Method and apparatus for adjusting the relative positioning of planar transparent objects, such as the glass plates of a liquid crystal display, and a liquid crystal display adjusted by the method and apparatus

An apparatus for adjusting the relative positioning of planar transparent objects, and in particular the two glass plates of a liquid crystal display (LCD) having transparent layer electrodes, said layer electrodes having transparent markings disposed thereon, comprising:

• illuminating and imaging means for directing a collimated light beam through said transparent markings of said planar transparent objects, said light beam locally phase modulated as said light beam passes through said markings, said illuminating and imaging means comprising a luminous source, collimator means for beaming the light eminating from said luminous source, dark field stop means for intercepting light leaving said collimator means and passing through said planar transparent objects, and objective means for imaging said markings;
• and
• image detection means for detecting said images of said markings and for determining the position of said planar transparent objects, said image detection means comprising differential photodiode means for detecting said images of said markings and for determining said position of said objects, said differential photodiode means including a separate differential photodiode for each of said markings on both of said planar transparent objects.