Abstract: An optical information reproducing apparatus for reproducing information from an optical recording medium that has a recording and reproducing and information-rewritable track region, which is composed of a header region having information, such as a sector start mark, track number and sector number, in a pit shape formed when the recording medium has been manufactured and a recording and reproducing user data region that has no pit and enables information to be recorded and reproduced, the optical information reproducing apparatus having a semiconductor laser output control circuit for controlling a quantity of a semiconductor laser beam to be emitted to a predetermined value such that a detected quantity of an emitted semiconductor laser beam is obtained in only the user data region when the quantity of the laser beam emitted by a semiconductor laser that irradiates the recording medium with a semiconductor laser beam is detected.

Abstract: A focused light beam is projected upon an optical recording medium through an optical system in an optical pickup, and a light reflected from the recording medium is received to detect a focus error signal and a tracking error signal. Further, the focus control and the tracking control are both achieved through a servo feedback loop in response to the detected focus and tracking error signals. In this optical information recording and reproducing system, track formats are provided from which lights of different intensities are reflected, the track formats are discriminated by a projection position detecting circuit, and the focusing and tracking operations are controlled by selectively adjusting the gain of the servo feedback system according to the detected track format, so that the control operation is stable in recording or reproducing information data to or from a recording medium of a high density type, in particular.

Abstract: A surgical microscope apparatus provided with a failure detecting device for conducting an initial examination and an ordinary examination of an illumination device and a failure detecting device for conducting the ordinary examination of an electric magnification and focusing device, in order to make it possible to self-examine what is defective and indicate the result when failure is caused. The failure of the illumination device is immediately indicated by the self examination of the failure detecting device when a power source is turned on for use.

Abstract: An apparatus for recording and reproducing optical information is disclosed.

Abstract: An optical information recording and reproducing system comprises a light source for emitting a working beam from a front end thereof and a monitoring beam from a rear end thereof, an optical system control circuit, a loop gain adjusting circuit and a photo detector. The monitoring beam emitted from the rear end of the light source is detected by the photo detector, and the loop gain of the servo loop control circuit for the focusing and/or tracking is automatically adjusted by means of the loop gain adjusting circuit according to the detected signal so that a desired closed loop control of the working beam can be performed according to the operation modes and the light beam power variation.

Abstract: In an auto-focussing system, an actuator which moves together with an objective lens is vertically movable against a rotating optical disc and radiates a light beam so as to form a light spot on an information plane of the disc. A focus servo unit moves the actuator so that an optical distance between the actuator and the disc is within a proper distance region and performs the focus control of the light spot on the disc. While the actuator is approaching the optical disc, an auto-focus/focus servo controller initially makes the servo unit nonoperative and, when the actuator reaches a too-far position in a suitable servo loop distance region specified by a servo loop of the focus servo unit, the controller temporarily stops the movement of the actuator and then moves the actuator again from the too-far position by only a predetermined distance, thereby causing the actuator to be located within the focus loop distance region.

Abstract: A detecting circuit for detecting an operating center of an actuator of an optical head includes a first comparator for comparing a tracking signal based on a reproduced signal coming from the optical head with a reference voltage approximate to zero voltage level, and a second comparator for comparing the tracking signal of which the DC component is removed with a second reference voltage approximate to zero voltage level. A level inversion of a binary output signal of the first comparator is detected at a level inverting point of a binary output signal of the second comparator. The operating center of the actuator is checked with the detection of the level inversion.

Abstract: An optical disk apparatus has an optical disk for recording data into a recording area on an optical disk and reproducing the recorded data from the recording area. The optical disk is provided at the center with a first section with the same reflectivity as that of the recording area and a second section with a different reflectivity from that of the recording area. A photosensor sense detects the first section and produces a signal representing a reflectivity on the first section. The reflectivity data obtained from the signal level is used for controlling a gain of the servo system according to the reflectivity data.