The so-called "single lens" refers to the common lens of the photographic exposure light path and the view path, and there is no independent lens in the view light path like the side axis camera or the double reverse camera "Reflection" refers to a plane reflector in the camera to separate two light paths: when taking a scene, the reflector falls, and reflects the light of the lens to the pentaprism, and then to the view window; The reflector is lifted rapidly during shooting, and the light can be irradiated on the film or sensor CMOS or CCD.