So Just How Do I Choose a Telescope?

Thereís no question at all that the sky is a wonderful place Ė there is just so much to see. But unless you know where to look and have at least some understanding of what it is you are looking at, an aspiring astronomer can very quickly lose interest.  So our first important message is that it matters quite a bit just how you get your first experience of the sky.  Some peopleís first real look is just with their eyes or through binoculars, while others might be lucky enough to be able to look through a telescope.  Both experiences can capture (or lose you) as an astronomer forever, depending on a number of things which might seem irrelevant at the time, but which can seriously impact how you enjoy your "first time".  What you are looking at, what you are using to look at it with, and the knowledge level of the person who is helping you (if indeed you have anyone to help you) are all relevant, and contrary to what you might expect, there are some objects which actually look better through binoculars than through a telescope.  The most important thing is to try to share your first experience with someone who at least partly knows the sky, and who can point out things which otherwise you might miss.  From the first moment you glimpse that clear, crisp image of Saturnís rings, or see a close-up of the Moonís craters, or the majestic glow of the Great Orion Nebula, or the cloud bands on Jupiter, you will know whether or not you are destined to be an astronomer.

Astronomy appeals to different people for different reasons.  Some people enjoy "discovering" other worlds with their own eyes, and for others astronomy offers a relaxing escape from the day to day routine of "normal" life.  Itís also a great family activity, allowing parents and children to explore new frontiers together, to learn together.  If you are the sort of person who enjoys teaching others, then there is tremendous scope for this, while at the same time enjoying your hobby.  We are volunteer workers at the George Observatory in south west Houston, travelling there most Saturday nights and using our own telescopes and the telescopes at that facility to show families and visitors from all parts of the world the mysteries of the night sky.  One of the most rewarding parts of these evenings is to see the look of wonder in the eyes of young and old alike as they see for the first time the almost unreal images of Saturn and itís rings, or Jupiter and its moons, looking as if I have placed a colour slide in front of the telescope.  Fathers bring children, and usually end up more entranced than the siblings they have brought.  Mothers bring mothers and grandmothers, and we end up speaking French, Russian, German and lots of other languages.  All languages are the language of astronomy.  If you become really interested, consider joining an astronomy club.  There are amateur astronomy clubs all over the world, and most of them organize regular star parties where you can mix with other enthusiasts and learn from them.

If you live in the United States and are ever near to the Houston area, we would strongly recommend that you make a trip to the Brazos Bend State Park in south west Houston.  There you will find the George Observatory, and every weekend (Saturday nights are best) the Fort Bend Astronomy Club, of which we are members, puts on a star party for the public.  The facility has three large telescopes in domes, and numerous club members like us also turn up with their own telescopes to let the public look at the stars and planets and to answer questions on astronomy.  It's well worth a visit, and if you want more information on the George Observatory, click here.

So you've thought about it and have decided that you definitely want to buy a telescope.  Where do you start?

How To Choose the Right Telescope - Overview

Like choosing a house, a car or a wife/husband, buying a first telescope is a highly subjective decision.  There is no "best" telescope for everyone.  The one that's right for you will depend on your lifestyle, where you plan to use it, where you are able to store it, and also on what you wish to do with it in your astronomy.  Let's look at some of the most important considerations that might influence your choice of a scope.


Forget about "power." It's diameter that counts.
You will see many telescope advertisements which brag about the magnifying power. Ignore them! A telescope's most important feature is not its magnifying power, but rather its ability to gather light and to display the image in a sharp, easy to see manner.  Light gathering power is determined by the diameter (aperture) of the main lens or mirror.  The more light gathered, the better you will be able to see the objects when they are magnified.  Telescopes advertised on the basis of high magnification ("450x!") are virtually always of inferior quality.  In all telescopes, power is adjusted by changing eyepieces, lower powers providing brighter, sharper images.  So you can boost the power as high as you like on any telescope, but all this does is make the image larger.  If the optical system quality is poor - as it will be in a cheapo telescope - then you will have a poor quality, fuzzy image to start with, and magnifying it will only make it more and more fuzzy.  So remember, the sharpness and clarity of an image is usually most dependent on the quality of the optical system.  The worse the alignment and quality of the various lenses and mirrors, the worse the image will be.

How big a scope do you need?
Well, that depends on what you want to do.  For viewing craters on the Moon, the rings of Saturn, and Jupiter with its four bright moons, a 60mm (2.5 inch) or 70mm (3 inch) refractor or a 3 to 6 inch reflector will do the job.  A slightly larger instrument Ė perhaps an 80mm (3.5 inch) to 100mm (4 inch) refractor or 8 inch to 10 inch reflector will show more planetary and lunar detail as well as glowing nebulae and sparkling star clusters.  Going bigger still, under dark, non-light-polluted skies, a scope of 10 inches or more diameter can produce magnificent images of fainter clusters and nebulae, and start to show some detail in galaxies.

