JP2008191363A - Reading lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reading lens that copes with high resolution, is small and bright and has a wide field angle. <P>SOLUTION: The reading lens includes, in order from the object 100 side, a first lens group G<SB>11</SB>having negative refractive power, a second lens group G<SB>12</SB>having positive refractive power, and a third lens group G<SB>13</SB>having negative refractive power. The first lens group G<SB>11</SB>has, in order from the object 100 side, a negative lens 111 and a meniscus lens 112 the convex face of which is oriented on the image face 101 side. The second lens group G<SB>12</SB>includes a first lens 121 having positive refractive power and aspherical faces on both sides. The third lens group G<SB>13</SB>is composed of two meniscus concave lenses 131 and 132, the convex faces of which are oriented on the image face 101 side. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a reading lens for reading image information and the like.

  Conventionally, an image scanner, a copy camera, a document camera, and the like are known as devices for reading information such as an image printed on a barcode or paper. Such an apparatus is provided with a reading lens for reading image information (see, for example, Patent Documents 1 to 4).

  For the reading lens, it is desired that various aberrations such as distortion and chromatic aberration be corrected satisfactorily. In recent years, downsizing of the apparatus has been promoted, and further reduction in the size and wide angle of the reading lens is required. Furthermore, when reading barcodes, high resolution is required to cope with complex two-dimensional barcode reading from the conventional simple one-dimensional, and high resolution and high contrast MTF performance is required. .

Japanese Patent Laid-Open No. 5-45583 JP-A-6-94993 JP 2005-10197 A JP 2002-214527 A

  In Patent Document 1, a retrofocus type lens is proposed. However, although the lens disclosed in Patent Document 1 has a high resolution in the meridional direction, it has a large astigmatism and a low resolution in the sagittal direction, so that it is not suitable as a lens for reading images.

  Conventionally, a so-called Gaussian optical system in which an optical system sandwiching a stop is substantially symmetric has been widely used as a reading lens. A Gaussian optical system generates a small amount of distortion, but changes in sagittal and meridional field curvatures change in opposite directions at an intermediate angle of view, and a large astigmatic difference is likely to occur. For this reason, the Gauss type optical system has a problem that its performance is insufficient for use in an image reading apparatus that requires high resolution.

  In addition, since the Gauss type optical system cannot take a large angle of view, there is a problem that the optical system has to be enlarged in order to obtain a high resolution and is not suitable for downsizing. Furthermore, to correct aberrations, it is difficult to achieve high resolution up to the periphery of the screen because the astigmatic difference cannot be reduced by simply adding the number of lenses while maintaining a symmetric type, and the aberration cannot be reduced sufficiently. Met.

  Patent Document 2 proposes an optical system in which two lenses are added to a Gaussian optical system to solve the above problems. Certainly, the optical system disclosed in Patent Document 2 has a good resolution balance between the meridional direction and the sagittal direction, but the overall resolution is not improved.

  Also in Patent Document 3, an optical system is proposed in which the conventional Gaussian optical system is improved to improve the resolution. In the optical system disclosed in Patent Document 3, higher resolution than that in the optical systems disclosed in Patent Document 1 and Patent Document 2 can be obtained. However, even if the resolution is further improved, astigmatism and coma do not become small, and so much effect cannot be expected.

  On the other hand, Patent Document 4 proposes an optical system having a configuration different from that of a conventional Gaussian optical system. However, the optical system disclosed in Patent Document 4 has a dark F number of 5.5, and a resolution exceeding the optical system disclosed in Patent Document 3 cannot be obtained. As inappropriate.

  An object of the present invention is to provide a bright reading lens having a small size and a wide angle of view while corresponding to a high resolution in order to solve the above-described problems caused by the conventional technology.

In order to solve the above-described problems and achieve the object, the reading lens according to the first aspect of the present invention includes, in order from the object side, one or two negative lenses and a meniscus lens having a convex surface facing the image surface side. And a first lens group having a negative refractive power as a whole, and a first lens having a positive refractive power and an aspheric surface formed on one or both sides, and has a positive refractive power as a whole. And a second lens group having a negative refractive power as a whole, and a second lens group having a negative refractive power as a whole. When L _{a is} the total length of the first lens group and L ₂ is the distance from the first lens first surface of the first lens group to the second lens first surface of the second lens group, the following conditional expression is satisfied: Features.
(1) 0.25 <L ₂ / L _a <0.45

  According to the first aspect of the present invention, it is possible to provide a bright reading lens that is small and has a wide angle of view while supporting high resolution. Specifically, by forming an aspheric surface on the first lens included in the second lens group, various aberrations such as spherical aberration and coma can be effectively corrected up to the periphery of the screen. Further, by configuring the third lens group using a meniscus lens, it is possible to achieve a wide angle of view with a small lens without increasing distortion. In particular, when the conditional expression (1) is satisfied, the lens can be reduced in size without degrading the optical performance.

