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The Geneva· Cam or Maltese Cross Movement: This intermittent motion of the film through a 35mm
projector is achieved by a mechanical movement perfected by experimenters like Edison, Lumiere and Friese~
Greene around about 1895. It is known as the Geneva, or Maltese Cross and Cam, m6vement.

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PERIOD PULL-DOWN IN MID- POSITION JUST COMPLETED

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STAR WHEEL PIN ENTERS STAR WHEEL PIN IS EXITING FROM
IS LOCKED & SLOT IN HAS ROTATED 45° SLOT-STAR WHEEL HAS
CANNOT ROTATE STAR WHEEL SEEN ROTATE!:' A TOTL OF 90°

Maltese-Cross and Cam-Pin Movement of a Geneva-type Intermittent System

If you look carefully at the diagram, you should be able to see how it operates.

What is called the "Star Wheel" in the diagram is on the same shaft as a "Four-Picture" sprocket...that is a
sprocket which has 16 teeth, and therefore, if it revolves a 1/4 of a turn, it moves exactly one complete frame
of film - there being on the film 4 sprocket holes to each picture. This sprocket is known as the Intermittent
Sprocket because it is turned or rotated intermittently by the pin on the cam.

The Cam revolves at 24 revolutions per second or 1440 revolutions per minute. Once the Star Wheel has been
revolved 1/4 turn by the pin on the cam engaging the slot on the star wheel, the Star Wheel is virtually locked
on the cam, because its curved edge fits snugly and accurately against the curved perimeter of the cam.
This ensures that the image being projected onto the screen at that moment cannot possibly move even the
tiniest fraction. It is while the Intermittent Sprocket is moving that a shutter cuts off the light from the film. Once
the Intermittent Sprocket stops moving, the light beam again passes through the film and onto the screen. All
this happens 1440 times a minute or 86400 times every hour.

So next time you go to the movies, spare a thought for the little pin on that cam doing all that work just so that
you can see Tom Hanks or Nicole Kidman or even Mickey Mouse. Is it any•wonder that very often, the first part
to wear out on a 35mm or Cinema Projector is that pin. It gets so tired of belting away on the maltese cross,
1440 times a minute.

As we said, the pioneers 100 years ago devised the Geneva Movement of Cross and Cam. It is still the heart
of every Cinema Projector built today. So the amazing fact is that the basic operation of a cinema projector has
not changed, been modified, or improved upon for the last hundred years.

Of course, there have been revolutionary changes in cinema projectors over the last century and the films run
through them. We now have sound, colour and wide screen formats; but like "01' Man River", the Maltese
Cross and Cam still keep rolling along.

Note: Before any technicians shout "you have'nt mentioned anything about 2 bladed shutters in sound projec-
tors, to alleviate flicker, which means is actually interrupted 48 times/sec and not 24". WE know that. We were
trying to keep it simple. What has been described in this article is a basic operation of a 35mm or 75mm
Projector. The 16mm 9.5mm and Super 8 Projectors have a different, and possibly more easily produced
intermittent movement, which because of the smaller dimensions of the film, does not have such a heavy work
load. But that could be the subject of a later article.

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