JP2007279547A - Imaging optical system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging optical system that is wide in view angle and reduced in distortion aberration. <P>SOLUTION: The imaging optical system includes a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, and a diaphragm STO. If the effective radius of the face S1 of the first lens group G1 closest to an object is SDa and the effective radius SDb of the face S2 of the first lens group G1, furthest therefrom is SDb, the imaging optical system satisfies the conditional formula (1): 2.9<SDa/SDb<13. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an imaging optical system, and more particularly to an imaging optical system using near infrared rays.

  In recent years, research and development of biometric authentication technology for identifying individuals using biometric features has been progressing rapidly. As one of biometric authentication techniques, a vein authentication system using a finger is known. In such a finger vein authentication system, personal authentication is performed using a finger vein pattern.

  In the finger vein authentication system, the near-infrared rays that are not harmful to the human body are used, and hemoglobin in the finger blood is imaged by the imaging optical system. Then, the vein pattern is discriminated by image processing the photographing result. By using the vein pattern inside the living body, it has a feature that it is difficult to forge and tamper as compared with fingerprints and irises. Moreover, the probability of malfunctioning is low and high-precision security can be realized. For this reason, for example, the vein authentication system is used for an entry / exit system or logon authentication of a personal computer. Thus, the vein authentication system using a finger is expected to be usable in a wide range of fields.

  The vein authentication system requires an optical system with a wide angle of view. A wide-angle optical system has been proposed in Patent Document 1, for example.

JP 2000-171700 A

  However, the optical system of the prior art widens the angle of view in a state where distortion is considerably large. When an optical system having a large distortion is used for the vein authentication system, the shape of the vein pattern to be imaged is distorted. For this reason, the problem that authentication accuracy will fall arises.

  The present invention has been made in view of the above, and an object thereof is to provide an imaging optical system having a wide angle of view and a reduced distortion.

In order to solve the above-described problems and achieve the object, according to the present invention, a first lens group having a negative refractive power and a second lens group having a positive refractive power are provided, and an object in the first lens group. When the effective radius of the surface closest to the side is SDa and the effective radius of the surface farthest from the object side in the first lens group is SDb, the following conditional expression (1) is satisfied: An imaging optical system can be provided.
2.9 <SDa / SDb <13 (1)

  When the lower limit value of conditional expression (1) is exceeded or when the upper limit value is exceeded, distortion is greatly generated in a state in which the degree of field curvature and astigmatism is well maintained.

  Further, in conditional expression (1), if the lower limit value is 3.5, and further 4.5, distortion can be further reduced in a state where the degree of field curvature and astigmatism is maintained well. .

  Further, when the upper limit value is set to 10 and further to 8.5, the distortion aberration can be further reduced while maintaining the degree of curvature of field and astigmatism.

Further, according to a preferred aspect of the present invention, the air equivalent length along the optical axis from the object to the surface closest to the object side of the first lens group is DOB and the total thickness along the optical axis of the first lens group. It is desirable that the following conditional expression (2) is satisfied when the thickness is DG1.
0.18 <DOB / DG1 <2.8 (2)

  When the lower limit value of conditional expression (2) is exceeded, or when the upper limit value is exceeded, distortion is greatly generated in a state where the degree of field curvature and astigmatism is well maintained.

  Here, the “air equivalent length” is obtained by dividing the thickness of the medium by the refractive index of the medium. For example, in each embodiment described below, a cover glass may be disposed in the optical path between the object and the first lens group. In this case, the optical path between the object and the first lens group includes a cover glass layer and an air layer. The air equivalent length in the cover glass portion is a value obtained by dividing the thickness of the cover glass (medium) by the refractive index of the cover glass (medium). In addition, the air-converted length in the air portion is a value as it is in the air thickness. That is, the “air conversion length” in this case refers to a value obtained by adding the air conversion length in the cover glass portion and the air conversion length in the air portion.

  Further, regarding conditional expression (2), if the lower limit value is 0.6, and further 0.8, distortion can be further reduced while maintaining the degree of field curvature and astigmatism. .

  Further, when the upper limit value is 2.2, and further 2.0, distortion can be further reduced while maintaining the degree of field curvature and astigmatism.

