Light measuring arrangement for a single lens reflex camera

摘要

In a finder optic system having the structure in which a tiltable mirror, in its reflecting position, reflects light entering through the camera objective upward onto a focusing screen where an image of the object to be photographed is formed and light from the image is radiated upward through the condenser lens and a pentaprism into an eyepiece, a light meter arrangement in accordance with an embodiment of the invention comprises a single photo-cell and a glass plate provided with an angular surface formed therein for acceptance of the photo-cell. The glass plate is cemented at one of the surfaces parallel to the exit surface of the pentaprism in front of the eyepiece and is oriented so that the angular surface is rearwardly inclined with respect to the axis of the finder optic, whereby a light beam from one of two different portions outside the central portion of the image is directed through the pentaprism with regular reflections therein to the angular surface to reach the photo-cell and a light beam from the other is directed through the pentaprism without any regular reflection to the angular surface to reach the same photo-cell. The arrangement permits the photo-cell to produce a light value which is, in effect, substantially equal to that sensed by a photo-cell positioned to receive a light beam from the central portion of the image.