Binoculars

Binocular size: is expressed with two numbers. 7 X 50 is an example. The first number is the power; the second represents the diameter, or aperture of the front lens in millimeters.

Exit Pupil: This is the diameter of the light beam that meets the eye. It can be calculated by dividing the aperture by the power. 7 X 50 binoculars have an exit pupil of 7mm, matching the eye of most young people. As we age, the pupil doesn't open as wide so 10 X 50's would be more practical.

Eye Relief: This is the distance from the eyepiece to the image. If you wear glasses for astigmatism you will need more eye relief for viewing with glasses on.

Reflectors - Refractors - Binoculars - Schmidt Cas- Mountings - Eyepieces - Filters - Goto Telescopes
	Binoculars Perhaps the best way to begin with the hobby of astronomy is with a good pair of binoculars. They offer a wide field of view, usually of around 5 degrees, compared with the small field of around on-half of a degree, the apparent size of the moon, for most telescopes. The image appears erect and matches what we see on a star chart. And of course we can use binoculars for other activities such as nature watching or sports. Binoculars used for astronomy purposes must have several features not needed for daytime use, however. Since light gathering is most important, astronomy binoculars need to be large. An aperture, the diameter of the front lens, of 50mm or more is necessary to show bright images. Higher power will magnify an unsteady hand, so power above 10 will need a tripod for steady viewing. Binoculars larger than 50 mm become heavy and hard to hold steady as well. As with all optics, larger sizes mean greater cost, and cost is also related directly to quality in many cases. 7 X 50 binoculars cost around $100 for a good pair. 10 X 50's are pretty ideal in many ways, but expect to pay over $200 for quality necessary for astronomy. The best way to purchase binoculars is to try them out first. Make sure you are able to return them if you are not satisfied. When looking through binoculars at distant points of light, such as stars, it is extremely Important that the points of light converge into one image. If distant star images do not come easily to focus for you eyes, return the binoculars.	Binocular size: is expressed with two numbers. 7 X 50 is an example. The first number is the power; the second represents the diameter, or aperture of the front lens in millimeters. Exit Pupil: This is the diameter of the light beam that meets the eye. It can be calculated by dividing the aperture by the power. 7 X 50 binoculars have an exit pupil of 7mm, matching the eye of most young people. As we age, the pupil doesn't open as wide so 10 X 50's would be more practical. Eye Relief: This is the distance from the eyepiece to the image. If you wear glasses for astigmatism you will need more eye relief for viewing with glasses on.