  The imaging optical system according to the present invention has an effect that the distortion is small with a wide angle of view.

  Examples 1 to 9 of the imaging optical system according to the present invention will be described below. Lens sectional views of Examples 1 to 9 are shown in FIGS. 1 to 9, respectively. In the drawing, the first lens group is indicated by G1, the second lens group is indicated by G2, the parallel flat cover glass is indicated by CG1, CG2, the object plane is indicated by O, and the image plane is indicated by I.

The imaging lens of the present invention includes a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power, and the effective radius of the surface closest to the object side in the first lens group G1 is defined as SDa. When the effective radius of the surface farthest from the object side in the first lens group G1 is SDb, the following conditional expression (1) is satisfied.
2.9 <SDa / SDb <13 (1)

Also, the air equivalent length along the optical axis AX from the object to the surface closest to the object side of the first lens group G1 is DOB, and the total thickness along the optical axis AX of the first lens group G1 is DG1. The following conditional expression (2) is satisfied.
0.18 <DOB / DG1 <2.8 (2)

Hereinafter, each example will be described. In the present application, the notations such as “plano-convex”, “biconvex”, and “plano-concave” representing the shape of the lens are described taking into account only the paraxial radius of curvature of each lens surface. For this reason, it may not be suitable for the general shape of the lens cross-sectional view.
As shown in FIG. 1, the imaging optical system according to the first exemplary embodiment includes, in order from the object side, a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power.

  In order from the object side, the first lens group G1 includes a planoconcave negative lens L11, and has a negative refracting power as a whole. The second lens group G2 includes a positive meniscus lens L21 having a convex surface directed toward the image surface side and a plano-convex positive lens L22, and has a positive refractive power as a whole.

  The aspheric surfaces are provided on the five surfaces, ie, both surfaces S1 and S2 of the planoconcave negative lens L11, the image side surface S4 of the positive meniscus lens L21, and both surfaces S5 and S6 of the planoconvex positive lens L22.

  The S3 surface on the object side of the positive meniscus lens L21 in the second lens group G2 also serves as a stop.

  As shown in FIG. 2, the imaging optical system of Example 2 includes, in order from the object side, a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power.

  In order from the object side, the first lens group G1 includes a planoconcave negative lens L11, and has a negative refracting power as a whole. The second lens group G2 includes a biconvex positive lens L21 and a planoconvex positive lens L22, and has a positive refractive power as a whole.

  The aspheric surfaces are provided on the five surfaces, that is, both surfaces S1 and S2 of the planoconcave negative lens L11, the image side surface S4 of the biconvex positive lens L21, and both surfaces S5 and S6 of the planoconvex positive lens L22.

  The S3 surface on the object side of the biconvex positive lens L21 of the second lens group G2 also serves as a stop.

  As shown in FIG. 3, the imaging optical system of Example 3 includes, in order from the object side, a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power.

  In order from the object side, the first lens group G1 includes a planoconcave negative lens L11, and has a negative refracting power as a whole. The second lens group G2 includes a biconvex positive lens L21 and a planoconvex positive lens L22, and has a positive refractive power as a whole.

  The aspheric surfaces are provided on the five surfaces, that is, both surfaces S1 and S2 of the planoconcave negative lens L11, the image side surface S4 of the biconvex positive lens L21, and both surfaces S5 and S6 of the planoconvex positive lens L22.

  The S3 surface on the object side of the biconvex positive lens L21 of the second lens group G2 also serves as a stop.

  As shown in FIG. 4, the imaging optical system of Example 4 includes, in order from the object side, a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power. The cover glass CG1 is not provided on the object plane O.

  In order from the object side, the first lens group G1 includes a planoconcave negative lens L11, and has a negative refracting power as a whole. The second lens group G2 includes a biconvex positive lens L21 and a planoconvex positive lens L22, and has a positive refractive power as a whole.

  The aspheric surfaces are provided on the five surfaces, that is, both surfaces S1 and S2 of the planoconcave negative lens L11, the image side surface S4 of the biconvex positive lens L21, and both surfaces S5 and S6 of the planoconvex positive lens L22.

