How to Stargaze with Binoculars by Aurora with Central Coast Astronomy and Supercharged Science

Stargazing: centralcoastastronomy.org/stargaze

How to Use Binoculars for Stargazing

How can you tell if your pair of binoculars are good for stargazing? And what's the difference between a $50 pair and a $500 pair that are the same size and magnification?  Does it really matter?

The more expensive pair will have clearer, crisper images. Around the edge of the view will continue to be clear without any distortion, but this isn't as important for stargazing as it is for day use. A little out of focus is okay. If the edge is way out of focus, try a different brand.

Stargazing binoculars generally are between a magnification of 7x to 10x. The objective lenses (the larger lenses) are usually between 35mm to 60mm, although I don't recommend anything larger than 50mm because it gets hard to hold steady the longer you look through them. I wouldn't go any smaller than 7x35 for stargazing. 7x50 or 10x50 are a perfect size for astronomy.

For older stargazers, exit pupil size matters. This is the size of the bright disk of light you see in the eyepiece when you hold up the binoculars. A 7x50 pair of binoculars will have an exit pupil of 50/7 = 7mm.  If this number is larger than the size of your pupil (when adapted to the dark), that will be light that doesn't enter your eye. If that's you, then look for binoculars with an exit pupil of 5-6mm.  You can easily (and carefully!) have someone  measure the size of your pupils using a ruler.

In general, you don't use eyeglasses when you look through the binoculars. The binoculars can adapt to your eyes, unless you have an astigmatism. Try looking both with glasses on and off to see if you need to keep them on when stargazing. If you find you do need to wear eyeglasses  when using binoculars, then look for a pair that has at least 15mm of eye relief (most binoculars will have this already).

When you pick up a pair of binoculars, look at the light reflected in the objective lenses. They should be mostly dark, if they are white or red, try a different brand. Now look through the lens at the prisms inside. If they have a good anti-reflection coating, you'll see a rainbow colored surface. If it's white, try a different brand. 

I've outlined the main points above, and then I thought it might be easier to show you a video how to test for everything you need to know to be sure your pair is good for the night sky (and chances are, they are!)