Copyright (c) 1998 Slc.Dennis Bishop All rights reserved.
Translated into HTML by Michael Richmond
This FAQ is under construction There may be some sections that are not totally done yet.
Questions in this FAQ:
Contributors to this posting include:
Pierre Asselin Dana Bunner Doug Caprette Mike Collins Kevin Deane Jay Freeman Chuck Grant Dyer Lytle Christopher Gunn Doug McDonald Andy Michael Dave Nash Jim Van Nuland Bill Nelson Leigh Palmer Alan Peterman Tom Randolph David Smith Geoff Steer Mario Wolczko C. Taylor Sutherland Paul Zander David Knisely
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.
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.
With these thoughts in mind, I can make some general comments.
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.
Let me regroup that information into three questions telescope buyers often ask:
Usually, a high-quality refractor.
Usually, a Schmidt-Cassegrain.
Usually, a big Dobson.
My "Big Iron" is a Celestron 14, with a little tiny single-axle cargo trailer to haul it.
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.
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.
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.
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:
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 Dobsons) 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 telextenders, 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 Plossl, 32, 20, and 12.4 mm Erfles, and 7 and 4 mm Orthoscopics. The 55 and 32 mm eyepieces were in 2-inch barrels, the others in 1.25 inch barrels. All were 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 Plossls 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 four 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.
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.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. 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.
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,
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.
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.
Clear sky, and enjoy your telescope.
OK, by popular request, here is a glossary of common astronomy terms encountered in amateur astronomy.
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); 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 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.
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.
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 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 problem for visual astronomy, but a limitation on astrophotography.
In the United States, there are two popular astronomy magazines: Sky and Telescope (S&T), and Astronomy. Of the two, S&T is more technical, 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.
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.
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 Starcharts.
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 (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 telescope you are using your rods,and you aren't seeing a lot of color.
What Company Makes the Best Telescopes?
This is a very unfair question at the best. There are many companys which make good telescopes. A lot will depend on just how much you want to spend for a telescope. The Major companys that make and/or sell telescopes are as follows: Orion Telescopes, Meade, and Celestron, but you have to be carefull with what you buy from even these companys,as they ALL are selling telescopes which are coming from Prison factorys in 'RED CHINA' and are the same as the Junk department store telescopes. There are other smaller companys that make good scopes too. There are some Japanese companys 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 sold at Toys R Us, K-Mart, & Wal-Mart,etc. Waste of Money. Notice: Tasco has taken over Celestron, they are now one company, only time will tell if this inproves Tasco or Degrades Celestron.
Simmons: Total waste of money, worst than Tasco.
Bushnell: I have looked at this companys telescopes 1st hand and I do not belive that they would withstand one full night of useage 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 companys poping up that are selling the same 'Made in Red China' telescopes uder names never seen before it would be a good idea to stay away from them too.
There are some companys importing telescopes from Russia, I have not seen these scopes first hand, but have read some good reports of them.
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 telecope. This does not apply to department store telescope, though. Really.
As the numbers of companys 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 companys that market telescopes. The best idea would be to contact the comapnys 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.
Well, there are three basic places:
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.
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.
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. Box 1158 Santa Cruz, CA 95061 (also San Francisco and Cupertino) 800-447-1001 firstname.lastname@example.org
Orion Telescopes carries a wide selection of binoculars, telescopes, and accessories (Celestron, Tele Vue, and their house brand; they do not carry Meade). They have a 30 day "no questions, satisfaction guaranteed" refund policy, which they do seem serious about. A fair number of people (myself included) have bought at Orion and all are very satisfied with the way they were treated. If you need technical assistance when you call, ask for Steve or Eric. They have a very good service and support record.
Lumicon 2111 Research Dr. #5 Livermore,Ca.94550
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 Tee Circle Suites 105/106 Norman, OK 73069
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/TASCO. 2835 Columbia St. Torrance,Ca.90503
This company also sells many types of telescopes. From SCT's to DOBs. Have seen both Good and Bad posted about them. As Noted above this company is now owned by TASCO.
