Minimal eye relief is a minimum distance between the eye and eye-piece lens (rear of the scope, some manufacturers call the eyepiece ocular). For safety reasons, due to the recoil of the rifle, minimum eye relief for rifle scopes has to be at least 80mm. Larger rifle calibers produce higher recoil, so it is advised to have a minimal eye relief of 90mm or even more. Due to safety reasons, new rifle scopes have longer eye relief than older. Longer eye-reliefs were achieved with an advance of optical technology. The eye relief slightly changes when changing magnification and usually the eye relief is bigger at small magnifications and smaller on big magnifications. The difference is usually 10 millimeters or less.
Because of safety reason, some rifle scopes for safari rifles have extended eye-relief of more than 120mm. Scout and pistol scopes more than 500mm eye-relief, since they are usually mounted far away from the user.
Safety should always be on 1. place when handling guns and shooters often ignore, so make sure that you don`t get a »black eye« injury and choose the scope with a minimal eye relief of at least 80mm.
Source: Revija Lovec