Movies for TV - Early Television Foundation

PRINCIPLES OF MOVIES 7
time ago, before 16 mm, 8 mm or 17.5 mm film, another size was
introduced 28 mm but this did not become popular and very
soon was forgotten.
Photography depends on chemistry for its operation. This is not
intended as a primer on photography, but a very brief explanation
of what goes on inside the camera will help the student appreciate
some of the problems he will face in the film and television industry.
Photography has come a long way since the crude experiments in
the eighteenth century, but it still depends on the same thing the
chemical effect of light on a film coated with certain chemicals.
Despite all the progress that has been made, silver still plays a very
important part in the operation.
The base is made by combining various ingredients, which de-
pend on the type of film being made, and pouring the resulting
thick liquid onto a slowly rotating drum perhaps 5-6 feet wide. The
drum speed is designed so that all the volatile solvents have evapo-
rated in a little less than one revolution. The resulting sheet is pulled
off continuously and rolled for convenience; it may be as long as
2000 feet and is of uniform thickness except for the edges which are
discarded. Since the characteristics of every batch of base mixture
are not constant, but vary even from roll to roll, the advice to obtain
all film for a particular production with the same batch num-
ber is readily understood in its application to base as well as
emulsion.
The coating is really much more important, for it is this which
takes and records the product of the producers, cameramen, actors,
and the whole film company. Therefore, it is essential that it be
uniform in as many respects as possible. Gelatin is used to support
the particles of silver salts which constitute the active agents in the
emulsion. It also acts in the same way as manganese dioxide in a
dry cell: that is, it is a depolarizer and removes halogen produced
on the silver salts.
by the action of light
Emulsion is made by dissolving gelatin and heating it. Silver
bromide is added and an excessive quantity of potassium bromide,
the latter being added as a sort of catalyst. Silver nitrate is then
added, and minute crystals of silver halide are precipitated; these