JP3240749B2 - Rear focus zoom lens - Google Patents

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, and the like.
Further, the present invention relates to a rear focus type zoom lens having a wide angle of view of 65 degrees or more at a wide angle end used for a broadcast camera or the like and having a high zoom ratio of 8 to 13.

[0002]

2. Description of the Related Art In recent years, with the reduction in size and weight of photographic cameras and home video cameras for 35 mm film, zoom lenses used for photographing have a predetermined zoom ratio, and have a wide angle of view. It is demanded that the entire lens system having a short lens length and a small front lens diameter is small and lightweight.

As a zoom lens which satisfies these needs relatively well, there is a rear focus type zoom lens which performs focusing by moving a lens unit other than the first unit on the object side.

In general, a rear focus type zoom lens has a smaller effective diameter of the first lens group than a front lens focus type zoom lens which moves and focuses the first lens group, so that the size of the entire lens system can be easily reduced. Become, close-up photography,
In particular, extremely close-up photography is facilitated, and the relatively small and lightweight lens group is moved, so that the driving force of the lens group can be small and quick focusing can be performed.

As such a rear focus type zoom lens, for example, Japanese Patent Application Laid-Open Nos. 62-247316 and 62-24213 disclose a first group having a positive refractive power and a negative refractive power in order from the object side. It has four lens groups, a second group of power, a third group of positive refractive power, and a fourth group of positive refractive power. The second group is moved to perform zooming, and the fourth group is moved. In this way, correction and focusing of the image plane fluctuation due to zooming are performed.

Japanese Patent Application Laid-Open No. 58-160913 discloses a first group of positive refractive power and a second group of negative refractive power in order from the object side.
It has four lens groups: a group, a third group having a positive refractive power, and a fourth group having a positive refractive power. The first group and the second group are moved to perform zooming, and an image accompanying the zooming is performed. The correction of the surface variation is performed by moving the fourth lens unit. Then, focusing is performed by moving one or more of these lens groups.

In Japanese Patent Application Laid-Open No. 57-111507,
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 focusing during zooming; these second lens group and third lens group are provided. During zooming, the third lens group moves in opposite directions, and the third lens group includes two positive lens groups, each of which moves independently, a so-called four-group zoom lens having positive, negative, positive, and positive refractive powers. Has been proposed. In this publication, an aperture stop (aperture stop) is positioned in the third lens group.

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

Since the first lens group focuses, the diameter of the front lens is increased in order to secure a luminous flux to the peripheral angle of view at a close distance, and the rear focus method is used to reduce the size of the front lens. When trying to adapt, there is a problem that the refractive power arrangement is not optimal, and the fluctuation of the focus aberration due to the rear focusing is not sufficiently corrected.

Japanese Patent Application Laid-Open No. 3-200113 also has a similar configuration. During zooming in order from the object side, a fixed positive first lens unit, a negative second lens unit moving back and forth for zooming, A zoom lens comprising a positive third lens group that moves in association with the movement of the two lens groups, and a positive fourth lens group that partially or wholly moves the correction of the focal position accompanying zooming is proposed. I have.

According to the publication, the movement of the positive third lens group, which moves in relation to the movement of the second lens group, is performed to reduce the amount of image plane movement correction performed by the fourth lens group. , A part of the correction function is assigned to the third lens group. 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 unit and the third lens unit move in opposite directions, it is necessary to widen the interval between the second and third lens units on the wide-angle side, and the entrance pupil position at the wide-angle end becomes large. It will be closest to the image surface side,
There was a problem that miniaturization of the whole system was difficult.

Similarly, in Japanese Patent Application Laid-Open No. 3-158613, the first lens unit, the second negative lens unit, the third positive lens unit, and the fourth positive lens unit 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 perform zooming, 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. The third lens group having an aperture stop is located closest to the image at the wide-angle end, and at the wide-angle end where the front lens diameter is the largest or at a position slightly zoomed from the wide-angle end. Near the image side, the entrance pupil position is deeper, which is disadvantageous for reducing the front lens diameter. Also, distortion at the wide-angle end is large, and the front lens diameter is reduced with good performance by removing this. There is a problem that it is difficult to reduce the size.

