JPH10111454A - Wide angle lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a wide angle lens constituted of a small number of lenses, made compact and inexpensive, realizing a very long flange back and having excellent optical performance by constituting the lens of plural lens groups, that is, a negative 1st group, a negative 2nd group, a positive 3rd group and a positive 4th group and making the lens satisfy a specified condition. SOLUTION: This wide angle lens is constituted, of four lens groups, that is, the negative 1st group, the negative 2nd group, the positive 3rd group and the positive 4th group in order from an object side. Then, the negative 1st group and the positive 3rd group are constituted of a single lens, and the negative 2nd lens group and the positive 4th lens group are respectively constituted by sticking or proximately arranging one positive lens and one negative lens. The wide angle lens satisfies the condition, that is, an expression -1.2<f/fIII <-0.3, an expression 0.15<f<fIII IV<0.65 and an expression 0.15<f<fIV/<0.35. In the expressions, (f) is the focal length of an entire system, fII is the composite focal length of the 1st and the 2nd lens groups, fIII IV/ is the composite focal length of the 3rd and the 4th lens groups, and fIV is the composite focal length of the 4th lens group.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a large-diameter F-number (1.4 number) used for a CCD camera, a still camera, and the like.
2.0 rank) Ultra-wide-angle (angle of view around 130 °) lens.

[0002]

2. Description of the Related Art In recent years, there has been a strong demand for miniaturization, weight reduction and cost reduction of lenses for CCD cameras and photographic lenses. Conventionally, this class of lenses is composed of 8 to 10 spherical lenses, so that the cost is generally high and the overall length is long.

An improved version of this is disclosed in, for example, Japanese Patent Application Laid-Open No.
No. 38313 is known.

[0004]

However, in Japanese Patent Application Laid-Open No. 4-238313, the cost is high due to the use of an aspherical surface, although it has a six-group, seven-lens configuration. In addition, although the focal length becomes shorter and shorter as the CCD becomes smaller, it is difficult to sufficiently increase the length of the flange back, and it is no longer possible to meet recent demands.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides a wide-angle lens having a small number of components, a small size, a low price, a sufficiently long flange back, and good optical performance. It is intended to be.

[0006]

The wide-angle lens according to the present invention comprises:
In order to achieve the above object, in order from the object side, the first lens unit includes four lens units including a first negative unit, a second negative unit, a third positive unit, and a fourth positive unit. The group is composed of a single lens, the second negative group is composed of a single negative lens or one lens each of positive and negative, and the third positive group is composed of a single positive lens or positive and negative. The fourth lens unit is composed of one lens each, and the fourth positive lens unit is composed of a cemented lens of a positive lens and a negative lens.

More specifically, the lens system includes four lens units of a negative first unit, a negative second unit, a positive third unit, and a positive fourth unit in order from the object side. The first group and the positive third group are composed of a single lens, and the negative second lens group and the positive fourth lens group respectively bond one positive lens and one negative lens, or It is characterized by being arranged.

In the above-mentioned wide-angle lens, (a) -1.2 <f / fI II <-0.3 (b) 0.15 <f / fIII IV <0.65 (c) 0.15 < The condition of f / fIV <0.35 is satisfied.

Where f is the focal length of the entire system, and fI II is the first focal length.
And the combined focal length of the second lens group, fIII IV is the third and fourth
The combined focal length of the lens group, fIV, is the combined focal length of the fourth lens group. (D) νII + -νII-<-15 (e) νIV + -νIV-> 20 (f) νI, νIII> 40 (g) 1.2 <R2 / f, R5 / f <4.0 (h) -3 0.0 <R8 / R10 <-0.3.

Here, νII + is the Abbe number of the d-line of the positive lens of the second lens group, and νII− is d of the negative lens of the second lens group.
Abbe number of the line, νIV + is the Abbe number of the d line of the positive lens of the fourth lens group, νIV− is the Abbe number of the d line of the negative lens of the fourth lens group, and νI is the Abbe number of the d line of the first lens group. , ΝIII
Is the Abbe number of the d-line of the third lens group, R2 is the radius of curvature of the first lens group on the image side, R5 is the radius of curvature of the second lens group on the image side, R8 is the radius of curvature of the fourth lens group on the object side, R10 is 4th
The radius of curvature on the image plane side of the lens group is used.

