Reflex camera light detecting arrangement

In a camera of the reflex type which has an optical path including a mirror adapted to reflect light from a lens to a focusing screen to produce an image formed by the lens thereon, a system for viewing the image on the screen comprising a pentaprism having light entrance and exit surfaces with first and second reflecting surfaces therebetween on said optical path, said prism having a planar third surface not on said optical path extending between said reflecting surfaces, and an eyepiece lens on said optical path behind said exit surface, said eyepiece lens having elements defined by front and rear surfaces, the improvement comprising;

• means defining a partial light reflecting surface at one of said exit surface and an eyepiece element surface in said optical path, said partially reflecting surface angled from the perpendicular to said optical path to reflect an image of said focusing screen to said third surface on said prism, and light detecting means located adjacent the third surface at the position of the image reflected thereto by said partially reflecting surface.