The present applicant discloses in Japanese Patent Application Laid-Open No. 3-215810 a first group of positive refractive power, a second group of negative refractive power, a stop, and a third group of positive refractive power in order from the object side. And a fourth lens unit having a positive refractive power. In zooming from the wide-angle end to the telephoto end, the second unit is moved to the image plane side, and the stop, A rear-focusing type zoom lens which is moved independently of each other so that each of the third lens unit and the fourth lens unit has a locus convex toward the object side and moves the fourth lens unit for focusing. is suggesting.

[0016]

Generally, when a rear focus system is employed in a zoom lens, the entire lens system is reduced in size, and quick focusing becomes possible.

On the other hand, however, aberration fluctuations during focusing increase, and it becomes very difficult to obtain high optical performance while miniaturizing the entire lens system over the entire object distance from an object at infinity to an object at a short distance. Problem arises.

In particular, a zoom lens having a large aperture ratio and a high zoom ratio and a wide angle of view has a problem that it becomes very difficult to obtain high optical performance over the entire zoom range and over the entire object distance. come.

For example, in Japanese Patent Application Laid-Open Nos. Sho 62-24213 and Sho 63-247316, if an attempt is made to further increase the angle of view, an off-axis light flux to the first lens group is set at an intermediate zoom position near the wide angle end. The incident height increases, and as a result, the effective lens diameter of the first lens group increases. First
In order to reduce the effective diameter of the lens unit, there is a method of shortening the distance between the first lens unit and the stop.

However, the second lens unit, which is the main zooming lens unit, is located between the first lens unit and the stop. When the distance between the first lens unit and the stop is reduced, the second lens unit moves for zooming. Space becomes insufficient, and a desired zoom ratio cannot be secured. If an attempt is made to obtain a desired zoom ratio in a state where the distance between the first lens unit and the aperture is reduced, the negative refractive power of the second lens unit becomes strong, the Petzval sum increases negatively, and the image plane becomes over. Tend to fall. In addition, the sensitivity of the position of the second lens group to the focal plane is increased, and the manufacturing accuracy is severe, which is not preferable.

The present invention has been disclosed by the present applicant in Japanese Patent Application Laid-Open No. 3-215.
The rear focus zoom lens proposed in Japanese Patent Publication No. 810 is further improved to achieve a large aperture ratio and a high zoom ratio while securing a shooting angle of view (2ω) of 65 degrees or more at the wide-angle end, and the entire lens system. While miniaturizing, the various aberrations, such as distortion when widening the angle of view, are reduced over the entire zoom range from the wide-angle end to the telephoto end, and over the entire object distance from an object at infinity to an object at a close distance. It is an object of the present invention to provide a rear-focus type zoom lens having a high optical performance corrected well.

[0022]

A rear focus type zoom lens according to the present invention comprises, in order from the object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, and a positive refractive power having a stop. The zoom lens has four lens units, a third unit and a fourth unit having a positive refractive power. When zooming from the wide-angle end to the telephoto end, the second unit is moved to the image plane side and the stop is moved. And the third group are integrally moved to have a locus convex toward the object side, and
The group is moved so as to have a locus convex toward the object side, and the focusing is performed by moving the fourth group. The focal length of the second group is f2, and the focal length of the second group is changed from the wide-angle end to the telephoto end. The moving amount of the second unit due to zooming is M2, and the maximum moving amount of the third unit due to zooming is M3m.
ax, when the maximum value of the amount of movement of the fourth unit from the wide-angle end when the object distance is infinity due to zooming is M4max, 2.0 <M2 / | f2 | <4.5 (1b) M4max / M3max> 1.2 (4) The condition (4) is satisfied.

