Reflex camera is a type of camera that uses a movable mirror placed between the lens and the film to project the image seen through the lens to a matte-focusing screen. It uses a roof pentaprism or pentamirror to observe the image via an eyepiece, but there are also other finder arrangements, such as the waist-level finder or porro prism. Any camera using a mirror between the lens and a focussing screen. Allows the image to be seen and composed right way up.