A reading lens according to a second aspect of the present invention is the reading lens according to the first aspect, wherein the second lens group is a second lens made of a convex lens disposed on the image plane side of the first lens. And a third lens made of a concave lens, wherein when the Abbe number of the second lens is ν ₂ and the Abbe number of the third lens is ν ₃ , the following conditional expression is satisfied: .
(2) 31 <ν ₂ −ν ₃

  According to the second aspect of the invention, in addition to the effect brought about by the first aspect of the invention, the longitudinal chromatic aberration and the chromatic aberration of magnification can be corrected more satisfactorily.

Further, such reading lens to the invention of claim 3 is the invention according to claim 1 or 2, wherein the focal length of the reading lens system f, and the focal length of the third lens group when the f ₃ The following conditional expression is satisfied.
(3) −1.08 <f / f ₃ <−0.51

  According to the invention described in claim 3, in addition to the effects brought about by the invention described in claim 1 or 2, distortion and astigmatism can be corrected more favorably.

  According to the present invention, it is possible to provide a bright reading lens with a small size and a wide angle of view while supporting high resolution. By satisfying predetermined conditions, the reading lens can achieve a reduction in size and a wide angle of view and good aberration correction.

    Hereinafter, preferred embodiments of a reading lens according to the present invention will be described in detail.

  The reading lens according to this embodiment includes, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a negative refractive power. Are arranged.

  The first lens group includes, in order from the object side, one or two negative lenses and a meniscus lens having a convex surface facing the image surface, and has a negative refractive power as a whole. . The meniscus lens included in the first lens group may be composed of a cemented lens as long as the convex surface faces the image surface side.

  The second lens group includes, in order from the object side, a plurality of lenses including a first lens having a positive refractive power and an aspheric surface formed on one side or both sides, and has a positive refractive power as a whole. ing. By forming an aspheric surface on the first lens included in the second lens group, various aberrations such as spherical aberration and coma can be effectively corrected to the periphery of the screen.

  The third lens group is composed of one or two meniscus concave lenses having a convex surface facing the image surface side, and has a negative refractive power as a whole. By configuring the third lens group using a meniscus lens, it is possible to achieve a wide angle of view without increasing distortion by a small lens.

  An object of the present invention is to provide a reading lens that is small, has a wide field angle (half field angle of 23 ° or more), and is bright (F number is about 4) while supporting high resolution. Therefore, in order to achieve such an object, various conditions as shown below are set in addition to the above-described configuration.

First, when the total length of the reading lens is L _a and the distance from the first lens first surface of the first lens group to the second lens first surface of the second lens group is L ₂ , the following conditional expression: Is preferably satisfied.
(1) 0.25 <L ₂ / L _a <0.45

  Conditional expression (1) is an expression showing conditions for maintaining the balance between aberration correction and lens shape in the reading lens according to this embodiment. By satisfying this conditional expression (1), it is possible to reduce the size of the lens without degrading the optical performance. If the lower limit of conditional expression (1) is not reached, it is difficult to correct chromatic aberration of magnification, and the optical performance of the reading lens cannot be maintained. On the other hand, if the upper limit in conditional expression (1) is exceeded, the incident light beam will spread too much and the lens will have to be enlarged, leading to an increase in the size of the reading lens.

The second lens group may include a second lens made of a convex lens and a third lens made of a concave lens, which are arranged on the image plane side of the first lens. At this time, when the Abbe number of the second lens is ν ₂ and the Abbe number of the third lens is ν ₃ , it is preferable that the following conditional expression is satisfied.
(2) 31 <ν ₂ −ν ₃

  Conditional expression (2) is an expression showing conditions for satisfactorily correcting axial chromatic aberration and chromatic aberration of magnification in the reading lens according to this embodiment. By satisfying this conditional expression (2), axial chromatic aberration and lateral chromatic aberration can be satisfactorily corrected. If the lower limit of conditional expression (2) is not reached, the longitudinal chromatic aberration and the chromatic aberration of magnification become too large, making it difficult to correct the aberration.