Mag 1 Instruments 16342 Coachlight Dr. new Berlin,Wi.53151
Markets their 'Portaball' style DOBs in 8in and 12.5in size.
Meade Instruments Corps. 6001 Oak Canyon Irvine,Ca.92620
Markets many types of Telescopes, from junk to High End.
Coulter Optical Div. of Murnaghan Instruments 1781 Primrose Ln. West Palm Beach,Fl.33414
They market a full line of DOBs.
Obsession Telescopes P.O.Box 804a Lake Mills,Wi.53551
Markets Dob's from 15in to 30in!
Pocono Mountain Optics 104 N.Plaza Moscow,Pa.18444
Enthusiastically recommended by a few people on the net.Owned by Glenn Jacobs who goes to most of the astronomy get-togethers in the NY-NJ-PA-CT area so you actually meet him if you live in the area. Often willing to cut a package deal if you are buying big ticket items. No problems returning things with which you are dissatisfied.
Roger Tuthill 11 Tanglewood Lane Dept. ST Mountainside,N.J. 07092
Enthusiastically recommended by a person on the net. Not the least expensive, but top-notch service. Roger unpacks, inspects and collimates every scope he sells, and is very good about refunding your money if you are dissatisfied.
Stargazer Steve 1752 Rutherglen Cr. Sudbury, Ontario P3A 2K3 Canada
Markets a 4 1/4inch DOB in both Kit form and/or ready-to-use. Both under $300.00.
Starsplitter Telescopes 3228 Rikkard Dr. Thousand Oaks,Ca.91362
Markets DOBs from 8in to 30in.
University Optics P.O.Box 1205 Ann Arbor,Mi.48106
A few people have reported using University Optics, and all report receiving good service. I have heard no complaints.
Parks Optical 270 Easy St. Simi Vally,Ca.93065
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 knowledgeble to bubbleheaded.
Adorama 42 West 18th Street New York, NY 10011 orders: (800) 223-2500 info: (212) 741-0052
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 13th Avenue Brooklyn, NY 11219 orders: (800) 221-0828 info: (718) 436-1518
Refer to Adorama. Same comments apply.
Pauli's Wholesale Optical Danbury, CT
A lot of bad reports, order at your own risk!
Also there is the AstroMall.
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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 perfuses his telescopes and his book. The book includes the only detailed biography;wonderful vignettes from the Sidewalk Astronomers'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. Exclusive source. Send $39.95 + $5.00 shipping to Everything in the Universe, 185 John Street, Oakland, CA 94611.
The video (also excerpted from the order form): For the first time on video, John Dobson shows how you can build your own low-cost Dobsonian Telescope. The 90-minute video is a complete step-by-step guide, covering telescopes from 8 inches to 16 inches in diameter. $39.95 +$3.50 shipping.
What is the Best Mount?
EQUATORIALS Vs. ALTAZIMUTHS: 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 sytstem.
The ALTAZIMUTH (ie: Dobsonian, ect.). 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.
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, ect.
NOTE: none of these disadvantages will eliminate a mount design from use by the amateur. For strictly visual use (especially for the beginner), the altazimuth can easily be recommended, while for long-exposure photography, the equatorial is often the mount of choice. For very large apertures intended for easy portability, the altazimuth almost has to be used. However, the compact split-ring equatorial design can also remain fairly portable even with telescopes as large as 18 inches. Computers and computerized driving systems have narrowed the choice between the two mounting systems (and driven up their prices), but their basic characteristics have not changed. In any case, both the altazimuth and the equatorial have a firm place in amateur astronomy.
In addition to a telescope, you absolutely must have a mounting and a tripod. You will also need a few eyepieces, a telescope with only one eyepiece is like a piano with one key.
These accessories don't come cheap, expect to pay as much for the mounting and tripod as you paid for the optical tube. For a first telescope,you probably will want to buy an entire system it tends to be less expensive that way.