  The S3 surface on the object side of the biconvex positive lens L21 of the second lens group G2 also serves as a stop.

  As shown in FIG. 5, the imaging optical system of Example 5 includes, in order from the object side, a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power.

  In order from the object side, the first lens group G1 includes a planoconcave negative lens L11, and has a negative refracting power as a whole. The second lens group G2 includes a positive meniscus lens L21 having a convex surface directed toward the image surface side and a plano-convex positive lens L22, and has a positive refractive power as a whole.

  The aspheric surfaces are provided on the five surfaces, ie, both surfaces S1 and S2 of the planoconcave negative lens L11, the image side surface S4 of the positive meniscus lens L21, and both surfaces S5 and S6 of the planoconvex positive lens L22.

  The S3 surface on the object side of the positive meniscus lens L21 in the second lens group G2 also serves as a stop.

  As shown in FIG. 6, the imaging optical system of Example 6 includes, in order from the object side, a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power.

  In order from the object side, the first lens group G1 includes a planoconcave negative lens L11, and has a negative refracting power as a whole. The second lens group G2 includes a biconvex positive lens L21 and a planoconvex positive lens L22, and has a positive refractive power as a whole.

  The aspheric surfaces are provided on the five surfaces, that is, both surfaces S1 and S2 of the planoconcave negative lens L11, the image side surface S5 of the biconvex positive lens L21, and both surfaces S6 and S7 of the planoconvex positive lens L22.

  The diaphragm S3 is provided between the first lens group G1 and the second lens group G2.

  As shown in FIG. 7, the imaging optical system according to the seventh embodiment includes, in order from the object side, a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power.

  In order from the object side, the first lens group G1 includes a planoconcave negative lens L11, and has a negative refracting power as a whole. The second lens group G2 includes a biconvex positive lens L21 and a planoconvex positive lens L22, and has a positive refractive power as a whole.

  The aspheric surfaces are provided on the five surfaces, that is, both surfaces S1 and S2 of the planoconcave negative lens L11, the image side surface S5 of the biconvex positive lens L21, and both surfaces S6 and S7 of the planoconvex positive lens L22.

  The diaphragm S3 is provided between the first lens group G1 and the second lens group G2.

  As shown in FIG. 8, the imaging optical system according to the eighth embodiment includes, in order from the object side, a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power.

  In order from the object side, the first lens group G1 includes a planoconcave negative lens L11 and a negative meniscus lens L12 having a convex surface directed toward the object side, and has a negative refracting power as a whole. The second lens group G2 includes a biconvex positive lens L21 and a planoconvex positive lens L22, and has a positive refractive power as a whole.

  The aspheric surfaces are both surfaces S1 and S2 of the plano-concave negative lens L11, both surfaces S3 and S4 of the negative meniscus lens L12, the image-side surface S6 of the biconvex positive lens L21, and both surfaces S7 and S8 of the plano-convex positive lens L22. And is provided on seven sides.

  The S5 surface on the object side of the biconvex positive lens L21 of the second lens group G2 also serves as a stop.

  As shown in FIG. 9, the imaging optical system of Example 9 includes, in order from the object side, a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power.

  In order from the object side, the first lens group G1 includes a planoconcave negative lens L11, and has a negative refracting power as a whole. The second lens group G2 includes a positive meniscus lens L21 having a convex surface directed to the image surface side, a positive meniscus lens L22 having a convex surface directed to the image surface side, and a planoconvex positive lens L23, and is positively refracted as a whole. Have power.

  The aspheric surfaces are both surfaces S1 and S2 of the plano-concave negative lens L11, the image side surface S4 of the positive meniscus lens L21, both surfaces S5 and S6 of the positive meniscus lens L22, and both surfaces S7 and S8 of the plano-convex positive lens L23. And is provided on seven sides.

  The S3 surface on the object side of the positive meniscus lens L21 in the second lens group G2 also serves as a stop.

  Next, numerical data of each of the above embodiments will be shown. Hereinafter, in the numerical data of all the examples, r represents the radius of curvature of each lens surface, d represents the thickness or air spacing of each lens, and n represents the refractive index of each lens medium at the used wavelength.

