980, I bought 6, 12 and 25 mm Ramsden eyepieces -- an old, simple,
design -- for about ten dollars each. I use them at star parties without
telling what they are. They have only 4 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 -- f/10 or longer -- they give up nothing to new designs; images
are superb.

(b) Finders. What kind of finder you get depends on how you use it. If you
plan on looking mostly at fine details in bright objects, then you might
buy a big finder, in the hope that most of what you look at in the main
telescope will be visible in it, too. But that won't work if you push your
telescope to its faint-object limits -- you would need a finder as big as
the main telescope. You might then consider a finder that will show stars
exactly as faint as on your charts. It helps a lot in identifying what you
are looking at through the finder, if every star you see is charted, and
vice-versa. Once the right pattern of stars is in the finder, you can put
the crosshair where the object lies, even if it is too faint to see.

In dark sky, the 10x40 finder on my C-14 shows stars to about magnitude
9.5, which matches 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), thus matches many naked-eye star atlases.

Unit-power finders, like the Telrad, let you to stare at the sky with both
eyes open and see a dot, circle or crosshair of light where your telescope
is pointing. A peep sight, made by taping bits of cardboard to your
telescope tube, may work as well, and will be much cheaper, and any
magnifying "straight-through" finder (in which you look in the direction
the finder is pointing) can be used with both eyes open -- let your brain
fuse the images, so you can use the finder's crosshair with the other eye.
I tried a unit-power finder (Orion's) on my 90 mm refractor, but found it
always inferior to the original 6x30 finder. My opinion about unit-power
finders is in the minority. Many prefer them to those which magnify. Some
folks use the Telrad's circles of known diameter to measure angular
distances when finding things.

(c) Charts. Preferences vary greatly. What I find useful, in order from
simple to complicated, is more or less the following:

(c.1)A simple planisphere, preferably a plastic one that won't sog out with
dew and that may survive being sat upon. It's a fast way to find out
whether a particular object is up before I go observing, or to determine
how long I have to wait before it is well-placed.

(c.2)A "pocket atlas". I am particularly fond of Ridpath and Tirion's The
Night Sky, from Running Press in Philadelphia, PA. It is about three by
five inches and half an inch thick, and it is out of print. Write Running
Press and complain.

(c.3)A "table atlas", bound as a book that will lie reasonably flat,
showing stars to the naked-eye limit and lots of deep-sky objects to boot.
I happen to use an old Norton's Star Atlas; there are lots of others.

(c.4)A "deep atlas", such as _Uranometria_2000_ or the AAVSO atlas, with a
stellar magnitude limit of 9 or 9.5 and a vast number of objects. What's
important here is to have enough stars charted that there are plenty in
every finder field.

(c.5)A planetarium computer program (Bill Arnett reminded me). If you are a
beginning astronomer, I do *not* suggest you rush out and buy a computer,
but if you already own one, you might bear in mind that there are programs
that will turn your console into a window onto the simulated heavens, with
features for finding, displaying, and identifying things. I happen to have
the rather old Voyager 1.2 for my even older Macintosh II; there are plenty
more, both for Macs and for the world of MS-DOS and its descendents.
(Editor note: Atari Planetarium / or Big Sky works on all ST/TT/Falcon
computers)

Some folks run such a program on a laptop, at the telescope. Please put red
cellophane over your console, if you do.

I have had limited 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 most of 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.

(d) A red flashlight, so you can read your charts and notes without ruining
your night vision, or that of people near you. The kinds that have a red
light-emitting diode (LED) instead of a flashlight bulb are particularly
good. If other observers scream and throw things, your light is probably
too bright.

(e) A logbook. This item is not for everyone, but I find it useful to
record my observations, even if I don't do anything other than note that I
saw a certain object with a certain telescope and magnification. Logbooks
make fun reading when it is cold or cloudy, and often there will be reason
to look up something long after the fact. Besides, if you quote frequently
from your logbook, you can make your friends think you are an active
observer when you really gave it up years ago.

