Dual-mode light meter system for SLR camera using beam-splitting reflex mirror

摘要

A light meter for a SLR camera implements both initial exposure time display and automatic exposure time control using a single light sensing element 8. The reflex mirror 3is formed as a beam splitter or half-mirror. When lowered, some of the viewfinder light passes through the mirror and is reflected onto the sensing face of the element 8 by the shutter curtains 9 or 10 to enable the time display function. When the mirror is raised and the lens diaphragm 2 reduced, the light is again reflected from the curtains and/or film surface 11 onto the sensing element face to enable the time control function.