JP3063459B2 - Rear focus type zoom lens and camera using the same - 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 a rear focus type zoom lens having a wide angle of view at a wide angle end used for a broadcast camera or the like including a wide angle of view of about 60 degrees, and having a high zoom ratio of about 8 to 13 and a long back focus. It relates to a camera using the same.

[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.

In Japanese Patent Application Laid-Open No. 3-200113, a similar configuration is adopted. During zooming in order from the object side, a fixed positive first lens group, a negative second lens group 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 group and the third lens group move in opposite directions, it is necessary to widen the interval 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 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 reduction of 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 overall lens system is reduced in size as described above, quick focusing is possible, and close-up photographing is facilitated. can get.

On the other hand, on the other hand, aberration fluctuation at the time of focusing becomes large, and the entire lens system is reduced in size over the entire object distance from an object at infinity to an object at a short distance.
There is a problem that it is very difficult to obtain high optical performance.

At present, single-panel video cameras are mainly used for consumer video cameras, and multi-panel video cameras are mainly used for professional video cameras. A multi-plate video camera uses a color separation prism as a color separation system. For this reason, it is necessary for a zoom lens for a multi-plate video camera to have a long back focus enough to secure a sufficient 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 employs a rear focus type zoom lens, and when aiming for a large aperture ratio and a high zoom ratio, while miniaturizing the entire lens system, over the entire object distance from the wide-angle end to the telephoto end. It is an object of the present invention to provide a rear focus type zoom lens having a simple configuration having good optical performance and a long back focus, and a camera using the same.

[0021]

According to a first aspect of the present invention, there is provided a rear focus type zoom lens having a first group having a positive refractive power, a second group having a negative refractive power, and a positive lens having an aperture. The zoom lens has five lens units: a third unit having a refractive power, a fourth unit having a positive refractive power, and a fifth unit having a positive refractive power. The second lens unit is used for zooming from the wide-angle end to the telephoto end. The lens group is moved to the image plane side, the stop and the third lens group are moved together, and the image plane fluctuation caused by zooming is corrected by moving the fourth lens group. A rear focus type zoom lens for moving the fourth lens group, wherein when the focal length of the i-th lens group is Fi, the following condition is satisfied: 2.5 <F3 / F4 (1) Features.

[0022]

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 lens unit having a positive refractive power, L2 is a second lens unit having a negative refractive power, L3 is a third lens unit having a positive refractive power, and L4 is a positive lens.
Denotes a fourth unit having a positive refractive power, and L5 denotes a fifth unit having a positive refractive power. SP denotes an aperture stop, which is disposed in the third group or in front of the third group. G is a glass block such as a color separation prism, a face plate, and a filter, and 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 lens unit is moved so as to have a convex locus, and the image plane fluctuation caused by zooming is corrected by moving the fourth lens unit independently of the third lens unit 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 achieve a wide angle of view of about 60 degrees at the wide angle end while securing a predetermined back focus, and to achieve a full zoom range. Good optical performance over a wide range. In addition, a rear focus type in which the fourth unit is moved on the optical axis to perform focusing is adopted.

A solid line curve 4a and a dotted line curve 4b of the fourth lens group shown in FIG. 4 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 and the fifth group are 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 drawing, the zoom lens is moved so as to have a convex locus toward the object side when 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 has been effectively reduced.

Also, at the time of zooming, the third lens unit is moved so as to have a convex locus on the object side similarly to the fourth lens unit so as to effectively use the space between the second lens unit and the third lens unit. I have.

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 unit, so that the first lens unit 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.

Then, the aperture stop SP is arranged in the third lens unit or between the second lens unit and the third lens unit, and at the time of zooming, is moved integrally with the third lens unit. By reducing aberration fluctuations and 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 aperture is set in the third group or the third group.
Positioned on the object side of the group and moved so as to have a convex trajectory on the object side integrally with the third group with zooming from the wide-angle end to the telephoto end, so that the entrance pupil is closer to the first group. Thus, the zoom position having the highest incident height is set near the wide-angle end, thereby effectively reducing the effective diameter of the first lens unit.

