HIGH CONTRAST–A term expressing a relationship
of image tones in which highlights and shadows are
represented by extreme differences of density.
HIGH KEY–A term applied to a photographic print or
subject consisting entirely of light tones with little
contrast; also applied to a method of lighting a
subject.
HIGHLIGHT–The bright parts of a picture or subject
that are rendered as dense areas in the negative and
by very low density in the print.
HUE–That attribute of certain color perceptions in
respect to which they differ characteristically from
the gray of the same lightness and which permits
them to be classed as reddish, yellowish, greenish,
or bluish.
HYDROMETER–Generic term for various
instruments designed to determine the specific
gravity of liquids. (PIA)
HYDROQUINONE C6H4(OH)2–Common photo-
graphic developing agent para-dihydoxybenzene.
HYPERFOCAL DISTANCE–The distance from the
optical center of lens forward to the nearest plane in
acceptable focus when the lens is focused at infinity
distance.
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ILLUMINANCE –Luminous flux incident per unit area
of a surface. Widely known as illumination.
IMAGE, LATENT–The invisible image produced by
the action of radiant energy on a photosensitive
surface. It may be made visible by the process of
photographic development.
IMAGE, NEGATIVE–A photographic image in which
the values of light and shade of the original subject
are represented in inverse order. In a negative, light
objects are represented by high densities and dark
objects are represented by low densities.
IMAGE, POSITIVE–A photographic image in which
the values of light and shade of the original subject
are represented in their natural order. In a positive,
light objects are represented by low densities and
dark objects are represented by high densities.
IMAGE PLANE–The plane in which the image lies or
is formed It is perpendicular to the axis of the lens.
A real image formed by a converging lens would be
visible upon a screen placed in this plane.
INCANDESCENT –Glowing with heat, such as the
tungsten filament in an incandescent lamp.
LAMP HOUSE–That portion of an enlarger, reader, or
projector that contains the light source and
condensers or mirror.
INCIDENCE–The act of falling upon or affecting, as
light upon a surface.
INFINITY–A distance so far removed from an observer
that the rays of light reflected to a lens from a point
at that distance may be regarded as parallel. A
distance setting on a camera-focusing scale.
INFRARED–Pertaining to or designating those rays
which lie just beyond the red end of the visible
spectrum. They are invisible and are detected by
their thermal, photoelectric, and photographic
effects. Their wavelengths are longer than those of
light and shorter than those of radio waves.
INTERNEGATIVE –An internegative film is a nega-
tive derived directly from a color reversal original
film. All other color-duplicating negatives derived
from any other than reversal film are known as
color-duplicating negatives regardless of the
generation.
INVERSE SQUARE LAW–The intensity of light
received at a point (irradiance) varies inversely as
the square of the distance from the source. The law
holds for relatively small sources only and is useful
in calculating photographic exposures. (PIA)
IRIS DIAPHRAGM–Term applied to the adjustable
aperture fitted into the barrel of the photographic
lenses and so-called because of the contraction of
the aperture resembles that of the iris (pupil) in the
human eye. It consists of a series of thin metal
tongues overlapping each other and fastened to a
ring on the lens barrel, the aperture made smaller or
larger by turning the ring. (PIA)
JOGGING –Frame-by-frame advancement of
videotape.
KELVIN (°K)–Measurement of the color of light in
degrees. Numerically, the Kelvin temperature is
equal to the Centigrade temperature plus 273
degrees.
KEY LIGHT–The main source of illumination on a
subject. (PIA)
LAMP, PHOTOFLOOD–A lamp designed to yield
brilliant diffuse illumination. These lamps are
generally short-lived. (NMA)
LAMP, REFLECTOR FLOOD–Light bulb with
self-contained silvered surface to act as a reflector.
