JP3397459B2 - Achromatic lens system - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an achromatic lens system, and more particularly to 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.

As an achromatic lens system that does not use low dispersion glass, Japanese Patent Laid-Open Nos. 3-96912 and 5-142468 disclose a lens system in which a chromatic aberration correction lens group is provided in the middle of the lens system. is suggesting. However, the former is a method of achromatizing three wavelengths by exchanging the cemented lens and the plane parallel plate, and has a complicated structure. The latter has an achromatic wavelength range of about 486 nm (F line) to 656 nm.
(C line) and a little narrow hate.

[0004]

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

[0005]

SUMMARY OF THE INVENTION The achromatic lens system of the present invention has been completed by devising a method of correcting axial chromatic aberration of blue, green and red among three wavelengths. According to one aspect of the achromatic lens system of the present invention, in an achromatic lens system including a front lens group, a chromatic aberration correction lens group, and a rear lens group in order from the object side, a front lens group and a rear lens group are provided. Corrects spherical aberration, coma aberration, astigmatism, field curvature, and axial chromatic aberration in the wavelength range of light from green to red, while correcting axial chromatic aberration in the wavelength range of blue light to the plus side. The chromatic aberration correction lens group is caused to correct axial chromatic aberration in the wavelength range of blue light generated by the front lens group and the rear lens group , and further this chromatic aberration correction lens
The group consists of at least one positive lens and one
A lens group including a negative lens, which satisfies the following conditional expression (1):
It can consist of a lens group that satisfies the condition (3)
It _{(1) | ν P -ν N} | <5.0 (2) | N P -N N
│ <0.01 (3) 1 <(Δθ (g, F) _P ) / (Δθ (g,
F) _N ) <10 However, ν _P : Positive lens of the chromatic aberration correction lens group
Abbe's number of the d-line, ν _N : Negative aberration of the chromatic aberration correction lens group
Abbe number of the d-line of the lens , N _P : Positive of the chromatic aberration correction lens group
Refractive index of d-line of lens, N _N : Negative of chromatic aberration correction lens group
Refractive index of d-line of lens, Δθ (g, F) _P : Chromatic aberration correction lens
Deviation of the partial dispersion ratio of the gF line of the positive lens of the group from the standard line
Difference, Δθ (g, F) _N : g− of the negative lens of the chromatic aberration correction lens group
The deviation of the partial dispersion ratio of the F line from the standard line .

[0006]

The chromatic aberration correction lens group can be composed of one lens for each of the positive and negative lenses in the simplest case. In this case, the order of the positive and negative lenses does not matter. Further, it may be composed of three lenses each of positive, negative, positive, or negative, positive, negative in order from the object side. In any of these aspects, the above conditional expressions (1) to (3) are satisfied, and in the case where there are two positive lenses or two negative lenses in the chromatic aberration correction lens group, the positive expression in the conditional expression is satisfied. A lens and a negative lens are read as a positive lens and a negative lens, respectively.

These four modes, positive, negative,
Negative, positive, positive, negative, positive, and negative, positive, negative can all be cemented lenses.
Further, in the case of the three-lens configuration, it is possible to have a symmetrical shape with respect to the center of the middle lens of the three lenses. With the symmetrical shape, the manufacturing cost can be reduced, and the mistake of inserting the lens before and after can be eliminated when assembling the lens.

In the four modes, the achromatic lens system of the present invention preferably further satisfies the following conditional expressions (4) and (5). (4) 2 <f / f _CP <10 (5) | f / f _CP + f / f _CN | <0.1 where f: focal length of the entire system f _CP : composition of positive lens in chromatic aberration correction lens group Focal length, f _CN : Composite focal length of the negative lens in the chromatic aberration correction lens group.