Further, when the focal length of the entire reading lens system is f and the focal length of the third lens group is f ₃ , it is preferable that the following conditional expression is satisfied.
(3) −1.08 <f / f ₃ <−0.51

  Conditional expression (3) is an expression showing conditions for satisfactorily correcting distortion and astigmatism in the reading lens according to this embodiment. By satisfying this conditional expression (3), it is possible to satisfactorily correct distortion and astigmatism. If the lower limit of conditional expression (3) is not reached, it will be difficult to correct astigmatism, and the resolution at the periphery of the screen will be reduced. Alternatively, it is necessary to compensate for the power shortage, and as a result, the optical system becomes large. On the other hand, if the upper limit of conditional expression (3) is exceeded, the negative power for the entire system of the third lens group becomes too strong, making it difficult to correct distortion.

  In addition to the above-described configuration, the reading lens according to this embodiment has high optical performance capable of effectively correcting various aberrations as long as all the conditional expressions (1) to (3) are satisfied. A small, wide-angle, bright reading lens. In addition, the reading lens can handle high resolution. Moreover, even if all of the conditional expressions (1) to (3) are not satisfied, if any of them is satisfied, a small size and a wide angle of view with high optical performance can be obtained. Thus, a bright reading lens can be realized.

  In addition, if the range of each numerical value shown by said conditional expression (1)-(3) is a value near the said numerical value, the effect anticipated by this invention will be acquired.

  Examples of the reading lens according to the present invention will be described below.

(Example 1)
FIG. 1 is a cross-sectional view along the optical axis showing the configuration of the reading lens according to the first example. The reading lens includes, in order from the object 100 side, a first lens group G ₁₁ having a negative refractive power, a second lens group G ₁₂ having a positive refractive power, and a third lens group G having a negative refractive power. ₁₃ is arranged and configured.

The first lens group G ₁₁ includes a negative lens 111 and a meniscus lens 112 with a convex surface facing the image plane 101 in order from the object 100 side.

The second lens group G ₁₂ includes, arranged from the object 100 side in this order, a first lens 121 having a positive refractive power, a positive third lens having a second lens 122, and a negative refractive power having a refractive power 123 It is comprised including. Aspheric surfaces are formed on both surfaces of the first lens 121. The second lens 122 and the third lens 123 are constituted by a convex lens and a concave lens, respectively. Further, the second lens 122 and the third lens 123 are cemented. A diaphragm 124 is disposed on the image plane 101 side of the third lens 123. Furthermore, the final (closest to the image plane 101 side) surface of the second lens group G ₁₂ are aspheric joined.

The third lens group G ₁₃ is constituted by two meniscus concave lenses 131 and 132 having a convex surface directed toward the image surface 101 side.

Further, an optical filter (or cover glass) 141 is disposed between the third lens group G ₁₃ and the image plane 101. In addition, this optical filter (or cover glass) 141 is arrange | positioned as needed, and can be abbreviate | omitted when unnecessary.

  Various numerical data relating to the reading lens according to Example 1 will be described below.

Focal length (f) of the entire reading lens system = 31.1
F number (Fno.) = 4.0
Half angle of view (ω) = 23.2 °

