Reflex finder

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A reflex finder is a viewfinder system employing a mirror placed behind a lens. The light passing through the lens is reflected upwards by the mirror, and focused onto a ground glass. The image formed on this ground glass can be observed directly, in a waist level finder; or it may be optically redirected (with a set of mirrors or a prism) for eye-level viewing, giving an eye level 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 device or a microprism. Today's reflex cameras usually incorporate autofocus; so the reflex image is no longer the primary method of focusing.

Reflex cameras may be classified as:

  • single lens reflex or SLR cameras, using the same lens for viewing and making the exposure
  • twin lens reflex or TLR cameras, with one lens for viewing and one lens for taking the picture