Optical low-pass filter

Claim 2

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, the optical system comprising filter means including a plurality of sets of laminae for introducing phase retardation, laminae in each set being arranged in parallel with each other and disposed at an angle to the laminae of at least one other set, and laminae 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) > OR = cos delta > OR = 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, each set of laminae being respectively mounted on a transparent base plate to form a low-pass filter, and an objective lens on both sides of which the low-pass filters are disposed perpendicularly to the optical axis of the objective lens.

Claim 3

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, the optical system comprising low-pass filter means including a pair of low-pass filters, each of said filters including a transparent support and optical means disposed on said transparent support for introducing phase retardation to light transmitted through the filter; said optical means having an upper surface and being so formed that the section of one side of the filter taken along in at least one direction is the shape of rectangular wave in which the width of each projection and the space between adjoining projections are respectively equal to each other; and said optical means having the size in the direction perpendicular to the upper surface thereof to provide phase retardation delta selected from the range given by the following formula: a. cos delta < or = 1 - 0.35 (q+1) b. cos delta > or = 1 - 0.65 (q+1) under the conditions that the ratio of both formula (a) and (b) are met, simultaneously, and wherein the character q is the ratio between the total sum of areas on the upper surface of said optical means on the transparent support, said ratio being selected to be not less than 1; said filters being disposed at an angle to each other.

Claim 4

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, the optical system comprising low-pass filter means including a pair of low-pass filters, each of said filters including a transparent support and optical means disposed on said transparent support for introducing phase retardation to light transmitted through the filter; said optical means having an upper surface and being so formed that the section of one side of the filter taken along in at least one direction is the shape of rectangular wave in which the width of each projection and the space between adjoining projections are respectively equal to each other; and said optical means having the size in the direction perpendicular to the upper surface thereof to provide phase retardation delta selected from the range given by the following formula: a. cos delta < or = 1 - 0.35 (q+1) b. cos delta > or = 1 - 0.65 (q+1) under the conditions that the ratio of both formula (a) and (b) are met, simultaneously, and wherein the character q is the ratio between the total sum of areas on the upper surface of said optical means on the transparent support, said ratio being selected to be not less than 1; said filters being disposed at an angle to each other.

Claim 5

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; the optical system comprising low-pass filter means including a pair of low-pass filters, each of said low-pass filters including a transparent support and a plurality of optical elements disposed on said support for introducing phase retardation in light transmitted through the filter; each of said optical elements being composed of a transparent lamina continuous in one direction and having a flat upper surface and side surfaces perpendicular thereto, said optical elemeNts being arranged in parallel to each other so that the section of one side of the filter taken along in the direction normal to the longitudinal direction of the laminae is the shape of rectangular wave in which the width of each projection a and the space between adjoining projections are respectively equal to each other, and that a phase grating filter is defined; and each of said optical elements being of a size to provide a phase retardation delta selected from the range given by the following formula:

Claim 6

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; the optical system comprising low-pass filter means including a pair of low-pass filters, each of said low-pass filters including a transparent support and a plurality of optical elements disposed on said support for introducing phase retardation in light transmitted through the filter; each of said optical elements being composed of a transparent lamina continuous in one direction and having a flat upper surface and side surfaces perpendicular thereto, said optical elemeNts being arranged in parallel to each other so that the section of one side of the filter taken along in the direction normal to the longitudinal direction of the laminae is the shape of rectangular wave in which the width of each projection a and the space between adjoining projections are respectively equal to each other, and that a phase grating filter is defined; and each of said optical elements being of a size to provide a phase retardation delta selected from the range given by the following formula: