What is a "dual-lens reflex camera"?

Double-lens viewfinder camera, referred to as "double-reverse camera".

This system consists of two sets of lenses with the same focal length. The upper lens usually cannot adjust the aperture and is only used for framing; The lower lens has an aperture shutter adjustment device for actual exposure. The double-opposition system is simple and durable, and has been widely accepted by journalists and the public. However, due to its inherent parallax and lens limitation, it has been rarely produced and used.

Characteristics of dual-lens reflex camera;

It is inconvenient to look down at the object in front of you in a waist-level way. Modern TLR cameras can overcome this shortcoming by adding an eye horizontal viewfinder accessory called Porro viewfinder.

Because of its inherent characteristics and large volume, the dual-lens system needs to replace both lenses at the same time. This is really a problem for the current large aperture fast lens.

The interchangeability of lenses is limited. If you change the photographic lens, you must also change the viewfinder lens. Today's TLR cameras usually provide interchangeable dual-lens devices.

The imaging is left and right opposite.

Because the viewfinder lens and the photographic lens are separated, TLR has the same parallax problem as the paraxial viewfinder camera (that is, what you see is what you get) The disadvantages of this problem will be more obvious when shooting close-up objects. Therefore, some modern TLR cameras have built-in parallax automatic compensation devices in their framing systems.

Compared with optical viewfinder or rangefinder, the image on ground glass is not very bright.