JPH08313802A - Wide angle lens - Google Patents

Abstract

PURPOSE: To provide an optical system having sufficient efficiency of aperture by improving sagittal coma aberration and the curvature of field for the problem of making a symmetric wide-angle lens a large aperture ratio. CONSTITUTION: This lens is composed of three fundamental lens groups of a first group G1 of negative refractive power, a second group G2 of positive refractive power having an aperture diaphragm and a third group G3 of negative refractive power, the second group G2 is composed of two lens groups of a front group G21 and a rear group G22 having positive refractive powers interposing the aperture diaphragm between them, the first group G1 has at least one negative meniscus lens whose convex surface confronts the object side, the front group G21 of the second group G2 has at least a set of joined lens including a positive lens and a negative lens, the rear group G22 of the second group G2 is composed of a set of joined lens including a positive lens and a negative lens, the third group G3 is composed of at least one negative meniscus lens whose convex surface confronts the image plane side and an aspherical surface is arranged in any lens group.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wide-angle lens, and more particularly to a symmetric wide-angle lens which is suitable for a photographic lens and an optical system for electronic image equipment and has a wide angle of view and a large aperture ratio and is relatively small.

[0002]

2. Description of the Related Art In a wide-angle lens having an angle of view of about 72 ° or more, an imaging lens for a single-lens reflex camera needs to have a mirror movable space. Therefore, the back focus is ensured by adopting the reverse telephoto type, which is composed of a front group having a negative refractive power and a rear group having a positive refractive power from the object side. In the case of this type, the refractive power arrangement is asymmetric with respect to the aperture stop, which causes deterioration of various off-axis aberrations. In particular,
As the aperture ratio increases, chromatic aberration of magnification, field curvature, sagittal coma and the like tend to become more prominent. In addition, the number of lenses is increased, which causes a decrease in transmittance and a ghost image on the lens surface.

On the other hand, in a camera having a range finder, the back focus is loosely limited. Therefore, a symmetrical wide-angle lens which is advantageous in correcting aberrations has been made as a unique proposal of a spherical system, such as US Pat. No. 2,721,499 and US Pat. No. 2,781,695.

[0004]

These symmetrical wide-angle lenses have been applied not only to photographic lenses but also to aerial surveying. On the other hand, it was also used as an optical system for copying. However, the first lens group has a negative refracting power, and the aperture ratio is generally small in order that the divergent on-axis light beam enters the second lens group and increases the burden on aberration correction.

The present invention has been made in view of such a situation, and its object is to deal with the problem of increasing the aperture ratio of the symmetrical wide-angle lens, which is intended for an optical system for a photographic lens or an electronic image device. Then, sagittal coma aberration and field curvature are improved, and an optical system having sufficient aperture efficiency is provided.

[0006]

A wide-angle lens according to the present invention that achieves the above object has, in order from the object side, a first lens group having a negative refractive power and a second lens having an aperture stop and having a positive refractive power. And a third lens group having negative refracting power, the second lens group comprises
It is composed of two lens groups of a front group (G ₂₁ ) and a rear group (G ₂₂ ) having positive refracting power across an aperture stop, and the first lens group has a convex surface facing at least one object side. A negative meniscus lens, and the front group of the second lens group has at least one cemented lens including a positive lens and a negative lens,
The rear group of the second lens group includes at least one set of cemented lenses including a positive lens and a negative lens, and the third lens group includes at least one negative meniscus lens having a convex surface facing the image plane side. And has an aspherical surface in any one of the lens groups.

Another wide-angle lens of the present invention has, in order from the object side, a first lens group having a negative refractive power, a second lens group having an aperture stop and having a positive refractive power, and a negative refractive power. It is composed of three basic lens groups including a third lens group, and the second lens group is divided into two lens groups of a front group (G ₂₁ ) and a rear group (G ₂₂ ) having positive refracting power with an aperture stop interposed therebetween. The first lens group includes at least one negative meniscus lens having a convex surface directed toward the object side, and the front group of the second lens group includes at least a cemented lens including a positive lens and a negative lens. The rear group of the second lens group has at least one cemented lens including a positive lens and a negative lens, and the third lens group has at least one convex surface on the image side. A negative meniscus lens for Has a spherical surface, the following conditions (1) -
It is characterized by satisfying (4). _{0.2 <-f 1 / f <30} ··· (1) 0.15 <f 1 / f 3 <25 ··· (2) 0.2 <f 21 / f 22 <5 ··· (3 ) -3 <e '/ f < 20 ··· (4) However, f _1: focal length of the first lens group, f _3: the focal length of the third lens group, f: the focal length of the entire system, f ₂₁ the focal length of the front group of the second lens group, f ₂₂ the focal length of the rear group of the second lens group, e ': a first lens group to the front group of the second lens group as a single lens group, and, Is the principal point spacing when the rear lens group of the second lens group and the third lens group are one lens group.

In these, for example, it is desirable to use at least one aspherical surface for the first lens group.

[0009]

The reason why the above structure is adopted and the function of the present invention will be described below. The symmetrical wide-angle lens targeted by the present invention has negative meniscus lens groups arranged substantially concentrically before and after a converging system including an aperture stop.
This optical system is very advantageous from the viewpoint of aberration correction, and facilitates correction of sagittal coma aberration, which is remarkable in wide-angle systems and difficult to correct in optical systems that use only spherical surfaces, and can be used as a power series of angle of view. The developed distortion can also be relatively easily corrected due to the symmetry of the optical system.

However, it has been a difficult problem for a wide-angle lens that the image surface is required to be flat from the center of the screen to the peripheral portion like a photographic lens.
On the other hand, the optical system is required to have a large aperture when the depiction is taken into consideration or when a film having fine graininess is used. In the conventional proposal, even if the angle of view is constant, the aperture ratio is 1: 3.4, which is a relatively large aperture, and the angle of view is 9
The 0 ° proposal is shown in the aforementioned US Pat. No. 2,721,499, but uses two negative meniscus lenses in the first lens group. Further, although a proposal of an angle of view of 120 ° and an aperture ratio of 1: 5.6 is shown in US Pat. No. 3,154,628, each of the first lens group and the third lens group has a negative structure of three lenses. Meniscus lenses are used.

In view of these, the current manufacturing technology allows
With the intention of improving these excellent optical systems, an aspheric lens is effectively used, and a large aperture ratio is realized without incurring deterioration such as distortion and sagittal coma. It is a wide-angle lens of the invention.

Here, the concrete contents of the wide-angle lens of the present invention and the conditional expressions will be described.

