What is “eye relief” (also called “Exit Pupil Distance”) rating on a pair of general purpose or astronomical binoculars?
Eye relief, also known as exit pupil distance, is the distance the pupil should be from the ocular (eyepiece) for optimum performance. Eye relief generally decreases as power increases. Low eye relief (less than 10mm) requires you to get very close to the eyepieces, while higher eye relief (greater than 15mm) allows more distance.
