JP3097395B2 - 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 large zoom ratio of about 8 to 10 and an F number of about 1.6 to 2 used for a photographic camera, a video camera, a broadcast camera and the like. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear focus type zoom lens having a large back focal length and a high zoom ratio with an aperture ratio.

[0002]

2. Description of the Related Art Conventionally, various types of zoom lenses such as a photographic camera and a video camera adopting a so-called rear focus system in which a lens group other than the first group on the object side is moved to perform focusing is proposed. ing.

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

For example, Japanese Patent Application Laid-Open No. 63-44614 discloses a rear focus type zoom lens having a first lens unit having a positive refractive power, a second lens unit having a negative refractive power for zooming, and a zoom lens. In a so-called four-unit zoom lens composed of four lens units, a third unit having a negative refractive power and a fourth unit having a positive refractive power, for correcting an image plane variation caused by magnification, the third unit is moved. The focus is on. However, in this zoom lens, the moving space of the third lens group must be secured, and the overall length of the lens tends to increase.

In Japanese Patent Application Laid-Open No. 58-136012, a zooming unit is composed of three or more lens groups, and focusing is performed by moving some of the lens groups.

In JP-A-63-247316 and JP-A-62-24213, in order from the object side, a first group of positive refractive power, a second group of negative refractive power, and a third group of positive refractive power. group,
The zoom lens has four lens units of a fourth group having a positive refractive power. The second unit is moved to perform zooming, and the fourth unit is moved to perform image plane fluctuation and focusing caused by zooming. .

In JP-A-58-160913, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, and
The zoom lens has four lens groups, a third lens group having a positive refractive power and a fourth lens group having a positive refractive power. The first and second groups are moved to perform zooming, and the image plane varies with zooming. Is performed by moving the fourth group. Then, focusing is performed by moving one or more of these lens groups.

In Japanese Patent Application Laid-Open No. 63-278013, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a negative refractive power, and a positive lens having a positive refractive power are arranged in order from the object side. Fourth group 4
It has two lens groups, and moves the second group to perform zooming,
The fourth lens unit is moved to correct the image plane fluctuation caused by zooming, and the focus is performed.

[0009]

In general, 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 fluctuation 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 object at infinity to an object at a short distance. The problem arises. In particular, a zoom lens having a large aperture ratio and a high zoom ratio has a problem that it becomes very difficult to obtain high optical performance over the entire zoom range and over the entire object distance.

At present, single-panel cameras are used for many imaging means of consumer video cameras. In this case, the back focus of the single-plate type zoom lens is relatively short because it is not necessary to use a color separation prism or the like used for a multi-plate type zoom lens mainly used for business use.

In the case of the multi-plate type, a color separation prism and the like are arranged behind a photographing lens (zoom lens). For this reason, a multi-lens type zoom lens requires a relatively long back focus as compared with a single-panel type consumer video camera zoom lens.

The present invention employs a rear focus system, achieves a large aperture ratio and a high zoom ratio, and achieves miniaturization of the entire lens system, over the entire zoom range 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 excellent optical performance and a predetermined back focus over an entire object distance from an object at infinity to an object at a short distance.

[0014]

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 third lens unit having a positive refractive power. The zoom lens has four lens units of a fourth group having a positive refractive power, and moves the second unit to the image plane side to perform zooming from the wide-angle end to the telephoto end. The fourth unit is moved and corrected, and the fourth unit is moved to perform focusing.
When the focal length of the group is Fi, the following condition is satisfied: 3.5 <F3 / F4 ‥‥‥ (1)

[0015]

FIG. 1 is a schematic view of an embodiment showing a paraxial refractive power arrangement of a rear focus type zoom lens according to the present invention. 2 to 9 are lens cross-sectional views of Numerical Examples 1 to 8 to be described later. 10 to 25 show Numerical Examples 1 to 5 of the present invention.
8 is an aberrational diagram of FIG.

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 lens unit L3. G is a glass block such as a color separation prism and a filter, and IP is an image plane. This embodiment shows a case where the present invention is applied to a camera in which a color separation prism, a filter, and the like are arranged on the image plane side of a zoom lens.