According to another expression, the achromatic lens system of the present invention comprises two lenses, a positive lens and a negative lens, in the intermediate part of the lens system, and the following conditional expressions (1) to (3) are used. It is characterized by having a chromatic aberration correction lens group that satisfies the above condition. It does not matter whether the positive lens or the negative lens is before or after. _{(1) | ν P -ν N} | <5.0 (2) | N P -N N | <0.01 (3) 1 <(Δθ (g, F) P) / (Δθ (g, F) _N ) <10 where ν _{P is} the Abbe number of the d line of the positive lens of the chromatic aberration correction lens group, ν _{N is} the Abbe number of the d line of the negative lens of the chromatic aberration correction lens group, and N _{P is} the positive lens of the chromatic aberration correction lens group D line refractive index, N _N : d line refractive index of the negative lens of the chromatic aberration correction lens group, Δθ (g, F) _P : standard of partial dispersion ratio of gF line of the positive lens of the chromatic aberration correction lens group Deviation from the line, Δθ (g,
F) _N : The deviation of the partial dispersion ratio of the gF line of the negative lens of the chromatic aberration correction lens group from the standard line.

According to another aspect of the present invention, the chromatic aberration correction lens group includes a positive lens, a negative lens, and a positive lens which satisfy the same conditional expressions (1) to (3) as described above. It may be composed of a single lens.

According to another aspect of the present invention, the chromatic aberration correction lens group includes three lenses, a negative lens, a positive lens and a negative lens, which satisfy the same conditional expressions (1) to (3) as described above. You may comprise from the lens.

The chromatic aberration correction lens group in the lens system of the present invention has the above-mentioned three aspects, that is, the chromatic aberration correction lens group is positive, negative, positive, negative, positive, or negative, positive, negative. It is preferable that the following conditional expressions (4) and (5) are satisfied. (4) 2 <f / f _CP <10 (5) | f / f _CP + f / f _CN | <0.1 where f: focal length of the entire system f _CP : composition of positive lens in chromatic aberration correction lens group Focal length, f _CN : Composite focal length of the negative lens in the chromatic aberration correction lens group.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The achromatic lens system of the present invention is capable of suppressing aberrations such as spherical surface, coma, astigmatism, and image plane curvature by lenses other than the chromatic aberration correction lens group, that is, the lens groups before and after the chromatic aberration correction lens group. In addition to correcting almost all axial chromatic aberration in the wavelength range from green to red, it also causes only blue axial chromatic aberration to occur slightly on the plus side compared to other wavelength chromatic aberrations. Of the positive lens and the negative lens, which have the same refractive index with respect to the wavelengths from green to red so as to satisfy the upper limits of the conditional expressions (1) and (2), and refraction of the blue wavelength. The ratio is changed slightly within the range of the conditional expression (3), and the axial chromatic aberration of blue is changed by a larger amount (to the negative side) than the amount of change of the axial chromatic aberration of other wavelengths. As extensive Achromatic long area, and the other aberrations are those that could be corrected at the same time.

If the upper limits of conditional expressions (1) and (2) are exceeded, the balance of chromatic aberration between the chromatic-aberration correction lens group and the lens groups before and after it is lost, making it difficult to correct chromatic aberration in a wide wavelength range. Become.

The conditional expressions (1) and (2) are also effective for correcting axial chromatic aberration and off-axis color astigmatism. If it exceeds the upper limit, this correction cannot be performed sufficiently.

Conditional expression (3) is defined by a standard line (S7, K7-F2) of the partial dispersion ratio θ (g, F) of the blue wavelength (g, F line).
This is a condition related to the ratio of the positive lens to the negative lens of the deviation Δθ (g, F) from the standard). Beyond the upper limit, not only blue,
The difference in refractive index between the positive lens and the negative lens of wavelengths from green to red becomes large, and it becomes difficult to balance the correction lens and the lens groups before and after it. If the lower limit is exceeded, chromatic aberration cannot be corrected.

In conditional expression (2), the upper limit is 0.0.
01, when 5 the upper limit of conditional expression (3), _{i.e., (2 ') | N P} -N N | <0.001 (3') 1 <(Δθ (g, F) P) / (Δθ ( If g, F) _N ) <5, the refractive index in the wavelengths of red to green is almost the same, and only the refractive index in the wavelength of blue is slightly different. Therefore, only the chromatic aberration of blue is corrected without changing other aberrations by changing only the radius of curvature of the bonding surface of the correction lens according to the correction status of the chromatic aberration of the lens groups before and after the chromatic aberration correction lens group. You can control.

