JP5164648B2 - Imaging optics - Google Patents

Description

  The present invention relates to an imaging optical system for forming an image of an object, and more particularly to an imaging optical system suitable for an object arranged at a finite distance.

As an imaging optical system used for visual inspections such as FPD (Flat Panel Display), it has high resolution with advanced aberration correction as the test object becomes more precise and the CCD camera pitch becomes more precise Is required. An imaging optical system having a high resolving power in which chromatic aberration is corrected well is known (for example, see Patent Document 1).
Japanese Patent Laid-Open No. 3-288112

  In conventional imaging optical systems, when the angle of view increases, the chromatic aberration of magnification, astigmatism, and field curvature increase near the center of the image near the maximum image height, so the resolution around the image deteriorates. There was a problem that. In the imaging optical system of Patent Document 1, astigmatism is large, and the sagittal image plane and the meridional image plane do not coincide with the best image plane for the on-axis ray in the off-axis ray. For this reason, it is considered that the resolution is greatly deteriorated due to a manufacturing error of the lens. Moreover, the longitudinal chromatic aberration in the visible region is also large.

  The present invention has been made in view of such problems, and various aberrations are satisfactorily corrected for a large angle of view in the visible region while suppressing the number of constituent lenses, and uniform from the center to the periphery of the image. An object of the present invention is to provide an imaging optical system having a high resolving power.

In order to achieve such an object, one aspect of the imaging optical system of the present invention includes a front group having a positive refractive power, an aperture stop, and a rear group having a positive refractive power, which are arranged in order from the object side. essentially consists of two lens groups by the said front group is arranged in order from the object side, it has a first cemented lens having a negative refractive power with a convex surface facing the object side, a positive refractive power A second cemented lens having a negative refractive power and a meniscus shape with a concave surface facing the image side, and the rear group is arranged in order from the object side and is negative with a meniscus shape with the concave surface facing the object side a third cemented lens having a refractive power, a lens having a positive refractive power consists of a fourth cemented lens having a negative refractive power with a convex surface facing the image side, e line of the first cemented lens ( The focal length at a wavelength of 546.07 nm is fL1, and the entire lens system is When the formed focal length is f, characterized in that the following conditional expression is satisfied: -25.5 <fL1 / f <-5.0.

  According to the present invention, it is possible to provide an imaging optical system in which various aberrations are favorably corrected for a large angle of view in the visible region while suppressing the number of constituent lenses, and the image has a uniform resolution from the center to the periphery of the image. Can do.

  Hereinafter, embodiments will be described with reference to the drawings. As shown in FIG. 1, the imaging optical system according to this embodiment includes a front group GF having a positive refractive power, an aperture stop SP, and a rear group GR having a positive refractive power, which are arranged in order from the object side. The front group GF is arranged in order from the object side, and includes a first cemented lens L1 having a negative refractive power with a convex surface facing the object side, a lens L2 having a positive refractive power, and an image side. A second meniscus lens L3 having a negative refractive power and a negative refractive power, and the rear group GR is arranged in order from the object side, and has a negative refractive power in a meniscus shape with the concave surface facing the object side. A third cemented lens L4, a lens L5 having a positive refractive power, and a fourth cemented lens L6 having a negative refractive power with a convex surface facing the image side.

  As described above, the imaging optical system according to the present embodiment is a so-called Gaussian optical system in which lenses are arranged almost symmetrically with respect to the aperture stop SP as a basic configuration, and potentially has lateral chromatic aberration and distortion. It has a configuration that can be kept small. This is because the degree of freedom of correction possessed by the optical system can be distributed to other aberrations, so that various aberrations can be corrected satisfactorily from the center to the periphery of the image.

  Further, by making the object side lens surface of the first cemented lens L1 and the image side lens surface of the fourth cemented lens L6 convex, respectively, the off-axis light beam smoothly enters the first cemented lens L1, and the fourth lens surface smoothly. The light is emitted from the cemented lens L6. This serves to suppress higher-order aberrations of meridional field curvature, so that the effect of conditional expression (1) described later can be maximized.