In the present invention, the aperture stop and the third lens unit reciprocate almost completely along a locus convex toward the object side, so that the diameter of the front lens can be easily reduced and the angle of view can be easily widened.

In the present invention, the above-mentioned conditional expression (1) is satisfied in order to secure high optical performance over the entire screen while further reducing the size of the entire lens system.

[0037]

Conditional expression (1) has good optical performance over the entire zoom range from the wide-angle end to the telephoto end and the entire object distance while preventing the entire lens system from being enlarged, and has a long back focus. This is for obtaining a rear-focus type zoom lens having a simple configuration.

That is, the conditional expression (1) relates to the focal lengths of the third and fourth lens units, while achieving compactness after the stop,
This is for keeping the back focus sufficiently long to maintain good optical performance. If the focal length of the third lens unit becomes shorter than the lower limit value of the conditional expression (1), it becomes difficult to correct a change in spherical aberration due to zooming or during focusing.
Also, it is difficult to secure sufficient back focus,
There is also a problem that the amount of movement of the fourth lens unit becomes large, and the fluctuation of aberration due to zooming or focusing becomes large.

In the present invention, it is desirable to satisfy at least one of the following conditions in order to achieve good optical performance while further reducing the overall length of the lens. (1-1) Assuming that the focal length of the entire system at the wide-angle end is Fw, -0.8 <Fw / F2 <-0.4 {(2) 0.1 <F4 / F5 <1.2} Satisfies the following condition (3).

Conditional expression (2) relates to the ratio between the focal length of the entire system and the focal length of the second lens group at the wide-angle end. If the focal length of the second lens unit becomes shorter than the upper limit of conditional expression (2), the Petzval sum increases in the under direction, and it becomes difficult to correct aberrations such as image plane tilt. Conversely, the second
When the focal length of the lens group becomes longer, the amount of movement of the second lens group with zooming increases, causing a problem that the diameter of the front lens becomes too large.

Conditional expression (3) relates to the ratio between the focal lengths of the fourth and fifth lens units, and achieves compactness after the stop while maintaining a sufficiently long back focus and maintaining good optical performance. It is for. If the focal length of the fifth lens unit is longer than the lower limit of conditional expression (3) and the focal length of the fourth lens unit is short, it becomes difficult to satisfactorily correct spherical aberration and the like while securing a sufficient back focus. Become. Conversely, if the focal length of the fourth lens unit becomes longer than the upper limit value, the amount of movement of the fourth lens unit during zooming and focusing increases, causing a problem that fluctuations in aberrations during zooming and focusing increase.

(1-2) It is preferable that the outgoing light of the axial light beam emitted from the third lens unit is substantially afocal or weakly divergent.

According to this, the back focus and the exit pupil can be effectively lengthened while minimizing aberration fluctuations during zooming or focusing.

(1-3) To reduce the diameter of the front lens effectively, the first lens unit should be arranged in order from the object side, with a negative meniscus eleventh lens having a convex surface facing the object side, and with an air gap. A positive twelfth lens having a convex surface facing the object side, and a positive thirteenth lens having a convex surface facing the object side, and the air lens composed of the eleventh lens and the twelfth lens has a negative refractive power. It is preferred to have.

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

3.5 <Bfw / Fw <6.0 (4) Here, 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).

This equation (4) is necessary for effectively reducing the size of the entire system. When the value exceeds the lower limit, 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.

(1-5) In order to reduce the diameter of the front lens, it is preferable to satisfy the following expression.

6.0 <F1 / Fw <15.0 (5) This equation is an equation relating to the object point for the second lens unit, 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.

More specifically, if the value exceeds the upper limit of the expression (5), the object point for the second lens unit becomes distant, the imaging magnification of the second lens unit becomes low, and it is difficult to reduce the size effectively.

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.