Further, the object can be achieved by the following configuration. That is, in order from the object side, the lens unit includes four lens units of a negative first unit, a negative second unit, a positive third unit, and a positive fourth unit, and includes a negative first unit and a negative second unit. Indicates that each of the third positive lens unit and the fourth positive lens unit is configured by bonding one positive lens and one negative lens or by arranging them close to each other. Features.

In the above-mentioned wide-angle lens, the condition of (i) -1.5 <f / fI II <-0.5 (j) 0.2 <f / fIII IV <0.5 is satisfied.

Where f is the focal length of the entire system, and fI II is the first focal length.
And the combined focal length of the second lens group, fIII IV is the third and fourth
The combined focal length of the lens groups. (K) 40 <(νI + νII) / 2 (l) 50 <(νIII + −νIII −) + (νIV + −νIV)
−) (M) 0.5 <fI / fII <1.5 (n) 0.7 <fIV / fIII <2.5 (o) 1.0 <R2 / f, R4 / f <3.5 (p Satisfies the condition of -1.0 <R8 / R10 <-0.3.

Here, νI is the Abbe number of the d-line of the first lens group, νII is the Abbe number of the d-line of the second lens group, νIII + is the Abbe number of the d-line of the positive lens of the third lens group, and νIII− is Abbe number of the d-line of the negative lens of the third lens group, νIV + is the Abbe number of the d-line of the positive lens of the fourth lens group, and νIV− is the fourth.
Abbe number of the d-line of the negative lens of the lens group, fI is the focal length of the first lens group, fII is the focal length of the second lens group, fII
I is the composite focal length of the third lens group fIV is the composite focal length of the fourth lens group, R2 is the radius of curvature of the first lens group on the image plane side,
R4 is the radius of curvature of the second lens group on the image side, R8 is the radius of curvature of the fourth lens group on the object side, and R10 is the radius of curvature of the fourth lens group on the image side.

Further, the object can be achieved by the following configuration. That is, in order from the object side,
4 of the negative first group, the negative second group, the positive third group, and the positive fourth group
The first negative lens unit, the second negative lens unit, and the third positive lens unit each include a single lens, and the fourth positive lens unit includes one positive lens and one negative lens. It is characterized by being bonded or arranged close to each other.

In the above-mentioned wide-angle lens, the condition of (q) -1.5 <f / fI II <-0.5 (r) 0.2 <f / fIII IV <0.4 is satisfied.

Here, f is the focal length of the entire system, and fI II is the first focal length.
And the combined focal length of the second lens group, fIII IV is the third and fourth
The combined focal length of the lens groups. (S) 40 <(νI + νII) / 2 (t) 25 <νIV + −νIV− (u) NIII <1.65 (v) 0.2 <fI / fII <1.2 (w) 0.5 <fIV / The conditions of fIII <1.5 (x) 1.0 <R2 / f, R4 / f <3.5 (y) -1.0 <R7 / R9 <-0.2 are satisfied.

Where νI is the Abbe number of the d-line of the first lens group νII is the Abbe number of the d-line of the second lens group, and νIV + is the fourth
Abbe number of the d-line of the positive lens of the lens group, νIV- is the Abbe number of the d-line of the negative lens of the fourth lens group, NIII is the refractive index of the d-line of the third lens group, and fI is the focal point of the first lens group. distance,
fII is the focal length of the second lens group, fIII is the focal length of the third lens group, fIV is the composite focal length of the fourth lens group, R2
Is the radius of curvature of the image side of the first lens group, R4 is the radius of curvature of the image side of the second lens group, R7 is the radius of curvature of the object side of the fourth lens group, R9 is the radius of curvature of the image side of the fourth lens group. I do.

It is characterized by satisfying the above conditions.

[0020]

The structure suitable for an ultra-wide-angle lens having a long flange back as in the present invention is a retrofocus type.

