F

file format

The data structure of a computer file that determines how the information is organized. File format determines the compatibility of a file with various software applications.

file type

See [file format]

focusing rails

A tripod-based focusing system, consisting of a pair of rails and a camera mount. A turn wheel moves the camera along the rails in very small, controlled increments, shifting the focus point in the image. This tool is valuable for close-up photography and other situations in which there is an extremely narrow depth of field.

f-stop

A fractional value that measures the opening of a lens. The value is arrived at by dividing the focal length of the lens by the diameter. The wider the opening, the lower the f-number, which lets more light through the lens. Each f-stop value represents a halving or doubling of light.