Abstract: Display apparatus for forming an image from a plurality of image modulators located at different distances from an image surface includes illumination means for forming an illumination beam, a plurality of image forming modulators disposed at different distances from the image surface, for forming a composite image on the image surface, path length correcting means disposed between the plurality of image forming modulators and the image surface, for equalizing the optical path lengths between the image forming modulators and the image surface, so that the composite image can be focused.

Abstract: A full color liquid crystal display comprises first, second, and third subtractive LCD filters, each filter comprising means for independently subtracting one of the primary subtractive colors from a polychromatic light beam, without substantially affecting the other subtractive colors. Each of the subtractive LCD filters combines wavelength selective dichroic polarizers with a twisted nematic liquid crystal cell to provide a filter that can selectively subtract varying amounts of incident spectral radiant energy from within one of three primary energy bands. A first selective polarizer that linearly polarizes wavelengths in the appropriate one of the above mentioned color bands, while passing light in the other two bands substantially unaffected, a first liquid crystal cell, and a second selective dichroic polarizer identical to the first polarizer, but positioned wih its axis of polarization perpendicular to that of the first polarizer.

Abstract: In a floppy disk drive, the head position is controlled in accordance with prerecorded sets of sinusoidal bursts recorded first on the right side of each track and then on the left side of each track in the narrow separation space between each pair of adjacent disk sectors. The serial bursts are peak detected and then integrated by the same peak detector and the same integrator, the integrals of the right and left bursts being substracted and transmitted to the head tracking servo as a position error signal. The process of peak detecting prior to integration removes the detected wave shape (which changes with track radius) as a factor in the position error computation, thus eliminating dependency of the error computation on the track radius. Using a single channel--the same peak detector and the same integrator--to process both the right and left hand sinusoid bursts eliminates offset errors in the tracking error computation characteristic of dual channel devices.