On the set of Ben-Hur, 1959 - Academy Award winning director William Wyler looks through his finder attached to a giant Ultra Panavision 65mm camera. Though there was a bit of parallax, directors could get a solid sense of the frame and the camera operating. Gone are the days where directors sit next to the camera and get a real feel for what's happening on set. Peter Weir still sits nearby, but no one else I can remember does. The reason the camera looks so massive is because it is enclosed in a sound blimp. 65mm camera's were very noisy in the 50's, so for dialogue scenes the blimp was a critical part of production. All in, the camera, lenses, accessories, blimp and head weighed around 200 lbs. No Hand Held shots in this format! The other unique feature of Ultra Panavision was that it put a 1.25 anamorphic squeeze on the 65 frame rendering a wide screen aspect ratio of an eye-popping 2.76:1.
The "70" refers to the release print which was 2.5 mm wider on each side of the original 65mm color negative. In these 2.5mm margins resided the magnetic sound track.
After a hiatus of nearly 50 years - director Quentin Tarantino and cinematographer Robert Richardson, ASC, revived the format with some of the original Panavision lenses (re-housed) for "The Hateful Eight".
As far as I know - this is the widest aspect ratio Hollywood ever projected for any commercial theatrical release.