JPH07159691A - Achromatic lens system - Google Patents

Abstract

PURPOSE:To provide a chromatic aberration correction lens which is a chromatic aberration correction lens formed without using low dispersion glass and is capable of well correcting chromatic aberrations of a wider wavelength region, more preferably range from about 435nm (g line) to 656nm (C line). CONSTITUTION:This achromatic lens system is arranged with a positive meniscus lens, of which the concave face is directed to a diaphragm, at least either before or behind the diaphragm and is arranged with a negative lens, of which the concave face is directed to the diaphragm and positive lens groups 13F, 13R respectively both before and behind the diaphragm. The negative lenses 12F, 12R and positive meniscus lens 11 of the achromatic lens system satisfy the following conditions; (1) nuN<35. (2) 3nuN-nuP<15. (3) 0<f/fP<0.3, where nuN: the Abbe number of the d line of the negative lens, of which the concave face is directed to the diaphragm, nuP: the Abbe number of the d line of the positive meniscus lens, of which the concave face is directed to the diaphragm, fP: the focal length of the positive meniscus lens, of which the concave face is directed to the diaphragm, f: the focal length of the entire system.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an achromatic lens system, and more particularly to an achromatic lens system suitable for a color reading lens system for office machines.

[0002]

2. Description of the Related Art Conventionally, it has been known to use a special low dispersion glass as an achromatic lens system, but the low dispersion glass is expensive, easily scratched, and affected by temperature change. There was a problem that it was easily received.

Further, as an achromatic lens system which does not use low dispersion glass, there are disclosed in Japanese Patent Laid-Open No. 3-96912 and 5
Japanese Patent Laid-Open No. 142468 proposes a lens system in which a chromatic aberration correction lens is provided in an intermediate portion of the lens system. But,
The former is a method of achromatizing three wavelengths by exchanging a cemented lens and a plane parallel plate, and has a complicated structure. The latter has an achromatic wavelength range of about 486n.
There is a slight narrowness, such as m (F line) to 656 nm (C line).

[0004]

It is an object of the present invention to provide a chromatic aberration correcting lens which does not use low dispersion glass, and has a wider wavelength range, specifically, a chromatic aberration in a range of about 435 nm (g line) to 656 nm (C line). An object of the present invention is to obtain a chromatic aberration correction lens that can be excellently corrected.

[0005]

SUMMARY OF THE INVENTION The achromatic lens system of the present invention has been completed by devising a method of correcting chromatic aberration of a blue wavelength among three wavelengths of blue, green and red. The configuration of the lens of the present invention, at least one of the front and rear of the diaphragm, comprises a positive meniscus lens with a concave surface facing the diaphragm, both the front and the rear of the diaphragm, respectively, a negative lens with a concave surface facing the diaphragm, The positive lens group and the negative meniscus lens and the positive meniscus lens satisfy the following conditional expressions. (1) ν _N <35 (2) 3 <ν _N −ν _P <15 (3) 0 <f / f _P <0.3 where ν _N : Abbe of d line of negative lens with concave surface facing diaphragm Ν _{P is} the Abbe number of the d-line of the positive meniscus lens with the concave surface facing the diaphragm, f _{p is} the focal length of the positive meniscus lens with the concave surface facing the diaphragm, and f is the focal length of the entire system.

It is desirable that this achromatic lens system further satisfies the following conditional expression. (4) 3 <Δθ _{(g, F)} P / Δθ _{(g, F)} N where Δθ _{(g, F)} P: Standard of partial dispersion ratio of g-F line of positive meniscus lens with concave surface facing diaphragm Deviation from the line, Δθ _{(g, F)} N: Deviation from the standard line of the partial dispersion ratio of the gF line of the negative lens with the concave surface facing the diaphragm.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The achromatic lens of the present invention is provided with a positive meniscus lens having a concave surface facing the diaphragm at least one of the front and the rear of the diaphragm when the diaphragm is used as a reference. Both are provided with a negative lens having a concave surface facing the diaphragm and a positive lens group, respectively. The achromatic lens of the present invention is composed of a negative lens before and after a diaphragm that satisfies the conditional expression (1), and a positive lens group located outside the negative lens. The upper chromatic aberration is almost corrected, and only the blue chromatic aberration is generated on the plus side as compared with the chromatic aberrations of other wavelengths. Then, between at least one of the negative lens and the diaphragm, conditional expression (2),
By arranging a positive meniscus lens with a concave surface facing the diaphragm that satisfies the condition (3), the chromatic aberration of blue is changed to a negative side larger than the change amount of the chromatic aberration of other wavelengths, and thus the chromatic aberration of a wide range of wavelength regions is obtained. Was corrected, and other aberrations could be corrected at the same time.

