JPH0915496A - Zoom lens - Google Patents

Abstract

PURPOSE: To provide a small zoom lens having high optical performance by increasing the refractive power of a second lens group and making a third and a fourth lens groups the proper constitution. CONSTITUTION: This zoom lens is composed of a first positive lens group, a second negative lens group having mainly the variable power action, a third positive lens group and a fourth positive lens group for compensating an image position, focusing is performed by the third or the fourth lens groups or a part of their lenses, the third lens group is composed of a positive lens group, a negative lens group and a positive lens group, the fourth lens group is composed of a negative lens group and a positive lens group and the refractive powers of the positive lens group, the negative lens group of the second lens group and the fourth lens group are properly selected for attaining the purpose.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video camera and a still video camera, and more particularly to a zoom lens having high optical performance suitable for use in capturing recent high definition images.

[0002]

2. Description of the Related Art In a camera using a solid-state image pickup device, a zoom lens having an extremely large zoom ratio is generally used as a photographing lens, and since the size of an imager is relatively small, it is bright and A high performance optical system is required.

As means for achieving such an optical system, in order from the object side, a first lens group having a positive power, a second lens group having a negative power having a zooming effect, and a zooming lens at the time of zooming. A four-group zoom lens composed of a third lens group having a negative power for keeping the image surface constant and a fourth lens group having a positive power for forming an image is well known. Since it is necessary to secure a moving interval, and because the fourth lens group is divided into a front group that makes the divergent light flux emitted from the third lens group substantially parallel and a rear group that forms an image of that light flux, the overall lens length is It is difficult to meet the recent demand for downsizing video cameras.

Therefore, recently, a first lens unit having a positive power in order from the object side, a second lens unit having a negative power having a zooming effect, and a third lens unit having a positive power and fixed during zooming. A four-group zoom lens having a positive power and a fourth lens group that has a positive power and corrects a change in image plane position due to zooming, and performs focusing by moving the fourth lens group toward the object side is the mainstream. Is coming.

Known examples of this type of zoom lens include those disclosed in JP-A-62-178917, JP-A-62-215225, and JP-A-63-123009.

Further, in recent years, an image pickup device in which one pixel size is extremely small is being developed for the purpose of downsizing the image pickup device and photographing so-called high-definition images such as high-definition images. Generally, as the pixel size of the image pickup device becomes smaller, a high resolution is required for the taking lens, and thus the demand for improvement in optical performance is increasing more and more.

As a zoom lens satisfying such requirements, Japanese Patent Application Laid-Open No. 62-153913 and Japanese Patent Application Laid-Open No. 1-126 are known.
Conventional examples described in Japanese Patent Laid-Open No. 614 and JP-A-6-56453 are known.

[0008]

Generally, in order to obtain high optical performance, a method of achieving it by canceling out the aberrations generated on the respective refracting surfaces by positively and negatively canceling each other is adopted. However, in the case of a zoom lens, each state of zooming is taken. Since the way rays of light pass is greatly different, and therefore the way in which aberrations occur in each refracting surface also differs, it is very difficult to cancel out the aberrations occurring in each refracting surface for all focal lengths. In particular, in a zoom lens with a relatively simple zoom configuration, in order to reduce the overall length of the lens system, it becomes necessary to increase the refracting power of each lens group, so the aberrations that occur on each refracting surface also increase and the aberrations are canceled out. Matching is especially difficult.

In particular, in the four-group zoom lens of the type composed of the positive and negative positive and positive lens groups described above, the lens group having a negative refracting power is only the second lens group having a zooming effect, and the size is reduced. When the refracting power of the second lens group is strengthened, it becomes necessary to raise the refracting power of the third lens group or the fourth lens group, which makes it difficult to secure the back focus and difficult to obtain high optical performance.

Therefore, in order to achieve a zoom lens having an extremely high optical performance for capturing a high-definition image, the number of lenses is increased, and the light rays are refracted as little as many times as possible to form an image. It is conceivable to reduce the amount of aberration generated on the refracting surface or to complicate the zoom configuration to cancel each other out in a complicated manner, but in both cases, there is a drawback that the lens system becomes large.

