JP2001116992A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a small-sized four-group zoom lens which has four lens groups on the whole and has excellently compensated aberration variation accompanying power variation. SOLUTION: The zoom lens has a 1st lens group with negative refracting power, a 2nd lens group with positive refracting power, a 3rd lens group with negative refracting power, and a 4th lens group with positive refracting power. For power variation from the wide-angle end to the telephoto end, the 1st lens group moves toward the image side along a convex track, the 2nd lens group moves increasing the interval with the 1st lens, and the lens group moves decreasing the interval with the 3rd lens group; and the lens constitution of the respective lens group is properly set.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photographic camera for film, a video camera of an electronic recording system, a digital camera,
In addition, regarding a zoom lens suitable for an SV camera or the like, in particular, a lens group having a negative refractive power has four lens groups as a whole, and by appropriately setting the lens configuration of these four lens groups, The present invention relates to a negative lead type zoom lens which is reduced in size as a whole.

[0002]

2. Description of the Related Art Conventionally, a so-called negative lead type zoom lens, which is preceded by a lens group having a negative refractive power, has a relatively short close-up distance and is relatively easy to widen the angle of view. It is widely used for zoom lenses.

On the other hand, in the negative lead type zoom lens, at the telephoto end, the first lens group and the second lens group form a positive group as a whole, and the third lens group and the fourth lens group form a negative group as a whole. Since the optical system as a whole can be of a so-called telephoto type, it has the advantage that the telephoto end can be easily made to have a long focus.

[0004] For example, JP-A-60-87312, JP-A-2-201310, JP-A-5-241073
JP, JP-A-4-235515, JP-A-4-4-1
No. 63415, JP-A-5-313065,
Also, JP-A-58-95315 and JP-A-6-826.
No. 98, JP-A-5-19170, JP-A-7-170
In the publication No. 287168, the first group of negative refractive power, the second group of positive refractive power, the third group of negative refractive power,
A zoom lens having four lens units of a fourth lens unit having a positive refractive power and performing zooming by moving at least two of these lens units during zooming. are doing.

[0005]

In recent years, a standard zoom lens used for a single-lens reflex camera or a video camera has a predetermined zoom ratio, a wide angle of view, and a small overall lens system. Is required.

The negative lead type zoom type has four lens groups as compared with a two-group zoom, which is a simple standard zoom lens, which includes two lens groups having negative and positive refractive powers, ie, a so-called short zoom. Therefore, the number of lenses tends to increase.

In general, if the refractive power of each lens unit in a zoom lens is increased, the amount of movement of each lens unit for obtaining a predetermined zoom ratio is reduced, so that the angle of view is increased while shortening the overall length of the lens. Becomes possible.

However, if the refractive power of each lens group is simply increased, the fluctuation of aberration due to zooming becomes large, and it is difficult to obtain good optical performance over the entire zoom range, especially when widening the angle of view. There is a problem that comes.

According to the present invention, the zoom lens is composed of four lens groups as a whole, and the refracting power of each lens group, the lens configuration, and the conditions for moving each lens group during zooming are appropriately set. It is an object of the present invention to provide a zoom lens that has a small angle of view and high optical performance over the entire zoom range and that is reduced in size as a whole.

[0010]

According to a first aspect of the present invention, there is provided a zoom lens system comprising: a first lens unit having a negative refractive power in order from an object side;
A second lens group having a positive refractive power, a third lens group having a negative refractive power, and a fourth lens group having a positive refractive power. The first lens group is used for zooming from the wide-angle end to the telephoto end. The group moves along a locus convex toward the image side, the second lens group moves toward the object side so that the distance from the first lens group decreases, and the third lens group moves toward the image side. The zoom lens moves to the object side so that the distance increases, and the fourth lens group moves to the object side so as to reduce the distance from the third lens group. The negative 31 lens has an aspheric surface whose negative refractive power becomes weaker from the optical axis toward the periphery.

A second aspect of the present invention is characterized in that, in the first aspect of the present invention, the 31 lens is made of a plastic material.

According to a third aspect of the present invention, in the first aspect, the fourth lens group includes one positive 41 lens, and the 41 lens has a positive refractive power from the optical axis toward the periphery. It is characterized by having a weak aspheric surface.