[0023]

[0024]

[0025]

1 to 4 show a first embodiment of the present invention, which will be described later.
4 to 4 are lens cross-sectional views at the wide angle end, and FIGS.

In the figure, L1 is a first group having a positive refractive power, L2 is a second group having a negative refractive power, L3 is a third group having a positive refractive power, L4
Denotes a fourth group having a positive refractive power. SP is an aperture stop,
It is arranged in front of the third group. G is a face plate,
A glass block such as a filter, IP is an image plane.

In this embodiment, when zooming from the wide-angle end to the telephoto end, the second unit is monotonously moved to the image plane side as indicated by an arrow, and the stop SP and the third unit are integrally convex to the object side. The fourth group is moved independently so as to have a locus, and the fourth group is moved independently so as to have a locus convex toward the object side.

In this embodiment, the movement toward the image plane is defined as positive, and the opposite is defined as negative.

In this embodiment, by adopting such a zoom type, it is easy to increase the angle of view to about 70 degrees at the wide angle end, and excellent optical performance is obtained over the entire zoom range. . In addition, a rear focus type in which the fourth unit is moved on the optical axis to perform focusing is adopted.

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

In the present embodiment, zooming is performed by moving the fourth lens unit, and focusing is performed by moving the fourth lens unit.

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

In this embodiment, for example, when focusing from an object at infinity to an object at a short distance at the telephoto end,
This is performed by repeating the fourth group forward as indicated by the straight line 4c in FIG.

As described above, in the present embodiment, focusing is performed by using the fourth lens group, so that the first lens group is moved and focusing is performed. The effective diameter of the front lens group (first group) is reduced by making it easy to secure a light beam in the periphery.

By disposing the aperture stop SP between the second and third lens units and moving the lens unit integrally with the third lens unit during zooming as described above, aberration variations due to zooming can be reduced. By shortening the distance between the lens units in front of the aperture stop, it is easy to reduce the effective lens diameter of the first unit (front lens unit).

In the zoom type according to the present invention, for example, if the stop is between the third and fourth units, the entrance pupil is deeper (recessed) from the first unit, so The incident height of the off-axis light beam is highest at the intermediate zoom position near the wide-angle end.

Therefore, in the present invention, the stop is disposed on the object side of the third lens unit and is moved integrally with the third lens unit so as to have a convex locus on the object side with zooming from the wide-angle end to the telephoto end. hand,
The zoom position having the highest entrance height is set near the wide-angle end by setting the entrance pupil closer to the first unit, thereby effectively reducing the effective diameter of the first unit. In the zoom type according to the present invention, the moving amount M2 of the second group affects the size of the entire lens system and the size of the front lens diameter. For this reason, in the present invention, a predetermined zoom ratio is obtained while setting the moving amount M of the second lens unit so as to satisfy the above-mentioned conditional expression (1b), while reducing the size of the entire lens system. Here, if the value exceeds the upper limit of the conditional expression (1b), the moving amount is too large as compared with the refractive power of the second lens unit, which is not suitable for downsizing the entire system.
If the lower limit is exceeded, the imaging magnification of the second lens unit becomes too high,
The sensitivity of the position of the second group to the focus surface is increased, and the manufacturing accuracy becomes severe, which is not appropriate. Further, in the present invention, the above-mentioned conditional expression (4) is satisfied. Conditional expression (4) is an expression for shortening the overall length while reducing the diameter of the front lens. By appropriately selecting the movement of the third lens group, which is the aperture group, with respect to the movement of the fourth lens group, which is mainly used for correcting the image plane movement, it is possible to reduce the diameter of the front lens and the overall length. If the range of conditional expression (4) is exceeded, the amount of movement of the third lens unit will increase,
The front lens diameter and overall length are large, which is not appropriate.

Next, other features of the lens configuration of the zoom lens according to the present invention will be described.

(2-1) In the zoom type according to the present invention, the second lens unit generally has a lens configuration having a large negative refractive power in order to achieve a high magnification. For this reason, the refractive index of the material of the negative lens in the second group tends to use high refractive index glass in order to alleviate the negative Petzval sum.