In the optical system of the present invention, since it is difficult to widen the angle of view only with the second lens group which is an image forming system having an aperture stop, the first lens group having negative refracting power is arranged on the object side. Therefore, the incident angle to the second lens group is relaxed. This makes it possible to improve sagittal coma aberration. Further, the arrangement of the divergent lens group also has the effect of lengthening the back focus. On the other hand, by disposing the third lens unit having a negative refracting power, it is possible to correct field curvature aberration, which is a particularly large feature of wide-angle lenses. The above are the characteristics derived from the basic configuration of the optical system. As a matter of course, due to the symmetry, lateral chromatic aberration and distortion can be corrected extremely well. However, if the actual paraxial arrangement is different, it goes without saying that distortion and lateral chromatic aberration remain in addition to the apparent symmetry. Therefore, a conditional expression regarding the basic paraxial refractive power arrangement of the optical system will be described.

First, the conditional expression (1) defines the refractive power of the first lens group. If the lower limit of 0.2 to this conditional expression is not reached, it is advantageous for downsizing, but this is not preferable because it requires a large number of lens components for aberration correction. On the other hand, if the upper limit of 30 is exceeded, it is very advantageous for aberration correction, but the first lens group becomes large and the third lens group also becomes large to compensate for this, which is not desirable.

Conditional expression (2) represents the ratio of the refractive powers of the first lens unit and the third lens unit, and defines the symmetry of the negative lens unit. When the lower limit of 0.15 is exceeded, the first
As a result, the relative refractive power of the lens group becomes large, and it becomes necessary to form the lens group by a plurality of lens groups. In addition, the sagittal coma aberration becomes remarkable, and the size of the first lens group itself is strongly demanded. Becomes In addition, the lack of symmetry increases residual aberrations of the entire system, which is not desirable as a result.
When the value exceeds the upper limit of 25, the refractive power of the third lens group becomes relatively large, resulting in lack of symmetry, which hinders correction of image plane flatness, lateral chromatic aberration, and distortion. .

Conditional expression (3) defines the refractive power ratio of the front lens group (G ₂₁ ) and the rear lens group (G ₂₂ ) in the refractive power of the second lens group,
It means the symmetry in the refractive power before and after the aperture stop. When the lower limit value of 0.2 is exceeded, the relative refractive power of the front group becomes too large, which hinders spherical aberration correction and aberration correction that can be compensated for by symmetry. On the other hand, when the upper limit of 5 is exceeded, on the contrary, the relative refractive power of the rear group becomes excessively large, which tends to cause difficulty in correcting astigmatic difference and meridional coma aberration in addition to spherical aberration. So
Not preferred.

Next, the conditional expression (4) is for defining the principal point interval between the first lens group and the third lens group. When the value goes below the lower limit of -3, the refracting power tends to increase, including that of the first lens group, although it tends to be compact, and it is impossible to correct aberrations. Further, when the upper limit value 20 is exceeded, it means that the actual distance between the first lens group and the third lens group becomes large, which leads to an unnecessarily large size of the first lens group, which is not a desirable state.

Next, the purpose of the present invention is to newly aim at widening the angle or increasing the aperture ratio by using an aspherical surface in the above-mentioned basic optical system. On the other hand, the direction of shortening the total length of the optical system and reducing the number of constituent elements is actually the same, and it is nothing but the control of the refractive power of the surface by the aspherical surface.

In the present invention, the main purpose is to meet the requirements of higher specifications, and maintaining or improving the image forming performance without lowering the aperture efficiency cannot be realized by the same optical system. , Recognizes that only the eccentricity error sensitivity increases. Therefore, the aberration to be corrected and the aspherical surface to be used are clarified, and the widening of the angle and the large aperture ratio are logically realized.

In this regard, first, in order to correct spherical aberration associated with a large aperture ratio and maintain aperture efficiency, an example of using an aspherical surface for the purpose of correcting an off-axis light beam with increased light amount, especially a peripheral light beam, will be described later. This will be described through Example 1 showing data.

This embodiment is an example in which the aperture ratio is normal due to the specifications, but the viewpoint is focused on improving the imaging performance and shortening the overall length. In the negative group leading type optical system in which the first lens group has a negative refractive power like the optical system of the present invention, the burden on the second lens group for correcting spherical aberration increases. This is because the divergent luminous flux is the second
This is because the light is incident on the lens group, and by making the surface that contributes to spherical aberration correction in the second lens group aspherical, it is possible to make the spherical aberration that is undercorrected into a full correction type. Further, in a wide-angle lens, the peripheral image plane is not flat due to the influence of field curvature, and often has a direct relation to performance deterioration.
Therefore, it is possible to perform correction by using an aspherical surface for the final lens group that is effective for correcting the peripheral image plane on the lens surface.
Here, contrary to the converging lens, the divergent refractive power of the peripheral light flux is strengthened to raise the image plane and enhance the flatness.

Next, the operation of the optical system of Example 1 will be described. The lens configuration of this embodiment is shown in the sectional view of FIG. The spherical aberration which is overcorrected in the first lens group G1 is prevented from being overcorrected more than necessary by using an aspherical surface for the first surface of the second lens group G2. Corrected by the converging effect. In particular, the converging action of the refracting surface of the final surface of the second lens group G2 is strong. Also, the third
It reaches the image plane after being compensated by the diverging action of the lens group G3.
The 3rd-order spherical aberration coefficient is undercorrected and the 5th-order spherical aberration coefficient is overcorrected, and the entire system is well corrected. With respect to this fifth-order spherical aberration coefficient, the amount of aberration generated on the first surface and the final lens surface using the aspherical surface of the second lens group G2 is large, and they have a mutual correcting effect. Further, the action of the 7th-order aberration coefficient is extremely gentle.

With respect to the coma aberration coefficient, the third lens group G3 has an action of causing an image plane to be caused by insufficient correction in the first lens group G1 and the second lens group G2. Also in this case, the aberration generating surfaces are the aspherical surface of the first surface of the second lens group G2 and the final lens surface of the second lens group G2. This is
The same applies to the higher-order aberration correction coefficient.

As for the astigmatism, when viewed as a group, the correction situation is similar to coma, and the first lens group G1
And the second lens group G2 have the effect of causing the third lens group G3 to produce an image plane that is undercorrected. However, regarding the action of the higher-order aberration coefficient, as a result of using the aspherical surface for the concave surface of the third lens group G3, the fifth-order aberration coefficient acts to correct the image plane. Also, with respect to distortion, the third lens group G
The correction is made good by the action of the aspheric surface of 3.