As the color correction lens, at least two lenses of positive and negative or negative and positive are required. Two
In the case of a single lens, the advantage is that the number of constituent lenses is small, but since the power of both positive and negative lenses is large, the radius of curvature of the surfaces facing each other is small, and the lens thickness (edge thickness) at the periphery of the positive lens is small. It is easy to manufacture, so it is relatively difficult to manufacture. On the other hand, positive, negative, positive, or negative,
In the case of the positive and negative three-sheet structure, the number of sheets is increased by one, but there is an advantage that the radius of curvature of the surfaces facing each other is large and the peripheral thickness can be easily increased.

The conditional expressions (4) and (5) relate to the combined focal length of the positive lens and the negative lens in the chromatic aberration correction lens group, and by giving a large power to both the positive lens and the negative lens, the conditional expressions ( Even with a normal glass combination satisfying 1), (2), and (3), the chromatic aberration of blue in particular can be changed more than the chromatic aberration of other wavelengths, so that the chromatic aberration can be easily corrected.

If the upper limit of the conditional expression (4) is exceeded, it is advantageous to correct the chromatic aberration on the paraxial axis. However, if the lower limit of the conditional expression (4) is exceeded, the higher order aberration of the marginal chromatic aberration of the axial light beam occurs. Under the conditions of conditional expressions (1), (2), and (3), chromatic aberration is undercorrected.

Conditional expression (5) relates to the difference in power between the positive lens and the negative lens in the chromatic aberration correction lens group.
Both lenses have high power, but the difference is very small, as indicated by the upper limit of conditional expression (5). When the value exceeds the upper limit, not only chromatic aberration but also other aberrations occur in the chromatic aberration correction lens group, and it becomes difficult to balance with the aberrations generated in the front and rear lens groups.

[Embodiment 1] FIG. 1 shows a color according to the present invention, which is composed of a cemented lens composed of two lenses in one group between a front lens group 11 consisting of three lenses in two groups and a rear group lens 12 consisting of three lenses in two groups. Eraser 13 (face
It is a lens block diagram of the 1st Example of this invention which inserted No. 6-8).

Specific numerical data of this lens system are shown in Table 1, and various aberrations are shown in FIG. 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 table and drawings, F _NO is the F number when the object distance is ∞, f is the focal length, y is the image height, f _B is the back focus, M is the lateral magnification, and r is the radius of curvature of each lens surface. , D
Is the lens thickness or lens spacing, N _e is the refractive index of the e-line,
N _d is the refractive index of the d line, and ν _d is the Abbe number of the d line.

[0026]

[Table 1] F _NO = 4 f = 50.16 y = 18.74 f _B = 33.48 M = -0.165 plane NO rd N _e N _d ν _d 1 23.000 4.14 1.80642 1.80100 35.0 2 65.589 0.18---3 14.900 4.20 1.62287 1.62041 60.3 4 62.439 1.50 1.74618 1.74000 28.3 5 10.539 5.73---6 ∞ 3.56 1.81264 1.80518 25.4 7 -6.000 1.23 1.81265 1.80518 25.4 8 ∞ 7.27---9 -12.074 1.50 1.67158 1.66680 33.0 10 -41.418 3.80 1.74679 1.74320 49.3 11 -17.000 0.10-- -12 -260.000 4.66 1.72341 1.71999 50.2 13 -29.839----

Θ (g, F) = (n _g -n _F ) / (n _F -n _c ) surface No. 6 θ (g, F) _P = 0.6153 Δθ (g, F) _P = 0.0150 surface No. 7 θ (g, F) _N = 0.6100 Δθ (g, F) _N = 0.0097 θ (g, F) _P and Δθ (g, F) _P are characteristic values determined by the glass material.

[Embodiment 2] FIG. 3 shows a color according to the present invention comprising a cemented lens composed of two lenses in one group between a front lens group 11 consisting of three lenses in two groups and a rear lens group 12 consisting of three lenses in two groups. Eraser 13 (face
It is a lens block diagram of the 2nd Example of this invention which inserted No. 6-8). Table 2 shows specific numerical data for this lens system.
And various aberrations thereof are shown in FIG.

