Abstract

It has been proposed that the speed of a photographic emulsion be specified upon the basis of the exposure value at which the gradient of the H and D characteristic becomes equal to a definite fraction of the average gradient throughout the tonal range used in making the camera exposure. The adoption of such a criterion necessitates the use of easily applied methods and special instruments for the determination of gradients and gradient ratios. In this paper a number of such methods and instruments are discussed under the following headings: (1) The graphical method. (2) A device for reading speed directly from the plotted characteristic curve. (3) A direct visual photometric method (using a wedged sensitometric strip). (4) An alternative direct visual method (using a triple sensitometric wedge and a special photometric field). (5) A direct photoelectric method of measuring gradient (which reduces the error in gradient determination occurring in visual photometry). (6) A photoelectric method incorporating a constant gradient ratio device (which eliminates the need of mental calculation). (7) Making automatic the determination of speed (pointing out means for automatic recording of results). Errors introduced by non-uniformity of coating and processing and means for minimizing these errors are discussed.

© 1939 Optical Society of America

Minimum Useful Gradient as a Criterion of Photographic Speed*

Loyd A. Jones and M. E. Russell
J. Opt. Soc. Am. 25(12) 396-411 (1935)

Graphical Analysis of Photographic Exposure and a New Theoretical Formulation of the H and D Curve*

J. H. Webb
J. Opt. Soc. Am. 29(8) 314-326 (1939)

Simple Methods for Approximating the Fractional Gradient Speeds of Photographic Materials*

C. N. Nelson and J. L. Simonds
J. Opt. Soc. Am. 46(5) 324-333 (1956)

A Note on the Color Temperature-Candlepower Characteristic of Tungsten Lamps*

K. S. Weaver and H. E. Hussong
J. Opt. Soc. Am. 29(1) 16-19 (1939)

The Koremetron: An Instrument for Measuring Pupillary Diameters

R. Clark Jones
J. Opt. Soc. Am. 29(12) 531-534 (1939)