Numerical examples of the aberration coefficient of this embodiment are shown in Table 1 below for each lens group. An underline is added to the aberration coefficient value generated by the action of the aspherical surface of the third lens group G3. Table 1 SA ₃ SA ₅ CM ₃ CM ₅ AS ₃ AS ₅ DT ₃ DT ₅ G1 0.04287 0.0025 -0.0629 -0.00089-0.01766 0.0017 -0.61219 0.12823 G2 -0.09276 0.00795-0.1549 -0.06756-0.07656 0.06185-0.27615 0.13781 G3 0.03201 0.00334 0.26607 0.01467 0.19953 -0.74142 1.75811-5.49181 ──────────────────────────────────── Σ -0.01789 0.01378 0.04826-0.05378 0.10532 -0.67786 0.86977-5.22577.

The aspherical surface of the third lens group G3 also acts on the high-order coma aberration. That is, in the conventional spherical system, it is understood that the correction of off-axis aberrations such as astigmatism, distortion, and coma for increasing the aperture ratio and widening the angle has not been sufficient.

In Table 1, SA ₃ is a third-order spherical aberration coefficient, SA ₅ is a fifth-order spherical aberration coefficient, CM ₃ is a third-order coma aberration coefficient, CM ₅ is a fifth-order coma aberration coefficient, and AS ₃ is 3. The astigmatism coefficient, AS ₅ is the 5th astigmatism coefficient, DT ₃ is the 3rd distortion coefficient, and DT ₅ is the 5th distortion coefficient. Also,
Σ is the relaxation of the aberration coefficient of each group. Further, in this example, there is an air lens in the second lens group G2, which serves as an aberration generation surface and is involved in delicate aberration correction. The high-order aberration remaining here can be balanced by the high-order aberration generated by the aspherical surface.

Next, the angle of view is about 90 ° and the aperture ratio is 1 :.
The effect in the case of a lens system of about 2.8 will be described. Here, Example 5 described later will be described. As shown in the sectional view of FIG. 5, the lens structure of this embodiment has a symmetrical and very simple structure. The aspherical surface is the first
Lens group G1, second lens group G2, and third lens group G3
One side is used for each. That is, with only the basic configuration, if the lens system does not have the ability to correct various aberrations when the refractive power arrangement is determined by the correction of chromatic aberration,
It is difficult to meet high specifications. However, by effectively using the aspherical surface, it becomes possible to improve the imaging performance.

By using an aspherical surface, the first surface of the first lens group G1 directly affects correction of off-axis aberrational distortion. Further, it has a function of relaxing the off-axis light flux emitted to the second lens group G2 and suppressing the occurrence of sagittal coma aberration. In this case, it is possible to balance the entire system by generating overcorrected coma.
This action is more effective as the angle of view becomes wider, but in the spherical system alone, the problem is solved by arranging many negative meniscus lenses.
There is one in 199. However, this is nothing but an example of how difficult it is to satisfy the required imaging performance.

Next, the aspherical surface used for the final surface of the rear lens group G ₂₂ of the second lens group G2 having a relatively large refractive power is
It facilitates correction of off-axis meridional coma, astigmatism, distortion and field curvature. Further, by using an aspherical surface for the convex surface of the meniscus lens of the third lens group G3, it contributes to correction of off-axis coma aberration, distortion aberration, and field curvature aberration. Table 2 shows the aberration coefficients for each lens group in this example. The aberration diagram is shown in FIG.

Table 2 SA ₃ SA ₅ CM ₃ CM ₅ AS ₃ AS ₅ DT ₃ DT ₅ G1 0.07095 0.0067 -0.40601-0.04613 0.25962-0.03896-1.87280 0.54515 G2 -0.11656 0.04792 0.23886 0.25829-0.40952 0.11010 0.06285 0.56511 G3 0.01487 0.00115 0.15299 0.00939 0.18057-0.21544 2.14757-3.36526 ──────────────────────────────────── Σ-0.03074 0.05577 -0.01416 0.22154
0.03067-0.14430 0.33762-2.25501.

Here, the aspherical surface used for the first surface of the first lens group G1 has an eccentricity of 1, and the aspherical surface amount near the effective diameter is 396 μm, which is relatively large. It represents the magnitude of the action. In particular, the eigensurface coefficient of an aspherical surface has a large value as shown in Table 3 below. Table 3 SA ₃ SA ₅ CM ₃ CM ₅ AS ₃ AS ₅ DT ₃ DT ₅
1 side 0.00129 0.00013-0.09522-0.00262 0.10555 0.00011-0.92766 0.18319 9 side -0.07110 0.05596 0.74665 0.28818-0.18588 0.03465 0.69385-0.36207 11 side -0.00831-0.00045 0.01565 0.00422 0.09016-0.19631 1.05322-2.46005.

Due to the aberration coefficient on the aspherical surface used in Table 3, the spherical aberration has a large effect on the second lens group G2, and the coma aberration has a large effect on the aspherical surfaces of the first lens group G1 and the second lens group G2.
Astigmatism contributes to the action of each lens group in the third-order aberration coefficient, but it can be seen from the situation of occurrence of higher-order aberrations that the third lens group G3 makes a large contribution. Further, it is understood that the distortion is similar to the astigmatism, and the action of the aspherical surface of the third lens group G3 is great.

Further, regarding the effect of correcting the aberration of the aspherical surface, the same effect can be expected by using the concave surface in the first lens group G1 and the second lens group G2. This is shown in Example 7 described later. In this embodiment, the angle of view is about 75 °,
This type of lens system has a large aperture ratio of 1: 2.08, and in order to satisfactorily correct chromatic aberration and various off-axis aberrations, the concave surface of the negative meniscus lens of the first lens group G1 and the second lens group G2 By using an aspherical surface for the first surface and the concave surface of the negative meniscus lens of the third lens group G3, sufficient aperture efficiency and imaging performance are realized. This lens structure is shown in FIG. 7 and the aberration diagram is shown in FIG.

[0035]

EXAMPLES Examples 1 to 7 of the wide-angle lens of the present invention will be described below. Example 1 is a wide-angle lens having a focal length of 28.25 and an aperture ratio of 1: 2.85, and a lens cross-sectional view is shown in FIG. Configuration, the first lens group G1 is composed of one negative meniscus lens having a convex surface directed toward the object side, the front group G ₂₁ of the second lens group G2 includes a negative meniscus lens having a convex surface directed toward the object side, The second lens group G2 is composed of a biconvex lens and a cemented lens of a biconcave lens and is separated by an aperture stop.
The rear group G ₂₂ includes a biconcave lens, a biconvex lens, and a triplet cemented lens including a negative meniscus lens having a convex surface directed toward the image side. The third lens group G3 is composed of one negative meniscus lens having a convex surface directed toward the image plane side.