The conventional examples described in the above-mentioned JP-A-62-178917, JP-A-62-215225 and JP-A-63-123009 have a relatively simple lens construction, and Although it has been extremely miniaturized, its optical performance is insufficient as a taking lens for taking in high-definition images such as high-definition images.
No. 13, JP-A-1-126614, and JP-A-6-564.
Although the conventional example described in each publication of No. 53 achieves extremely high optical performance, it is sufficiently small in size because it uses a large number of lenses and complicates the aberrations by complicating the zoom configuration. It is hard to say that it has achieved a perfect lens system.

Therefore, in order to achieve miniaturization while maintaining high optical performance, it is possible to select a zoom type that is advantageous for miniaturization without complicating the lens structure, but excessively increase the refractive power of the lens group. It is desirable to achieve miniaturization by devising the configuration without strengthening. Specifically, while taking the so-called positive / negative / positive / positive four-group zoom lens configuration described above, the configurations of the third lens group and the fourth lens group are rather devised without increasing the refracting power of the second lens group too much. This is very important.

The present invention provides a zoom lens in which the refractive power of the second lens group is kept excessively large and the third lens group and the fourth lens group have appropriate structures.

[0014]

In order to solve the above-mentioned problems, the zoom lens of the present invention has a first lens group having positive power in order from the object side, and a negative lens having a negative power on the optical axis during zooming. Of the second lens group having a function of monotonously moving the zoom lens to mainly share the zooming effect, the third lens group having a positive power, and having a positive power and moving back and forth during zooming to accompany zooming. A zoom lens that includes a fourth lens group that corrects fluctuations in image plane position, and performs focusing by moving the third lens group, the fourth lens group, or a part of these lens groups. Is a positive lens group composed of at least one positive lens in order from the object side, and a negative lens group composed of at least one negative lens, and the fourth lens group is composed of at least one negative lens in order from the object side. A negative lens group including a lens, and a positive lens group composed of at least one positive lens, the following condition (1), (2) is characterized by satisfying the (3).

(1) −0.80 <f _W / f ₂ <−0.55 (2) −0.70 <f ₄ / f _4N <−0.30 (3) 0.60 <f _4P / f ₄ <0.70 where f _W , f ₂ , f ₄ , f _4N , and f _4P are the focal length of the entire lens system at the wide-angle end, the focal length of the second lens group, the focal length of the fourth lens group, and the fourth lens group, respectively. It is the focal length of the negative lens group and the positive lens group which constitute the lens group.

The condition (1) defines the refracting power of the second lens group. If the value exceeds the upper limit of the condition (1) and has a large value, the negative refracting power of the second lens group becomes insufficient and Even if the configuration of the lens group is devised, it becomes difficult to reduce the size and secure the back focus. Further, if the value is smaller than the lower limit, it is advantageous for downsizing and securing the back focus, but the positive refracting power of the third lens group or the fourth lens group must also be strengthened, so that deterioration of various aberrations can be prevented. As a result, high optical performance cannot be maintained.

The third lens group consists of two positive lenses and a negative lens in order from the object side, and the fourth lens group consists of a negative lens and two positive lenses in order from the object side. The lens group has a function of forming an image of the divergent light flux from the second lens group, but the fourth lens group has a stronger refractive power than the third lens group in order to secure the back focus. At this time, the negative lens group and the positive lens group forming the fourth lens group are configured so as to satisfy the conditions (2) and (3) and have a small value exceeding the lower limit of the condition (2), or When the value is smaller than the lower limit of the condition (3), the fourth lens group has a strong retrofocus type refractive power distribution, which is advantageous for securing the back focus, but causes deterioration of spherical aberration or astigmatism. In addition, the fluctuation of light rays is large and the occurrence of high-order aberrations is large, which is not preferable. If the value exceeds the upper limit of the condition (2) or has a large value exceeding the upper limit of the condition (3), it becomes difficult to secure the back focus, and it becomes difficult to correct spherical aberration and coma. .