What about observing skills?
===========================

Even some experienced amateur astronomers think that seeing things comes
free and easy, with no more effort than opening your eyes: But as currently
popular slang so evocatively articulates,

** NOT **.

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 bigger
telescope to see more is like buying a bigger kettle to be a better cook,
or buying a bigger computer to be a better programmer. Not that it won't
help -- it might -- but cooking and programming depend far more on
knowledge and experience than on artifacts. So does visual astronomy.
People with garages full of telescopes (pardon me while I try to close the
door to mine) are in great part victims of materialism, marketeering, and
hyperbole. Practice is cheaper, and works better. As I said near the
beginning of this article, an experienced observer may see things with a
small telescope that a beginner will miss with an instrument five times
larger, even with objects and sky conditions that favor both equally.

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.

a. Patience. It can take a long time to see everything in a field, even
if you know exactly what you are looking for.
b. Persistence. Eyes, telescope, and sky vary from night to night.
c. Dark adaptation. Avoid bright lights before observing: It takes your
eyes hours to reach their full power of seeing faint objects.
d. Averted vision. The part of your retina that sees detail best, sees
low light worst. Look "off to the side" to find lumps in the dark.
Many observers use averted vision on faint objects, but not for faint
detail in bright ones. Detecting something doesn't mean you've seen
all you can. Don't let the dazzle of a galaxy's lens keep you from
tracing spiral arms out beyond the width of the field. How about
increasing magnification, and using averted vision to see if you can
see more detail in the paler, but 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. That is, averted vision seems to facilitate the
detection of low contrasts as well as faint objects.
e. Stray light avoidance. Even when it's dark, background glow interferes
with detecting faint objects. Keep it out of your telescope and out of
your eyes. Try eye patches and eye cups for eyepieces. 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.
f. Moving the telescope. The eye sometimes detects motion, or changing
levels of brightness, more easily than static images. Jiggle the
telescope, or move it back and forth, to make an object "pop out". Try
it while using averted vision.
g. Not moving the telescope. The eye sometimes adds up photons over many
seconds; if you can hold your eye still for a long time, faint things
may appear. Try it with averted vision.
h. Respiratory and circulatory health. If you smoke, try taking a break
before and during observing -- carbon monoxide from incomplete
combustion interferes with the ability of the blood to transport
oxygen.

Clear sky, and enjoy your telescope.

-- Jay Freeman
freeman@netcom.com

3. What Does All the Jargon Mean?

OK, by popular request, here is a glossary of common astronomy terms
encountered in amateur astronomy.

alt-azimuth 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. Note: Dobsonian
Telescopes are mounted this way.

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.

binocular telescope
A set of Dobsonian telescopes mounted so their eyepieces form a Binocular
3D view of the sky.

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 magazine: 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, different
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 crystals (notably fluorite) are sometimes used to compensate
for the aberration. Such telescopes are termed "achromat," or "apochromat"
if the correction 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 have 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).

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. Note: That this design is now the #1 Design seen at many Star
parties.

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
magnifications) 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 measure 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 compromise); Erfle (wide
field of view, expensive); Plossel (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 generally
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 telescope 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 star
hopping 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 telescope 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 zenith). 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 equatorial mount).
A counterweight, which is required for balance, is placed on the other
end of the declination 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 problem for
visual astronomy, but a limitation on astrophotography.

light bucket
A common slang term for a large aperture. The cure for "Aperture Fever."

Maksutov-Cassegrain
See catadioptric.

Meridian An imaginary north/south line passing through the zenith.

Newtonian
See reflector.

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.

reflector
A reflector is any telescope which uses a mirror as its objective. 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 .

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.

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.

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 bird watching, or as a powerful telephoto lens on a SLR camera.

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 telescopes come with drives which compensate
for the mechanical defects.

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.

Nightwatch by Terence Dickinson is a good introductory book on Astronomy.
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 Star charts.

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 quality.

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 when in it's orbit it's
closer to Earth. 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 Hubble Space Telescope. If a $2000 telescope could get these, nobody
would have spent billions of dollars to put the HST in orbit.

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. Remember, many of them
are millions of Light Years away.

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 telescope 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?

This is a very unfair question at the best. There are many companies which
make good telescopes. A lot will depend on just how much you want to spend
for a telescope. The Major companies that make and/or sell telescopes are
as follows: Orion Telescopes, Meade, and Celestron, but you have to be
careful with what you buy from even these companies, as they ALL are
selling telescopes which are coming from factories in 'RED CHINA' and are
the same as the Junk department store telescopes. There are other smaller
companies that make good scopes too. There are some Japanese companies that
are selling some very good telescopes and also some poor ones too.

