GB617418A - Improvements in densitometers - Google Patents

Abstract

617,418. Densitometers utilizing photoelectric cells. KODAK, Ltd. Aug. 20, 1945, No. 21181. Convention date, Aug. 19, 1944. [Class 40 (iii)] [Also in Group XX] A densitometer comprises two independently adjustable density wedges and an illuminating device passing a light beam through a sensitometric strip or photograph and through said wedges, one of the wedges being associated with a scale indicating the density of selected steps of the strip or selected areas of the photograph and the other wedge being associated with a scale indicating the difference in density between any two of said selected steps or areas, preferably in terms of gamma. As shown in Fig. 5, a sensitometric strip 25 is placed over an aperture 14 in a housing (not shown) which carries therewithin two density wedges 22, 27 and a lamp 12. The latter is surrounded by a shutter 35, apertured at 36, which is rotatable to direct the light from the lamp alternately along a path through the wedges and strip and along an indirect path 19; these light paths intersect at a semi-reflector 15, above which is disposed a photo-electric cell 37 connected with a power supply 39 and a meter 44. Thus, the cell 37 alternately receives light which has passed through the wedges and strip and light which has followed the path 19. In operation, the strip is first removed and with the densest part of each wedge in the direct light beam the intensities of the beams are adjusted until photometric balance, indicated by zero reading on the meter, is attained. One step of the strip is then placed over the apertures and wedge 22 rotated until a zero reading is again obtained. Another step of the strip 25 is now placed over the aperture and the wedge 27 is rotated until the reading on the meter is again zero. Wedge 27 has a scale indicating gamma, the reading on this scale after adjustment of the wedge thereby giving the gamma of the strip 25. In another embodiment, the photoelectric cell and meter are not employed, photometric balances being judged by an observer of the reflector 15. The Specification as open to inspection under Sect. 91 describes an embodiment wherein light from the lamp follows the direct path only to a photo-electric cell 53, Fig. 5 (Cancelled), coupled with a power supply and a meter 56. This meter has a density scale 57 and a pointer 58, to which is imparted equal movements for equal changes in the density of the selected steps of strip 25. Above scale 57 is arranged a scale 60, indicating gamma, which is movable by a rack and pinion so that its zero mark coincides with the position of the pointer, when the latter has moved to indicate on scale 57 the density of one step of the strip. Thus, when a second step of the strip is positioned in the light path, the reading on the scale 60 corresponding to the new position of the pointer gives the gamma for the strip. This subjectmatter does not appear in the Specification as accepted.