A fourth aspect of the present invention is characterized in that, in the first and second aspects of the present invention, the 41 lens group is made of a plastic material.

According to a fifth aspect of the present invention, when the refractive index of the material of the 31 lens is n31, the condition of 1.53 <n31 ‥‥‥ (1) is satisfied. It is characterized by.

According to a sixth aspect of the present invention, in the third, fourth or fifth aspect, the Abbe number of the material of the 41 lens is ν 41
It is characterized by satisfying the condition of 55 <ν41 ‥‥‥ (2).

The invention of claim 7 is the invention of any one of claims 1 to 6, wherein the focal length of the i-th lens unit is fi and the focal length of the entire optical system at the wide-angle end is fw. 0 <| f1 / fw | <1.5 {(3) 0.5 <f2 / fw <1.0 {(4) 1.5 <| f3 / fw | <4.0} (5) It is characterized by satisfying a condition of 0.5 <f4 / fw <5.0 ‥‥‥ (6).

According to an eighth aspect of the present invention, in the invention of the seventh aspect, the first lens group includes, in order from the object side, a negative meniscus lens having a convex surface facing the object side, a negative lens, and a meniscus having a convex surface facing the object side. The second lens group includes a negative lens and a positive lens, or two positive lenses and one negative lens.

A ninth aspect of the present invention is characterized in that, in the eighth aspect of the present invention, the 31 lens has a meniscus shape with a convex surface facing the image surface side.

In a tenth aspect based on the eighth aspect, the 41 lens has a meniscus shape having a convex surface facing the image surface side.

[0020]

1 is a sectional view of a zoom lens according to a first numerical embodiment at a wide-angle end, FIG. 2 is an aberration diagram at a wide-angle end of the zoom lens according to the first numerical embodiment, and FIG. FIG. 4 is an aberration diagram at the telephoto end of the zoom lens according to Numerical Example 1. FIG.

FIG. 5 is a cross-sectional view of the zoom lens of Numerical Embodiment 2 at the wide-angle end, FIG. 6 is an aberration diagram of the zoom lens of Numerical Embodiment 2 at the wide-angle end, and FIG. 8 is an aberration diagram at the telephoto end of the zoom lens according to Numerical Example 2. FIG.

FIG. 9 is a sectional view of the zoom lens of Numerical Embodiment 3 at the wide-angle end, FIG. 10 is an aberration diagram of the zoom lens of Numerical Embodiment 3 at the wide-angle end, and FIG. FIG. 12 is an aberration diagram at the telephoto end of the zoom lens according to Numerical Example 3.

FIG. 13 is a sectional view of the zoom lens of Numerical Embodiment 4 at the wide-angle end, FIG. 14 is an aberration diagram of the zoom lens of Numerical Embodiment 4 at the wide-angle end, and FIG. FIG. 16 is an aberration diagram at the telephoto end of the zoom lens of Numerical Example 4.

In FIG. 1, (A) shows the wide-angle end, (B) shows the middle, and (C) shows the telephoto end. In each lens sectional view,
L1 is a first group having a negative refractive power (first lens group), L2 is a second group having a positive refractive power (second lens group), and L3 is a third group having a negative refractive power (third lens group). , L4 are a fourth group (fourth lens group) having a positive refractive power. SP is an aperture stop, FC is a fixed flare cut stop, and IP is an image plane.

Arrows indicate the movement trajectories of the respective lens units when zooming from the wide-angle end to the telephoto end. Note that at the wide-angle end and the telephoto end, the zoom positions are defined when the zooming lens group is located at both ends of a range that is mechanically movable on the optical axis.

In the present embodiment, when zooming from the wide-angle end to the telephoto end, the first lens unit L1 is substantially reciprocated while having a convex locus on the image plane side to reduce the image plane fluctuation accompanying the zooming. Correction is performed, and zooming is performed by moving the second, third, and fourth lens units to the object side.

At this time, the second lens unit L2 is moved so that the distance between the second lens unit and the first lens unit is reduced, and the third lens unit L3 is moved to the third lens unit.
Move the distance between the group and the second group so as to increase the distance.
The group L4 is moved so that the distance between the fourth group and the third group is reduced. In addition, although the focus is performed by moving the first group, the focus may be performed by another lens group.

