Abstract: In the method for detecting the point of immersion or emergence of a solid or porous body into or out of a liquid, surface waves are generated in the liquid and the light coming from a light source and reflected on the surface of the liquid is scanned photoelectrically. Only the alternating light component of the reflected light is detected here and the rectified alternating light signal is compared with a preset threshold value. When the actual value falls below or exceeds the threshold value, a control signal is then generated which can be utilized for control or regulating actions. For detecting the alternating light component, the photoelectric scanning signal is differentiated. Advantageously, scanning of the surface of the liquid is carried out at a plurality of points. The resulting rectified alternating light components can subsequently be added up, and the total value can be compared with the preset threshold value.

Abstract: An illuminating device with a diffused, radiating, surface light source (3) and an aperture system positioned between the light source and the object is provided. The aperture system is formed by two optically complementary aperture screens (4, 5) which are disposed in series, and are spaced apart. The first aperture screen (4) thereby consists of a large number of transparent circular discs (8), positioned at intervals on an opaque base, and a second aperture screen (5) consists of a large number of opaque circular discs (9), positioned at intervals on a transparent base. The diameter of the opaque circular discs (9) is larger than that of the transparent circular discs (8), so that the circular discs of the two aperture screens (4, 5) overlap in the projection.

Abstract: Successive frames of spliced-together exposed and developed photographic films are examined prior to introduction into a copying machine to prevent the reproduction of film frames having blurred images. Portions of or entire film frames at an examining station are spot scanned, line-by-line, and the resulting video signals are processed to determine one or more quotients which denote the ratio of maximum density gradient to density range of the respective film frames, the ratio of first and second density gradients obtained on scanning the entire frequency spectrum or the lower density portion of a film frame, and the ratio of frequency of occurrence of the first and second density gradients. Such quotient or quotients are compared with a threshold value and the results of comparison are used to classify the film frames as suitable or unfit for the making of reproductions.