JP2006091718A - Telephoto lens system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform image processing by inspecting an object at a finite distance with high definition, and when the wavelength of the light source is visible light, and when it is a mixed light of visible light and near infrared light. Thus, a telephoto lens system capable of obtaining a stable resolution performance with little focal shift is obtained.
A telephoto lens system having a four-lens structure including a first lens having a positive power, a second lens having a positive power, a third lens having a negative power, and a fourth lens having a positive power in order from the object side. Therefore, the following conditional expression (1) is satisfied.
(1) 0.15 <Dp / f <0.5
However,
Dp: the sum of the first lens group thickness and the second lens group thickness,
f: Focal length of the entire system.
[Selection] Figure 1

Description

  The present invention relates to a telephoto lens system for the purpose of inspecting an object at a finite distance with high definition and performing image processing.

Most conventional telephoto lens systems are photographic lenses and cannot be used for high-definition purposes for image processing. For example, Japanese Patent Laid-Open No. 8-201687 proposes a telephoto lens system having a four-group four-lens configuration, but is not suitable for high-definition image processing due to insufficient correction of chromatic aberration. In addition, there are JP-A-5-27163, JP-A-7-301749, and JP-A-8-234098, all of which are high-definition aimed at by the present invention, that is, the resolution of the entire screen is about the Nyquist frequency. It cannot be used for high-definition image processing such as 80 or more. In addition, for image processing, there are cases where only visible light is used as a light source and cases where mixed light of visible light and near infrared light is used, and there is a problem that the focal point movement between such visible light and mixed light is large. is there.
JP-A-8-201687 JP-A-5-27163 Japanese Patent Laid-Open No. 7-301749 JP-A-8-234098

  The present invention can perform image processing by inspecting an object at a finite distance with high definition, and when the wavelength of the light source is visible light and when it is a mixed light of visible light and near infrared light Thus, an object of the present invention is to obtain a telephoto lens system capable of obtaining stable resolution performance with little focal shift.

  The present invention can correct chromatic aberration satisfactorily and provide high-definition image processing when a sufficient thickness is given to the first lens and the second lens both having positive power in a four-group four-lens telephoto lens system. It has been made by finding that a telephoto lens system suitable for use can be obtained.

The telephoto lens system of the present invention has a four-lens configuration including, in order from the object side, a first lens having a positive power, a second lens having a positive power, a third lens having a negative power, and a fourth lens having a positive power. The telephoto lens system is characterized in that the following conditional expression (1) is satisfied.
(1) 0.15 <Dp / f <0.5
However,
Dp: the sum of the first lens group thickness and the second lens group thickness,
f: focal length of the entire system,
It is.

The telephoto lens system of the present invention preferably satisfies the following conditional expression (2).
(2) 70 <ν1p
However,
ν1p; Abbe number of the positive first lens,
It is.

Furthermore, it is preferable that the following conditional expression (2 ′) is satisfied.
(2 ′) 80 <ν1p

The telephoto lens system of the present invention preferably satisfies the following conditional expression (3).
(3) 70 <ν2p
However,
ν2p; Abbe number of the positive second lens,
It is.

Furthermore, it is preferable that the following conditional expression (3 ′) is satisfied.
(3 ′) 80 <ν2p

In addition, the telephoto lens system of the present invention includes four lenses including a first lens having a positive power, a second lens having a positive power, a third lens having a negative power, and a fourth lens having a positive power in order from the object side. The telephoto lens system having the above-described configuration is characterized in that the following conditional expressions (2) and (3) are satisfied.
(2) 70 <ν1p
(3) 70 <ν2p
However,
ν1p; Abbe number of the positive first lens,
ν2p; Abbe number of the positive second lens,
It is.

Furthermore, it is more preferable that the following conditional expressions (2 ′) and (3 ′) are satisfied.
(2 ′) 80 <ν1p
(3 ′) 80 <ν2p

  According to the telephoto lens system of the present invention, it is possible to perform image processing by inspecting an object at a finite distance with high definition, and when the wavelength of the light source is visible light, and visible light and near infrared light. With this mixed light, it is possible to obtain stable resolution performance with little focal shift.