The aspherical surface is used as the most object-side surface of the second lens group G2, and the amount of aspherical surface in the peripheral portion of the convex surface increases to gradually weaken the refractive power to the vicinity of the zonal, resulting in insufficient correction. This makes it easy to correct spherical aberration. Further, an aspherical surface is used for the concave surface of the negative meniscus lens forming the third lens group G3, which plays a role in flattening the peripheral image plane. Although the amount of aspherical surface is small on this surface, the refractive power of the surface is strengthened toward the peripheral portion of the lens. FIG. 8 shows an aberration diagram of this example. In the figure, (a) is spherical aberration, (b)
Represents astigmatism, (c) represents lateral chromatic aberration, and (d) represents distortion.

The second embodiment is a wide-angle lens having a focal length of 28.25 and an aperture ratio of 1: 2.83, and a lens sectional view is shown in FIG. The configuration is such that the first lens group G1 is composed of two lenses, a negative meniscus lens having a convex surface facing the object side and a positive meniscus lens having a convex surface facing the object side, and the second lens group G1.
The second front group G ₂₁ is composed of a cemented lens of a negative meniscus lens having a convex surface directed toward the object side and a biconvex lens. The rear lens group G ₂₂ of the second lens group G 2 is a biconcave lens biconvex lens with an aperture stop therebetween. It is composed of a cemented lens and a biconvex lens whose surface on the image side has a strong curvature. The third lens group G3 is composed of one negative meniscus lens having a convex surface directed toward the image plane side. The basic design concept of this lens group structure is that it is determined with particular consideration for compensation of aberrations during focusing, and that chromatic aberration correction is performed within the group.

Here, the aspherical surface is a concave surface which is the final surface of the first lens group G1 and the refractive power of the surface is strengthened toward the lens peripheral portion, contributing to correction of off-axis aberrations, for example, a delicate balance of sagittal coma aberration. To do. In addition, the third lens group G3
It is used for the concave surface which is the front surface of the, and strengthens the refracting power of the surface as it goes to the peripheral portion of the lens, thereby contributing to the improvement of the flatness of the image surface. This aspherical amount is 287 μm, which is relatively large in the vicinity of the effective diameter, which means that the effect on the peripheral image plane is large. FIG. 9 shows an aberration diagram similar to that of FIG. 8 of this example. From this aberration diagram, it is clear that spherical aberration, astigmatism, lateral chromatic aberration, and distortion are well corrected.

The third embodiment is a wide-angle lens having a focal length of 28.25 and an aperture ratio of 1: 2.82. A lens sectional view is shown in FIG. Configuration, the first lens group G1 is composed of one negative meniscus lens having a convex surface directed toward the object side, the front group G ₂₁ of the second lens group G2, a positive meniscus thick having a convex surface on the object side The rear lens group G ₂₂ of the second lens group G 2 is composed of a lens, a biconvex lens, a biconcave lens having a strong curvature, and a triplet cemented lens of a negative meniscus lens having a convex surface directed toward the object side. It is composed of a cemented lens made up of a concave lens and a biconvex lens, and a cemented lens made up of a biconcave lens and a biconvex lens having a small refractive power. The third lens group G3 is composed of one negative meniscus lens having a strong curvature with its convex surface facing the image plane side.

The aspherical surface is used for the rear surface of the negative meniscus lens of the first lens group G1, and the refracting power of the surface becomes stronger toward the peripheral portion of the lens. As a result, it becomes possible to more easily correct sagittal coma aberration. In addition, it is used as the most object-side surface of the triplet cemented lens of the front group G ₂₁ of the second lens group G2, and has a shape capable of acting so as to weaken the convergent refractive power toward the peripheral portion of the lens surface. , Facilitates correction of spherical aberration. It was confirmed that this configuration can further increase the wide angle and the large aperture ratio.
FIG. 10 shows an aberration diagram similar to that of FIG. 8 of this example. As is clear from this aberration diagram, spherical aberration, lateral chromatic aberration, and distortion could be corrected very well. The distortion is almost zero.

The fourth embodiment is a wide-angle lens having a focal length of 28.2 and an aperture ratio of 1: 2.88, and a lens sectional view is shown in FIG. As for the full length, the telephoto ratio is 2.3, which is compact. Configuration, the first lens group G1 is composed of one negative meniscus lens having a convex surface directed toward the object side, the front group G ₂₁ of the second lens group G2 is composed of a biconvex lens and a biconcave lens of the cemented lens, aperture at a stop, the group G ₂₂ after the second lens group G2 is composed of a biconcave lens and a cemented lens of a biconvex lens having a stronger curvature concave surface facing the image side. The third lens group G3 is composed of one negative meniscus lens having a convex surface directed toward the image plane side. In particular, the rear group G of the second lens group G2
It is a major feature that ₂₂ includes a thick negative lens.

The aspherical surface is used on the most image side surface of the rear group G ₂₂ of the second lens group G2. The aspherical surface has a refracting power that is less convergent toward the outer peripheral portion of the lens, and contributes to correction of image plane flatness. The amount of aspherical surface is about 56 μm near the effective diameter. FIG. 11 shows an aberration diagram similar to that of FIG. 8 of this example. From this aberration diagram, as in Example 3,
It can be seen that the distortion aberration is almost zero.

The fifth embodiment is a wide-angle lens having a focal length of 21.15 and an aperture ratio of 1: 2.85, and a lens sectional view is shown in FIG. This lens system has a six-element configuration similar to that of the fourth embodiment. However, the angle of view exceeds 90 ° and the aperture ratio is large. Configuration, the first lens group G1 is composed of a negative meniscus lens one having a convex surface facing the object side, the front group G ₂₁ of the second lens group G2 includes a negative having a convex surface directed toward the biconvex lens and the image plane side a cemented lens of a meniscus lens, at a aperture stop, the group G ₂₂ after the second lens group G2 is composed of a biconcave lens and a cemented lens of a biconvex lens. The third lens group G3 is composed of one negative meniscus lens having a convex surface directed toward the image plane side.

The aspherical surfaces are used for the first surface, which is the object side surface of the first lens group G1, the final surface of the second lens group G2, and the image side surface or the final surface of the third lens group G3. The aspherical surface of the first surface is used for the convex surface of the negative meniscus lens, and has a shape in which the aspherical surface amount increases sharply toward the peripheral edge, and it effectively acts to correct sagittal coma aberration etc. to the peripheral light flux. To do. Further, the aspherical surface used as the final surface of the second lens group G2 effectively acts on coma aberration correction and astigmatism correction. Further, the aspherical surface used as the convex surface of the negative meniscus lens of the third lens group G3 weakens the refractive power of the surface at the lens peripheral portion and effectively acts to improve the flatness of the image surface. At this time, the amount of aspherical surface near the effective diameter is 1013 μm. FIG. 12 shows an aberration diagram similar to that of FIG. 8 of this example. According to this embodiment, the telephoto ratio is 2.6.
Thus, a lens system having an extremely good image plane was obtained.

