Abstract: A focusing detection apparatus comprises an optical system for forming a plurality of images a relative positional relation of which changes in accordance with a focusing state of an object lens, a sensor for producing signals representing the images by detecting the images by a plurality of photo-electric elements, and arithmetic circuitry for determining the focusing state of the object lens based on the signals from the sensor. In order to determine the focusing state, the arithmetic circuitry carries out an operation of ##EQU1## where V is a correlation, a(i) and b(i) are outputs of i-th photoelectric element of the sensor for the respective images, and {x.quadrature.y} is a constant operational relationship for two real numbers x and y.

Abstract: An apparatus and method for detecting focus condition of an imaging optical system is disclosed.

Abstract: Disclosed is an automatic focus control system including an active type automatic focusing device. The system further includes detecting apparatus which produces a characteristic signal when detecting that an image forming optical apparatus is in an out-of-focus condition, and control means which renders the automatic focusing device in an inoperative condition when the optical apparatus reaches an in-focus condition. It also renders the focusing device in an operative condition in response to the characteristic signal produced by the detecting apparatus.

Abstract: A photo-detecting device employed for photo-detecting a storage type photo-sensor which produces information stored therein according to light inputs on the form of signals integrated in a real time and nondestructive manner. Timing for reading out the output of the photo-detecting apparatus by a control circuit which controls on the basis of the output of the photo-detecting apparatus is to be determined according to the output of the photo-detecting apparatus when the photo-detecting means stores information corresponding to the light inputs. A period of time after storage is started by the photo-detecting means and before the information is read out by the control circuit is determined during the process of storing the information.

Abstract: A focus detecting apparatus having an optical device movable to cause the light from an object to be imaged on a predetermined plane and comparing the different imaged conditions of the light from the object on the predetermined plane comprises a light intensity distribution detecting device for detecting the distribution of the intensity of light on the predetermined plane and putting out a detection signal indicative of the distribution of the intensity of light on the predetermined plane, a device for taking out a high frequency component from the detection signal, a device for rectifying the taken out high frequency component, a device for forming the envelope of the rectified high frequency component, a device for integrating the envelope at any time and putting out an integrated value, and a focus detecting device for detecting, on the basis of the integrated value of the envelope, the amount of movement necessary for the imaging optical device to cause the light from the object to be imaged on the pred

Abstract: In a signal accumulating time control method and apparatus for a signal accumulating type radiation sensing device which produces an electrical signal corresponding to the amount of incident radiation and accumulates the same, an accumulating time controller has first and second different control modes and is adapted to change over from one of said first and second control modes to the other when the intensity of said incident radiation fluctuates a large amount.

Abstract: A relay optical system used for focus detection including an optical lens system for forming the image of the exit pupil of a photographing lens, all or a part of said lens optical system for forming a secondary image of an image which is formed on a focusing plane by the photographing lens and a reflecting mirror provided in a plane where the image of said exit pupil is formed. The reflecting mirror is made up of a plurality of reflecting mirror portions which are obtained by dividing the reflecting mirror. The mirror portions divide the image of the exit pupil and have different optical axes, so that an image formed by the photographing lens is formed into secondary images the number of which is equal to the number of mirror parts. Sensor arrays are provided to receive the secondary images, respectively, to detect focusing from correlation of the images.

Abstract: Disclosed is an automatic focusing apparatus which comprises an objective disposed in opposition to a substrate with patterns formed thereon, a first line sensor disposed at a first focal point of the focal length of the objective, second and third line sensors which are disposed closer to and farther from the objective by a given distance with respect to second and third focal points of the focal length of the objective, first to third differential circuits for differentiating the output signals from the first to third line sensors, a detecting circuit for detecting a displacement of the substrate from a predetermined proper distance between the objective and the substrate on the basis of the output signals from the first to third differential circuits, and a correcting device for correcting the displacement on the basis of the output signal from the detecting circuit. Thus, a single optical system is used for automatically correcting focus and pattern inspection.

Abstract: An automatic focus control device for adjusting the height of a lens above a surface of a workpiece used in an exposure apparatus for exposing the sample with a light beam including a first light emitting device for emitting a first light ray to a sample; a second light emitting device for emitting a second light ray to the sample. First and second light detecting devices for detect the second and first light rays reflected by a surface of the sample, respectively. The first and second light detecting device have a plurality of light detecting elements. A discriminating device discriminating between an inclination of the sample and a variation of the height of the lens above the surface of the sample on the basis of an output of the first and second light detecting devices.

