RAM: Random Access Memory. Your computer’s system memory.

rangefinder camera: A type of camera that includes a focusing mechanism which allows the photographer to measure the subject distance and take photographs in sharp focus.

rear curtain sync: An electronic flash synchronization technique in which the flash fires only when the second (rear) curtain of the focal plane shutter begins to move at the end of the exposure.

red eye: An effect from flash photography that appears to make a person or animal’s eyes glow red. Caused by light bouncing from the retina of the eye.

resolution: A term used to describe the capabilities of digital cameras, scanners, printers, and monitors; means different things depending on the device.

RGB: The standard color model for digital images; all colors are created by mixing red, green, and blue light.

rule of thirds: A way of mentally dividing your picture horizontally and vertically into thirds, then placing important subject matter where these lines intersect.