Movies for TV - Early Television Foundation

134 FUNDAMENTALS
of the fastest action which can be photographed with a given
emulsion speed and shutter depends on the greatest quantity of
light which can be placed on the film in the time that the shutter
is open. The greater the lens opening, the more light will reach
the film while the shutter is open. This means that if the action is
very fast in order to "stop" the motion (that is,
arrest it so that
there will not be a blur due to movement being recorded while
the shutter is open), the exposure must be short. To get sufficient
light to record the picture a large or "fast" lens is required.
On the other hand, sometimes there is too much light in which
case it becomes necessary to reduce the amount of light passing
in front of it which
through the lens by closing a small diaphragm
is known as an iris, so called because of the very large number of
leaves of extremely thin metal which close or open in a circular
motion as the control is operated. The action is very similar in
appearance to the action of the iris of the human eye, or pupil as
it is sometimes called. This brings up the next point which is care
of the lens and its characteristics.
It should be regarded and treated in the same way as the
human eye, or at least sometimes as the human pair of spectacles.
A lens must be kept scrupulously clean; the faintest bit of dirt
on it will reduce the amount of light being transmitted and since
this is one of the main functions of a lens great care must be ex-
ercised in handling it. A handkerchief should never be used to
clean a lens, for one of two things will result; it will either scratch
it or leave lint on the surface. This is even more important in the
case of coated lenses, for careless cleaning can result in removing
the surface in small areas and so cause shadows on the finished
picture.
The coating mentioned above is a comparatively new development
designed to reduce the amount of light reflection by the
glass of the lens. It operates by preventing the reflection of light
and thus permitting more of the light rays which strike the lens
to enter instead of being reflected by the surface of the glass. A
number of different substances are used, each operator having a
formula. Any
lens can be coated even if it is an