Televue has a very good reputation, at a somewhat higher price.

Tasco is now owned by Bushnell. Another maker of Junk telescopes.

Bushnell: I have looked at this company's telescopes 1st hand and I do not
believe that they would withstand one full night of usage viewing the sky.
They are even WORST than Simmons! They are so bad they make Tasco junk look
good!

There are now a lot of smaller companies popping up that are selling the
same 'Made in Red China' telescopes under names never seen before it would
be a good idea to stay away from them too. Even the bigger companies are
now selling scopes made in 'Red China'.

There are some companies importing telescopes from Russia, I have not seen
these scopes first hand, but have read some good reports of them.


6.2. What Is The Best Telescope To Buy?

Once more this will depend on the answers of questions you need to ask
yourself. Are you going to use the telescope for just viewing? or are you
going to into the field of Astrophotography? Also it will depend on how
much you want to spend too. In the end, only YOU can answer this question.

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 telescope. This does not apply to department store
telescope, though. Really.

As the numbers of companies who now either make and/or just sell Telescopes
of ALL price ranges, the list is just to much to put into this FAQ,
instead, the next section will list a number of both large and small
companies that market telescopes. The best idea would be to contact the
companies and find out what kind of telescope they market in your price
range. Then if you can, Find one of those telescopes at a Star party.

7. OK, Where Do I Buy My Telescope?

Well, there are three basic places:

1) A Store:
Yes, the obvious-you find a store (NOT a department store) which sells
telescopes and write a check (or, if they won't give you a cash discount,
use a credit card that offers buyer protection, or gives you bonus miles,
or some such).

The advantages of this method is that you have someplace to return the
telescope to if you have problems with it. Some places even offer your
money back if you change your mind within some grace period.

The disadvantage is that you generally pay more for the telescope itself,
and you pay sales tax.

2) Mail Order:
There are two sorts of mail order: the discount stores that sell all sorts
of stuff through the mail, and telescope stores that sell through the mail
in addition to selling from their store.

The advantages and disadvantages of mail order are obvious: you cannot take
the merchandise back easily if something goes wrong, but it's cheaper and
you probably pay no sales tax.

3) Other People:
You can find some great deals in used telescopes. Many people buy expensive
telescopes, use them two or three times, get bored and sell them. The
advantage is strictly monetary: you pay significantly less (and, of course,
no tax).

The disadvantage is that you are buying something "as is" which you may
want to think twice about doing if you are buying an expensive telescope.
Also, both Meade and Celestron offer (limited) lifetime warranties on their
optics, which are not transferable.

All that having been said, here is a list of places you can buy telescopes,
with comments as applicable. Note that not all will sell or will ship. To
you, some you must go to a store.

Orion Telescopes
P.O.&nbspBox&nbsp1158
Santa&nbspCruz,&nbspCA &nbsp95061
(also San Francisco and Cupertino)
800-447-1001
sales@oriontel.com

Orion Telescopes carries a wide selection of binoculars, telescopes, and
accessories They have a 30 day "no questions, satisfaction guaranteed"
refund policy, which they do seem serious about. Orion seems to be heading
for the low end of the telescope market now.

Lumicon
2111&nbspResearch&nbspDr. #5
Livermore,&nbspCA &nbsp94550

While I have not had any dealings with this company, the messages I've seen
on sci.astro.am have all had good things to say about them.

Astronomics
2401&nbspTee&nbspCircle,&nbspSuites&nbsp105/106
Norman,&nbspOK &nbsp73069

Higher prices than Adorama and Focus (see below), but lower than Orion and
Lumicon. Enthusiastically recommended by a couple of people on the net. As
with all mail order, make sure the shipping price is included.

Celestron International
2835&nbspColumbia&nbspSt.
Torrance,&nbspCA &nbsp90503

This company is no longer part of TASCO, they no longer sell DOB's. Main
line is GOTO scopes.

