The history of SLR camera and its working principle

The so-called rangefinder camera is a camera in which the viewfinder and the optical axis of the lens are independent. In 1925, the German Leitz Company improved the Barnac camera and produced a 135 rangefinder head-up viewfinder camera with Elma lens, called Leica I. Because the optical axis of the viewfinder is mostly on the upper body above the lens, the two optical axes are not conjugate, and the position of the object seen in the viewfinder is inconsistent with the position of the object taken by the lens, which causes parallax. This insurmountable congenital defect is the incentive and motivation for the further development of dual-lens reflex cameras and coaxial viewfinder cameras.

In 1929 (1938), the German Rollei Company produced the first 120 dual-lens reflex camera, called Rolleiflex. The upper part of the dual-lens reflex camera is the viewfinder lens (viewing through a 45° mirror), and the lower part is the photographic lens. Its two optical axes are almost parallel (parallax), and the two lenses zoom in sync, thereby indirectly realizing "what you see is what you shoot." Dual-lens reflex cameras and rangefinder viewfinder cameras also have parallax, and the parallax increases as the shooting distance decreases. Because the viewfinder lens and the photographic lens are not conjugate, it is still equivalent to a rangefinder camera. However, the dual-lens reflex camera is an improved version of a single-lens head-up rangefinder camera, because the viewfinder lens is equivalent to an indirect rangefinder viewfinder. The frosted glass of the waist-level viewfinder can see whether the manual focus is clear, which solves the manual focus. The problem. The design and application of the mirror laid the foundation for the birth of the single-lens reflex camera.

In 1935 (say in 1933) Germany's Yihege company developed the EXAKTA camera, which formed the prototype of a single-lens reflex camera, and in 1937 produced the world's first 135 single-lens reflex camera. In the same year, Sweden produced the first 135 single-lens reflex camera with a pentaprism, named the Hasselblad (Hasselblad) camera. The single-lens reflex camera is an improved version of the dual-lens camera, which truly achieves the "what you see is what you shoot" effect. The birth of the single-lens reflex camera is a milestone in the history of camera development.

Single-lens reflex cameras are classified by model, including 135 single-lens reflex cameras and 120 single-lens reflex cameras; classified by imaging carriers, there are film single-lens reflex cameras and digital single-lens reflex cameras. Both a digital back and a film back are called digital film universal single-lens reflex cameras. Such as Hasselblad H3D.

The working principle of a single-lens reflex camera. A single-lens reflex camera has both functions of photography and viewfinder. There is a mirror (with reflective coating on the surface) between the lens and the imaging carrier, which is usually in a descending state. The light (object image) from the lens can only be projected on the mirror first, and then refracted into the viewfinder by the mirror through the pentaprism, so that the photographer can view, compose, and adjust the focus. When the shutter is fully pressed, the mirror immediately rises (framing is interrupted), and then the shutter opens, and the light from the lens is directly projected onto the imaging carrier (film or sensor), and finally the exposure is completed. After that, the mirror automatically resets and returns to the down state.