RADIANT  ENERGY–Energy   in   the   form   of   an electromagnetic  wave;  for  example,  gamma  rays, X rays, ultraviolet energy, light, infrared energy, radiant heat, and radio waves. RADIATION –The process of emitting electromagnetic energy. RECIPROCITY  LAW–Exposure   is   equal   to   the intensity of the exposing light multiplied by the time during which it acts. The same density should be produced in a photosensitive material by an equal exposure obtained by doubling the intensity of the light and cutting the time of the exposure in half. This  law  is  only  approximately  followed  by photographic materials, and deviations from it are known as “reciprocity law failures.” RECTILINEAR –In a straight line. When applied to a lens,  it  indicates  that  images  of  straight  lines produced  by  the  lens  are  not  distorted. REDUCING  AGENT–A chemical constituent of a photographic  developer  that  changes  the  exposed silver  halide  to  metallic  silver.  Reducing  agents must be combined with other chemicals to confine their activity to the silver grains that have been exposed, to control the rate of reaction, and to preserve the agent from combining with oxygen in the air before it can do the work of development. Reducing  agents  are  also  called  photographic developers. AI-13 REFLECTED  LIGHT–Light that has been deflected from  an  opaque  surface;  not  having  been  absorbed. RELATIVE  APERTURE–The relative aperture is the ratio of equivalent focal length to the diameter of the effective aperture. The symbol for relative aperture written as a fraction is f/ followed by a numerical value. To illustrate, the expression f/2 signifies that the diameter of the effective aperture is one half of the focal length. RELATIVE   HUMIDITY–Ration of aqueous vapor present  in  a  space  at  a  given  temperature,  as compared with the greatest amount it could possibly contain  at  that  temperature. REPLENISHER–An additional agent used to maintain the chemical strength of a processing solution at a constant level. (NMA) RESOLUTION –In optics, the ability of a lens system to reproduce an image in its finest details. See RESOLVING POWER. SHADOW–General term for the thinner areas of a negative or the darker areas of an original. SHOT–(1) Motion picture. The most basic unit of a film; a single scene; the continuous action occurring from the time the camera is turned on to the time it is turned off. (2) Still picture. A single exposure or photograph. SHUTTER,   BETWEEN-THE-LENS–A    shutter whose blades operate between two elements of the RESOLVING POWER–The degree to which a lens, optical system, or film emulsion is able to define the details  of  an  image,  expressed  as  the  maximum number of black lines, with equal white interspaces per  millimeter  discernible  in  the  image.  Results obtainable for a given lens or emulsion vary with contrast   of   the   original   image   and   with development. RESTRAINER–The  ingredient  of  a  photographic developer that prevents too rapid development and that  minimizes  chemical  fog. RETICULATION –A   processing   defect   affecting gelatin layers on a photographic film which, upon drying,  shows  an  irregular  surface  due  to  the formation of small, irregular scaly patterns. Sharp differences  in  the  temperatures  of  successive processing solutions and insufficient hardening of the  gelatin  are  the  usual  causes  of  reticulation. RGB–The   separate   red,   green,   and   blue   color (chrominance), or “C”, video signals. SCALE,  FOCUSING–A calibrated scale that permits focusing a camera without the use of a range finder or ground glass. SCRIM–Diffusing medium placed in front of lamps. SEMIMATTE–A    surface    having    a    moderate, interrupted  sheen  midway  between  glossy  and  dull, or  full  matte. SENSITIVITY –The degree to which an emulsion reacts by the formation of a latent image under given exposure conditions, especially as this relates to exposure  by  different  wavelengths  (colors)  of  light. (NMA) SENSITIZING  DYE–Any     dyestuff     used     for sensitizing  a  photographic  emulsion. SENSITOMETER–An   instrument   with   which   a photographic emulsion is given a graduated series of exposures to light of controlled spectral quality, intensity, and duration.