An Improved Sector Wheel for Hurter and Driffield Sensitometry
WEFIND in “Investigations on the Theory of the Photographic process,”1 that as early as 1840 the sector wheel, a disk with successively increasing angular apertures, was proposed by Claudet. Hurter and Driffield adopted a sector wheel having nine apertures, ranging from 180 degrees for the largest, to 0.703 degrees for the smallest, each succeeding angular aperture from the center being half that of the preceding one (Fig. A). The disk is caused to revolve before a light source usually at one meter distance. A sensitive photographic emulsion, sufficiently exposed behind such a disk, is impressed with nine different light exposures, the ratio of any adjacent pair being as 1 : 2. The radius of this disk, measuring from the center to the circle including the outermost aperture, is about 12 cm. The usual procedure is to expose to a constant light intensity for different times as occasion demands.
- Print ISSN
- 0096-6460
- Published
- 1925-05
- Content type
- Original Research
- DOI
- 10.5594/J10335