In the zoom lens of the present invention described above, the first lens group is configured to include, in order from the object side, a negative meniscus lens having a convex surface facing the object side and a positive lens group including at least one positive lens. It is preferable that the structure satisfy the following condition (4).

(4) 0.0 <1 / SF _1N <0.42 where SF _1N is the shaping factor SF of the negative meniscus lens of the first lens group.

Here, the shaping factor is represented by the following equation, where r _{a is} the radius of curvature of the object side surface of the single lens and r _b is the radius of curvature of the image side surface of the same single lens.

SF = (r _a + r _b ) / (r _a −r _b ) The condition (4) is a condition for defining the shape of the negative lens of the first lens group. Positive astigmatism at the end becomes large, and positive spherical aberration, negative coma, and positive astigmatism worsen at the telephoto end. If the value exceeds the lower limit and has a small value, the negative spherical aberration and the positive coma aberration at the telephoto end are deteriorated, which is not preferable.

In the zoom lens of the present invention, the second lens
In order from the object side of the lens group, a negative lens with the surface having the strong curvature facing the image side, a negative lens, and the following positive lens with the surface having the strongest curvature on the image side facing the object side. It is preferable that the lens group is composed of the arranged lesbian group and the following conditions (5) and (6) are satisfied.

(5) 0.65 <1 / SF _2N <1.80 (6) −1.00 <1 / SF _2P <−0.30 However, SF _2N is arranged on the most object side of the second lens group. The shaping factor of the negative lens, SF _2P, is the shaping factor of the positive lens arranged closest to the image side in the second lens group.

The condition (5) defines the shape of the negative lens closest to the object in the second lens group. If the value exceeds the upper limit and has a large value, the negative distortion and the positive astigmatism at the wide-angle end. Aberration becomes large, and spherical aberration and positive astigmatism worsen at the telephoto end. If the value is smaller than the lower limit, the positive astigmatism and the negative distortion at the wide-angle end and the positive spherical aberration and the negative astigmatism at the telephoto end are deteriorated, which is not preferable. The condition (6) defines the shape of the positive lens closest to the image side in the second lens group. If the value exceeds the upper limit and has a large value, the negative astigmatism at the wide-angle end becomes large, and the telephoto end becomes large. In, the negative spherical aberration becomes worse. If the value is smaller than the lower limit, the positive astigmatism at the wide-angle end and the positive spherical aberration at the telephoto end are deteriorated, which is not preferable.

[0025]