Abstract: A focusing detecting system for discriminating a focusing state of an object lens by detecting a relative positional relation of a plurality of object images formed by light fluxes from the object lens, by photo-sensing means is disclosed. A plurality of object images are formed based on a light flux from a center area of the object lens around an optical axis and a plurality of object images are formed based on a light flux an area in the periphery of the center area around the optical axis, by optical means disposed behind an image plane of the object lens. Light shielding means having a plurality of slits is disposed near the image plane. By those means, a state is which the object images based on the light fluxes from the center area of the object lens around the optical axis and the peripheral area are detectable and a state is which the object images based on only the light flux from the center area of the object lens around the optical axis is detectable are discriminated.

Abstract: In a camera, a focus condition of an objective lens system is automatically detected in accordance with a combination of two different type detection methods. A light flux emanating from the objective lens system is divided into two light fluxes by means of a prism having a half mirror and a reflecting mirror and a first light flux transmitted through the half mirror is received by a first light receiving element array via a lenticular lens array and a second light flux reflected by the half mirror and reflecting mirror successively is directly received by a second light receiving element array. The lenticular lens array is so arranged that an exit pupil of the objective lens and the first light receiving element array are conjugated with each other and thus divided images of the exit pupil are projected upon respective elements of each pair of adjacent light receiving elements.

Abstract: A focus detection apparatus has a pair of photoelectric element arrays, a plurality of filters having different MTF characteristics, and an operation unit. A filter is selected from the plurality of filters in accordance with an object or a focusing state. The selected filter filters the data from the photoelectric element arrays, and the operation unit calculates a focus detection signal based on the filtered data.

Abstract: A method and apparatus for detecting focus conditions of a photographic optical system is disclosed. The invention comprises a member for dividing the wavefront of a light beam from a photographic optical system in an image space thereof, a first light receiving device including two photocell arrays provided in the front and the rear of a surface conjugated to a predetermined focal plane of the optical system, and a second light receiving device including at least one photocell array provided at a surface conjugated to one of the photocell arrays in the first light receiving device. A first signal representing horizontal shift of an optical image is detected based on outputs of at least one photocell array in the second light receiving device and one photocell array in the first light receiving device having a relation conjugated to the photocell array in the second light receiving device.

Abstract: In a focus detecting device, an object's image formed on a prescribed image plane of a photo-taking lens is once again formed by a secondary imaging optical system disposed behind the prescribed image plane into two non-superposed object's images based on light flux portions symmetrically split relative to the optical axis of the photo-taking lens; light sensitive elements are respectively disposed in positions where these images of the object are re-imaged by the secondary imaging optical system; and an in-focus state of the photo-taking lens is arranged to be detected by detecting the relative positional relation of these reformed images of the object by means of these light sensitive elements. The focus detecting device includes light splitting means which is arranged in the secondary imaging optical system to split a light flux coming from the exit pupil of the photo-taking lens into a middle part portion and a peripheral portion.

Abstract: Disclosed is a focus detecting system in which the exit pupil of an imaging optical system is divided into a plurality of exit pupils by an optical device, a plurality of object images are formed by light beams passed through the divided exit pupils, photoelectric conversion element arrays each comprising a plurality of elements and putting out signals corresponding to the imaged states of the object images are disposed at locations whereat the object images are formed, and the relative positional relation between the object images is found by a signal processing operation cirucit by the use of the output signals from the photoelectric conversion element arrays, the minimum or maximum of such signals being processed, whereby the state of focus of the imaging optical system is discriminated.

Abstract: Apparatus for automatically aligning a tri-beam electron gun mount, which mount includes an electrode having an optical passage therethrough, relative to the phosphor pattern in a CRT bulb destined to receive the mount. The gun mount is rotatably supported, with its geometric axis coincident with an extension of the bulb's neck axis, for presentation to a driver. A laser beam is split to form a pair of beams which are directed along paths which intersect within the optical passage and are thereafter individually intercepted by an assigned light detector. The detectors develop signals which are applied to an error detector comprising a differential amplifier. A central signal derived from the amplifier energizes the gun mount driver which rotates the gun mount until identical signals are outputed by the light detectors. With the gun mount then optimally oriented, it is locked preparatory to its insertion in the CRT bulb.

