Planetary Telescope Eyepieces

Viewing the planets of our solar system with your telescope requires different considerations when choosing you eyepieces than deep sky work.

You will usually want to push the magnification as much as you can. But even on the nights of the best "seeing" (that is where the air is the steadiest) the highest magnification you will be able to use is 50X per inch of aperture. So, with my 200mm f10 reflector that would be: 200mm/25=8 inches, so 8 inches X 50 power per inch = 200 maximum. So what eyepiece would that be?

For that you need the focal length of the telescope. That is objective width (200mm with my reflector) time the focal ratio (f10 in this case). So 200mm X f10 = 2000mm focal length.

Now the magnification of a given eyepiece is the telescope focal length divided by the eyepiece focal length. Simple math says 2000mm divided by eyepiece fl = 200. So a 10mm eyepiece would do the trick.

However the atmosphere doesn't always co-operate so a few other fl eyepieces should be in your eyepiece case. Since I have various telescopes as well I have eyepieces that range from 3.5mm all the way up to 25mm which are used mostly for solar system viewing.

Find Some Planetary Telescope Eyepieces

You should look to pick up at least 2 eyepieces for work on the planets. You may also consider using a Barlow lens which will double your eyepieces if you pick wisely. I personally only use a Barlow for planetary photography with a webcam, but others like the idea.

More on Barlows