The aspherical shape is expressed by the following equation when the optical axis direction is z, the direction orthogonal to the optical axis is y, the conic coefficient is K, and the aspherical coefficients are A, B, C, and D. .
z = (y ² / r) / [1+ {1− (1 + K) (y / r) ² } ^1/2 ] + Ay ⁴ + By ⁶ + Cy ⁸ + Dy ¹⁰
In the aspheric coefficient of the following numerical data, E represents a power of 10. For example, “E-01” represents 10 minus the first power.

  Further, the surface numbers are those obtained by counting from the object surface O to the imaging surface (image surface) I including the surfaces of the cover glasses CG1 and CG2.

  Further, in the following specification value table, OBJ represents an object plane, IMG represents an imaging plane (imaging plane), Flat represents a plane (curvature radius = infinity), ASP represents an aspheric surface, and STO represents an aperture. . In addition, the “effective radius” refers to “the maximum value of the distance from the optical axis of a point in the region through which light rays pass on the lens surface”. The value indicating the length is the length in mm.

The following specification values are common to all the embodiments, but are not limited to these values.
Total length from object plane O to imaging plane I = 14 mm
Object height = 29.16mm
Half diagonal length of image pickup surface of image pickup element = 2.25 mm
F number = 3.0

  In addition, although shaping | molding of a lens presupposes a shaping | molding process, it is not specifically limited.

Example 1

Surface number rdn
OBJ Flat 0.000000
1 Flat 0.700000 1.508645
2 Flat 4.486007
3 (S1) Flat ASP 2.500000 1.517856
4 (S2) 1.158144 ASP 1.874902
STO (S3) -10.467103 1.263844 1.517856
6 (S4) -1.049490 ASP 0.300000
7 (S5) Flat ASP 1.775246 1.517856
8 (S6) -0.723301 ASP 0.300000
9 Flat 0.500000 1.508645
10 Flat 0.300000
IMG Flat 0.000000


(Aspheric coefficient)
3 (S1):
K: 0.000000
A: 0.680429E-03 B: -0.472182E-05
C: 0.000000E + 00 D: 0.000000E + 00

4 (S2):
K: -0.830258
A: -0.587345E-01 B: 0.000000E + 00
C: 0.000000E + 00 D: 0.000000E + 00

6 (S4):
K: -5.126992
A: -0.109577E-02 B: -0.119343E + 00
C: 0.000000E + 00 D: 0.000000E + 00

7 (S5):
K: 0.000000
A: 0.283302E-02 B: -0.772299E-04
C: 0.000000E + 00 D: 0.000000E + 00

8 (S6):
K: -1.012728
A: 0.125284E + 00 B: -0.575442E-01
C: 0.169680E-01 D: 0.000000E + 00

Example 2

Surface number rdn
OBJ Flat 0.000000
1 Flat 0.700000 1.508645
2 Flat 2.013984
3 (S1) Flat ASP 3.754452 1.517856
4 (S2) 0.850696 ASP 2.761102
STO (S3) 5.555242 1.774824 1.517856
6 (S4) -1.198906 ASP 0.300000
7 (S5) Flat ASP 1.595638 1.517856
8 (S6) -0.915607 ASP 0.300000
9 Flat 0.500000 1.508645
10 Flat 0.300000
IMG Flat 0.000000


(Aspheric coefficient)
3 (S1):
K: 0.000000
A: 0.200762E-03 B: -0.285262E-07
C: 0.000000E + 00 D: 0.000000E + 00

4 (S2):
K: -0.840629
A: -0.123767E-01 B: 0.000000E + 00
C: 0.000000E + 00 D: 0.000000E + 00

6 (S4):
K: -2.772873
A: -0.331840E-01 B: 0.146860E-01
C: 0.000000E + 00 D: 0.000000E + 00

7 (S5):
K: 0.000000
A: -0.158513E-01 B: 0.119198E-01
C: 0.000000E + 00 D: 0.000000E + 00

8 (S6):
K: -0.766459
A: 0.132951E + 00 B: -0.325204E-01
C: 0.139424E-01 D: 0.000000E + 00

Example 3

Surface number rdn
OBJ Flat 0.000000
1 Flat 0.700000 1.508645
2 Flat 3.860211
3 (S1) Flat ASP 4.500000 1.517856
4 (S2) 0.520567 ASP 0.500130
STO (S3) 3.681974 1.468622 1.517856
6 (S4) -0.802630 ASP 0.300000
7 (S5) Flat ASP 1.571038 1.517856
8 (S6) -0.860122 ASP 0.300000
9 Flat 0.500000 1.508645
10 Flat 0.300000
IMG Flat 0.000000