Abstract: In a focus condition detecting device of the type in which a pair of re-imaging lenses together with a condenser lens form a pair of re-images of an object image on a line sensor such that the distance between the corresponding points of the re-images on the line-sensor varies with the focus condition of a camera objective lens forming the objective image, the line sensor is located in front of a plane conjugate with a predetermined focal plane of the camera objective lens with respect to the condenser lens and the re-imaging lenses, so that the distance between the corresponding points of the first and second re-images on the line-sensor can be detected with resolution higher than one pitch length of the photocells of the line sensor.

Abstract: A photosensor apparatus for detecting focal position or the like, which uses a plurality of light-receiving elements arranged in a matrix array, is disclosed. Simultaneous light integration is started with respect to all the light-receiving elements, while all the outputs of the light-receiving elements are progressively scanned immediately after the start of the simultaneous light integration. When at least one of the outputs reaches a first reference level, all the outputs are held. If at least one of the held outputs is above a second reference level of a different level, check as to whether all the outputs are below the second reference level is repeatedly done for progressively reducing light integration periods until all the outputs of the light-receiving elements are at a fixed level.

Abstract: A focus detecting apparatus is disclosed which includes a focusing optical system for forming an object image on a predetermined focal plane and photoelectric devices disposed before and behind the focal plane at substantially equal distances from the plane. The photoelectric devices detect the focus states of the object images formed thereon respectively. The focus state of the object image on the focal plane is detected depending on whether or not the focus states on the photoelectric devices are equal to each other. According to the invention such a focus detecting apparatus further includes a mask for gradually decreasing the quantity of light incident upon the photoelectric devices in the direction away from the center of the incident beam. Under the action of such a mask, the focus states of object images before and behind the predetermined focal plane at substantially equal distances from the focal plane are made approximately equal to each other.

Abstract: A focus detector adaptable to a camera or other similar optical instrument is disclosed. The focus detector includes a pair of concave mirrors as refocusing optical system for forming secondary images the positional relationship of which is detected for focus detection. In order to eliminate the adverse effect of aberrations on the secondary image formation and to improve the accuracy of focus detection, the concave mirrors are inclined to satisfy a particularly determined condition on the incident angle to the mirrors. The condition is that the incidence angle should be less than about .sqroot.0.04/R wherein R is the maximum diameter of the mirror measured in mm.

Abstract: Point-to-point film exposure for recording rasters continuous tone images and linework characters in scanner technology wherein the exposure spot is defined by the light intensity, the size, the focus and intensity distribution which are controlled to achieve a uniform and high contrast exposure.

Abstract: Disclosed is an automatic focusing apparatus for an optical imaging system which utilizes a focus detector which monitors the contrast of the image at the focal plane of the imaging system, the image being deemed to be in focus when the contrast of the image is maximized. The focus detector comprise a plurality of detector/converter elements arranged in an array in the focal plane. Each detector/converter senses the light intensity in a respective portion of the image at the focal plane and provides a pulse signal having a pulse-width which is approximately inversely proportional to the sensed light intensity. A detection circuit receives the pulses provided by the detector/converter elements and derives a digital quantity which is related to the difference between the maximum and minimum pulse-widths of the pulses. The digital quantity is received by a digital servosystem which appropriately adjusts the focusing of the imaging system to maximize the digital quantity provided by the detection circuit.

Abstract: A method of detecting focusing conditions used for optical machinery is disclosed. The focusing conditions of an optical image projected onto photodetector arrays arranged on both sides of the focal plane with a certain optical distance are detected based on an evaluation function representing a sum of absolute values of differences between output signals of adjacent photodetectors. When a value of a first evaluation function represented by the largest absolute value is less than a predetermined threshold a second evaluation function represented by a sum of the maximum and next largest absolute values is used thereby detecting the focusing conditions for a graded image.

Abstract: The focusing detecting device determines whether or not the optical image of an object to be photographed is in a focusing state in which the image is clearly formed on a predetermined image forming surface through a photographing or image forming optical system. The device can be used with a dark optical system.

Abstract: A photodetector output circuit comprises a plurality of adjacent photodetectors grouped into pairs having first and second photodetectors for generating signals indicative of levels of light falling thereon, a first shift register for receiving the signals from the first photodetectors in the pairs, a second shift register for receiving the signals from the second photodetectors in the pairs, and a pair of first and second sample and hold circuits for successively sampling and holding outputs from final stages of the first and second shift registers, respectively. A comparator receives as inputs outputs from the first and second sample and hold circuits for delivering out signals when the received inputs have a level difference of a predetermined value or higher. With this arrangement, the photodetector output circuit can produce digital signals indicative only of abrupt changes in the level of incident light and excludes any influence due to gradual light level variations which would result from shading.