(Numerical values related to conditional expression (1))
L ₂ / L _a = 0.38

(Numerical value related to conditional expression (2))
ν ₂ −ν ₃ = 40.9

(Numerical values related to conditional expression (3))
f / f ₃ = -0.98

d ₀ = 500.00
r ₁ = -65.6733
d ₁ = 1.40 nd ₁ = 1.69680 νd ₁ = 55.53
r ₂ = 138.6762
d ₂ = 2.40
r ₃ = -36.1974
d ₃ = 10.00 nd ₂ = 1.77250 νd ₂ = 49.60
r ₄ = -50.7183
d ₄ = 1.00
r ₅ = 16.7646 (aspherical surface)
d ₅ = 6.70 nd ₃ = 1.58313 νd ₃ = 59.38
r ₆ = 713.4134 (aspherical surface)
d ₆ = 1.50
r ₇ = 16.7333
d ₇ = 3.00 nd ₄ = 1.49700 νd ₄ = 81.61
r ₈ = -52.4998
d ₈ = 1.85 nd ₅ = 1.58144 νd ₅ = 40.75
r ₉ = 12.3912
d ₉ = 0.75
r ₁₀ = ∞ (aperture)
d ₁₀ = 1.70
r ₁₁ = 13.7184
d ₁₁ = 3.20 nd ₆ = 1.61800 νd ₆ = 63.39
r ₁₂ = -18.2020
d ₁₂ = 0.20
r ₁₃ = -30.1333
d ₁₃ = 1.65 nd ₇ = 1.54072 νd ₇ = 47.23
r ₁₄ = 28.5417
d ₁₄ = 1.55
r ₁₅ = -23.1121
d ₁₅ = 1.00 nd ₈ = 1.58913 νd ₈ = 61.18
r ₁₆ = 17.0779
d ₁₆ = 3.00 nd ₉ = 1.64769 νd ₉ = 33.80
r ₁₇ = -65.1790
d ₁₇ = 0.20 nd ₁₀ = 1.53610 νd ₁₀ = 41.20
r ₁₈ = -31.8914 (aspherical surface)
d ₁₈ = 1.80
r ₁₉ = -15.0550
d ₁₉ = 2.00 nd ₁₁ = 1.92286 νd ₁₁ = 20.88
r ₂₀ = -23.6063
d ₂₀ = 1.00
r ₂₁ = -14.9138
d ₂₁ = 1.40 nd ₁₂ = 1.88300 νd ₁₂ = 40.78
r ₂₂ = -19.3749
d ₂₂ = 10.00
r ₂₃ = ∞
d ₂₃ = 2.00 nd ₁₃ = 1.51633 νd ₁₃ = 64.15
r ₂₄ = ∞
d ₂₄ = 2.70
r ₂₅ = ∞

Cone coefficient (k) and aspheric coefficient (A, B, C, D, E)
(5th page)
k = 1.53960, A = 0,
B = -2.12567 × 10 ⁻⁵ , C = 5.71791 × 10 ⁻⁸ ,
D = -8.56117 × 10 ⁻¹⁰ , E = 2.36604 × 10 ⁻¹¹
(Sixth surface)
k = 530.6548, A = 0,
B = 2.28718 × 10 ⁻⁵ , C = 2.30484 × 10 ⁻⁷ ,
D = 2.53946 × 10 ^-9 , E = 4.52233 × 10 ^-11
(18th page)
k = -22.9259, A = 0,
B = 4.76294 × 10 ⁻⁵ , C = 1.49881 × 10 ⁻⁶ ,
D = -9.30561 × 10 ^-9 , E = 1.59096 × 10 ^-10

  FIG. 2 is a diagram illustrating various aberrations of the reading lens according to the first example.

(Example 2)
FIG. 3 is a cross-sectional view along the optical axis showing the configuration of the reading lens according to the second example. The reading lens includes, in order from the object 200 side, a first lens group G ₂₁ having a negative refractive power, a second lens group G ₂₂ having a positive refractive power, and a third lens group G having a negative refractive power. ₂₃ is arranged and configured.

The first lens group G ₂₁ includes a negative lens 211 and a meniscus lens 212 having a convex surface directed toward the image plane 201 in order from the object 200 side.

The second lens group G ₂₂ includes a first lens 221 having a positive refractive power, a second lens 222 having a positive refractive power, and a third lens 223 having a negative refractive power, which are arranged in order from the object 200 side. It is comprised including. An aspheric surface is bonded to the side surface of the image surface 201 of the first lens 221. The second lens 222 and the third lens 223 are configured by a convex lens and a concave lens, respectively. Further, the second lens 222 and the third lens 223 are cemented. A diaphragm 224 is disposed on the image plane 201 side of the third lens 223. Furthermore, the final (closest to the image plane 201 side) surface of the second lens group G ₂₂ are aspheric joined.

The third lens group G ₂₃ is constituted by a meniscus concave lens 231 having a convex surface directed toward the image surface 201 side.

Between the third lens group G ₂₃ and the image plane 201, an optical filter (or cover glass) 241 is disposed. The optical filter (or cover glass) 241 is disposed as necessary, and can be omitted if unnecessary.

  Various numerical data relating to the reading lens according to the second example will be described below.

