Einäugige Spiegelreflexkamera

A single-lens reflex camera comprises a quick return mirror which can be positioned at an object observing position (or an inclined position) and a photographing position (or a horizontal position). A photoreceptor element is disposed in such a manner that a light receiving surface of the photoreceptor element faces a shutter, so that a light beam reflected by the shutter is led to the photoreceptor element. When the quick return mirror is retreated to the photographing position, the light beam is received by the photoreceptor element. When a change in the amount of received light by the photoreceptor element exceeds a predetermined range while the mirror is retreated to the photographing position before the shutter release operation, a warning is output.