JPH06317750A - Rear focus type zoom lens - Google Patents

Abstract

PURPOSE:To miniaturize the whole lens system, to make the photo-graphying viewing angle of a wide-angle end a wide angle and to obtain a large variable power ratio by moving four lens groups, performing power variation and focusing and specifying the ratio of the focal lengths of a third group and a fourth group. CONSTITUTION:At the time of varying a power from a wide-angle end to a telescopic end, a second group L2 is monotonously moved to the side of an image plane, a diaphragm SP and a third group L3 are integrally moved to the object side so as to have a projected locus and a fourth group L4 is moved to the object side so as to have a projected locus independently of each other. By representing thefocal length of an ith group by Fi, the zoom lens is composed so as to satisfy the condition shown by 2.5<F3/F4. This condition is related to the ratio of the focal lengths F3, F4 of the third and the fourth groups L3, L4 and is useful for making a back-focus sufficiently long and maintaining good optical characteristic while attainig the compact system from a diaphragm SP on.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear focus type zoom lens, and more particularly to a photographic camera, a video camera,
Further, the present invention relates to a rear focus type zoom lens having a wide field angle of 65 degrees or more at a wide angle end used for a broadcasting camera and the like, and having a high zoom ratio of 10 to 13 and a long back focus. Is.

[0002]

2. Description of the Related Art Recently, in a photographic camera for 35 mm film, a home video camera, etc., the zoom lens used for the photographic camera has a predetermined zoom ratio and a wide angle of view because the size and weight of the camera are reduced. In addition, it is required that the entire lens system having a short overall lens length and a small front lens diameter is compact and lightweight.

As a zoom lens satisfying these demands relatively well, there is a rear focus type zoom lens which moves by moving a lens unit other than the first lens unit on the object side.

Generally, in a rear focus type zoom lens, the effective diameter of the first group is smaller than that of a front lens focus type zoom lens in which the first group is moved to perform focusing, and it is easy to downsize the entire lens system. And close-up photography,
In particular, extremely close-up photography becomes easy, and since the relatively small and lightweight lens group is moved, the driving force of the lens group is small and quick focusing is possible.

As such a rear focus type zoom lens, for example, in JP-A-62-247316 and JP-A-62-24213, the first group having a positive refractive power and the negative refractive power are arranged in order from the object side. It has four lens groups, a second lens group of power, a third lens group of positive refractive power, and a fourth lens group of positive refractive power, and moves the second lens group to perform zooming and move the fourth lens group. Then, the correction of the image plane variation due to the magnification change and the focusing are performed.

In Japanese Patent Laid-Open No. 58-160913, the first group having a positive refractive power and the second group having a negative refractive power are arranged in this order from the object side.
An image associated with zooming, which has four lens groups, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power, and moving the first lens group and the second lens group for zooming. The surface variation is corrected by moving the fourth group. Then, one or two or more lens groups of these lens groups are moved to perform focusing.

Further, in JP-A-57-111507,
It has a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power for performing fixed focusing during zooming. The second lens group and the third lens The zoom lens has a so-called positive, negative, positive, and positive refracting power group, in which the group moves in opposite directions during zooming, and the third lens group has two positive lens groups, each of which moves separately. Is proposed. In this publication, the aperture stop (aperture stop) is positioned in the third lens group.

However, in this structure, since the second lens group and the third lens group move in opposite directions, it is necessary to widen the distance between the second lens group and the third lens group at the wide-angle end, and the diaphragm is the third.
Since it is in the lens group, the entrance pupil position at the wide-angle end is closest to the image plane side, which is not suitable for downsizing the front lens diameter and the entire system.

Since the first lens group is used for focusing, the diameter of the front lens is increased in order to secure the light flux to the peripheral field angle at a close range, and this is changed to the rear focus method for downsizing. When trying to adapt, there are problems that the refractive power arrangement is not optimal, and that focus aberration fluctuations due to rear focusing are not sufficiently corrected.

