A Message To Readers On Limited Budgets
MANY TELESCOPES UNDER $500 ARE JUNK.
Almost all of the "how to buy a telescope" guides that I have
seen on the Net don't mention places to buy in Australia. Nor do they
describe some specific hazards awaiting the Aussie beginner. So here
I have been using telescopes seriously for over 20 years and doing public astronomy for nearly as long. It saddens me when I have to tell a beginner that they just wasted a lot of money on their first telescope; because they got conned about its capabilities. And usually the seller doesn't have a clue either.
Buying a telescope is like buying a car; because both can be expensive, there are different types for different tasks, and if you get one of poor quality it will only disappoint you. The retail costs are comparable too eg: $500 buys you something basic, $5000 buys something good, $50000 buys something to brag about.
Like cars, each type of telescope has its devotees and its critics, and some types are better for certain tasks. Also like cars, virtually all telescope designs are a compromise between cost, performance, and purpose.
Although lawyers won't let me mention the names of the manufacturers on this site, Department Store Telescopes are easily recognized by the outrageous lies printed on the packaging (or in the catalogue); such as: magnify up to 600x, see trillions of km into space, see spiral galaxies and nebulae -- in short, implying that you will see as much detail as the professional observatory photos on the box.
What they don't mention is that the 600x image will be a useless blur (assuming the telescope stops wobbling for long enough), that most of us can see things thousands of lightyears away with the naked eye (for example the Large Magellanic Cloud at 190,000 lightyears), and that professional photos go much fainter than the eye can see. Furthermore, the optical quality of these wallet-slimmers is questionable. I personally have seen $500 Department Store Telescopes outperformed by $80 finder scopes!
If you're wondering "how do they get away with selling this junk?" the short answer is that most buyers (and sellers) don't know any better! One manufacturer was convicted of misleading telescope advertising in the English courts a few years ago; but as far as I know no-one has been prosecuted in Australia. Buyers who know better, buy a better telescope in the first place.
Some (not all) Department Store Telescopes can be improved with good eyepieces and a stable mount. If you have gone out and bought one of these things in ignorance (or you were given one as a present), see my suggestions for improvement.
There are only four things you can use an unimproved Department Store Telescope for:
Really cheap refractors may have an objective lens consisting of a single piece of glass (or plastic!). Avoid these -- they produce images with garishly coloured haloes. You should buy a scope with an "achromatic" or "apochromatic" objective. Achromatics use two pieces of glass (one behind the other) in the objective lens, apochromats use three pieces of glass. Both will focus all the colours of light to virtually the same point, which gives you a better, brighter image.
Recent developments in optical glass technology -- the so-called "ED" lenses -- allow refractors to be made shorter than ever before, while still providing proper colour rendition and sharp images. The tube can be as short as 5 times its diameter.
One problem with larger reflectors is the height of the eyepiece. You may need a strong free-standing ladder to reach the eyepiece when the telescope is pointed high in the sky. But any telescope that big will also be hard to transport.
Telescope optics do (occasionally) need cleaning. Descriptions of how and what you can (and can't) clean at home are available.
Better telescopes are frequently described as "diffraction limited". This means that in perfect observing conditions, the clarity and resolution of the telescope's images are constrained only by the laws of optical physics. This image illustrates what a diffraction-limited image of a single star looks like through a refractor.
A reflector's image is similar (provided its secondary mirror is not unduly large); but you may also see evenly-spaced "spikes" emerging from the image of a bright star. This is normal for a reflector. A Schmidt-Cassegrain's image does not have these spikes.
Of course what you see in the eyepiece is a tiny version of this image -- I've greatly magnified it here!
The Airy rings are an example of a diffraction pattern; caused by the light from a point source -- the star -- being perceived via a circular aperture. The circular aperture in this case being the objective lens or primary mirror. Read an introductory physics book for an explanation of diffraction)
To the experienced eye, the size, shape, spacing and relative brightness of the Airy rings (and the star image) provides clues to various optical defects, focusing problems; and the atmospheric conditions. An adequately illustrated discussion of this topic would overflow my website, so you won't get it here ;-) But I do have a few notes on optical problems.
