Film Gauge – 65 mm aka 70 mm film

When I was a kid someone gave me a film roll (negative). My friend and I took this to a room. As my friend lit torchlight I rolled the film in front of it. We placed a lens in front of the film and projected it onto a white dhoti hung on the wall. It was fascinating to see actual images on the white dhoti. They moved in discrete steps, as the roll was moving. My friend said the lines on the side contained sound but we did not know how to reproduce it. Still it was a fascinating experience. From then on we started collecting such films and tried projecting them. Some of these films were narrower and few of them were wider. We did not realize the wider ones were 70mm and the narrower ones were 35 mm film.

In this week’s Friday fundas I would talk about what the numbers actually mean.

You might guess that 70mm denotes a length of something. The unit denotes the “film gauge” which is the width of the film stock. The width of the film is actually 65 mm but is printed on 70 mm film. The additional 5 mm hold 4 magnetic strips that are used to hold 6 tracks of sound. In the later years 70 mm film used digital sound encoding.

70 mm film is a wide high-resolution format of movies. The aspect ratio of these movies were 2.20 : 1. Due to its wider length it produced a greater visual grandeur compared to its 35 mm predecessor. However the many of the theaters that time did not have 70 mm screen. Hence many of the 70 mm movies were released on 35 mm prints so that it can be widely distributed. Hence you see wide screen edition and a normal edition of a movie. 35 mm films had a aspect ration of 1.3 : 1.

When you look at a film negative you see holes punched on its ends. These holes are called perforations. In terms of perforations 35 mm film were 4 perforations tall and 70 mm film were 5 perforations tall. A horizontal variant of the 70 mm film was introduced and is widely used in IMAX screens. In this format a single frame covers 15 perforations.

The recent movie Jurassic World was shot on a 65 mm film the makers chose to do it to match the visual aesthetics of the previous trilogy. The film camera captures more dynamic range of light than that of a digital camera. Also they released it with an aspect ratio of 2:1, which suits the IMAX screen. Hence the movie would be more appealing on a IMAX screen than a normal screen.