However, generally distributed glass tends to have a small Abbe number in order to obtain a high refractive index. Therefore, a high refractive index, low dispersion glass is used for the negative lens, and various chromatic aberrations on the axis and the magnification are insufficiently corrected.
It becomes difficult to achieve high magnification and high performance.

For this reason, in the present invention, the second group is composed of a negative meniscus lens having a convex surface facing the object side and a negative second lens.
Having three lenses, a lens and a positive twenty-third lens,
When the Abbe number of the material of the lens having the higher refractive index of the 21st lens or the 22nd lens is νN, the following condition is satisfied: 35 <νN (1a).

Thus, chromatic aberration is corrected in a well-balanced manner.

[0043]

[0044]

[0045]

[0046]

(2-2) In the zoom type according to the present invention, the effective diameter of the first lens unit is generally determined by the angle of view on the wide-angle side. However, if a large aperture is desired, the F-number F at the telephoto end is required.
no also has a significant effect. Therefore, in order to increase the wide-angle and the large-diameter, it is necessary to appropriately determine the thickness D of the first lens unit in order not to increase the diameter of the front lens.

Therefore, in the present invention, the focal length of the first lens unit is set to f
1. Assuming that the lens thickness of the first group is D, the following condition is satisfied: 0.3 <D / f1 <1.0 (1c).

When the lens thickness D is smaller than the lower limit of the conditional expression (1c), when a predetermined front lens diameter is to be secured by widening the angle and increasing the diameter, the peripheral edge portion of the positive lens is not sufficient. When the lens thickness D exceeds the upper limit and the lens thickness D increases, the weight of the front lens increases, making it difficult to reduce the size and weight.

If the rear focus type zoom lens of the present invention satisfies one of the above conditions, it is possible to obtain a rear focus type zoom lens having an effect corresponding to each conditional expression.

Next, in the present invention, it is preferable that at least one of the following conditions be satisfied as a rear focus type zoom lens.

(3-1) The appropriate movement of the third lens unit and the stop for setting the highest position of the incident height of the off-axis light beam to the first lens unit near the wide angle end is as follows in the entire zoom range. Preferably, it is in position.

0.05 <(Fm−Fw) / (Ft−Fw) <0.3 (2) where Fw and Ft are the focal lengths of the entire system at the wide-angle end and the telephoto end, respectively, and Fm is the focal length. This is the focal length of the entire system at the position where the third lens group and the diaphragm move to the object side (the focal length when the maximum amount of movement (negative value) M3max associated with zooming of the third lens group is achieved).

Regardless of either the upper limit or the lower limit of the equation (2), the highest position of the incident height of the off-axis light beam to the first lens unit cannot be set near the wide-angle end, and the third unit and the stop must be properly adjusted. No movement is given. That is, it is not appropriate because it leads to an increase in the front lens diameter and the entire system.

(3-2) In order to reduce the diameter of the front lens and shorten the overall optical length, it is necessary to appropriately select the movement of the second lens unit and the movement of the third lens unit.

The second and third units move in opposite directions up to the position of the focal length Fm described above, and must not mechanically interfere with each other. The movement amount of the second lens unit, which is the main variable power lens unit, is directly related to the variable power ratio, and it is necessary to appropriately correlate with the total lens length. For that purpose, it is preferable that the following conditional expression is satisfied.

−0.4 <M3max / M2 <−0.04 (3) where M2 is the amount of movement of the second lens unit during zooming from the wide-angle end to the telephoto end. M3max is the maximum movement amount of the third lens unit during zooming.

When the value exceeds the upper limit of the expression (3), the moving distance of the second lens unit becomes large, the total length and the front lens diameter become large, and the absolute value of M3max becomes small. The highest position of the incident height of the light beam cannot be set near the wide angle end, which leads to an increase in the diameter of the front lens, which is not appropriate. If the upper limit is exceeded, the moving distance of the second lens group becomes small, a desired telephoto ratio cannot be secured, and the absolute value of M3max becomes large, causing an increase in the size of the entire system and interference between the second and third lens groups. It is not suitable because it becomes easy.

