Rangefinder – An instrument that measures the distance from the photographer to a particular object and assists in proper focus.
Reflex Camera – A camera with a mirror directly behind the lens that captures the image and reflects the image to a viewing screen.
Refraction – A change of direction in a ray of light. When light strikes the lens at different angles it is forced to bend. Very small lens openings will cause distortion of light on your image.
Roll Film – Film with a light proof backing that is rolled on a spool and contains a strip of film to allow more than one exposure.