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Ghost images

Bright spots of light, often taking the shape of the aperture, which appear in the camera viewfinder or in the final photograph when a lens is pointed at a bright light like the sun; controllable through the use of multilayer coating of the lens elements.

GN (Guide number)

Used to express the power output of the flash nit. It indicates the power of a flash in relation to ISO film speed. Guide numbers are quoted in either meters or feet. Guide numbers are used to calculate the f/stop for correct exposure as follows: Number calculated by multiplying proper flash exposure aperture by the subject distance.

GPD

Gallium Photo Diode. Metering cells for measuring exposure, using gallium arsenide-phosphide, just like SPD or Cds cells.

Grain.

Minute metallic silver deposit, forming in quantity the photographic image. The individual grain is never visible, even in an enlargement, but the random nature of their distribution in the emulsion causes over-lapping, or clumping, which can lead to graininess in the final image. Also cross check with below for graininess.

Graininess

The sand-like or granular appearance of a negative, print, or slide. Graininess becomes more pronounced with faster film and the degree of enlargement.

Grey card (18% Grey Card).

Tone used as representative of mid-tone of average subject. The standard grey card reflects 18 per cent of the light falling on it.