[0059]

[0060]

(3-3) In order to set a wide angle of view at the wide-angle end, if the principal point distance e1 between the positive first lens unit and the negative second lens unit at the wide-angle end is short, the focal length of the entire system is further increased. It can be shortened, and a wide angle can be obtained. However, a minimum air gap is required between the first group and the second group, and it is not appropriate to collide with each other.

For this reason, it is preferable that the image-side principal point of the first group is set closer to the second group, or that the object-side principal point of the second group is set closer to the first group.

In particular, in the first lens unit, it is preferable to satisfy the following conditional expression because the size of the front lens is also involved.

−0.1 <H1 ′ / F1 <0.1 (5) where H1 ′ is the distance between the vertex of the image-side surface of the first unit and the image-side principal point of the first unit. (− Is the object side, + is the image side), and F1 represents the focal length of the first group.

Conditional expression (5) is necessary to reduce the distance between the principal points of the first and second lens units as described above. If the lower limit value is exceeded, the principal point position of the first lens group goes too far to the object side, and the principal point interval e1 described above cannot be shortened, and the desired wide angle cannot be obtained. If the upper limit is exceeded, the distance between the first lens unit and the second lens unit increases, and the diameter of the front lens becomes large, which is not appropriate.

(3-4) When miniaturizing the whole system, it is preferable to satisfy the following conditions.

2.5 <Bfw / Fw <4.0 ‥‥‥ (6) where Bfw is the back focus at the infinity of the object distance at the wide-angle end (“G” in the embodiment such as a glass block and a filter). Excluding).

Equation (6) is an equation necessary for effectively reducing the size of the entire system. If the lower limit is exceeded, not only is it impossible to insert a block such as a filter, but also the exit pupil becomes shorter. For example, when the present invention is applied to a video camera or the like, an image formed on an image sensor is shifted from a telecentric system. If the upper limit is exceeded, the size will increase.

(3-5) In order to reduce the diameter of the front lens, it is preferable to satisfy the following expression.

5.7 <F1 <Fw <9.0 (7) This equation is an equation relating to the object point for the second group, that is, the magnification. In order to set the entire system to be small, it is preferable that the second lens unit be placed at the same magnification during zooming. With the same magnification, the locus of zooming of the fourth lens unit is substantially reciprocating, and high zooming is possible with the most effective space efficiency.

Specifically, if the value exceeds the upper limit of the expression (7), the object point with respect to the second lens unit becomes far, the imaging magnification of the second lens unit becomes low, and it is difficult to effectively reduce the size.

Further, the distance between the first group and the second group is increased,
It is difficult to achieve miniaturization. If the lower limit is exceeded, the second
The magnification of the group increases, making it difficult to achieve high magnification.

(3-6) As described in the expression (6), it is one of the important points how the distance e1 between the principal points of the first lens unit and the second lens unit can be reduced at the wide-angle end for widening the angle. It is. For this purpose, the first group preferably has the following configuration.

The first lens unit includes, in order from the object side, a negative meniscus lens L11 having a convex surface on the object side, 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 constituted by the positive lens L12 has a negative refractive power. As another configuration of the first group, a configuration in which a biconcave lens L11, a positive lens L12 adhered thereto, and at least one positive lens may be arranged in order from the object side.

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

(3-7) Principal point interval e1 in the second lens unit
It is desirable to widen the angle that the second group has the object-side principal point set to the object side in order to shorten the distance at the wide-angle end.

(3-8) If the amount of movement of the diaphragm and the third lens unit is relatively large, the zoom fluctuation of spherical aberration becomes large, especially in the middle area of zooming, and spherical aberration tends to be overcorrected. In order to eliminate this, it is preferable to introduce an aspherical surface on the surface near the stop of the third lens unit. The specific shape of the aspherical surface is preferably such that the positive refractive power becomes weaker or the negative refractive power becomes stronger toward the periphery of the lens.