Further, in Japanese Patent Laid-Open No. 3-200113, the same construction is used. During zooming in order from the object side, the first positive lens group is fixed, the second negative lens group is moved forward and backward for zooming, and Proposal of a zoom lens including a positive third lens group that moves in relation to the movement of the two lens groups and a positive fourth lens group that partially or wholly corrects the focal position due to zooming There is.

According to the publication, the movement of the positive third lens group, which moves in association with the movement of the second lens group, is performed in order to reduce the image plane movement correction amount performed by the fourth lens group. , A movement for allowing the third lens group to share a part of the correction function. Specifically, it is desirable to move from the image side to the object side from the intermediate focal length to the telephoto end.

However, in this configuration, since the second lens group and the third lens group move in opposite directions, it is necessary to widen the distance between the second and third lens groups on the wide-angle side, and the entrance pupil position at the wide-angle end becomes large. It will be closest to the image side, and the front lens diameter
There was a problem that miniaturization of the entire system was difficult.

Similarly, in JP-A-3-158813, a positive first lens group, a negative second lens group, a positive third lens group, and a positive fourth lens group are arranged in this order from the object side. Discloses a zoom lens in which the second lens group and the third lens group are moved along the optical axis to change the magnification, and the aperture stop is moved integrally with the third lens group.

According to the publication, the distance between the second lens group and the third lens group decreases with zooming from the wide-angle end to the telephoto end. Further, the third lens group having an aperture stop is located closest to the image side at the wide-angle end, and at the wide-angle end at which the front lens diameter becomes the largest or at a position slightly zoomed from the wide-angle end, the vicinity of the third lens group having the stop is Since it is located closest to the image side and the entrance pupil position is recessed, it is disadvantageous for reducing the front lens diameter, and the distortion at the wide-angle end is large. There was a problem that it was difficult to downsize.

Further, the applicant of the present invention discloses in Japanese Patent Laid-Open No. 3-215810 that the first group having a positive refractive power, the second group having a negative refractive power, the diaphragm, and the third group having a positive refractive power are arranged in this order from the object side. , And a fourth lens unit of the fourth lens unit having a positive refractive power, when the magnification is changed from the wide-angle end to the telephoto end, the second unit is moved to the image plane side and the stop, A rear-focus type zoom lens in which the third group and the fourth group are independently moved so as to have a convex locus on the object side, and the fourth group is moved when focusing is performed. is suggesting.

[0016]

Generally, when the rear focus system is adopted in the zoom lens, the entire lens system is downsized as described above, quick focusing is possible, and further close-up photography is facilitated. To be

On the other hand, however, the aberration variation at the time of focusing becomes large, and it becomes very difficult to obtain high optical performance while miniaturizing the entire lens system over the entire object distance from an infinite object to a short-distance object. The problem arises.

At present, a single-panel type is mainly used for consumer video cameras, and a multi-panel type is mainly used for commercial video cameras.

A multi-plate type video camera uses a color separation prism as a color separation system. For this reason, it is necessary for the zoom lens for a multi-plate video camera to have a long back focus enough to secure the optical path length of the color separation prism. However, simply increasing the back focus causes a problem that the entire lens system becomes large.

The present invention, while adopting the rear focus system, achieves a good overall aperture distance from the wide-angle end to the telephoto end while attaining a large aperture ratio and a high zoom ratio, while making the entire lens system compact. It is an object of the present invention to provide a rear focus type zoom lens having optical performance and a simple structure with long back focus.

[0021]

A rear focus type zoom lens according to the present invention comprises a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, and a positive lens unit having a positive refractive power in order from the object side. The zoom lens system has four lens units, a third lens unit and a fourth lens unit having a positive refracting power, and moves the second lens unit toward the image plane side and the aperture stop during zooming from the wide-angle end to the telephoto end. And the third group are integrally moved so as to have a convex locus on the object side, and
When the lens unit is moved so as to have a convex locus on the object side and the fourth lens unit is moved during focusing, and the focal length of the i-th lens unit is Fi, then 2.5 <F3 / F4 ... (1) is characterized by satisfying the condition.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIGS.
5 to 5 are sectional views of the lens at the wide-angle end, and FIGS. 6 to 15 are various aberration diagrams of Numerical Examples 1 to 5 to be described later of the present invention.

