A reflex finder is a
viewfinder
In photography, a viewfinder is what the photographer looks through to compose, and, in many cases, to focus the picture. Most viewfinders are separate, and suffer parallax, while the single-lens reflex camera lets the viewfinder use the main ...
system with a mirror placed behind a
lens
A lens is a transmissive optical device which 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 w ...
, 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 glassw ...
. 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, you can focus the image on the ground glass and frame your 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
An autofocus (or AF) optical system uses a sensor, a control system and a motor to focus on an automatically or manually selected point or area. An electronic rangefinder has a display instead of the motor; the adjustment of the optical system ...
.
Reflex finders are found in:
*
Single-lens reflex
A single-lens reflex camera (SLR) is a camera that typically uses a mirror and prism system (hence "reflex" from the mirror's reflection) that permits the photographer to view through the lens and see exactly what will be captured. With twin le ...
(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 viewfind ...
(TLR) cameras, with one lens for viewing and one lens for taking the picture
Cameras
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