Abstract: A scanning device for optical record carriers is provided with an objective lens (7) suitable for scanning record carriers (1, 21) having a transparent substrate (2, 23) of different thicknesses. The lens comprises an outer annular part (25) and an inner central part (26) within the annular part. Only the central part of the lens is used for forming a focus through a first substrate (2) having a first thickness. The central part is corrected for the spherical aberration of the first substrate. The annular and central part of the lens are used for forming a focus through a second substrate (23) having a different, second thickness. The annular part is corrected for the spherical aberration of the second substrate.

Abstract: Imaging conditions for the aperture rays of an axial pencil, for example Abbe's sine condition, determine how an object volume will be imaged in the image space of an optical lens system. The invention provides an optical lens element having an imaging condition which analytically should lead to the largest possible volume in an image space wherein possible aberrations (spherical aberration and coma) remain below a certain prescribed level.

Abstract: An optical scanning device can scan two types of record carriers each having a transparent layer with a different thickness, in which a focused radiation beam scans an information layer of the record carrier through the transparent layer. When scanning a first type of record carrier the best focus of the radiation beam is positioned on the information layer and when scanning a second type of record carrier the paraxial focus of the radiation beam is positioned on the information layer. The lens system focusing the radiation beam comprises an opaque ring between a transparent central area and a transparent annular area.

Abstract: A device for optically scanning an information layer by means of a focused radiation beam. Radiation reflected from the information layer is made astigmatic by an oblique plane parallel plate and subsequently detected by a detection system. An electronic circuit derives two focus error signals, each representing the distance between the focal point of the radiation beam and the information plane. The first focus error signal is formed from the high-frequency components in the electrical detector signals, and the second focus error signal is formed from the low-frequency components in the same detector signals. A second electronic circuit combines the two focus error signals into a combined focus error signal to control a focus servo loop. The circuit changes the control gradually from one focus error signal to the other.

Abstract: A device for optically scanning an information layer by means of a focused radiation beam. Radiation reflected from the information layer is made astigmatic by an oblique plane parallel plate and subsequently detected by a detection system. An electronic circuit derives a focus error signal, representing the distance between the focal point of the radiation beam and the information plane, from the electrical detector signals by using the high-frequency components in the detector signals. The influence of stray light falling on the detection system on the focus error signal is thereby reduced.

Abstract: A device for optically scanning an information layer by means of a focused radiation beam. Radiation reflected from the information layer is made astigmatic by an oblique plane parallel plate and subsequently detected by a detection system. An electronic circuit 26 derives two focus error signals, each representing the distance between the focal point of the radiation beam and the information plane. The first focus error signal is formed from the high-frequency components in the electrical detector signals, and the second focus error signal is formed from the low-frequency components in the same detector signals. A second electronic circuit combines the two focus error signals to a combined focus error signal.

Abstract: An imaging system with at least one reflective surface for forming an image by means of ultraviolet radiation, the reflective surface being provided with a correction layer which is transparent to the wavelength of the radiation used. This layer compensates for phase differences caused by deviations of form of the reflective surfaces. The correction layer has a refractive index which differs only slightly from 1, so that the requirements imposed as regards the precision of the surface of the transparent layer are significantly less severe than for the reflective layer.

Abstract: A wide angle objective system is described for, inter alia CCD cameras, which system is compact, inexpensive and satisfactorily corrected. It comprises a front meniscus lens (L.sub.1), a thick convex-concave central lens element (L.sub.2) and a biconvex lens element (L.sub.3), the two last-mentioned elements preferably being cemented together, the pupil (P) being present at the area of the exit surface (4) of the second lens element and the first and the third element (L.sub.1,L.sub.3) being made of, for example PMMA and the second element (L.sub.2) being made of, for example PC.

Abstract: A record carrier having standard and high-density information layers. The standard density layer, e.g. in a standard CD format, is positioned at the bottom of a substrate, and is read out through the substrate with a laser beam. The thickness of the substrate is within the CD specification, e.g. 1.2 mm. At least one high-density layer is formed by a material which is (nearly) transparent for the laser wavelength of standard CD players (.lambda.=780 nm), but is (at least partially) reflective for shorter wavelengths used for high-density discs (.lambda.=635 nm). To achieve a high density, a smaller track pitch and smaller pits are used in the high-density layer(s). To achieve better reading signals from both layers, the high-density layer is positioned closer to the side of entrance of the laser beam in the substrate. A higher numeric aperture of the focusing lens and, therefore, a smaller spot for the shorter wavelength results. The high-density layer is preferably positioned midway in the substrate, e.g.