Focal length (f) of the entire reading lens system = 31.1
F number (Fno.) = 4.0
Half angle of view (ω) = 23.1 °

(Numerical values related to conditional expression (1))
L ₂ / L _a = 0.30

(Numerical value related to conditional expression (2))
ν ₂ −ν ₃ = 40.9

(Numerical values related to conditional expression (3))
f / f ₃ = -0.79

d ₀ = 500.00
r ₁ = -43.3746
d ₁ = 1.40 nd ₁ = 1.80400 νd ₁ = 46.58
r ₂ = -836.3476
d ₂ = 1.60
r ₃ = -22.7267
d ₃ = 6.00 nd ₂ = 1.75520 νd ₂ = 27.51
r ₄ = -25.3354
d ₄ = 0.20
r ₅ = 15.6577
d ₅ = 4.75 nd ₃ = 1.69680 νd ₃ = 55.53
r ₆ = 65.6324
d ₆ = 0.30 nd ₄ = 1.53610 νd ₄ = 41.20
r ₇ = 45.7849 (aspherical surface)
d ₇ = 1.65
r ₈ = 14.1380
d ₈ = 3.00 nd ₅ = 1.49700 νd ₅ = 81.61
r ₉ = -23.5101
d ₉ = 0.80 nd ₆ = 1.58144 νd ₆ = 40.75
r ₁₀ = 13.1334
d ₁₀ = 0.85
r ₁₁ = ∞ (aperture)
d ₁₁ = 2.50
r ₁₂ = 15.4532
d ₁₂ = 2.48 nd ₇ = 1.61800 νd ₇ = 63.39
r ₁₃ = -39.2644
d ₁₃ = 0.60
r ₁₄ = -122.4597
d ₁₄ = 1.30 nd ₈ = 1.54072 νd ₈ = 47.23
r ₁₅ = 79.0782
d ₁₅ = 1.40
r ₁₆ = -17.3949
d ₁₆ = 2.35 nd ₉ = 1.58913 νd ₉ = 61.18
r ₁₇ = 15.7153
d ₁₇ = 3.65 nd ₁₀ = 1.64769 νd ₁₀ = 33.80
r ₁₈ = -68.1338
d ₁₈ = 0.20 nd ₁₁ = 1.53610 νd ₁₁ = 41.20
r ₁₉ = -40.8482 (aspherical surface)
d ₁₉ = 2.10
r ₂₀ = -15.6739
d ₂₀ = 2.00 nd ₁₂ = 1.92286 νd ₁₂ = 20.88
r ₂₁ = -29.3490
d ₂₁ = 10.00
r ₂₂ = ∞
d ₂₂ = 2.00 nd ₁₃ = 1.51633 νd ₁₃ = 64.15
r ₂₃ = ∞
d ₂₃ = 2.30
r ₂₄ = ∞

Cone coefficient (k) and aspheric coefficient (A, B, C, D, E)
(Seventh side)
k = 16.4646, A = 0,
B = 5.30388 × 10 ⁻⁶ , C = −2.550319 × 10 ⁻⁷ ,
D = 4.16395 × 10 ^-9 , E = -4.88257 × 10 ^-11
(19th page)
k = -66.7243, A = 0,
B = 1.69196 × 10 ⁻⁶ , C = 1.78594 × 10 ⁻⁶ ,
D = -1.36092 × 10 ^-8 , E = 4.996713 × 10 ^-11

  FIG. 4 is a diagram illustrating various aberrations of the reading lens according to the second example.

(Example 3)
FIG. 5 is a cross-sectional view along the optical axis showing the configuration of the reading lens according to the third example. The reading lens includes, in order from the object 300 side, a first lens group G ₃₁ having a negative refractive power, a second lens group G ₃₂ having a positive refractive power, and a third lens group G having a negative refractive power. ₃₃ is arranged and configured.

The first lens group G ₃₁ includes a negative lens 311, a negative lens 312, and a meniscus lens 313 having a convex surface directed toward the image plane 301 in order from the object 300 side.

The second lens group G ₃₂ includes a first lens 321 having a positive refractive power, a second lens 322 having a positive refractive power, and a third lens 323 having a negative refractive power, which are arranged in order from the object 300 side. It is comprised including. Aspherical surfaces are formed on both surfaces of the first lens 321. The second lens 322 and the third lens 323 are respectively constituted by a convex lens and a concave lens. Further, the second lens 322 and the third lens 323 are cemented. A diaphragm 324 is disposed on the image plane 301 side of the third lens 323. Furthermore, the final (closest to the image plane 301 side) surface of the second lens group G ₃₂ are aspheric joined.

The third lens group G ₃₃ includes two meniscus concave lenses 331 and 332 having a convex surface directed toward the image plane 301 side.

Further, an optical filter (or cover glass) 341 is disposed between the third lens group G ₃₃ and the image plane 301. The optical filter (or cover glass) 341 is disposed as necessary, and can be omitted if unnecessary.

  Various numerical data relating to the reading lens according to Example 3 will be described below.