In order to achieve an ultra-wide angle, the negative lens system of the front group is
The rear lens group is divided into two (a first lens group and a second lens group), and the rear group positive lens system is divided into two (a third lens group and a fourth lens group).

By making the power of the front group relatively strong, a sufficiently long back focus is obtained, and the luminous flux diverged by the front group is given the positive power of the rear group to correct spherical aberration. By making the fourth lens group a cemented lens of a positive lens and a negative lens, high performance is realized, and sufficient correction is made especially for chromatic aberration. In addition, the first lens unit is made compact by using a single lens, and a wide-angle lens is realized with a small number of lenses by generating distortion having a practically large size.

The second lens group and the third lens group can be composed of only a single lens, and can be composed of a combination of a positive lens and a negative lens for higher performance. It is.

More specifically, in the second to fifth aspects, the second lens group and the fourth lens group are bonded with one positive lens and one negative lens, or are disposed close to each other. Wide angle and high performance.

Hereinafter, the conditions (a) to (h) will be described.

The condition (a) relates to the power of the front lens unit negative lens system. If the upper limit is exceeded, the power of the negative lens unit in the front group decreases, and the distance between the front group unit and the rear unit unit must be increased in order to correct this. However, in such a case, the entire length of the lens becomes long. If the lower limit is exceeded, the power of the negative lens of the front group becomes large, and the distance between the front group and the rear group becomes short. However, the spherical aberration, coma aberration and chromatic aberration of magnification become extremely large, and the performance decreases.

The condition (b) relates to the power of the rear lens unit. If the upper limit is exceeded, the power of the rear group positive lens becomes large, and the spherical aberration and coma become extremely large, and the performance is reduced. If the lower limit is exceeded, the power of the rear group positive lens decreases, and to correct this, the power of the front group negative lens must be reduced. In such a case, the overall length of the lens becomes longer, and the size reduction of the object of the present invention cannot be achieved.

The condition (c) relates to the power distribution of the rear group positive lens. That is, this is a condition relating to the power of the fourth lens unit of the cemented lens and a condition relating to an appropriate arrangement of the third and fourth lens units. If the upper limit is exceeded, the power of the fourth lens unit will increase significantly. If the lower limit is exceeded, the power of the third lens unit will increase significantly, making it difficult to correct spherical aberration and coma.

(D) to (f) are conditions relating to correction of chromatic aberration (axial chromatic aberration, chromatic aberration of magnification).

The condition (d) is a condition relating to the achromatic condition of the second lens group. By achromatizing the second lens group,
Particularly, occurrence of lateral chromatic aberration in the front group is suppressed. If this condition is not satisfied, chromatic aberration will deteriorate.

The condition (e) is a condition relating to achromatism of the fourth lens group. In other words, the conditions relate to correction of lateral chromatic aberration that cannot be corrected by the first to third lens groups. If this condition is not satisfied, lateral chromatic aberration will deteriorate.

The condition (f) is a condition for reducing the occurrence of chromatic aberration of the single lens, and both require a glass material having a large Abbe number and a small dispersion as shown in (f).

The condition (g) is a condition for forming a concentric surface with little occurrence of aberration with respect to an incident light beam. When the value exceeds the upper limit, correction of spherical aberration is insufficient, distortion becomes extremely large, and performance deteriorates. If the lower limit is exceeded, the coma aberration becomes extremely large, and the performance deteriorates.

The condition (h) is a condition relating to correction of spherical aberration and coma. Spherical aberration and coma from the first lens group to the third lens group are corrected by the fourth lens group. If this condition is not satisfied, the balance between spherical aberration and coma aberration will be lost, and performance will be reduced.

More specifically, in the sixth to ninth aspects, the third lens group and the fourth lens group are bonded to each other with one positive lens and one negative lens, or are arranged close to each other. As a result, high performance is realized at a wide angle.

Hereinafter, the conditions (i) to (p) will be described.

