Agfa-gevaert Ag

Josef Ganser

Kurt Borowski

Otto Butz

Dieter Wauer

Herbert Plaschke

An arrangement for determining two or more superimposed film sheets, particularly X-ray film sheets, in a transport after their withdrawal from the film sheet stack, has a light barrier with a light source at one side of the transport path and a photoreceiver at the other side thereof, and an evaluating circuit connected with the photoreceiver for producing a signal corresponding to the presence of two or more sheets and including a computer supplied with a value of the density of a first or test sheet introduced into the light barrier between the light source and the photoreceiver, so that the supplied value serves as a reference signal for measuring the next film sheet.

Arrangement for and method of determining two or more superimposed film

Upon exposure initiation, a shutter opens abruptly, an exposure-light diaphragm begins to open progressively, and a control diaphragm, behind whose aperture the light sensor is located, also begins to open progressively. The signal from the light sensor is integrated, and when the requisite total-light amount is reached the shutter falls closed abruptly. Accordingly, the system decides, on its own, what the exposure duration and exposure-light aperture size upon exposure termination will be. The user, however, can modify this fully automatic selection in the sense of longer exposures and smaller aperture, or else shorter exposures and larger aperture, by varying the motion-retarding force supplied by an electromagnetic motion retarder, which controls the speed at which the exposure-light aperture opens up. Prior to exposure initiation, the control aperture is at a minimum, but non-zero size, permitting scene-light-sufficiency measurement. The motion-retarding force is automatically lowered in response to temperature decreases and automatically boosted in response to scene-light increases, to counteract low-temperature slowness of mechanical movements and to prevent the need for unrealizably brief exposure durations. The electromagnetic motion-retarder is not connected to a current source, but instead generates magnetic motion-retarding force in response to movement of inductance-modifying structure in accordance with Lenz' law. When the user wishes to predispose the fully automatic system towards longer or shorter exposure durations or larger or smaller aperture sizes, the light-sufficiency indicator is automatically adjusted to take this into account.

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Munich, Germany

Josef Ganser