  In the present embodiment, when the focal length of the first cemented lens L1 at the e-line (wavelength 546.07 nm) is fL1 and the combined focal length at the e-line of the entire lens system is f, Satisfy the condition (1).

  −25.5 <fL1 / f <−5.0 (1)

  Conditional expression (1) indicates an appropriate range of the focal length fL1 of the first cemented lens L1. Conditional expression (1) is an important condition for correcting spherical aberration and high-order aberrations of meridional field curvature well and obtaining uniform and high resolution from the center to the periphery of the image. If the upper limit value of the conditional expression (1) is exceeded, the refractive power of the first cemented lens L1 becomes too strong and the axial light ray jumps up by the lens L1. This is because the incident height of the axial ray incident after the positive refracting power lens L2 in the front group GF is increased, so that higher-order aberrations are likely to occur in the spherical aberration, and the resolving power is reduced over the entire image. On the other hand, if the lower limit of conditional expression (1) is not reached, the refractive power of the first cemented lens L1 becomes too weak, and the incident height of off-axis rays incident on the lens L1 increases. This is because high-order aberrations are likely to occur in the meridional field curvature, and astigmatism increases around the image, making it difficult to obtain uniform resolution from the center to the periphery of the image.

  In order to secure the effect of the present embodiment, it is preferable to set the upper limit value of conditional expression (1) to −8.0. In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (1) to −13.0.

  In the present embodiment, the first cemented lens L1 includes at least one positive lens (positive lens L1a in FIG. 1) and at least one negative lens (negative lens L1b in FIG. 1). When the positive lens in the first cemented lens L1 has a higher Abbe number than the negative lens, and the Abbe number νd1 with respect to the d line of the positive lens in the first cemented lens L1, the following expression (2) It is preferable to satisfy the following conditions.

  νd1> 60 (2)

  Conditional expression (2) represents an appropriate range of the Abbe number νd1 of the positive lens included in the first cemented lens L1. This condition is effective for sufficient correction of chromatic aberration. As described above, in the first cemented lens L1, the positive lens has a higher Abbe number than the negative lens. For this reason, the first cemented lens L1 has a so-called coloration effect in which chromatic aberration is greatly increased, but the chromatic aberration can be satisfactorily corrected even for a large field angle as the entire imaging optical system. If the lower limit value of conditional expression (2) is not reached, the effect of color development is weakened in the first cemented lens L1, and chromatic aberration correction is not sufficient.

  In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (2) to 80.

  In the present embodiment, the fourth cemented lens L6 includes at least one negative lens (negative lens L6a in FIG. 1) and at least one positive lens (positive lens L6b in FIG. 1). When the positive lens in the 4-junction lens L6 has a higher Abbe number than the negative lens, and the Abbe number νd6 with respect to the d-line of the positive lens in the fourth cemented lens L6, the condition of the following expression (3) Is preferably satisfied.

  νd6> 60 (3)

  Conditional expression (3) shows an appropriate range of the Abbe number νd6 of the positive lens included in the fourth cemented lens L6. This condition is effective for sufficient correction of chromatic aberration. As described above, in the fourth cemented lens L6, the positive lens has a higher Abbe number than the negative lens. For this reason, the fourth cemented lens L6 has a so-called coloration effect in which chromatic aberration is greatly increased, but the chromatic aberration can be satisfactorily corrected even for a large field angle as the entire imaging optical system. If the lower limit value of the conditional expression (3) is not reached, the fourth cemented lens L6 has a weak color development effect, and chromatic aberration correction is not sufficient.

  In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (3) to 80.

