IMAX 70 can't be used to record speech from actors because the cameras are extremely noisy and drown out their voices. This forces the use of other cameras for any scenes with dialog.
That is why the IMAX showings of Dark Knight/Dark Knight Rises/Interstellar/Dunkirk expand to the full IMAX height for non-speaking scenes, but collapse down to normal movie dimensions whenever someone is speaking.
Going to step up on a soapbox and rant at Hollywood for a bit......
What gets me is the way the rest of Hollywood tries to mimic Christopher Nolan's use of IMAX 70 film but most of them completely fail to understand the point of using such a medium (the point is the extremely high resolution). They waste tons of money recording scenes on super high resolution IMAX 70 film. Because the cameras are noisy they have record their dialog on a format that collapses the image back down to normal movie dimensions. And then after going to all that expense/trouble the only thing they do with all that high resolution raw footage is create a 4K digital master that is a small fraction of 70mm resolution and which could easily have been created with digital cameras.
Even worse, since digital cameras don't drown out people talking, had the morons not wastefully used IMAX film and instead used one of those digital cameras, they could have produced their entire movie at IMAX screen height instead of shrinking the picture whenever they encountered dialog.
4K digital resolution is 4096 × 2160. If you stretch those pixels to fit the full IMAX screen height, the image would fit an area equal to 4096 × 2864 non-stretched pixels. The Arri Alexa 65 digital camera has a resolution of 6560 x 3100 pixels, more than enough resolution to capture such an image.
Note on these IMDB technical pages "Negative Format - 65 mm (horizontal)
" and then under "Cinematographic Process
" there is no mention of any low-resolution digital intermediate:
The Dark Knight (2008)
The Dark Knight Rises (2012)
is how you properly
use 70mm IMAX to make a movie.
Now note on these IMDB technical pages "Negative Format - 65 mm (horizontal)
" and "Cinematographic Process - Digital Intermediate (4K) (master format)
Star Wars: The Force Awakens (2015)
Batman v Superman: Dawn of Justice (2016)
Star Wars: The Last Jedi (2017)
how you waste a ton of money on high resolution film stock producing a (comparatively) low resolution movie.
I'm not saying a 4K movie is bad. But if you make a 4K movie, for the love of God don't waste precious 70mm film on it. Use a digital camera instead.
And if you do waste IMAX film making a 4K movie, don't go blabbering about 70mm trying to fool people into thinking that your 4K film is somehow comparable to a Christopher Nolan production.
Not everyone in Hollywood is incompetent though. Here are two movies that are made with a 4K digital master, that used digital cameras and didn't waste any 70mm IMAX film to record at a resolution that they were never going to use, and as a consequence were able to record voice dialog without collapsing the tall IMAX image down to normal movie dimensions:
Avengers: Infinity War (2018)
If you're going to make an IMAX movie with a 4K digital master, that's
the proper way to do it.
Although I note that they made their movie so it only expands up to the partial height of a LIEmax theater rather than the full height of true IMAX. I guess they wanted their movies fully compatible with all IMAX screens. It should be possible for an enterprising filmmaker to use an Arri Alexa 65 to make a 4K movie that expands up to full IMAX height though, if he or she chooses to.
OK, I'm finished with my ranting.
Oh, one other thing. If anyone is confused over 65mm vs 70mm, they are the same thing. It is 65mm in the camera and 70mm in the projector. The extra 5mm are for audio tracks.