The following tables may equally be considered to be “Focus Split” or even “Circle of Confusion Tables.” Depending upon which way they are used they may be used to determine:
- Depth of Field. (Given the focus distance together with the lens focal length, the acceptable c of c and the lens aperture, determine the Near and Far Distances in acceptable focus.)
- Focus Split. (Given the near and far distances, the lens focal length, the acceptable c of c and the lens aperture, determine the Focus Distance to hold that Focus Split.)
- Minimum Aperture. (Given the near and far distances, the lens focal length, the acceptable c of c and the lens aperture, determine the minimum aperture required to hold that focus split.)
- Maximum Focal Length. (Given the near and far distances, the accept able c of c and the lens aperture, determine the longest focal length with which it is possible to hold that split.)
- Acceptable Circle of Confusion. (Given an acceptable degree of ‘out–of–focusness’ of a known near and far distance, and the lens focal length and aperture, determine with what minimum c of c it is possible to hold that focus split in acceptable focus.)
The c of c used in practical cinematography is as much a measure of acceptable ‘out–of–focusness’ as it is of ‘what–you–can–get–away–with.’
With older type lenses and/or with diffusion filters, fog filters, star filters and nets in front of the lens, and/or with smoke all over the set, etc., everything is unsharp and it is possible to get away with a c of c of 1/500”, or even larger. With average lenses, 1/1000” is a reasonable starting point but with PANAVISION PRIMO lenses, be they prime or zoom, with no diffusion of any kind, contrasty lighting and wanting a maximum hard look then 1/2000”, or even smaller, is what is needed.
There is only one sure way to tell what is the correct c of c to work to and that is to know what you did and what you expected on a previous test or take and then to look at properly projected dailies to make a subjective judgement to apply to future set–ups.
To use the following tables it is recommended that the user first determine the largest c of c that is safe to use (top left of the table), then move along the line to the aperture to be used, then down the column to select the closest near and far distances to what is required and from there move to the left to note the Focus Distance. It will still be necessary to make a mental adjustment according to how close to reality the selected near and far distances are.
Note: The following tables are computer generated. They take into consideraton Entrance Pupil positions and the fact that we measure focus distances from the film plane. They should, however, only be taken as a guide and a basis for photographic tests.