EXAMPLES Next, examples of the zoom lens of the present invention will be described. The first embodiment f = 9.111 ~25.460~71.784, F = 2.0 , 2ω = 50.05 ° ~18.29 ° ~6.42 ° r 1 = 73.7539 d 1 = 2.0000 n 1 = 1.81264 ν 1 = 25.43 r 2 = 45.5015 d 2 = 6.7348 n ₂ = 1.57098 ν ₂ ＝ 71.30 r ₃ ＝ 5906.5945 d ₃ = 0.1000 r ₄ ＝ 37.5124 d ₄ ＝ 4.7882 n ₃ ＝ 1.57098 ν ₃ ＝ 71.30 r ₅ ＝ 85.2972 d ₅ ＝ D ₁ (variable) r ₆ ＝ 92.0724 d ₆ = 1.2000 n ₄ = 1.60548 ν ₄ ＝ 60.70 r ₇ = 10.8422 d ₇ ＝ 6.7907 r ₈ ＝ −22.5869 d ₈ = 1.2000 n ₅ = 1.60548 ν ₅ ＝ 60.70 r ₉ ＝ 43.6931 d ₉ ＝ 0.1500 r ₁₀ ＝ 24.6146 d ₁₀ 5.0000 n ₆ = 1.84281 ν ₆ = 21.00 r ₁₁ = 85.1768 d ₁₁ = D ₂ (variable) r ₁₂ = ∞ (aperture) d ₁₂ = 1.0000 r ₁₃ = 121.6395 d ₁₃ = 2.5000 n ₇ = 1.60520 ν ₇ = 65.48 r _{14 = -40.0294 d 14 = 0.1500 r 15} = 19.9110 d 15 = 6.5000 n 8 = 1.60520 ν 8 = 65.48 r 16 = -249.2357 d 16 = 2.5770 r 17 = -42.6270 d 17 = 1.0000 n 9 = 1.85504 ν 9 = 23.78 r _{1 8 = 75.3501 d 18 = D 3} ( _{variable) r 19 = 35.5656 d 19 =} 6.5006 n 10 = 1.67158 ν 10 = 33.04 r 20 = 16.8551 d 20 = 1.3634 r 21 = 45.5948 d 21 = 2.5000 n 11 = 1.60520 ν 11 = _{65.48 r 22 = -34.5358 d 22 =} 0.8734 r 23 = 15.7466 d 23 = 6.5000 n 12 = 1.60520 ν 12 = 65.48 r 24 = 44.1299 d 24 = 2.0000 r 25 = ∞ d 25 = 5.0000 n 13 = 1.51825 ν 13 = 64.15 r ₂₆ = ∞ f 9.1114 25.4599 71.7835 D ₁ 1.5000 23.9493 38.8934 D ₂ 38.8934 16.4476 1.5000 D ₃ 6.3241 1.5942 2.5239 f _W / f ₂ = -0.648, f ₄ / f _4N = -0.480, f _4P / f ₄ = 0.651 1 / SF _1N = 0.237, 1 / SF _2N = 0.789, 1 / SF _2P = -0.552 1 / SF _4N = 0.357 where r ₁ , r ₂ , ... Are the radii of curvature of each lens surface, d
₁ , d ₂ , ... Is the thickness of each lens and the lens interval, n
₁ , n ₂ , ... Are the refractive indices of each lens at the e-line, ν ₁ , ν
₂ , ... are Abbe numbers of d-line of each lens.

The first embodiment has a structure as shown in FIG. 1, and in order from the object side, the first lens group having a positive refractive power and the negative lens having a negative refractive power and monotonically on the optical axis during zooming. A second lens group that moves to have a zooming effect, a third lens group that has a positive refractive power, and a function that has a positive refractive power and moves back and forth on the optical axis during zooming to correct the image plane position. And a fourth lens group having Further, the first lens group has, in order from the object side, a negative meniscus lens having a convex surface facing the object side and a surface having a strong curvature facing the object side.
The second lens group is composed of a single positive lens, and the second lens group has, in order from the object side, a negative lens having a surface having a strong curvature facing the image side, a negative lens, and a positive lens having a surface having a strong curvature facing the object side. Consists of. This second lens group maintains the refractive power so as to satisfy the above condition (1).

The third lens group consists of two positive lenses and a negative lens in order from the object side, and the fourth lens group consists of a negative lens and two positive lenses in order from the object side. The lens group has a function of forming an image of the divergent light flux from the second lens group, but the fourth lens group has a stronger refractive power than the third lens group in order to secure the back focus. At this time, the negative lens group and the positive lens group forming the fourth lens group are configured to satisfy the conditions (2) and (3).

The negative lens closest to the object in the first lens group of the first embodiment satisfies the condition (4).

The negative lens closest to the object side and the positive lens closest to the image side of the second lens group satisfy the above conditions (5) and (6), respectively.

Further, in order to keep the optical performance of the zoom lens of the present invention high, the following condition (1) 'is used instead of the condition (1), or the following condition (2)' is used instead of the condition (2). Alternatively, it is desirable to satisfy the following condition (3) ′ instead of the condition (3).

(1) ′ −0.75 <f _W / f ₂ <−0.63 (2) ′ −0.65 <f ₄ / f _4N <−0.40 (3) ′ 0.62 <f _4P / f ₄ <0.68 As described above, the negative lens closest to the object in the first lens group is configured to satisfy the condition (4), but in order to maintain higher optical performance, It is desirable to satisfy the following condition (4) 'instead of this condition (4).