Next, numerical examples of the present invention will be described. 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 spacing from the object side, and Ni and νi are the i-th lens surfaces in order from the object side. The refractive index and Abbe number of glass.

In the numerical examples, the last two lens surfaces are glass blocks such as a face plate and a filter. Table 1 shows the relationship between the above-mentioned conditional expressions and various numerical values in the numerical examples. Aspherical shape is X in the optical axis direction
Axis, the H axis perpendicular to the optical axis, the light traveling direction is positive, and R
Is the paraxial radius of curvature, and K, A ₂ , A ₃ , A ₄ , and A ₅ are aspherical coefficients, respectively.

[0080]

(Equation 2) It is represented by the following expression. "D-OX" is displayed as "10
^-X ".

<Numerical Example 1> F = 1.0 to 12.5 Fno = 1: 1.85 to 2.6 2ω = 69.8 ° to 6.4 ° R 1 = 15.449 D 1 = 0.26 N 1 = 1.84666 ν 1 = 23.8 R 2 = 6.090 D 2 = 0.28 R 3 = 9.215 D 3 = 0.83 N 2 = 1.69680 ν 2 = 55.5 R 4 = -64.894 D 4 = 0.04 R 5 = 4.815 D 5 = 0.96 N 3 = 1.69680 ν 3 = 55.5 R 6 = 51.436 D 6 = Variable R 7 = 15.137 D 7 = 0.17 N 4 = 1.77250 ν 4 = 49.6 R 8 = 1.407 D 8 = 0.63 R 9 = -4.105 D 9 = 0.15 N 5 = 1.72000 ν 5 = 50.3 R10 = 1.987 D10 = 0.17 R11 = 2.307 D11 = 0.48 N 6 = 1.84666 ν 6 = 23.8 R12 = 14.465 D12 = Variable R13 = ∞ (Aperture) D13 = 0.33 R14 = 6.786 D14 = 0.65 N 7 = 1.58313 ν 7 = 59.4 R15 = -3.034 D15 = 0.11 R16 = -2.251 D16 = 0.22 N 8 = 1.60342 ν 8 = 38.0 R17 = -3.452 D17 = Variable R18 = 3.160 D18 = 0.17 N 9 = 1.84666 ν 9 = 23.8 R19 = 1.761 D19 = 0.74 N10 = 1.51633 ν10 = 64.2 R20 = -6.350 D20 = 0.04 R21 = 51.743 D21 = 0.41 N11 = 1.48749 ν11 = 70.2 R22 = -6.787 D22 = 1.09 R23 = ∞ D23 = 1.09 N12 = 1.51633 ν12 = 64.2 R24 = 移動 Moving parameter a = 4.574 b = -1.858 c = 2.246

[0082]