[0029]

[Table 2] F _NO = 4 f = 48.57 y = 18.74 f _B = 32.19 M = −0.165 plane NO rd N _e N _d ν _d 1 23.435 4.14 1.80642 1.80100 35.0 2 72.312 0.18-- -3 14.953 4.53 1.62286 1.62041 60.3 4 79.475 1.50 1.74618 1.74000 28.3 5 10.290 5.94---6 ∞ 1.23 1.79177 1.78470 26.2 7 9.652 3.56 1.79192 1.78472 25.7 8 ∞ 6.68---9 -12.363 1.50 1.67766 1.67270 32.1 10 -49.656 4.01 1.74679 1.74 49.3 11 -16.771 0.10---12 -634.527 4.66 1.72341 1.71999 50.2 13 -31.670----

Surface No. 6 θ (g, F) _N = 0.6082 Δθ (g, F) _N = 0.0092 Surface No. 7 θ (g, F) _P = 0.6159 Δθ (g, F) _P = 0.0160

[Embodiment 3] FIG. 5 shows a color of the present invention composed of a cemented lens composed of two lenses in one group between a front lens group 11 consisting of three lenses in two groups and a rear group lens 12 consisting of two lenses in three groups. Eraser 13 (face
It is a lens block diagram of the 3rd Example of this invention which inserted No. 6-8). Table 3 shows specific numerical data of this lens system.
And various aberrations thereof are shown in FIG.

[0032]

[Table 3] F _NO = 4 f = 49.49 y = 18.74 f _B = 29.78 M = -0.165 plane NO rd N _e N _d ν _d 1 24.387 4.14 1.80642 1.80100 35.0 2 77.965 0.18---3 14.930 4.79 1.66103 1.65830 57.3 4 113.734 1.50 1.76859 1.76182 26.6 5 10.350 5.96---6 ∞ 2.86 1.81675 1.80834 22.6 7 -10.722 1.23 1.81265 1.80518 25.4 8 ∞ 8.17---9 -13.012 1.50 1.69417 1.68893 31.1 10 -73.798 4.48 1.77621 1.77250 49.6 11 -17.645 0.10-- -12 393.426 4.66 1.68082 1.67790 55.3 13 -37.418----

Surface No. 6 θ (g, F) _P = 0.6288 Δθ (g, F) _P = 0.0213 Surface No. 7 θ (g, F) _N = 0.6100 Δθ (g, F) _N = 0.0097

[Embodiment 4] FIG. 7 shows a color according to the present invention, which is composed of a cemented lens composed of three lenses in one group between a front lens group 11 consisting of three lenses in two groups and a rear lens group 12 consisting of three lenses in two groups. Eraser 14 (surface
It is a lens block diagram of the 4th Example of this invention which inserted No. 6-9). Table 4 shows specific numerical data of this lens system.
And various aberrations thereof are shown in FIG. The achromatic lens 14 of the present invention is a cemented lens having a negative, positive, and negative three-element configuration, and has a symmetrical shape with respect to the center of the positive lens at the center.

[0035]

[Table 4] F _NO = 4 f = 50.16 y = 18.74 f _B = 33.48 M = -0.165 plane NO rd N _e N _d ν _d 1 23.000 4.14 1.80642 1.80100 35.0 2 65.589 0.18---3 14.900 4.20 1.62287 1.62041 60.3 4 62.439 1.50 1.74618 1.74000 28.3 5 10.539 5.73---6 ∞ 0.80 1.81265 1.80518 25.4 7 12.000 3.19 1.81264 1.80518 25.4 8 -12.000 0.80 1.81265 1.80518 25.4 9 ∞ 7.27---10 -12.074 1.50 1.67158 1.66680 33.0 11 -41.418 3.80 1.74679 1.74 12 -17.000 0.10---13 -260.000 4.66 1.72341 1.71999 50.2 14 -29.839----

Surface No. 6 θ (g, F) _N = 0.6100 Δθ (g, F) _N = 0.0097 Surface No. 7 θ (g, F) _P = 0.6153 Δθ (g, F) _P = 0.0150 Surface No. 8 θ (g, F) _N = 0.6100 Δθ (g, F) _N = 0.0097

[Embodiment 5] FIG. 9 shows a color of the present invention comprising a cemented lens composed of three lenses in one group between a front lens group 11 composed of two groups and three lenses and a rear group lens 12 composed of two groups and three elements. Eraser 14 (surface
It is a lens block diagram of the 5th Example of this invention which inserted No. 6-9). Table 5 shows specific numerical data of this lens system.
And various aberrations thereof are shown in FIG. The achromatic lens 14 of the present invention is a cemented lens having a three-element structure of positive, negative and positive,
It has a symmetrical shape with respect to the center of the center negative lens.