  In the present embodiment, the image side lens surface of the second cemented lens L3 (the eighth surface from the object side in FIG. 1) has a strong concave shape on the image side, and the object side lens of the third cemented lens L4. The surface (10th surface from the object side in FIG. 1) has a strong concave shape on the object side, the radius of curvature of the image side lens surface of the second cemented lens L3 is rS1, and the object side lens of the third cemented lens L4 It is preferable that the conditions of the following expressions (4) and (5) are satisfied, where rS2 is the curvature radius of the surface and f is the combined focal length of the entire lens system at the e-line.

| RS1 | / f> 0.16 (4)
| RS2 | / f> 0.16 (5)

  Conditional expression (4) shows an appropriate range of the radius of curvature rS1 of the image side lens surface of the second cemented lens L3. This condition is an important condition for correcting the coma flare well and obtaining a high resolution in the entire image area. If the lower limit value of the conditional expression (4) is not reached, the refractive power of the image side lens surface of the second cemented lens L3 becomes too strong, the coma flare becomes large, and the resolving power is reduced over the entire image area.

  In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (4) to 0.17.

  Conditional expression (5) shows an appropriate range of the radius of curvature rS2 of the object side lens surface of the third cemented lens L4. This condition is an important condition for correcting the coma flare satisfactorily and obtaining a high resolving power in the entire image area as in the conditional expression (4). If the lower limit value of conditional expression (5) is not reached, the refractive power of the object-side lens surface of the third cemented lens L4 becomes too strong, so the coma flare increases and the resolving power decreases over the entire image area.

  In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (5) to 0.17.

  In addition, in order to make the invention which concerns on this embodiment easy to understand, although it attached and demonstrated the component requirement of the said embodiment, it cannot be overemphasized that this invention is not limited to this.

  Hereinafter, each example according to the present embodiment will be described with reference to the drawings. 1, 3, 5, and 7 are cross-sectional views illustrating the configuration of the imaging optical system according to each example. As described above, the image forming optical systems according to the respective embodiments are arranged in order from the object side, the front group GF having positive refractive power, the aperture stop SP, and the rear group GR having positive refractive power. The front group GF is arranged in order from the object side, and includes a first cemented lens L1 having a negative refractive power with a convex surface facing the object side, a lens L2 having a positive refractive power, and an image side. A second meniscus lens L3 having a negative refractive power and a negative refractive power, and the rear group GR is arranged in order from the object side, and has a negative refractive power in a meniscus shape with the concave surface facing the object side. A third cemented lens L4, a lens L5 having a positive refractive power, and a fourth cemented lens L6 having a negative refractive power with a convex surface facing the image side. It is a system.

  Tables 1 to 4 are shown below, but these are tables of specifications in the first to fourth examples. In [Overall Specifications], f is the combined focal length of the entire lens system at the e-line, β is the magnification of the entire lens system at the e-line, NA is the numerical aperture on the object side of the e-line, 2ω is the angle of view, and TL is the lens The total system length (distance from the first lens surface to the image plane) and the conjugate length indicate the distance from the object plane to the image plane. In [Lens Data], the surface number is the order of the lens surfaces from the object side (the 0th surface corresponds to the object surface), r is the radius of curvature corresponding to each surface number, and d is on the optical axis corresponding to each surface number. Lens thickness and air spacing (value on the 0th surface corresponds to the air spacing from the object surface to the first surface), and νd is based on the d-line (wavelength 587.6 nm) of the glass material corresponding to each surface number Abbe number, ne indicates the refractive index of e-line corresponding to each surface number. The curvature radius r of “0.0000” indicates a plane or an opening. Further, the description of the refractive index “1.00000” of air is omitted. In [Conditional Expression], the conditional expressions (1) to (5) and values corresponding thereto are shown.

  In the table, “mm” is generally used as the unit of focal length f, radius of curvature r, surface interval d, and other lengths. However, since the optical system can obtain the same optical performance even when proportionally enlarged or proportionally reduced, the unit is not limited to “mm”, and other appropriate units can be used.

  The description of the above table is the same in other examples, and the description thereof is omitted.