There are two major species of telescope mountings:
A variation on the alt-azimuth design -- the Dobsonian mounting -- is commonly used for larger reflectors and home-made telescopes. The Dobsonian rotates (in azimuth) upon a large baseplate, and the baseplate supports two uprights with semi-circular cutouts. The telescope tube is mounted (rather like an old cannon) between two large circular bearing surfaces resting in these cutouts. Here are some schematics for making your own Dobsonian mount.
However, many beginners are baffled by equatorial mounts; and are
bewildered by the (sometimes peculiar) manoevures needed to aim in some
directions. The eyepiece can also end up in some awkward positions.
Two common variants of equatorial mounts are the German, which features a counterweight on a bar opposite the tube; and the Fork, which has the tube supported between two thick arms emerging from a turntable-like assembly. Fork mounts are common on Schmidt-Cassegrain telescopes (eg: the larger Meade and Celestron models).
Elaborations to both types of mounting include slow-motion controls, setting circles, computer readouts or controls, clever precision engineering, and semi-automated polar alignment. All of these things add to the cost of the telescope.
Poor mountings are a universal characteristic of Department Store Telescopes, but they can (sometimes) be replaced with something better. See my suggestions.
It is possible to engineer most mechanical and optical problems out of a telescope, which is why a good quality scope costs a lot. However, engineering out the instabilities of the Earth's atmosphere requires adaptive optics - which cost a huge amount of money. The Earth's atmosphere is rarely stable enough to permit useful magnifications beyond about 250x; especially if you are observing from metropolitan areas.
If it's a Department Store Telescope then you should FORGET about the "magnify up to XXX times" claimed by the manufacturer. It's meaningless; it's like saying that a Volkswagen Beetle will do 300km/h if you install a Formula 1 speedometer in it. Maybe if you drive the Beetle over a cliff...?
Avoid a telescope that boasts about magnification; look instead for
terms like "diffraction-limited" , "coated optics"
and allusions to the clarity of the images and the stability of the
A good telescope has a maximum useable magnification -- under excellent rural skies -- equal to:
|(aperture in mm) x 2.4|
|magnification = (focal length of telescope) / (focal length of eyepiece)|
The focal length of the telescope may be written on the tube
(eg:"F=760mm" or "F=2000mm"); or alternatively the
focal ratio (usually written as f/(number) may be recorded.
This is related to focal length via the formula:
|(focal length) = (focal ratio) x (aperture)|
A popular accessory is the Barlow lens, which increases the
apparent focal length of the telescope by a fixed ratio (eg: 2 times);
thereby increasing the magnification of any eyepiece by the same ratio.
The Barlow goes into the eyepiece holder on the scope, and the eyepiece is then put into the Barlow lens' barrel. You could get by with a single eyepiece and a Barlow if you choose carefully; or use a Barlow to effectively 'double' your choice of magnifications and save buying extra eyepieces.
There are also 50mm (2 inch) eyepiece barrels, originally designed for big telescopes (and with a big price tag). These too are available with a variety of designs and accessories; and an increasing number of smaller telescopes are supplied with eyepiece holders that take both 50mm and 32mm diameter eyepieces.
Eyepiece designs are numerous, and prices vary enormously. Department Store Telescopes invariably come with cheap rubbish designs like Huygenian or Ramsden -- look for H, R or AR codes on the barrels. Kellners (codes K, KE or RKE) are acceptable on telescopes with larger focal ratios (f/8 or higher) or for low magnifications. Orthoscopics (codes O or Or) and Plossls (code Pl) are a good choice for most telescopes. You can also get other excellent -- and expensive -- designs such as Panoptics, Naglers or Pretorias.
Some eyepieces give a very wide apparent field of view, seemingly like looking through a window into space rather than a small hole! This should not be confused with the true field of view which depends on several factors. You need to know the true field of your eyepieces for more effective use of your star charts. One simple way to find the true field is to use the Moon, which is about 1/2 degree in angular diameter. How many "Moon-diameters" can you fit into your eyepiece's view?
If you have eyesight problems or a disability, some more advice is available.
Do not attempt any telescope astrophotography or CCD imaging until you have had several hundred hours of observing experience. Taking good pictures through a telescope is not simple, and can get very expensive. Be a visual observer first.
Don't rush into buying a telescope, especially if you fall into any of
If you're buying for a child then don't be surprised if their astronomical enthusiasm declines or vanishes during adolescence. This is a very common phenomenon :) but in many cases their enthusiasm returns later in life.
