Abstract: A mechanism for setting an optical system accurately to any of various reproduction ratios comprises at least one carrier which has an optical element or elements mounted thereon and is movable along an optical axis to any selected one of several set positions corresponding to desired reproduction ratios by a buffered four-position pneumatic cylinder having oppositely extending piston rods connected respectively with the carrier and a frame part. The four-position cylinder can be adjusted to set the carrier exactly at the position required for a desired reproduction ratio without affecting the settings that provide other ratios. The carrier may be an objective carrier carrying an objective holder that can be moved relative to it in a plane perpendicular to the optical axis and is so moved as the carrier is moved between its set positions; and a movable part of the objective is adjusted at the same time.

Abstract: For reversal development of an electrical potential pattern formed by imagewise exposure of a uniformly charged photoconductive layer, the charging of the layer is restricted to such a level below its breakdown voltage that the contact between the photoconductive layer and the toner powder used in the development step is insulating, and a magnetisable and inductively attractable toner powder is applied for the development. The toner powder is applied by means of a magnetic brush device comprising a conductive development roller which is provided with an electrical potential suited for reversal development. Preferably the photoconductive layer is charged to a level of at most 35-75% of its breakdown voltage, and a scorotron preferably is used for the charging. The photoconductive layer may comprise a photoconductive polymer and/or a bisazo pigment as photosensitive compound, or may be a layer of "pink" zinc oxide dispersed in a binder.

Abstract: An electrophotographic element that comprises an electrically conductive support and a photoconductive layer containing a photosensitive azo-compound dispersed in a film-forming polymeric binder is prepared by synthesizing the photosensitive azo-compound in situ, by reaction between a diazonium compound and an azo-coupling component, in the film-forming polymeric layer on the support. The azo-compounds thus synthetized are distributed in the binder layer in an almost perfectly homogeneous form. Under an electron microscope screen scan they are not distinguishable as separate particles, even at a ten thousand fold magnification. By forming a very thin photoconductive layer in this way and coating it with a charge transporting top layer, especially useful electrophotographic elements are obtained. The invention relates also to electrophotographic elements prepared according to the process.

Abstract: Apparatus for transporting sheetlike originals past an exposure plate (10) of a copying apparatus, of the kind in which a flight of at least one endless belt (25) is driven over the exposure plate, is provided with a device (80) for applying a solid abherent material (85) to that surface of the belt (25) which comes into contact with the exposure plate (10).

Abstract: Transverse areas lying between image areas of a moving photoconductive element can be discharged efficiently with sharp demarcations between the respective areas by an exposure device in which a flash lamp is disposed perpendicularly between two elongate side walls of a reflective housing having an open side and an elongate light-reflecting rear wall. A protective cover fixed near the lamp at the open side prevents direct radiation of the element from the lamp. Scatter of the reflected light is prevented by partitions fixed in parallel to the side walls in end regions of the housing space.

Abstract: In a system for developing electrostatic images on a moving photoconductive support by contact with a brush of two-component developer powder carried on a moving surface, in which the toner content of the powder is controlled in response to optical sensings of the reflectance of the brush at a location just beyond the developing zone, objectionable fluctuations of the toner concentration are avoided by shaping the developer brush to a constant layer thickness, for instance by reducing its thickness to about 0.5 to 0.6 mm, as the brush is being transported from the developing zone so that the sensings of the reflectance will occur at a constant distance from the brush. As an aid for adjusting or checking the operation of the toner control system, a reference surface having the same reflectance as a developer layer of the prescribed thickness and toner concentration is inserted in place of the brush at the location where reflectance is sensed.

Abstract: An improved process for transferring a magnetizable developing powder from an insulating substitute, such as an electrostatic duplication master or photoconductive element to a receiving material, such as paper, in electrostatic image development enables the transfer of powder having a specific resistance greater than 10.sup.13 Ohm.cm. without the need for specially treated paper. The powder is applied imagewise, corresponding to a charge image, on an insulating substrate, the substrate with the powder image brought in contact with the receiving material to which the powder is to be transferred, two separate charges are applied to the free side of the receiving material during the period of contact with the substrate, the first of such charges, a pre-transfer charge, having a polarity opposite to that of the charge image and the second of such charges, a transfer charge, being greater than the first and having the same polarity as that of the charge image, and the powder transferred.

Abstract: Diazotype material which after imagewise exposure can be developed by applying onto its sensitized surface between 1.5 and 4.5 cm.sup.3 per square meter of developing solution, consists of a paper support, the same side of which is coated successively with a sealing layer containing as a filmforming binder polyvinylacetate or a copolymer of styrene with butadiene and a light-sensitive layer having a dry weight of at most 8 g per square meter and comprising a diazonium compound, polyvinyl alcohol with a degree of hydrolysis over 75% and starch particles, whereby the weight ratio polyvinyl alcohol to starch particles is 1 : 5 to 20. The light-sensitive layer may also comprise an azo-coupling component.