Patent GB-529297-A (GB)
Title: Improvements in or relating to focal plane photographic shutters
IPC: G03B9/34
Filed: 1939-06-07
Abstract: 529,297. Photographic shutters. KODAK, Ltd. June 7, 1939, No. 16683. Convention date, June 7, 1938. [Class 98 (i)] A focal-plane shutter including a pair of curtains, each wound at one end on to a winding roller and separately latched against the action of a spring-driven roller carrying the other end, is provided with means including a pawl and a ratchet with differentially-spaced teeth for establishing and maintaining during exposure an exposed slit between the curtains in accordance with the desired exposure values. The pawl and ratchet constitutes a clutch between the winding rollers of the two curtains. In the form shown, the shutter comprises a front curtain FC which, when set, is wound on a roller 36 rotatable on a shaft 34, and a rear curtain to which tapes RR are secured and wound on spools 33 secured to the shaft 34. Shutter-setting.- The shutter is set by the operation of a crank 22 which, as described in Specification 513,738, operates a crown gear 17 through a ratchet drive, and thence through a gear 15 the film sprocket shaft 16. The top of the shaft 16 engages and drives a stub shaft 30, Fig. 6, which drives the take-up spool 13, Fig. 2, through gears 28 and an over-running clutch (not shown). A collar 37 on the stub shaft 30 has a shoulder 38, Fig. 9, engaging a spring pressed pawl 40 pivoted at 41 on a gear 42. which is thus driven when the shaft is rotated and rotates the shaft 34 through gears 45, 46 to wind the shutter. The rear curtain is first drawn across the exposure aperture, after which the spool 36 is rotated through a lost-motion drive to wind the front curtain. This drive comprises a loose washer 52, Figs. 6, 7, having an upstanding lug 51 which is engaged by a lug 50 projecting from a collar 49 on the shaft 34 and also a lug 53 which engages a pin 54 projecting from the end of the roller 36. A ratchet and pawl prevent anti-clockwise rotation of the stub shaft 30 and so maintain the blind wound. Fast automatic exposures.-Depression of the release button 55 rocks a bell-crank lever 56, which through a link 58 rocks a lever or release member 59 about its pivot 60, Fig. 9. so that a lug 63 on it engages the end of the pawl 40 and releases it from the shoulder 38 of the collar 37, thus allowing the rear curtain to move. The release of the front curtain is delayed to form the desired slit between the curtains as determined by the setting of the speed indicator. For this purpose, a pawl 67, Fig. 14, engages a shoulder 36a on the front curtain roller 36. It also moves a pawl 64 on the roller 36 from engagement with a ratchet 66 on the spindle 34, so that the preliminary movement of the rear curtain to establish the slit may occur independently of the front curtain. When this has occurred, the 'pawl 67 is moved to the position shown in Fig. 14, in which it releases the front curtain roller 36 and allows the pawl 64 to engage the ratchet 66, the teeth of which are differentially spaced to correspond to the required widths of slit. Both curtains then move together. The operation of the pawl 67 is effected at the desired time by means of a cam 75, secured to the gear 42 and engaged by a pin 79 on a bell-crank lever 77 pivoted at 76, so that as the cam rotates during movement of the rear curtain the lever 77 rotates clockwise, carrying with it a trip lever 80 pivoted to it at 81. When upstanding lugs 87 on the right-hand end of the lever 80 strike the end of a timing lever 82, so arresting movement of this end, the other end moves until it engages the upturned end 73 of a lever 70 carried by the spindle 68 of the pawl 67, so moving the pawl to the releasing position shown in Fig. 14. The lever 82 is adjusted about its pivot 83, to vary the width of slit, by rotation of a disc 86 having a cam slot in which a pin 84 on the lever engages, the point at which the end of the trip lever 80 is arrested being thereby varied. Slow automatic exposures.-The fast automatic exposure dial is set to 1/25 second, so allowing the rear curtain to move to fully open position before release of the front curtain. A detent 120, Fig. 15, engages a square pin 125 depending from the cam 75 after it has rotated about threequarters of a revolution and holds it, preventing release of the front curtain. A retard lever 95, urged downwardly and to the right by a spring (not shown), is held at one end by a stud 97 passing through a slot in it, and carries at the other end a spring-pressed rack 100 which engages a ratchet 102 on a retard gear train 103, which is similar to that described in Specification 520,956. A coil spring 109, Figs. 9, 15 is engaged and wound by a pin 110 on the cam 75 when the shutter is wound, and when released by the counterclockwise rotation of the cam at the beginning of the exposure its end 111 forces the lever 95 to the left, against the retarding action of the gear. During this movement, a cam surface 123 on the lever engages a pin 122 on the detent and finally lifts the latter clear of the pin 125, allowing the cam to complete its rotation and free the front curtain. The duartion of the exposure is determined by varying the travel of the rack before it runs off the ratchet 102, for which purpose the initial position of the lever 95 is adjusted by a regulator 91 having a pin 94 which engages a shoulder 98 on the lever. The regulator is itself adjusted by a slow-speed dial having a pin 90 engaging it at one end, the other end being guided by a pin 93 engaging a curved slot 92 in it. For successively higher speeds, the regulator is moved farther to the left; so diminishing the travel of the lever 95, and the contour of the slot 92 is such that when the slow-speed dial is set to " I " and the regulator is in its extreme left-hand position, the rack is lifted from engagement with the ratchet. Time exposures.-The slow-speed dial being set at " T " the lever 91 occupies the position shown in Fig. 15, and a pin 130 on the lever 95 engages in a recess 128 in a member 126, Fig. 18, which is slidably mounted by a, pin passing through a slot 127. On the first actuation of the release the same action occurs as in a slow automatic exposure, but the pin 130 on the lever 95 engages a shoulder 129 in the member 126 and carries it to the left to the limit allowed by the slot 127, the lever being thus arrested before it has released the detent 120. A lug 131 on the member 126 is now opposite an arm 132, Fig. 9, on the release member 59, so that a second actuation of the release moves the member 126 and with it the lever 95 upwards, causing the latter to lift the detent 120 to free the cam 75 and release the second curtain. Delayed-action exposures.-The gear train 103 comprises a one-way clutch through which the latter part only of the gearing is driven by the rack 100 for timing slow automatic exposures The earlier part of the train includes a shaft 107, Fig. 17, carrying a cam 113 and a helical driving spring (not shown) which may be wound by an external crank without rotating the gears beyond the clutch. Unwinding is prevented by a lug 116 on the release member 95 which engages in a notch 117 in the cam. On operation of the release, the cam is freed and rotates under the retarding action of the whole gear train 103, a spiral edge 119 engaging the lug 116 and moving the member 95 until it finally releases the shutter. An arm 115 on the cam engages the lug 116 when the release is depressed and prevents the member moving sufficiently to release the shutter at this time. Exposure indicator.-A slide 42, Fig. 9, with an upturned end 143, Fig. 6, carries a hook 144 engaging ratchet teeth on the underside of a dial 138 and is reciprocated to advance one tooth at a time by a lug at one end, which is engaged alternately on each side by a downward extension of the pawl pivot 41 as the shutter is wound and released.