In the figure, L1 is the first group of positive refractive power, L2 is the second group of negative refractive power, L3 is the third group of positive refractive power, L4.
Is the fourth group of positive refractive power. SP is an aperture stop,
It is placed in front of the third group. G is a color separation prism, a face plate, and a glass block such as a filter, and IP is an image plane.

In this embodiment, during zooming from the wide-angle end to the telephoto end, the second lens unit is monotonically moved to the image side as indicated by the arrow, and the aperture stop SP and the third lens unit are integrally projected toward the object side. The fourth group is moved independently of each other so as to have a convex locus on the object side.

In this embodiment, by adopting such a zoom type, it is possible to easily widen the shooting angle of view to about 70 degrees at the wide angle end while ensuring a predetermined back focus and to cover the entire zoom range. Good optical performance is obtained. Also, a rear focus type is adopted in which the fourth group is moved on the optical axis for focusing.

The solid curve 4a and the dotted curve 4b of the fourth group shown in the same figure are images at the time of zooming from the wide-angle end to the telephoto end when focusing on an object at infinity and a near object, respectively. The movement locus for correcting the surface variation is shown. The first
The group is fixed during zooming and focusing.

In the present embodiment, the fourth lens unit is moved for zooming, and the fourth lens unit is moved for focusing.

In particular, as shown by the curves 4a and 4b in the figure, the zoom lens is moved so as to have a convex locus toward the object side during zooming from the wide-angle end to the telephoto end. As a result, the third group and the fourth group
By effectively utilizing the space with the group, the overall length of the lens is effectively shortened.

In the present embodiment, for example, when focusing on an object at infinity from a near object at the telephoto end,
This is performed by repeating the fourth group forward as indicated by a straight line 4c in the figure.

As described above, in the present embodiment, the focusing is performed by using the fourth lens group to move the first lens group to perform the focusing. Compared to the so-called front lens focusing method, the screen at the time of shooting a close-up object on the wide angle side is used. The effective diameter of the front lens group (first group) is reduced by facilitating the securing of the luminous flux in the periphery.

The aperture stop SP is arranged between the second and third lens units, and when zooming, it is moved integrally with the third lens unit as described above, so that fluctuations in aberrations due to zooming are reduced. By shortening the distance between the lens groups in front of the aperture stop, the effective lens diameter of the first lens group (front lens group) can be easily reduced.

Further, the refractive powers of the third and fourth groups are made to satisfy the conditional expression (1), whereby the size of the entire lens system is reduced, a predetermined back focus is secured, and the magnification is changed. This makes it easy to correct the aberration variation due to.

Conditional expression (1) relates to the ratio of the focal lengths of the third lens unit and the fourth lens unit, and in order to maintain a good optical performance by sufficiently lengthening the back focus while achieving compactness after the stop. belongs to. If the lower limit of conditional expression (1) is exceeded and the focal length of the third lens unit becomes short, it becomes difficult to correct the variation of spherical aberration due to zooming or focusing. In addition, it is difficult to secure a sufficient back focus, and the amount of movement of the fourth lens unit due to zooming and focusing becomes large, which causes problems such as large variation in aberration due to zooming and focusing. Absent.

In the present invention, it is preferable to satisfy at least one of the following conditions in order to secure high optical performance over the entire screen while further downsizing the entire lens system.

(1-1) When the focal length of the entire system at the wide-angle end is Fw, the condition of -0.70 <Fw / F2 <-0.4 (2) should be satisfied.

Conditional expression (2) relates to the ratio between the focal length of the entire system and the focal length of the second lens unit at the wide-angle end. When the upper limit of conditional expression (2) is exceeded and the focal length of the second lens unit becomes short, the Petzval sum becomes large in the under direction, and it becomes difficult to correct aberrations such as image plane tilt. Conversely, if the lower limit is exceeded, the second
If the focal length of the lens unit becomes long, the amount of movement of the second lens unit due to zooming increases and the front lens diameter becomes too large.

