On the view camera, this ground glass is placed where the film will ultimately go, and is replaced by a sheet of film once focus is correct. Twin lens reflex cameras use two lenses that are mechanically linked, one for focusing and the other to take the photograph. Single lens reflex cameras, meanwhile, use the same objective lens for both purposes, with a mirror to direct the light to either the focusing screen or the film.
On a view camera, this ground glass is positioned where the film will ultimately be placed, and it's replaced by a sheet of film once focus is achieved. Twin lens reflex cameras employ two lenses that are mechanically linked, one for focusing and the other to capture the image. Single lens reflex cameras utilize the same objective lens for both purposes, with a mirror directing light either to the focusing screen or the film.