(4) '0.2 <1 / SF _1N <0.3 Further, the negative lens closest to the object side and the positive lens closest to the image side of the second lens group satisfy the conditions (5) and (6), respectively. Satisfaction, but condition (5) to maintain higher optical performance
It is desirable that the following condition (5) ′ is satisfied instead of the above condition, or the following condition (6) ′ is satisfied instead of the condition (6).

(5) ′ 0.65 <SF _2N <1.30 (6) ′ −0.80 <1 / SF _2P <−0.40 Further, in the zoom lens of the present invention, the most object of the fourth lens group. It is desirable that the negative lens on the side satisfy the following condition (7).

(7) 0.20 <1 / SF _4N <1.00 where SF _4N is the shaping factor of the negative lens closest to the object in the fourth lens group.

The condition (7) defines the shape of the negative lens closest to the object in the fourth lens unit. If the value exceeds the upper limit and has a large value, negative astigmatism from the wide-angle end to the telephoto end will occur. If the value becomes large and exceeds the lower limit and has a small value, the positive spherical aberration and the positive astigmatism from the wide-angle end to the telephoto end deteriorate, which is not preferable.

In order to maintain higher optical performance, it is desirable to satisfy the following condition (7) 'instead of the condition (7).

(7) '0.30 <1 / SF _4N <0.
60 second embodiment f = 9.126 ~25.454~71.982, F = 2.0 , 2ω = 49.84 ° ~17.95 ° ~6.25 ° r 1 = 69.7910 d 1 = 2.0000 n 1 = 1.81264 ν 1 = 25.43 r 2 = 41.0696 d 2 = 7.8005 n ₂ = 1.57098 ν ₂ ＝ 71.30 r ₃ ＝ -402.1761 d ₃ ＝ 0.1000 r ₄ ＝ 33.8895 d ₄ ＝ 5.3665 n ₃ ＝ 1.57098 ν ₃ ＝ 71.30 r ₅ ＝ 119.1882 d ₅ ＝ D ₁ (variable) r ₆ ＝ 308.9133 _{d 6 = 1.2000 n 4 = 1.73234} ν 4 = 54.68 r 7 = 11.4798 d 7 = 4.9238 r 8 = -18.1393 d 8 = 1.2000 n 5 = 1.51905 ν 5 = 69.56 r 9 = 34.2351 d 9 = 0.1500 r 10 = 23.8419 d ₁₀ = 2.5000 n ₆ = 1.84281 ν ₆ = 21.00 r ₁₁ = 103.2619 d ₁₁ = D ₂ (variable) r ₁₂ = ∞ (aperture) d ₁₂ = 1.0000 r ₁₃ = 431.8399 d ₁₃ = 1.5000 n ₇ = 1.67279 ν ₇ = 57.33 _{r 14 = -50.3196 d 14 = 0.1500} r 15 = 18.6805 d 15 = 9.8589 n 8 = 1.43985 ν 8 = 94.97 r 16 = 847.0418 d 16 = 3.1334 r 17 = -25.0553 d 17 = 1.5000 n 9 = 1.85504 ν 9 = 2 3.78 r ₁₈ = -41.4964 d ₁₈ = D ₃ (variable) r ₁₉ = 48.2049 d ₁₉ = 1.5000 n ₁₀ = 1.81675 ν ₁₀ = 22.62 r ₂₀ = 19.1868 d ₂₀ = 1.7705 r ₂₁ = 61.5311 d ₂₁ = 2.5000 n ₁₁ = 1.67279 v ₁₁ = 57.33 r ₂₂ = -49.5960 d ₂₂ = 0.1500 r ₂₃ = 17.4781 d ₂₃ = 12.5000 n ₁₂ = 1.69979 v ₁₂ = 55.52 r ₂₄ = 221.9526 d ₂₄ = 2.0000 r ₂₅ = ∞ d ₂₅ = 5.0000 n ₁₃ = 1.51825 v ₁₃ = 64.15 r ₂₆ = ∞ f 9.1259 25.4540 71.9821 D ₁ 1.5000 19.9170 30.5474 D ₂ 30.5474 12.1320 1.5000 D ₃ 9.6562 6.2532 10.3792 D ₃ '9.5677 5.6562 6.2060 f _W / f ₂ = -0.751, f ₄ / f _4N = -0.622, f _4P / f ₄ = 0.650 1 / SF _1N = 0.259, 1 / SF _2N = 0.928, 1 / SF _2P = -0.625 1 / SF _4N = 0.431 This second embodiment is as shown in FIG. Focusing is performed by adopting the same configuration as in the above example and further moving the fourth lens unit to the object side. Therefore, the third lens group and the fourth lens group are spaced apart to make it difficult to secure the back focus by weakening the refractive power of the third lens group and increasing the refractive power of the fourth lens group. In the data, D ₃ 'is the distance between the third lens group and the fourth lens group when focusing on an object of 1 m.

