The black curtains that frame the picture are driven by motors between two set positions, wide and flat, and the motors log their run time for servicing. Screen 2's masking is found every morning at a position that is neither, narrower than anything we show, and the motors have logged a run in the night that nobody sent.
I am the technical manager for a two screen cinema, and the masking is one of the few moving parts in the building.
How it works.
Side masking is a pair of black curtains on tracks, driven by a motor each, and they stop on limit switches at two positions: wide, for scope films, and flat, for everything else. The automation sends one of two commands before a show. There is no third position, because there is no third shape of film, and the limit switches would stop it anyway.
The motors have hour counters, because the service contract is on hours.
Screen 2's masking is found most mornings at a third position.
Narrower than flat. The curtains sit about a metre in from the flat limit on each side, framing a picture that would be nearly square, taller than it is wide, a shape nothing we have ever shown comes in.
The motors' hour counters show a run in the night of about forty seconds each, which is about the time it takes to travel from flat to where they are found.
The automation log shows no command. The last command in it is the previous evening's, to flat, for the last show, and the masking was at flat when the usher cleared the room, because the usher checks.
There is nowhere to send the masking that is not wide or flat. The controller has two outputs. The position it is found in cannot be commanded.
What has been checked.
The motors, which are simple and old, and which have been serviced and had their brakes checked, because a motor with a failed brake can drift. A drifting motor does not log forty seconds of running time.
The limit switches. If the flat limit had failed the motors would overrun to the mechanical stop, which is wider, not narrower.
The controller, replaced in 2022. The night after it went in the masking was found at the third position with forty seconds on each motor.
And the position itself, which I have measured with a tape from the screen edge, eleven mornings. It is the same to within a couple of centimetres each time. Something is putting the masking at a specific place, repeatably, and the place is not one the system knows.
The ratio.
I worked out what shape it frames, because I am a technical manager and that is the kind of thing I do at two in the afternoon.
One point one nine to one. Taller than the standard early sound ratio, which is the squarest shape anybody has projected commercially in this country. Nothing has been made at that shape. I have asked people who would know.
What has been done about it.
Nothing needs to be. The morning check finds it, the usher sends it to flat from the panel, and it goes, and it stays there all day and behaves through every show.
The service company have the hour logs and have written that the motors are operating within their expected life and that the overnight run events are consistent with a command being issued, and that they cannot say from where.
What I do.
I check the automation logs and I do the morning walk.
The one change is that I do screen 2's morning walk from the back of the stalls and not from the front.
You check the masking from the front, because from the front you can see whether it is straight and seated in its tracks.
In 2023 I was at the front of screen 2 at half past eight, with the masking at its third position and the house lights at half, looking up at a near square of white screen framed in black, and the projector was off, and the screen was not white.
It was lit. Not bright. The faint grey that a screen has when something is being projected onto it at very low level, and there were shapes in it, and they moved the way a picture moves, and the masking was cut exactly to their edges, and I turned round and looked up at the porthole and the booth behind it was dark.