Patent GB-520957-A (GB)
Title: Improvements in or relating to focal plane photographic shutters
IPC: G03B9/34
Filed: 1938-11-04
Abstract: 520,957. Photographic cameras. KODAK, Ltd. Nov. 4, 1938, No. 31992. Convention date, Dec. 22, 1937. [A Specification was laid open to inspection under Sect. 91 of the Acts, May 15, 19391. [Class 98 (i)] [Also in Group XL] A focal-plane shutter has two separately-controlled ranges of speeds, the exposures in the higher range (used for "hand" exposures) being automatically timed 'by a light-sensitive cell which controls the width of the slit by positioning a selector member acting a stop for an element adapted to release shutter curtain latching means, and the exposures in the lower range being timed by an independent manuallyadjustable means which can be used when the necessary exposure is outside the range controlled by the light-sensitive cell, and which determines the speed at which the widest slit traverses the exposure aperture. In the shutter illustrated the front curtain FC and the straps R of the rear curtain.are wound on roller 38 and spools 39 respectively, the curtains being wound up through the gear 51 on roller 38, and a series of gears connected to a film wind-up spool 23 and through a ratchet mechanism to a handle on the back of the camera, as described in Specification 513,738. The spools 39 are pinned on the spindle 40, but the roller 38 is revolvable thereon, being connected to the spindle 40 through a clutch disc 41, which frictionally engages a toothed clutch member 42. The shaft 40 carries a ratchet 47 having two teeth, and a shaft 56 carries a single toothed ratchet 57, normally engaged by as spring biased pawl 60 pivoted on the gear 63, so that when the shaft 56 is rotated on pressing the shutter winding handle, the gears 63, 64, 65 are also rotated to wind the roller 38 through its gear 51, and the spools 39 through the clutch 41, 42. Above the gear 63 is mounted a cam 100, while a ratchet wheel 85 is carried on the same shaft as the gears 64, 65. Instantaneous exposures.-When the release button 74 is depressed it operates a bell-crank lever 75 connected by a link 77 to a release member 72 which is thus turned clockwise about its pivot 73. A projection 82 on this lever releases the pawl 60 from the ratchet 57, thus permitting the gear 63, cam 100, and ratchet wheel 85 to rotate under the pull of the front curtain. During rotation of the cam 100 a pin 99 on a bell-crank lever 97 follows its contour, causing the lever to turn clockwise, carrying with it a floating lever or intercepter 95 pivoted to it at 96. This lever has an unturned end 94, Fig. 21, which is adapted to engage a selector 178 formed by the pointer of a meter of which 176 is the moving coil. Before the depression of the release button, the selector 178 is positioned according to the outlet from a photoelectric cell 175, Fig. 19, to which light received from the objective is reflected by an inclined mirror 289, which is raised out of the path of the rays when the release is depressed by a bell-crank lever 293 moved by a sliding bar 187. At the same time a bell-crank lever 183 which normally supports a hinged arcuate comb 179 is moved so as to allow the comb to be depressed by a spring and entrap the selector 178 in the position occupied by it. When therefore the end 94 of the interceptor level 95 engages the selector 178 the motion of this end is arrested, and the continual movement of the interceptor by the bell-crank lever 97 causes its other end 102 to strike the upturned end 69 of a latch lever 66 pivoted at 67, rotating it counterclockwise to release a pawl 83 which then engages the ratchet wheel 85, stopping the rewinding of the front curtain. Simultaneously the shoulder 68 on the latch lever 66 is disengaged from the shoulder 50 of the ratchet 47, releasing the second curtain, which however is temporarily retained by the projection 79 on release member 72 engaging the second tooth 49 of the ratchet 47. A slit is thus established the width of which is determined by the position of the selector 178 in accordance with the light falling on the photo-electric cell. On releasing the button 74 the tooth 49 is released and simultaneously a projection 86 on the release lever 72 strikes a lug 87 on the pawl 83, both curtains being thus released to make an exposure. Automatic slow exposures.-For automatic slow exposures the diaphragm is adjusted so that the photo-electric meter registers the slowest speed, when the slit formed is equal to the picture space. The regulator lever 106, pivoted at the slot 108, carries at one end a pin 105 mounted eccentrically in an external adjusting knob, and at the other end a pin 109 constituting a stop for a driving member 110, pivoted on a pin 111 in a slot, and biased by a spring 112. The member 110 carries a rack 113 pivoted at 114, and adapted to engage a ratchet wheel 115 mounted on an intermediate member of a train of gear wheels retarded by a pallet. An arm 118 is adapted to engage the driving member 110 to force it upwards. On pressing the release button 74, the hook 124 on the release member 72 pulls a pin 125 on arm 118 until it is caught by the latch 126, the driving member 110 following the arm 118 until arrested by the pin 109. On releasing the button 74, the gear 63 turns until the pin 101 thereon strikes the shoulder 128 on the driving member 110, which is then moved to the left, bringing the rack 113 into contact with the ratchet wheel, its end 122 also striking and releasing the latch 126 and thus the arm 118, which then forces the driving member 110 upwards at a rate determined by the escapement mechanism, until the pin 101 slips off the shoulder 128, allowing the shutter to close. The length of the expose is determined by the point along the rack which is initially engaged with the ratchet wheel, this depending on the position of the stop pin 109 as set by the exposure adjusting knob. Time exposures are obtained when the regulator 106 is in such a position, as shown in Fig. 14, that its end 129 strikes a lug 137 on the rack 113, preventing it from engaging the ratchet wheel, and a projection 138 engages a lug 139 on the lever 118, so that the latter is swung downwards and held by the latch 126. When the button 74 is pressed for the first time, the pin 101 moves the driver 110 to the left and brings a lug 140 thereon into the path of a projection 141 on the release member 72. When the button 74 is again pressed, therefore, the driving member 110 is moved upwards, releasing the pin 101. Delayed action exposures are obtained by a clockwork motor wound up by the external handle 153 and controlled by the same escapement mechanism as the automatic slow exposures, to which it is connected by a one-way coupling. The cam 157, connected to a member of the gear train, is released by prong 160 on the release member 72 to move clockwise when the button 74 is pressed, preventing the member 72 from returning until the edge 158 has passed the prong 160. The edge 158 is bevelled, the springiness of the prong 160 allowing it to pass over the cam 157 during winding of the motor. Counting mechanism consists of a dial 130 having ratchet teeth on its underside. A hook 134 on a bar 135 engages these teeth, and on winding the shutter, the pin 101 strikes a lug 136 on the bar 135, to move it the space of one tooth, moving it back to its original position on release. Specifications 451,659 and 520,954 also are referred to. Hand-set instantaneous exposures.-The Specification as open to inspection under Sect 91 comprises also a construction in which the speed settings in the higher range are made by hand, the photoelectric meter being omitted. In this construction, the selector member 178 of the photoelectric meter is replaced by a selector 92, Fig. 13 (Cancelled), which is adjusted in position by means of a slotted cam 89 rotated by an external speed control knob. This subject-matter does not appear in the Specification as accepted.