70mm celluloid film is cinema’s premier format. In the “golden age” of cinema films were often shot on 70mm reels and then reduced down to the more pedestrian, and more portable 35mm format (like the stuff we put in our cameras).
When used in cinema 70mm looks sharper and more defined than a film that is shot in 35mm, this is because the 70mm image is larger to start with, being twice as wide.
As the film is much bigger than 35mm there is more space to store “extra” information such as sound data. In fact it is possible to store 6 channels of totally uncompressed sound on a frame of 70mm film on magnetic strips running along the side of the frame.
70mm film is capable of producing a more refined image and better quality sound. Unfortunately 70mm films are hard to come by because of the rise of lenses that make a film look like it’s 70mm; e.g. Cinemascope, Super35, and Panavision. Due to cost very few films are shot or distributed in the format as very few cinemas have the capacity to show 70mm films as it is cheaper to buy Anamorphic lenses.