1 The Director of Photography – an overview

The motion picture camera 41
Figure 4.3 The twin-bladed shutter
Light
Path
Objective
Lens
Shutter
Film
Gate
Register Pin
Aperture
Claw
laterally, as its neighbours. The gate is usually several frames long and
will have a slot in it to allow the claw to enter the perforations in the film
and another to allow a register pin if this is used in the camera’s design.
The claw
The most common mechanism for moving the film from one frame
to the next is known as a claw, simply because when they were
invented they looked like an animal’s claw, an arm with a hook or nail
on the end. Figure 4.4 shows an early Williamson mahogany-cased,
hand-cranked camera, which has recently shot some very good pictures.
Despite its age, it graphically shows the classic layout of an intermittent
mechanism.
Figure 4.5 shows the current Panavision lightweight camera mechanism,
one of the best in the business. Despite being much more
sophisticated, it has remarkable similarities to the Williamson – two
sprockets top and bottom of the camera box and claw, now much more
sophisticated and precise, with the addition of a register pin. In order
to improve the vertical alignment, many cameras now provide a register
pin or pins that are inserted into perforations adjacent to the aperture
just as the claw is retracting and remain there for the duration of
the exposure. Figure 4.5 shows Panavision’s solution to this challenge.
The horizontal bar with the drilled holes right in the middle of the picture
is the register pin operating leg; there is a drop bar just behind the
gate to locate the actual register pins in the two perforations at the
bottom of the frame. In this camera, the claw mechanism is operated
by a link mechanism, which can be seen just below the register pin
actuating bar.
In many camera mechanisms, one of the complications is that if the
gate is straight the claw must have some means of converting the rotary
motion of the drive shaft into an absolutely straight movement at the
claw tip, as in the Williamson layout. This can lead to inaccuracies,