 In the single-lens reflex camera, the photographer sees the scene through the camera lens.This avoids the problem of parallax which occurs when the viewfinder or viewing lens is separated from the taking lens.Single-lens reflex cameras have been made in several formats including sheet film 5x7" and 4x5", roll film 220/120 taking 8,10, 12 or 16 photographs on a 120 roll and twice that number of a 220 film.