During zooming, the second and fourth units may be moved integrally or independently.
The stop SP is moved integrally with the third lens unit.

In the present embodiment, the third lens group comprises one negative 31 lens, and the negative 31 lens has an aspheric surface whose negative refractive power becomes weaker from the optical axis toward the periphery. .

In order to reduce the weight while simplifying the zoom lens, the number of lenses may be reduced.

In the case of the zoom type of the present invention, the first lens unit having a negative refractive power and the second lens unit having a positive refractive power have a positive combined refractive power as a whole at the telephoto end. That is, it plays the role of the positive front group in the telephoto type refractive power arrangement.

Therefore, at the telephoto end, the first negative refractive power
The on-axis light flux diameter passing through the lens group and the second lens group having a positive refractive power is large, and spherical aberration is particularly likely to occur. For this reason, it is difficult to extremely reduce the number of lenses of the first lens group having a negative refractive power and the second lens group having a positive refractive power, and if forcibly reducing the number, the optical performance deteriorates. I will.

Therefore, the present invention focuses on the third lens group having a negative refractive power, and simplifies and reduces the weight by configuring the third lens group with one negative 31 lens.

However, although the third lens group is suitable for reducing the number of lenses, it is difficult for only one negative lens to suppress the coma generated in the third lens group.

Therefore, in the present invention, an aspherical surface whose negative refractive power becomes weaker as the distance from the optical axis is increased is arranged on the negative 31 lens so that the coma can be easily corrected well.

As described above, the lens system is composed of four lens groups, and by changing the distance between the lens groups at the time of zooming, a zoom lens having a wide zoom angle, a high zoom ratio, and a high zoom ratio is achieved.

During zooming, the stop SP arranged near the third lens unit moves integrally with the third lens unit. Further, the flare cut stop FC is disposed between the fourth unit and the image plane,
Unnecessary light rays on the wide-angle side and the middle angle of view are cut to improve image quality.

The zoom lens of the present invention can be realized by satisfying the above conditions. In order to further reduce the total length of the lens while maintaining good optical performance,
It is desirable to satisfy at least one of the following conditions.

(A-1) The 31 lenses are made of a plastic material. According to this, the weight of the entire lens system can be easily reduced.

(A-2) The fourth lens group is composed of one positive 41 lens. The 41 lens has an aspheric surface whose positive refractive power becomes weaker from the optical axis toward the periphery. It is that you are.

The fact that the first lens unit having a negative refractive power and the second lens unit having a positive refractive power are not suitable for reducing the number of lenses is as follows.
As described above, in addition to the third lens group having a negative refractive power, the fourth lens group having a positive refractive power is also suitable for reducing the number of lenses.

However, although the fourth lens group is suitable for reducing the number of lenses, only one positive lens can suppress the coma generated in the fourth lens group and the negative distortion at the wide-angle end. Have difficulty.

Therefore, in the present invention, if the aspherical surface whose positive refractive power becomes weaker as the distance from the optical axis increases is arranged on the 41 lens, it is easy to satisfactorily correct the coma and distortion.

(A-3) The 41 lens group is made of a plastic material. According to this, the weight of the entire lens system can be easily reduced.

(A-4) Assuming that the refractive index of the material of the 31 lens is n31, the condition 1.53 <n31３１ (1) must be satisfied.

If conditional expression (1) is satisfied, the Petzval sum can be easily set appropriately, and the image surface characteristics particularly at the wide-angle end can be improved.

Desirably, conditional expression (1) is set in the following range.

1.58 <n31 ‥‥‥ (1a) (A-5) When the Abbe number of the material of the 41 lens is ν41, the condition of 55 <ν41 ‥‥‥ (2) must be satisfied.

If conditional expression (2) is satisfied, the negative chromatic aberration of magnification at the wide-angle end can be improved.

Desirably, conditional expression (2) is set in the following range.

57 <ν41 ‥‥‥ (2a) (A-6) When the focal length of the ith lens unit is fi and the focal length of the entire optical system at the wide-angle end is fw, 1.0 <| f1 / fw | <1.5 ‥‥‥ (3) 0.5 <f2 / fw <1.0 ‥‥‥ (4) 1.5 <| f3 / fw | <4.0 ‥‥‥ (5) 0.5 <F4 / fw <5.0 ‥‥‥ (6)

In general, like the zoom lens according to the present invention, a zoom lens in which a lens group having a negative refractive power precedes a zoom lens of a so-called negative lead type has a first negative refractive power.
Increasing the refractive power of the lens group is advantageous in reducing the front lens diameter.

