Patent GB-699291-A (GB)
Title: Exposure indicator for taking photographs
IPC: G01J1/42
Filed: 1949-12-08
Abstract: 699,291. Photographic exposure indicators. CARQUILLAT, P. H. Dec. 8, 1949 [Dec. 8, 1948], No. 31548/49. Class 98 (i). The indicator, which may take the form shown in Figs. 1 and 2 or the form shown in Fig. 3, comprises a watch-like dial, Fig. 1, graduated at 32 to indicate the hours of the day, a pivoted hand corresponding to the hour hand of a watch movable in relation to the hour graduations, a plurality of scales 31 arranged concentrically about the hand pivot, each scale corresponding to a period of the year and being divided into sectors to represent arbitrarily the average provailing light intensity for selected hours (shown as dotted shading for 10 a.m. to 3 p.m. for June-July), circumferentially arranged guide marks 34 corresponding to the sectors, and, shown opposite to the guide marks 34, a scale 33 indicating periods of exposure. A movable scale carrying member arranged rotatably on the watch-like dial, but shown separately in Fig. 2, is provided with a circumferentially arranged arbitrary correction scale having indices 35 concerning, collectively, atmospheric conditions, subject to be photo. graphed and speed of emulsion to be used, and, opposite to the correction indices, a scale of lens aperture ranges 36; whereby rotation of the movable member of Fig. 2 to bring a selected correction index (35) into coincidence with a guide mark (34) corresponding to the pre. vailing light intensity of the time of day and period of year enables a lens aperture 36 corresponding to any chosen exposure period 33 to be selected. The correction index (35) to be used for any set of conditions is simply the sum of chosen numerals from scale A (Fig. 2) representing conditions of the sky, scale B for values with regard to varying subjects to be photographed, and scale C for emulsion speeds. The indicator may constitute a real watch with a rotatable cover glass inscribed with the features shown in Fig. 2. In Fig. 3 the watch-like dial is provided with similar concentric scales, now designated " 47," and correspondingly shaded guide marks 42, and is provided also with eight conventionalized drawings 43. Of two rotatable scale carrying members the inner carries indices 44 corresponding to atmospheric conditions and a scale 46 of lens aperture ranges, and the outer carries indices 45 corresponding to emulsion speeds and a scale 41 of periods of exposure; whereby rotation of the inner member to bring a selected index 44 into coincidence with one of the drawings 43, and then rotation of the outer member to bring an index 45 into coincidence with a guide mark 42 corresponding to the shading of the concentric scale 47 for a particular hour and period of the year, a lens aperture 46 corresponding to any chosen exposure period 41 may be selected. The Specification as open to inspection under Sect. 91 comprises also an indicator characterized by clockwork mechanism adapted to move a movable scale in terms of the hour of the day and of the season of the year and by at least one other movable scale. This subject-matter does not appear in the Specification as accepted.