(1-6) The performance can be further improved by using a lens having an aspherical surface.
It is possible to increase the brightness of no and reduce the number of lenses.

In particular, by using a lens having an aspherical surface in the fourth unit, it is possible to reduce the number of lenses, and at the same time, it is possible to effectively achieve spherical aberration and the like by using an aspherical surface.

Further, by using a lens having an aspheric surface in the fifth unit, coma aberration and the like can be effectively corrected.

(1-7) The second group includes, in order from the object side, a negative twenty-first meniscus lens having a convex surface facing the object side, a negative twenty-second lens having both concave lens surfaces concave, and a positive twenty-third lens. It is preferable to have it in order to reduce aberration fluctuations accompanying zooming.

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 three 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, B, C, D, and E are aspherical coefficients, respectively.

[0059]

(Equation 1) It is represented by the following expression. "D-0x" is displayed as "10-
x ".

<Numerical Example 1> F = 1 to 10.0 Fno = 1: 1.65 2ω = 60.0 ° to 6.6 ° R 1 = 16.764 D 1 = 0.365 N 1 = 1.80518 ν 1 = 25.4 R 2 = 6.729 D 2 = 1.500 N 2 = 1.60311 ν 2 = 60.7 R 3 = -27.650 D 3 = 0.038 R 4 = 6.196 D 4 = 0.730 N 3 = 1.71300 ν 3 = 53.8 R 5 = 18.529 D 5 = Variable R 6 = 8.884 D 6 = 0.173 N 4 = 1.88300 ν 4 = 40.8 R 7 = 1.979 D 7 = 0.923 R 8 = -2.438 D 8 = 0.173 N 5 = 1.69680 ν 5 = 55.5 R 9 = 2.653 D 9 = 0.576 N 6 = 1.84666 ν 6 = 23.8 R10 = -22.105 D10 = Variable R11 = 100.867 D11 = 0.134 N 7 = 1.60311 ν 7 = 60.7 R12 = 2.619 D12 = 0.769 R13 = (Aperture) D13 = 0.288 R14 = 5.736 D14 = 0.769 N 8 = 1.60342 ν 8 = 38.0 R15 =- 7.212 D15 = Variable R16 = 14.834 D16 = 0.653 N 9 = 1.51633 ν 9 = 64.2 R17 = -7.247 D17 = 0.028 R18 = 8.312 D18 = 0.173 N10 = 1.80518 ν10 = 25.4 R19 = 3.021 D19 = 1.153 N11 = 1.48749 ν11 = 70.2 R20 = -6.831 D20 = Variable R21 = 4.127 D21 = 0.500 N12 = 1.48749 ν12 = 70.2 R22 = 8.802 D22 = 0.769 R23 = ∞ D23 = 0.480 N13 = 1.51633 ν13 = 64.2 R24 = ∞ D24 = 3.846 N14 = 1.60342 ν14 = 38.0 R25 = ∞

[0061]

[Table 1] <Numerical Example 2> F = 1 to 8 Fno = 1: 1.65 2ω = 58.1 ° to 7.9 ° R 1 = 12.184 D 1 = 0.296 N 1 = 1.84666 ν 1 = 23.8 R 2 = 5.537 D 2 = 1.277 N 2 = 1.60311 ν 2 = 60.7 R 3 = -19.188 D 3 = 0.037 R 4 = 4.609 D 4 = 0.629 N 3 = 1.69680 ν 3 = 55.5 R 5 = 12.642 D 5 = Variable R 6 = 13.075 D 6 = 0.166 N 4 = 1.88300 ν 4 = 40.8 R 7 = 1.692 D 7 = 0.720 R 8 = -2.032 D 8 = 0.166 N 5 = 1.69680 ν 5 = 55.5 R 9 = 2.173 D 9 = 0.444 N 6 = 1.84666 ν 6 = 23.8 R10 = -15.701 D10 = Variable R11 = -274.990 D11 = 0.129 N 7 = 1.60311 ν 7 = 60.7 R12 = 2.469 D12 = 0.740 R13 = (Aperture) D13 = 0.277 R14 = 5.816 D14 = 0.648 N 8 = 1.60342 ν 8 = 38.0 R15 = -6.169 D15 = Variable R16 = 12.953 D16 = 0.629 N 9 = 1.51633 ν 9 = 64.2 R17 = -6.978 D17 = 0.027 R18 = 5.893 D18 = 0.166 N10 = 1.84666 ν10 = 23.8 R19 = 2.746 D19 = 1.111 N11 = 1.48749 ν11 = 70.2 R20 =- 7.051 D20 = Variable R21 = 3.844 D21 = 0.407 N12 = 1.48749 ν12 = 70.2 R22 = 6.512 D22 = 0.740 R23 = ∞ D23 = 0.493 N13 = 1.51633 ν13 = 64.2 R24 = ∞ D24 = 3.703 N14 = 1.60342 ν14 = 38.0 R25 = ∞