(Aspheric coefficient)
3 (S1):
K: 0.000000
A: 0.408439E-03 B: 0.161974E-05
C: 0.000000E + 00 D: 0.000000E + 00

4 (S2)
K: -3.377107
A: 0.985455E + 00 B: 0.000000E + 00
C: 0.000000E + 00 D: 0.000000E + 00

6 (S4):
K: -1.051984
A: -0.125937E + 00 B: 0.982128E-01
C: 0.000000E + 00 D: 0.000000E + 00

7 (S5):
K: 0.000000
A: -0.565757E-01 B: 0.128686E-01
C: 0.000000E + 00 D: 0.000000E + 00

8 (S6):
K: -0.929871
A: 0.178978E + 00 B: -0.899813E-01
C: 0.203261E-01 D: 0.000000E + 00

Example 4

Surface number rdn
OBJ Flat 0.000000
1 Flat 0.000000 1.508645
2 Flat 6.750000
3 (S1) Flat ASP 2.500000 1.517856
4 (S2) 0.484625 ASP 0.561186
STO (S3) 1.111639 0.882032 1.517856
6 (S4) -1.290375 ASP 0.300000
7 (S5) Flat ASP 1.906782 1.517856
8 (S6) -0.628686 ASP 0.300000
9 Flat 0.500000 1.508645
10 Flat 0.300000
IMG Flat 0.000000


(Aspheric coefficient)
3 (S1):
K: 0.000000
A: 0.240490E-02 B: 0.496866E-05
C: 0.000000E + 00 D: 0.000000E + 00

4 (S2):
K: -0.159450
A: -0.453100E + 00 B: 0.000000E + 00
C: 0.000000E + 00 D: 0.000000E + 00

6 (S4):
K: -17.222636
A: -0.137295E + 00 B: 0.869398E + 00
C: 0.000000E + 00 D: 0.000000E + 00

7 (S5):
K: 0.000000
A: -0.272576E-01 B: -0.163533E-02
C: 0.000000E + 00 D: 0.000000E + 00

8 (S6):
K: -0.851861
A: 0.297995E + 00 B: -0.931650E-01
C: 0.304168E-01 D: 0.000000E + 00

Example 5

Surface number rdn
OBJ Flat 0.000000
1 Flat 0.700000 1.508645
2 Flat 2.700000
3 (S1) Flat ASP 2.648013 1.517856
4 (S2) 0.958015 ASP 3.467316
STO (S3) -89.250626 1.716189 1.517856
6 (S4) -0.928282 ASP 0.300000
7 (S5) Flat ASP 1.368482 1.517856
8 (S6) -1.668314 ASP 0.300000
9 Flat 0.500000 1.508645
10 Flat 0.300000
IMG Flat 0.000000


(Aspheric coefficient)
3 (S1):
K: 0.000000
A: 0.252131E-03 B: -0.383353E-06
C: 0.000000E + 00 D: 0.000000E + 00

4 (S2):
K: -1.000041
A: -0.238073E-01 B: 0.000000E + 00
C: 0.000000E + 00 D: 0.000000E + 00

6 (S4):
K: -1.494428
A: -0.110821E + 00 B: 0.287963E-01
C: 0.000000E + 00 D: 0.000000E + 00

7 (S5):
K: 0.000000
A: -0.979332E-01 B: 0.232352E-01
C: 0.000000E + 00 D: 0.000000E + 00

8 (S6):
K: -0.947313
A: -0.887905E-01 B: 0.343075E-01
C: -0.244566E-02 D: 0.000000E + 00

Example 6

Surface number rdn
OBJ Flat 0.000000
1 Flat 0.700000 1.508645
2 Flat 3.360553
3 (S1) Flat ASP 3.381561 1.517856
4 (S2) 0.852507 ASP 1.894692
STO (S3) Flat 0.300000
6 (S4) 56.209077 1.499431 1.517856
7 (S5) -0.940840 ASP 0.300000
8 (S6) Flat ASP 1.463763 1.517856
9 (S7) -1.121715 ASP 0.300000
10 Flat 0.500000 1.508645
11 Flat 0.300000
IMG Flat 0.000000