However, if the negative refracting power of the first lens group is too strong, it becomes difficult to correct distortion, coma and field curvature particularly at the wide-angle end, and furthermore, a telephoto type refracting power arrangement at the telephoto end. Therefore, it is difficult to secure a bright F-number at the telephoto end.

The conditional expression (3) is set in view of the above-mentioned reason. If the upper limit is exceeded, it becomes difficult to reduce the size of the entire optical system. If the lower limit is exceeded, distortion, coma and image aberration at the wide-angle end are reduced. Since it becomes difficult to correct the surface curvature or to make it difficult to provide a telephoto type refractive power arrangement at the telephoto end, it becomes difficult to secure a bright F-number at the telephoto end.

Conditional expression (4) is a condition for appropriately setting the focal length of the second lens unit. If the focal length exceeds the upper limit, it becomes difficult to secure a necessary zoom ratio, or telephoto at the telephoto end. Since it becomes difficult to provide a type of refractive power arrangement, it becomes difficult to secure a bright F-number at the telephoto end. If the lower limit is exceeded, it becomes difficult to correct spherical aberration particularly at the telephoto end.

Conditional expression (5) appropriately sets the focal length of the third lens unit. If the focal length exceeds the upper limit, the combined refractive power of the third and fourth lens units at the telephoto end is sufficiently negative. Since it becomes difficult to obtain a refractive power of the telephoto type, it is difficult to arrange a refractive power of a telephoto type.
It becomes difficult to secure numbers. If the lower limit is exceeded, it becomes difficult to correct coma and distortion particularly over the entire focal length range.

Conditional expression (6) sets the focal length of the fourth lens group appropriately. If the upper limit is exceeded, it becomes particularly difficult to correct spherical aberration at the telephoto end. Correction of negative distortion becomes difficult.

Desirably, conditional expressions (3) to (6) are set in the following ranges.

1.0 <| f1 / fw | <1.4 ‥‥‥ (3a) 0.6 <f2 / fw <0.9 ‥‥‥ (4a) 1.9 <| f3 / fw | <3 1.5 ‥‥‥ (5a) 1.1 <f4 / fw <3.8 ‥‥‥ (6a) (A-7) The first lens group has a meniscus shape with a convex surface facing the object side in order from the object side. It is composed of a negative lens, a negative lens, a meniscus-shaped positive lens with the convex surface facing the object side,
The second lens group includes a negative lens and a positive lens, or two positive lenses and one negative lens.

If the first lens group is composed of a negative meniscus lens having a convex surface facing the object side in order from the object side, a negative lens, and a positive meniscus lens having a convex surface facing the object side,
It is easy to correct negative distortion and astigmatism at the wide-angle end, and spherical aberration at the telephoto end.Since the lens configuration is relatively simple, simplification and compactness of the entire optical system are not impaired. .

In the case of the zoom type of the present invention, the second lens group is the main variable power group and, at the same time, the lens group that has the largest positive refractive power of the entire optical system from the wide-angle end to the telephoto end. Relatively strong refractive power is required.

For this purpose, a plurality of positive lenses may be disposed in the second lens group. However, if the number of lenses is excessively increased, the axial thickness of the second lens group becomes large. The distance becomes large, and as a result, not only the second lens group but also the first lens group tends to be large.

In view of this, in the present invention, the second lens group has a simple configuration in which only a negative lens and a positive lens, or two positive lenses and one negative lens are arranged.

In this configuration, one negative lens has a role of correcting various aberrations generated by the two positive lenses, particularly spherical aberration at the telephoto end.

(A-8) The 31 lens has a meniscus shape with the convex surface facing the image surface side.

(A-9) The 41 lens has a meniscus shape with the convex surface facing the image plane side.

(A-10) When the Abbe number of the material of the 31 lens in the third lens group is ν31, it is preferable that 25 <ν31 <40 ‥‥‥ (7). According to this, it is possible to satisfactorily correct a change in chromatic aberration due to zooming.

