BINOCULAR TOOLS / RELATIVE BRIGHTNESS Compare two brightness indexes, not two promises. Enter the magnification and objective size for two binocular configurations. Compare the traditional squared-exit-pupil indexes side by side, with the limits of that calculation kept visible. COMPARE TWO CONFIGURATIONS Enter the four specification numbers Read an 8×42 label as 8× magnification and a
BINOCULAR TOOLS / EXIT PUPIL Find the exit pupil behind the numbers. Enter the two numbers on a binocular specification, such as 8×42. The calculator divides objective diameter by magnification to give the theoretical exit pupil in millimeters. YOUR BINOCULAR SPECIFICATION Enter magnification and lens size For an 8×42 binocular, enter 8 for magnification and
Exit pupil is a geometric specification calculated by dividing objective diameter by magnification. The result tells you the diameter of the light beam leaving the eyepiece, but it does not measure every loss that occurs inside the optical system. Relative brightness carries the same geometry one step farther by squaring the exit pupil, so it
The second number in a binocular label such as 10×50 is the effective diameter of the objective lenses in millimeters. A larger objective can collect more light at the same magnification, but it also tends to increase the physical size and weight of the binocular. That number does not tell you how wide the scene
Magnification tells you how large or apparently close a distant subject looks through binoculars, but the larger number is not automatically the more useful view. Moving from 8x to 10x or 12x increases image scale while also changing how visible hand movement becomes and, in many designs, how much scene fits inside the view. At