  The telephoto lens system of the present embodiment is shown in FIG. 1 (Numerical Example 1), FIG. 3 (Numerical Example 2), FIG. 5 (Numerical Example 3), FIG. 7 (Numerical Example 4), and FIG. Example 5) and in each example of FIG. 11 (Numerical Example 6), in order from the object side, a biconvex positive lens (positive first lens) 10 and a convex positive meniscus lens (positive positive on the object side) It consists of four lenses, a second lens 20, a biconcave negative lens (negative third lens) 30, and a biconvex positive lens (positive fourth lens) 40, and is between the third lens 30 and the fourth lens 40. A diaphragm S is located in the position. Focusing is performed by extending the entire system.

  Conditional expression (1) is a condition regarding the thicknesses of the first lens and the second lens both having positive power. In order to correct chromatic aberration, it is preferable that the lens thickness of the positive lens is large. When combined with a low dispersion glass material that satisfies the conditional expressions (2) and (3), chromatic aberration can be corrected more suitably. If the lower limit of conditional expression (1) is exceeded, chromatic aberration is insufficiently corrected, and if the upper limit is exceeded, it is advantageous for correcting chromatic aberration, but the third lens group and the fourth lens group are close to the stop. Correction of aberration, astigmatism and distortion becomes difficult.

  In general, it is known that chromatic aberration can be reduced by using low-dispersion glass for a positive lens on the object side of a telephoto lens system. However, in the present embodiment, a positive first lens (single lens) and a positive first lens are used. Another feature is that both of the two lenses (single lens) are made of low dispersion glass satisfying conditional expressions (2) and (3). Chromatic aberration cannot be sufficiently corrected with a glass material that does not satisfy conditional expressions (2) and (3). In order to sufficiently correct chromatic aberration, it is more preferable to satisfy conditional expressions (2 ′) and (3 ′).

Next, specific numerical examples will be shown. These numerical examples are examples designed based on a finite object distance in front of the first surface 250 (D0 = 250). In the various aberration diagrams, the d-line, g-line, C-line, and A'-line in the chromatic aberration (axial chromatic aberration) diagram and the lateral chromatic aberration diagram represented by spherical aberration are aberrations for the respective wavelengths, and S is sagittal, M Is a meridional. In the tables and drawings, FNO. And F are F numbers for an object at infinity, f is a focal length of the entire system, m is a lateral magnification, y is an image height, f _B is a back focus, r is a radius of curvature, and d is a curvature radius. Lens thickness or lens interval, N _d is the refractive index of the d-line, and ν is the Abbe number.

(Numerical example 1)
1 and 2 and Table 1 show Numerical Example 1 of the telephoto lens system of the present invention. FIG. 1 is a lens configuration diagram, FIG. 2 is a diagram of various aberrations, and Table 1 is numerical data thereof. This telephoto lens system includes, in order from the object side, a biconvex positive lens (positive first lens) 10, a positive meniscus lens (positive second lens) 20 convex on the object side, and a biconcave negative lens (negative third lens). Lens) 30 and biconvex positive lens (positive fourth lens) 40, and a diaphragm S is located between the third lens 30 and the fourth lens 40. CG (surface Nos. 9 to 10) is a cover glass. The diaphragm S is located at a position 1.867 behind (image side) the six surfaces (third lens 30).

(Table 1)
FNO. = 1: 2.8
f = 49.98
m = -0.252
f _B = 31.07
Surface No. r d N _d ν
1 22.648 6.56 1.49700 81.6
2 -180.000 1.50--
3 18.227 7.90 1.48749 70.2
4 30.052 1.24--
5 -57.127 5.97 1.71736 29.5
6 13.579 5.98--
7 34.201 2.80 1.80 100 35.0
8 -82.172 1.00--
9 ∞ 0.75 1.49782 66.8

(Numerical example 2)
3 and 4 and Table 2 show Numerical Example 2 of the telephoto lens system of the present invention. FIG. 3 shows the lens configuration, FIG. 4 shows the various aberrations, and Table 2 shows the numerical data. The basic lens configuration of the numerical example is the same as that of the numerical example 1. The diaphragm S is located at a position 1.867 behind (image side) the six surfaces (third lens 30).