(1-2) It is preferable that the emitted light of the on-axis light flux emitted from the third lens unit is substantially afocal or weakly divergent light. According to this, the back focus and the exit pupil can be effectively lengthened while suppressing the aberration variation during zooming or focusing as much as possible.

(1-3) In the zoom type according to the present invention, for example, if the diaphragm is located between the third group and the fourth group, the entrance pupil will be at a deep position (recessed position) from the first group. First
The height of incidence of the off-axis light beam on the group is highest at the intermediate zoom position near the wide-angle end.

Therefore, in the present invention, an aperture stop is arranged on the object side of the third lens unit, or in the third lens unit, and when the zooming from the wide-angle end to the telephoto end is performed, a convex shape is formed integrally with the third lens unit on the object side. The zoom lens is moved so that it has a locus so that the entrance pupil is closer to the first group and the zoom position with the highest entrance height is near the wide-angle end. Is efficiently reduced.

In the present invention, the diaphragm and the third lens group are caused to reciprocate almost completely on the object side in a convex locus, so that the front lens diameter can be easily reduced and the angle of view can be widened.

Next, other features of the lens structure of the zoom lens of the present invention will be described.

(1-4) When miniaturizing the entire system, it is preferable to satisfy the following conditions.

3.5 <Bfw / Fw <6.0 (3) Here, Bfw is the back focus when the object distance is infinity at the wide-angle end (glass block, filter, etc., in which “G” in the examples is used). Except).

This formula (3) is a formula necessary for effectively miniaturizing the entire system. If the lower limit value is exceeded, not only is it impossible to insert blocks such as filters and color separation prisms, The exit pupil becomes short, and when the present invention is applied to, for example, a video camera, the image formation on the image pickup element deviates from the telecentric system. If the upper limit is exceeded, the size will increase.

(1-5) In order to make the front lens diameter small, it is preferable to satisfy the following formula.

6.0 <F1 / Fw <15.0 (4) This equation relates to the object point for the second group, that is, the magnification. In order to set the whole system to be small, it is preferable that the second group sandwiches the same magnification during zooming. If the same magnification is sandwiched, the locus of zooming of the fourth lens group becomes a substantially reciprocating movement, and it becomes possible to achieve high magnification variation with the most effective space efficiency.

Specifically, if the upper limit of the equation (4) is exceeded, the object point with respect to the second lens unit will become far away, and the image forming magnification of the second lens unit will decrease, making effective miniaturization difficult.

Further, the distance between the first group and the second group becomes large,
Achieving miniaturization becomes difficult. If the lower limit is exceeded, the second
The magnification of the group becomes large and it becomes difficult to achieve high multiplication.

(1-6) Principal point interval e1 between the first group and the second group
One of the important points in widening the angle is how small the angle can be made at the wide-angle end. For that purpose, the shape of the first group is preferably specifically as follows.

A meniscus negative lens L11 having a convex surface on the object side in the order from the object side of the first lens group, a positive lens L12 having a convex surface on the object side with an air gap, and a positive lens L13 having a convex surface on the object side. The negative lens L
11. The air lens composed of the positive lens L12 has a negative refracting power.

With this arrangement, the image-side principal point of the first lens unit is set closer to the second lens unit, the principal point distance e1 between the first lens unit and the second lens unit at the wide-angle end can be shortened, and the wide angle can be increased. Is effective for.

(1-7) Principal point interval e1 in the second group
It is desirable for widening the angle that the object-side principal point of the second lens unit is set to the object side in order to shorten at the wide-angle end.

Specifically, in order from the object side of the second lens group, the negative meniscus lens L21 having a convex surface on the object side, the biconcave negative lens L21, and the positive lens L23 with an air gap therebetween are arranged in this order. . This air gap causes the object-side principal point of the second lens group to be closer to the first lens group, and the principal point distance e1 on the wide-angle side can be easily shortened, which is effective for widening the angle.

