Compensation of the Aperture Ratio Markings of a Photographic Lens for Absorption, Reflection, and Vignetting Losses

At present the diaphragm markings of a photographic lens are based entirely upon geometrical considerations and do not take into account the losses of light resulting from absorption, reflection, and scattering. A method of equivalent marking is described in which, for example, the marking 8 does not correspond to the geometrically determined aperture ratio 1:8 but to an opening sufficiently larger to permit the transmission of as much light as would be transmitted by the aperture 1:8 in the absence of any losses due to absorption, reflection, and vignetting. Such a system of apertures may be referred to as equivalent or compensated apertures. — Two systems of compensation are given, one based upon the illumination at the center of the field and the other based upon the average illumination over the entire field thus taking vignetting into account. A relatively simple photometric procedure for determining either of the two systems of compensated graduation is described. For use during a transition period a system of markings is described which will permit exposures to be determined either with light losses compensated or by the present method without compensation. Except for the change of markings on a lens no other instrumental changes are required to apply the new system of exposure determination.

Print ISSN

0097-5834

Published

1947-08

Content type

Original Research

DOI

10.5594/J17821