Patent GB-535994-A (GB)
Title: Improvements in or relating to automatic diaphragm control mechanism for photographic cameras
IPC: G03B7/12
Filed: 1940-05-08
Abstract: 535,994. Photo-electric control of photographic exposure. KODAK, Ltd. May 8, 1940, No. 8276. Convention date, July 26, 1939. Addition to 451,658 and 451,659. [Class 40 (iii)] [Also in Group XX] The invention of the parent Specifications, in which the diaphragm of a camera objective is manually adjusted to an opening determined by a stop formed by a meter element which is set by the output from a photo-electric cell and locked in this position prior to being engaged by the diaphragm setting mechanism, is applied to a camera comprising an iris diaphragm needing unequal angular adjustments of the blade ring for producing successive F/apertures, together with a cell-controlled meter element moving in successively longer steps for each equal increase of light intensity. The cell-controlled element serves as a stop for a movable follower member, which in moving up to the stop, effects corresponding movement of the diaphragm through cam means. In the kinematograph camera shown, a photo-electric cell C, is connected to the moving coil 46 of a meter, the coil being pivotally mounted between the poles of a magnet 49 and carrying a pointer 50. On depression of the release lever 18 a pin 20 carried by it and operating in a slotted lug 23a bent rearwardly from a slidable plate 23 raises this plate, which is formed with slots 24 engaged by guide pins 25. A forwardly-bent lug 56 on the plate 23 is thus moved out of engagement with a bracket 57 on one arm 52 of an arcuate comb member 51 the comb being then turned rearwardly, about its pivots 53, by a spring 55 to trap the pointer 50 between two of the comb teeth in the position it has been caused to occupy by the output from the photoelectric cell. The plate 23 is formed with a shoulder 40 engaging a pin 39 on a follower member or arm 37 which is pivoted at 38, so that as the plate 23 moves upwardly it allows a spring 41 to turn the follower 37 in an anticlockwise direction until it is arrested by the engagement of lugs 58 on its end with the pointer 50. During this movement, a pin 43 on the follower 37 operating in a cam slot 36 in a cam member 34 rotates the latter about its pivot 35, the member 34 operating the blade ring 29 of the iris diaphragm through a pin and slot connection 32, 33. The cam slot 23 is so formed as to give the correct aperture corresponding to the light intensity, despite the fact that the movement of the pointer 50 and the necessary movements of the diaphragm ring respectively increase and decrease for equal increments in light intensity as this intensity increases. Towards the end of the vertical movement of the plate 23 the lug 23a raises a slide-bar 16 to disengage it from the tooth 17 of a stop member 15, thus releasing the operating mechanism of the camera. To prevent operation of the camera in insufficient light, a pivoted latch 59 urged in a clockwise direction by a spring 61 is provided with a lug 60 which normally lies in the path of a hook 63 on the plate 23, so preventing movement of the latter. When the light is sufficient the initial movement of the follower 37 allowed by the pointer 50 causes a lug 62 on it to engage the lug 60 of the latch 59 and turn it out of the path of the hook 63. Should it be desired to make an exposure despite insufficiency of light the latch may be removed to inoperative position by a press-button 64.