RADIANT ENERGYEnergy 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
RECIPROCITY LAWExposure 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 AGENTA 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
REFLECTED LIGHTLight that has been deflected
from an opaque surface; not having been absorbed.
RELATIVE APERTUREThe 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 HUMIDITYRation of aqueous vapor
present in a space at a given temperature, as
compared with the greatest amount it could possibly
contain at that temperature.
REPLENISHERAn 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
SHADOWGeneral 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
SHUTTER, BETWEEN-THE-LENSA shutter
whose blades operate between two elements of the
RESOLVING POWERThe 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
RESTRAINERThe 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.
RGBThe separate red, green, and blue color
(chrominance), or C, video signals.
SCALE, FOCUSINGA calibrated scale that permits
focusing a camera without the use of a range finder
or ground glass.
SCRIMDiffusing medium placed in front of lamps.
SEMIMATTEA 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.
SENSITIZING DYEAny dyestuff used for
sensitizing a photographic emulsion.
SENSITOMETERAn instrument with which a
photographic emulsion is given a graduated series
of exposures to light of controlled spectral quality,
intensity, and duration.