Patent GB-684684-A (GB)
Title: Improvements in or relating to photographic cameras and shutter mechanism therefor
IPC: G03B9/42
Filed: 1949-10-05
Abstract: 684,684. Focal plane shutters. MAYO, A. C. Sept. 22, 1950 [Oct. 5, 1949], No. 25594/49, Class 98 (i). The shutter system of photographic camera includes leading and trailing shutters which move in succession across the picture gate for an exposure, one shutter comprising a group of overlapping relatively slidable plates movable from a telescoped position in which they lie wholly to one side of the picture gate to an extended position in which they form a blind extending wholly over the picture gate, the other shutter comprising a similar group of plates movable from a telescoped position in which they lie wholly to the other side of the picture gate to an extended position in which they form a blind extending wholly over the picture gate, and the plates of each shutter are provided with interengaging portions to retain them in overlapping relation when the shutter is extended. The camera shown includes a removable chassis 13 carrying the shutter and film winding mechanism. This chassis comprises a die casting 27, Fig. 5, having upper and lower plates 28, 29 separated by vertical struts 33 and secured to the casting is a back wall 34 and a front wall 35. and a front wall 35. Between the wall 35 and the front wall 31 of a shutter housing 32 extends a light tunnel 37 and the walls 31, 34 and 35 have aligned apertures of which the aperture 36 in wall 34 forms a picture gate. Apertures 54 in rearwardly extending flanges 53 of the wall 31 accommodate bars 65 and through said apertures project the ends of bars 48, 49 respectively secured to flat plates 43, 46, Fig. 6, forming parts of a shutter system 38, 39 in the housing 32. As shown in Fig. 6, the plates 43, 46 of the shutters 38, 39 have ears 47 engaged by hooks on plates 42, 45 which are each formed with bent-over parts and are similarly attached to similar plates 41, 44. Each shutter when extended covers the picture gate 36, but, when telescoped, lies clear of the light path therethrough. An angle strip consisting of flanges 95 and 138 and secured to plate 46 provides self-capping of the shutter system. The bar 48 of the leading shutter 38 is linked at 56, Fig. 3, to arms 58 mounted to turn with a rod 69, journalled in lugs on the underside of plate 28 and having an arm 61 projecting through a notch in plate 28, and is linked at 57 to a rod 63 journalled in lugs 64 on struts 33 and having an arm 65 to which is secured a spring 66 anchored to plate 29 and urging the rod 63 to rotate in such direction as to pull bar 48 downwardly and thus telescope shutter 38. Bar 49 is linked at 67 to a rod 69 also journalled in the struts 33 and having an arm 71 spring urged at 72 to pull bar 49 downwardly and thus extend the trailing shutter 39; when this shutter is in extended position, the ears 47 on plate 44 thereof engage the upper edges of bars 55. The shutter system is set and the film is wound on by rotation of an external knob 78, Fig. 9, which is geared at 76, 75 to a film sprocket shaft 73, which drives an exposure counter 136, is mounted between the plates 28, 29 and has a squared end which projects through plate 28 and has a pinion 79 slidable thereon. This pinion is spring urged at 83 so that a boss therein normally engages a plate 127 and the pinion meshes with a sector gear 84, Figs. 8 and 9, pivoted at 85 on the plate 28 and having a projection 86, Fig. 8, lying in the path of the arm 61 of rod 59. Thus, as the knob 78 is rotated, the sprocket 74 winds on the film and the projection 86 rotates arm 61 whereby the shutter 38 is extended and the shutter 39 telescoped. Shutter 39 is held in its set position by a catch, pivoted on the wall 31 and having a nose spring urged to engage below the flange 95 of the angle strip attached to plate 46; shutter 38 is held in its set position by friction. The set position of the shutters is determined by a stop 88 on an adjustable plate 89 pivoted at 85, which stop co-operates with a stop pin 87 on the sector gear 84. Slidable between plate 28 and a guide plate 99 attached thereto is a striker 101 in the form of a flat metal strip. This striker is adjustably secured at 102 to a link 103 pivoted to an arm 104 which is itself pivoted at 105 and is spring connected at 106 with the striker. Arm 104 engages at 107 a cam 108 mounted on a shaft 109 on plate 28 for rotation through 180 degrees, such rotation being limited by a stop disc 112 also on the shaft 109. The cam is so shaped that at one limit of its rotation, the striker is at one end of its linear movement and rotation of the cam through 90 degrees moves the striker continuously towards the other end of its movement, further movement of the cam causing the striker to return towards its initial position and finally to reach a point beyond that which it occupies at the end of the first 90 degrees rotation of the cam. The rear edge of the striker includes straight portions 114, 115 joined by a ramp 116 and engaged behind the rear edge of the striker is a projection 119 on a rod 118 pivoted to the sector gear, this projection passing downwardly through a slot 121 in the plate 99. A plate 97 is pivoted below the upper edge thereof and said edge contacts fingers on the catch holding the shutter 39 in set position. When the projection 119 engages the straight portion 115 of the striker, said portion is prevented from rocking the plate 97, but when the projection engages the portion 114 of the striker, the portion 115 engages the plate 97 so that the catch and the shutter 39 are released. The position of the striker 101 relative to the projection 119 before release of the shutter system thus determines the exposure time and such position is controlled by the cam 108 operated by an external knob 113 marked with exposure times and co-operating with an index on the case. Knob 113 may be operated before or after the shutters are moved to the set position. Release of the shutter systems is effected by depressing a trigger 126 so that a plate 127 contacting the boss of pinion 79 is pressed downwards and the pinion 79 is thus moved to its lowered position against the action of spring 83 so that the sector gear 84 is released and the shutter 38 immediately telescopes under the action of the spring 66. At the same time, the projection 119 moves along the rear edge of the striker, which, when said projection moves along ramp 116 on to the straight portion 114, is rocked by spring 106 so that the straight portion 115 actuates the plate 97 to release the catch and the shutter 39, which moves to its extended position and thus terminates the exposure. For longer exposure times, movement of the striker, when the projection 119 reaches the ramp 116, is retarded by the engagement of a stud 123 on the striker with a retard mechanism 125. The plate 127 contacting the boss of pinion 79 is provided with downwardly projecting fingers 129, 131 of which the finger 129 acts as a guide and passes through aligned slots in the plates 99, 28. Finger 131 passes through a slot 134 in the guide plate 99 and is separated from plate 28 by, a spring. For a bulb exposure, striker 101 is moved by cam 108 until a projection 117 thereon is opposite the finger 131 so that when trigger 126 is depressed, the finger 131 moves into position to prevent movement of the striker to release the shutter 39 until the trigger is released. When a time exposure is desired, knob 113 is rotated so that cam 108 moves the striker to such a position that, upon release, the sector gear has returned to its initial position before the projection 119 has engaged the straight portion 114. In order to release the shutter 39 it is necessary in this case to rotate knob 113 in the reverse direction to move the striker so that the projection 119 moves down the ramp 116 and the straight portion 115 actuates the catch 92. The shutter system may be in form of flat plates linked together so that there is no overlap at the meeting edges of the two shutters and a separate capping shutter may be provided.