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Calculates the depth of field of an optical system as a function of the aperture diameter, the focal length, the distance from the primary principal plane to the object plane and the maximum spot size authorized. The aperture is located on a principal plane (primary principal plane if in the object space or secondary principal plane if in the image space).

The depth of field is defined there as the distance between the limit positions of the object plane for which the spot size in the fixed image plane is equal to the maximum authorized diameter.