A combination optical low pass filter adapted for use in a single or double tube color television camera is provided with a phase retarding pattern on a transparent substrate. The pattern includes optical elements having a transmissivity which varies with the wavelength of light passing there through...http://www.google.com.au/patents/US4068260?utm_source=gb-gplus-sharePatent US4068260 - Combination optical low pass filter capable of phase and amplitude modulation