The sixth embodiment is a wide-angle lens having a focal length of 28.25 and an aperture ratio of 1: 2.08, and a lens sectional view is shown in FIG. The first lens group G1 is composed of one thick negative meniscus lens having a convex surface facing the object side,
Front group G ₂₁ of the second lens group G2 includes a positive meniscus lens having a convex surface directed toward the object side and a double-convex lens and a double-concave lens, at a aperture stop, the second lens group G
The second rear group G ₂₂ includes a triplet cemented lens including a negative meniscus lens having a convex surface directed toward the object side, a biconvex lens, and a negative meniscus lens having a convex surface directed toward the image side. The third lens group G3 is a negative meniscus lens 1 having a convex surface facing the image plane side.
It consists of pieces. The negative lens of the third lens group G3 is known to be a biconcave lens due to the limitation of back focus, but it is clear that this is not a good idea for improving peripheral performance. The most object-side lens of the second lens group G2 was determined by selecting a glass type having a small dispersion for the first lens group G1 itself. In some cases, the first
When used for correcting chromatic aberration in the lens group G1, it may be used as the first lens group G1.

The aspherical surface is used as the most object-side convex surface of the second lens group G2, and has a shape in which the refracting power of the surface becomes weaker toward the periphery of the lens and is effective in correcting coma aberration and spherical aberration. Act on. In particular, it works effectively when the diameter is large. It can be seen that the aspheric amount near the effective diameter is 951 μm, which is a large effect. Further, an aspherical surface is used for the concave surface of the third lens group G3, which is used for correcting the flatness of the image surface. When the aperture ratio is large, the marginal luminous flux becomes large in order to maintain the aperture efficiency, so that the amount of aspherical surface also increases, and it has 128 μm near the effective diameter. FIG. 13 shows an aberration diagram similar to that of FIG. 8 of this example. Although high-order aberration remains in the distortion, very good correction is possible.

The seventh embodiment is a wide-angle lens having a focal length of 28.24 and an aperture ratio of 1: 2.08, and a lens sectional view is shown in FIG. The first lens group G1 is composed of two negative meniscus lenses each having a convex surface facing the object side, and a positive meniscus lens having a strong curvature on the object side across an air lens, and the second lens group G2. The front group G _{21 of the above} is composed of a cemented lens of a negative meniscus lens having a convex surface facing the object side and a positive meniscus lens. The rear group G ₂₂ of the second lens group G 2 is a biconcave lens and a biconvex lens with an aperture stop. It consists of a cemented lens and a biconvex lens. In addition, the third lens group G
3 is composed of one negative meniscus lens having a convex surface facing the image plane side.

The aspherical surface is adopted as the concave surface of the first meniscus lens of the first lens group G1, and has a shape in which the divergent refracting power becomes stronger toward the peripheral portion of the lens, and remains on the peripheral image plane. It has a great effect on correction of sagittal coma aberration. It also has an effect on correction of distortion. Further, it is used on the most object side of the second lens group G2, and exerts a great effect on spherical aberration correction. This is important for increasing the aperture ratio. Further, by being used for the concave surface of the negative meniscus lens of the third lens group G3, it is effective in improving the flatness of the off-axis image surface. FIG. 14 shows an aberration diagram similar to that of FIG. 8 of this example. For any aberration,
Very well corrected.

In all cases, the meridional and sagittal coma aberrations are well corrected, and a great improvement is seen over the conventional lens system and the reverse telephoto type, which are increased in size by only the spherical surface.

Numerical data of each of the above-mentioned examples will be shown below. In addition to the above, the symbols are f, the focal length of the entire system, F _NO is the F number, ω is the half angle of view, r ₁ , r ₂ ... The curvature radii of the lens surfaces, d ₁ , d ₂ ... _Are the intervals between the lens surfaces, n _d1 , n _d2 .
Is the d-line refractive index of each lens, and ν _d1 , ν _d2 ... Is the Abbe number of each lens. The aspherical shape is expressed by the following equation, where x is an optical axis with the traveling direction of light being positive and y is a direction orthogonal to the optical axis. x = (y ² / r) / [1+ {1-P (y /
r) ² } ^1/2 ] + A ₄ y ⁴ + A ₆ y ⁶ + A ₈ y ⁸ + A ₁₀ y ¹⁰ However, r is a paraxial radius of curvature, P is a conic coefficient, A ₄ , A ₆ ,
A ₈ and A ₁₀ are aspherical coefficients of the 4th, 6th, 8th and 10th orders, respectively.

Example 1 f = 28.25, F _NO = 2.85, ω = 37.55 ° r ₁ = 45.7477 d ₁ = 2.000 n _d1 = 1.52249 ν _d1 = 59.79 r ₂ = 20.2273 d ₂ = 13.505 r ₃ = 31.8802 (aspherical surface) ) D ₃ = 2.200 n _d2 = 1.77250 ν _d2 = 49.60 r ₄ = 17.3560 d ₄ = 0.626 r ₅ = 17.9470 d ₅ = 5.000 n _d3 = 1.77250 ν _d3 = 49.60 r ₆ = -18.0589 d ₆ = 0.850 n _d4 = 1.58267 ν _d4 = 46.33 r ₇ = 61.2202 d ₇ = 3.461 r ₈ = ∞ (aperture) d ₈ = 3.460 r ₉ = -175.6281 d ₉ = 2.000 n _d5 = 1.62364 ν _d5 = 36.54 r ₁₀ = 30.8634 d ₁₀ = 5.362 n _d6 = 1.74400 ν _d6 = 44.79 r ₁₁ = -10.2656 d ₁₁ = 2.749 n _d7 = 1.80518 ν _d7 = 25.43 r ₁₂ = -21.9822 d ₁₂ = 12.771 r ₁₃ = -12.5639 (aspherical surface) d ₁₃ = 1.650 n _d8 = 1.48749 ν _d8 = 70.21 r ₁₄ = -28.6432 Aspherical surface third surface P = 1.0000 A ₄ = -0.20326 × 10 ^-4 A ₆ = -0.97541 × 10 ^-7 A ₈ = 0.18268 × 10 ^-9 A ₁₀ = -0.19504 × 10 ^-11 thirteenth surface _{P = 1.0208 A 4 = -0.53251 ×} 10 -4 A 6 = 0.10680 × 10 -5 A 8 = -0.10632 × 10 -7 A 10 = 0.48187 × 10 ^-Ten
.

