Abstract: 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.

Abstract: 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.