Optical low-pass filter

Claim 2

An optical low pass filter comprising: 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 having, an upper surface and a side surface perpendicular thereto, said optical elements being so arranged 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 each of said optical elements being of a size to provide phase retardation delta selected from the range given by the following formula cos delta > OR = -1, 1 - 0.35(q+1) > OR = cos delta > OR = 1 - 0.65(q+1) wherein the character q is the ratio equal to the total sum of areas not covered by said optical elements divided by the total sum of areas covered by said optical elements, said ratio being not less than 1.

Claim 3

AN optical low pass filter as set forth in claim 1, wherein said plurality of optical elements for introducing phase retardation are composed of the a number of spots of the same shape and the same dimensions which are formed on said transparent support.

Claim 4

An optical low pass filter as set forth in claim 2, wherein said spots are circular spots having the same diameters.

Claim 5

An optical low pass filter as set forth in claim 2, wherein said spots are oval spots having the same shape and dimension as each other.

Claim 6

An optical low pass filter as set forth in claim 2, wherein said spots are rectangular spots having the same shapes and dimensions.

Claim 7

An optical low pass filter as set forth in claim 1, wherein said plurality of optical elements for introducing phase retardation are composed of circular zones having the same width and arranged concentrically in the same intervals on said transparent support.

Claim 8

An optical low pass filter as set forth in claim 1, wherein said plurality of optical elements for introducing phase retardation are composed of oval zones having the same widths and arranged concentrically in the same intervals on said transparent support.

Claim 9

An optical low pass filter as set forth in claim 1, wherein said plurality of optical elements are composed of magnesium fluride evaporated on a glass plate as the transparent support be means of vacuum evaporation.

Claim 10

The optical low pass filter of claim 1 wherein said transparent support is a lens.

Claim 11

An optical low pass filter comprising: 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 cos delta > or = -1 cos delta > or = 1 - 0.35 (q+1) cos delta > or = 1 - 0.65 (q+1) wherein th character q is the ratio between the total sum of the areas on the upper surface of said optical means and the total sum of areas on portions not covered by said optical means on he transparenT support, said ratio being selected to be not less than 1.

Claim 12

An optical low pass filter comprising: 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 cos delta > or = -1 cos delta > or = 1 - 0.35 (q+1) cos delta > or = 1 - 0.65 (q+1) wherein th character q is the ratio between the total sum of the areas on the upper surface of said optical means and the total sum of areas on portions not covered by said optical means on he transparenT support, said ratio being selected to be not less than 1.

Claim 13

An optical low pass filter as in claim 10, wherein said optical means includes a number of slots formed thereon each having side walls perpendicular to said upper surface, and said character q is the ratio given by the following formula

Claim 14

An optical low pass filter as in claim 10, wherein said optical means includes a number of transparent laminae so arranged on said transparent support to form a striped pattern and make the filter a phase grating.

Claim 15

An optical low pass filter comprising: 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. cos delta > or = 1 cos delta > or = 1 - 0.35 (X/A) cos delta > or = 1 - 0.65 (X/A) in which A a (when a > or = X - a) A X - a (when a > or = X - a) and the character X is the grating period of the stripe filter.

Claim 16

An optical low pass filter comprising: 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. cos delta > or = 1 cos delta > or = 1 - 0.35 (X/A) cos delta > or = 1 - 0.65 (X/A) in which A a (when a > or = X - a) A X - a (when a > or = X - a) and the character X is the grating period of the stripe filter.

Claim 17

The optical low pass filter of claim 13 wherein said transparent support is a lens.