Next, numerical examples of the present invention will be described. In the numerical examples, Ri is the radius of curvature of the ith surface in order from the object side, Di is the thickness or air space of the ith optical member, and Ni and νi are the refractive index and Abbe number of the ith optical member. .

The aspherical surface shape has a radius of curvature R at the center of the lens surface, the X axis is the optical axis direction (the traveling direction of light), the Y axis is a direction perpendicular to the optical axis, and A, B, C, When D and E are aspheric coefficients respectively

[0070]

(Equation 1)

It is assumed that Note that “ ^ex ” represents “× 10 ^−X ”. Table 1 shows the relationship between some of the above-described conditional expressions and various numerical values in the numerical examples. (Numerical Example 1) f = 36.23 to 77.20 Fno = 3.98 to 5.88 2ω = 61.7 to 31.3 R 1 = 37.039 D 1 = 1.50 N 1 = 1.516330 ν 1 = 61.1 R 2 = 17.203 D 2 = 7.44 R 3 = -73.749 D 3 = 1.30 N 2 = 1.516330 ν 2 = 64.1 R 4 = 31.922 D 4 = 1.56 R 5 = 27.018 D 5 = 3.08 N 3 = 1.620041 ν 3 = 36.3 R 6 = 97.359 D 6 = Variable R 7 = 20.893 D 7 = 4.85 N 4 = 1.658441 ν 4 = 50.9 R 8 = -26.772 D 8 = 1.20 N 5 = 1.805181 ν 5 = 25.4 R 9 = -85.684 D 9 = Variable R10 = Aperture D10 = 4.00 * R11 = -26.038 D11 = 1.70 N 6 = 1.583060 ν 6 = 30.2 R12 = -60.262 D12 = variable * R13 = -46.065 D13 = 2.18 N 7 = 1.491710 ν 7 = 57.4 R14 = -33.078 D14 = variable R15 = flare cutter ＼focal length 36.23 50.00 77.20 variable interval ＼ D 6 25.59 12.75 1.10 D 9 2.00 2.94 3.92 D12 4.49 3.55 2.57 D14 0.00 9.76 29.57 * Aspherical surface 11: A = 0 B = 2.28574e-05 C = 9.79017e-08 D = 1.72620e-10 E = 0 13th surface: A = 0 B = -6.70505e-05 C = -2.62458e-07 D = -9.68465e-10 E = 0 (Numerical example 2) f = 36.23-77.20 Fno = 4.00-5.88 2ω = 61.7- 31.3 R 1 = 28.139 D 1 = 1.50 N 1 = 1.516330 ν 1 = 64.1 R 2 = 15.969 D 2 = 6.81 R 3 = -80.509 D 3 = 1.30 N 2 = 1.516330 ν 2 = 64.1 R 4 = 24.573 D 4 = 1.60 R 5 = 22.216 D 5 = 2.71 N 3 = 1.620041 ν 3 = 36.3 R 6 = 52.285 D 6 = Variable R 7 = 19.875 D 7 = 5.00 N 4 = 1.658441 ν 4 = 50.9 R 8 = -23.651 D 8 = 1.20 N 5 = 1.805181 ν 5 = 25.4 R 9 = -71.380 D 9 = Variable R10 = Aperture D10 = 2.82 * R11 = -18.118 D11 = 1.70 N 6 = 1.583060 ν 6 = 30.2 R12 = -28.640 D12 = variable * R13 = -53.037 D13 = 2.18 N 7 = 1.491710 ν 7 = 57.4 