Depth of Field Calculations for Cinematography

The American Cinematographer Manual provides depth of field tables for 35mm and 16mm formats. The tables are based on the simplified depth of field equations. The DOFMaster programs can be used in place of the tables if the appropriate circle of confusion is used for a particular film format.

The 1986 edition of the manual recommends 0.025 mm (0.001 inch) for the circle of confusion for 35mm format. 0.015 mm (0.0006 inch) is recommended for 16mm format. Earlier editions recommended somewhat larger circles of confusion.

The f-number, rather than the T-stop, should be used in depth of field calculations. The depth of field equations were derived using the physical diameter of the lens opening. The f-number defines the actual diameter of the aperture, while a T-stop is a measure of the light transmission of a lens.

Here's an good article by Peter Gray about depth of field in cinematography.