Conditional expression (1) relates to the Abbe number of the negative lens. For the negative lens, a glass material having a small Abbe number (large dispersion) less than the upper limit of this conditional expression is used. If this upper limit is exceeded, correction of chromatic aberration of the entire system will be insufficient.

One of the characteristics of the present invention is that the Abbe number between the negative lens having a small Abbe number and the diaphragm is smaller than that of the negative lens satisfying the conditional expression (2) (larger dispersion). That is, a positive meniscus lens is arranged.
As a result, it was possible to correct chromatic aberration in a wide range from blue to red. If the upper limit of conditional expression (2) is exceeded, it is advantageous for correction of axial chromatic aberration, but it becomes difficult to correct lateral chromatic aberration of magnification. If the lower limit of conditional expression (2) is exceeded, correction of axial blue chromatic aberration is insufficient. .

Conditional expression (3) relates to the power of the positive meniscus lens. When the upper limit is exceeded, the power becomes too large, and the chromatic aberration on the axis and the lateral chromatic aberration of magnification, the chromatic astigmatism, and other chromatic aberrations. It becomes difficult to balance with various aberrations. Further, the performance deterioration due to the manufacturing error due to the distance between the negative lens and the positive meniscus lens and decentering becomes large. When the value goes below the lower limit, it is impossible to correct chromatic aberration, which is the object of the present invention.

In the achromatic lens system of the present invention, if a positive meniscus lens is arranged in either the front group or the rear group around the diaphragm, the effect of chromatic aberration correction can be recognized. Also,
If positive meniscus lenses are arranged in both the front and rear groups, the effect is improved as compared with the case of one, but the effect is not so great.

Conditional expression (4) relates to the partial dispersion ratio of the gF line of the negative lens and the positive meniscus lens, and is a conditional expression supplementing the conditional expressions (1) and (2). Where g-
The partial dispersion ratio θ _{(g, F) of the} F line is θ _{(g, F)} = _ng −n _F
The deviation from the standard line θ _{(g, F)} given by / n _F −n _c is the deviation from the standard line in the θ _{(g, F)} −ν _d diagram of Shot Company K7-F2. . If the lower limit of conditional expression (4) is exceeded, the change in blue chromatic aberration will be small, and it will be difficult to correct chromatic aberration over a wide range.

[Embodiment 1] FIG. 1 is a structural diagram of a lens of Embodiment 1 of an achromatic lens system of the present invention. In this embodiment, when a positive meniscus lens 11 having a concave surface facing the diaphragm is arranged in front of the diaphragm S, negative lenses 12F and 12R having concave surfaces facing the diaphragm are provided in front of and behind the diaphragm S, respectively, and a positive lens. The groups 13F and 13R are arranged. Positive lens group 1
3F and 13R each have a two-lens configuration, and the negative lens
The one on the 13R side is cemented to the negative lens.

Table 1 shows specific numerical data of this lens system, and FIG. 2 shows various aberrations. In the various aberration diagrams, SA is spherical aberration, SC is sine condition, e-line, d-line, F-line, c-line, and g-line are chromatic aberration and chromatic aberration of magnification indicated by spherical aberration at respective wavelengths, and S is sagittal. M indicates meridional.

In the tables and drawings, F _NO is the aperture ratio when the object distance is infinity, f is the focal length, Y is the image height, M is the lateral magnification, f _B is the back focus, and r _i is each lens surface. Radius of curvature, d _i is the lens thickness or lens spacing, N _e is the refractive index for the e-line, N _d is the refractive index for the d-line, and ν is the Abbe number for the d-line.

[0016]

[Table 1] F _NO = 4 f = 46.00 M = -0.165 Y = 18.74 f _B = 29.07 No. rd N _e N _d ν 1 25.087 7.03 1.80642 1.80100 35.0 2 68.685 0.18---3 16.220 4.97 1.65425 1.65160 58.5 4 131.069 1.30 1.74618 1.74000 28.3 5 10.051 2.92---6 19.826 2.52 1.81675 1.80834 22.6 7 19.552 2.35---Aperture ∞ 8.60---8 -13.776 1.30 1.67158 1.66680 33.0 9 -89.993 4.97 1.77621 1.77250 49.6 10 -16.523 0.10--- 11 156.216 6.05 1.69979 1.69680 55.5 12 -39.497----

