Rangefinder - An instrument for measuring the distance from the observer to a particular object, as for adjusting the focus of a camera. A rangefinder is included as an integral part of many cameras as a focusing aid.
RC - Resin-coated.
Ready Light - A small light on a flash unit that indicates whether there is adequate power to fire the flash.
Reciprocity Failure - When a film’s speed cannot be relied upon for proper exposure at slow shutter speed, reciprocity failure (or the “Reciprocity effect”) is said to occur. Additional exposure is required in order to achieve proper exposure for that film, even though your light meter may say differently. The additional problem of a shift in colour balance that occurs with reciprocity failure can be more troublesome.
Reciprocity Law - The reciprocity law states that Exposure = Intensity X Time. “Intensity” is the amount of light, and “Time” refers to how long that amount of light is allowed to act on the film’s emulsion. Intensity is generally controlled by the aperture and time is generally controlled by the shutter speed. The reciprocity law therefore means that an exposure provided by ƒ8 and 1/250 sec will gave the same results as ƒ11 and 1/125 sec., or ƒ16 and 1/60 sec., and so on. If one choice of settings provides proper exposure, then the others will as well. The law “fails,” however, when slow shutter speeds change the film’s apparent speed characteristics, making it seem to have a slower speed and produce colour shift.
-The time between a flash going off and the generator recharging to 100%.
Red eye - The bright red color of the pupil of the eye that sometimes disfigures pictures taken by flash. It is caused by reflection of the flash unit's light from layers of the retina rich in blood vessels. Red eye can be avoided by making sure that the subject is not looking directly at the camera or by using of camera or bounce flash. Some cameras with built-in flash units have a red eye reduction control. When this is activated, the flash emits a beam of light just before the flash fires, causing the subject's pupils to contract, which lessens the risk of red eye.
Red eye reduction - A feature of some cameras or flash units that is meant to reduce the effect of red eye by emitting multiple bursts of light immediately before the picture is taken. The intended result is a forced reduction in the size of the subject's iris.
Reflected light reading - An exposure meter reading of light reflected by a subject. The exposure meters in most cameras are reflected light meters.
Reflector - Any surface capable of reflecting light: in photography, generally understood to mean sheets of white, gray or silvered material used to reflect light into shadow areas. Lamp reflectors are generally dish-shaped mirrors, with the lamp recessed into the concave interior, which points toward the subject. Studio electronic flash equipment is often combined with an umbrella reflector, usually silvered, mounted on a stand.
Reflex camera - A camera employing a mirror in the viewing system to reflect the image onto a viewing screen. The most popular type is the single lens reflex (SLR), which reflects the light from the same lens that is used to take the picture. The twin lens reflex (TLR) has an additional lens for viewing. A single lens reflex camera shows the image in the viewfinder, as it will appear on the film, whatever the focal length of the lens used.
Rim lighting - Lighting in which the subject appears outlined against a dark background. Usually the light source is above and behind the subject, but rim lit photographs can look quite different from conventional backlit images, in which the background is usually bright.
Refraction - Refraction is a change of direction of a ray of light. Light that is travelling in a straight line alters course - bends - when it strikes light-transmitting substances at any angle other than perpendicular.
Release - Refers to a Model Release - a contract in which a model consents to the use of his or her images by the photographer or a third party.
Resin coated paper - Paper that has a water repellent base and is used for making photographic prints.
Resolution - (1) Fine detail in an image. (2) Also means “Resolving power.”
Resolving power - Ability of film, lens or both together to reproduce fine detail.
Reticulation - Occurs during processing when the emulsion becomes cracked or distorted. The cause is usually exaggerated temperature variance or differences in chemical activity between solutions.
Retouch - To manually alter the appearance of a negative, slide or print using non-photographic methods, such as air-brushing, with the intention of improving the image’s appearance.
RGB - An acronym for the primary colours of light, Red, Green and Blue.
Ring Flash - A circular-shaped electronic flash unit that fits around a lens and provides shadowless, uniform frontal lighting, especially useful in closeup photography.