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Ground glass is glass
Glass

Glass generally refers to a Hardness, brittle, transparency amorphous solid, such as that used for windows, many Glass Bottles, or eyewear, including, but not limited to, soda-lime glass, borosilicate glass, acrylic glass, sugar glass, Muscovite , or aluminium oxynitride....
 whose surface has been ground to produce a flat but rough (matte) finish. A sheet of ground glass is used for the manual focusing
Focus (optics)

In geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge ....
 of both still
Camera

A camera is a device that records images, either as a still photograph or as moving images known as videos or movies. The term comes from the camera obscura , an early mechanism of projecting images where an entire room functioned as a real-time imaging system; the modern camera evolved from the camera obscura....
 and motion picture cameras.

Some cameras have no separate viewfinder
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 more complex single-lens reflex camera lets the viewfinder use the main optical system....
, 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
Large format

Large format describes large photographic films, large cameras, view cameras and processes that use a film or digital sensor, generally 4 x 5 inches or larger....
 cameras (cameras which use film
Photographic film

Photographic film is a sheet of plastic coated with an emulsion containing light-sensitive silver halide salts with variable crystal sizes that determine the sensitivity, contrast and of the film....
 4×5 inches or larger).






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Ground glass is glass
Glass

Glass generally refers to a Hardness, brittle, transparency amorphous solid, such as that used for windows, many Glass Bottles, or eyewear, including, but not limited to, soda-lime glass, borosilicate glass, acrylic glass, sugar glass, Muscovite , or aluminium oxynitride....
 whose surface has been ground to produce a flat but rough (matte) finish. A sheet of ground glass is used for the manual focusing
Focus (optics)

In geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge ....
 of both still
Camera

A camera is a device that records images, either as a still photograph or as moving images known as videos or movies. The term comes from the camera obscura , an early mechanism of projecting images where an entire room functioned as a real-time imaging system; the modern camera evolved from the camera obscura....
 and motion picture cameras.

Some cameras have no separate viewfinder
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 more complex single-lens reflex camera lets the viewfinder use the main optical system....
, 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
Large format

Large format describes large photographic films, large cameras, view cameras and processes that use a film or digital sensor, generally 4 x 5 inches or larger....
 cameras (cameras which use film
Photographic film

Photographic film is a sheet of plastic coated with an emulsion containing light-sensitive silver halide salts with variable crystal sizes that determine the sensitivity, contrast and of the 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
Aperture

In optics, an aperture is a hole or an opening through which light is admitted. More specifically, the aperture of an optical system is the opening that determines the cone angle of a bundle of ray that come to a focus in the ....
. 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
Magnifying glass

A magnifying glass is a Lens #Types of lenses which is used to produce a magnification of an object. The lens is usually mounted in a frame with a handle ....
 (or loupe
Loupe

A loupe , is a type of magnification device used to see things one is looking at more closely. In this respect, they are simply a form of a modified microscope, allowing the user to be able to better apply the phenomenon of microscopy to his or her trade....
). 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
Reflex finder

A reflex finder is a viewfinder system with a mirror placed behind a lens . The light passing through the lens is reflected by the mirror to a ground glass....
 of an SLR
Single-lens reflex camera

The single-lens reflex camera uses an automatic moving mirror system which permits the photographer to see exactly what will be captured by the film or digital imaging system, as opposed to non-SLR cameras where the view through the viewfinder could be significantly different from what was captured on film....
 or TLR
Twin-lens reflex camera

A twin-lens reflex camera is a type of camera with two objective Photographic lens of the same focal length. One of the lenses is the photographic objective , while the other is used for the waist-level viewfinder system....
 camera.

In motion picture cameras, the ground glass is a small, usually removable piece of transparent glass that sits between the rotary disc shutter
Rotary disc shutter

A rotary disc shutter is a type of shutter. It is notably used in motion picture cameras.Rotary disc are semicircular mirrors which rotate in front of the film gate, and thus expose the film....
 and the viewfinder. The ground glass usually contains precise markings to show the camera operator the boundaries of the frame or the center crosshair
Crosshair

A crosshair or reticle is a shape superimposed on an image that is used for precise alignment of a device, most notably that of a scope rifle....
, 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
Aspect ratio (image)

The aspect ratio of an is its width divided by its height.Aspect ratios are mathematically expressed as x :y and x?y . The most common aspect ratios used today in the presentation of films in movie theaters are 1.85:1 and 2.39:1....
. 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.

See also

  • Focusing screen
    Focusing screen

    A focusing screen is a flat translucent material, usually ground glass, found in a system camera that allows the user of the camera to preview the framed image in a viewfinder....
  • Ground glass joint
    Ground glass joint

    Ground glass joints are used in laboratories to quickly and easily fit leak-tight apparatus together from commonly available parts. For example, a round bottom flask, Liebig condenser, and oil bubbler with ground glass joints may be rapidly fitted together to reflux a reaction mixture....
    s


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