Movies for TV - Early Television Foundation

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FILM TRANSMISSION EQUIPMENT 107
projected picture. Bias lighting is used in much the same way as
grid bias in a vacuum tube and changes the sensitivity of the tube
to prevent grid current in the amplifier. (These controls are not
generally adjusted during transmission.)
While a program is on the air, a technician, known as the
shading technician, sits watching a monitor on which is shown the
picture from the camera. He has similar controls to those used
by the studio camera control operator; in addition, he has four
shading controls. These are two forms of vertical shading saw
tooth and parabolic. The names refer to the shape of the wave
forms produced. The former corrects top or bottom shadows or
flare and the latter similar faults in the middle of the picture. The
horizontal shading controls are similar except that they correct for
right- or left-hand side and center shadows and flare.
While this job does not call for a lot of engineering knowledge
but merely the ability to make rapid decisions and to act on them
at once, it is one of the most important during
the time that a film
is on the air. A skilled shading technician can make all the differ-
ence between a good and a poor film show. Almost every scene in
a film has a different light value and causes different spurious
emissions from the previous scene; therefore, the shading man
has to be wide awake all the time to correct the picture continu-
ously. An added feature of the film camera is the fact that it is
possible to reverse film electronically. This means that if a negative
film is the only one available it can still be used by setting the
polarity switch on the top left-hand side of the camera to "nega-
tive." This will now produce positive pictures over the television
system. In the "positive" position, it operates normally. For special
effects, a reversed, negative picture results from positive film and
the switch in the "negative" position.
The illustration of the RCA film camera shows the projector
directly into the camera, but this does not mean that
there has to be one camera for every film projector or slide projector.
RCA has introduced a device called a Multiplexer which
makes it possible for two film projectors and one slide projector