Good binoculars for astronomy include 7x50, 10x50 or 12x50 models. Bigger and more expensive binoculars are also sold for astronomy, but you will need to support them on something -- big binoculars are heavy. The numbers on binoculars refer to "magnification x aperture" so 7x50s have a magnification of 7 and an aperture of 50mm. Avoid models with smaller apertures, or which don't have "fully coated optics". There are also some finderscopes (eg: 8x50 or 12x60, as accessories to big telescopes) or spotting scopes which make a good first instrument. If you're buying a spotting scope with tripod for your astronomy, then a model with an angled eyepiece will be more comfortable than a "straight-through" design.
Use your binoculars for several months. THEN go looking for a telescope if you are still keen about astronomy. Your binoculars are not a waste of money -- in fact you will continue to use them for marvellous wide-field views of the sky, for looking at any bright comets, and for taking on holidays, to the beach, to the cricket....
My first purchase was 7x50 binoculars in 1972 and I was still using them frequently until I dropped them onto concrete in late 2000... I might mention that these binoculars were among the first instruments on Earth to detect Comet SOHO (C/1998 J1). For further details, read my reports in the International Comet Quarterly.
If you lose interest in astronomy at this stage, note that binoculars are easier to sell than a telescope. However I'm going to assume that you stayed interested and still want a telescope. The "delay" doesn't really matter. In the long term, the true purchase price for any good telescope model will fall. Or if it stays fixed, then next year's telescope will have more features or better accessories than this year's. Rather like computers....
So your next question is "how much money can I spend?" Be realistic; a fabulous telescope will be no fun if you go deeply into debt.
In general; refractors become very expensive above 100mm aperture, while reflectors are considerably cheaper. This is why bigger telescopes are usually all reflectors. And you guessed it, the bigger the aperture, the bigger the price - and the relationship is very non-linear!
In Australia, expect to spend at least $300 on a telescope, even if you build it yourself. Any telescope retailing for under $300 is junk, and a lot of $300-$500 telescopes are also junk. As I said earlier, if your dollars are limited, get binoculars. $300 is unlikely to get you a decent telescope; but it will almost certainly buy you a good pair of binoculars and a useful star atlas.
Australian retail prices can fluctuate rapidly according to the value of the Aussie dollar, the manufacturing cost of the telescope, and the greed of the manufacturer, distributor and retailer. The prices in overseas magazines may look good; but don't forget the freight costs, Australian import duty and GST, and the problems you may have with your warranty.
Australian price ranges (GST inclusive) for typical
models in late 2001 were:
|Instrument type||Retail prices|
|7x50 to 12x50 binoculars||130 to 700+ (for really good ones)|
Add 80 to 200 extra for a good tripod and binocular adaptor.
|Finder scopes or spotting scopes||150 to 900|
Add 60 to 180 extra for a good tripod.
|60mm alt-azimuth refractors.|
Beware -- most of these are Department Store Telescopes!
|180 to 550|
|110mm alt-azimuth reflectors.|
Many manufacturers offer this size. Some are Department Store Telescopes.
|400 to 950|
|150mm alt-azimuth reflectors.||600 to 1000|
|200mm alt-azimuth reflectors.||900 to 1700|
|250mm alt-azimuth reflectors.||1250 to 2200|
A telescope on an equatorial mounting will cost $100 to $1000 more. And for go-to computer control, add lots more money. Even a small go-to telescope will cost you at least $800.
Many of the cheaper go-to telescopes don't understand Australian time zones (that stupid +9h30m in SA and NT is particularly problematic); although this can be worked around...usually by lying about your longitude or your local time. But some cheap go-to controllers don't even know there's a southern hemisphere - so the telescope runs as though it is on the equator.
You can expect one or two eyepieces to be included in the price of a telescope -- but not necessarily the best ones. Some manufacturers may offer more (or better) eyepieces and accessories; have better after-sales service, include "free" starcharts, etc. And just like cars, you can get expensive "prestige" telescopes which are as much for show as for use!
If you choose to save money by building your own scope, then you can start anywhere from some slabs of glass plus grinding grit, right up to finished mirrors plus fittings that you assemble. The cost of finished mirrors has fallen substantially in recent years, so if you don't feel confident of making your own then buy them.
