Abstract: Optical system for use with attachments for a conventional reflex motion picture camera to permit stereographic cinematography are disclosed. The optical systems include lens systems having four powered elements having negative, positive, negative, and positive focal lengths respectively. The lens systems are adapted to be used with the Bernier stereographic cinematography attachment system as modified for reflex motion cameras. The lens systems include a normal lens system, a wide angle lens system, and a telephoto lens system. The wide angle lens system further includes plane parallel refractive elements to increase its overall length without changing its back focal length, and the telephoto lens system is adapted to be used with internal displacement prisms which bring the images produced by the telephoto lens system into the camera flange opening.

Abstract: The present invention generally relates to playback systems for monitoring the performance of cassette tape duplicating recorders and is specifically directed to a performance monitoring playback system including precision equalization circuitry and an active tape tensioning mechanism which together produce stable high frequency system response.

Abstract: In the production of records, a mother is formed from a metal master having a nickel core and a silver coating. To produce the mother, the silver coating is removed from the nickel core and the nickel is passivated by treating the metal master with an aqueous solution containing ammonium persulphate. The same aqueous solution can be used for passivating the mother before the mother is electroplated to form a stamper.

Abstract: A phonograph record groove eccentricity tester senses the eccentricity of the circular groove at the inner side of the spiral groove, by means of a groove engaging stylus on a pivoted arm operating a sensor that produces an output signal a peak value of which is displayed.