G L O S S A RY counteracted by giving a long exposure time. But this reciprocal relationship (half the brightness = double the exposure time) increasingly breaks down with exposure times beyond 1 second. The film then behaves as if having a lower speed rating. Color films may also show incorrect balance. `Red eye' The iris of each eye in portraits shows red instead of black. Caused by using f lash directed from close to the lens. Reflex camera Camera with viewfinder system using a mirror and focusing screen. Refraction Change of direction of a ray of light passing obliquely from one transparent medium into another of different density, e.g. from air into glass. The basic reason why lenses bend light rays and so form images. Resin-coated (RC) bromide paper Bromide paper having a water-repellent plastic base. RC Sheet film Film supplied as individual sheets, usually 10 or 25 to a box. Shutter Mechanical device to control the time the light is allowed to act on the film. Usually consists of metal blades within the lens, or two blinds passing one after another just in front of the film, the exposure occurring in the gap between them (focal plane shutter). Silver halides Light-sensitive compounds of silver with the halogens (iodine, bromide, etc.). Normally white or creamy yellow in color. Used as the main sensitive constituent of photographic emulsions. Single lens reflex (SLR) Camera in which the viewfinder image is formed by the picture-taking lens. Soft focus Image in which outlines are slightly spread or diffused. `Soft' light sources See Diffuse lighting.