Patent GB-528851-A (GB)
Title: Improved photographic apparatus
IPC: G03B27/58
Filed: 1939-04-29
Abstract: 528,851. Photographic cameras. WATSON & SONS., Ltd., W., PERKINS, S., and FRY, C. H. April 29, 1939, No. 12885. [Class 98 (i)] In a camera having an adjustable mark for varying the size of the exposure aperture and means for correspondingly varying the amount of film fed at each operation of the feeding means, a constant-stroke operating member operates through a variable-ratio connection a driven member which engages and feeds the film, and selecting means are connected to both the variable-ratio connection and to the mask so that the latter is automatically adjusted in accordance with the mask setting to feed the film through a distance corresponding to the size of the exposure aperture when the operating member is moved through its constant stroke. In the document-copying camera shown the film is fed and the sliding-plate shutter is set and released at each operation of a rock-shaft 56, which may be performed by a lever 171 secured to it or by a Bowden cable operated by a pedal 179, the cable passing round a drum 175 having an arcuate slot in which engages a pin 174 projecting from the lever 171. When the drum is rotated by the cable the end of the slot engages the pin and operates the lever, but the latter may be operated independently by hand. Coiled springs 173, 197 respectively return the arm 171 and drum 175. Film-feed. The detachable film magazine 12, the lower edges of which engage in grooves in the top of the lower housing containing the mechanism, is divided by a partition 24 into two compartments, one containing a take-off spool 25, from which the film passes over a sprocket 27 and through the film gate to a driver sprocket 29, and thence to a take-up spool 30 in the other compartment. The sprocket 29 and take-up spool 30 are driven, the latter through a slipping clutch, through gearing (not shown) from a gear 47 (Fig. 7) which is rotated through a two-ratic gear from the rock-shaft 56. The two-ratio gear includes a main driving gear 58 loose on the shaft 56 and rotated by it through a ratchet and pawl 59, 60, to gether with idler gears 51 52 meshing with it, these latter being carried between a pair of plates 54, 55 pivotally carried on the shaft 56. When negatives of half the full size are to be taken the idler 25 mesheswith and drives the gear 47, as shown in Fig. 7. When full-size negatives are being taken, the plates 54, 55 are rocked about the shaft 56 to disengage the idler 52 and cause the idler 51 to mesh with a gear 53 fast with the gear 47 and of half its diameter, so that the film is fed through twice the distance at each operation. The plates 54, 55 are rocked by means of a cam 124 on a shaft 125 operated by an external knob, the cam operating in a rectangular recess in a link 121 pivoted to the plates, a further cam 127 operating a lever 128 having a nose 130 which engages in one of a pair of notches 131, 132, in the plate 55 to lock the plates in either position. Simultaneously, a slidable masking plate 106 having an opening 107 of the smaller picture size is moved over or away from the exposure aperture by a linkage system comprising arms 109, 111 rotatable on a spindle 110, connected by a link 102 to the masking plate and by a link 115 to a lever 116 which is pivoted at 17 and is rocked by a pin 119 on the plate 55. A spring connection between the arm 111 and link 115 allows excess movement to be given to the parts 116, 115 to eliminate the effects of imperfections in the linkage. Shutter-setting mechanism. The shutter comprises two sliding blades 75, 101, shown in Fig. 2 in the unset position. They are operated respectively by arms 70, 98 having bent ends with apertures in which engage pins 74, 100 secured to the blades. Coil-springs about the pivots of the arms tend to turn them in an anticlockwise direction. The rotation of the shaft 56 causes a pin 68 carried by a disc 63 on the shaft to move a slotted link 67 pivoted to the arm 70 to the right, thereby rotating the arm 70 clockwise and moving the shutter blade 75 to the set position, in which it is held by a latch 193, which engages behind a lug 195 on it. The blade 101 is pushed by the blade 75 to the set position, in which it is held by a latch 93, which engages a pin 96 on the arm 98. Simultaneously with these movements a slotted link 78, Fig. 3 carried by a sector 76 secured to the shaft 56, rotates an arm 80 clockwise, together with an arm 83 on the same shaft, a pivoted finger 86 on the end of this latter arm wiping over a pin 146 on an escapement device 143. The arms 80, 83 are finally held by a latch 88 which engages a pin on a further arm 220 on the same shaft. Shutter release. On the return movement of the rock-shaft 56, during which the slotted links 67, 78 move idly, a pin 65 carried between flanges 63, 64, Fig. 9, trips the latch 193, releasing the blade 75. Towards the end of the movement of this blade a projection 90 on the arm 70 trips the latch 88, so releasing the arms 220, 83 and 80, which then move anti-clockwise under the action of a spring 199. The finger 86 on the arm 83 drives the escapement until it falls clear of the pin 146, when the right-hand end of the arm 220 rises and lifts a lever 92 which disengages the latch 93 to release the second blade. Automatically - timed exposures. Two escapements, giving two speed ranges, are mounted to be rocked about a common centre by means of a link 150, Fig. 1, pivoted to an arm 151 which is engaged by a cam 152 on the shaft 153 of the speed-adjusting knob, the angular adjustment of the escapements determining the point at which the finger 81 is freed and hence the time of exposure. To change from one speed range to the other, a cam 169, Fig. 9, is rotated to give axial movement to a spring-pressed shaft 262, an arm 167 on this shaft engaging the bush 46 of the escapement arm 83 which is thereby moved along its shaft to engage with the pin of one or other of the two escapements. For the fastest exposure the arm is adjusted so that the finger 86 passes between the two pins. Time exposures. The escapements are adjusted so that the pins are in a dead-centre position relative to the finger 86, which is thus permanently arrested when the first blade is released. The exposure is terminated by depression of a finger-lever 200, Fig. 3, which engages and lifts the lever 92 to release the latch 93 holding the second blade. To indicate that an exposure is being made, two switch contacts in series circuit with an indicating lamp 209 are closed by a projection 204 on the shutter blade 75 and a pin 206 on the arm 98 when the blades are in open position. A second lamp 211 is lit to indicate that the film spool 25 is nearly exhausted by the closure of a content by means of a blade 213 which engages the periphery of the film. A counter 187 indicating the exposures is operated by a chain 184 connected to a spring-retracted plate 183 which is moved to the left at each operation of the rock-shaft 56 by means of a projection 77 on the sector 76.