Patent GB-677228-A (GB)
Title: Improvements in or relating to photographic camera shutter mechanism
IPC: G03B9/10
Filed: 1948-01-07
Abstract: 677,228. Photographic shutters. INTERNATIONAL POLAROID CORPORATION. Jan. 7, 1948 [Feb. 7, 1947], No. 498/48. Class 98 (i). A photographic shutter comprises means for holding the closure element stationary covering the camera exposure aperture, means for applying a sharp impact to said member to free it from the holding means and to rotate it, and a rebound member disposed in the path of said rotary movement so as to engage a part moving with said element and arranged to apply through an elastic member a reversing movement to the closure element, said rebound and impact-applying members being mounted so as to engage the closure member for only a small portion of its total travel and the holding means being adapted to re-engage and hold the closure element upon its return to its normal stationary position. As shown, a shutter blade 12 having a hub 20 and a counterweight 14 is rotatably mounted by means of a shaft 22 secured to the hub in fixed bearings 26 and is normally held to close the exposure aperture by a horseshoe magnet 30 which attracts a block of magnetic material 32 carried by the counterweight. The shutter is opened by applying an impulse to the edge 40a of a lug 40 on the counterweight so that the shutter blade rotates clockwise until it reaches a spring 42 from which it rebounds to close the exposure aperture, the blade 12 being finally arrested by the magnet 30 which is attached to a shock-absorbing block 34 and slidable in a guide 36, 36a, a pin 38 holding the magnet in the guide. The length of the exposure is adjusted by moving the rebound spring 42 which is carried on a toothed wheel 44 having a hub 48 freely rotatable on a fixed axle 50 secured concentrically with the shaft 22 to the fixed arms 26, a pinion 64 engaging the wheel being rotatable by a knob 66. Stops 56, 58 engaged by a pin 60 on the wheel limit its movement, and a ball catch 54 locks the wheel at chosen exposure time settings. A diaphragm plate 16 provided with apertures of different sizes is rotatably mounted on a fixed axle 70 arranged concentrically of the axle 50 and shaft 22 and is adjustable to positions determined by a ball catch 86 by means of a pinion 74 rotated by knob 76 engaging the toothed periphery 72 of the plate, the limits of rotation of the plate being determined by a pin 89 on it engaging lugs as 88. As shown, the shutter blade is about to open the aperture. At rest, the trigger arm 112 pivoted to the casing at 110 and having an operating handle 116 urged clockwise by a spring 122 rests against a stop 128 and an arm 108 pivoted at 110 on the trigger rests against a stop 126. A bell-crank lever pivoted at 106 on the arm 108 has one arm 90 engaging the edge 40a of the lug 40 and this arm carries a shoulder 93 which is engaged by a recess 94a at the end of an anticlockwise-pressed pivoted latch arm 94. On moving the handle 116 to the right, the trigger 112 and arm 108 move anti-clockwise and a lateral arm 124 on the trigger engages the latch 94 so that when the lever 108 is engaged by a pin 114 the latch is moved clear of the shoulder 93, whereupon the arm 90 under the pull of the spring 92 drives the lug 40 clockwise to make an exposure. The travel of the bell-crank lever is limited by its arm 104 striking the pin 114 but prior to this the arm 90 strikes a pair of springy arms 102, which may be switch contacts in a flashlamp circuit, and which together with the greater power of spring 122 overcoming spring 92 reverse the direction of movement of the arm 90 to return it to the rest position, tensioning the spring 92 driving the impulse-applying member 90, when the shoulder 93 rides along the nose 94c of the latch into the recess 94a. For bulb exposures, a slidably-mounted arm 140 is withdrawn to a position determined by a dog 152 on it engaging the casing 18. This movement causes a bell-crank lever 132 to be rotated clockwise by engagement of an extension 138 on the lever 132 in a slot 144 in the arm 140 and a spring arm 130 on the lever 132 to be moved into the path of the lug 40. An arm 154 pivoted on the trigger at 156 and urged counterclockwise by a spring 158 rests on the edge 160a of an arm 160 projecting from the lever 132. On operating the trigger the shutter blade lug brushes past the spring arm 130 but on its return after rebounding from the spring 42 the blade is latched by the arm 130 engaging the edge 40a of the lug, while the arm 154 slips off the edge 160a and rotates anti-clockwise into contact with the edge 140a of the arm 140. On releasing the handle 116 to allow the shutter to close under the action of a weak coil-spring 136, the arm 154 moves upwardly and strikes the edge 160b of the arm 160 rotating the bellcrank lever anti-clockwise and simultaneously freeing the blade lug and moving the arm 140 inwardly so that a spring latch 146 mounted on a guide 148 enters a recess 150 in the arm, the arm 154 finally sliding off the edge 160b into contact with the edge 160a. During instantaneous exposures the arm 154 slides past the edges 160a, 140a without moving them. The tension of the spring 92 may be adjustable to provide further different exposure times. Specification 677,314 is referred to. The Specification as open to inspection under Sect. 91 comprises also the additional subjectmatter described and claimed in Specification 677,314 and also states that for the slowest speed the rebound springs may be dispensed with and closing of the shutter effected by the spring 136 or by a similar spring having adjustable torsional characteristics to provide several slow speeds. None of this subject-matter appears in the Specification as accepted.