(1-8) When the amount of movement of the diaphragm and the third lens group becomes large, the zoom variation of spherical aberration becomes large especially in the intermediate region of zooming, and the spherical aberration tends to be overcorrected. To remove this, it is preferable to introduce at least one aspherical surface into the third group. The specific shape of the aspherical surface is preferably such that the positive refracting power becomes weaker or the negative refracting power becomes stronger toward the periphery of the lens.

It is preferable to provide an aspherical surface on at least one lens surface of the fourth lens group, because coma aberration can be corrected well.

Next, numerical examples of the present invention will be shown. In the numerical examples, Ri is the radius of curvature of the i-th lens surface in order from the object side, Di is the i-th lens thickness and air gap from the object side, and Ni and νi are respectively from the object side of the i-th lens. The refractive index of glass and the Abbe number.

In the numerical examples, the final three lens surfaces are glass blocks such as color separation prisms, face plates and filters. Table 1 shows the relationship between the above-mentioned conditional expressions and various numerical values in the numerical examples. The aspherical shape has an X axis in the optical axis direction, an H axis in the direction perpendicular to the optical axis, a positive traveling direction of light, R is a paraxial radius of curvature, K, A, B, C, D, E
When each is an aspherical coefficient,

[0058]

[Equation 1] It is expressed by the formula.

Numerical Embodiment 1 F = 1 to 12.65 Fno = 1: 1.6 to 1.9 2 ω = 66.2 ° to 5.9 ° R 1 = 35.931 D 1 = 0.391 N 1 = 1.80518 ν 1 = 25.4 R 2 = 8.393 D 2 = 0.342 R 3 = 12.050 D 3 = 1.239 N 2 = 1.69680 ν 2 = 55.5 R 4 = -36.035 D 4 = 0.043 R 5 = 6.370 D 5 = 1.043 N 3 = 1.69680 ν 3 = 55.5 R 6 = 58.643 D 6 = Variable R 7 = 9.634 D 7 = 0.173 N 4 = 1.88 300 ν 4 = 40.8 R 8 = 1.857 D 8 = 0.844 R 9 = -3.185 D 9 = 0.152 N 5 = 1.69680 ν 5 = 55.5 R10 = 3.140 D10 = 0.217 R11 = 3.696 D11 = 0.500 N 6 = 1.84666 ν 6 = 23.8 R12 = -21.979 D12 = Variable R13 = (Aperture) D13 = 0.326 R14 = -31.104 D14 = 0.152 N 7 = 1.60311 ν 7 = 60.7 R15 = 4.653 D15 = 0.264 R16 = -9.342 D16 = 0.434 N 8 = 1.60342 ν 8 = 38.0 R17 = -4.597 D17 = 0.652 R18 = 4.592 D18 = 0.239 N 9 = 1.60342 ν 9 = 38.0 R19 = -2.721 D19 = 0.195 N10 = 1.78590 ν10 = 44.2 R20 =- 51.472 D20 = Variable R21 = 47.709 D21 = 0.652 N11 = 1.51633 ν11 = 64.2 R22 = -4.925 D22 = 0.032 R23 = 11.157 D23 = 0.195 N12 = 1.80518 ν12 = 25.4 R24 = 2.984 D24 = 1.130 N13 = 1.48749 ν13 = 70.2 R25 =- 23.396 D25 = 0.032 R26 = 5.008 D26 = 0.739 N14 = 1 .48749 ν14 = 70.2 R27 = -15.870 D27 = 0.869 R28 = ∞ D28 = 0.543 N15 = 1.51633 ν15 = 64.2 R29 = ∞ D29 = 4.347 N16 = 1.60342 ν16 = 38.0 R30 = ∞

[0060]

