>>4301821It's a little confusing, but there's 65mm film and 70mm film. I believe imax is shot on 65mm and then copied onto 70mm positive film and the extra space lets you put the sound info on the film. Maybe. All that really matters is that you can only get kodak vision3 films on 65mm format, so you need to adapt spools/film backs if you wanted to shoot it on 70mm cameras.
There's a few 70mm film stocks that you can get on ebay. Agfa aviphot is one, and sometimes you can get kodak spools like this plusx aerial.
Imagine 120 film, but with added sprockets on both sides to make it 70mm, and no backing paper.
This is one of my aerial cameras. She's a really baddy, and a lot of fun to use with an external viewfinder. The expired plusx is very grainy, but the images are coming out very sharp. I have a few more to go through then I'll post some.
It has a 15 or 16 blade aperture for some reason, and it uses a curtain shutter to expose 6x6 negatives. Very satisfying cocking and shutter release sound.