(First embodiment)
The imaging optical system according to the first example will be described with reference to FIGS. As shown in FIG. 1, in the imaging optical system according to the first example, the front group GF includes a first cemented lens L1 composed of a biconvex lens L1a and a biconcave lens L1b, arranged in order from the object side, and the object side. A positive meniscus lens L2 having a strong convex surface facing the lens, a second meniscus lens L3 having a positive meniscus lens L3a having a strong convex surface facing the object side, and a negative meniscus lens L3b having a strong concave surface facing the image side, The rear group GR includes, in order from the object side, a third cemented lens L4 including a negative meniscus lens L4a having a strong concave surface facing the object side and a positive meniscus lens L4b having a strong convex surface facing the image side, and an image side. It has a positive meniscus lens L5 having a strong convex surface and a fourth cemented lens L6 composed of a biconcave lens L6a and a biconvex lens L6b.

  Table 1 below shows a table of specifications in the first embodiment. The surface numbers 1 to 17 in Table 1 correspond to the surfaces 1 to 17 shown in FIG.

(Table 1)
[Overall specifications]
f = 122.00
β = -0.25
NA = 0.020
2ω = 26.10 °
TL = 219.19
Conjugate length = 746.58
[Lens data]
Surface number r d ne νd
0 527.3924
1 299.0077 10.0000 1.49845 81.6
2 -59.5464 3.20000 1.51825 64.1
3 186.3666 24.0000
4 40.2428 6.3000 1.67340 47.3
5 195.2620 3.6000
6 32.4629 7.8000 1.49845 81.6
7 672.4109 2.4000 1.61669 44.3
8 21.9074 12.8000
9 0.0000 12.8000 (Aperture stop SP)
10 -20.4519 2.4000 1.61669 44.3
11 -1599.5198 7.8000 1.49845 81.6
12 -28.4512 2.6000
13 -331.5376 6.3000 1.67340 47.3
14 -42.8723 3.0000
15 -372.8512 3.0000 1.51825 64.1
16 58.2845 8.2000 1.49845 81.6
17 -1000.0000 72.2907
[Lens group data]
Start surface Focal length Front group GF 1 174.25
Rear group GR 10 145.93
[Conditional expression]
fL1 = -712.337
f = 122.00
νd1 = 81.6
νd6 = 81.6
rS1 = 21.9074
rS2 = -20.4519
Conditional expression (1) fL1 / f = -5.84
Conditional expression (2) νd1 = 81.6
Conditional expression (3) νd6 = 81.6
Conditional expression (4) | rS1 | /f=0.180
Conditional expression (5) | rS2 | /f=0.168

  From the table of specifications shown in Table 1, it can be seen that the imaging optical system according to the first example satisfies all the conditional expressions (1) to (5).

  FIG. 2 is a diagram showing various aberrations (specifically, a spherical aberration diagram, an astigmatism diagram, a distortion diagram, a lateral chromatic aberration diagram, and a lateral aberration diagram) of the imaging optical system according to the first example. In each aberration diagram, the maximum numerical aperture is 0.020 and the maximum image height is 35 mm. Further, e represents various aberrations for e-line (wavelength 546.07 nm), g for g-line (wavelength 435.83 nm), C for C-line (wavelength 656.27 nm), and F for F-line (wavelength 486.13 nm). In the astigmatism diagram, the dotted line indicates the meridional image plane, and the solid line indicates the sagittal image plane. In the lateral aberration diagram, Y indicates the image height.

  The explanation of the above aberration diagrams is the same in the other examples, and the explanation is omitted.

  As is apparent from the respective aberration diagrams, the imaging optical system according to the first example has a large angle of view and various aberrations in the entire image area even though vignetting is almost 0% to the periphery of the image. Is corrected well, and it can be seen that the image has a uniform and high resolving power over the entire image.

(Second embodiment)
The imaging optical system according to the second example will be described with reference to FIGS. 3 and 4 and Table 2. FIG. As shown in FIG. 3, in the imaging optical system according to the second example, the front group GF includes a first cemented lens L1 composed of a biconvex lens L1a and a biconcave lens L1b, arranged in order from the object side, and an image side. A cemented lens L2 having a positive refractive power and a positive meniscus lens L3a having a strong convex surface facing the object side, and a negative meniscus lens L2a having a strong concave surface facing the lens and a positive meniscus lens L2b having a strong convex surface facing the object side A second cemented lens L3 composed of a negative meniscus lens L3b having a strong concave surface facing the image side, and the rear group GR is composed of a biconcave lens L4a and a biconvex lens L4b arranged in order from the object side. A cemented lens L having a positive refractive power, which includes a lens L4, a positive meniscus lens L5a having a strong convex surface facing the image side, and a negative meniscus lens L5b having a strong concave surface facing the object side. When, and a fourth cemented lens L6 comprising a biconcave lens L6a and a biconvex lens L6b.

