Patent GB-478710-A (GB)
Title: Improvements in photographic shutters
IPC: G03B9/42
Filed: 1936-07-22
Abstract: 478,710. Photographic sliding-plate shutters. BROOKMAN, O. J. R. July 22, 1936, No. 20309. [Class 98 (i)] The two blades of a focal plane shutter are movable independently of one another and either or both of the blades is or are formed of two or more plates slidable one over the other. The leading and following blades each comprise two plates 1, 1a and 2, 2a respectively, slidable in guides 3, 4. Flanges 1b, 1c, on the leading blade slide on guides 5 on which are mounted buffer springs 6. Two helical springs 7, 8 are attached to a vertical strip 9 on the plate 1a. Similarly the following blade has guide rods 10, buffer springs 11 and driving springs 12, 13. A link 16 is pivoted to the leading blade and to a control lever 17 pivoted on a spindle 18. Slidably and rotatably mounted on this spindle is a toothed wheel 19 which is urged axially by a spring 20 to engage a pin 21 on the control lever 17. The wheel 19 is rotated by a setting knob 22 through a gear 23, reverse rotation of the wheel after moving the blades being prevented by a ratchet detent 23a. The shutter is released by a pushrod 27 which actuates a pivoted lever 24 having a forked end 26 to move the wheel 19 out of engagement with the pin 21. The push-rod when disengaged is returned by a spring 28a. The following blade 2, 2a is pushed into the set position by the leading blade. When the push-rod 27 is depressed, the lever 24 moves a flat spring arm 32 pivoted at 33, to engage a detent 32a with a pin 29a on the bell crank lever 29 holding the following blade. After the leading blade has run down a predetermined amount, an extension 17a of the lever 17 engages an abutment 32b to depress the arm 32 and release the following blade. In order to vary the slit width and the time of exposure, the position of the abutment 32b is adjustable, a pin on the arm 34 carrying the abutment being adjustable in a curved slot 32c. When the pin is at the extreme end of the slot, the extension 17a cannot then engage the abutment 32b and this forms the setting for " bulb " exposures. The edges of the two blades may be provided with rubber or other flexible facings, and the edges are bent at 1d, 2d to bring the exposure slit as close as possible to the focal plane. In a modification shown in Fig. 7, the driving springs 40, 41, are connected to the arms 17, 29 of the blades. Attached to the control arm is a toothed sector 36a which is wound through gears 37, 38. The shutter is released by moving the pinion 37 in an axial direction out of engagement with the sector 36a. The release of the following blade is effected by an adjustable arm 42 attached to the sector 36a. The arm engages a detent 45 which holds a pin 43a mounted on a pivoted lever attached to the arm 29. When the shutter is released, a spring-urged rocker arm 46a moves the detent 45 into engagement with the pin 43a. After the detent has been disengaged, the arm 42 moves further and engages the lever carrying the pin 43a, whereby the following blind is given the same velocity as the leading blind. The arm 42 engages the sector 36a by means of a pin 42a and is movable axially to bring it out of engagement therewith in order to adjust the relative position of the arm and hence the slit width of the shutter. The extreme position of the arm is such that the detent is not engaged and provides the condition for " bulb " exposure. The spring 41 is sufficiently weak to avoid the following blade gaining on the leading blind.