Guide to Binoculars in Astronomy

Binoculars provide a excellent way to view the night sky and allows you to see larger areas of sky at a time than a telescope will allow. Binoculars also have the advantage of utilizing both eyes; These increases the contrast by about 40% and eliminates the phenomena of "floaters" that more mature observers, like myself, sometimes suffer from.

Binoculars by the Numbers

Binocular are designated by 2 numbers, such as 7x35 or 10x50. The first number is the "magnification" or "power". the second number is the "aperture" of the main lens. A pair of binoculars designated as "7x35" would be 7 power and have the aperture of 35mm and a pair designated as "10x50" would be 10 power and have an aperture of 50mm.

Sometimes you will see a binocular designated with 3 numbers such as 8-12x30. Three numbers are a designation for zoom binoculars. For example, "8-12x30" would have 8 to 12 power with the aperture of 30mm. Because zoom binoculars are more complex optically they typically do not have the same clarity as single magnification binoculars.

Power

Having lots of power is not always a good thing. Consider these facts:

• The human body is a collection of moving parts; we breath, our heart beats, our muscles twitch and shake. It is difficult to hold a steady view with hand-held optics over 10 power. Some people can handle 12 power binoculars, usually 10 power is the limit and most binoculars are manufactured under 12 power. High magnifications will require some sort of stabilizing by using a tripod or monopod, or else by using binoculars which are "image stabilized" electronically.
• The higher the power, the dimmer the view. The more we magnify a view, the dimmer the view will get because the light is being spread out in all directions. The brightness changes in squares, so that is we cut the magnification in half we will increase the brightness by four. While this phenomena is not as apparent during the day because there is so much light, at nighttime this will be significant.
• All other things being equal the higher the power the wider the view. at lower power objects will appear smaller and so more information can get into the view.
• The only time power is really useful in astronomy is viewing the moon and planets. For dimmer targets like comets, star clusters, nebulae and galaxies - lower power is usually better.

Aperture

For astronomy, aperture is more important than magnification. The more aperture the more light can be pulled by the optical system, and all that light is brought to focus to the same point - Your eye. Because the light is gather on the whole surface of the lens, the light gathering power of the optics, known as "lightgrasp" is a function of the area of the circle and it goes up in squares as the aperture increases. If we double the diameter of the aperture we will increase the light gathering power by four.

For example, A 50mm binocular has the lightgrasp of 51, that is it is 51 times brighter than the naked eye. The lightgrasp of a 100mm binocular will be 204!

Any size binocular will provide a better view than can be seen with the naked eye, but typically is recogmended to get at least 50mm of aperture.

Image Stabilization

Even if you have magnifications under 12 power, you will probably want to stabilize the binoculars since holding the binoculars still and pointed skyward for a length of time can be fatiguing.

Giant Binoculars with apertures over 70mm, typically have a mounting post attached to the hinge of the binoculars with a 0.25" by 20 thread. This threead is the standard mounting thread used by the camera industry and will allow the binoculars to be mounted on a photo tripod.

Most standard size binocular have a 0.25" by 20 thread at the outside end of the binocular hinge. This is usually under a cap the screws off. You can buy an "L" bracket that attaches to the binocular at this point and then can be attached to a photo tripod by another .025" by 20 thread at the bottom of the bracket.

You can get binoculars that are electronically image stabilized. While these binoculars work great for astronomy, they can be a bit expensive.

With image stabilization you can use higher magnification tha 10x, see more detail and reduce fatigue.

Recommendations for Binoculars for Astronomy

• Get at least 50mm of aperture. While any binocular is better than none, 50mm and higher will greatly improve your views.
• Even if your binoculars are 10 power or less you will probably want to tripod mount it. Check to see if your binocular have a mounting thread in the hinge area of the binocular.
• Check the binoculars for flatness of field and color fringing near the edge of the field of view. All binoculars will have a little of this, but binos with poor optics will have noticably more.

...and now a word from our sponsors...

SUPER DEALS at Telescopes.net

Celestron SkyMaster Giant Binoculars

Canon Image Stabilized Binocular

Meade Astronomy Binoculars

Celestron Sky Map Planisphere

Meade LightBridge Dobsonian Telescopes

Celestron Starhopper Dobsonian Telescopes

Binoculars at Telescopes.net