Light-measuring systems for single lens reflex cameras

Claim 1

In a single lens reflex camera, objective means forming one of a plurality of objective means respectively having different focal lengths and adapted to be used interchangeably, said objective means having an optical axis along which light travels through said objective means into the camera, main mirror means situated behind said objective means and viewfinder means situated above said main mirror means, said main mirror means reflecting light which has traveled through said objective means to said viewfinder means, and said main mirror means having a semitransparent portion through which part of the light which has traveled through said objective means passes, auxiliary mirror means situated behind said semitransparent portion of said main mirror means for receiving the part of the light which passes through said semitransparent portion of said main mirror means, said auxiliary mirror means reflecting the light received thereby along a predetermined path, and photosensitive means situated along said path for receiving the light reflected by said auxiliary mirror means and for participating in the measurement thereof, said main mirror means having at said semitransparent portion thereof a front surface from which light is reflected to said viewfinder means and an opposed rear surface beyond which light travels to said auxiliary mirror means and said auxiliary mirror means having a reflecting surface which directs the light along said predetermined path to said photosensitive means, said rear surface of said main mirror means and said reflecting surface of said auxiliary mirror means forming a pair of surfaces one of which has the property of diffusing light, so that said photosensitive means receives diffused light, reflected from said auxiliary mirror means, for reducing the difference in the operation of said photosensitive means with respect to a plurality of objective means of different focal lengths.