Method for designing and method for manufacturing diffraction-grating lens
View Patent ↗A method for designing a diffraction grating lens of the present invention is a method for designing a diffraction grating lens having a diffraction grating composed of a plurality of diffraction zones, the method including the steps of: (a) determining widths of the plurality of diffraction zones; and (b) determining an aspherical coefficient of a diffraction surface on which the diffraction grating is provided while the determined widths of the plurality of diffraction zones are fixed, after the step (a).
1. A method for designing a diffraction grating lens having a diffraction grating composed of a plurality of diffraction zones, the method comprising the steps of:
(a) determining respective widths of the plurality of diffraction zones; and
(b) determining an aspherical coefficient of a diffraction surface on which the diffraction grating is provided while the determined respective widths of the plurality of diffraction zones are kept unchanged, after the step (a).
2. The method for designing a diffraction grating lens of claim 1 , wherein in the step (a), the respective widths of the plurality of diffraction zones are set to be non-uniform.
3. The method for designing a diffraction grating lens of claim 1 , wherein the step (a) includes a step (a1)) of setting widths of the diffraction zones while changing the widths of the diffraction zones by changing a coefficient of a phase function.
4. The method for designing a diffraction grating lens of claim 3 , wherein the step (a) includes:
a step (a2) of calculating a Fraunhofer diffraction image occurring from each of the plurality of diffraction zones;
a step (a3) of estimating an intensity of fringe flare light by superposing together the Fraunhofer diffraction images occurring from the plurality of diffraction zones; and
a step (a4) of determining the widths of the plurality of diffraction zones based on the fringe flare light.
5. The method for designing a diffraction grating lens of claim 1 , wherein:
the diffraction grating includes q diffraction zones; and
the repsective widths of the plurality of diffraction zones are determined in the step (a) so that at least one m satisfying 3<m≦q satisfies Exp. 4 below, where P 1 , P 2 , P m-1 and P m denote widths of 1 st , 2 nd , m−1 th and m th diffraction zones, respectively, counting from an optical axis
k
=
(
1
P
m
-
1
·
P
m
-
1
-
P
m
P
m
-
1
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P
m
)
/
(
1
P
1
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P
1
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P
2
P
1
·
P
2
)
>
1.6
.
[
Exp
.
4
]
6. The method for designing a diffraction grating lens of claim 1 , wherein the diffraction grating is formed only on one surface.
7. A method for manufacturing a diffraction grating lens, comprising designing a diffraction grating lens in accordance with the method of claim 1 ; and manufacturing the diffraction grating lens based on the design.
8. A method for designing an image pickup optical system, the image pickup optical system comprising:
a diffraction grating lens having a diffraction grating composed of a plurality of diffraction zones;
a spherical surface or an aspherical lens; and
a stop, the method comprising the steps of:
(a) determining respective widths of the plurality of diffraction zones; and
(b) determining an aspherical coefficient of a diffraction surface on which the diffraction grating is provided while the determined respective widths of the plurality of diffraction zones are kept unchanged, after the step (a).
9. The method for designing an image pickup optical system of claim 8 , wherein the respective widths of the plurality of diffraction zones are determined in the step (a) so as to satisfy Exp. 13 below, where P 1 and P 2 denote the widths of 1 st and 2 nd diffraction zones counting from the optical axis side, P max denotes the width of the diffraction zone at a position of an effective diameter h max , and P max-1 denotes the width of the second diffraction zone counting from the position of the effective diameter h max toward an optical axis side
k
=
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1
P
max
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1
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P
max
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1
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max
P
max
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1
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max
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1
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1
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P
2
P
1
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P
2
)
>
1.6
.
[
Exp
.
13
]
10. The method for designing an image pickup optical system of claim 8 , wherein the respective widths of the plurality of diffraction zones are set to be non-uniform in the step (a).
11. The method for designing an image pickup optical system of claim 8 , wherein the step (a) includes a step (a1)) of setting the widths of the diffraction zones while changing the widths of the diffraction zones by changing a coefficient of a phase function.
12. The method for designing an image pickup optical system of claim 11 , the step (a) includes the steps of:
(a2) calculating Fraunhofer diffraction images occurring from the plurality of diffraction zones;
(a3) estimating an intensity of fringe flare light by superposing together the Fraunhofer diffraction images occurring from the plurality of diffraction zones; and
(a4) determining the widths of the plurality of diffraction zones based on the fringe flare light.
13. A method for manufacturing an image pickup optical system, comprising designing an image pickup optical system in accordance with the method of claim 8 ; and manufacturing the image pickup optical system based on the design.