[Table 1] <Numerical Example 2> F = 1.0 to 12.64 Fno = 1: 1.85 to 2.85 2ω = 69.8 ° to 6.3 ° R 1 = -22.354 D 1 = 0.26 N 1 = 1.84666 ν 1 = 23.8 R 2 = 5.376 D 2 = 1.23 N 2 = 1.51742 ν 2 = 52.4 R 3 = -12.734 D 3 = 0.04 R 4 = 15.398 D 4 = 0.65 N 3 = 1.60342 ν 3 = 38.0 R 5 = -18.466 D 5 = 0.04 R 6 = 4.777 D 6 = 0.87 N 4 = 1.60342 ν 4 = 38.0 R 7 = -977.699 D 7 = Variable R 8 = 6.447 D 8 = 0.17 N 5 = 1.77250 ν 5 = 49.6 R 9 = 1.112 D 9 = 0.62 R10 = -2.134 D10 = 0.15 N 6 = 1.69680 ν 6 = 55.5 R11 = 2.771 D11 = 0.04 R12 = 2.435 D12 = 0.44 N 7 = 1.84666 ν 7 = 23.8 R13 = -16.915 D13 = Variable R14 = ∞ (Aperture) D14 = 0.33 R15 = 5.693 D15 = 0.65 N 8 = 1.63854 ν 8 = 55.4 R16 = -5.861 D16 = 0.03 R17 = 3.664 D17 = 0.70 N 9 = 1.56732 ν 9 = 42.8 R18 = -41.762 D18 = 0.13 R19 = -4.724 D19 = 0.17 N10 = 1.69895 ν10 = 30.1 R20 = 6.276 D20 = Variable R21 = 3.722 D21 = 0.17 N11 = 1.84666 ν11 = 23.8 R22 = 1.871 D22 = 0.85 N12 = 1.51633 ν12 = 64.2 R23 = -5.448 D23 = 0.03 R24 = 6.399 D24 = 0.54 N13 = 1.51633 ν13 = 64.2 R25 = -9.080 D25 = 1.09 R26 = ∞ D26 = 1.09 N14 = 1.51633 ν14 = 64.2 R27 = ∞ Parameters a = 4.20 b = −2.177 c = 2.177

[0083]

[Table 2] <Numerical Example 3> F = 1.0 to 7.76 Fno = 1: 1.85 to 2.18 2ω = 69.3 ° to 10.2 ° R 1 = 11.653 D 1 = 0.26 N 1 = 1.84666 ν 1 = 23.8 R 2 = 5.012 D 2 = 0.29 R 3 = 8.979 D 3 = 0.65 N 2 = 1.69680 ν 2 = 55.5 R 4 = -42.221 D 4 = 0.04 R 5 = 3.990 D 5 = 0.70 N 3 = 1.69680 ν 3 = 55.5 R 6 = 76.537 D 6 = Variable R 7 = 12.126 D 7 = 0.17 N 4 = 1.77250 ν 4 = 49.6 R 8 = 1.393 D 8 = 0.47 R 9 = -2.895 D 9 = 0.15 N 5 = 1.72000 ν 5 = 50.3 R10 = 1.780 D10 = 0.22 R11 = 2.323 D11 = 0.52 N 6 = 1.84666 ν 6 = 23.8 R12 = 17.726 D12 = Variable R13 = ∞ (aperture) D13 = 0.32 * R14 = 5.632 D14 = 0.76 N 7 = 1.58313 ν 7 = 59.4 R15 = -4.605 D15 = Variable R16 = 4.658 D16 = 0.17 N 8 = 1.84666 ν 8 = 23.8 R17 = 1.971 D17 = 0.73 N 9 = 1.51633 ν 9 = 64.2 R18 = -4.748 D18 = 0.22 R19 = -188.790 D19 = 0.41 N10 = 1.48749 ν10 = 70.2 R20 = -3.969 D20 = 1.08 R21 = ∞ D21 = 1.08 N11 = 1.51633 ν11 = 64.2 R22 = ∞ Movement parameter a = 3.238 b = -3.022 c = 2.929

[0084]

[Table 3] <Numerical Example 4> F = 1.0 to 11.91 Fno = 1: 1.85 to 2.45 2ω = 71.6 ° to 6.9 ° R 1 = 33.501 D 1 = 0.27 N 1 = 1.84666 ν 1 = 23.8 R 2 = 6.372 D 2 = 0.30 R 3 = 10.526 D 3 = 0.96 N 2 = 1.69680 ν 2 = 55.5 R 4 = -22.822 D 4 = 0.05 R 5 = 5.032 D 5 = 1.00 N 3 = 1.69680 ν 3 = 55.5 R 6 = -1092.792 D 6 = Variable R 7 = 45.309 D 7 = 0.18 N 4 = 1.78590 ν 4 = 44.2 R 8 = 1.364 D 8 = 0.79 R 9 = -3.106 D 9 = 0.16 N 5 = 1.72000 ν 5 = 50.3 R10 = 1.444 D10 = 0.68 N 6 = 1.84666 ν 6 = 23.8 R11 = -19.691 D11 = variable R12 = ∞ (aperture) D12 = 0.34 * R13 = 3.664 D13 = 0.79 N 7 = 1.58313 ν 7 = 59.4 * R14 = -22.698 D14 = variable R15 = 3.803 D15 = 0.18 N 8 = 1.84666 ν 8 = 23.8 R16 = 1.826 D16 = 0.05 R17 = 1.888 D17 = 0.77 N 9 = 1.48749 ν 9 = 70.2 R18 = -4.340 D18 = 0.23 R19 = 23.887 D19 = 0.43 N10 = 1.48749 ν10 = 70.2 R20 = -6.068 D20 = 1.13 R21 = ∞ D21 = 1.13 N11 = 1.51633 ν11 = 64.2 R22 = 移動 Movement parameter a = 4.734 b = -1.748 c = 1.9555

