I just watched a (https://www.tiktok.com/t/ZPR3vNfYt/) of a guy in an IMAX projector room loading Dune 2 into the projector. But he first had to weave it through dozens of rollers. The film snaked all over the room, requiring the guy to duck under it to cross the room.
Why do they do this? Why can’t he just feed it straight into the projector and straight out?
In: Engineering
If the reel bit and the projector bit were built together in one machine, they’d be a lot harder to use and service. I also suspect that keeping the film far away from the heat of the projector is important. Routing the film all over the room is a small price to pay.
The main reason for all those extra rollers is to manage the slack between the storage platters and the projector. The extra loops act as a cushion.
For 70mm IMAX the film alone weights 500+ lbs and moves at 5.6 feet per second, so there’s a lot of momentum on those platters. If it came straight off and fed into the projector, any tiny hiccup could tear the film or damage the projector.
Secondary to the slack, those platter racks (“Quick Turn Reel Unit”) can hold 4-5 platters, with the film spooling off of any one level and back onto any other level. Thus a few of those rollers are just to get the film alignment off and on to the correct levels.
Thirdly, the green rollers near the back of the projector are sticky, and are meant to clean off any dust that’s on the film.
Fun facts about the QTRU: They are operated via a [Palm Pilot](https://www.reddit.com/r/imax/comments/152ybjn/havent_even_heard_of_palm_pilots_in_20_years/) (or an emulated Palm Pilot on an iPad) and they use [light bulbs from Mercedes](https://www.reddit.com/r/imax/comments/194fbak/imax_fun_fact/)
The reels are just way to dang big to do it.
You’ll note that that holder has several slots on it. So you can have multiple movies stored ready to go at the same time.
You need that because once a reel is put together you can’t actually pick it up in one piece by hand. It’s several hundred pounds per film. To get them on and off they are spliced from multiple smaller reels that can actually be lifted.
So given that the holder is fixed in place you need some space around it to be able to add in the rollers for shifting height and direction. They also need those multiple rollers in small areas with a zig zag (those sets of 4) to maintain good tension and keep things from just flapping around. At the speeds the film is going through them it’s becomes an aerodynamic issue.
One time I saw this they were using 1 reel of film to project into 3 different theatres. They had set up pulleys and rollers and springs and had it all lined up ready to roll. It was a success, however this wasn’t IMAX, but it could be done with IMAX.
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