Good books on telescope making include Howard's Standard Handbook for Telescope Making, Jean Texereau's classic How to Make a Telescope (translated from "La construction du telescope d'amateur") and Richard Berry's Build your own telescope. The two latter titles are available from Willmann-Bell.
If you are buying a scope from a magazine advertisement, read the fine print! A common trick is to show a picture of the fully-featured model, and print the price for the no-features model. This is not illegal, because if you look carefully you may see a tiny note such as " Shown with optional High-Z Quasar Locator and optional Ultra GigaStar9000 Controller." But seriously -- be careful.
Another problem is that many overseas companies offer no warranty protection to "foreign buyers". Some dealers take advantage of this fact to sell off their inferior stock. It has happened before and your Consumer Affairs office are powerless to stop it happening again (they have no jurisdiction outside Australia). Again, carefully read the fine print.
Avoid having lots of clever gadgets, because the best telescope is one that is uncomplicated and easy for you to use. As a beginner you will have enough to do without wondering which of 237 controls to use next. Fortunately some manufacturers are now selling computer-controlled telescopes which can be used by beginners; but they come with a big price tag.
A 100 to 200mm aperture telescope is a good starting size for several reasons:
Things you will NEVER see through your Earth-bound telescope include:
If you do buy a computer-controlled telescope -- or even one with a simple tracking motor -- make sure that it works correctly for the Southern Hemisphere.
Our sky spins clockwise -- the opposite direction to the Northern Hemisphere. And no, you can't fix it simply by reversing the battery connections; doing this is likely to destroy the electronics and your warranty! You need a reversing switch (a.k.a. hemisphere switch or N-S switch), or a permanently rewired motor.
On a related issue, if you live in SA or NT check that your computer controller (or astronomical software) accepts Australian Central Standard Time. Some products just can't understand that stupid half hour...!
Another problem with the cheaper equatorial telescopes: the supplied RA setting circle index scale (from 0h to "24h") is usually "backwards" for Southern Hemisphere users, as shown in this diagram. You can make your own index by attaching a strip of paper, with the correct labels, over the existing index scale. Better equatorials will have two index scales -- and instructions on which one to use in each hemisphere.
Your telescope may come with various gadgets and accessories but one accessory to avoid is the so-called "Sun Filter" designed to be screwed into an eyepiece for viewing the Sun directly. Eyepiece sun filters are extremely dangerous to use and have been banned from sale in Australia. If you still have one, destroy it. With a big hammer.
Why? Because a telescope collects far more sunlight -- and heat -- than your eye; and will cause enormous thermal stresses in an eyepiece filter. Furthermore, your eyeball contains no pain nerves; which means that you cannot rely on your pain-avoiding reflexes to save you if the eyepiece filter fails. Therefore if the eyepiece filter cracks while you're looking at the Sun, you WILL get permanent and irreparable eye damage. 7x50 binoculars can be used to burn holes in wood. A 100mm telescope can melt holes in aluminium!
There are only two safe ways to telescopically view the Sun.
Cheap substitutes such as dark or coloured or sooty glass, overexposed photographic film, Polaroid plastic, "crossed" Polaroids, oxyacetylene welding goggles, conventional sunglasses, wine cooler bags, ordinary aluminised plastic sheets, aluminised food wrappers, Compact Discs (CD/DVD), black plastic sheets, or conveniently-placed clouds ARE NOT SAFE! These products may block a lot of visible light BUT they STILL allow dangerous amounts of UV or infrared to reach your eye.
Several manufacturers sell eclipse sunglasses. Their lenses are made from a high-quality aluminised plastic and are capable of protecting your eyes during direct naked-eye viewing of the Sun. They are NOT designed to protect your eyes if you look through unfiltered binoculars or telescopes. The intense heat coming from the eyepiece may destroy them.
Knowing your sky will make it MUCH easier to find things with your telescope (and to impress people with your knowledge). Even if you have a "fully computer-controlled" telescope, you will be able to initialize it much quicker. And you will be prepared for the inevitable night when your telescope's batteries go flat.
The all-sky charts in the astronomy magazines will help you begin. Sky & Space, Sky & Telescope and Astronomy have charts each month; and you should soon learn where the principal constellations and brighter stars are. These magazines also describe the current locations of the planets.