R14 = -40.645 D14 = variable R15 = flare cutter ＼focal length 36.23 50.02 77.20 variable interval ＼ D 6 22.53 11.77 2.09 D 9 1.92 3.25 4.65 D12 4.87 3.53 2.14 D14 0.00 9.92 30.19 * Aspherical surface 11: A = 0 B = 4.58944e-05 C = 7.46281e-08 D = 2.50700e-10 E = 0 13th surface: A = 0 B = -8.78897e-05 C = -2.36569e-07 D = -1.40243e-09 E = 0 (Numerical Example 3) f = 36.23 ~ 77.20 Fno = 4.08 ~ 5.88 2ω = 61.7 ~ 31.3 R 1 = 51.066 D 1 = 1.50 N 1 = 1.516330 ν 1 = 64.1 R 2 = 18.544 D 2 = 7.13 R 3 = -62.190 D 3 = 1.30 N 2 = 1.516330 ν 2 = 64.1 R 4 = 43.196 D 4 = 1.56 R 5 = 32.833 D 5 = 2.89 N 3 = 1.620041 ν 3 = 36.3 R 6 = 151.880 D 6 = Variable R 7 = 153.608 D 7 = 1.80 N 4 = 1.603112 ν 4 = 60.6 R 8 = -194.256 D 8 = 0.10 R 9 = 25.717 D 9 = 4.50 N 5 = 1.603112 ν 5 = 60.6 R10 = -45.960 D10 = 1.20 N 6 = 1.846660 ν 6 = 23.8 R11 =- 95.946 D11 = Variable R12 = Aperture D12 = 4.67 * R13 = -34.383 D13 = 1.70 N 7 = 1.583060 ν 7 = 30.2 R14 = -849.437 D14 = Variable * R15 = -143.047 D15 = 2.18 N 8 = 1.491710 ν 8 = 57.4 R16 = -39.277 D16 = Variable R17 = Flare cutter ＼ Focal length 36.23 50.00 77.20 Variable interval ＼ D 6 26.38 13.10 1.10 D11 2.13 3.49 5.34 D14 7.84 6.49 4.64 D16 0.00 9.85 29.57 * Aspheric coefficient 13: A = 0 B = 1.44480e -05 C = 1.14489e-08 D = -1.98926e-10 E = 0 15th side: A = 0 B = -3.61723e-05 C = -5.52453e-08 D = -1.92670e-10 E = 0 (Numerical value) Example 4) f = 28.90 to 77.20 Fno = 3.88 to 5.88 2ω = 73.6 to 31.3 R 1 = 50.286 D 1 = 1.50 N 1 = 1.622992 ν 1 = 58.2 R 2 = 20.237 D 2 = 8.40 R 3 = -135.710 D 3 = 1.30 N 2 = 1.603112 ν 2 = 60.6 R 4 = 40.887 D 4 = 1.60 R 5 = 29.263 D 5 = 2.69 N 3 = 1.784723 ν 3 = 25.7 R 6 = 50.803 D 6 = Variable R 7 = 68.961 D 7 = 1.80 N 4 = 1.622992 ν 4 = 58.2 R 8 = -162.198 D 8 = 0.10 R 9 = 24.280 D 9 = 1.20 N 5 = 1.728 250 ν 5 = 28.5 R10 = 13.965 D10 = 4.50 N 6 = 1.622992 ν 6 = 58.2 R11 = 124.730 D11 = Variable R12 = Aperture D12 = 4.52 * R13 = -46.645 D13 = 1.70 N 7 = 1.583060 ν 7 = 30.2 R14 =- 184.758 D14 = variable * R15 = -190.167 D15 = 2.18 N 8 = 1.491710 ν 8 = 57.4 R16 = -48.838 D16 = variable R17 = flare cutter ＼focal length 28.90 50.00 77.20 variable interval＼ D 6 34.78 13.29 3.74 D11 2.80 10.14 13.65 D14 11.35 4.01 0.49 D16 0.11 15.24 37.38 * Aspherical surface 13: A = 0 B = 1.04611e-05 C = 1.96016e-08 D = 1.51654e-10 E = 0 15: A = 0 B = -3.26497e- 05 C = -4.18192e-08 D = -5.23570e-10 E = 0

