How to Size Binoculars

Decide how you will be using the camera, and how portable you need it to be. Full-size binoculars generally outperform compact binoculars, but they are much heavier and larger in size. It's best to get a smaller size when necessary, sacrificing the quality of the image for usability.

Calculate how far away you will need to see. The magnification is given in the binocular's label, and is designated by the first number. For example, 8x40 means that a pair of binoculars has a magnification or power, of eight. According to Universe Today, "Binoculars with 12-15X magnifying power offer almost telescopic views," and binoculars of 7X or less is great for most applications, including astronomy, and offer the greatest amount of eye relief. Generally, the larger the magnification, the larger the size of the binoculars.

Select the lens diameter you need. The diameter of the lens is the second number in the binocular's label. For example, binoculars labeled 8x40 have diameter of the front lens is 40 mm. A larger lens diameter means that you will have better image quality, but will mean that camera is larger. Generally, a lens of over 70mm requires external support, such as a tripod. An aperture of up to 40mm is fine for most uses.