Which eyepieces should you start with? I'd suggest three or four, maybe a 30mm, 25mm, 20mm, 8mm and a 2x Barlow (which will give you coverage of 30,25, 20, 15, 12.5, 10, 8, and 4 mm). Buy eyepieces of like quality to your telescope. Putting a $300 Nagler eyepiece on a $150 telescope is pointless (it would also probably tip over the entire telescope).
This section was written by Jim Van Nuland
9.1 What Are They?
Digital Setting Circles (DSCs) are a small special purpose computer, mounted on or near a telescope. The scope has shaft encoders attached to sense the motion of the scope's axes, and the computer then converts these motions to the position of the telescope, and displays it (for instance) in Right Ascension (RA) and Declination. An 8-conductor cable runs from the computer to the encoders, with 4 wires to each encoder. RJ-45 telephone connectors are used at the computer.
They do NOT move the scope. You push it by hand, and the DSCs tell you which way to move and how much.
What makes DSCs so desirable is that they work on alt/az-mounted scopes; and even with equatorial mountings, it is not necessary to polar align the mount. (However, it's desirable to have the mount at least roughly polar-aligned so it follows an object.)
Additionally, most models have an internal catalog and a "guide" mode.One selects an object (or, in some,a planet), and the DSCs tell which way to move each axis.
They are marketed by Lumicon, Jim's Mobile, Inc., Celestron, and Orion Telescope Centers. The various brands and models differ mostly in their internal catalogs of celestial objects. All are actually manufactured by the same company, Tangent Instruments of Palo Alto, California, USA, who, however does not sell directly to individuals. I own the NGC-MAX from JMI, so some of my statements may not apply to other versions.
9.2. Must the ground board be leveled?
No. An alt/az mount must have a fiduciary mark such that the tube can be placed accurately at 90 degrees to the elevation axis. One way to do this is to (one time only) level the ground board, then the tube. Make the mark in such a manner that it can be adjusted when something changes. Some models of DSCs allow an alt/az mount to be initialized in a vertical position. When starting the DSCs, the tube must be set horizontal (or vertical), and then two stars are used to align. The stars must be at least 20 degrees apart in the sky (90 is ideal), and the first may not be Polaris.
9.3. How does one set up an equatorial mounting?
If the mount is known to be accurately polar aligned, you may still use two stars as mentioned above. Or you may set the DSCs to take advantage of the known alignment, and it will require only one object,and no zero degree reference mark is needed.
If an equatorial mount is not polar aligned, it must have a reference mark at zero degrees declination, and must use the two-star setup. For a German mount, the mark may be on either side of the scope (tube pointing east or west), and the DSCs set to correspond. The mount may be driven or undriven. As for an alt/az mount, the stars must be at least 20 degrees apart, and the first may not be Polaris.
9.4. Do the DSCs support a Poncet platform?
Probably depends on the model. The NGC-MAX provides telescope type ET(equatorial table). It assumes that the table is carrying an alt/az scope, and that the scope is initialized with the tube horizontal. I believe that an equatorial mount could be used, but have not tried to simulate it.
9.5. How accurate is the device?
The position of the scope is displayed to one minute of RA and 10 minutes of dec. Guide mode displays position error to 0.1 degree of arc. The actual accuracy depends on the care with which the alignment was done, the accuracy of the mounting, accuracy with which the shaft encoders were installed, the resolution of the encoders, and a bit of luck. If the level or zero was not set accurately, the system will work poorly, and it should be re-started. If star settings were done carelessly, one can simply re-do one or both of them.
The "luck" factor stems from the digital nature of the shaft encoders. If the encoder is on the verge of a step, you could be off by one step.
The absolute theoretical resolution is three encoder steps, assuming everything else is perfect. In practice, I get about 0.2 to 0.3 degrees, and closer near the alignment stars. If I move a long way across the sky, the error is perhaps 0.5, but then I re-align on a convenient nearby star. It's not too unusual to get 0.1 if all has gone especially well during alignment. This with 4000 step encoders.
