Optical low pass filter

An optical low-pass filter for use in a television camera optical system of the type having a color encoding filter means disposed in the light path of said optical system and serving to spatially modulate at least two color images with respect to the camera scanning direction, the low-pass filter comprising a transparent substrate and a plurality of laminae which are regularly arranged on a face of said substrate and are delineated by at least two sets of channels for introducing phase retardation, the channels in each set being arranged in parallel with each other and disposed at an angle of not less than 15.degree. and not more than 45.degree. to the channels of the other set and the angle between a line bisecting the acute angle between said sets of channels and the perpendicular to said scanning direction being no greater than half said acute angle .

A color television camera including optical low-pass filter for use in an optical system of the type having a color-encoding filter means disposed in the light path of said optical system and serving to spatially modulate at least two color images with respect to a scanning direction and scanning means for detecting said images and producing chrominance and luminance signals,

• the optical system comprising phase diffraction filter means including a plurality of laminae which are delineated by at least two sets of channels for introducing phase retardation, channels of each set being arranged in parallel with each other and disposed at an angle of not less than 15.degree. and not more than 45.degree. to the channels of the other set, the angle between a line bisecting the acute angle between said sets of channels and the perpendicular to said scanning direction being no greater than half said acute angle, and channels in a set having the same size to provide phase retardations selected from the range given by the following formula:
• 1 - 0.35 (q + 1) .gtoreq. cos .delta. .gtoreq. 1-0.65 (q+1)
• wherein q is the ratio equal to the total sum of areas not covered by said laminae divided by the total sum of areas covered by the laminae, said ratio being not less than 1, and .delta. is the phase retardation.