Originally Posted by imagic
The distribution of most films was via 35mm reels, but 70mm was often used for filming. Back in the pre-IMAX days, a film shot and presented in 70mm was the equivalent to 4K digital, which is now sold as an "IMAX presentation", or one of the other "premium auditorium" brands like Regal's RPX. What most people saw at their local theater, in the form of a 3'rd or 4'th gen 35mm dupe, was the equivalent of a movie filmed in 4K and presented in 2K, but with myriad issues that are directly related to film projection.
Here's an interesting read about "The Master", which was released in 70mm: http://twitchfilm.com/2012/09/jason-gorbers-cineruminations-70mm-4k-and-the-master-split-personality.html
It ought to be noted that there are differences between the 70mm used and distributed before IMAX was invented.
70mm "regular" 5perf. back in the heyday of 70mm widescreen until the early 1970's was a regular Medium Format stills film fed vertical through the film camera.
The IMAX 70mm is the same film stock but fed horizontal through the camera and is thereby about twice the image size and resolution of 8perf. 70mm, and about three times the image size and resolution of 5perf. 70mm, which was the format used for the most famous 70mm movie releases.
Some similarity of 35mm film, where the same film stock is used by 35mm movies as in 35mm stills cameras, which we now with DSLR know as Full Frame 35mm. The 35mm Cine film was fed vertical through the Cinema cameras and horizontal through stills cameras, giving Cinema movies about half the size and resolution of 35mm stills cameras.
Vista Vision used the same 35mm film stock fed horizontal through the camera (8prf. 35mm) and have then about double the size and resolution as regular 35mm Cinema film.
The Vista Vision name is best known for this format, but in reality the almost identical format called Technirama produced more features.
When 70mm was abandoned for cost and size reasons, it is very sad that studios went with 35mm vertical and didn't keep VistaVison/Technirama.
Then we would have at least had 40 years of twice the resolution in cinemas.