Accuracy is best between the alignment stars, and the DSCs calculate a "warp" so as to spread out the error. When re-aligning, only one star sighting is needed. The DSCs retain only the two most-recent star settings, provided they are at least 20 degrees apart in the sky.
9.6. What objects are in the internal catalog?
This is the major difference between models. All have a few dozen named stars, used especially for initial alignment. Some have the planets. The Lumicon models have a catalog of planetary nebulae, which is Dr. Jack Marling's specialty.
The NGC-MAX version 3.94 (July, 1992) has the planets;28 user defined objects; the Messier catalog (including M40 and M110); the full NGC,including the so-called "non-existent" objects; about half of the IC catalog; a catalog of 951 interesting stars (multiple, red, variable);and a list of 367 additional deep-sky objects, many of which are very faint.
For each object, the catalog has the position, magnitude, size (diameter or separation), constellation, name (if any) and/or catalog number, and the type of object. Some have a word or two of description. This probably varies with the brand and model.
9.7. May I add my own objects? Comets, for instance?
The NGC-MAX accepts user objects, and I presume most other high-end models do as well. I like to put in the Sun and Moon, so that I can align during the day. This must be done carefully, with the Sun filter attached. THIS IS DANGEROUS, as the filter must be removed when sighting on the Moon, and if you come back to the Sun, you MUST have first re-attached the filter! The moon is a poor alignment object because it has up to a degree of parallax, and it moves about 0.5 degrees per hour. But it provides a start, and it may be enough to locate some bright stars, and re-align.
9.8. What is "identify" mode?
Identify mode is present in the NGC-MAX, and probably other models. One specifies the class of object, and the faintest magnitude, then the DSC selects the nearest to the telescope's position. Very nice, but in the Realm of Galaxies, alignment is critical and then there are too many to be certain. To check, read out the magnitude and description, and go to Guide mode and see how far away the object is.
It's especially useful in clouds, as one may point the scope into a clear spot, then ask what is nearby. One must separately search for galaxies, clusters, etc.
Identify mode runs continuously, so that, as the scope is moved, the DSCs will (after a few seconds), indicate the new (or nearest) object.
Some models allow alignment on ANY catalog object, which is helpful, but I find that accuracy is best on stars or very round objects. I find that planetary positions are especially suspect. The computer carries only the date, not the hour. (Use UT date.) I have often had poor alignments when using planets, and do so only for daylight set- ups; I re-align on stars as soon as I can find any. Open clusters are especially unreliable; galaxies are not much better.
9.9. Can it replace star charts?
For comparatively easy objects, probably. In a crowded field, no.Some models support the Tiron Atlas 2000 and the Uranometria 2000, by indicating, for each object, the page on which it (the object) will be found. These models also indicate the chart corresponding to the position of the scope, regardless of specific object.
9.10. What other functions are present?
This varies heavily with model. The NGC-MAX (here we go again) has two that have not already been discussed.
"Timer" counts up in hours, minutes, and seconds. It can be stopped,reset, and re-started, but can't be restarted without first being reset.
"Encoder" shows the encoder positions in degrees. If an alt/az scope was pointed north when the DSC was powered up, then encoder mode will read elevation and azimuth, if the scope is also standing reasonably level.
9.11. How is it powered? How long does the battery last?
There is an internal 9-volt transistor battery. The load is 18 to 40mA (NGC-MAX), depending on how bright the display is. I suppose this might depend on the model, too. The maker claims 30 to 50 hours on an alkaline battery. They do last a good long time. There is a "low battery" indicator which would turn on at about 4.5 volts, but in practice, I get "encoder error" messages before that.
Some models have a second connector (serial port) by which external 9- 15 volts DC may be supplied. This does not require the internal battery to be removed; the two supplies are in parallel with diodes to prevent back-circuits. It does not recharge the internal battery.
9.12. How accurately SHOULD the mount be constructed?
The brief answer is, as accurately as you'd like the DSCs to operate.For an equatorial mount, there must be little flexure; the RA axis must be perpendicular to the dec axis, which in turn must be perpendicular to the optical axis of the tube.
