Projectionists' Guide - Projection Equipment
Projection Equipment with Instructions
By Alexander Wright
The projection equipment can be divided into four parts:
The projector, the film, the
spool tower, and the Dolby system.
There now follows an idiot's guide to each part:
The heart of the system. The projector pulls film from the spool tower, passes it around several sprockets and wheels, and then lets it out the bottom. On the way, the film passes through the gate, where the light is shone through it and onto the screen, and the sound head. The light used to project the film comes from a Xenon arc lamp situated in the lamp box at the back of the projector. A dowser, controlled by the black handle on the front of the lamp box, is used to prevent light reaching the film when the projector is not running. The dowser should always be closed while the projector motor is not running.
THE LAMP BOX MUST NEVER BE OPENED.
The bulb is powered from a separate power supply situated on the righthand side of the projector underneath windows facing into PX001. Power is first applied by the circuit breaker at near the spool tower. When this switch is turned on, check that the fans on top of the Lamp Box and on the power supply are running correctly.|
There are two switches on the front of the power supply, the power switch and the current selector switch. The current selector switch should always be set to 6, if it is not, or you have any questions, please ask the Technical Officer. To power the bulb, switch the power switch on the front of the supply from 'off' to 'on'. Check that both lights on the supply are alight, and the dowser on the lamp box is shut, then go to the back of the projector, and briefly but firmly press the red striker switch. If the bulb does not strike first time, seek help from the technical officer.
The projector is powered from a plug just above the bulb power supply. Switch the plug on while setting up.
The bulb supply delivers a stabilised DC voltage for the bulb. During use the meter on the front of the power supply should read from 75 to 85 amps. If this gauge exceeds 85 amps for more than a short period, the lamp should be turned off immediately using the switch on the power supply!, and help sought from the Technical Officer. Do not switch the power supply off at the circuit breaker on the wall, as this will turn the fans off possibly causing an explosion.
The sound head has a separate bulb that shines light through the sound track at the side of the film, and onto a photo cell. It is powered from the switch on the back of the projector.
Care should be taken when cleaning this area not to upset components of the sound head - they are critically set.
Films arrive in reels lasting about twenty minutes. This is a hangover from the early days of film, where films were lit from carbon arc lamps. These lamps had carbon electrodes that were gradually burnt up, and lasted about twenty minutes. It was therefore convenient to make reels the same size, as they could then both be changed at the same time.
When xenon lamps started to be used, the fixed reel size had become a standard, and it has remained the same ever since. However, as the xenon lamps could be kept on for long periods of time, it made sense to only have one projector instead of two, saving money. The reels of film are joined together with optical tape, forming one large reel. This can then be shown in one go, without having to keep changing reels. It is especially popular with multiples cinemas, who show the same film over and over again. It is this single projector system that we use. The process of joining the reels together is called making up, and the process of separating them again is called making down.
format uses the whole frame on the film (the most logical) and the image on the screen is in roughly the same format as a TV; i.e., 4:3 aspect ratio.
This is the oldest of the formats, and is only really used on the oldest of films, and the odd short.
('Scope) was developed to provide film makers with a much more impressive view of the world. Its larger format used the whole frame, and so did not suffer any loss of resolution, while providing an extra wide and expansive picture on the screen.
developed later, as a cut down and cheaper form of 'Scope. It does not use the whole frame, rather a narrow band in the middle is used to give a wide picture on the screen. This is cheaper than 'Scope, as no special lenses are needed to film and project. What you lose, however, is quality of picture. Because you are not using the whole frame, you lose picture area that you could otherwise be using. Due to the increased quality and resolution of modern film, this is no longer a problem and you will be hard pressed to tell the difference in quality between widescreen and 'Scope, except that 'Scope has a slightly larger aspect ratio (ratio of height to width).
Note: Some Widescreen films are, in fact, full frame, but with no distortion. This is to make it easier to copy the film to video. These should be shown with the Widescreen lens and mask as normal.
A frame of film, without sprocket holes. The sound track is the two white lines along the left hand side.