(Aspheric coefficient)
3 (S1):
K: 0.000000
A: 0.367937E-03 B: -0.930017E-06
C: 0.000000E + 00 D: 0.000000E + 00

4 (S2):
K: -0.999942
A: -0.468065E-01 B: 0.000000E + 00
C: 0.000000E + 00 D: 0.000000E + 00

7 (S5):
K: -1.626417
A: -0.384370E-01 B: -0.120676E-01
C: 0.000000E + 00 D: 0.000000E + 00

8 (S6):
K: 0.000000
A: 0.231906E-01 B: -0.605877E-03
C: 0.000000E + 00 D: 0.000000E + 00

9 (S7):
K: -1.146529
A: 0.305497E-01 B: 0.116674E-01
C: 0.000000E + 00 D: 0.000000E + 00

Example 7

Surface number rdn
OBJ Flat 0.000000
1 Flat 0.700000 1.508645
2 Flat 2.994123
3 (S1) Flat ASP 4.011736 1.517856
4 (S2) 0.744101 ASP 1.717954
STO (S3) Flat 0.300000
6 (S4) 3.927789 1.529534 1.517856
7 (S5) -1.026943 ASP 0.300000
8 (S6) Flat ASP 1.346652 1.517856
9 (S7) -1.113552 ASP 0.300000
10 Flat 0.500000 1.508645
11 Flat 0.300000
IMG Flat 0.000000


(Aspheric coefficient)
3 (S1):
K: 0.000000
A: 0.314015E-03 B: -0.960617E-07
C: 0.000000E + 00 D: 0.000000E + 00

4 (S2):
K: -0.830738
A: -0.352792E-01 B: 0.000000E + 00
C: 0.000000E + 00 D: 0.000000E + 00

7 (S5):
K: -2.417602
A: -0.678379E-01 B: 0.155341E-01
C: 0.000000E + 00 D: 0.000000E + 00

8 (S6):
K: 0.000000
A: 0.269251E-01 B: -0.134111E-01
C: 0.000000E + 00 D: 0.000000E + 00

9 (S7):
K: -1.219707
A: 0.549711E-01 B: -0.355696E-02
C: 0.811632E-03 D: 0.000000E + 00

Example 8

Surface number rdn
OBJ Flat 0.000000
1 Flat 0.700000 1.508645
2 Flat 0.531284
3 (S1) Flat ASP 3.339394 1.517856
4 (S2) 6.536761 ASP 0.975062
5 (S3) 12.595805 ASP 2.000000 1.517856
6 (S4) 0.773270 ASP 1.993654
STO (S5) 14.396703 1.549408 1.517856
8 (S6) -0.953017 ASP 0.300000
9 (S7) Flat ASP 1.511198 1.517856
10 (S8) -1.041347 ASP 0.300000
11 Flat 0.500000 1.508645
12 Flat 0.300000
IMG Flat 0.000000


(Aspheric coefficient)
3 (S1):
K: 0.000000
A: 0.104061E-03 B: 0.774186E-07
C: 0.000000E + 00 D: 0.000000E + 00

