telescope calculator tool
Eyepieces have focal lengths too — 25mm or 10mm, for example . To find the magnification any combination of telescope and eyepiece yields, simply divide the focal length of the scope by that of the eyepiece. For instance, a 1,000-mm focal-length scope, used with a 25-mm eyepiece, delivers 1,000 / 25 = 40 power (or 40×). Switch to an eyepiece with a shorter focal length for higher magnifications: a 10-mm eyepiece used on the same scope delivers 1,000 / 25 = 100×. Notice that it’s only the telescope’s focal length that matters here — the size of its main mirror or lens does not affect the magnification. Our telescope calculator tool offers an easy way to make these calculations.