Since focusing is performed by using a lens group that corrects the fluctuation of the image plane during zooming as in this embodiment, a large fluctuation of the image plane occurs during focusing unless astigmatism is corrected. Therefore, in the present embodiment, the central thickness d satisfies the following condition (8) in order to suppress deterioration of astigmatism during focusing in the fourth lens unit, generally in the lens unit for focusing. It is desirable to arrange at least one positive lens.

(8) 0.7 <d / f _W <2.0

If all the positive lenses of the focusing lens group have a small value below the lower limit of the condition (8), it becomes difficult to correct astigmatism, and the remaining astigmatism causes
The image plane fluctuates greatly during zooming or focusing, which is not preferable. Further, if all the positive lenses in the focusing lens group have a large value exceeding the upper limit, it becomes difficult to process the lens and the weight of the movable group increases, so that a driving force is required, which is not preferable.

In particular, in order to suppress the generation of astigmatism, it is desirable to satisfy the following condition (8) 'instead of the condition (8).

(8) ′ 1.0 <d / f _W <2.0 In this example as well, by satisfying each condition, high optical performance is maintained, and aberration fluctuation during focusing is kept small. This can be seen from the aberration diagram shown in FIG.

In each embodiment, the flat glass disposed on the image side of the lens system is a low-pass filter for protecting the image pickup surface of the solid-state image pickup device, a low-pass filter for preventing moire when photographing with an electronic image pickup device, and an infrared cutoff. Represents a filter, etc.

In addition to the focusing method using the fourth lens group shown in the embodiment, a focusing method using the third lens group, or the third lens group or the fourth lens group is used.
It is clear that the present invention is also effective in the focusing method using a part of the lens group.

In the present invention, in addition to the zoom lens described in each of the claims, the zoom lens described in each of the following items also achieves the object of the present invention.

(1) In the lens system described in claim 1, claim 2 or claim 3, the negative lens closest to the object side in the fourth lens group satisfies the following condition (7): And a zoom lens. (7) 0.20 <1 / SF _4N <1.00

(2) Focusing is performed by moving the fourth lens group to the object side in the lens system described in claims 1, 2 or 3 of the claims or in (1). A zoom lens characterized in that the positive lens in the fourth lens group satisfies the following condition (8). (8) 0.7 <d / f _W <2.0

(3) A zoom lens according to any one of claims 1, 2, 3, (1), or (2), which satisfies the following condition. (1) ′ −0.75 <f _W / f ₂ <−0.63

(4) Claims 1, 2, 3, (1), (2)
Alternatively, in (3), a zoom lens characterized by satisfying the following condition. (2) ′ −0.65 <f ₄ / f _4N <−0.40

(5) Claims 1, 2, 3, (1),
(2), (3), or (4), the zoom lens characterized by satisfying the following conditions. (3) '0.62 <f _4P / f ₄ <0.68

(6) Claims 1, 2, 3, (1),
In (2), (3), (4) or (5), the first lens group comprises, in order from the object side, a negative meniscus lens having a convex surface directed toward the object side and at least one positive lens.
A zoom lens characterized by satisfying the following conditions. (4) '0.2 <1 / SF _1N <0.3