Abstract: A focus detector of image correlation type projects an image of an object onto a first and a second array of photoelectric transducer elements. Each of the transducer elements produces an output in accordance with the distribution of light intensity of image incident thereon. A characteristic point is retrieved from the distribution of outputs from the first array, and a corresponding characteristic point is retrieved from the distribution of outputs from the second array which corresponds to the first mentioned characteristic point. An in-focus condition is detected on the basis of the relative position between those transducer elements which produce outputs for these characteristic points.

Abstract: A focus condition detecting device of the type in which a pair of re-imaging lenses together with a condenser lens form a pair of re-images of an object image on a linesensor, such that the distance between the corresponding points of the re-images on the linesensor varies with the focus condition of a camera objective lens has an improved construction for positioning the linesensor with respect to the device with high accuracy. A field aperture mask having a field aperture is arranged optically behind a plane conjugate with the linesensor with respect to the re-imaging lenses and the condenser lens such that a pair of defocused images of the field aperture are formed on the linesensor by the re-imaging lenses and the condenser lens with respective one side blurred borders of the defocused images overlapping one another to make a V-shaped peak or dip of illuminance on a photocell of the linesensor located on the optical axis of the device, when the field aperture mask is uniformly illuminated.

Abstract: An automatic focus detecting device comprising an image sensor for electrically converting distributions of two images of an object which are formed by two restricted light beams passed through different areas in a zooming lens system into time sequence video signals which in turn are extracted at predetermined extraction intervals and directed to a correlator for deciding the degree of agreement between the two images. The video signal extraction is effected in two operation modes; one is for a high accuracy focus detection and the other for a rough accuracy focus detection. In the former operation mode, a time sequence video signal of a narrow image is extracted at short intervals and on the other hand, in the latter operation mode, a time sequence video signal of a wide image is extracted at long intervals.

Abstract: An optical system is automatically focussed by deriving an electrical signal which has a frequency distribution corresponding to the spatial frequency distribution of an image received from a focussing lens; applying to the electrical signal an amplification which is greater at high frequencies than at low frequencies; and adjusting the optical system to maximize the amplified signal.

Abstract: An automatic focus adjusting device comprises a charge accumulating type photoelectric conversion element array, a circuit for outputting from the output of the photoelectric conversion element array a signal indicative of the in-focus state of the image of an object to be photographed on a film surface, a circuit for modifying the newest detection signal on the basis of at least one past detection signal and outputting out a modification signal, a circuit for selecting one of the detection signal and the modification signal in accordance with the brightness of the object to be photographed, and a circuit for driving a picture-taking lens in a direction in which the image of the object to be photographed is focused on the film surface, on the basis of the signal selected by the selecting circuit.

Abstract: An automatic focusing device includes an optical head which comprises a focusing lens system and an optical sensor. The focusing lens system focuses a reading laser beam or a recording laser beam on an optical disk. The optical sensor generates photoelectric signals which correspond to the sections of a beam spot formed by a laser beam reflected from the optical disk. Record signal components corresponding to a recording laser beam are removed from the photoelectric signals by switch circuits. The photoelectric signals no longer containing record signal components are supplied to envelope detectors. The envelope detectors generate envelope signals each formed of signal components which correspond to a laser beam reflected from the surface of the optical disk. According to the difference between the envelope signals the focusing lens system is driven to thereby focus a laser beam on the optical disk.

Abstract: A vibration detection apparatus detects the vibration of an optical system such as a camera by dividing the incoming rays of light and causing pairs of photosensors to receive the divided rays of light and then comparing the shifts in the phases of the signals output from the pairs of photosensors.

Abstract: Apparatus for illuminating a remote object first with uniform intensity and second with a pattern so the detector array may view the object to determine its characteristics and view the pattern to determine the range to the object.

Abstract: An image plane deviation amount detecting device includes means for converting the amount of lateral deviation between two object images formed by two light beams passing through two areas of the exit pupil of a focus detecting lens into an amount of image plane deviation including the sign and absolute amount thereof, whereby when utilized in an automatic focus apparatus, it is not only capable of effecting quick automatic focusing operation even when there is a response delay in the focus detecting device, but also capable of displaying the focus adjusted condition in the form of a quantitative amount of image plane deviation when utilized in a display device.