For an alt/az mount, the ground board must be rigid, the azimuth bearing surface must be flat, dent-free and stiff; and the side bearings must be the identical height, that is, the elevation and azimuth axes must be accurately perpendicular. In addition, the optical axis of the tube must be perpendicular to the elevation axis. There is a terrible irony here: the Dobsonian mount works precisely because its kinematically stable design does NOT require that it be accurately constructed!
9.13. How accurately should encoders be installed?
Again, the short answer is, as accurately as you'd like the DSCs to operate. One can't do the job with a hand-held drill. OTOH, careful work with a modest lathe and drill press is quite sufficient, especially if performed by a modest machinist. Most astronomy clubs have such a person.
Best accuracy is obtained with high-resolution encoders. Standard encoders have 2048 steps per revolution, and high-res type has 4000.One can also use gears to provide greater resolution, but see below.
If the encoder is connected directly to a shaft, the hole in the shaft must not be oversize. It must be straight, well centered, and parallel to the axis. The body of the encoder must be held so that it cannot rotate with the shaft. If it is connected by gears, the shafts must be parallel, and there must be no backlash.
Encoders are not especially delicate, but they do not like to be bent.They require very little torque, and rotate continuously. The setscrew should not deform the shaft. The 4-wire connector should be looped so it does not pull on the encoder. They may be mounted such that the shaft is stationary, with the body moving, or the usual way;the direction is set in the DSCs' setup option.
In an alt/az mount, the azimuth encoder is typically mounted atop the center bolt. In this case, the bolt must be nicely perpendicular to the ground board, and the comments about shaft mounting (above) apply. If the rocker box has any side play, it will be nearly impossible to avoid some runout. This can be reduced by using a very long lever arm to hold the body of the encoder.
Both side bearings must be round (especially the one with the encoder), the center must be carefully located, and the encoder shaft parallel to the elevation axis. Any runout There will cause serious inaccuracies when moving across the sky.
9.14. How accurately MUST the mount be constructed?
Please don't feel that only a million dollar mount can be equipped with DSCs. My 1972 Optical Craftsman (German) mount works very well,even with about 0.5 degrees of error if I shift the mounting and return to an object. This was the economy model! A machinist friend helped me drill the holes for the encoder shafts.
I used UGMA grade 10 precision gears to step up the dec shaft speed. The designer of the DSCs was amazed at that, and admitted that he used UGMA 4 with adequate results. I don't know how to calculate how much more accuracy I might be getting from my expensive gears.
My alt/az mount, crafted of wood in my shop with only hand tools, carries a 108mm f/4 scope, and *always* puts an object in a low-power field. OTOH, if I re-collimate the scope, I must also re-position the vertical mark. I usually re-align after moving far across the sky.
If the mounting is less than perfect, it means that you will need tore-align more often. But if the mount is *really* sloppy, it probably will not be satisfactory.
9.15. Can I connect the DSCs to my own computer?
Yes, for some models. The NGC-MAX, and probably others,has a serial port that may be used with an external computer, so that the screen shows a dynamic star map, identifies objects, etc.
But the attached computer must take over ALL functions, including the prompting for "level me," pointing at particular alignment stars,guiding, calculating the conversions for RA and Dec, etc. I understand The_Sky, from Software Bisque, does all this, but I have not seen it in use nor heard from a live user.
The port is a modular telephone connector (RJ11). It has four wires:B+, data in, data out, and ground. External to the NGC-MAX, the cable must route DTR back to the attached computer as DSR, CD, and/or CTS,as needed by the attached computer. The 4th wire is +Battery, a 9 to 15 volt external power supply, which does not charge the internal battery. It is not necessary to remove the internal battery,
When the NGC-MAX is operating in "BOX" mode, it blanks its own display, and does nothing but pass the shaft encoders' values over the serial port. It multiplies them by the encoder ratios (the latter set in the NGC-MAX setup function), and scales them such that 00000 is the position at power-on, and 32767 is just under 1 rotation.