Abstract: An optical scanning device can scan two types of record carriers each having a transparent layer with a different thickness, in which a radiation beam scans an information layer of the record carrier through the transparent layer. When scanning a first type of record carrier the best focus of a scanning radiation beam is positioned on the information layer and when scanning a second type of record carrier the paraxial focus of the radiation beam is positioned on the information layer.

Abstract: A measuring device for determining the displacement of a movable object includes a graduation element which is mechanically connected to the object whose displacement is to be determined. The graduation element comprises at least a track which is formed by a plurality of successive grating strips located transversely to the direction of movement of the object. The measuring device also includes a radiation source, a detector and a reflective optical system which comprises at least a beam collimating element. The reflective optical system guides the radiation from the radiation source to the graduation element and changes it to an elongate radiation beam which is parallel on average in the cross-section perpendicular to the grating strips.

Abstract: A beam-shaping element for converting a beam having an elliptical cross-section into a beam having a circular cross-section. This element has a cylindrical entrance surface and a toriodal exit surface and can be arranged close to a diode laser so that the risk of wavefront deviations due to defocusing is reduced. The element has a high coupling efficiency.

Abstract: A device for detecting a centering error of a rotationally symmetrical surface (0.sub.1, 0.sub.2) of an object (0) with respect to a rotational axis (AR) about which axis the object is rotated for the purpose of the centering error detection is described. Two beams (b.sub.1, b.sub.2 ; b.sub.3, b.sub.4) at angles of approximately 90.degree. are directed onto the object and the variation in the phase difference caused by the centering error (.epsilon.) between the two beams (b.sub.1, b.sub.2 ; b.sub.3, b.sub.4) reflected by the surface is determined.

Abstract: A record carrier having information stored thereon in tracks comprised of areas separated from each other in the track direction by intermediate regions which are optically distinguishable from the areas. The areas in adjacent tracks have a different phase depth and are therefore also optically distinguishable from each other so that the tracks may be crowded closer together. A player is also disclosed having two detectors offset from each other in the direction of the tracks and producing signals that are alternately added and subtracted to produce a tracking signal.

Abstract: A zoom lens is described for an electronic camera for still pictures, comprising a front group (G.sub.1), a variator group (G.sub.2) and a main group (G.sub.4). The lens is designed in such a manner that the sum of the spherical aberrations of the front group and the variator group is constant throughout the zoom range and is adapted to that of the main group.

Abstract: A grating objective comprises at least three gratings and in which an axial ray and a border ray of a radiation beam are interchanged at least two times so that the objective has a wavelength-independent behavior, a relatively large image field and a satifactorily uniform intensity distribution. A beam shaper and a grating objective with a built-in beam shaper are described based on the same principle.

Abstract: An optical scanning device is described with a mirror-objective (30) arranged between a radiation source (40) and an object (10) to be scanned, which mirror objective comprises two radiation windows (31, 34) and two reflectors (32, 33). By giving one of the windows (31, 34) an aspherical shape, the mirror objective is well corrected for spherical aberrations, while no stringent requirements need to be imposed on the accuracy of the shape of the aspherical surface (35).

Abstract: A projection lens system for projecting a magnified image from an image source (3, 4, 5) on a projection screen (10) comprises from the image end successively a first, positive lens group (L.sub.1) and at least a second, negative lens group (L.sub.3) whose surface (S.sub.6) facing the image end is concave. The first lens group consists of a single lens element (L.sub.1) which in addition to a first refractive surface (S.sub.1) facing the image end and a second refractive surface (S.sub.2) facing the object end has a third radiation-reflecting surface (S.sub.3) which is located between the first and the second surface.

Abstract: A projection-lens system for projecting a magnified image of a scene formed by means of a reproduction element onto a projection screen, which system has two correction groups and one main group which provides substantially the entire power of the system. The main group includes a glass preform of which at least one of the outer surfaces is provided with a layer of a transparent plastics having an aspheric outer profile. This projection-lens system is substantially temperature-independent, provides a satisfactory correction for aberrations, and has a short focal length and a comparatively large numerical aperture.

Abstract: An objective lens (20) and an optical scanning device (30, 20, 50) provided with such a lens are described, of which lens both surfaces (22, 23), viewed from the object side, are concave, while the focal length is considerably smaller than its thickness (d) of along the axis and the surface (23) at the image side is aspherical. When using this objective lens, the scanning device may be very compact.