A mirror is held against a pointed supporting member by a magnetic field of attraction between a first magnetic assembly attached to the mirror and a second magnetic assembly spaced from the first assembly and directly or indirectly attached to the supporting member. The mirror can pivot in two directions in response to magnetic control fields produced by coils around the first magnetic assembly but is prevented by interlocking magnetic fields from rotating on an axis in a third direction. The interlocking fields may be produced by assymmetrically located magnetic members attached to the first and second magnetic assemblies or by dividing both the first and second magnetic assemblies into similar oppositely polarized sectors.

A tracking mirror device, in particular for a video disc player, in which for following an information track on a video disc with a beam of radiation, use is made of a mirror which oscillates at a high frequency, which causes the beam of radiation, which serves for scanning the information track, to oscillate transversely to the information track at a high frequency and a small amplitude, while the filtered out high-frequency signal, as a function of its amplitude and its phase relationship with the high frequency voltage which is applied to the oscillating mirror, yields a control signal for following the information track. In accordance with the invention, use is made of an oscillating mirror which is driven electromagnetically and which is connected to oscillation compensation elements by means of springs which elements oscillate in phase opposition to the mirror. Thus, an oscillator mirror is obtained which can readily be excited to natural resonance and thus requires little power. On the mirror a piezo-electric miniature acceleration transducer can be mounted, which can provide a feedback signal so that the oscillating mirror can be included in a self-oscillating circuit.

An automatic optical focussing system, suitable for a video disc player, comprising an optical focussing device with an objective which is moved to and fro at high frequency in the direction of its optical axis by electro-dynamic drive means, the superimposed high frequency component of the signal which has been modulated by the information tracks on the video disc being employed for automatic control of the position of the objective. In view of a low power consumption the objective is connected to an oscillation-compensation element by means of at least one resilient element, for example a circular plate, which compensation element is axially movable or relative thereto, and which together with the objective and the resilient element constitutes a mechanical resonant system. On the resonant system a piezo-electric acceleration transducer may be mounted with the aid of which the mechanical resonant system can be included in a self-oscillating loop.

In a recording and/or reproducing apparatus having a rotated record carrier, for example, in the form of a disc, adapted to have video or other signals optically recorded in successive turns of a spiral track on a surface of the record disc, a recording and/or reproducing transducer or head assembly with an optical system including a movable lens for focusing a light beam at the disc surface and/or a movable mirror for deflecting the light beam so as to cause the latter to scan the track, and a servo system for detecting deviations from the proper focused and/or scanned conditions, for example, due to fluctuations of the rotated record disc in directions normal to, or in the plane of rotation thereof, and for correspondingly displacing the lens and/or mirror, respectively, so as to maintain the proper focused and scanned conditions; such servo system is provided with a gain-frequency characteristic having peaks at a fundamental frequency corresponding to the rotational speed of the record disc and at least at one harmonic of such fundamental frequency so as to improve the accuracy with which the servo system responds to fluctuations of the record disc for maintaining the proper focused and/or scanned condition.

In a capacitance distance sensor apparatus in a focus servo loop for an optical disc playback and record system, stable high servo loop gain and small closed-loop error correction signals are achieved despite surface variations of the disc by compensating for the periodic error command signals generated by the surface variations. A comb filter is provided in the loop tuned to major error component frequencies. The comb filter is formed of a plurality of parallel, bandpass filters that are tuned to frequencies substantially corresponding to the disc rotation frequency and several harmonics thereof. In the distance sensor servo focus control loop, the loop gain can be maintained at a high value to achieve proper beam focus within 0.5 micron (0.5.times.10.sup.-6 meters) for disc surface amplitude variation of three mils (0.0075 centimeters) peak-to-peak.