Discovery Telescopes
615&nbspS.&nbspTremont&nbspSt.
Oceanside,&nbspCA &nbsp92054
760-967-6598

They make not only Dobs, but also equatorial reflectors and equatorial
refractors too. Their scopes are made in USA and are very good scopes.

Mag 1 Instruments
16342&nbspCoachlight&nbspDr.
New&nbspBerlin,&nbspWI &nbsp53151

Markets their 'Portaball' style DOBs in 8in and 12.5in size.

Meade Instruments Corp.
6001&nbspOak&nbspCanyon
Irvine,&nbspCA &nbsp92620

Markets many types of Telescopes, from junk to High End. No longer lists
Dobs.

Obsession Telescopes
P.O.&nbspBox&nbsp804a
Lake&nbspMills, WI &nbsp53551

Markets Dob's from 15in to 30in!

Stargazer Steve
1752&nbspRutherglen&nbspCr.
Sudbury,&nbspOntario
P3A&nbsp2K3&nbspCanada

Markets a 4 1/4inch DOB in both Kit form and/or ready-to-use. Both under
$300.00. Also a 6inch DOB kit for $424.00 with shipping.

Starsplitter Telescopes
3228&nbspRikkard&nbspDr.
Thousand&nbspOaks, CA &nbsp91362

Markets DOBs from 8in to 30in.

University Optics
P.O.&nbspBox&nbsp1205
Ann&nbspArbor,&nbspMI &nbsp48106

A few people have reported using University Optics, and all report
receiving good service. I have heard no complaints.

Parks Optical
270&nbspEasy&nbspSt.
Simi&nbspVally,&nbspCA &nbsp93065

A couple of people have mentioned that shipment can be pretty delayed, but
the quality of their equipment appears to be high, and improving.
Salespeople vary from knowledgeable to bubble-headed.

Adorama
42&nbspWest&nbsp18th&nbspStreet
New&nbspYork,&nbspNY&nbsp10011
orders:(800)&nbsp223-2500
info: (212)&nbsp741-0052

Along with Focus Camera (see below), the lowest prices you will find.
Expect no dealer support, and make sure you find out how much they will
charge for shipping before placing your order. And pray that the optics
arrive intact. I really would recommend that you not buy telescopes from
these guys. Eyepieces and other accessories, however, are probably worth
the risk if the price difference is significant.

Focus Camera
4419-21&nbsp13th&nbspAve.
Brooklyn,&nbspNY&nbsp11219
orders: (800)&nbsp221-0828
info: (718)&nbsp436-1518

Refer to Adorama. Same comments apply.

Pauli's Wholesale Optical
Danbury,&nbspCT

A lot of bad reports, order at your own risk!

For Both Used and New Scopes and other goodies you can try:

http://www.astromart.com/
Good place.

7.2. What About Building A Telescope?

This section was written by Andy Michael.

We just took a rather unusual approach to getting a beginning telescope: we
took John Dobson's telescope building class and built an 8"and a 12.5"
reflector on Dobsonian mounts (of course). We went this way for a few
reasons: to get large aperture for seeing deep sky objects and higher
magnification with good resolution when compared to small refractors in
this price range, to keep the price down, and to soak up John's wit and
wisdom. The down side is that these telescopes are not suited for
astro-photography (at least not without building a different mount) but
that didn't bother us. Also they are large. The 8" tube we broke into two
pieces for easy portability, but the 12.5" one will probably go on the roof
rack. These are about f/7 telescopes so the tube lengths are 56" and 7'
respectively. Of course, when you build yours you can make whatever size
you want. On the other hand you can pack your clothes in them; try that
with an SCT. The cost was about $250 for the 8" telescope, $450 for the
12.5"er plus about 24 to 30 hours of work and 16 - 24 hours of class. It's
a challenging project but the first time you focus on something with a
mirror you ground is an incredible thrill. Another benefit is that we now
know a lot about telescope design and if we ever have problems with them we
know how to fix them.

If you don't have access to John's (or other peoples) classes then you can
try building one by reading his book and by watching the video. Our class
was the first to see parts of the video and had great success at finishing
the telescopes fast and without needing to correct the mirrors very much.
Coincidence? Class consensus was no.