The condition (i) relates to the power of the negative lens system in the front group. If the upper limit is exceeded, the power of the negative lens unit in the front group decreases, and the distance between the front group unit and the rear unit unit must be increased in order to correct this. However, in such a case, the entire length of the lens becomes long. If the lower limit is exceeded, the power of the negative lens of the front group becomes large, and the distance between the front group and the rear group becomes short. However, the spherical aberration, coma aberration and chromatic aberration of magnification become extremely large, and the performance decreases.

The condition (j) relates to the power of the rear lens unit. If the upper limit is exceeded, the power of the rear group positive lens becomes large, and the spherical aberration and coma become extremely large, and the performance is reduced. On the other hand, if the lower limit is exceeded, the rear group positive lens power becomes small. To correct this, the power of the front group negative lens must be reduced. In such a case, the overall length of the lens becomes longer, and the size reduction of the object of the present invention cannot be achieved.

(K) and (l) are conditions relating to correction of chromatic aberration (axial chromatic aberration, chromatic aberration of magnification).

The condition (k) relates to the chromatic aberration of the negative lens system in the front group. Particularly, occurrence of lateral chromatic aberration in the front group is suppressed. If this condition is not satisfied, the chromatic aberration of magnification deteriorates.

The condition (1) relates to the achromatic condition of the rear lens group positive lens system. This is a condition relating to correction of lateral chromatic aberration that cannot be completely corrected by the front lens unit. If this condition is not satisfied, chromatic aberration will deteriorate.

The condition (m) relates to the power distribution of the front group negative lens. By setting the power distribution of the front group negative lens as (m), various aberrations can be corrected in a well-balanced manner. If the upper limit is exceeded, the power of the second lens group becomes excessive, and if the lower limit is exceeded, the power of the first lens group becomes excessive, and the balance between spherical aberration, coma aberration and field curvature deteriorates.

The condition (n) relates to the power distribution of the rear group positive lens. In order to correct large positive spherical aberration generated in the front group in the rear group, power distribution under the condition (n) is necessary. If the upper limit or the lower limit is exceeded, the power of the third or fourth lens unit becomes excessive, and accordingly, the negative spherical aberration of the third or fourth lens unit becomes excessive.

The condition (o) is a condition for forming a concentric surface with little occurrence of aberration with respect to an incident light beam. When the value exceeds the upper limit, correction of spherical aberration is insufficient, distortion becomes extremely large, and performance deteriorates. If the lower limit is exceeded, the coma aberration becomes extremely large, and the performance deteriorates.

Further, the condition (p) relates to the correction of spherical aberration and coma. Spherical aberration and coma from the first lens group to the third lens group are corrected by the fourth lens group. If this condition is not satisfied, the balance between spherical aberration and coma aberration will be lost, and performance will be reduced.

More specifically, claims 10 to 1
In the third aspect, the number of the second to fifth aspects can be further reduced, and the fourth lens group is bonded with one positive lens and one negative lens, or is disposed close to the fourth lens group. Wide angle and high performance.

Hereinafter, the conditions (q) to (y) will be described.

The condition (q) relates to the power of the front lens unit negative lens system. If the upper limit is exceeded, the power of the negative lens unit in the front group decreases, and the distance between the front group unit and the rear unit unit must be increased in order to correct this. However, in such a case, the entire length of the lens becomes long. If the lower limit is exceeded, the power of the negative lens of the front group becomes large, and the distance between the front group and the rear group becomes short. However, the spherical aberration, coma aberration and chromatic aberration of magnification become extremely large, and the performance decreases.

The condition (r) relates to the power of the rear lens unit. If the upper limit is exceeded, the power of the rear group positive lens becomes large, and the spherical aberration and coma become extremely large, and the performance is reduced. On the other hand, if the lower limit is exceeded, the rear group positive lens power becomes small. To correct this, the power of the front group negative lens must be reduced. In such a case, the overall length of the lens becomes longer, and the size reduction of the object of the present invention cannot be achieved.

(S) and (t) are conditions relating to correction of chromatic aberration (axial chromatic aberration and chromatic aberration of magnification).

