This week, the film path.

Once the film is built, it is stored between showings on a platter- a 5' diameter horizontal disc, very smooth, clean surface that revolves to pay out, or take up the film to and from the projector.

platter
Looking down on the #2 projector, with the film being fed from the inside of the film mass, through the brain in the center of the platter, and then on to the blue pole, where it heads over to the projector (top right corner of photo). There is a loose 'girdle' of film around the feature that keeps it on the platter and allows the tail of the film to freely travel off of the platter at the end.

Starting on the feed out platter, the film travels through the platter brain to the payout assembly on the platter system, and descends into the top of the projector.


projector
This side view of the projector & sound head shows the sprocket rollers and lens as the film is running. Hard to see the film because it's a 90 degree viewing angle. The failsafe location is visible at the very bottom of the soundhead.

Once inside the projector, the film encounters 5-6 rollers with teeth along their edges that engage the sprocket holes on the edges of the film and keep the picture in perfect sync with the sound as it is projected through the porthole glass into the auditorium, where you are sitting.

Inside the projector itself, the precise loading of the film is critical to a good performance, which depends on the skills of the projectionist.

A 2 hour film contains about 2 miles of film! Each foot of film contains 16 frames, and the film runs through the projector at 24 frames per second. The film must advance one frame, pause for a fraction of a second and then advance to the next frame, while a shutter passes in front of the light path- so you don't see the film moving during this process. When you watch a film you are actually seeing a series of still images projected in such rapid order that you perceive it to be in motion.

The critical film movement is accomplished using a unique sprocket wheel mounted just below the aperture gate called the 'intermittent' assembly. This intermittent sprocket rotates just far enough to pull the film down one frame, pauses and then rotates again. All of the other sprocket rollers move at a constant rate, while the intermittent makes 24 pull-downs every second. The film is stretched over a couple of bars as it passes in front of the lens. The bars serve to keep the film focused and properly aligned. The film also passes through a digital or optical audio decoder mounted before or after the lens assembly. After the picture has been projected and the sound picked up, the film descends from the bottom of the projector and crosses a series of metal rollers that sense metal cues the projectionist places on the film during the build that tell the automation system when to raise or lower house lights or shut the projector down. This device, a 'failsafe', will shut the projector off immediately if it detects any slack in the film indicating a delivery problem. Once the film leaves the failsafe, it is carried on a series of rollers to a take-up platter, where it will be wound up for the next presentation.

failsafe
The failsafe has 2 arms located directly below the name CHRISTIE- if the film slackens, the arms drop and shut down the projector. Also located on the failsafe are the cue detectors, which look like red buttons on the left of the photo. Depending on where foil tape is placed on the film, one of the cue detectors will trigger events like house light control.

Once we start a film, it isn't possible to fast forward or rewind the film a little bit. Stopping the film and restarting it requires physically cutting the film, which means we must generally run it all the way through once we press the start button.

Seeing the projectors running is exciting, and we're happy to show you the projection room if you're interested the next time you come in- if we're not too busy with customers in the lobby. You can call the manager/projectionist before you come in to see if a tour is possible at 577-1686. Most of our tours include an actual piece of 35mm film that we have exhibited on screen.