Reflex cameras — how do they work?

The idea of placing a movable mirror in the camera, allowing for the projection of the image from the lens onto the horizontally mounted focusing screen, was first attempted at the turn of the 1850s and 1860s. At the end of the 19th century, many companies began to manufacture cameras that used a mirror which allowed the tracking of the image on the focusing screen, and, after lifting it, to quickly record the image on the photosensitive material placed in the cassette at the back of the camera.
Many years later — in 1936 — a similar solution was used in the Exakta camera. Since then, single-lens reflex cameras (SLR) have become one of the most popular 135 film camera designs.

Elaborated by Marek Maszczak (Museum of Photography  in Kraków), © all rights reserved

See reflex camera from the collection of The Museum of Photography in Kraków:

Primar Reflex camera
Ernoflex — camera by Heinrich Ernemann A.G. Company