  Table 2 shows a table of specifications in the second embodiment. The surface numbers 1 to 19 in Table 2 correspond to the surfaces 1 to 19 shown in FIG.

(Table 2)
[Overall specifications]
f = 122.00
β = -0.50
NA = 0.035
2ω = 19.38 °
TL = 250.41
Conjugate length = 536.48
[Lens data]
Surface number r d ne νd
0 286.0696
1 1000.0000 8.8000 1.49845 81.6
2 -53.2369 3.20000 1.51825 64.1
3 332.2782 24.0000
4 57.0977 3.5000 1.57392 53.0
5 34.5169 6.3000 1.70346 48.1
6 371.5063 3.6000
7 28.4886 7.8000 1.49845 81.6
8 159.9514 2.4000 1.61669 44.3
9 21.3490 12.8000
10 0.0000 13.0000 (Aperture stop SP)
11 -24.2700 2.4000 1.61669 44.3
12 119.8966 7.8000 1.49845 81.6
13 -32.0448 2.6000
14 -513.0950 7.0000 1.67340 47.3
15 -28.0537 3.0000 1.51976 52.4
16 -61.2792 3.0000
17 -330.7996 3.0000 1.51825 64.1
18 76.7442 8.2000 1.49845 81.6
19 -638.4147 128.0130
[Lens group data]
Start focal length Front group GF 1 161.00
Rear group GR 11 158.88
[Conditional expression]
fL1 = -700.729
f = 122.00
νd1 = 81.6
νd6 = 81.6
rS1 = 21.3490
rS2 = -24.2670
Conditional expression (1) fL1 / f = -5.74
Conditional expression (2) νd1 = 81.6
Conditional expression (3) νd6 = 81.6
Conditional expression (4) | rS1 | /f=0.175
Conditional expression (5) | rS2 | /f=0.199

  From the table of specifications shown in Table 2, it can be seen that the imaging optical system according to the second example satisfies all the conditional expressions (1) to (5).

  FIG. 4 is a diagram illustrating various aberrations of the imaging optical system according to the second example. In each aberration diagram, the maximum numerical aperture is 0.035 and the maximum image height is 31 mm. FIG. 10 is a diagram illustrating all aberrations of the imaging optical system according to Example 2. As is apparent from the respective aberration diagrams, the imaging optical system according to the second example has a large angle of view and various aberrations in the entire image area even though vignetting is almost 0% to the periphery of the image. Is corrected well, and it can be seen that the image has a uniform and high resolving power over the entire image.

(Third embodiment)
The imaging optical system according to the third example will be described with reference to FIGS. As shown in FIG. 5, in the imaging optical system according to the third example, the front group GF includes a first cemented lens L1 composed of a biconvex lens L1a and a biconcave lens L1b, arranged in order from the object side, and the object side. A biconvex lens L4a and a biconvex lens, each having a positive meniscus lens L2 having a strong convex surface and a second cemented lens L3 composed of a biconvex lens L3a and a biconcave lens L3b. A third cemented lens L4 composed of L4b, a positive meniscus lens L5 having a strong convex surface facing the image side, and a fourth cemented lens L6 composed of a biconcave lens L6a and a biconvex lens L6b.

  Table 3 shows a table of specifications in the third embodiment. The surface numbers 1 to 17 in Table 3 correspond to the surfaces 1 to 17 shown in FIG.

