The history of the single-lens reflex camera

Single-lens reflex camera

A single-lens reflex camera is a camera that typically uses a semi-automatic moving mirror system that permits the photographer to see exactly what will be captured by the film or digital imaging system, as opposed to pre-SLR cameras where the view through the viewfinder could be significantly...

predates the invention of photography in 1826/27 by one and a half centuries with the use of a reflex mirror in a camera obscura

Camera obscura

The camera obscura is an optical device that projects an image of its surroundings on a screen. It is used in drawing and for entertainment, and was one of the inventions that led to photography. The device consists of a box or room with a hole in one side...

 first described in 1676. Such SLR devices were popular as drawing aids throughout the 18th century, because an artist could trace over the ground glass image to produce a true-life realistic picture.

A British patent was granted in 1861 for the first internal mirror SLR photographic camera, but the first production photographic SLR did not appear until 1884 in America.

These primitive SLR cameras began to mature in the early 20th century, but their many disadvantages continued to make them unsatisfactory for general photographic use for decades.