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This production involved a projector screen that would appear from time to time
in a cave-like space. On this appeared images that varied in both their content
and in the way they were projected. The image on the screen had to be able to
immediately slow down or even freeze at any time. It may then have needed to
suddenly resume normal speed. In addition, it had the capability to zoom in on
any point of the image at any time. All this had to be done in silence: the
screen was on a sound stage.
The OEPPy ( Optical Effects Process Projector ) projector was specifically
designed and built to meet these demands. Because the OEPPy projector could
perform such sophisticated functions, it represented the cutting edge of
film-projector technology.
System Specifications
| Speed Range |
24, 24/2, 24/3, 24/4, 24/5 frames per second to freeze frame |
| Movement Motor Speed |
24 frames per second continuous |
| Film load |
500 feet max |
| Lamp Power |
7 kW |
| Power Supply |
10 kW 3 phase 4 wire |
| Air Supply |
5 hp with dessicator |
| Motion Control System |
Kuper with 486PC |
| Number of axes |
6 |
| Lenses |
28-105mm f3.2-4.5 zoom,
50mm f1.6 prime
70mm f2.0 prime
100 mm prime
two 0.8-1.25 zoom converters |
| Sound Level |
For use on Sound Stage |
The Cooling Systems
The first requirement of the projector was to make a screen image that would be
bright enough -- at minimum focal length -- to fit in with the rest of the lit set.
This meant that a quite powerful 7 kilowatt lamp had to be used.
The projector had to slow -- or even freeze -- the image on the screen and,
consequently, leave the film in the projector light beam for a much longer time
than a conventional projector would. Unprotected, the film would simply burn up
from the light's heat after a few tenths of a second.
Several lines of defense were used to protect the film from burning. The light from
the lamp was first reflected off a specially coated mirror that took some of the heat
out of the light. This heat then goes into the mirror and into a water jacket on the
back of the mirror. The water flowing through this jacket is circulated through a fine
filter and a plastic tub by a small pump. The water in this tub is cooled by a small
radiator that is immersed in it. Ice water is pumped through this radiator.
The partially cooled light that is reflected from the heat mirror is fed through the
second line of defense against film-burning - the water cell. This is a water-filled
aluminum box with two glass windows that allow the light beam to pass through it. The
water takes heat out of the light shining through it. The water is pumped through this
water cell and through a cooling system similar to the one described for the heat
mirror.
After passing through two heat extraction systems the light beam has had most of
its heat removed. However, the reason that film is placed in front of the light beam
in the first place is to selectively block the light across the area of the beam which
then makes an image. The light that is blocked by the film is converted to heat within
the film itself. The last line of defense against film-burning is the system that pulls
this heat out of the film.
This system is comprised of an array of air-jets that push the film that is in the
light beam against one of the cool glass windows of the water cell. This physical
contact conducts heat out of the film. The action of the air jets blowing over the
other side of the film also takes heat out of the film.
A final line of defense against film-burning involves pulsing the light beam with a
spinning shutter. The film in the camera that is filming the screen will only be
exposed in pulses. For 1/48th of a second the film will be exposed then for another
1/48th of a second the film will be occluded by the shutter in the camera. There is no
need for the projector to show an image on the screen during the time the camera film
is occluded. The projector shutter is electronically locked to the shutter in the
camera so that when the film in the camera is occluded, so too is the projector light
beam. This gives the film in the projector a little time to cool before its next
exposure.
The projector is mounted within a sound-proof box. Any heat generated within this box
must be taken out. Heat extracted from the light beam by the systems described above
must be removed and so too must the heat generated by the lamp bulb and its associated
electrical system.
The bulb is cooled by air pumped through its housing. The exhaust air from this housing
is passed through a set of radiators that have iced water passing through them. These
take the heat out of this air, cooling it before it is circulated around inside the box
and back into the lamp housing.
The iced water used in the heat-mirror, water cell and lamp bulb cooling systems is
fed into the sound proof box from the outside by a pump immersed in a large tub of
ice-cubes and water. The iced-water circulates first through the radiator immersed
in the water cell coolant tub. From this it flows through the radiator that is
immersed in the heat mirror coolant tub and then through the radiators at the exhaust
of the lamp housing. After all this, it flows back out of the sound proof box and back
into the iced-water tub.
The Movement
This projector uses a modified Geneva movement. The pin of this movement can
be disengaged and re-engaged from the geneva star to stop and start the movement
of film. There is only a small part or window of the revolution of the pin during
which an engage or disengage may safely occur. If an engage or disengage is
attempted outside of this safety window, then the projector movement will be
destroyed.
The geneva pin is coupled to a gang of powerful spring-return solenoids through
a lever. These solenoids are commanded to energize or de-energize by a small
micro-computer. This microcomputer also simultaneously monitors electronic sensors
to detect just when it is safe to perform an engage or disengage to start or stop
film movement coming from the motion control system.
If the micro-computer sees that the motion control system wants to stop the film,
it first waits for the next window of safety to appear. It then energizes the
solenoids which, in turn, retract the geneva pin. This then stops the film motion.
The Motion Control System
The coordination of film flow, movement of the center of frame and lens zooming is
done with a computer based program called the Kuper Motion Control System.
A motion control system is similar to a multi-track tape recorder. The user can
individually program just where an axis should be for a given position on the tape.
Once several tracks have been programmed, the tape can be rewound and played. All
programmed axes will then simultaneously perform coordinated movements as the tape
plays.
One of these tracks gives the command to start or stop the film.
This system allows the user to program coordinated moves of all the various 'axes'.
The projector has several axes - zoom, focus, iris, douser, horizontal frame
movement, vertical frame movement and the movement motor.
The replay of this tape is synchronized to the camera shooting the screen.
Various moves can be stored and recalled.
The positions of the various axes are sent from the motion control system in the
form of direction and step. These signals are sent to the motor drivers. There is
one driver for each axis.
The motor is coupled to this driver by wires running from the projector and down
the umbilical. The drivers are mounted in the electrical cabinet.
The Film Transport
The ability of this projector to stop and start the film within 1/24th of a second
means that the mechanisms used to feed film through the projector had to be designed
to soften the shock to the film.
OEPPy Sr. is capable of shifting from regular speed to a freeze frame - essentially,
from full speed to a dead stop - instantly. When a freeze frame is requested, the
movement immediately stops needing film. The sprockets feeding the loops must stop or
the loops will grow. But if these sprockets stop instantly, the feed reel will roll
on and on, spewing film indiscriminately about. The film moving to the takeup reel
will be snapped by the sudden tension created by the freeze frame's instant dead stop.
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