Factor:  a number that tells how many times exposure must be increased to compensate for loss of light (for example, when using a filter on the lens)

Farmer’s Reducer:  a solution of potassium ferricyanide and sodium thiosulfate that is used to decrease the silver in a developed image

Fast: describes 1) a film or paper that is very sensitive to light, 2) a lens that opens to a very wide aperture, 3) a short shutter speed. Opposite: slow

Fiber-base paper formerly the standard type of paper available, now replaced to an extent by resin-coated papers.   The optimum paper for longevity of prints, and best choice for exhibition quality prints

Fill light a source of illumination that lightens shadows cast by the main light and thereby reduces the contrast in a photograph

Film plane:  see focal plane

Film speed:  the relative sensitivity to light of a film.   Several rating systems are used: ISO (most common in the U.S. & Great Britain), DIN (common in Europe), & others.  Film speed ratings increase as the sensitivity of the film increases

Filter:  1) a piece of colored glass, plastic, or other material that selectively absorbs some of the wavelengths of light passing through it.  2) To use such a filter to modify the wavelengths of light reaching a light-sensitive material

Filter factor: see factor

Fixer:  chemical solution (sodium thiosulfate or ammonium thiosulfate) that makes a photographic image insensitive to light.   It dissolves unexposed silver halide crystals while leaving the developed silver image.  Also called hypo

Flare: unwanted light that reflects & scatters inside the lens of a camera.  Upon reaching the film, it causes a loss of contrast in the image

Flash 1) a light source, such as a flashbulb or electronic flash, which emits a very brief, bright burst of light. 2) To blacken an area in a print by exposing it to white light, such as from a penlight flashlight

Flash meter an exposure meter that measures the brightness of flash lighting to determine the correct exposure for a particular setup

Flat:  a scene, negative, or print with very little difference in brightness between light and dark areas. Opposite: contrasty.  Also see: reflector.

Floodlight: an electric light designed to produce a broad, relatively diffused beam of light

f-number: a number that equals the focal length of a lens divided by the diameter of the aperture at a given setting.  Theoretically, all lenses at the same f-number produce images of equal brightness.   Also called f-stop or relative aperture.

Focal length the distance from the lens to the focal plane when the lens is focused on infinity.  The longer the focal length, the greater the magnification of the image

Focal plane the plane or surface on which a focused lens forms a sharp image.  Also called the film plane.

Focal-plane shutter a camera mechanism that admits light to expose film by moving a slit or opening in a roller blind just in front of the film  (focal) plane

Focal point the point on a focused image where the rays of light intersect after reflecting from a single point of a subject

Focus: 1) the position at which rays of light from a lens converge to form a sharp image. 2) to adjust the distance between lens and image to make the image as sharp as possible

Focusing cloth:  a dark cloth used in focusing a view camera.  The cloth fits over the camera back & the photographer’s head to keep out light and to make the ground-glass image easier to see

Fog:  an overall density in the photographic image caused by unintentional exposure to light or unwanted chemical activity

Frame: 1) the edges of an image. 2) a single image in a roll of film

f-stop: the common term for the aperture setting of a lens.

Full-scale:  describes a print having a wide range of tonal values from deep, rich black through many shades of gray to brilliant white