Magnification vs. Aperture
Jun 21 '00
Most people focus their attention on magnifying power when they consider purchasing a telescope. This is probably to be expected since the whole point in buying a telescope is to enlarge far away objects. Also, a telescope's magnifying power is usually the main characteristic described by the manufacturer. However, magnifying power is certainly not the single most important factor to consider.
Magnification
If you are looking at planets, the moon, or terrestrial objects, then you probably want all the magnifying power you can get. Unfortunately, celestial objects do not hold still and travel across the sky at the rate of about one degree of arc (1/360 of a circle) every four minutes. For example, the moon covers about 1/2 a degree of arc. This means that if you have the moon filling the vision in your scope, then within two minutes the moon will totally vanish from your field of vision. If you increase the magnification to see more detail on any particular part of the moon, then the area you are observing will vanish from sight proportionally faster. Consequently, unless you have a motorized tracking system attached to your scope, you are going to be continually pointing your scope.
Motorized tracking systems are great, but they will cost you hundreds of dollars just by themselves. The telescopes you see in stores and magazines for $200 or less will not have any good means for tracking objects across the sky. You will find yourself spending all your time adjusting how your scope is pointed and then waiting for the vibrations from touching it to fade away so you can see the object. By the time the scope has quit vibrating, it will be time to adjust the scope's position again. This is a major frustration to most first time telescope buyers and one of the main reasons telescopes end up gathering dust in a corner without ever getting used. Buying a scope with fine-adjustment (pointing) levers help, but don't solve the problem. With these telescopes, anytime you magnify an object over 100 power, you are essentially going to be spending all your time fine tuning where it is pointed and never spend any time actually observing anything.
Barlow Lenses
Also, be aware that the actual magnification power of discount store scopes is usually only 1/2 (or less) of what is stated on the box. These scopes typically include a Barlow lens which doubles (or sometimes triple) the size of the image. For example, I still own a 60mm by 700mm refractor scope (yeah, it's a piece of junk, but I knew that when I bought it). Its stated power is 234x, but its actual maximum magnifying power is 117x. The 2x Barlow lens that came with it (and which I certainly never bother using) will double the apparent size of any object viewed through it (thus giving the 234x claimed by the manufacturer), but will not bring out any greater detail. All using a Barlow lens does is to guarantee you will have to repoint the telescope twice as often. So... unless you are prepared to spend a $1,000 or more for a telescope, any power much over 100x is going to be useless.
Aperture
We talked about viewing the moon and planets, but how about the really neat stuff, i.e., galaxies and nebulae? This brings us to our other major issue: aperture. Aperture (read diameter), or light gathering ability of your telescope is much more important than magnification when viewing faint objects like nebulae and galaxies. Actually these objects usually don't require any more magnifying power than a pair of binoculars, but what they do require is the capability to take in lots of light. The larger the telescope's diameter is, the greater its light gathering ability. Since most telescopes of over 2 inches diameter designed for amateurs are of the mirror type (reflector telescopes), a reflector telescope is definitely the way to go if you want to look at more than just the moon, planets, or terrestrial objects. A four inch diameter reflector type is about the smallest you will find and typically will cost you probably $400-500. However, an 8" one is much better, while a 12" starts getting you into the "light bucket" range. The point here is that what you want to look for is not magnifying ability, but light gathering ability which is based primarily on the telescope's diameter.
Keep in mind that the color pictures you may have seen from the Hubble space telescope are just that: pictures from the Hubble space telescope. No backyard telescope is going to come remotely close to giving you those types of images. However, if you have an automated tracking system and a good 35mm camera (along with the telescope mounting attachment for it), you can get some really good images that you will enjoy for a lifetime. To see the kind of pictures you can take, both Sky and Telescope and Astronomy magazines regularly publishes such pictures sent in by readers. The implication here, of course, is that seeing details in such faint objects tend to require time exposure photography. All the human eye will tend to see is faint fuzzy objects. This is not to say that viewing such objects with the human eye is dull. Quite to the contrary, my favorite viewing object is the Andromeda galaxy at 2 million light-years distance. In the 60mm scope I mentioned above, it barely shows up as a fuzzy patch of light, but it still thrills me to know I am observing another galaxy beyond our own Milky Way galaxy.
Conclusion
In conclusion, a good scope is going to cost you at least $500, and that is without a motorized tracking system. Unless you buy a telescope with a motorized tracking system, any magnification much over 100x (and that's without a Barlow lens) is going to be a waste of time. Consequently, don't concern yourself with high-power magnification, but concentrate on aperture (and tracking systems if you want a really good scope) if you want to look for faint objects like nebulae and galaxies.
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Epinions.com ID:
rdmonroe
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Member: Rick Monroe
Location: Indiana
Reviews written: 6
Trusted by: 2 members
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