Example 2 f = 28.25, F _NO = 2.83, ω = 37.66 ° r ₁ = 71.8061 d ₁ = 1.850 n _d1 = 1.48749 ν _d1 = 70.21 r ₂ = 16.8902 d ₂ = 3.578 r ₃ = 24.6507 d ₃ = 5.296 n _d2 = 1.84666 ν _d2 = 23.88 r ₄ = 25.6113 (aspherical surface) d ₄ = 5.443 r ₅ = 20.1463 d ₅ = 5.645 n _d3 = 1.80518 ν _d3 = 25.43 r ₆ = 9.7186 d ₆ = 5.253 n _d4 = 1.56965 ν _d4 = 49.33 r ₇ = -48.8544 d ₇ = 0.515 r ₈ = ∞ (aperture) d ₈ = 1.714 r ₉ = -19.9631 d ₉ = 2.200 n _d5 = 1.60323 ν _d5 = 42.32 r ₁₀ = 18.6011 d ₁₀ = 4.544 n _{d6 = 1.77250 ν d6 = 49.60 r 11} = -24.3183 d 11 = 4.349 r 12 = 261.7147 d 12 = 2.898 n d7 = 1.69680 ν d7 = 55.53 r 13 = -34.6477 d 13 = 11.664 r 14 = -13.5483 ( aspherical) d _{14 = 0.900 n d8 = 1.48749 ν} d8 = 70.21 r 15 = -70.3472 aspherical coefficients fourth surface _{P = 1.0000 A 4 = 0.35387 ×} 10 -5 A 6 = 0.15947 × 10 -7 A 8 = 0.13970 × 10 -10 A ₁₀ = -0.20336 x 10 ^-12 14th surface P = 1.0818 A ₄ = -0.41008 x 10 ^-4 A ₆ = 0.61779 x 10 ^-6 A ₈ = -0 .57324 × 10 ^-8 A ₁₀ = 0.22400 × 10 ^-10
.

Example 3 f = 28.25, F _NO = 2.82, ω = 37.503 ° r ₁ = 41.3997 d ₁ = 3.200 n _d1 = 1.61700 ν _d1 = 62.80 r ₂ = 14.7518 (aspherical surface) d ₂ = 7.344 r ₃ = _{21.6666 d 3 = 7.110 n d2 =} 1.66680 ν d2 = 33.04 r 4 = 35.1779 d 4 = 3.117 r 5 = 40.7851 ( _{aspherical) d 5 = 4.192 n d3 =} 1.79500 ν d3 = 45.29 r 6 = -18.7082 d 6 = 1.200 n _d4 = 1.62045 ν _d4 = 38.12 r ₇ = 10.2699 d ₇ = 3.974 n _d5 = 1.49700 ν _d5 = 81.61 r ₈ = 62.8082 d ₈ = 0.808 r ₉ = ∞ (diaphragm) d ₉ = 0.583 r ₁₀ = -212.1168 d ₁₀ = 1.500 n _d6 = 1.58313 ν _d6 = 59.38 r ₁₁ = 14.3300 d ₁₁ = 4.556 n _d7 = 1.74100 ν _d7 = 52.65 r ₁₂ = -19.3044 d ₁₂ = 0.150 r ₁₃ = -67.0967 d ₁₃ = 1.000 n _d8 = 1.67270 ν _d8 = 32.10 r ₁₄ = 52.4027 d ₁₄ = 1.982 n _d9 = 1.77250 ν _d9 = 49.60 r ₁₅ = -304.9685 d ₁₅ = 14.384 r ₁₆ = -11.5442 d ₁₆ = 1.200 n _d10 = 1.65830 ν _d10 = 57.33 r ₁₇ = -18.3544 non Spherical coefficient 2nd surface P = 1.0000 A ₄ = 0.32710 × 10 ^-5 A ₆ = -0.48022 × 10 ^-7 A ₈ = 0.40963 × 10 ^-9 A ₁₀ = -0.12681 × 10 ^-11 Fifth surface P = 1.0000 A ₄ = -0.32015 × 10 ^-4 A ₆ = -0.16426 × 10 ^-6 A ₈ = 0.56575 × 10 ^-9 A ₁₀ = -0.52037 × 10 ^-11
.

Example 4 f = 28.2, F _NO = 2.88, ω = 37.462 ° r ₁ = 18.5447 d ₁ = 3.693 nd ₁ = 1.67790 ν _d1 = 55.33 r ₂ = 11.9475 d ₂ = 15.687 r ₃ = 24.4378 d ₃ = 2.610 n _d2 = 1.77250 ν _d2 = 49.60 r ₄ = -88.4690 d ₄ = 0.800 n _d3 = 1.63636 ν _d3 = 35.37 r ₅ = 55.1463 d ₅ = 1.163 r ₆ = ∞ (aperture) d ₆ = 0.850 r ₇ = -64133.6418 d ₇ = 10.197 n _d4 = 1.71736 ν _d4 = 29.51 r ₈ = 15.3380 d ₈ = 4.279 n _d5 = 1.77250 ν _d5 = 49.60 r ₉ = -27.1236 (aspheric) d ₉ = 16.764 r ₁₀ = -14.2958 d ₁₀ = 1.650 _{n d6 = 1.48749 ν d6 = 70.21} r 11 = -40.8089 aspherical coefficients ninth surface _{P = 1.0000 A 4 = 0.19710 ×} 10 -4 A 6 = 0.68681 × 10 -7 A 8 = -0.73357 × 10 -9 A 10 = 0.78900 x 10 ^-11
.

