Report of Lens-Calibration Subcommittee

This subcommittee of the Standards Committee was appointed primarily to establish a standard method of photometrically calibrating diaphragm openings for motion picture camera lenses as distinguished from the well-known f system of aperture markings. The demand for a photometric type of aperture calibration (“T stop”) is becoming increasingly felt, and it has the advantage that diaphragms of any shape, pentagonal, scalloped, or irregular, can be correctly labeled with as much ease as a circular aperture. The presence or absence of antireflection coatings is automatically included in the calibration, and so also are factory variations in the focal length and in the iris mechanism. The illumination on the film in the center of the field will therefore be the same for all lenses at the same T stop, assuming that the object is a uniform plane surface perpendicular to the lens axis. It is implicit, also, that each lens shall be individually calibrated if the photometric method is used.

Print ISSN
Published
1949-10
Content type
Original Research
DOI
10.5594/J15203