The condition (s) relates to the chromatic aberration of the negative lens system in the front group. Particularly, occurrence of lateral chromatic aberration in the front group is suppressed. If this condition is not satisfied, the chromatic aberration of magnification deteriorates.

The condition (t) relates to the achromatic condition of the rear positive lens system. This is a condition relating to correction of lateral chromatic aberration that cannot be completely corrected by the front group negative lens system. If this condition is not satisfied, chromatic aberration will deteriorate.

The condition (u) is a condition for correcting the field curvature. In the present invention, since the first lens unit and the second lens unit have strong negative power, the Petzval sum tends to be negative and the positive curvature of field tends to be excessive. Therefore, as in the condition (u), by reducing the refractive index of the positive third lens unit, the positive Petzval is increased, and the Petzval sum of the whole is set to an appropriate value. Therefore, if the value exceeds the upper limit in the condition (u), the Petzval sum becomes negative, and it becomes difficult to correct the field curvature.

The condition (v) relates to the power distribution of the front group negative lens. By setting the power distribution of the front group negative lens as shown in (v), various aberrations can be corrected with good balance. If the upper limit is exceeded, the power of the second lens group becomes excessive, and if the lower limit is exceeded, the power of the first lens group becomes excessive, and the balance between spherical aberration, coma aberration and field curvature deteriorates.

The condition (w) relates to the power distribution of the rear group positive lens. In order to correct large positive spherical aberration generated in the front group in the rear group, power distribution under condition (w) is necessary. If the upper limit or the lower limit is exceeded, the power of the third or fourth lens unit becomes excessive, and accordingly, the negative spherical aberration of the third or fourth lens unit becomes excessive.

The condition (x) is a condition for forming a concentric surface with little occurrence of aberration with respect to the incident light beam. When the value exceeds the upper limit, correction of spherical aberration is insufficient, distortion becomes extremely large, and performance deteriorates. If the lower limit is exceeded, the coma aberration becomes extremely large, and the performance deteriorates.

The condition (y) is a condition relating to correction of spherical aberration and coma. Spherical aberration and coma from the first lens group to the third lens group are corrected by the fourth lens group.

If this condition is not satisfied, the balance between spherical aberration and coma aberration will be lost, and the performance will decrease.

[0059]

Embodiments of the present invention will be described below.

However, Examples 1 to 5 show the examples of Claims 2 to 5, Examples 6 to 8 show the examples of Claims 6 to 9, and Examples 9 to 11 show the claims. 10 to 13 are shown.
Further, f is the focal length of the entire system, FNO is the aperture ratio, r is the radius of curvature of each lens surface, d is the thickness of the lens, or the air gap between lens surfaces, n is the refractive index of the d line of each lens, ν indicates the Abbe number of each lens at the d-line.

In the numerical data of the embodiment, the plane-parallel plate disposed closest to the image plane is a combination of filters, face plates, and the like used for video cameras and the like.

Example 1 is shown in Table 1.

Example 2 is shown in Table 2.

Example 3 is shown in Table 3.

Example 4 is shown in Table 4.

Example 5 is shown in Table 5.

Table 6 shows the correspondence between the above-described embodiments (1) to (5) and the conditional expressions (a) to (h).

Example 6 is shown in Table 7.

Example 7 is shown in Table 8.

Example 9 is shown in Table 9.

Table 10 shows the correspondence between the above-described embodiments (6) to (8) and the conditional expressions (i) to (p).

Example 9 is shown in Table 11.

Example 12 is shown in Table 12.

Example 13 is shown in Table 13.

Table 14 shows correspondences between the above-described embodiments (9) to (11) and conditional expressions (q) to (y).

[0076]

As described above, according to the present invention, as can be seen from the above embodiment and the aberration curve, in order from the object side, the negative first lens unit, the negative second lens unit, and the positive third lens unit. The first and second negative lens units are composed of a single lens, and the fourth positive lens unit is composed of a cemented lens of a positive lens and a negative lens. It is possible to obtain a small-sized, low-cost, wide-angle lens with a sufficiently long flange back with a configuration in which the performance is corrected well and the number of sheets is small.

