Patent GB-1087373-A (GB)
Title: Photographic shutter and camera including the same
IPC: G03B7/081
Filed: 1966-03-08
Abstract: 1,087,373. Photographic diaphragmshutters. AGFA-GEVAERT A. G. March 8, 1966 [March 13, 1965], No.10071/66. Heading G2A. A photographic shutter of the type including one or more movable shutter blades return spring- loaded into the closed position and an acceleration member for transmitting an impulse to the blade or blades to effect momentary opening of the shutter against the spring loading further includes, for varying the degree of opening movement of the blade or blades during operation of the shutter - which variation results in a corresponding variation of the shutter speed and of the magnitude of the effective shutter aperture - an exposure value setting device including a solenoid which exerts a magnetic force upon a component of the shutter and means for varying the electric current which can pass through the solenoid. In the embodiment shown, the solenoid 25 is wired in series with a photo-resistor 27 and a current source 28, and the single shutter blade 3 is carried on a pivoted arm 4 which also carries a permanent magnet 23. Depression of a release slider 15 closes the circuit to the solenoid 25, which is thereby energized, and rotates the acceleration member 9 in the direction c until a pivoted pawl 13 on the slider 15 escapes from the member 9 which is free to rotate anti-clockwise (as shown) under spring action. The member 9 then strikes the arm 4 causing it to move against the return spring 6 and uncover the aperture 2. The permanent magnet 23 enters the field of the solenoid 25 and, since opposed areas of the fields of the magnet and solenoid are arranged to have the same polarity, the arm 4 is retarded by the solenoid field of force. Depending on the magnitude of the force, the blade 3 is arrested after a variable time, and then returns to its initial position under the action of spring 6. The aperture is provided with a fixed cover blade 32, and the blade 3 is so shaped that with small opening movements of the shutter blade the exposure area of aperture 2 is centred closely on the central axis of the full shutter aperture. In another embodiment Fig.2 (not shown), an electromagnet (40) co-operating with a plate (41) of magnetic material on the arm (4) is provided for setting the exposure values. The impulse transmitted to the arm (4) by the acceleration member (9) after the pawl (13) has escaped therefrom has to overcome the attraction between the plate (41) and the electromagnet (40), which attraction varies in strength depending on the current flowing in the electromagnet. Thus a constant impulse applied to the arm (4) will, owing to this current variation, cause the blade (3) to move at differing speeds and for differing distances in the direction opposite to (a). In a further embodiment Fig. 3 (not shown), a shutter is used having two movable blades (50, 51), and the accelerator member (61) carries a permanent magnet (63) co-operating with a fixed electromagnet (64), like poles being adjacent. In this case, when the pawl (65) has escaped from the member (61), the movement of the member (61) under spring action is retarded to a greater or lesser extent by the magnetic field of the electromagnet (64). The two blades thus receive differing impulses, and pivot for differing distances and times in opposite directions against springs (57, 58) to effect the exposure. Any or all of the arrangements described above may have the associated circuit modified so that a flag (89) Fig.4 (not shown), is visible in a viewfinder (90) when there is insufficient illumination. There is also provided a fixed resistance (85) which may be switched into the circuit, presence of the flag in the viewfinder then indicating that the current source (84) needs changing or re-charging. A manually adjustable resistor or other photo-sensitive element may be used in place of the photo-resistor.