Surface No. 4 θ _{(g, F)} N = 0.6017, Δθ _{(g, F)} N = 0.0060 Surface No. 6 θ _{(g, F)} P = 0.6288, Δθ _{(g, F)} P = 0.0213 ν _N = 28.3, ν _P = 22.6, ν _N −ν _P = 5.7, f / f _p = 0.08
3, Δθ _{(g, F)} P / Δθ _{(g, F)} N = 3.55

[Embodiment 2] FIG. 3 is a lens configuration diagram of an achromatic lens system according to Embodiment 2 of the present invention. In this embodiment, a positive meniscus lens 15 having a concave surface facing the diaphragm is arranged behind the diaphragm S, and both in front of and behind the diaphragm S.
Negative lenses 16F and 16R having concave surfaces facing the diaphragm S and positive lens groups 17F and 17R are arranged. Positive lens group 17
Each of F and 17R has two lenses, and the negative lenses 16F and 1
That on the 6R side is cemented to the negative lens. Table 2 shows specific numerical data of this lens system, and FIG. 4 shows various aberrations thereof.

[0019]

[Table 2] F _NO = 4 f = 46.00 M = -0.1653 Y = 18.74 f _B = 30.12 surface No. rd N _e N _d ν 1 23.463 5.57 1.80642 1.80100 35.0 2 71.379 0.18---3 15.433 4.29 1.65425 1.65160 58.5 4 117.080 1.30 1.74618 1.74000 28.3 5 10.620 5.23---Aperture ∞ 6.28---6 -25.217 1.98 1.81675 1.80834 22.6 7 -23.865 1.69---8 -11.371 1.30 1.65223 1.64769 33.8 9 -54.327 4.51 1.77621 1.77250 49.6 10 -16.098 0.10- --11 481.302 5.60 1.65425 1.65160 58.5 12 -36.142----

Surface No. 6 θ _{(g, F)} P = 0.6288, Δθ _{(g, F)} P = 0.0213 Surface No. 8 θ _{(g, F)} N = 0.5883, Δθ _{(g, F)} N = 0.0015 ν _{N = 33.8, ν P = 22.6} , ν N -ν P = 11.2, f / f p = 0.14 Δθ (g, F) P / Δθ (g, F) N = 14.2

[Embodiment 3] FIG. 5 is a lens configuration diagram of an achromatic lens system according to Embodiment 3 of the present invention. In this embodiment, a positive meniscus lens 11 having a concave surface facing the diaphragm S, a negative lens 12F having a concave surface facing the diaphragm S, and a positive lens group 13F are arranged in this order in front of the diaphragm S as a reference. Similarly, to the rear side, a positive meniscus lens 15 having a concave surface facing the diaphragm S and a negative lens 16 having a concave surface facing the diaphragm S are similarly provided.
The R and the positive lens group 17R are arranged in order. Each of the positive lens groups 13F and 17R includes two lenses, and the negative lens 12
Those on the F and 16R sides are cemented to the negative lens.
Table 3 shows specific numerical data of this lens system, and FIG. 6 shows various aberrations thereof.

[0022]

[Table 3] F _NO = 4 f = 46.25 M = 0.165 Y = 18.74 f _B = 28.68 No. rd N _e N _d ν 1 22.641 4.81 1.72391 1.72000 43.7 2 65.232 0.18---3 15.401 4.42 1.65425 1.65160 58.5 4 75.561 1.30 1.69417 1.68893 31.1 5 10.136 1.07---6 17.281 1.78 1.81675 1.80834 22.6 7 17.356 3.35---Aperture ∞ 6.76---8 -22.955 1.94 1.75918 1.75211 25.0 9 -23.347 1.47---10 -12.492 1.30 1.67158 1.66680 33.0 11 -67.162 4.56 1.77621 1.77250 49.6 12 -17.173 0.10---13 266.804 5.97 1.67279 1.67000 57.4 14 -35.753----

Front group surface No. 4 θ _{(g, F)} N = 0.5943, Δθ _{(g, F)} N = 0.0031 Surface No. 6 θ _{(g, F)} P = 0.6288, Δθ _{(g, F)} P = 0.0213 ν _N = 31.1, ν _{P = 22.6, ν N -ν P =} 8.5, f / f p =
0.11 Δθ _{(g, F)} P / Δθ _{(g, F)} N = 6.9 Rear group surface No.8 θ _{(g, F)} P = 0.6191, Δθ _{(g, F)} P = 0.0159 Surface No.10 θ _{(g , F) N = 0.5894, Δθ} (g, F) N = 0.0014 ν N = 33.0, ν P = 25.0, ν N -ν P = 7.9, f / f p = 0.029 Δθ (g, F) P / Δθ ( _{g, F)} N = 11.4