The book (excerpted from the order form): "How and Why to Make a
User-Friendly Sidewalk Telescope" by John Dobson with Norm Sperling. To
appreciate why Dobson makes each factor just so, learn how he thinks about
it. His philosophy of star-gazing per fuses his telescopes and his book.
The book includes the only detailed biography; wonderful vignettes from the
Sidewalk Astronomer's many expeditions; their own special way of describing
celestial objects; and, of course, complete details for making a Dobsonian.
169 pages; 154 clear, friendly line drawings; 9 photos. Hardbound in
plywood, Dobson's favorite material.

Note: This book is no longer being printed. If you find a copy 4 sale
anyplace GRAB IT!

7.3 What is the Best Mount?

EQUATORIAL Vs. ALTAZIMUTH: THE TRUTH

The various telescope mounting systems available for use by amateur
astronomers have been discussed at length on sci.astro.amateur. There has
been a great deal of debate, a little ill-informed opinion, and some real
misconceptions concerning each of the basic mounting schemes, so perhaps it
is time to clear the air. One basic and irrefutable fact must be stated up
front: NO MOUNT SYSTEM IS PERFECT FOR ALL SITUATIONS! Any attempt to
champion one mount scheme over another without considering all the facts is
doomed to failure. Below are the true advantages and difficulties of the
two most popular mounting system.

The ALTAZIMUTH (i.e.: Dobsonian, etc..). This mounting system has gained
considerable popularity over the past 20 years, evolving from the old
"pillar and claw" system originally used only in inexpensive small
telescopes, to a modern well-designed one which boasts of supporting some
of the largest apertures in amateur astronomy today.

++Altazimuth Advantages++

1. Simple and stable mounting system requiring no axis counterweights or
heavy off-center concentrations of weight to induce vibration or mount
flexure problems. Only two vertical and one horizontal bearings are
needed.
2. Easy and intuitive mount for beginners to learn on.
3. More portable than many equatorial mounting schemes, especially for
apertures over eight inches (often faster setup time).
4. Easy to build, and often allows simpler mirror-support schemes to be
used.
5. Lower overall cost, especially for large apertures.

--Altazimuth Disadvantages--:

1. Unable to track objects with single axis motor drive system. For long
term tracking, an altazimuth must be computer dual-axis controlled, or
supported on an equatorial platform (only 1.25hrs maximum tracking
time on such a platform). Cannot track objects directly through the
zenith in dual axis driven mode ("Dobson's" hole).
2. Lack of fixed field orientation makes star hopping the primary mode of
faint object location in non-computerized altazimuth mounts
(right-angle sweep and R.A./Dec. setting circles cannot be used).
Objects not located in easy-to recognize star fields can be more
difficult to find manually.
3. Changing altitude and azimuth coordinates can make finding objects
more difficult using only altitude and azimuth circles, often
requiring computer readouts or nearly continuous manual calculations
to keep track of pointing directions for locating objects.
4. Field rotation limits photography to short exposures (unless expensive
field de-rotators are used). Guiding long exposures can be very
difficult, since corrections for drift are sometimes non-intuitive.

EQUATORIAL MOUNTS: These mounts are aligned to the celestial coordinate
system, and have been the mainstay of serious amateur and professional
astronomical telescopes for over a century. They come in a variety of
designs: German Equatorial, English Yoke, English Cross-axis, Polar disk,
Fork, Split Ring, etc..

++Equatorial Advantages++

1. Can use one "clock-drive" motor to drive the telescope in right
ascension for long-term tracking of celestial objects.
2. Most equatorial schemes (except for Yoke mount) can reach and track
through all areas of the sky.
3. No field rotation enables easier long-exposure photography with more
intuitive guiding corrections. Also makes planetary observations a bit
easier, since the object in the field does not rotate.
4. Finding techniques such as the "right-angle sweep" or star drift
method can be used to make locating faint objects easier and faster,
even with non-clock driven scopes (only one nearby visible reference
star is needed).
5. R.A./Dec. Setting circles (both digital and analog) can be used for
locating non-visible objects. Digital circle design for equatorial
scopes can be simpler, since no real-time guiding calculations need to
be performed.

END OF PART 1 - PLEASE PROCEED TO PART 2.
The Boldly Go Where No Meade Has Gone Before
Captain, RSS Enterprise NCC1701R
United Federation of the Planets
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