Example 5 f = 21.15, F _NO = 2.85, ω = 45.811 ° r ₁ = 21.9601 (aspherical surface) d ₁ = 2.000 n _d1 = 1.65160 ν _d1 = 58.52 r ₂ = 11.8035 d ₂ = 18.104 r ₃ = 21.5082 d ₃ = 2.824 n _d2 = 1.78590 ν _d2 = 44.19 r ₄ = -34.1116 d ₄ = 0.800 n _d3 = 1.58267 ν _d3 = 46.33 r ₅ = -413.1548 d ₅ = 1.063 r ₆ = ∞ (aperture) d ₆ = 1.271 r ₇ = -31.4484 d ₇ = 2.200 n _d4 = 1.72151 ν _d4 = 29.24 r ₈ = 13.9583 d ₈ = 3.058 n _d5 = 1.75500 ν _d5 = 52.33 r ₉ = -20.9744 (aspherical surface) d ₉ = 15.141 r ₁₀ =- _{10.1789 d 10 = 1.650 n d6 =} 1.48749 ν d6 = 70.21 r 11 = -16.2012 ( aspherical) aspherical coefficients first surface _{P = 1.0000 A 4 = -0.56299 ×} 10 -5 A 6 = -0.14684 × 10 -7 A ₈ = -0.64865 × 10 ^-10 A ₁₀ = 0.18261 × 10 ^-12 9th surface P = 1.0000 A ₄ = 0.32302 × 10 ^-4 A ₆ = 0.84780 × 10 ^-6 A ₈ = -0.27757 × 10 ^-7 A ₁₀ = 0.33334 × 10 ^-9 11th surface P = 1.0000 A ₄ = 0.64096 × 10 ^-4 A ₆ = -0.25094 × 10 ^-6 A ₈ = 0.11385 × 10 ^-8 A ₁₀ = 0.92702 × 10 ^-12
.

Example 6 f = 28.25, F _NO = 2.08, ω = 37.685 ° r ₁ = 140.9251 d ₁ = 10.040 n _d1 = 1.48749 ν _d1 = 70.21 r ₂ = 19.3851 d ₂ = 3.175 r ₃ = 29.6952 (aspherical surface) ) D ₃ = 2.000 n _d2 = 1.74100 ν _d2 = 52.65 r ₄ = 63.4375 d ₄ = 6.529 r ₅ = 63.0315 d ₅ = 4.280 n _d3 = 1.77250 ν _d3 = 49.60 r ₆ = -15.6267 d ₆ = 0.800 n _d4 = 1.58215 ν _d4 = 42.09 r ₇ = 57.7250 d ₇ = 1.372 r ₈ = ∞ (aperture) d ₈ = 1.475 r ₉ = 123.0481 d ₉ = 2.524 n _d5 = 1.62364 ν _d5 = 36.54 r ₁₀ = 16.4456 d ₁₀ = 4.405 n _d6 = 1.77250 ν _d6 = 49.60 r ₁₁ = -19.3728 d ₁₁ = 2.200 n _d7 = 1.84666 ν _d7 = 23.88 r ₁₂ = -31.8861 d ₁₂ = 11.576 r ₁₃ = -23.4321 (aspherical surface) d ₁₃ = 3.073 n _d8 = 1.48749 ν _d8 = 70.21 r ₁₄ = -961.4600 aspherical coefficients third surface _{P = 1.0000 A 4 = -0.26049 ×} 10 -4 A 6 = -0.15919 × 10 -6 A 8 = 0.20286 × 10 -9 A 10 = -0.34506 × 10 - ^11th surface P = 2.8226 A ₄ = -0.74032 × 10 ^-4 A ₆ = 0.16831 × 10 ^-6 A ₈ = -0.19821 × 10 ^-8 A ₁₀ = 0
.

Example 7 f = 28.24, F _NO = 2.08, ω = 37.548 ° r ₁ = 67.0467 d ₁ = 1.850 n _d1 = 1.60717 ν _d1 = 40.26 r ₂ = 22.8105 (aspherical surface) d ₂ = 6.695 r ₃ = 128.5307 d ₃ = 1.300 n _d2 = 1.49700 ν _d2 = 81.61 r ₄ = 26.7744 d ₄ = 2.025 r ₅ = 29.0729 d ₅ = 5.227 n _d3 = 1.80100 ν _d3 = 34.97 r ₆ = 4926.3414 d ₆ = 10.616 r ₇ = 28.5297 ( _{aspherical) d 7 = 4.687 n d4 =} 1.80518 ν d4 = 25.43 r 8 = 11.2876 d 8 = 7.334 n d5 = 1.60300 ν d5 = 65.48 r 9 = 300.5721 d 9 = 1.000 r 10 = ∞ ( stop) d ₁₀ = 1.550 r ₁₁ = -45.7434 d ₁₁ = 1.943 n _d6 = 1.54041 ν _d6 = 51.00 r ₁₂ = 15.6189 d ₁₂ = 4.014 n _d7 = 1.77250 ν _d7 = 49.60 r ₁₃ = -144.5286 d ₁₃ = 0.221 r ₁₄ = 80.4465 d ₁₄ = 2.496 n _d8 = 1.79500 ν _d8 = 45.29 r ₁₅ = -44.4001 d ₁₅ = 12.595 r ₁₆ = -14.5662 (aspherical surface) d ₁₆ = 1.650 n _d9 = 1.62045 ν _d9 = 38.12 r ₁₇ = -39.6495 aspherical surface second surface P = 1.3864 A ₄ = 0.31056 × 10 ^-5 A ₆ = -0.18594 × 10 ^-7 A ₈ = 0.9 1239 x 10 ^-10 A ₁₀ = -0.1977 8 x 10 ^-12 7th surface P = 1.0000 A ₄ = 0.12792 x 10 ^-5 A ₆ = -0.528 11 x 10 ^-7 A ₈ = 0.56840 x 10 ^-9 A ₁₀ = -0.24022 × 10 ^-11 16th surface P = 1.5704 A ₄ = -0.27588 × 10 ^-4 A ₆ = 0.22412 × 10 ^-6 A ₈ = -0.35098 × 10 ^-8 A ₁₀ = 0.14958 × 10 ^-10
.

Next, the above conditions (1)-
The values for (4) are shown in the following table.

[0059]

The wide-angle lens of the present invention described above can be constructed, for example, as follows. [1] Three basic lenses, in order from the object side, a first lens group having negative refractive power, a second lens group including an aperture stop and having positive refractive power, and a third lens group having negative refractive power. The second lens group is composed of two lens groups, a front lens group (G ₂₁ ) and a rear lens group (G ₂₂ ), each having a positive refractive power with an aperture stop interposed therebetween, and the first lens group is A negative meniscus lens having a convex surface directed toward the object side, the front group of the second lens group includes at least one cemented lens including a positive lens and a negative lens, and the second lens group The rear group is composed of at least one set of cemented lenses including a positive lens and a negative lens, and the third lens group is composed of at least one negative meniscus lens having a convex surface facing the image side, A wide-angle lens characterized by having an aspherical surface in any lens group. .