There is no need to learn every star or all 88 constellations.
I never bothered -- that's why I have star atlases -- and, frankly, most
official depictions of constellations can't be deciphered without the
help of alcohol ;-)
When you become experienced with your sky, the Sky Atlas 2000 or Uranometria 2000 are good atlases for finding fainter objects. Sky Atlas shows everything visible to 7x50 binoculars (~43000 objects), Uranometria goes even fainter. And for even greater detail in printed star maps, try the Herald-Bobroff AstroAtlas or Sky Publishing's Millennium Star Atlas. Both of these depict over one million objects.
Many astronomy programs are available as freeware or shareware from Australian mirrors of popular archives such as SimTel. Look in the "astronomy" sub-directories under your operating system's directory.
Again, if you live in SA or NT check that your chosen astronomical software accepts Australian Central Standard Time. One good planetarium program for beginners is KlassM Software's SkyGlobe 3.6, which runs on any DOS or Windows system capable of displaying graphics. It also runs in the Linux DOS emulators, and I'm told it also works in the MacOS DOS/Windows emulators. You can download a copy here. (350kB)
More advanced programs generally run from a CD-ROM, and many can interface with professional-level data sources. Guide, for example, comes in DOS and Windows 3.x/95 versions and all can display over 20 million objects from the databases on the CD-ROM. All Guides can also use data from the RealSky CD-ROMs, the Digitized Sky Survey, and the 520 million objects in the USNO A1.0 or A2.0 Catalogues. The asteroid and comet databases can also be updated from online sources such as the Central Bureau for Astronomical Telegrams. And it can be used to control some telescopes.
If you live in the Southern Hemisphere and you're about to buy a book that doesn't discuss the Southern Cross (a.k.a. Crux), Carina, or how to find south -- put it down and keep looking. One of the classic beginner's books for Southern Hemisphere readers is The Southern Sky by Reidy and Wallace. Norton's Star Atlas and Reference Handbook -- the latest edition is called Norton's 2000.0 -- also contains much useful information for observers everywhere. And (fortunately) there are now an increasing number of observing guides which cover both hemispheres.
There is a difference between "books about astronomy" and "observing guides". The books will tell you a lot about What Is Out There and How Things Were Discovered; but the observing guides actually tell you where to find specific things and what you can expect to see in your instrument. Note, however, that most observing guides are designed to be used in conjunction with a good star atlas. The classic observer's guide for the Southern Hemisphere is Hartung's Astronomical Objects for Southern Telescopes (recently updated by Malin and Frew). The 3-volume Burnham's Celestial Handbook is another classic, covering both hemispheres; but its coverage of very southern objects is patchy. Harrington's Touring the Universe through Binoculars is an ideal guide for binocular users.
Astronomers have been compiling catalogues for centuries. Among the most famous is the Messier Catalogue, prepared by the French comet-hunter Charles Messier (and friends) in the 18th century, all using small telescopes in Europe. This catalogue -- the first list of what are now called "deep-sky objects" -- was originally intended as an aid to comet-hunters. Many comets look like fuzzy blobs in a small telescope. Many star clusters, nebulae and galaxies also look like fuzzy blobs; so comet-hunters (then and now) have to know which is which.
The Messier Catalogue is listed in many books but it ignores much of the southern sky. Hardly surprising because the compilers couldn't see that far south! The Bennett Catalogue -- also compiled by a comet-hunter (in the 20th century) -- is a Southern Hemisphere version; and the Caldwell Catalogue is a whole-sky version. All three catalogues contain many deep-sky objects suitable for small telescopes.
The Caldwell Catalogue originally appeared in an issue of Sky &Telescope, and Sky Publishing now offers both a printed and an online version. The Bennett Catalogue is available online from the Astronomical Society of South Africa's Deep-sky Observer's Companion. This excellent site also contains many descriptions of southern nebulae, galaxies, and clusters, as seen through a variety of telescopes. It also has a good online description of Southern Hemisphere Polar Alignment.
Some Australian astronomical society
And some dimwits think astronomy and space exploration are a waste of money....
URL for this page is http://www.fraserf.id.au/astronomy/scope.htm
Copyright © 1996-2005 Fraser Farrell. All rights reserved.
Some mornings it's just not worth gnawing through the straps.