Expert: Paul Wagner - 12/7/2006

Question
I am an expert in Yosemite National Park, but have a question about telescopes. When I was young, the power of microscopes was very easy to understand (e.g. 200x, 600x etc.) I am now interested in telescopes, and find it completely confusing. Who know what the binocular numbers mean, it might be something like 20x30. Then there are the number of inches for reflectors on reflector telescopes, and I do not know if something is overpriced or a bargain because I cannot compare their power. How can you compare these things? I just bought a small telescope which said 50x and 100x because it was something I could understand.

Answer
Hi Jon:

Given where you are, you should have a GREAT telescope.  I worked their as a guide 35 years ago...and never saw better stars in all my life!

With optics, two things really matter:  the magnifiying power, and the aperture.  But with telescopes, the ability to gather light is much more important that the magnification.  So the larger diameter the scope, the more you will see.

With binoculars, the first number is always the magnification, and the second is the aperture in mm.  So a 10x50 bincular will have a mangification of 10, and the lenses will have a diameter of about 2 inches.

With telescopes, one of the things you learn quickly is that magnification is not really hlepful at levels above about 50x the aperture in inches.  A three-inch scope might use 150X--but not more.  So those little telescopes that you can see in the department that offer a magnification of 600x, are not really much good.  Yes, the image is larger--but it is also so muddy that you can't see anything.  And some of the companies even stoop to listing the FOCAL length of the scope, rather than the aperture.  So they say that the scope has 600 power, and 1200mm focal length.  Big deal.  That scope has a lens of about 50 mm, and the most power you can use is not above 100X.  And you would be able to see twice as much stuff with a pair of 10x50 binoculars--if only because you can use both eyes!

With astronomical scopes, go for the largest aperture you can afford.  A few eyepieces will give you a good range of usable magnification--all you need. I have a 17 inch scope, and I still rarely use it at magnifications above 300x.  But it sure makes those dim things appear out of nowhere!

Orion Telescopes has a great informational section on their website.  Check it out before you buy any equipment!

Paul Wagner