[Table 1] <Numerical Example 2> F = 1 to 12.65 Fno = 1: 1.8 to 1.9 2 ω = 66.2 ° to 5.9 ° R 1 = 35.975 D 1 = 0.391 N 1 = 1.80518 ν 1 = 25.4 R 2 = 8.396 D 2 = 0.272 R 3 = 11.644 D 3 = 1.130 N 2 = 1.69680 ν 2 = 55.5 R 4 = -37.605 D 4 = 0.043 R 5 = 6.400 D 5 = 1.195 N 3 = 1.69680 ν 3 = 55.5 R 6 = 60.254 D 6 = Variable R 7 = 8.615 D 7 = 0.173 N 4 = 1.88300 ν 4 = 40.8 R 8 = 1.785 D 8 = 0.823 R 9 = -3.019 D 9 = 0.152 N 5 = 1.69680 ν 5 = 55.5 R10 = 3.112 D10 = 0.217 R11 = 3.676 D11 = 0.500 N 6 = 1.84666 ν 6 = 23.8 R12 = -16.603 D12 = Variable R13 = (Aperture) D13 = 1.413 R14 = 5.119 D14 = 1.043 N 7 = 1.60342 ν 7 = 38.0 R15 = -3.506 D15 = 0.195 N 8 = 1.88300 ν 8 = 40.8 R16 = -46.563 D16 = Variable R17 = 58.011 D17 = 0.434 N 9 = 1.51633 ν 9 = 64.2 R18 = -5.449 D18 = 0.032 R19 = 7.785 D19 = 0.195 N10 = 1.80518 ν10 = 25.4 R20 = 2.794 D20 = 0.869 N11 = 1.48749 ν11 = 70.2 R21 = -14.358 D21 = 0.032 R22 = 3.399 D22 = 0.434 N12 = 1.48749 ν12 = 70.2 R23 = 23.023 D23 = 0.869 R24 = ∞ D24 = 0.543 N13 = 1.51633 ν13 = 64.2 R25 = ∞ D25 = 3.260 N14 = 1.60342 ν14 = 38.0 R26 = ∞

[0061]

[Table 2] Aspherical surface R14 surface K = 2.597 × 10 ⁻² A = −9.137 × 10 ⁻⁴ B = 1.986 × 10 ⁻⁴ C = −1.129 × 10 ⁻⁴ D = −1.168 × 10 ⁻⁵ <Numerical example 3> F = 1 to 12.65 Fno = 1: 1.8 to 1.9 2 ω = 66.2 ° to 5.9 ° R 1 = 36.928 D 1 = 0.391 N 1 = 1.80518 ν 1 = 25.4 R 2 = 8.368 D 2 = 0.312 R 3 = 11.877 D 3 = 1.130 N 2 = 1.69680 ν 2 = 55.5 R 4 = -36.615 D 4 = 0.043 R 5 = 6.411 D 5 = 1.195 N 3 = 1.69680 ν 3 = 55.5 R 6 = 66.685 D 6 = variable R 7 = 9.469 D 7 = 0.173 N 4 = 1.88300 ν 4 = 40.8 R 8 = 1.788 D 8 = 0.820 R 9 = -3.019 D 9 = 0.152 N 5 = 1.69680 ν 5 = 55.5 R10 = 3.123 D10 = 0.217 R11 = 3.695 D11 = 0.500 N 6 = 1.84666 ν 6 = 23.8 R12 = -14.962 D12 = Variable R13 = (Aperture) D13 = 1.413 R14 = 5.247 D14 = 0.652 N 7 = 1.60342 ν 7 = 38.0 R15 = 17.260 D15 = Variable R16 = -13.719 D16 = 0.434 N 8 = 1.51633 ν 8 = 64.2 R17 = -5.243 D17 = 0.032 R18 = 7.556 D18 = 0.195 N 9 = 1.80518 ν 9 = 25.4 R19 = 2.779 D19 = 0.869 N10 = 1.48749 ν10 = 70.2 R20 = -23.427 D20 = 0.032 R21 = 3.644 D21 = 0.434 N11 = 1.48749 ν11 = 70.2 R22 = -16.329 D22 = 0.869 R23 = ∞ D23 = 0.543 N12 = 1.51633 ν12 = 64.2 R24 = ∞ D24 = 3.260 N13 = 1.60342 ν13 = 38.0 R25 = ∞

[0062]