4 (S2):
K: -0.677387
A: -0.532486E-03 B: 0.000000E + 00
C: 0.000000E + 00 D: 0.000000E + 00

5 (S3):
K: 1.537080
A: 0.873207E-05 B: 0.000000E + 00
C: 0.000000E + 00 D: 0.000000E + 00

6 (S4):
K: -0.999170
A: 0.495474E-01 B: 0.000000E + 00
C: 0.000000E + 00 D: 0.000000E + 00

8 (S6):
K: -1.923042
A: -0.637268E-01 B: -0.120068E-01
C: 0.000000E + 00 D: 0.000000E + 00

9 (S7):
K: 0.000000
A: -0.816885E-02 B: 0.539088E-02
C: 0.000000E + 00 D: 0.000000E + 00

10 (S8):
K: -1.015500
A: 0.399889E-01 B: 0.460290E-02
C: 0.781512E-03 D: 0.000000E + 00

Example 9

Surface number rdn
OBJ Flat 0.000000
1 Flat 0.700000 1.508645
2 Flat 3.789718
3 (S1) Flat ASP 2.000000 1.517856
4 (S2) 0.810125 ASP 2.330509
STO (S3) -31.352437 0.898788 1.517856
6 (S4) -2.505478 ASP 0.300000
7 (S5) -19.995259 ASP 1.174427 1.517856
8 (S6) -1.235322 ASP 0.300000
9 (S7) Flat ASP 1.406558 1.517856
10 (S8) -1.203698 ASP 0.300000
11 Flat 0.500000 1.508645
12 Flat 0.300000
IMG Flat 0.000000


(Aspheric coefficient)
3 (S1):
K: 0.000000
A: 0.845270E-03 B: -0.253685E-05
C: 0.000000E + 00 D: 0.000000E + 00

4 (S2):
K: -0.759711
A: -0.770034E-01 B: 0.000000E + 00
C: 0.000000E + 00 D: 0.000000E + 00

6 (S4):
K: -1.000703
A: -0.209637E-02 B: 0.000000E + 00
C: 0.000000E + 00 D: 0.000000E + 00

7 (S5):
K: 275.165461
A: 0.700185E-01 B: 0.000000E + 00
C: 0.000000E + 00 D: 0.000000E + 00

8 (S6):
K: -1.455465
A: 0.444584E-01 B: 0.120591E-01
C: 0.000000E + 00 D: 0.000000E + 00

9 (S7):
K: 0.000000
A: 0.209667E-01 B: -0.634491E-03
C: 0.000000E + 00 D: 0.000000E + 00

10 (S8):
K: -0.615693
A: 0.985644E-01 B: -0.104216E-01
C: 0.622079E-02 D: 0.000000E + 00

  10 to 18 show the (vertical) spherical aberration, astigmatism, and distortion of the imaging optical systems of Examples 1 to 9, respectively. In the spherical aberration diagram, the vertical axis represents the aperture ratio. In the astigmatism diagram, the broken line indicates the tangential surface, and the solid line indicates the sagittal surface. In the present invention, the distortion is within about 8% as is clear from each aberration diagram, while the wide field angle that the object height is about twice as large as the total length. The oblique incident angle of the light beam with respect to the image sensor (imager) is 20 degrees or less.

The values of conditional expressions (1) and (2) in Examples 1 to 9 are as follows.

SDa SDb Conditional expression (1) Conditional expression (2) Radius of aperture stop Example 1 6.131 2.093 2.930 1.980 0.186
Example 2 9.146 1.632 5.606 0.660 0.222
Example 3 7.266 0.582 12.480 0.961 0.162
Example 4 4.090 0.496 8.240 2.700 0.193
Example 5 8.968 2.639 3.398 1.195 0.243
Example 6 7.017 1.532 4.580 1.131 0.200
Example 7 8.018 1.234 6.500 0.862 0.206
Example 8 12.848 1.421 9.039 0.186 0.212
Example 9 5.710 1.445 3.951 2.127 0.223

  The imaging optical system according to the present invention can be applied to a vein authentication system when infrared light is used as a light source. Furthermore, when visible light is used, it can be applied to a proximity imaging apparatus such as a fingerprint authentication system. However, it is necessary that the lens medium has a refractive index listed in the numerical data described above at the wavelength used.

  In the above embodiment, since the optical system is constituted by a small number of lenses, the optical system can be thinned. Further, the number of assembly steps of the optical system can be reduced. However, the number of lenses is not limited to three or four described in the above embodiment.

  In Examples 6 and 7, the diaphragm is provided by disposing a member different from the lens in the optical system. Specifically, a thin plate having an opening is disposed to form a diaphragm.