(Table 3)
[Overall specifications]
f = 122.00
β = -1.00
NA = 0.052
2ω = 16.36
TL = 285.08
Conjugate length = 469.25
[Lens data]
Surface number r d ne νd
0 184.1765
1 2758.7543 8.8000 1.49845 81.6
2 -58.3475 3.20000 1.51825 64.1
3 709.2732 6.0000
4 40.2423 6.3000 1.67340 47.3
5 218.5362 3.2000
6 31.0574 7.8000 1.49845 81.6
7 -6938.1867 2.4000 1.61669 44.3
8 21.0578 12.7500
9 0.0000 12.7500 (Aperture stop SP)
10 -21.0578 2.4000 1.61669 44.3
11 6938.1867 7.8000 1.49845 81.6
12 -31.0574 3.2000
13 -218.5362 6.3000 1.67340 47.3
14 -40.2423 6.0000
15 -709.2732 3.2000 1.51825 64.1
16 58.3475 8.8000 1.49845 81.6
17 -2758.7543 184.1765
[Lens group data]
Start focal length Front group GF 1 155.43
Rear group GR 10 155.43
[Conditional expression]
fL1 = -1125.55
f = 122.00
νd1 = 81.6
νd6 = 81.6
rS1 = 21.0578
rS2 = -21.0578
Conditional expression (1) fL1 / f = -9.23
Conditional expression (2) νd1 = 81.6
Conditional expression (3) νd6 = 81.6
Conditional expression (4) | rS1 | /f=0.173
Conditional expression (5) | rS2 | /f=0.173

  From the table of specifications shown in Table 3, it can be seen that the imaging optical system according to the third example satisfies all the conditional expressions (1) to (5).

  FIG. 6 is a diagram illustrating various aberrations of the imaging optical system according to the third example. In each aberration diagram, the maximum numerical aperture is 0.052 and the maximum image height is 35 mm. As is apparent from the aberration diagrams shown in FIG. 6, the imaging optical system according to the third example has a large angle of view and the vignetting to the periphery of the image is almost 0%. It can be seen that various aberrations are well corrected over the entire area, and that the entire image has a uniform and high resolution.

(Fourth embodiment)
An imaging optical system according to the fourth example will be described with reference to FIGS. As shown in FIG. 7, in the imaging optical system according to the fourth example, the front group GF has a negative meniscus lens L1a arranged in order from the object side and having a strong concave surface facing the image side and a strong convex surface on the object side. A first cemented lens L1 composed of an oriented positive meniscus lens L1b, a positive meniscus lens L2 oriented with a strong convex surface on the object side, and a second cemented lens L3 composed of a biconvex lens L3a and a biconcave lens L3b. The rear group GR has a third cemented lens L4 composed of a biconcave lens L4a and a biconvex lens L4b, a positive meniscus lens L5 having a strong convex surface on the image side, and a strong convex surface on the image side. And a fourth cemented lens L6 composed of a positive meniscus lens L6a and a negative meniscus lens L6b with a strong concave surface facing the object side.

  Table 4 shows a table of specifications in the fourth embodiment. The surface numbers 1 to 17 in Table 4 correspond to the surfaces 1 to 17 shown in FIG.

(Table 4)
[Overall specifications]
f = 122.00
β = -0.70
NA = 0.044
2ω = 19.28
TL = 250.28
Conjugate length = 477.68
[Lens data]
Surface number r d ne νd
0 227.4091
1 230.1076 3.2000 1.51825 64.1
2 36.4439 8.8000 1.49845 81.6
3 238.0564 10.0000
4 37.6703 6.3000 1.67340 47.3
5 166.0258 3.4000
6 32.7918 7.8000 1.49845 81.6
7 -632.8700 2.4000 1.61669 44.3
8 21.1776 12.6000
9 0.0000 13.0000 (Aperture stop SP)
10 -20.3896 2.4000 1.61669 44.3
11 1098.0754 7.8000 1.49845 81.6
12 -30.6971 2.9000
13 -203.2757 6.3000 1.67340 47.3
14 -38.8490 10.0000
15 -211.8234 8.2000 1.49845 81.6
16 -40.2307 8.2000 1.51825 64.1
17 -208.8130 142.1758
[Lens group data]
Start surface Focal length Front group GF 1 154.69
Rear group GR 10 144.03
[Conditional expression]
fL1 = -2846.08
f = 122.00
νd1 = 81.6
νd6 = 81.6
rS1 = 21.1776
rS2 = -20.3896
Conditional expression (1) fL1 / f = -23.33
Conditional expression (2) νd1 = 81.6
Conditional expression (3) νd6 = 81.6
Conditional expression (4) | rS1 | /f=0.174
Conditional expression (5) | rS2 | /f=0.167

