162 Moving Images: Making Movies, Understanding MediaFocal length – Measurement that defi nes the type of a particular lens, such as
16mm, 25mm, 50mm, or 150mm, typically determined inside the body of the
lens: it is the length from the rear nodal point of the lens (where light is being
sent back by refraction) to the fi lm plane when the lens is focused at infi nity.
Focus – In optics, focus is the point at which light rays converge so the image
appears sharp when viewing it. A lens must be adjusted—either manually or
automatically—to achieve a focused view of subjects at a particular distance.
Focus pull – A change in the focus plane during a shot. At the beginning of a
take, the lens will be set at a distance (for example, at fi ve feet), and during the
shot this can be changed manually or remotely to another distance to follow an
actor, adjust with a camera move, or shift visual information and attention.
Foot-candle – Unit of measurement of light that equals the illuminating
intensity from one candle falling on one square foot of surface at a distance
of one foot.
Frames per second – Th e rate at which individual frames are advanced per
second through a camera, projector, or other moving image device. For
American motion picture photography, the projection standard is 24 fps and
for television, it is 29.97 fps (rounded to 30).
F-stop – Number that is measured by dividing the focal length of a lens by the
eff ective diameter of its aperture and is used for setting the iris. Th e standard
range of f-stops is: 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, and 22, in which each higher
value in this logarithmic scale cuts the light by one half. An f-stop number
can also be understood as the denominator of a fraction in which the focal
length of the lens is the numerator, the solution for which equals the aperture
diameter. F-stop is also known as relative aperture.
Gate – Th e opening on the camera behind the lens through which light passes
onto the fi lm which rests on a metal plate that forms the back of the gate.
Grain – Granular texture in negatives that emerges as a result of clumping of
silver-halide particles during processing, viewable under magnifi cation.
Incident light meter – Light meter that measures the intensity of light falling
on the precise spot where the meter is turned to the source.
Iris – In the eye, the iris is the membrane suspended between the cornea and
the lens and is perforated by the pupil. In photography, the iris diaphragm is
composed of metal elements that open and close to let in more or less light.
ISO rating – From the International Standardization Organization, scale for
measuring the sensitivity of fi lm to light. Commonly described as the fi lm speed,
in which a slow fi lm requires more signifi cant exposure (either more time or
more relative light) and a fast fi lm less light for the same quality of exposure.
Light – Visible light is a form of electromagnetic radiation that the human
eye can perceive. Th e spectrum of visible light lies in a relatively small band
of wavelengths that register as a series of colors such as those seen in a
rainbow.
Light Meter – An instrument used for measuring the intensity of light on a
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