[0077]

[Brief description of the drawings]

FIG. 1 is a sectional view of a lens according to a first embodiment.

FIG. 2 is an aberration diagram in the first embodiment.

FIG. 3 is a sectional view of a lens according to a second embodiment.

FIG. 4 is an aberration diagram in the second embodiment.

FIG. 5 is a sectional view of a lens according to a third embodiment.

FIG. 6 is an aberration diagram in the third embodiment.

FIG. 7 is a sectional view of a lens according to a fourth embodiment.

FIG. 8 is an aberration diagram in the fourth embodiment.

FIG. 9 is a sectional view of a lens according to a fifth embodiment.

FIG. 10 is an aberration diagram in Example 5.

FIG. 11 is a sectional view of a lens according to a sixth embodiment.

FIG. 12 is an aberration diagram in the sixth embodiment.

FIG. 13 is a sectional view of a lens according to a seventh embodiment.

FIG. 14 is an aberration diagram in the seventh embodiment.

FIG. 15 is a sectional view of a lens according to an eighth embodiment.

FIG. 16 is an aberration diagram in the eighth embodiment.

FIG. 17 is a sectional view of a lens according to a ninth embodiment.

FIG. 18 is an aberration diagram in the ninth embodiment.

FIG. 19 is a sectional view of a lens according to a tenth embodiment.

FIG. 20 is an aberration diagram in Example 10.

FIG. 21 is a sectional view of a lens according to an eleventh embodiment.

FIG. 22 is an aberration diagram in the eleventh embodiment.

[0078]

[Explanation of symbols]

r Curvature radius of each lens surface d Thickness of lens or air gap between lens surfaces SC Sine condition S Sagittal image plane M Meridional image plane

[Table 1]

[Table 2]

[Table 3]

[Table 4]

[Table 5]

[Table 6]

[Table 7]

[Table 8]

[Table 9]

[Table 10]

[Table 11]

[Table 12]

[Table 13]

[Table 14]

Claims (13)