(Table 2)
FNO. = 1: 2.8
f = 49.98
m = -0.253
f _B = 30.97
Surface No. r d N _d ν
1 22.049 6.30 1.43875 95.0
2 -180.000 2.47--
3 18.414 8.43 1.51633 64.1
4 32.828 1.19--
5 -52.607 6.08 1.69895 30.1
6 13.426 5.30--
7 31.760 2.80 1.80 100 35.0
8 -88.192 1.00--
9 ∞ 0.75 1.49782 66.8
10 ∞----

(Numerical example 3)
5 and 6 and Table 3 show Numerical Example 3 of the telephoto lens system of the present invention. FIG. 5 shows the lens configuration, FIG. 6 shows the various aberrations, and Table 3 shows the numerical data. The basic lens configuration of the numerical example is the same as that of the numerical example 1. The diaphragm S is located at a position 1.867 behind (image side) the six surfaces (third lens 30).

(Table 3)
FNO. = 1: 2.8
f = 49.98
m = -0.263
f _B = 29.85
Surface No. r d N _d ν
1 22.327 8.32 1.48749 70.2
2 -173.093 1.50--
3 17.326 6.06 1.48749 70.2
4 35.452 1.15--
5 -85.486 9.06 1.76182 26.5
6 12.230 4.62--
7 25.312 2.80 1.80518 25.4
8 -867.520 1.00 ‐ ‐
9 ∞ 0.75 1.49782 66.8
10 ∞----

(Numerical example 4)
7 and 8 and Table 4 show Numerical Example 4 of the telephoto lens system of the present invention. FIG. 7 shows the lens configuration, FIG. 8 shows the various aberrations, and Table 4 shows the numerical data. The basic lens configuration of the numerical example is the same as that of the numerical example 1. The diaphragm S is located at a position 1.867 behind (image side) the six surfaces (third lens 30).

(Table 4)
FNO. = 1: 2.8
f = 49.98
m = -0.264
f _B = 29.81
Surface No. r d N _d ν
1 23.034 6.48 1.51633 64.1
2 -178.423 1.50--
3 16.947 6.00 1.43875 95.0
4 41.296 1.09--
5 -108.168 9.00 1.75520 27.5
6 12.091 5.43--
7 27.345 2.80 1.80518 25.4
8 2739.602 1.00 ‐ ‐
9 ∞ 0.75 1.49782 66.8
10 ∞----

(Numerical example 5)
9 and 10 and Table 5 show Numerical Example 5 of the telephoto lens system of the present invention. FIG. 9 shows the lens configuration, FIG. 10 shows the various aberrations, and Table 5 shows the numerical data. The basic lens configuration of the numerical example is the same as that of the numerical example 1. The diaphragm S is located at a position 1.867 behind (image side) the six surfaces (third lens 30).

(Table 5)
FNO. = 1: 2.8
f = 49.98
m = -0.253
f _B = 31.39
Surface No. r d N _d ν
1 23.945 6.00 1.49700 81.6
2 -214.882 1.50--
3 18.704 8.43 1.49700 81.6
4 31.535 1.19--
5 -71.473 5.94 1.69895 30.1
6 13.599 5.92--
7 34.407 2.80 1.80 100 35.0
8 -98.871 1.00 ‐ ‐
9 ∞ 0.75 1.49782 66.8
10 ∞----

(Numerical example 6)
11 and 12 and Table 6 show Numerical Example 6 of the telephoto lens system of the present invention. FIG. 11 shows the lens configuration, FIG. 12 shows the various aberrations, and Table 6 shows the numerical data. The basic lens configuration of the numerical example is the same as that of the numerical example 1. The diaphragm S is located at a position 1.867 behind (image side) the six surfaces (third lens 30).

