Bi-level phase grating focusing plate

Claim 2

A bi-level phase grating focusing plate for use in a camera viewfinder, comprising a substrate having a first surface and a number of unit patterns which are repeatedly and adjacently arranged on said first surface of said substrate so as to be sectioned from each other by imaginary boundaries therebetween in such a manner as to be defined by a minimum repetition pitch of the repeated arrangement thereof, respectively, wherein each of said unit patterns includes a plurality of means for creating a level difference for diffraction of light, each of which has a second surface which is parallel with and different in level from said first surface of said substrate such that each of said unit patterns causes diffraction of light due to the level difference between said first and second surfaces, the minimum repetition pitch defining the smallest division of the focusing plate that can repeat the plurality of means for creating a level difference in a pattern of repetitive juxtaposition to each other on the focusing plate, and wherein said plurality of means of each said unit pattern is arranged within the minimum repetition pitch in an identical manner with those in the other unit patters and spaced nonconcentrically from each other, with the centers of said plurality of means being at different positions, respectively, to provide a symmetrical configuration.

Claim 3

A bi-level phase grating focusing plate as defined in claim 1, wherein the ratio γ, which is the sum of the areas of said second level surfaces of said plurality of means divided by the overall areas of said unit patterns, satisfies the inequality of 0.25≦γ<0.5 and the phase difference φ of the light due to the level difference between said first and second surfaces is approximately π radians for light having a desired wavelength ranging from 0.45 μm to 0.64 μm.

Claim 4

A bi-level phase grating focusing plate as defined in claim 2, wherein said unit pattern are arranged in a quadrate configuration and each of said unit patterns in a quadrate.

Claim 5

A bi-level phase grating focusing plate as defined in claim 1, wherein said unit patterns are arranged in an equilateral triangular configuration and each of said unit patterns is an equilateral hexagon.

Claim 6

A bi-level phase grating focusing plate as defined in claim 1, wherein each of said plurality of means has a circular cross section in a plane parallel to said first and second level surfaces.

Claim 7

A bi-level phase grating focusing plate as defined in claim 1, wherein said substrate and said plurality of means are light transmissive.

Claim 8

A bi-level phase grating focusing plate as defined in claim 1, wherein said first and second surfaces are light reflective.

Claim 9

A bi-level phase grating focusing plate for use in a camera viewfinder, having on a surface thereof, a number of unit patterns repeatedly and adjacently arranged so as to be sectioned from each other by imaginary boundaries therebetween and so as to be defined by a minimum repetition pitch of the repeated arrangement thereof, respectively, wherein each of said unit patterns includes a first region with a first level surface which is co-planar with said surface of said focusing plate and a second region with a second level surface which is parallel with and different in level from said first level surface such that each of said unit patterns causes diffraction of light due to the level difference between the first and second level surfaces, the minimum repetition pitch defining the smallest division of the focusing plate that can repeat the first and second regions in a pattern of repetitive juxtaposition to each other on the focusing plate, each of said unit patterns being indivisible into more minute unit patterns having a repeated arrangement, wherein one of said first and second regions in each of said unit patterns has a plurality of portions which are spaced nonconcentrically from each other with the centers of said plurality of portions being at different positions, respectively, to provide a symmetrical configuration; and wherein the arrangement of said plurality of portions in each said unit patterns is identical.

Claim 10

A bi-level phase grating focusing plate for use in a camera viewfinder, having on a surface thereof, a number of unit patterns repeatedly and adjacently arranged so as to be sectioned from each other by imaginary boundaries therebetween and so as to be defined by a minimum repetition pitch of the repeated arrangement thereof, respectively, wherein each of said unit patterns includes a first region with a first level surface which is co-planar with said surface of said focusing plate and a second region with a second level surface which is parallel with and different in level from said first level surface such that each of said unit patterns causes diffraction of light due to the level difference between the first and second level surfaces, the minimum repetition pitch defining the smallest division of the focusing plate that can repeat the first and second regions in a pattern of repetitive juxtaposition to each other on the focusing plate, each of said unit patterns being indivisible into more minute unit patterns having a repeated arrangement, wherein one of said first and second regions in each of said unit patterns has a plurality of portions which are spaced nonconcentrically from each other with the centers of said plurality of portions being at different positions, respectively, to provide a symmetrical configuration; and wherein the arrangement of said plurality of portions in each said unit patterns is identical.

Claim 11

A bi-level phase grating focusing plate as defined in claim 8, wherein said first region includes said plurality of portions spaced nonconcentrically from each other to provide the symmetrical configuration.

Claim 12

A bi-level phase grating focusing plate as defined in claim 9, wherein said second region includes a portion centered at the center of said unit pattern and said plurality of portions of said first region are arranged on said portion of said second region so as to be centered at other than the center of the unit pattern.

Claim 13

A bi-level phase grating focusing plate as defined in claim 10, wherein said unit patterns are arranged in an equilateral triangular configuration and each of said unit patterns is an equilateral hexagon.

Claim 14

A bi-level phase grating focusing plate as defined in claim 8, wherein said second region includes said plurality of portions nonconcentrically spaced from each other to provide the symmetrical configuration.

Claim 15

A bi-level phase grating focusing plate as defined in claim 12, wherein one of said plurality portions of said second region is centered at the center of said unit pattern while the others are centered at other than the center of said unit pattern.

Claim 16

A bi-level phase grating focusing plate as defined in claim 13, wherein all of said plurality of portions of said second region are circular in a plan view.

Claim 17

A bi-level phase grating focusing plate as defined in claim 12, wherein all of said plurality of portions of said second region are centered at other than the center of said unit pattern.

Claim 18

A bi-level phase grating focusing plate as defined in claim 15, wherein all of said plurality of portions of said second region are circular in a plan view.

Claim 19

A bi-level phase grating focusing plate as defined in claim 12, wherein said unit patterns are arranged in a quadrate configuration and each of said unit patterns in a quadrate.

Claim 20

A bi-level phase grating focusing plate as defined in claim 12, wherein said unit patterns are arranged in an equilateral triangular configuration and each of said unit patterns is an equilateral hexagon.

Claim 21

A bi-level phase grating focusing plate as defined in claim 8, wherein the ration γ, which is the sum of the area of said plurality of portions divided by the overall areas of said unit pattern, satisfies the inequality 0.25≦γ<0.5 and the phase difference φ of the light due to the level difference between said first and second surfaces approximately is π radians for light having a desired wavelength ranging from 0.46 μm to 0.46 μm.