(7) Claims 1, 2, 3, (1),
In (2), (3), (4), (5), or (6), the second lens group has, in order from the object side, a negative lens whose surface having a strong curvature faces the image side, and a negative lens. And a lens group that is arranged subsequent to the lens group having a positive lens with the surface having the strongest curvature on the image side facing the object side, and which satisfies the following conditions. (5) ′ 0.65 <1 / SF _2N <1.30 (6) ′ −0.80 <1 / SF _2P <−0.40

(8) Claims 1, 2, 3, (1),
(2), (3), (4), (5), (6) or (7)
2. A zoom lens, wherein the fourth lens group is moved toward the object side for focusing to a short distance, and the fourth lens group includes a positive lens satisfying the following condition. (8) '1.0 <d / f _W <2.0

[0054]

INDUSTRIAL APPLICABILITY According to the present invention, it is suitable for a video camera or a still video camera, and particularly for an electronic camera using an image pickup device having a large number of pixels, which is suitable for use in capturing recent high-definition images and has a simple structure. Moreover, a compact zoom lens can be realized.

[Brief description of the drawings]

FIG. 1 is a sectional view of a first embodiment of the present invention.

FIG. 2 is a sectional view of a second embodiment of the present invention.

FIG. 3 is an aberration curve diagram at the wide-angle end according to Example 1 of the present invention.

FIG. 4 is an aberration curve diagram at an intermediate focal length according to the first embodiment of the present invention.

FIG. 5 is an aberration curve diagram of Example 1 of the present invention at the telephoto end.

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

FIG. 7 is an aberration curve diagram for Example 2 of the present invention at an intermediate focal length.

FIG. 8 is an aberration curve diagram for Example 2 of the present invention at the telephoto end.

FIG. 9 is an object point distance 1 at the telephoto end according to the second embodiment of the present invention.
Aberration curve diagram of m

Claims (3)

[Claims] 1. A first lens group having a positive power in order from the object side, and a second lens having a negative power and having a function of monotonically moving along the optical axis during zooming to mainly share a zooming effect. A third lens group having a positive power, and a fourth lens group having a positive power and moving back and forth during zooming to correct a change in image plane position due to zooming.
In a zoom lens for focusing by moving the lens group or the fourth lens group, or a part of them, the third lens group includes a positive lens group including at least one positive lens in order from the object side. A negative lens group including at least one negative lens, wherein the fourth lens group includes, in order from the object side, a negative lens group including at least one negative lens, and a positive lens group including at least one positive lens. The zoom lens is characterized by satisfying the following conditions. _{(1) -0.80 <f W /} f 2 <-0.55 (2) -0.70 <f 4 / f 4N <-0.30 (3) 0.60 <f 4P / f 4 <0 .70 where f _W , f ₂ , f ₄ , f _4N , and f _4P are the focal length of the entire lens system at the wide-angle end, the focal length of the second lens group, the focal length of the fourth lens group, and the fourth lens group, respectively. It is the composite focal length of the negative lens group that constitutes it and the composite focal length of the positive lens group that constitutes the fourth lens group. 2. The first lens group includes, in order from the object side, a negative meniscus lens having a convex surface facing the object side and a positive lens group including at least one positive lens, and the following condition (4) is satisfied. The zoom lens according to claim 1, wherein (4) 0.0 <1 / SF _1N <0.42 However, SF _1N is a shaping factor of the negative meniscus lens arranged closest to the object side in the first lens group. Here, the shaping factor is the object side of the single lens,
When the radii of curvature of the image-side surface are r _a and r _b , respectively,
It refers to SF represented by the following formula. SF = (r _a + r _b ) / (r _a −r _b ) 3. A negative lens and a negative lens in which the surface of the second lens group having a strong curvature in order from the object side is directed to the image side,
And a lens group in which a positive lens having a surface having the strongest curvature on the image side toward the object side is arranged, and the following conditions (5) and (6) are satisfied. Item 1 zoom lens. (5) 0.65 <1 / SF _2N <1.80 (6) −1.00 <1 / SF _2P <−0.30 However, SF _2N and SF _2P are located on the most object side of the second lens group, respectively. It is the shaping factor of the negative lens and the positive lens located closest to the image side.