Communication is at 9600,8,N,1. When the NGC-MAX powers on, it sends a hello message such as "V2.94". When the attached computer sends a character (the sample program uses "Q" but anything seems to work) down the port; and the NGC-MAX replies with 13 characters of the format "+00000t+00000" where the "t" is ASCII 9, and the 00000s are the two encoder values.
I don't use this facility, but I'm too curious not to have tried it.I used my modem program to supply the computer side. I use the NGC-MAX whenever I'm doing general observing, and I like it very well.But I don't have a portable computer to use with it, and don't too much see the need. OTOH, if I fell into a laptop, I'd surely want to try connecting them.
The quick answer is because you already have them, so you do not have to spend any money. Certainly going right out and buying the Fujinon 25x150 Astronomical Binocular ($11,000 list price) would be a pretty stupid thing to do, no matter how good the binoculars are.
You should also avoid the quick-focus binoculars, as they are easy to de-focus as well.
The remainder of this section was written by Paul Zander.
Based on my experience, I suggest that you start with a pair of 7x50 binoculars. This is the most popular size and hence good ones are available from many stores, even some of the discounters. Be sure to get ones that have anti-reflection coatings on the mirrors and lens. If you wear eyeglasses, you may be able to find binoculars which can focus without them (unless you have significant astigmatism). Make sure the image is sharp at the center and edges at the same time.
"7x" is the magnification. Most people can hand hold these without needing to bother with tripods, etc. The "50" means 50mm (~2 inch) objectives (aperture). This gives light gathering ability similar to many small telescopes. Many advanced star gazers regularly use binoculars to either locate items to focus telescopes on, or just for the wider field of view.
When trying to view near the zenith, use a reclining lawn lounger: you can lie back and support your arms on the chair, giving a steadier view. You also will not get a crick in your neck.
You might also use a plastic pad to lie on.
10.1. How Do I Hold Binoculars?
This section was written by Jay Freeman.
If you don't have a tripod (and tripods are sometimes a little clumsy, and are often difficult to use when the binocular is pointing near the zenith), it is important to know how to hold a binocular correctly to achieve maximum steadiness.
The way most people tend to hold a binocular is with one hand on each side of the middle of the body-roughly where the prisms are in a conventional 7x50, say, so that the left hand is directly to the left of the center of gravity of the instrument and the right hand is directly opposite it, to the right of the center of gravity.
For most people, there is a better position. Imagine that you are holding the binocular to your eyes, with your hands positioned as just described. Now, slide your hands along the body of the instrument,toward your face, until only your pinky and ring fingers are curled around the back end of the binocular body. In this position, the binocular feels a little nose-heavy, because you are supporting it behind its center of gravity.
Now curl each thumb up as if you were making a fist, and flex your hands so that the second bone in from the tip of your thumbs are pressed up against your cheekbones (counting the bone in the part of your thumb where the thumbnail is, as the first bone). This makes a quite solid structural connection between the body of the binocular, through your hands and thumbs, to your face, and markedly improves how steadily you can hold the instrument. Similarly, curl the first and middle fingers of each hand around the corresponding binocular eyepiece, to provide a little more structural connection (and perhaps also some protection from stray light). In this position, your hands are not far from where they would be if you brought them to your face to block out stray reflections while peering through a store window at night.
For most people, this position leads to markedly steadier viewing, but if the binocular is especially long and heavy (say, a 10x70 or an 11x80), the out-of-balance position can be quite tiring. In that case, move *one* hand out to the objective end of its side of the binocular, so that you are supporting the instrument on opposite sides of its center of gravity, but with some structural connection between it and your face; namely, the other hand. When the hand way out there gets tired-just switch hands.