  From the table of specifications shown in Table 4, it can be seen that the imaging optical system according to the fourth example satisfies all the conditional expressions (1) to (5).

  FIG. 8 is a diagram illustrating various aberrations of the imaging optical system according to the fourth example. In each aberration diagram, the maximum numerical aperture is 0.044 and the maximum image height is 35 mm. As is apparent from the aberration diagrams shown in FIG. 8, the imaging optical system according to the fourth example has a large angle of view and the vignetting to the periphery of the image is almost 0%. It can be seen that various aberrations are well corrected over the entire area, and that the entire image has a uniform and high resolution.

It is sectional drawing which shows the structure of the imaging optical system which concerns on 1st Example. FIG. 6 is a diagram showing various aberrations of the first example. It is sectional drawing which shows the structure of the imaging optical system which concerns on 2nd Example. FIG. 6 is a diagram showing aberrations of the second example. It is sectional drawing which shows the structure of the imaging optical system which concerns on 3rd Example. FIG. 9 is a diagram showing aberrations of the third example. It is sectional drawing which shows the structure of the imaging optical system which concerns on 4th Example. FIG. 10 is a diagram showing aberrations of the fourth example.

Explanation of symbols

GF front group GR rear group L1 first cemented lens L2 lens having positive refractive power L3 second cemented lens SP aperture stop L4 third cemented lens L5 lens having positive refractive power L6 fourth cemented lenses L1a to L6a Lens on the object side in the lens L1b to L6b Lens on the image side in each cemented lens

Claims (4)

It consists of two lens groups , which are arranged in order from the object side, including a front group having positive refractive power, an aperture stop, and a rear group having positive refractive power,
The front group is arranged in order from the object side and has a first cemented lens having a negative refractive power with a convex surface facing the object side, a lens having a positive refractive power, and a meniscus shape with a concave surface facing the image side. consists of a second cemented lens having a negative refractive power,
The rear group is arranged in order from the object side, the third cemented lens having a negative refractive power in a meniscus shape having a concave surface directed toward the object side, a lens having a positive refractive power, and a convex surface directed toward the image side. consists of a fourth cemented lens having a negative refractive power,
When the focal length at the e-line (wavelength 546.07 nm) of the first cemented lens is fL1, and the combined focal length at the e-line of the entire lens system is f, the following formula −25.5 <fL1 / f <−5. 0
An imaging optical system characterized by satisfying the following conditions. The first cemented lens includes at least one positive lens and at least one negative lens;
The positive lens in the first cemented lens has a higher Abbe number than the negative lens;
When the Abbe number with respect to the d-line of the positive lens in the first cemented lens is νd1, the following equation νd1> 60
The imaging optical system according to claim 1, wherein the following condition is satisfied. The fourth cemented lens includes at least one positive lens and at least one negative lens;
The positive lens in the fourth cemented lens has a higher Abbe number than the negative lens;
When the Abbe number νd6 with respect to the d-line of the positive lens in the fourth cemented lens is given, the following equation νd6> 60
The imaging optical system according to claim 1, wherein the following condition is satisfied. When the radius of curvature of the image side lens surface of the second cemented lens is rS1, the radius of curvature of the object side lens surface of the third cemented lens is rS2, and the combined focal length at the e-line of the entire lens system is f. The following formula | rS1 | / f> 0.16
| RS2 | / f> 0.16
The imaging optical system according to claim 1, wherein the following condition is satisfied.

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