(Table 6)
FNO. = 1: 2.8
f = 49.98
m = -0.252
f _B = 30.89
Surface No. r d N _d ν
1 -29.250 1.00 1.84666 23.8
1 22.586 6.84 1.49700 81.6
2 -293.546 1.50--
3 17.392 9.00 1.43875 95.0
4 27.680 1.39--
5 -48.122 4.77 1.71736 29.5
6 13.506 5.04--
7 31.305 4.09 1.80 100 35.0
8 -66.433 1.00--
9 ∞ 0.75 1.49782 66.8
10 ∞----

Table 7 shows values for the conditional expressions of the numerical examples.
(Table 7)
Example 1 Example 2 Example 3 Example 4 Example 5 Example 6
Conditional expression (1) 0.289 0.295 0.288 0.250 0.289 0.357
Conditional expression (2) 81.6 95.0 70.2 64.1 81.6 81.6
Conditional expression (3) 70.2 64.1 70.2 95.0 81.6 95.0

As is apparent from Table 7, the numerical values of Numerical Example 1 to Numerical Example 6 satisfy the conditional expressions, and various aberrations are well corrected. In particular, as clearly shown in the chromatic aberration diagram and the magnification chromatic aberration diagram indicated by the spherical aberration, the difference between the aberration of the A ′ line (near infrared light) and the aberration of the d line, g line, and C line is small. It can be seen that there is little focal shift due to mixed light with near infrared light.

It is a lens block diagram of Numerical Example 1 of a telephoto lens system according to the present invention. FIG. 2 is a diagram illustrating various aberrations of the lens configuration in FIG. 1. It is a lens block diagram of Numerical Example 2 of the telephoto lens system by this invention. FIG. 4 is a diagram illustrating various aberrations of the lens configuration in FIG. 3. It is a lens block diagram of numerical Example 3 of the telephoto lens system by this invention. FIG. 6 is a diagram illustrating various aberrations of the lens configuration in FIG. 5. It is a lens block diagram of numerical Example 4 of the telephoto lens system by this invention. FIG. 8 is a diagram illustrating various aberrations of the lens configuration in FIG. 7. It is a lens block diagram of numerical Example 5 of the telephoto lens system by this invention. FIG. 10 is a diagram illustrating various aberrations of the lens configuration in FIG. 9. It is a lens block diagram of Numerical Example 6 of the telephoto lens system by this invention. FIG. 12 is a diagram illustrating various aberrations of the lens configuration in FIG. 11.

Claims (7)

A telephoto lens system having a four-lens structure including a first lens having a positive power, a second lens having a positive power, a third lens having a negative power, and a fourth lens having a positive power in order from the object side,
A telephoto lens system satisfying the following conditional expression (1):
(1) 0.15 <Dp / f <0.5
However,
Dp: the sum of the first lens group thickness and the second lens group thickness,
f: Focal length of the entire system. The telephoto lens system according to claim 1, wherein the telephoto lens system satisfies the following conditional expression (2).
(2) 70 <ν1p
However,
ν1p: Abbe number of the positive first lens. The telephoto lens system according to claim 2, wherein the telephoto lens system satisfies the following conditional expression (2 ').
(2 ′) 80 <ν1p The telephoto lens system according to any one of claims 1 to 3, wherein the telephoto lens system satisfies the following conditional expression (3).
(3) 70 <ν2p
However,
ν2p: Abbe number of the positive second lens. 5. The telephoto lens system according to claim 4, wherein the telephoto lens system satisfies the following conditional expression (3 ′).
(3 ′) 80 <ν2p A telephoto lens system having a four-lens structure including a first lens having a positive power, a second lens having a positive power, a third lens having a negative power, and a fourth lens having a positive power in order from the object side,
A telephoto lens system satisfying the following conditional expressions (2) and (3):
(2) 70 <ν1p
(3) 70 <ν2p
However,
ν1p; Abbe number of the positive first lens,
ν2p: Abbe number of the positive second lens. The telephoto lens system according to claim 6, wherein the telephoto lens system satisfies the following conditional expressions (2 ') and (3').
(2 ′) 80 <ν1p
(3 ′) 80 <ν2p

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