Basic principles of projection

Part four : Screen formats

Numerous screen formats have been in use and will continue to be in use. Main aim of all the different formats is to mimic real life as much as possible. In fact to provide the eye with as much as it can handle. The table shown here shows the different formats as are current today.

Film masks and focal points of lenses play a crucial role in achieving the illusion.
Two filmmasks. They are used to limit the area of film which is exposed to the projection light beam. Normally the size of the opening is a little bit less the total exposed film frame during shooting of the film. In case this area is not proper aligned or not matching the screen aperture in the theatre you will be distracted from the picture by e.g. a projected sound track, projected perforation, images partly projected on the walls or ceilings of the theatre or by vague borders on the white projection screen.
The masks in the picture are part of my projector at home. You see the Normal and the WideScreen masks. (Which mask for what format? Perhaps you can tell by now.)

Format relative size aperture size
in mm
Normal 1 : 1.37 15,2 : 20.9
Widescreen 1.66 1 : 1.66 12.6 : 20.9
Widescreen 1.75 1 : 1.75 11.9 : 20.9
Widescreen 1.85 1 : 1.85 11.3 : 20.9

Optical sound
1 : 2.35 18.2 : 21.3
magnetic sound
1 : 2.55 18.2 : 23.4
Combi print
1 : 2.35 18.2 : 21.3
Superscope 1 : 2 18.2 : 18.2

Source : "Handboek der Bioscooptechniek Deel 1" 1957 ;
Stichting "Instituut voor opleiding van technisch bioscooppersoneel"

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