A twin-lens reflex camera, often referred to as TLR (Twin-Lens Reflex), has two lenses with identical focal length arranged one above the other. The upper lens serves the viewfinder system, while the lower lens is responsible for the actual exposure of the film. The photographer typically looks down onto a focusing screen in a waist-level finder.
These cameras were particularly widespread in medium format (e.g., the legendary Rolleiflex models). A major advantage of this system is vibration-free release, as no mirror needs to be flipped up at the moment of exposure. Additionally, the viewfinder image remains visible at all times, even during release.