Reflections are rays of light which strike a surface and bounce back again. Reflector is any substance from which light can be reflected. It also describes a white or gray card used to reflect from a main light source into shadow areas. Reflex camera is a camera system which uses a mirror to reflect incoming image rays on to a ground glass screen, providing a system of viewing and focusing. See also SLR .
Reflex lens is an alternative term for mirror lens .
Refraction is the change in direction of light rays as they pass obliquely from one transparent medium to another of different density, e.g. air to glass. Refractive index is a numerical value indicating the light bending power of a medium such as glass. The greater the bending power, the greater the refractive index. Register is the exact alignment when overlaying separate images. Register punch is the punched used to make alignment holes in film or paper for registering images.