Have realistic expectations and do not be fooled by advertising photographs showing bright galaxies, as presumably seen through a 3 inch telescope.  With the exception of some nebulae and the brighter planets, most astronomical objects are very faint.  Generally, the larger the telescope, the brighter will be the images and the more detail you will see, but be warned that even in my 14 inch telescope, most galaxies show up as nothing more than faint, fuzzy objects.  But don't bite off more size than you can chew.  Donít forget that you must be able to comfortably lift and transport it, and you will also need adequate space to store it somewhere safe and dry.  Many people have chosen a large scope, only to find that they canít be bothered to haul it out to use, or that it doesnít fit in the car or truck, or their aching back prevents them from lifting and carrying it around, or that it is too complicated to put together.  So these scopes collect dust in a cupboard until the day that the owner decides to sell them.  The correct choice is very important, and a good pair of binoculars might well have been more useful in these cases.

On the other hand, be careful not to buy something small and portable, only to be disappointed by what you can see through it.  Like I said before in this section, have realistic expectations before you buy.

Refractor, Reflector, or Catadioptric?
People do not normally know that there are several different types of telescope:

Refractors

Reflectors

Catadioptrics

The choice of which type to buy will to some extent be dictated by the choice factors discussed above Ė size, weight, ease of handling etc.  The different types of telescope all do the same thing: they collect and focus light, it's the way they do it which differs.  A refractor does it with a multi-element glass lens, while a reflector uses a concave mirror. A Catadioptric, or compound, telescope uses a mixture of both mirrors and lenses.  The Schmidt-Cassegrain is an example of one type of Catadioptric scope.

Reflector telescopes are designed exclusively for astronomy.  They deliver more light-gathering power for the money than other telescope types.  They produce an upside-down image, which is fine for astronomy (since there's no "right way up" in space) but is unsuitable for bird watching or other terrestrial observing.

Refractors and Catadioptrics work well for both astronomical and terrestrial viewing.  Refractors provide good image quality but larger sizes start to get quite expensive compared to reflectors, because of the difficulty of making large diameter, high quality glass lenses.  Mirrors are much easier and cheaper to make in larger sizes.  But because of the way they work, reflectors can be rather long and bulky at larger mirror sizes, which makes them tough to carry around.  Schmidt-Cassegrain and other Catadioptric scopes were developed to get around this problem.  You can think of them as "folded" telescopes and they work very well, but they are usually more expensive.  As an example, my 14 inch Schmidt has a focal length of nearly 4 meters but it fits in the trunk (boot) of our Taurus sedan. It cost more than $2000.


What about a mount or tripod?
Most telescopes come supplied with a way to hold them steady and allow you to find objects in the sky.  The mount holds the telescope at an appropriate angle for you to look through, and the tripod holds the scope steady and brings the eyepiece up to eye level.  A point to watch for is that the tripods supplied with some of the "cheaper" telescopes can be quite unstable, allowing the telescope to shake and wobble about in the wind or if touched.  There are sturdy, inexpensive tripods around and you should check how stable is the one you are being offered before you buy.  You should also check how easily the telescope can be moved left and right and up and down.  If itís difficult in the store in the daylight, imagine what it would be like in the dark, perhaps in a field.

I said "up and down" in the previous paragraph.  The simplest type of mount to use, what is called the "altazimuth", does indeed provide for up-down (altitude), left-right (azimuth) motions.  It performs well for terrestrial or casual astronomical viewing.


The more complex equatorial mount is designed solely for astronomy.  It has the advantage of letting the user "track" the motion of celestial objects with a single manual control or an electronic drive.  Although you can fit an electronic drive unit to a simple altaz mount, the resultant "up and down only" tracking prevents any use for astrophotography (see the section on imaging).  Many equatorial mounts also allow objects to be located by their celestial latitude and longitude coordinates.

In Summary . . .
Choosing a telescope involves a trade-off between size and convenience.  Bigger-diameter scopes will always show you more, but smaller scopes are easier to handle.  The "best" telescope is the one you will use most often.

For a first telescope, I suggest you look at a basic refractor of around 90 to 100mm aperture, or a Newtonian reflector of perhaps 6" aperture, unless you're really sure of yourself.  After you've learned the basics of observing and have developed an appreciation for the hobby, you can then move up to a bigger, fancier scope.

 

Now that you've read this summary, and feel ready for some more detailed information, then click here and read on!

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