Focal length (f) of the entire reading lens system = 31.1
F number (Fno.) = 4.0
Half angle of view (ω) = 30.7 °

(Numerical values related to conditional expression (1))
L ₂ / L _a = 0.39

(Numerical value related to conditional expression (2))
ν ₂ −ν ₃ = 40.9

(Numerical values related to conditional expression (3))
f / f ₃ = -0.77

d ₀ = 500.00
r ₁ = -727.5708
d ₁ = 1.80 nd ₁ = 1.51633 νd ₁ = 64.15
r ₂ = 52.9277
d ₂ = 0.95
r ₃ = 226.1759
d ₃ = 1.80 nd ₂ = 1.51633 νd ₂ = 64.15
r ₄ = 76.2756
d ₄ = 4.95
r ₅ = -27.8154
d ₅ = 6.60 nd ₃ = 1.75520 νd ₃ = 27.51
r ₆ = -34.5510
d ₆ = 0.45
r ₇ = 18.3484 (aspherical surface)
d ₇ = 6.00 nd ₄ = 1.58313 νd ₄ = 59.38
r ₈ = 124.0273 (aspherical surface)
d ₈ = 1.85
r ₉ = 14.2074
d ₉ = 3.00 nd ₅ = 1.49700 νd ₅ = 81.61
r ₁₀ = -122.5311
d ₁₀ = 1.00 nd ₆ = 1.58144 νd ₆ = 40.75
r ₁₁ = 14.2330
d ₁₁ = 0.75
r ₁₂ = ∞ (aperture)
d ₁₂ = 1.60
r ₁₃ = 16.4046
d ₁₃ = 3.30 nd ₇ = 1.61800 νd ₇ = 63.39
r ₁₄ = -16.6584
d ₁₄ = 0.20
r ₁₅ = -26.6596
d ₁₅ = 0.65 nd ₈ = 1.54072 νd ₈ = 47.23
r ₁₆ = 44.8887
d ₁₆ = 1.85
r ₁₇ = -19.5518
d ₁₇ = 1.00 nd ₉ = 1.58913 νd ₉ = 61.18
r ₁₈ = 55.8023
d ₁₈ = 2.40 nd ₁₀ = 1.64769 νd ₁₀ = 33.80
r ₁₉ = -88.6096
d ₁₉ = 0.20 nd ₁₁ = 1.53610 νd ₁₁ = 41.20
r ₂₀ = -36.3204 (aspherical surface)
d ₂₀ = 2.15
r ₂₁ = -15.0981
d ₂₁ = 2.00 nd ₁₂ = 1.92286 νd ₁₂ = 20.88
r ₂₂ = -17.8512
d ₂₂ = 2.50
r ₂₃ = -9.8386
d ₂₃ = 1.40 nd ₁₃ = 1.90366 νd ₁₃ = 31.32
r ₂₄ = -13.0094
d ₂₄ = 10.00
r ₂₅ = ∞
d ₂₅ = 2.00 nd ₁₄ = 1.51633 νd ₁₄ = 64.15
r ₂₆ = ∞
d ₂₆ = 2.99
r ₂₇ = ∞

Cone coefficient (k) and aspheric coefficient (A, B, C, D, E)
(Seventh side)
k = 1.5586, A = 0,
B = -2.48343 × 10 ⁻⁵ , C = 5.86660 × 10 ⁻⁸ ,
D = -1.39790 × 10 ^-9 , E = 2.70996 × 10 ^-11
(8th page)
k = -98.6639, A = 0,
B = 2.28612 × 10 ⁻⁵ , C = 2.05737 × 10 ⁻⁷ ,
D = 1.66122 x 10 ^-9 , E = 6.16610 x 10 ^-11
(20th page)
k = -32.4472, A = 0,
B = 1.94978 × 10 ⁻⁵ , C = 1.51941 × 10 ⁻⁶ ,
D = -8.95717 × 10 ^-9 , E = 7.95469 × 10 ^-11

  FIG. 6 is a diagram illustrating various aberrations of the reading lens according to the third example.

Example 4
FIG. 7 is a cross-sectional view along the optical axis showing the configuration of the reading lens according to the fourth example. The reading lens includes, in order from the object 400 side, a first lens group G ₄₁ having a negative refractive power, a second lens group G ₄₂ having a positive refractive power, and a third lens group G having a negative refractive power. ₄₃ is arranged and configured.

The first lens group G ₄₁ includes a negative lens 411 and a meniscus lens 412 having a convex surface directed toward the image plane 401 in order from the object 400 side.