[0038]

[Table 5] F _NO = 4 f = 50.17 y = 18.74 f _B = 33.48 M = -0.165 surface NO rd N _e N _d ν _d 1 23.000 4.14 1.80642 1.80100 35.0 2 65.589 0.18---3 14.900 4.20 1.62287 1.62041 60.3 4 62.439 1.50 1.74618 1.74000 28.3 5 10.539 5.73---6 ∞ 2.00 1.81264 1.80518 25.4 7 -12.000 0.80 1.81265 1.80518 25.4 8 12.000 2.00 1.81264 1.80518 25.4 9 ∞ 7.27---10 -12.074 1.50 1.67158 1.66680 33.0 11 -41.418 3.80 1.74679 1.74 12 -17.000 0.10---13 -260.000 4.66 1.72341 1.71999 50.2 14 -29.839----

Surface No. 6 θ (g, F) _P = 0.6153 Δθ (g, F) _P = 0.0150 Surface No. 7 θ (g, F) _N = 0.6100 Δθ (g, F) _N = 0.0097 Surface No. 8 θ (g, F) _P = 0.6153 Δθ (g, F) _P = 0.0150

The solid line in FIG. 11 is a diagram illustrating paraxial on-axis chromatic aberration in each wavelength range in the first embodiment. In the first embodiment, the chromatic aberration correction lens group 13 is composed of a positive lens and a negative lens made of different glass materials. On the other hand, the broken line in the figure shows the same chromatic aberration when the chromatic aberration correction lens group is composed of one lens. From this figure, it is effective to correct chromatic aberration in a wide wavelength range by inserting two or more glass chromatic aberration correction lens groups satisfying conditional expressions (1) to (3) in the middle part of the lens system. It turns out that

The paraxial on-axis chromatic aberrations of Examples 2 to 5 are also shown in FIG.
The correction is almost as good as the solid line of 1. However,
In Examples 2 and 3, the chromatic aberration when the correction lens is composed of one lens is a curved line in which the graph on the broken line is inclined.

Table 6 shows the values corresponding to the conditional expressions of Examples 1 to 5.

[Table 6]               Example 1 Example 2 Example 3 Example 4 Example 5 Conditional expression (1) 0.0 0.5 2.8 0.0 0.0 Conditional expression (2) 0.0 0.00002 0.00317 0.0 0.0 Conditional expression (3) 1.55 1.74 2.20 1.55 1.55 Conditional expression (4) 6.8 4.0 3.8 6.8 6.8 Conditional expression (5) 0.00 0.00 0.02 0.00 0.00

As is clear from Table 6, the numerical values of Examples 1 to 5 are all conditional expressions (1) to (5).
Are satisfied. Further, in the achromatic lens system of the present invention, various aberrations in each aberration diagram, particularly chromatic aberration, are corrected in a wide wavelength range not only on the axis but also off the axis in a well-balanced manner.

[0044]

According to the achromatic lens system of the present invention, it is possible to correct chromatic aberration over a wide wavelength range in good balance while satisfactorily correcting each aberration.

[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.

FIG. 7 is a lens configuration diagram showing a fourth example of the achromatic lens system according to the present invention.

FIG. 8 is a diagram of various types of aberration of the lens system in FIG.

FIG. 9 is a lens configuration diagram showing a fifth example of the achromatic lens system according to the present invention.

FIG. 10 is a diagram of various types of aberration of the lens system in FIG.

FIG. 11 is a graph showing paraxial on-axis chromatic aberration of the chromatic-aberration correction lens group of the first example and coaxial on-axis chromatic aberration when the chromatic-aberration correction lens group is composed of one lens.