[Table 3] Aspherical surface R14 surface K = -2.612 × 10 ^-1 A = -2.388 × 10 ^-3 B = 2.364 × 10 ^-4 C = -6.451 × 10 ^-5 D = -3.051 × 10 ^-5 <Numerical Example 4> F = 1 to 12.65 Fno = 1: 1.8 to 1.9 2 ω = 66.2 ° to 5.9 ° R 1 = 25.907 D 1 = 0.391 N 1 = 1.84666 ν 1 = 23.8 R 2 = 8.416 D 2 = 0.312 R 3 = 12.008 D 3 = 1.130 N 2 = 1.69680 ν 2 = 55.5 R 4 = -45.235 D 4 = 0.043 R 5 = 6.531 D 5 = 1.195 N 3 = 1.69680 ν 3 = 55.5 R 6 = 73.064 D 6 = Variable R 7 = 8.118 D 7 = 0.173 N 4 = 1.88300 ν 4 = 40.8 R 8 = 1.730 D 8 = 0.861 R 9 = -2.748 D 9 = 0.152 N 5 = 1.69680 ν 5 = 55.5 R10 = 3.014 D10 = 0.217 R11 = 3.614 D11 = 0.434 N 6 = 1.84666 ν 6 = 23.8 R12 = -11.227 D12 = variable R13 = (aperture) D13 = 1.413 R14 = 5.282 D14 = 0.434 N 7 = 1.60311 ν 7 = 60.7 R15 = 15.536 D15 = variable R16 = -5.179 D16 = 0.434 N 8 = 1.51742 ν 8 = 52.4 R17 = -4.751 D17 = 0.032 R18 = 6.988 D18 = 0.195 N 9 = 1.80518 ν 9 = 25.4 R19 = 3.039 D19 = 0.760 N10 = 1.48749 ν10 = 70.2 R20 = -5.586 D20 = 0.032 R21 = 3.239 D21 = 0.543 N11 = 1.48749 ν11 = 70.2 R22 = 13.677 D22 = 0.869 R23 = ∞ D23 = 0.543 N 12 = 1.51633 ν12 = 64.2 R24 = ∞ D24 = 3.260 N13 = 1.60342 ν13 = 38.0 R25 = ∞

[0063]

[Table 4] Aspheric coefficient R14 surface K = 3.610 × 10 ⁻³ A = −1.746 × 10 ⁻³ B = 4.681 × 10 ⁻⁵ C = 4.104 × 10 ⁻⁵ D = −3.320 × 10 ⁻⁵ <Numerical example 5> F = 1 to 10 Fno = 1: 1.6 to 1.7 2 ω = 60.0 ° to 6.6 ° R 1 = 12.083 D 1 = 0.346 N 1 = 1.80518 ν 1 = 25.4 R 2 = 5.692 D 2 = 1.538 N 2 = 1.60311 ν 2 = 60.7 R 3 = -26.824 D 3 = 0.038 R 4 = 5.854 D 4 = 0.653 N 3 = 1.71300 ν 3 = 53.8 R 5 = 15.975 D 5 = Variable R 6 = 9.280 D 6 = 0.173 N 4 = 1.88300 ν 4 = 40.8 R 7 = 1.826 D 7 = 0.685 R 8 = -2.629 D 8 = 0.153 N 5 = 1.69680 ν 5 = 55.5 R 9 = 2.658 D 9 = 0.192 R10 = 3.057 D10 = 0.403 N 6 = 1.84666 ν 6 = 23.8 R11 = 145.551 D11 = Variable R12 = -13.497 D12 = 0.134 N 7 = 1.60311 ν 7 = 60.7 R13 = 4.849 D13 = 0.192 R14 = -10.238 D14 = 0.384 N 8 = 1.60342 ν 8 = 38.0 R15 = -4.381 D15 = 0.288 R16 = (Aperture) D16 = 0.288 R17 = 4.709 D17 = 0.961 N 9 = 1.60342 ν 9 = 38.0 R18 = -2.543 D18 = 0.173 N10 = 1.78590 ν10 = 44.2 R19 = -52.529 D19 = variable R20 = 24.257 D20 = 0.576 N11 = 1.51633 ν11 = 64.2 R21 = -5.630 D21 = 0.028 R22 = 10.997 D22 = 0.211 N12 = 1.80518 ν12 = 25. 4 R23 = 3.332 D23 = 0.961 N13 = 1.48749 ν13 = 70.2 R24 = -8.681 D24 = 0.028 R25 = 4.292 D25 = 0.576 N14 = 1.48749 ν14 = 70.2 R26 = 128.098 D26 = 0.769 R27 = ∞ D27 = 0.384 N15 = 1.51633 ν15 = 64.2 R28 = ∞ D28 = 3.846 N16 = 1.60342 ν16 = 38.0 R29 = ∞