  On the other hand, in Examples 1 to 5 and Examples 8 and 9, a diaphragm is formed on the lens surface. Specifically, a very thin aperture can be formed by applying vapor deposition or black coating (paint or the like) to a portion of the lens surface that does not transmit light. For this reason, it is not necessary to separately provide a member for fixing the diaphragm, and the optical system can be assembled with a simple configuration. Further, by forming a stop on the lens surface, the thickness of the stop in the optical axis direction can be reduced.

  In actual use, it is desirable to use as a light source a semiconductor laser (LD) that supplies near-infrared light having a wavelength of 800 to 900 nm. The light source can be arbitrarily arranged. As a rule, the finger is placed in contact with the flat cover glass CG1. Based on the imaging result, the absorption of the amount of light by the vein is measured. For example, a living body transmits infrared light. On the other hand, a portion where near infrared light is absorbed by the vein is a dark portion. Such a light quantity distribution is guided to an image sensor by an imaging optical system to form an image. Moreover, when there is no cover glass CG1, it is preferable to provide at least one finger holding member. Specifically, it is preferable to provide a finger holding member for holding the tip of the finger or the base of the finger. According to this configuration, since there is no reflection of incident light by the cover glass, the amount of transmitted light that passes through the finger is larger than when the cover glass CG1 is present. Further, when the amount of transmitted light increases, the incident light on the image sensor can be easily imaged.

  As described above, the present invention is an imaging optical system with a wide angle of view and a small distortion, and is particularly suitable for an imaging optical system for a vein authentication system.

It is a figure which shows the cross-sectional structure of the imaging optical system which concerns on Example 1 of this invention. It is a figure which shows the cross-sectional structure of the imaging optical system which concerns on Example 2 of this invention. It is a figure which shows the cross-sectional structure of the imaging optical system which concerns on Example 3 of this invention. It is a figure which shows the cross-sectional structure of the imaging optical system which concerns on Example 4 of this invention. It is a figure which shows the cross-sectional structure of the imaging optical system which concerns on Example 5 of this invention. It is a figure which shows the cross-sectional structure of the imaging optical system which concerns on Example 6 of this invention. It is a figure which shows the cross-sectional structure of the imaging optical system which concerns on Example 7 of this invention. It is a figure which shows the cross-sectional structure of the imaging optical system which concerns on Example 8 of this invention. It is a figure which shows the cross-sectional structure of the imaging optical system which concerns on Example 9 of this invention. FIG. 3 is a diagram illustrating various aberrations of the imaging optical system according to Example 1. FIG. 6 is a diagram illustrating various aberrations of the imaging optical system according to Example 2. FIG. 6 is a diagram illustrating various aberrations of the imaging optical system according to Example 3. FIG. 6 is a diagram illustrating various aberrations of the imaging optical system according to Example 4. FIG. 10 is a diagram illustrating various aberrations of the imaging optical system according to Example 5. FIG. 10 is a diagram illustrating various aberrations of the imaging optical system according to Example 6. FIG. 10 is a diagram illustrating various aberrations of the imaging optical system according to Example 7. FIG. 10 is a diagram illustrating various aberrations of the imaging optical system according to Example 8. FIG. 10 is a diagram illustrating various aberrations of the imaging optical system according to Example 9.

Explanation of symbols

O Object surface I Imaging surface G1, G2 Lens group L11, L12, L21, L22, L23 Each lens S1, S2, S3, S4, S5, S6, S7, S8 Lens surface (aperture)
AX optical axis

Claims (2)

A first lens group having a negative refractive power and a second lens group having a positive refractive power;
SDa is the effective radius of the surface of the first lens group closest to the object side,
An imaging optical system satisfying the following conditional expression (1), where SDb is an effective radius of a surface farthest from the object side in the first lens group.
2.9 <SDa / SDb <13 (1) DOB is the air equivalent length along the optical axis from the object to the surface closest to the object side of the first lens group,
The imaging optical system according to claim 1, wherein the following conditional expression (2) is satisfied when a total thickness along the optical axis of the first lens group is DG1.
0.18 <DOB / DG1 <2.8 (2)

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