Abstract: An apparatus for detecting a focus condition of an imaging lens of a still camera by detecting a lateral shift of two images formed on a light receiving element array by means of light fluxes transmitted through different sections of the exit pupil of the imaging lens divided by a stripe mask is disclosed.

Abstract: A focusing state discriminating system of the invention discriminates the focusing state of an image forming optical system, based on signals F1, F2 and F3 representing image formation states of images formed at first, second and third positions of the optical system which substantially correspond to positions slightly in front of, coincident with and slightly behind the predetermined focal plane of the image forming optical system. The operation for discrimination in this system includes at least a comparison of .vertline.F1-F3.vertline. and K(F1+F2+F3), where K is a constant.

Abstract: An improved automatic rangefinder device of the type having means for projecting a beam of light to illuminate a spot on a distant object, and an image sensor for viewing the object and determining the distance thereto by the observed position of the illuminated spot is disclosed. The rangefinder includes improved means for forming the beam of light comprising an elongated light source and projection optics for forming a real image of the light source, thereby defining an elongated beam region in space corresponding to the image of the light source, extending generally away from the rangefinder, whereby an object located in said beam region will be illuminated by a spot of light having an in-focus component. The image sensor detects the position of the in-focus component of the light. The rangefinder device includes imaging optics for imaging the spot on the image sensor.

Abstract: A method of focus detection is disclosed, in which at least two pairs of light receiving element rows are arranged with respect to a photographing lens, and light splitters, each of which wave front splits the light flux from the photographing lens into two light fluxes, are provided for the respective light receiving element rows in the light receiving element row pairs. Light intensity distributions detected by the light receiving element rows at least between two light receiving element row pairs are compared to determine whether an image forming plane is in pre- or post-focus or in focus. Contrast signal values of the object image detected from the light receiving element rows between the light receiving element rows of at least one of the light receiving element row pairs are compared to determine whether the image forming plate is in pre- or post-focus or in focus. The result of at least either comparison is used for focus adjustment.

Abstract: An automatic focusing binocular is herein disclosed in which a light, signifying the inability of the automatic focusing system to operate due to the lack of available light contrast, is provided within the user's field of vision as he looks through the binocular. This is accomplished by the use of a focus detection module. When the reflected images from apertures proximate to the objective lens coincide in the module, a focusing signal is produced which terminates the motion of the eyepieces at a point corresponding to the distance of the object from the objective lens. When these coinciding images do not have sufficient light contrast for the module to produce the focus signal, a detection signal is produced which illuminates a warning light. A rod-shaped prism is disposed such that light from the light source condenses at the forward focal point of the eyepiece.

Abstract: A light beam splitter includes a splitter lens a light flux splitter, in which a splitter lens is disposed such that a light beam, having passed through substantially one half of the light emission area of a focusing lens defined by a substantial border line constituted by a straight line passing through the center of the light emission area and dividing the area into two regions, is incident on light receiving elements in one of two light receiving element arrays and a light beam having passed through the other region is incident on light receiving elements in the other light receiving element array individually corresponding to the first-mentioned light receiving elements.

Abstract: A totally reflecting strip mirror is utilized in a zoom lens system having an auto focus circuit replacing the partially reflective large mirror of the prior art to provide the same amount of radiation to the auto focus system with less waste, easier adjustment, and decreasing the necessary dimensions of the zoom lens system.

Abstract: A system having a scaled anti-aliasing random phase filter for use in optical imaging systems having a sampled focal plane or an automatic focussing device. The filter is scaled so that it may be placed near the focal plane or automatic focus sensing device, yet produce the effect of an anti-aliasing filter at the exit pupil of the optical system. In one example, the filter includes a scaled hologram of a Sayanagi filter located at the exit pupil. In a second example, the filter includes a scaled double chirped diffraction grating.

Abstract: A motor drive lens shifting system includes a picture taking lens, a drive device for driving the lens, a light receiving element for receiving light which has passed through the lens and forming an image thereon, a focus condition detector for detecting the focus condition of the image whether it is front-focus, in-focus or rear-focus, and a control device for controlling the drive device relatively to the detected focus condition such that the drive device first shifts the lens in a wide pitch to roughly adjust the lens position, and then, in a small pitch in steps to precisely adjust the lens position. The steps become gradually small in the manner of geometric progression.