[0085]

[Table 4]

[0086]

According to the present invention, by setting each element as described above, the size of the entire lens system can be reduced, and the angle of view at the wide-angle end can be as wide as 65 degrees or more, and a high zoom ratio can be obtained. Smoothly corrects various aberrations, such as distortion when widening the angle of view, over the entire zoom range from the wide-angle end to the telephoto end, and over the entire object distance from an object at infinity to a close object. A rear focus type zoom lens having high optical performance can be achieved.

[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 a sectional view of a lens according to a numerical example 2 of the present invention.

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

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

FIG. 5 is an aberration diagram at a wide-angle end according to Numerical Embodiment 1 of the present invention.

FIG. 6 is an intermediate aberration diagram of the numerical example 1 of the present invention.

FIG. 7 is an aberration diagram at a telephoto end in 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 intermediate aberration diagram of the numerical example 2 of the present invention.

FIG. 10 is an aberration diagram at a telephoto end in Numerical Example 2 of the present invention.

FIG. 11 is an aberration diagram at a wide angle end according to Numerical Example 3 of the present invention.

FIG. 12 is an intermediate aberration diagram of the numerical example 3 of the present invention.

FIG. 13 is an aberration diagram at a telephoto end in Numerical Example 3 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 lens unit L2 Second lens unit L3 Third lens unit L4 Fourth lens unit SP Aperture IP image plane G Glass block d d line g g line ΔS Sagittal image plane ΔM Meridional image plane

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00-25/04

Claims (4)

(57) [Claims] 1. a first unit having a positive refractive power, a second unit having a negative refractive power, a third unit having a positive refractive power having an aperture, and
The zoom lens has four lens units of a fourth group having a positive refractive power. When 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 moved integrally so as to have a convex trajectory toward the object side, and the fourth group is moved so as to have a convex trajectory toward the object side. And the focal length of the second group is f
2. The movement amount of the second lens unit at the time of zooming from the wide-angle end to the telephoto end is M2, the maximum movement amount of the third lens unit at the time of zooming is M3max,
When the maximum value of the amount of movement of the fourth unit from the wide-angle end when the object distance is at infinity due to zooming is M4max, 2.0 < M2 / | f2 | <4.5 M4max / M3max> 1.2. A rear focus zoom lens that satisfies the conditions. 2. The rear focus type zoom lens according to claim 1, wherein the stop is disposed on the object side of the third group. 3. When the focal lengths of the entire system at the wide-angle end and the telephoto end are Fw and Ft, respectively, and the focal length of the entire system at the position where the third lens group and the diaphragm move to the object side is Fm, 0.05 < 3. The rear focus type zoom lens according to claim 1, wherein a condition of (Fm-Fw) / (Ft-Fw) <0.3 is satisfied. 4. The moving amount of the second lens unit at the time of zooming from the wide-angle end to the telephoto end is M2, and the maximum moving amount of the third lens unit at the time of zooming is M3.
4. The rear focus type zoom lens according to claim 1, wherein the following conditional expression is satisfied: -0.4 <M3max / M2 <-0.04.