What is an exit pupil and a relative brightness ?
Exit pupil is the bright circle that is visible when the ocular lens is viewed at a distance of about 25pi10inchj with the objective lens facing towards a bright background or light source. The larger the exit pupil, the brighter the image will be under low-light conditions. Exit pupil = Objective lens diameter Magnification Relative brightness is a number used to compare the brightness of binoculars or spotting scopes of similar magnification. The larger the relative brightness number, the brighter the image. Relative Brightness = Exit Pupil2 (or Exit Pupil size in mm, multiplied by itself).