The second lens group _G42 includes a first lens 421 having a positive refractive power, a second lens 422 having a positive refractive power, and a third lens 423 having a negative refractive power, which are arranged in order from the object 400 side. It is comprised including. Aspherical surfaces are formed on both surfaces of the first lens 421. The second lens 422 and the third lens 423 are respectively constituted by a convex lens and a concave lens. A diaphragm 424 is disposed on the image plane 401 side of the third lens 423. Furthermore, the final (closest to the image plane 401 side) surface of the second lens group G ₄₂ are aspheric joined.

The third lens group G ₄₃ is constituted by two meniscus concave lenses 431 and 432 having a convex surface directed toward the image surface 401 side.

Further, an optical filter (or cover glass) 441 is disposed between the third lens group G ₄₃ and the image plane 401. In addition, this optical filter (or cover glass) 441 is arrange | positioned as needed, and can be abbreviate | omitted when unnecessary.

  Various numerical data relating to the reading lens according to Example 4 will be described below.

Focal length (f) of the entire reading lens system = 31.1
F number (Fno.) = 4.0
Half angle of view (ω) = 23.2 °

(Numerical values related to conditional expression (1))
L ₂ / L _a = 0.37

(Numerical value related to conditional expression (2))
ν ₂ −ν ₃ = 34.4

(Numerical values related to conditional expression (3))
f / f ₃ = -0.61

d ₀ = 500.00
r ₁ = -63.9506
d ₁ = 1.40 nd ₁ = 1.69680 νd ₁ = 55.53
r ₂ = 134.1755
d ₂ = 2.40
r ₃ = -42.6266
d ₃ = 10.00 nd ₂ = 1.77250 νd ₂ = 49.60
r ₄ = -71.7247
d ₄ = 1.00
r ₅ = 16.2767 (aspherical surface)
d ₅ = 6.70 nd ₃ = 1.58313 νd ₃ = 59.38
r ₆ = 177.5194 (aspherical surface)
d ₆ = 1.50
r ₇ = 17.8274
d ₇ = 3.00 nd ₄ = 1.49700 νd ₄ = 81.61
r ₈ = -34.7714
d ₈ = 0.30
r ₉ = -34.1290
d ₉ = 1.85 nd ₅ = 1.54072 νd ₅ = 47.23
r ₁₀ = 13.2442
d ₁₀ = 0.65
r ₁₁ = ∞ (aperture)
d ₁₁ = 1.80
r ₁₂ = 12.9643
d ₁₂ = 3.20 nd ₆ = 1.61800 νd ₆ = 63.39
r ₁₃ = -21.4012
d ₁₃ = 0.20
r ₁₄ = -50.0647
d ₁₄ = 1.65 nd ₇ = 1.58144 νd ₇ = 40.75
r ₁₅ = 33.6913
d ₁₅ = 1.55
r ₁₆ = -19.7095
d ₁₆ = 1.00 nd ₈ = 1.58913 νd ₈ = 61.18
r ₁₇ = -1073.0886
d ₁₇ = 3.00 nd ₉ = 1.63980 νd ₉ = 34.48
r ₁₈ = -71.8974
d ₁₈ = 0.20 nd ₁₀ = 1.53610 νd ₁₀ = 41.20
r ₁₉ = -57.9223 (aspherical surface)
d ₁₉ = 1.80
r ₂₀ = -15.1180
d ₂₀ = 2.00 nd ₁₁ = 1.92286 νd ₁₁ = 20.88
r ₂₁ = -16.4163
d ₂₁ = 1.20
r ₂₂ = -10.9682
d ₂₂ = 1.40 nd ₁₂ = 1.83400 νd ₁₂ = 37.17
r ₂₃ = -15.0200
d ₂₃ = 10.00
r ₂₄ = ∞
d ₂₄ = 2.00 nd ₁₃ = 1.51633 νd ₁₃ = 64.15
r ₂₅ = ∞
d ₂₅ = 2.77
r ₂₆ = ∞

Cone coefficient (k) and aspheric coefficient (A, B, C, D, E)
(5th page)
k = 1.5499, A = 0,
B = -1.90841 × 10 ⁻⁵ , C = 5.56012 × 10 ⁻⁸ ,
D = -7.87857 × 10 ^-10 , E = 1.63015 × 10 ^-11
(Sixth surface)
k = 400.7227, A = 0,
B = 2.26345 × 10 ⁻⁵ , C = 2.20318 × 10 ⁻⁷ ,
D = 1.9812 × 10 ^-9 , E = 2.92685 × 10 ^-11
(19th page)
k = -112.6197, A = 0,
B = 6.74916 × 10 ⁻⁵ , C = 2.01011 × 10 ⁻⁶ ,
D = 1.03809 × 10 ⁻⁸ , E = 1.84688 × 10 ⁻¹⁰

  FIG. 8 is a diagram illustrating various aberrations of the reading lens according to the fourth example.

