Middle left stick

Calculator stick

RAM (random access memory)

Used in a computer to store or access programs and data directly ie without using a sequential search process. It is therefore fast and used as a computer's primary memory.

Rangefinder

A device for measuring the distance between subject and viewer usually in order to focus a lens; hence rangefinder camera type.

RAW

A file format which stores image data as it is produced by the sensor. Conversion is necessary before editing can take place.

Reciprocity failure

A non-linear reaction to incident light of light-sensitive material. In the case of film, this generally occurs when exposures are longer than one second. Consequently, doubling the exposure time has less effect than opening the aperture by one stop.

Recycling time

The time taken for a flash gun to recharge after being fired. The time is at a maximum when the unit has been completely discharged.

Red-eye

A phenomenon revealed when light from a flash used close to the lens axis is reflected back by the subject's eyes. The reflected light is turned red or pink by blood vessels in the retina at the back of the eye, and is seen as a red circle.

Reflection

The deflection of a ray of light as a consequence of it hitting a reflecting surface. Incident and reflected rays remain on the same side of the surface.

Reflector

Typically a sheet of white, silver or gold material or card used to reflect light from a primary source back into poorly illuminated areas of a subject.

Refraction

The deflection of a ray of light as it crosses the boundary between one medium and another of a different refractive index. The ray moves from one side of the boundary to the other.

Remote release

A flexible device enabling the user to release a shutter without transferring the movement of the hand to the camera.

Reproduction ratio

The ratio of the size of an image of an object to the physical size of the object. It is sometimes known as magnification.

Resolution

In the case of a camera or scanner, a measure of ability to reproduce subject detail in an image. For printers, a measure of ability to address separate output lines or points.

Reversal film

A film which, when processed, produces positive images. It is commonly known as transparency film but also known as reversal film because one stage of the development process is designed to reverse what would otherwise be negative images.

RGB

Red, green and blue colour model which represents colours by their relative amounts of the three components. White is represented by maximum amounts of each component, and black by minimum amounts of each.

Ring-flash

An electronic flash unit consisting of one or more flash tubes formed into a near circle around a lens. It provides reasonably soft, shadowless frontal lighting suitable for close-ups.

ROM (read-only memory)

A digital memory whose data may be read but not edited.

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