Abstract: In the device disclosed, an image formed by an optical system is scanned by an image sensor composed of independently arranged photoelectric transducing elements to produce an image scanning signal. A detecting circuit detects the variation of the brightness between the adjacent image elements as a measure of the sharpness of the image and the focus of the optical system. The focus detection accuracy is improved by non-linear transformation of the brightness variation signal with a non-linear transformation circuit that weighs the brightness variation signal on the basis of the signal level.

Abstract: A distance measuring apparatus is provided with first and second imaging lenses for distance measurement for forming images of the same object, a first photoelectric device having a light-receiving surface for receiving the first image by the first imaging lens for distance measurement, a second photoelectric device having a light-receiving surface for receiving the second image by the second imaging lens for distance measurement, and varying means for varying the relative position of the light-receiving surface of the first photoelectric device and the first image thereon and the relative position of the light-receiving surface of the second photoelectric device and the second image thereon. The apparatus detects the distance to the object from the fact that the two relative positions have assumed a predetermined relation.

Abstract: This invention presents a range finding device when 1st and 2nd detection images of an object are scanned by signal storing type image sensing means to obtain image scan signals, which are quantized by quantization means to produce quantized image data for said 1st and 2nd detection images. On the basis of the thus obtained quantized image data, the location within the 2nd detection images of one set of M successive elements of the 2nd detection image which is most similar to M successive elements of the 1st detection image is detected, and with the aid of the data of this location, the distance between the device and the object is determined. According to this improved device, sequence control means, which controls a series of operations for range finding, will firstly cancel the signals stored in said image sensing means as unnecessary signals, when said series of operations is initiated, and then enables proper storing of image signals in the image sensing means so as to properly control the device.

Abstract: In an automatic continuous focusing device, two detected images of an object formed by a distance detection optical system with a relative distance therebetween associated with the object distance are scanned, the obtained scanning signals are quantized to generate quantized picture element data, the relative distance between the two detected images is detected on the basis of the quantized picture element data, and an imaging optical system to be focused on the object is controlled according to the detection result. The device also provides for invalidating the control of the imaging optical system when the results of detection of the quantized condition of the scanning signals indicate that the quantized condition of the scanning signals for at least one of the two detected images is not sound or reasonable.

Abstract: A phase type diffraction grating and a microprism for splitting the light beam from an objective lens into three light beams. The three light beams are split in one direction by the diffraction grating and are directed onto three rows of line sensors disposed on the same plane. In the two optical paths between the diffraction grating and the line sensors, there is disposed an optical path length difference imparting element for forming on the line sensors images at a predetermined focal plane of the objective lens and planes forward and rearward of the predetermined focal plane. Thus, the line sensors detect the images at the predetermined focal plane and at planes forward and rearward of the predetermined focal plane.

Abstract: Apparatus for reading information stored in a track pattern on a radiation reflecting record comprises a source of radiation such as a laser, a diffraction grating for providing at least a zero order beam component and a pair of first order beam components, an objective lens assembly, a photodetector array, the photodetector array comprising a unitary data photodetector disposed for impingement of the zero order beam component for sensing stored information and at least first and second paired photodetector arrays adjacent to the data photodetector including separated sectors disposed along an axis including the data photodetector for providing at least focus error correction signals to the objective lens assembly, and means provided in the optical path between the objective lens assembly and the photodetector array for providing a first portion of the reading beam components which remains relatively fixed in size and a second portion of the reading beam components which varies substantially linearly in size

Abstract: Apparatus for reading information stored in a track pattern on a radiation reflecting record comprises a source of radiation such as a laser for supplying at least a reading beam, an objective lens assembly for passing the reading beam to the record and for controllably focusing the reading beam at a plane of focus, a photodetector array disposed in an optical path with the lens assembly for sensing at least the recorded information and focusing errors, and an astigmatic element disposed in the optical path for producing an astigmatic image of the reading beam in which the photodetector array comprises a unitary data photodetector disposed for impingement thereon of a zero order reading beam component for sensing the recorded information, and a quadrant photodetector array adjacent to the unitary data photodetector and including separated sectors disposed along orthogonal axes for sensing relative differences of the astigmatic image along the orthogonal axes to provide at least focus error correction signals