[2] The first lens group having negative refracting power, the second lens group including an aperture stop and having positive refracting power, and the third lens group having negative refracting power in order from the object side.
The first lens group is composed of two basic lens groups, and the second lens group is composed of two lens groups of a front group (G ₂₁ ) and a rear group (G ₂₂ ) having positive refracting power across an aperture stop. The lens group includes at least one negative meniscus lens having a convex surface directed toward the object side, and the front group of the second lens group includes at least one cemented lens including a positive lens and a negative lens,
The rear group of the second lens group includes at least one set of cemented lenses including a positive lens and a negative lens, and the third lens group includes at least one negative meniscus lens having a convex surface facing the image plane side. And a wide-angle lens having an aspherical surface in any lens group and satisfying the following conditions (1) to (4).

0.2 <-f ₁ / f <30 (1) 0.15 <f ₁ / f ₃ <25 (2) 0.2 <f ₂₁ / f ₂₂ <5 ... · (3) -3 <e ' / f <20 ··· (4) However, f _1: focal length of the first lens group, f _3: the focal length of the third lens group, f: the focal length of the entire system F ₂₁ : focal length of front group of second lens group, f ₂₂ : focal length of rear group of second lens group, e ′: front group of first lens group and second lens group as one lens group And the principal point spacing when the rear lens group of the second lens group and the third lens group are one lens group.

[3] At least 1 in the first lens group
The wide-angle lens according to the above [1] or [2], wherein an aspherical surface is used.

[4] At least 1 in the second lens group
The wide-angle lens according to the above [1] or [2], wherein an aspherical surface is used.

[5] At least 1 in the third lens group
The wide-angle lens according to the above [1] or [2], wherein an aspherical surface is used.

[6] The wide-angle lens described in [1] or [2], wherein at least one aspherical surface is used for each of the first lens group and the second lens group.

[7] The wide-angle lens described in [1] or [2], wherein at least one aspherical surface is used for each of the second lens group and the third lens group.

[8] The wide-angle lens described in [1] or [2], wherein at least one aspherical surface is used for each of the first lens group and the third lens group.

[0069]

[9] The wide-angle lens according to [1] or [2], wherein at least one aspherical surface is used for each of the first lens group, the second lens group, and the third lens group.

[0070]

As is clear from the above description, in the wide-angle lens in which the negative lens group is arranged on the front side and the rear side of the symmetrical converging lens group including the aperture stop, which is the object of the present invention, sagittal coma aberration is called. In order to improve the flare peculiar to this type of wide-angle lens (especially when the angle of view becomes large), an aspherical surface is used for the meniscus lens of the first lens group. Further, an aspherical surface is used on the object side surface of the second lens group for correcting spherical aberration, and on the image side surface of the second lens group for correcting off-axis astigmatism. Furthermore, in order to improve the flatness of the image plane, the use of an aspherical surface in the third lens group has a great effect, and it is possible to give a large effect to the wide angle of the lens system or the large aperture ratio. It goes without saying that it is possible to provide a good lens system with a small number of constituent elements. As described above, according to the present invention, a wide-angle lens having a wide-angle and a large aperture ratio which has never been obtained is provided.
It can be provided as a relatively small lens system.

[Brief description of drawings]

FIG. 1 is a sectional view of a wide-angle lens according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a wide-angle lens according to a second embodiment of the present invention.

FIG. 3 is a sectional view of a wide-angle lens according to a third embodiment of the present invention.

FIG. 4 is a sectional view of a wide-angle lens of Example 4 of the present invention.

FIG. 5 is a sectional view of a wide-angle lens of Example 5 of the present invention.

FIG. 6 is a sectional view of a wide-angle lens according to Example 6 of the present invention.

FIG. 7 is a sectional view of a wide-angle lens according to Example 7 of the present invention.

FIG. 8 shows spherical aberration (a), astigmatism (b) of Example 1,
FIG. 6 is an aberration diagram showing chromatic aberration of magnification (c) and distortion (d).

FIG. 9 is an aberration diagram similar to FIG. 8 of Example 2.

FIG. 10 is an aberration diagram similar to FIG. 8 of Example 3.

FIG. 11 is an aberration diagram similar to FIG. 8 of Example 4.

FIG. 12 is an aberration diagram similar to FIG. 8 of Example 5.

FIG. 13 is an aberration diagram similar to FIG. 8 of Example 6.

FIG. 14 is an aberration diagram similar to FIG. 8 of Example 7.

[Explanation of symbols]

G1 ... rear group of the front group G ₂₂ ... second lens group of the first lens group G2 ... the second lens group G3 ... third lens group G ₂₁ ... the second lens group

Claims (3)

[Claims] 1. A first lens element having a negative refractive power in order from the object side.
The second lens group includes a lens group, a second lens group including an aperture stop and having a positive refractive power, and a third lens group having a negative refractive power, and the second lens group is an aperture stop. It is composed of two lens groups, a front lens group (G ₂₁ ) and a rear lens group (G ₂₂ ), each having positive refractive power, and the first lens group is at least one negative meniscus lens having a convex surface directed toward the object side. The front group of the second lens group has at least one cemented lens including a positive lens and a negative lens, and the rear group of the second lens group includes a cemented lens including a positive lens and a negative lens. The third lens group is composed of at least one set, and the third lens group is composed of at least one negative meniscus lens having a convex surface facing the image plane side, and has an aspherical surface in any one of the lens groups. Wide-angle lens that does. 2. A first lens element having a negative refractive power in order from the object side.
The second lens group includes a lens group, a second lens group including an aperture stop and having a positive refractive power, and a third lens group having a negative refractive power, and the second lens group is an aperture stop. It is composed of two lens groups, a front lens group (G ₂₁ ) and a rear lens group (G ₂₂ ), each having positive refractive power, and the first lens group is at least one negative meniscus lens having a convex surface directed toward the object side. And a front group of the second lens group includes at least one cemented lens including a positive lens and a negative lens, and a rear group of the second lens group includes at least one of a positive lens and a negative lens. The third lens group is composed of at least one negative meniscus lens having a convex surface facing the image plane side, and has an aspherical surface in any one of the following lens groups: Wide-angle lens characterized by satisfying conditions (1) to (4) _{0.2 <-f 1 / f <30} ··· (1) 0.15 <f 1 / f 3 <25 ··· (2) 0.2 <f 21 / f 22 <5 ··· (3 ) -3 <e '/ f < 20 ··· (4) However, f _1: focal length of the first lens group, f _3: the focal length of the third lens group, f: the focal length of the entire system, f ₂₁ the focal length of the front group of the second lens group, f ₂₂ the focal length of the rear group of the second lens group, e ': a first lens group to the front group of the second lens group as a single lens group, and, Is the principal point spacing when the rear lens group of the second lens group and the third lens group are one lens group. 3. The wide-angle lens according to claim 1, wherein at least one aspherical surface is used for the first lens group.