Ground glass

Ground glass

Ground glass is glass whose surface has been ground to produce a flat but rough (matte) finish. A sheet of ground glass is used for the manual focusing of both still and motion picture cameras.

Some cameras have no separate viewfinder, but instead use a piece of ground glass at the focal plane to focus the scene. This type of focusing and viewing system is typically used on so-called large format cameras (cameras which use film 4×5 inches or larger). In such a camera, before the picture is taken, the ground-glass viewer is inserted in the back of the camera, and the lens opened to its widest aperture. This projects the scene on the ground glass upside down and backwards. The photographer focuses and composes using this projected image, sometimes with the aid of a magnifying glass (or loupe). In order to see the image better, a dark cloth is used to block out light, whence came the image of the old-time photographer with his head stuck under a large black cloth.

A ground glass is also used in the reflex finder of an SLR or TLR camera.

In motion picture cameras, the ground glass is a small, usually removable piece of transparent glass that sits between the rotary disc shutter and the viewfinder. The ground glass usually contains precise markings to show the camera operator the boundaries of the frame or the center crosshair, or any other important information. Because the ground glass is positioned between the mirror shutter and the viewfinder, it does not interfere with the image reaching the film and is therefore not recorded over the final image, but rather serves as a reference for the camera operator.

Ground glasses commonly serve as a framing reference for a desired aspect ratio. Because most films shot with spherical lenses are shot full-frame and later masked during projection to a more widescreen aspect ratio, it is important not only for the operator to be able to see the boundaries of that aspect ratio, but also for the ground glass to be properly aligned in the camera so that the markings are an exact representation of the boundaries of the image recorded on film.

ee also

* Focusing screen
* Ground glass joints

External links

* [http://www.panavision.com/ground_glass.php/ Ground glasses available from Panavision]
* [http://www.xs4all.nl/~lommen9/focus/index.html Ground glas focusing with the Speed Graphic]


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Look at other dictionaries:

  • Ground glass — ground ground, imp. & p. p. of {Grind}. [1913 Webster] {ground cock}, a cock, the plug of which is ground into its seat, as distinguished from a compression cock. Knight.{Ground glass}, glass the transparency of which has been destroyed by having …   The Collaborative International Dictionary of English

  • ground glass — ► NOUN 1) glass with a smooth ground surface that makes it non transparent. 2) glass ground into an abrasive powder …   English terms dictionary

  • ground glass — n. 1. glass whose surface has been ground so that it diffuses light and is therefore not transparent 2. glass ground into fine particles …   English World dictionary

  • ground glass — ground′ glass′ n. 1) opt glass that has had its polished surface removed by fine grinding and that is used to diffuse light 2) glass that has been ground into fine particles, esp. for use as an abrasive …   From formal English to slang

  • ground glass — n [U] 1.) glass that has been made into a powder 2.) glass that has been rubbed on its surface so that you cannot see through it, but light passes through it used for example on a camera …   Dictionary of contemporary English

  • ground glass — noun uncount 1. ) glass that has been crushed into extremely small pieces 2. ) glass whose surface is rough so you cannot see through it …   Usage of the words and phrases in modern English

  • ground glass — noun 1. glass that diffuses light due to a rough surface produced by abrasion or etching (Freq. 1) • Hypernyms: ↑glass 2. particulate glass made by grinding and used as an abrasive • Hypernyms: ↑glass * * * noun 1. : glass whos …   Useful english dictionary

  • ground-glass — ˈ ̷ ̷| ̷ ̷ adjective Etymology: ground glass : relating to or characterized by ground glass: as a. : having a surface polished b. : having a surface ground or etched to a semitransparency c. : having a surface ground to fit …   Useful english dictionary

  • ground glass — matinis stiklas statusas T sritis chemija apibrėžtis Sklaidantis šviesą šiurkštaus paviršiaus stiklas. atitikmenys: angl. depolished glass; dimmer; etched glass; frosted glass; ground glass; matted glass; matte surface glass rus. матовое стекло …   Chemijos terminų aiškinamasis žodynas

  • ground glass — matinis stiklas statusas T sritis fizika atitikmenys: angl. clouded glass; frosted glass; ground glass vok. Mattglas, n rus. матированное стекло, n; матовое стекло, n pranc. verre dépoli, m; verre mat, m …   Fizikos terminų žodynas

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