Single lens reflex camera

A single lens reflex camera having a main mirror with a coating which is partly light-permeable in at least a portion thereof, the main mirror being pivotable into and out of an operative position where the light entering through an objective lens is reflected to a focusing screen, while the part of the light which passes through the main mirror is reflected out of the photo-taking light path by an auxiliary mirror positioned separately from the main mirror, and further having an automatic diaphragm actuator for stopping down a diaphragm device in the objective lens mounting. In this camera, the main mirror, the auxiliary mirror and the automatic diaphragm actuator are driven with only one common drive member responsive to actuation of a camera release for driving the main and auxiliary mirrors to flip out of the way of the light to the film and for driving the automatic diaphragm actuator to perform the stopping down operation of the diaphragm device.