It should be noted that the film actually runs through the projector upside down, so the sound track will be on the right hand side in the projector
(the side nearest to you). There are several different sound formats, both digital and analogue. We currently only use linear optical (analogue) sound,
either Dolby A, or Mono. Here is a brief description of all the currently used sound formats:
|Optical Mono||Twin linear tracks, each with the same information.|
|Optical Stereo||May be either Dolby 'A' or Dolby SR encoded (both systems are surround).|
|DTS||A digital format where the sound is stored on a set of CD's and synchronised to the film by a digital time code track between the linear optical track, and the picture.|
|Dolby Digital||A digital format with the digital information written in between the sprocket holes on the soundtrack side of the film.|
|SDDS||Yet another digital format pioneered by Sony; digital information is written along both edges of the film in a continuous band. The best sounding of the digital systems (in the correct location).|
|Various magnetic formats||Before optical sound was invented, sound was recorded in magnetic stripes where the optical track now is. Better quality than optical, it suffered due to the magnetic material peeling off the film.|
The Spool Tower
YSC uses a Westrex double sided spool tower. The spool tower holds the film and supplies it to the projector. It has two sides, and can be spun around, so that either side can be used for projecting. The projector needs the film to be passed to it with a given tension, and this is done by the spool tower. In addition to this, the other side of the tower can be used to make up and down the reels of film. The spool tower can be rotated, so either side can be used for rewinding / making up or down, or for playing. A control switch controls which side is used for rewind, and which is used for playback.
Spool Tower Controls
The spool tower has two separate sets of controls: one set for making up and down and rewinding, and another set for adjusting the tension of the film while playing.
The circles on the left and top of the control box are rotary controls. The playback / rewind side control adjusts which side is used for play and which is used for rewind. The power controls switch power to the play and rewind controls respectively. The rotary controls adjust the power supplied to the spool spindles.
The power control switches should never be switched off while spools are in motion.
|The Playback Controls||The Rewind Controls|
|Before starting a film, the tension controls have to be set correctly to payoff film to the projector, and to take up film from the projector.
- Ensure playback control switch is set to the correct side.
- Set both play controls to 0.
- Switch playback power on with the play switch
- With you hands, take up slack in the top (payoff) spool.
- Adjust the payoff rotary control until it reads 130 (written on thetower).
- Do the same with the take up spool, adjusting the rotary control to145.
- The film is now ready to start.
- After the film is started. Adjust the take up tension to 130.
- Adjust the pay off tension control during the film in small steps, so it ends up at about 80 by the end of the film.
- At the end of the film, switch power off at the playback switch, and set the two dials to 0.
|The single rewind control adjusts the relative tension between the top and bottom reel on the rewind side. The rewind control switch shouldonly be turned off when the film is stationary, or has snapped, or has come off one reel.
To spool film from one reel to another:
- Take up any slack between the two reels.
- Set the rewind dial to its middle position.
- Switch the rewind power switch on, being ready to adjust the rewind dial to get the film moving in the correct direction.
- Use the rotary control to slow the film down until it is stopped in the correct position.
Switch off the control switch, being careful not to switch off the playback power control.
The Dolby System
The Dolby system used by YSC is a CP65
model Cinema Sound Processor.
Our equipment includes three amplifiers to decode the stereo sound from the optical sound track, and encodes it onto five channels. There are two stereo channels either side of the screen, a centre channel, a surround channel, and hopefully soon, a subbass. The left, right, and surround channels are all that is needed to provide surround sound, but the centre channel is added to lock dialogue sounds to the centre of the screen. This prevents the audience from hearing people taking from one direction, while they are somewhere else on the screen.
The Dolby system is, itself, very easy to use, care being needed only to avoid deafening the audience....
The Dolby System
The main controls for the projectionist are the main power switch, and the monitor controls. There is also a type player for playing music before films.
The system has two sets of main sound controls, one on the unit itself, and another beside the projector, next to the screen control. They provide switching between the various suound inputs, together with a mute switch and volume control. The controls are in parallel, apart from the volume control. The volume control can be set to be active either on the local pannel on the front of the main system, or on the remote control box situated beside the projector. The system is set so that on power up the system defaults to tape input (non-sync) and local volume control (the control on the main unit). This volume control should be set to 4 1/2. The projectionist will use the remote controls most of the time.
The main feature should be played at a volume of 6, while adverts should be played slightly lower, 5.5 - 5.75, however the projectionist should monitor the sound in the theatre to ensure that it is correct.
In addition to the main sound system, there is a set of mpnitor speakers. These are controlled by a selector switch and volume control on the front panel of the sound system rack. The switch can select any one of the output channels, or the non-synchronos input (the tape player). This is used to check the output from the speakers to ensure that they are all working correctly.
Back to Main
In addition to the other settings, there is a summed output that is the sum of all the speaker outputs. This is the normal setting for the monitors.