Continuation of front page (56) Reference JP-A-5-150158 (JP, A) JP-A-5-142468 (JP, A) JP-A-3-96912 (JP, A) JP-A-6-235860 (JP , A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 13/00 G02B 9/00

Claims (14)

(57) [Claims] 1. An achromatic lens system including a front lens group, a chromatic aberration correction lens group, and a rear lens group in order from the object side, wherein spherical aberration, coma aberration, and astigmatism are formed by the front lens group and the rear lens group. Aberration, field curvature, and axial chromatic aberration in the wavelength range of light from green to red are corrected, while axial chromatic aberration is generated on the plus side in the wavelength range of blue light, and by the chromatic aberration correction lens group, The axial chromatic aberration in the wavelength range of the blue light generated by the front lens group and the rear lens group is corrected , and the chromatic aberration correction lens group includes at least one positive lens.
Lens and one negative lens, and the following conditional expression (1)
An achromatic lens system that satisfies item (3). _{(1) | ν P -ν N} | <5.0 (2) | N P -N N | <0.01 (3) 1 <(Δθ (g, F) P) / (Δθ (g, F) _N ) <10 where ν _{P is} the d-line angle of the positive lens of the chromatic aberration correction lens group
Abbe number, ν _N : of the d line of the negative lens of the chromatic aberration correction lens group
Abbe number, N _P : d-line of positive lens of chromatic aberration correction lens group
, N _N : d-line of the negative lens of the chromatic aberration correction lens group
Refractive index, Δθ (g, F) _P : Positive lens of chromatic aberration correction lens group
Deviation of the partial dispersion ratio of the g-F line from the standard line, Δθ (g,
F) _N : g-F line portion of the negative lens of the chromatic aberration correction lens group
Deviation of the variance ratio from the standard line . 2. The achromatic lens system according to claim 1, wherein the chromatic aberration correction lens group comprises, in order from the object side, one positive lens and one negative lens, or one negative lens and one positive lens. Achromatic lens system consisting of. 3. The achromatic lens system according to claim 2, wherein
An achromatic lens system in which one positive lens and one negative lens are bonded together. 4. The achromatic lens system according to claim 1, wherein the chromatic aberration correction lens group comprises, in order from the object side, one positive lens, one negative lens, and one positive lens. And an achromatic lens system that satisfies the following conditional expressions (1) to (3). _{(1) | ν P -ν N} | <5.0 (2) | N P -N N | <0.01 (3) 1 <(Δθ (g, F) P) / (Δθ (g, F) _N ) <10 where ν _{P is} the Abbe number of the d line of each positive lens of the chromatic aberration correction lens group, ν _{N is} the Abbe number of the d line of the negative lens of the chromatic aberration correction lens group, and N _P is each of the chromatic aberration correction lens group Refractive index of d-line of positive lens, N _N : Refractive index of d-line of negative lens of chromatic aberration correction lens group, Δθ (g, F) _P : Partial dispersion of g-F line of each positive lens of chromatic aberration correction lens group Deviation of the ratio from the standard line, Δ
θ (g, F) _N : Deviation from the standard line of the partial dispersion ratio of the gF line of the negative lens of the chromatic aberration correction lens group. 5. The achromatic lens system according to claim 1, wherein the chromatic aberration correction lens group comprises, in order from the object side, one negative lens, one positive lens, and one negative lens. And an achromatic lens system that satisfies the following conditional expressions (1) to (3). _{(1) | ν P -ν N} | <5.0 (2) | N P -N N | <0.01 (3) 1 <(Δθ (g, F) P) / (Δθ (g, F) _N ) <10 where ν _{P is} the Abbe number of the d-line of the positive lens of the chromatic aberration correction lens group, ν _{N is} the Abbe number of the d-line of each negative lens of the chromatic aberration correction lens group, and N _{P is} the positive of the chromatic aberration correction lens group Lens d
Refractive index of line, N _N : Refractive index of d line of each negative lens of chromatic aberration correction lens group, Δθ (g, F) _P : Standard line of partial dispersion ratio of gF line of positive lens of chromatic aberration correction lens group Deviation from Δθ