[0062]

[Table 2] <Numerical Example 3> F = 1 to 8 Fno = 1: 1.65 2ω = 58.1 ° to 7.9 ° R 1 = 10.019 D 1 = 0.277 N 1 = 1.80518 ν 1 = 25.4 R 2 = 4.876 D 2 = 1.259 N 2 = 1.60311 ν 2 = 60.7 R 3 = -39.080 D 3 = 0.037 R 4 = 4.790 D 4 = 0.703 N 3 = 1.69680 ν 3 = 55.5 R 5 = 15.516 D 5 = Variable R 6 = 12.553 D 6 = 0.166 N 4 = 1.88300 ν 4 = 40.8 R 7 = 1.538 D 7 = 0.635 R 8 = -2.510 D 8 = 0.129 N 5 = 1.69680 ν 5 = 55.5 R 9 = 2.733 D 9 = 0.185 R10 = 3.114 D10 = 0.370 N 6 = 1.84666 ν 6 = 23.8 R11 = -25.032 D11 = Variable R12 = 43.470 D12 = 0.129 N 7 = 1.60311 ν 7 = 60.7 R13 = 2.717 D13 = 0.740 R14 = (Aperture) D14 = 0.277 R15 = 5.891 D15 = 0.648 N 8 = 1.60342 ν 8 = 38.0 R16 = -5.939 D16 = Variable R17 = 10.288 D17 = 0.629 N 9 = 1.51633 ν 9 = 64.2 R18 = -6.932 D18 = 0.027 R19 = 7.417 D19 = 0.166 N10 = 1.80518 ν10 = 25.4 R20 = 2.617 D20 = 1.111 N11 = 1.48749 ν11 = 70.2 R21 = -6.833 D21 = Variable R22 = 3.163 D22 = 0.370 N12 = 1.58313 ν12 = 59.4 R23 = 4.993 D23 = 0.740 R24 = ∞ D24 = 0.463 N13 = 1.51633 ν13 = 64.2 R25 = ∞ D25 = 3.703 N14 = 1.60342 ν14 = 38.0 R26 = ∞

[0063]