[0064]

[Table 5]

[0065]

According to the present invention, by setting each element as described above, the overall lens system can be downsized, and the shooting angle of view at the wide-angle end is as wide as 65 degrees or more, and the large aperture ratio can be obtained. ,
It has a high zoom ratio, good optical performance over the entire zoom range from the wide-angle end to the telephoto end, and the entire object distance from infinity objects to short-distance objects, and has a predetermined back focus. It is possible to achieve a rear focus type zoom lens.

[Brief description of drawings]

FIG. 1 is a lens cross-sectional view of Numerical Example 1 of the present invention.

FIG. 2 is a lens cross-sectional view of Numerical Example 2 of the present invention.

FIG. 3 is a lens cross-sectional view of Numerical Example 3 of the present invention.

FIG. 4 is a lens cross-sectional view of Numerical Example 4 of the present invention.

FIG. 5 is a lens cross-sectional view of Numerical Example 5 of the present invention.

FIG. 6 is an aberration diagram at a wide-angle end according to Numerical Example 1 of the present invention.

FIG. 7 is an aberration diagram at a telephoto end according to Numerical Example 1 of the present invention.

FIG. 8 is an aberration diagram at a wide-angle end according to Numerical Example 2 of the present invention.

FIG. 9 is an aberration diagram at a telephoto end according to Numerical Example 2 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 aberration diagram at a telephoto end according to Numerical Example 3 of the present invention.

FIG. 12 is an aberration diagram at a wide-angle end according to Numerical Example 4 of the present invention.

FIG. 13 is an aberration diagram at a telephoto end according to Numerical Example 4 of the present invention.

FIG. 14 is an aberration diagram at a wide-angle end according to Numerical Example 5 of the present invention.

FIG. 15 is an aberration diagram at a telephoto end according to Numerical Example 5 of the present invention.

[Explanation of symbols]

 L1 First group L2 Second group L3 Third group L4 Fourth group SP Aperture IP Image plane G Glass block d d line g g line ΔS Sagittal image plane ΔM Meridional image plane

Claims (4)

[Claims] 1. A first group having a positive refracting power, a second group having a negative refracting power, and a third group having a positive refracting power having an aperture in order from the object side.
Further, it has four lens units of the fourth lens unit having a positive refractive power, and at the time of zooming from the wide-angle end to the telephoto end, the second unit is moved to the image plane side and the stop and the third lens unit are moved. The group is integrally moved so as to have a convex locus on the object side, and the fourth group is moved so as to have a convex locus on the object side, and the fourth group is moved at the time of focusing. A rear-focus type zoom lens, which satisfies the condition of 2.5 <F3 / F4, where Fi is the focal length of the i-th group. 2. When the focal length of the entire system at the wide-angle end is Fw, the condition of −0.70 <Fw / F2 <−0.4 is satisfied, which is the rear focus type of claim 1. Zoom lens. 3. The second lens unit is a negative meniscus lens having a convex surface facing the object side in order from the object side, a negative lens element having a concave surface on both lens surfaces, and a positive lens having a convex surface facing the object side. The rear focus type zoom-on lens of claim 1, wherein the rear focus type zoom-on lens comprises three single lenses of the 23rd lens. 4. The rear focus type zoom lens according to claim 1, wherein the respective elements are set such that the light emitted from the third group becomes a substantially afocal or weakly divergent light beam.