[Claims] 1. A lens system comprising, in order from an object side, a negative first lens unit, a negative second lens unit, a positive third lens unit, and a positive fourth lens unit. The second negative group is composed of a single negative lens or one positive and one negative lens. The third positive group is a single positive lens or one positive and one negative lens. A wide-angle lens comprising a lens, wherein the fourth positive lens unit comprises a cemented lens of a positive lens and a negative lens. 2. In order from the object side, the lens system includes four lens units of a negative first unit, a negative second unit, a positive third unit, and a positive fourth unit. The third group is composed of a single lens, and the negative second lens group and the positive fourth lens group are respectively
A wide-angle lens, wherein one positive lens and one negative lens are bonded or arranged close to each other. 3. A wide-angle lens wherein each lens group according to claim 2 is set as follows. (A) -1.2 <f / fI II <-0.3 (b) 0.15 <f / fIII IV <0.65 (c) 0.15 <f / fIV <0.35 where f is The focal length of the entire system, fI II is the combined focal length of the first and second lens groups, fIII IV is the combined focal length of the third and fourth lens groups, and fIV is the combined focal length of the fourth lens group. 4. A wide-angle lens wherein each lens group according to claim 2 or 3 is set under the following conditions. (D) νII + −νII − <− 15 (e) νIV + −νIV−> 20 (f) νI, νIII> 35 where νII + is the Abbe number of the d-line of the positive lens of the second lens group, and νII− is the second Abbe number of the d line of the negative lens of the lens group, νIV + is the Abbe number of the d line of the positive lens of the fourth lens group, νIV− is the Abbe number of the d line of the negative lens of the fourth lens group, and νI is the first lens The Abbe number νIII of the d-line of the group is the Abbe number of the d-line of the third lens group. 5. A wide-angle lens wherein each lens group according to claim 2, 3 or 4 is set as follows. (G) 1.2 <R2 / f, R5 / f <4.0 (h) -3.0 <R8 / R10 <-0.3 where R2 is the radius of curvature of the first lens group on the image side, R5 Is the second
The radius of curvature on the image side of the lens group, R8 is the radius of curvature on the object side of the fourth lens group, and R10 is the radius of curvature on the image side of the fourth lens group. 6. A lens system comprising, in order from the object side, a negative first unit, a negative second unit, a positive third unit, and a positive fourth unit, and a negative first unit and a negative fourth unit. The second group is composed of a single lens, and the positive third lens group and the positive fourth lens group are respectively
A wide-angle lens, wherein one positive lens and one negative lens are bonded or arranged close to each other. 7. A wide-angle lens wherein each lens group according to claim 6 is set under the following conditions. (I) -1.5 <f / fI II <-0.5 (j) 0.2 <f / fIII IV <0.5 where f is the focal length of the entire system, and fI II is the first and second. The combined focal length of the lens groups, fIIIIV, is the combined focal length of the third and fourth lens groups. 8. A wide-angle lens wherein each lens group according to claim 6 or 7 is set under the following conditions. (K) 40 <(νI + νII) / 2 (l) 50 <(νIII + −νIII −) + (νIV + −νIV)
−) (M) 0.5 <fI / fII <1.5 (n) 0.7 <fIV / fIII <2.5 where νI is the Abbe number of the d-line of the first lens group, and νII is the second lens The Abbe number of the d-line of the group, νIII + is the Abbe number of the d-line of the positive lens of the third lens group, νIII− is the Abbe number of the d-line of the negative lens of the third lens group, and νIV + is the positive lens of the fourth lens group. Is the Abbe number of the d-line, νIV- is the Abbe number of the d-line of the negative lens of the fourth lens group, fI is the focal length of the first lens group, fII is the focal length of the second lens group, and fIII is the third lens group. FIV is the combined focal length of the fourth lens group. 9. A wide-angle lens wherein each lens group according to claim 6, 7, or 8 is set as follows. (O) 1.0 <R2 / f, R4 / f <3.5 (p) -1.0 <R8 / R10 <-0.3 where R2 is the radius of curvature of the first lens unit on the image side, R4 Is the second
The radius of curvature on the image side of the lens group, R8 is the radius of curvature on the object side of the fourth lens group, and R10 is the radius of curvature on the image side of the fourth lens group. 10. A lens system comprising, in order from the object, a first lens unit, a second negative unit, a third positive unit, and a fourth positive lens unit. The second group and the positive third group are each composed of a single lens, and the positive fourth lens group is composed of one positive lens and one negative lens bonded together or arranged close to each other. A wide-angle lens characterized by the following. 11. A wide-angle lens wherein each lens group according to claim 10 is set as follows. (Q) -1.5 <f / fI II <-0.5 (r) 0.2 <f / fIII IV <0.4 where f is the focal length of the entire system, and fI II is the first and second. The combined focal length of the lens groups, fIIIIV, is the combined focal length of the third and fourth lens groups. 12. A wide-angle lens wherein each lens group according to claim 10 or 11 is set as follows. (S) 40 <(νI + νII) / 2 (t) 25 <νIV + −νIV− (u) NIII <1.65 (v) 0.2 <fI / fII <1.2 (w) 0.5 <fIV / fIII <1.5 where νI is the Abbe number of the d-line of the first lens group, νII is the Abbe number of the d-line of the second lens group, νIV + is the Abbe number of the d-line of the positive lens of the fourth lens group, νIV -Is the Abbe number of the d-line of the negative lens of the fourth lens group, NIII is the refractive index of the d-line of the third lens group, fI is the focal length of the first lens group, and fII is the second.
The focal length of the lens group, fIII is the focal length of the third lens group, and fIV is the combined focal length of the fourth lens group. 13. A wide-angle lens wherein each lens group according to claim 10, 11 or 12 is set as follows. (X) 1.0 <R2 / f, R4 / f <3.5 (y) -1.0 <R7 / R9 <-0.2 where R2 is the radius of curvature of the first lens unit on the image plane side, R4 Is the second
The radius of curvature on the image side of the lens group, R7 is the radius of curvature on the object side of the fourth lens group, and R9 is the radius of curvature on the image side of the fourth lens group.