A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Gelatin - A nearly transparent substance, obtained by boiling animal tissue in water, used as (1) the medium for suspending light-sensitive silver halide crystals on photographic film, and (2) in the manufacture of gelatin filters.

Gelatin filter - Also known as “gelatin slide” and “gel,” a thin sheet of translucent coloured gelatin for placing over lights to obtain lighting effects, and in the manufacture of photographic filters for lenses. Gels are available in a wide color variety.

Gels - Generic term used in reference to any colored translucent material (color media) that is used to colour a light, whether the material is made from gelatin, glass or plastic.

Ghost image - In time exposure photography, an object that is only partially recorded on the film and therefore has a translucent, ghost-like appearance. Ghosting also occurs when using electronic flash at a slow shutter speed, and a second image is captured on the film by ambient light. Some people also refer to “flare” as a ghost image.

Glossy paper - Shiny-surfaced paper used in making photographic prints.

GN - Abbreviation for Guide Number.

Gobo - A light-blocking device that falls under the general category of "Grip equipment." Generally used in a studio to prevent illumination from a studio light striking a portion of a scene. A "gobo" can be a simple piece of opaque cardboard or a sophisticated material in a specific shape, often a rectangle or square. "Barn doors" are gobos.

Golden mean - Also referred to as the “Golden section” and the “Gold mean,” the Golden mean is an ancient fine arts formula that mathematically defines a rectangle of specific proportions. This rectangle, called the “Golden rectangle,” is believed to frame objects in pleasing proportions. (See "Rule of Thirds" for more information.)

GOST - GOST is a standardization system developed by the All-Russian Scientific and Research Institute for Certification. Its coding system for film speeds, although similar to the ISO system, uses different numbers.

Gradation - (1) An image’s tonal contrast range. (2) The range of light and dark tones in a subject that a film is capable of showing (i.e. how a film reproduces contrast). (3) The gradual changing of one tint or shade to another by very small degrees.

Gradated filter - Also called a “Graduated” filter. A filter that is not uniformly dense, but that gradually changes its density across the filter’s field. A Gradated neutral density filter is clear from one edge to approximately the middle of the filter, then gradually increase in density towards the opposite edge. Colored gradated filters gradually change color density across the filter’s field.

Grade - A system of classifying the contrast of photographic papers used in making black and white prints, ranging from 0 to 5 (soft to hard).

Grain - Minute crystals of silver halides in the light-sensitive emulsion of film that react when exposed to light, turning black, are called “grains.” (See Graininess of film.)

Graininess - Graininess occurs when clumps of individual grains are large and irregularly spaced out in the negative. They are visible to the naked eye in the finished print, particularly enlargements, as sand-like particles. When this occurs, the picture appears “grainy.”

Granularity - Describes a negative or film that shows a granulated structure, usually used to describe the degree of granularity that is visible.

Grey card - Also known as the “Kodak neutral test card,” a grey card is an 8" X 10" (20 cm by 25.5 cm) card, about 1/8" thick, that is uniformly gray on one side. The gray side reflects precisely 18% of the white light that strikes it (corresponding to the calibration of a reflected-light meter). It is uniformly white on the other side, which reflects 90% of the light.

Ground glass screen - Flat sheet of glass in a camera treated so that it can be used for viewing and focusing an image, also known as the “Viewing screen.”

Graduated filter - A filter in which a clear and tinted half gradually blend into each other. A graduated filter can be used, for example, to enliven a dull sky in a landscape without affecting the rest of the image.

Grain - The granular texture appearing to some degree in all processed photographic materials. In black-and-white photographs the grains are minute particles of black metallic silver that constitute the dark areas of a photograph. In color photo­graphs the silver is removed chemically, but tiny blotches of dye retain the appear­ance of grain. The more sensitive - or faster-the film, the coarser the grain.

Guide number - A recommended number for a certain combination of head and reflector, by means of which the correct camera f-stop can be estimated. The given guide-number concerns the total energy of the generator in question, and a film speed of 100 ASA. Thus, the guide-number provides the correct f-stop if the source of light is placed one meter/foot from the subject, lighting it primarily from the front. If the light-source is further from the subject, the guide number is divided by the number of meters/feet, to arrive at the right f-stop. The following example will illustrate a situation using more complicated lighting with several flash-heads: In this case, the recommended guide-number is, say, 90. The flash-head lighting the subject is 2 meters away from it. The camera's f-stop should be 45. Another head, which is used as a background light, is not at all focused on the subject; however, it uses half of the flash-units energy, which means that the light on the subject is reduced by half. To compensate for this, the camera diaphragm is raised one f-stop to 32. Because we want a softer light, we set up an umbrella, which reduces the light again by half. We raise the diaphragm one more f-stop to 22, but we are using a film that is 200 ASA, so we have to lower the f-stop to 32. In summary: First, estimate the correct f-stop with the help of the guide-number, and add or subtract f-stops for each change you make.