A reflex finder is a
viewfinder
In photography, a viewfinder is a device on a camera that a photographer uses to determine exactly where the camera is pointed, and approximately how much of that view will be photographed. A viewfinder can be mechanical (indicating only direct ...
system with a mirror placed behind a
lens
A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements'') ...
. The light passing through the lens is reflected by the mirror to a
focusing screen
A focusing screen is a flat translucent material, either a ground glass or Fresnel lens, found in a system camera that allows the user of the camera to preview the framed image in a viewfinder. Often, focusing screens are available in variants wi ...
, usually
ground glass
Ground glass is glass whose surface has been ground to produce a flat but rough ( matte) finish, in which the glass is in small sharp fragments.
Ground glass surfaces have many applications, ranging from ornamentation on windows and table glass ...
. The image formed on this ground glass can be observed directly, giving a ''waist-level reflex finder,'' or through a redressing optical device (set of mirrors or prism) for eye-level viewing, giving an ''eye-level reflex finder''.
With a reflex finder, a photographer may focus the image on the ground glass and frame the picture at the same time. It is common to find a device on the center of the ground glass to help precise focusing, for example a
split-image or a
microprism device. Today's reflex cameras usually incorporate
autofocusing.
Reflex finders are found in:
*
Single-lens reflex
In photography, a single-lens reflex camera (SLR) is a type of camera that uses a mirror and prism system to allow photographers to view through the lens and see exactly what will be captured. SLRs became the dominant design for professional a ...
(SLR) cameras, with one lens for both viewing and taking the picture
*
Twin-lens reflex
A twin-lens reflex camera (TLR) is a type of camera with two objective lenses of the same focal length. One of the lenses is the photographic objective or "taking lens" (the lens that takes the picture), while the other is used for the viewfinde ...
(TLR) cameras, with one lens for viewing and one lens for taking the picture
*
Movie camera
A movie camera (also known as a film camera and cine-camera) is a type of photographic camera that rapidly takes a sequence of photographs, either onto film stock or an image sensor, in order to produce a moving image to display on a screen. In c ...
s
Cameras
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