In the above numerical data, r ₁ , r ₂ ,... Are the radii of curvature of the lenses and the diaphragm surface, and d ₀ , d ₁ ,. ... Nd ₁ , nd ₂ ,... Is the refractive index of d-line of each lens, optical filter, etc., and νd ₁ , νd ₂ ,. Shows the Abbe number.

  Each of the aspheric shapes is represented by the following formula, where X is the optical axis direction, Y is the height perpendicular to the optical axis, and the light traveling direction is positive.

  Here, R is a paraxial radius of curvature, k is a conical coefficient, and A, B, C, D, and E are second-order, fourth-order, sixth-order, eighth-order, and tenth-order aspheric coefficients, respectively.

  As described above, according to the present invention, there is provided a reading lens that is small, has a wide angle of view (half angle of view is 23 ° or more), and is bright (F number is about 4) while supporting high resolution. be able to. In particular, when the reading lens according to the present invention satisfies the above conditional expression, it is possible to achieve a reduction in size and a wide angle of view and a better aberration correction.

  In addition, since the reading lens according to the present invention includes a lens having an aspherical surface, various aberrations can be favorably corrected with a small number of lenses.

  As described above, the reading lens according to the present invention is useful for reading image information and the like, and is particularly suitable for a camera that reads barcode information, a copy camera that reads paper image information, a document camera, and the like. is there.

FIG. 3 is a cross-sectional view along the optical axis showing the configuration of the reading lens according to Example 1; FIG. 6 is a diagram illustrating all aberrations of the reading lens according to the first example. FIG. 6 is a cross-sectional view along the optical axis showing the configuration of a reading lens according to Example 2. FIG. 6 is a diagram illustrating various aberrations of the reading lens according to the second example. FIG. 6 is a cross-sectional view along the optical axis showing the configuration of a reading lens according to Example 3. FIG. 10 is a diagram illustrating all aberrations of the reading lens according to the third example. FIG. 6 is a cross-sectional view along the optical axis showing the configuration of a reading lens according to Example 4. FIG. 10 is a diagram illustrating all aberrations of the reading lens according to the fourth example.

Explanation of symbols

G ₁₁ , G ₂₁ , G ₃₁ , G ₄₁ , first lens group G ₁₂ , G ₂₂ , G ₃₂ , G ₄₂ , second lens group G ₁₃ , G ₂₃ , G ₃₃ , G ₄₃ , third lens group 100, 200, 300, 400 Object 101, 201, 301, 401 Image plane 111, 211, 311, 312, 311 Negative lens 112, 212, 313, 412 Meniscus lens 121, 221, 321, 421 First lens 122, 222, 322 , 422 Second lens 123, 223, 323, 423 Third lens 124, 224, 324, 424 Aperture 131, 132, 231, 331, 332, 431, 432 Meniscus concave lens 141, 241, 341, 441 Optical filter (or cover) Glass)
ΔS Sagittal image plane ΔM Meridional image plane

Claims (3)

From the object side,
A first lens group including one or two negative lenses and a meniscus lens having a convex surface facing the image surface side, and having negative refractive power as a whole;
A second lens group having a positive refractive power and including a first lens having an aspherical surface formed on one or both sides, and having a positive refractive power as a whole;
A third lens group composed of one or two meniscus concave lenses having a convex surface facing the image surface side and having negative refractive power as a whole;
Is arranged and configured,
When the total length of the optical system L _a, the distance from the first lens first surface of the first lens group to the second lens first surface of the second lens group and L _2, which satisfies the following condition: A reading lens.
0.25 <L ₂ / L _a <0.45 The second lens group includes a second lens made of a convex lens and a third lens made of a concave lens disposed on the image plane side of the first lens,
2. The reading lens according to claim 1, wherein when the Abbe number of the second lens is ν ₂ and the Abbe number of the third lens is ν ₃ , the following conditional expression is satisfied.
31 <ν ₂ −ν ₃ The focal length of the reading lens system f, the the focal length of the third lens group and f _3, the lens for retrieval according to claim 1 or 2, characterized by satisfying the following condition: .
−1.08 <f / f ₃ <−0.51

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