FIG. 7, FIG. 8 and FIG. 9 show the first embodiment, respectively.
FIG. 6 is a diagram in which the axial chromatic aberrations in 2 and 3 are shown by solid lines, and the axial chromatic aberrations when the positive meniscus lenses 11 and 15 near the diaphragm are removed to obtain the same magnification are drawn by broken lines and compared. From this figure, it can be seen that in the example in which the positive meniscus lens is removed, the axial chromatic aberration of blue (g line) changes more than twice as much as the axial chromatic aberration of red (C line). On the other hand, in the achromatic lens system of the present invention, about 435 nm (g
It was possible to satisfactorily correct chromatic aberration in the range of about (line) to 656 nm (C line).

Table 4 shows the values corresponding to the conditional expressions of Examples 1 to 3.

[Table 4] Example 1 Example 2 Example 3 Front group Rear group Front group Front group Rear group Conditional expression (1) 28.3 33.8 31.1 33.0 Conditional expression (2) 5.7 11.2 8.5 7.9 Conditional expression (3) 0.083 0.14 0.11 0.029 Conditional expression (4) 3.55 14.2 6.9 11.4

As is clear from Table 4, the numerical values of Examples 1 to 3 are all conditional expressions (1) to (4).
Are satisfied. Further, the achromatic lens system of the present invention satisfactorily corrects chromatic aberration in the range of about 435 nm (g line) to 656 nm (C line), and various aberrations in each aberration diagram are relatively well corrected. .

[0027]

The achromatic lens system of the present invention is a chromatic aberration correcting lens that does not use low dispersion glass, and has a wider wavelength range, specifically, from about 435 nm (g line) to 656 nm.
It is possible to excellently correct chromatic aberration in the range of about nm (C line).

[Brief description of drawings]

FIG. 1 is a lens configuration diagram showing a first embodiment of an achromatic lens system according to the present invention.

FIG. 2 is a diagram of various types of aberration of the lens system in FIG.

FIG. 3 is a lens configuration diagram showing a second embodiment of the achromatic lens system according to the present invention.

FIG. 4 is a diagram of various types of aberration of the lens system in FIG.

FIG. 5 is a lens configuration diagram showing a third embodiment of the achromatic lens system according to the present invention.

FIG. 6 is a diagram of various types of aberration of the lens system in FIG.

7A and 7B are diagrams of paraxial axial chromatic aberration and paraxial axial chromatic aberration when a positive meniscus lens near the diaphragm is removed in Example 1;

FIG. 8 is a diagram of paraxial on-axis chromatic aberration when paraxial axial chromatic aberration and a positive meniscus lens near the diaphragm are removed in Example 2;

FIG. 9 is a diagram of paraxial axial chromatic aberration when paraxial axial chromatic aberration and a positive meniscus lens near the diaphragm are removed in Example 3; S diaphragm 11 15 Positive meniscus lens 12F 12R 16F 16R Negative lens 13F 13R 17F 17R Positive lens group

Claims (2)

[Claims] 1. At least one of a front side and a rear side of the diaphragm,
A positive meniscus lens with a concave surface facing the diaphragm is provided, and a negative lens with a concave surface facing the diaphragm and a positive lens group are provided on both the front side and the rear side of the diaphragm, respectively, and the negative lens and the positive meniscus lens are , (1) below,
An achromatic lens system that satisfies the conditional expressions (2) and (3). (1) ν _N <35 (2) 3 <ν _N −ν _P <15 (3) 0 <f / f _P <0.3 where ν _N : Abbe of d line of negative lens with concave surface facing diaphragm Number, ν _P : Abbe's number of the d line of the positive meniscus lens with the concave surface facing the diaphragm, f _p : focal length of the positive meniscus lens with the concave surface facing the diaphragm, f: focal length of the entire system. 2. An achromatic lens system according to claim 1, further satisfying the following conditional expression (4). (4) 3 <Δθ _{(g, F)} P / Δθ _{(g, F)} N where Δθ _{(g, F)} P: standard of partial dispersion ratio of g-F line of positive meniscus lens with concave surface facing diaphragm Deviation from the line, Δθ _{(g, F)} N: Deviation from the standard line of the partial dispersion ratio of the gF line of the negative lens with the concave surface facing the diaphragm.