[0072]

[Table 1]

[0073]

According to the present invention, the zoom lens is composed of four lens groups as a whole, and the refracting power of each lens group, the lens configuration, and the moving conditions of each lens group during zooming are appropriately set. Accordingly, it is possible to achieve a zoom lens which has a wide angle of view and has high optical performance over the entire zooming range, and in which the size of the entire lens system is reduced.

In addition, according to the present invention, a standard zoom lens having a simplified, lightweight, and excellent optical performance is achieved while having a zoom ratio of about 2.3 to 3.0. be able to.

[Brief description of the drawings]

FIG. 1 is a sectional view of a lens according to a numerical example 1 of the present invention.

FIG. 2 is an aberration diagram at a wide-angle end according to Numerical Embodiment 1 of the present invention.

FIG. 3 is an intermediate aberration diagram of the numerical example 1 of the present invention.

FIG. 4 is an aberration diagram at a telephoto end in Numerical Example 1 of the present invention;

FIG. 5 is a sectional view of a lens according to a second numerical embodiment of the present invention;

FIG. 6 is an aberration diagram at a wide angle end according to Numerical Example 2 of the present invention.

FIG. 7 is an intermediate aberration diagram of the numerical example 2 of the present invention.

FIG. 8 is an aberration diagram at a telephoto end in Numerical Example 2 of the present invention.

FIG. 9 is a sectional view of a lens according to a numerical example 3 of the present invention.

FIG. 10 is an aberration diagram at a wide angle end according to Numerical Example 3 of the present invention.

FIG. 11 is an intermediate aberration diagram of the numerical example 3 of the present invention.

FIG. 12 is an aberration diagram at a telephoto end in Numerical Example 3 of the present invention.

FIG. 13 is a sectional view of a lens according to a numerical example 4 of the present invention.

FIG. 14 is an aberration diagram at a wide angle end according to Numerical Example 4 of the present invention.

FIG. 15 is an intermediate aberration diagram of the numerical example 4 of the present invention.

FIG. 16 is an aberration diagram at a telephoto end in Numerical Example 4 of the present invention.

[Explanation of symbols]

 L1 First group L2 Second group L3 Third group L4 Fourth group SP stop FC flare cut stop IP image plane d d-line g g-line ΔS sagittal image plane ΔM meridional image plane

Continued on the front page F term (reference) 2H087 KA03 MA12 MA13 MA14 MA15 PA06 PA07 PA18 PB07 PB08 QA02 QA07 QA17 QA22 QA25 QA32 QA42 QA46 RA05 RA13 RA31 RA36 SA24 SA26 SA30 SA32 SA62 SA63 SA64 SA65 SB04 SB13 SB14 SB22 SB32 UA

Claims (10)

[Claims] 1. A first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a fourth lens group having a positive refractive power are arranged in order from the object side. During zooming from the wide-angle end to the telephoto end, the first lens unit moves along a locus convex toward the image side, and the distance between the second lens unit and the first lens unit decreases. Move to the object side, the third lens group moves to the object side so that the distance between the second lenses increases, and the distance between the fourth lens group and the third lens group decreases. Zoom lens that moves to the object side
The third lens group includes one negative 31 lens, and the negative 31 lens has an aspheric surface whose negative refractive power becomes weaker from the optical axis toward the periphery. lens. 2. The zoom lens according to claim 1, wherein said 31 lens is made of a plastic material. 3. The fourth lens group comprises one positive 41 lens, and the 41 lens has an aspheric surface whose positive refractive power becomes weaker from the optical axis toward the periphery. The zoom lens according to claim 1, wherein: 4. The zoom lens according to claim 1, wherein said 41 lens group is made of a plastic material. 5. The refractive index of the material of said 31 lens is n31.
5. The zoom lens according to claim 2, wherein the condition 1.53 <n31 is satisfied. 6. The Abbe number of the material of the 41 lens is ν4
6. The zoom lens according to claim 3, wherein when 1 is satisfied, the condition of 55 <.nu.41 is satisfied. 7. When the focal length of the i-th lens unit is fi and the focal length of the entire optical system at the wide-angle end is fw, 1.0 <| f1 / fw | <1.5 0.5 <f2 / fw The zoom according to any one of claims 1 to 6, wherein a condition of <1.0 1.5 <| f3 / fw | <4.0 0.5 <f4 / fw <5.0 is satisfied. lens. 8. A meniscus negative lens having a convex surface facing the object side in order from the object side, a negative lens,
The second lens group includes a negative lens and a positive lens, or a positive lens having a meniscus shape having a convex surface facing the object side.
The zoom lens according to claim 7, comprising one positive lens and one negative lens. 9. The zoom lens according to claim 8, wherein said 31 lens has a meniscus shape with a convex surface facing the image surface side. 10. The zoom lens according to claim 8, wherein said 41 lens has a meniscus shape with a convex surface facing the image surface side.