Movies for TV - Early Television Foundation

W FUNDAMENTALS
There is no apparent change in the emulsion, but on being im-
mersed in a developer, an image or picture is produced. This is in
a negative form in which the objects which were black in the
original are white, and those which were white are black. More
light is reflected from the light-colored sections of the scene and,
therefore, more chemical action takes place in the corresponding
section of the film. When this is developed, silver is deposited in
the dark areas, and in the lighter areas where there was no light,
the undeposited silver is washed away.
Before the film so made can be used, it is necessary to reverse it,
thus making a positive
which has the same colors and shades of
light as the original. This can be done in two ways. One method is
by direct reversal in which the film which was in the camera, known
as a reversal film, is chemically treated a second time. This treat-
ment literally reverses the colors of the film, and parts which were
white become black, and those which were black become white.
The film then has the same color-shade values as the original scene,
and is known as a direct-reversal positive. In the other, and more
onto another
generally used system, the negative is photographed
film. In exactly the same manner in which the color values were
reversed when the negative was made, so are the colors again re-
versed on the second film. By virture of this double reversing, the
second film becomes a positive which is then used for projection or
televising. It will be seen that the former method suffers from the
drawback that only one film exists, and if anything happens to it
there is no way of replacing it.
There are many different types of film stock available. The
various manufacturers have their own trade names for them, but
film emulsions fall into certain well-defined categories. Negative
and positive stocks have already been mentioned. In this case, the
difference in the raw (unexposed) film is in the speed and fineness
of grain. Emulsion speed is the main difference between the differ-
ent types. By emulsion speed is meant the sensitivity of the emulsion
to light and the speed with which a picture is formed on the film.
Modern chemistry has achieved a great deal in preparing fast emul-
sions, but unfortunately as the speed of the film increases another