For each person, there is a limit to how heavy and / or how powerful a binocular can be, before there is no way for that person to hold it steady enough. I am an averaged-sized adult male in reasonable physical condition, and I find I can hold a 10x70 (Orion's) steadily enough to use indefinitely on astronomical objects. But I have an old Celestron 11x80, that doesn't look much bigger or heavier than the 10x70,that I can only use for a few minutes before my arms get tired. As a 12-year old I am sure I could have used a 7x50 indefinitely with no problem, but at a younger age I might have had difficulty using one continuously. Your experience may vary with your strength, size and condition. Try before you buy, if at all possible.
10.2. What Are Some Eye Relief Figures?
If you need to wear eyeglasses while looking through binoculars (presumably you have astigmatism, but if you require many diopters of correction you might need to as well) you need reasonably good eye relief. Dana Bunner contributes the following table:
Model Advertised ER Measured ER Bausch & Lomb 7x26 Custom 16 15 Celestron 10x50 Pro 15 10 Celestron 7x42 Ultima 23 19 Celestron 7x50 Ultima 20 16 Celestron 10x50 Ultima 19 17 Celestron 8x56 Ultima 21 11 Fujinon 8x40 BFL 19 17 Fujinon 7x50 FMT-SX 23 20 Fujinon 10x70 FMT-SX 19 17 Minolta 7x50 Standard 18 16 Minolta 10x50 Standard ? 9 (FYI) Minolta 10x50 XL 18 16 Nikon 8x30E Criterion 13 13 Nikon 7x50 Windjammer 16 16 Optolyth 10x40 Touring 13 12 Pentax 8x24 UCF 13 8 Pentax 7x35 PCF 14 9 Pentax 7x50 PCF 20 10 Swift 8x25 Micron 13 11 Zeiss 7x42 B/GA T Dialyt 19 18 Zeiss 20x60S ? 14 (FYI)
If you don't know the constellations, you might want a book that will help you learn them. A "fun" book for those just learning the stars is The Stars, A New Way of Seeing Them by H. Rey, which presents a non-orthodox way of drawing the constellations so they are easier to visualize.
You will probably want a beginner's guide, such as the book by Sherrod mentioned above. Sky Publishing has some introductory materials which would probably be as useful, which you get for free when you subscribe to Sky and Telescope.
Petersen's Field Guide to the Stars and Planets comes highly recommended. It is very inexpensive ($13), small and handy to use at the telescope. It has a good discussion about stars, planets, nebulae, and galaxies; and has a very complete albeit small-scale star chart, along with a the usual tables. It hasm long lists of deep-sky objects for each area of the sky.
You will need a bigger star chart than is included in Petersen's. Try Sky Atlas 2000.0, by Wil Tirion. The field edition, which has white stars on a black field, is probably more useful than the desk guide. It is also printed on heavier paper, so is more resistant to dew and the rigors of the night. For beginners, buying Uranometria 2000.0 is probably a mistake. Yes, it is the "best" star chart, but the scale is impossibly small- when the Orion constellation takes up four separate pages it is really hard to use for beginners.
Burnham's Celestial Handbook ($36). This three volume set is billed as "An Observer's Guide to the Universe Beyond the Solar System" rather all-encompassing claim, which it manages to live up too. Information on every item of interest you can think of: galaxies, double stars (optical and binary),variable stars, nebulae, etc. More information than you could use in a lifetime. I consider this a necessity.
Sky and Telescope's 100 Best Deep Sky Objects. About $5, which is kind of expensive for a list, but it sure makes it easier to figure out what to look at when you are just beginning. The items are sorted by Right Ascension, which makes it real easy to figure out which ones are currently up.
All the materials listed are available from:
Sky Publishing Corporation P.O. Box 9111 Belmont, MA 02178-9918 USA
Their catalog is free.
11.1. What About Computer Programs?
There are to many types of computer programs that I can NOT review, as they do not run on my machine. I think there should be a FAQ just for all the computer programs.
This FAQ is a copyright work. You have my permission to reproduce it however you like, as long as you don't make any money off of it and you leave all the attributions and the copyright notices. While this is a FREE FAQ, any little Donations ($5.00) sent to the address below will go upgrade my telescope.
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