[Table 3] <Numerical Example 4> F = 1 to 12.65 Fno = 1: 1.7 to 2.4 2ω = 64.0 ° to 5.7 ° R 1 = 21.532 D 1 = 0.312 N 1 = 1.84666 ν 1 = 23.8 R 2 = 8.061 D 2 = 0.091 R 3 = 9.418 D 3 = 0.916 N 2 = 1.69680 ν 2 = 55.5 R 4 = -49.597 D 4 = 0.041 R 5 = 6.245 D 5 = 0.645 N 3 = 1.69680 ν 3 = 55.5 R 6 = 31.447 D 6 = Variable R 7 = 9.270 D 7 = 0.166 N 4 = 1.88300 ν 4 = 40.8 R 8 = 1.615 D 8 = 0.713 R 9 = -2.851 D 9 = 0.145 N 5 = 1.69680 ν 5 = 55.5 R10 = 4.253 D10 = 0.208 R11 = 4.042 D11 = 0.416 N 6 = 1.84666 ν 6 = 23.8 R12 = -15.249 D12 = Variable R13 = (Aperture) D13 = 0.937 R14 = 5.515 D14 = 1.000 N 7 = 1.60342 ν 7 = 38.0 R15 = -5.139 D15 = 0.187 N 8 = 1.88300 ν 8 = 40.8 R16 = -70.309 D16 = Variable R17 = 14.435 D17 = 0.479 N 9 = 1.51633 ν 9 = 64.2 R18 = -6.403 D18 = 0.031 R19 = 6.120 D19 = 0.187 N10 = 1.80518 ν10 = 25.4 R20 = 2.617 D20 = 0.937 N11 = 1.48749 ν11 = 70.2 R21 = -6.615 D21 = Variable R22 = 3.194 D22 = 0.416 N12 = 1.48749 ν12 = 70.2 R23 = 4.564 D23 = 0.833 R24 = ∞ D24 = 0.520 N13 = 1.51633 ν13 = 64.2 R25 = ∞ D25 = 3.125 N14 = 1.60342 ν14 = 38.0 R26 = ∞

[0064]

[Table 4]

[0065]

[Table 5]

[0066]

According to the present invention, by setting each element as described above, the photographing angle of view at the wide-angle end is as wide as about 60 degrees while the size of the entire lens system is reduced, and the zoom ratio is high. A rear-focus type zoom lens with a long back focus and excellent optical performance 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 camera using it 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 aberration diagram at a telephoto end in Numerical Example 1 of the present invention;

FIG. 7 is an aberration diagram at a wide angle end according to Numerical Embodiment 2 of the present invention.

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

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

FIG. 10 is an aberration diagram at a telephoto end in Numerical Example 3 of the present invention.

FIG. 11 is an aberration diagram at a wide angle end according to Numerical Example 4 of the present invention.

FIG. 12 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 L5 Fifth lens unit SP Aperture IP image plane G Glass block d d-line g g-line ΔS Sagittal image plane ΔM Meridional image plane

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00-25/04

Claims (8)

(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
It has five lens units, a fourth lens unit having a positive refractive power and a fifth lens unit having a positive refractive power. When zooming from the wide-angle end to the telephoto end,
The second lens unit is moved to the image plane side, the stop and the third lens unit are moved integrally, and the image plane fluctuation caused by zooming is corrected by moving the fourth lens unit. Moves the fourth group
Rear-focus type zoom lens, wherein
When the focal length of the zoom lens is Fi, a condition of 2.5 <F3 / F4 is satisfied . 2. The rear focus according to claim 1, wherein the stop and the third lens unit move so as to have a convex locus on the object side during zooming from the wide-angle end to the telephoto end. Formula zoom lens. 3. The focal length of the entire system at the wide-angle end is represented by Fw.
3. The rear focus type zoom lens according to claim 1, wherein the following condition is satisfied : -0.8 <Fw / F2 <-0.4 0.1 <F4 / F5 <1.2. 4. The second group includes a negative meniscus lens having a convex surface facing the object side in order from the object side, a negative second lens having both lens surfaces concave, and a positive twenty-third lens. 4. The method according to claim 1, wherein
Item rear focus zoom lens. 5. The rear-focusing system according to claim 1 , wherein each element is set such that an on-axis light beam emitted from said third group is substantially afocal or weakly divergent. Zoom lens. 6. When the back focus when the object distance is infinity in the wide-angle end and Bfw, 3.5 <Bfw / Fw <claims 3 to 5 have and satisfies 6.0 condition:
The rear focus zoom lens of item 1 . 7. The method according to claim 3 , wherein a condition of 6.0 <F1 / Fw <15.0 is satisfied.
The rear focus zoom lens of item 1 . 8. A camera comprising the rear focus type zoom lens according to claim 1.