(g, F) _N : Deviation from the standard line of the partial dispersion ratio of the gF line of each negative lens of the chromatic aberration correction lens group. 6. The achromatic lens system according to claim 4 or 5, wherein three lenses are attached to each other. 7. The achromatic lens system according to claim 1, 4 or 5, further satisfying the following conditional expressions (4) and (5). (4) 2 <f / f _CP <10 (5) | f / f _CP + f /
f _CN | <0.1 where f: focal length of the entire system f _CP : composite focal length of positive lens in chromatic aberration correction lens group, f _CN : composite focal length of negative lens in chromatic aberration correction lens group. 8. The achromatic lens system according to any one of claims 4 to 7, wherein the chromatic aberration correction lens group is symmetrical with respect to the center of the middle lens of the three lenses. 9. An achromatic lens system having a chromatic aberration correction lens group, which is composed of two lenses, a positive lens and a negative lens, and which satisfies the following conditional expressions (1) to (3) in the middle of the lens system. _{(1) | ν P -ν N} | <5.0 (2) | N P -N N | <0.01 (3) 1 <(Δθ (g, F) P) / (Δθ (g, F) _N ) <10 where ν _{P is} the Abbe number of the d line of the positive lens of the chromatic aberration correction lens group, ν _{N is} the Abbe number of the d line of the negative lens of the chromatic aberration correction lens group, and N _{P is} the positive lens of the chromatic aberration correction lens group D line refractive index, N _N : d line refractive index of the negative lens of the chromatic aberration correction lens group, Δθ (g, F) _P : standard of partial dispersion ratio of gF line of the positive lens of the chromatic aberration correction lens group 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 of the chromatic aberration correction lens group. 10. An achromatic lens having a chromatic-aberration correction lens group, which is composed of three lenses, a positive lens, a negative lens, and a positive lens, and which satisfies the following conditional expressions (1) to (3) in the middle of the lens system. Lens system. _{(1) | ν P -ν N} | <5.0 (2) | N P -N N | <0.01 (3) 1 <(Δθ (g, F) P) / (Δθ (g, F) _N ) <10 where ν _{P is} the Abbe number of the d line of the positive lens of the chromatic aberration correction lens group, ν _{N is} the Abbe number of the d line of the negative lens of the chromatic aberration correction lens group, and N _{P is} the positive lens of the chromatic aberration correction lens group Refractive index of the d-line, N _N : Refractive index of the d-line of the negative lens of the chromatic aberration correction lens group, Δθ (g, F) _P : Standard of partial dispersion ratio of the g-F line of the positive lens of the chromatic aberration correction lens group 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 of the chromatic aberration correction lens group. 11. An achromatic lens having a chromatic-aberration-correcting lens group which is composed of three lenses, a negative lens, a positive lens, and a negative lens, and which satisfies the following conditional expressions (1) to (3) in the middle part of the lens system. Lens system. _{(1) | ν P -ν N} | <5.0 (2) | N P -N N | <0.01 (3) 1 <(Δθ (g, F) P) / (Δθ (g, F) _N ) <10 where ν _{P is} the Abbe number of the d line of the positive lens of the chromatic aberration correction lens group, ν _{N is} the Abbe number of the d line of the negative lens of the chromatic aberration correction lens group, and N _{P is} the positive lens of the chromatic aberration correction lens group Refractive index of the d-line, N _N : Refractive index of the d-line of the negative lens of the chromatic aberration correction lens group, Δθ (g, F) _P : Standard of partial dispersion ratio of the g-F line of the positive lens of the chromatic aberration correction lens group 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 of the chromatic aberration correction lens group. 12. An achromatic lens system according to any one of claims 1 and 2, further satisfying the following conditional expressions (4) and (5). (4) 2 <f / f _CP <10 (5) | f / f _CP + f / f _CN | <0.1 where f: focal length of the entire system f _CP : composition of positive lens in chromatic aberration correction lens group Focal length, f _CN : Composite focal length of the negative lens in the chromatic aberration correction lens group. 13. The achromatic lens system according to claim 10 or 11, wherein the chromatic aberration correction lens group is symmetrical with respect to the center of the central lens. 14. The achromatic lens system according to any one of claims 10 to 13, wherein the chromatic aberration correction lens group is a cemented lens.