Abstract: In a module for monitoring the print quality of a dot printer (10), comprising a radiation source (41), a condenser lens system (43?) for forming an illuminated area (45) on a printing medium (13) and an imaging lens system (87,89) for imaging the illuminated area on a detector (49?), the detector comprises at least a linear array of detector elements and the imaging system is configured in such a way that both the illuminated area and a small portion thereof can be imaged. This allows detection of both the gray scale of a print line (35) and the size and colour of an individual dot. A dot printer provided with this modules gives an improved print quality.

Abstract: In a module for monitoring the print quality of a dot printer (10), comprising a radiation source (41), a condenser lens system (43′) for forming an illuminated area (45) on a printing medium (13) and an imaging lens system (87, 89) for imaging the illuminated area on a detector (49′), the detector comprises at least a linear array of detector elements and the imaging system is configured in such a way that both the illuminated area and a small portion thereof can be imaged. This allows detection of both the gray scale of a print line (35) and the size and colour of an individual dot. A dot printer provided with this modules gives an improved print quality.

Abstract: In a module for monitoring the print quality of a dot printer (10), comprising a radiation source (41), a condensor lens system (43′) for forming an illuminated area (45) on a printing medium (13) and an imaging lens system (87,89) for imaging the illuminated area on a detector (49′), the detector comprises at least a linear array of detector elements and the imaging system is configured in such a way that both the illuminated area and a small portion thereof can be imaged. This allows detection of both the gray scale of a print line (35) and the size and color of an individual dot. A dot printer provided with this modules gives an improved print quality.

Abstract: In a module for monitoring the print quality of a dot printer (10), comprising a radiation source (41), a condensor lens system (43′) for forming an illuminated area (45) on a printing medium (13) and an imaging lens system (87,89) for imaging the illuminated area on a detector (49′), the detector comprises at least a linear array of detector elements and the imaging system is configured in such a way that both the illuminated area and a small portion thereof can be imaged. This allows detection of both the gray scale of a print line (35) and the size and colour of an individual dot. A dot printer provided with this modules gives an improved print quality.

Abstract: An image projection device comprising at least one display panel (26, 27, 28), a projection lens system (C) and a focus error detection system (FS) is described. Since the radiation source (50) and the radiation-sensitive detector (51) of the focus error detection system are arranged in planes which effectively coincide with the plane of the display panel (28), and a focus measuring beam b traverses the projection lens system twice on its path to and from a projection screen (D), an accurate and reliable focus error signal (S.sub.f) is obtained.

Abstract: An efficient illumination system for an image projection apparatus is described, which system comprises a radiation source (20), a concave reflector (21) and a first and a second lens plate (25, 28) each being provided with a matrix of lenses (26, 29) for forming superimposed images of the radiation source on the object (1) to be illuminated, the aspect ratio of the lenses (26, 29) corresponding to that of the object (1).

Abstract: In a liquid crystal projection t.v. system the color gradient over the projected image, which is due to angular sensitivity of the dichroic mirrors, is minimized by introducing a field lens (61,62,63) next to the light values or LC-panels (21, 22, 23) in the light paths of the blue (b.sub.B), green (b.sub.G) and red (b.sub.R) beams. By chosing different length light paths before and after the light valves and LC-panels a difference in angular sensitivity of the separation mirror (41,42) and the recombination mirrors (52,53) can be compensated for.