GB748083A - Improvements in or relating to photographic exposure meters - Google Patents

Abstract

748,083. Photo-electric exposure meter. SANGAMO WESTON, Ltd. Nov. 20, 1952 [Dec. 20, 1951], No. 29369/52. Class 40 (3). [Also in Group XX] A meter comprising a casing 10 having at one side a photo-cell 18 exposable to light through an aperture 17 in the casing and at the opposite side a moving coil electrical measuring unit (Fig. 1, not shown) having a pointer actuated in response to the photo-cell current, a scale for the pointer calibrated to read in one of the exposure factors consisting of camera diaphragm stop, film speed, and shutter speed, and a masking disc 28 pivotally mounted at 29 on the outside of the casing so as to vary the aperture of the photo-cell and calibrated in another of the exposure factors 30, said disc being rotatable with respect to a fixed set of marks 23, 24 representing the third exposure factor. As shown, the disc 28 may bear a scale of film speeds arranged so that for settings indicating increasing speeds the exposed area of the cell increases, the marks 23, 24 indicate shutter speeds, viz. 1/34 and 1/50 second, respectively, corresponding also to 16 and 24 frames per second, and the electrical meter scale is calibrated in diaphragm stops. Alternatively, the masking disc scale indicates exposure times and the fixed marks represent film speeds or the electrical metal scale may indicate shutter speeds and the masking disc scale may represent film speed or diaphragm stops. Preferably, the masking disc has an opening 31 overlaying the photo-cell when the disc covers a major portion of the aperture 17 so as to minimize the differences in response of different parts of the cell. The meter may carry a table showing the relationship between the exposure factor in which the electrical meter scale is calibrated and that indicated by either the scale on the masking disc or the fixed scale, the table preferably being visible in the window of the electrical meter. The member 22 carrying the fixed scale may be adjustable for calibration purposes, as may the zero setting screw 19 of the electrical meter.