Friday, July 4, 2008

High Magnification: Forget it!

One of the things that lots of people worry about when buying a telescope is how high of magnification it will provide. Don't do this!

The magnifications you want are from 50x to 150x (50 power to 150 powers.) That's all. A beginner will do 90% of their observing at around 50x, and the other 10% at 150x or less. And they'll see a lot. As an experienced observer, I still spend nearly all my observing time in this magnification range.

High Magnification is Bad

High magnification is bad for a lot of reasons. I only use it when it's necessary, then switch back to low magnification as soon as I can. Here are some reasons why magnifications over 200x are bad:
  1. It's harder to get what you want to see in the telescope.
  2. Things in the telescope leave its field of view easier.
  3. It's a lot harder to get a good focus.
  4. Any stray light problems get worse (glare, nearby lights, etc.)
  5. Any instability in the telescope gets magnified, too!
For most beginner scopes, you're going to want two eyepieces. One should give you a magnification of about 40-60x, the other should give a magnification of about 100-150x. My two favorite eyepieces give magnifications of about 50x and 120x with my two main telescopes. (Magnification is determined by both the telescope and the eyepiece--more later.)

For most scopes, this means you'll want eyepieces of about 25mm focal length, and about 15mm focal length. A 25mm eyepiece with a 2x Barlow lens can work well, too (a 2x Barlow lens doubles the magnification of the eyepiece.)