At the time of zooming from the wide-angle end to the telephoto end, the second lens unit is moved to the image plane side as indicated by an arrow, and the image plane fluctuation caused by zooming is corrected by moving the fourth lens unit.

Also, a rear focus system is employed in which the fourth unit is moved on the optical axis to perform focusing. A solid line curve 4a and a dotted line curve 4b of the fourth lens group shown in the same figure show the image plane fluctuation caused by 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 correction is shown. The first and third units are fixed during zooming and focusing.

In the present embodiment, the fourth lens unit is moved to correct the image plane fluctuation accompanying zooming, and the fourth lens unit is moved to perform focusing. In particular, curve 4 in FIG.
When zooming from the wide-angle end to the telephoto end, the lens is moved so as to have a convex trajectory toward the object side as shown in FIGS.
Thus, the space between the third and fourth units is effectively used, and the overall length of the lens is 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, the fourth unit is moved forward as shown by a straight line 4c in FIG.

In the present embodiment, the effective lens diameter of the first group is increased by adopting the rear focus method as described above in comparison with a conventional four-group zoom lens in which the first group is extended and focused. Prevention.

By arranging the aperture stop immediately before the third lens unit, aberration fluctuation due to the movable lens unit is reduced, and the distance between the lens units in front of the aperture stop is shortened to reduce the diameter of the front lens. Is easily achieved.

By specifying the refractive power and the like of each lens unit as described above, it is possible to reduce the size of the entire lens system, secure a predetermined back focus, and improve the entire object range over the entire zoom range. A high zoom ratio zoom lens having optical performance has been obtained.

Next, the technical meaning of each of the above conditional expressions will be described.

Conditional expression (1) relates to the ratio of the focal length of the third lens unit to the focal length of the fourth lens unit. It is for maintaining.

When the focal length of the third lens unit becomes short beyond the lower limit value of the conditional expression (1), it becomes difficult to correct a change in spherical aberration caused by zooming or during focusing. Also, it is difficult to secure a sufficient back focus, and the amount of movement of the fourth lens unit becomes large, so that the fluctuation of aberration due to zooming or focusing becomes large.

In the present invention, the following conditions should be satisfied in order to obtain good optical performance over the entire zoom range and all object distances while further miniaturizing the entire lens system.

(2-1) When the focal length of the entire system at the wide-angle end is Fw and the back focus at the wide-angle end is bfw, 3 <bfw / Fw <5５ (2) −0.8 <Fw / F2 <−0.4 ‥‥‥ (3) 5 <F1 / Fw <12 ‥‥‥ (4)

Conditional expression (2) relates to the ratio of the back focus bfw to the focal length Fw at the wide-angle end.
If the lower limit of conditional expression (2) is exceeded and the back focus becomes shorter, it becomes impossible to dispose a color separation prism or the like, or it will be displaced from the telecentric system, and the angle of the light beam incident on the color separation prism will be sharp, and color Not good because shading occurs.

Conversely, if the back focus exceeds the upper limit and the back focus becomes too long, the effective diameter of the fourth lens unit becomes large and the lens system becomes heavy, so that there arises a problem that focusing cannot be performed smoothly.

Conditional expression (3) relates to the ratio between the focal length at the wide-angle end and the focal length of the second lens unit. If the focal length of the second lens unit becomes too short beyond the upper limit of conditional expression (3), the Petzval sum increases in the under direction, and it becomes difficult to correct various aberrations such as image plane tilt.

Conversely, if the focal length of the second lens unit becomes too long beyond the lower limit, the amount of movement of the second lens unit due to zooming increases, and the diameter of the front lens becomes too large.

The conditional expression (4) is an expression relating to the object point for the second lens unit, that is, the magnification. In order to set the entire lens system to be small, it is preferable that the second lens unit is 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, when the value exceeds the upper limit of the conditional expression (4), the object point with respect to the second lens unit becomes distant, the imaging magnification of the second lens unit becomes low, and an effective miniaturization of the lens system is achieved. Becomes difficult.

Further, the distance between the first lens unit and the second lens unit becomes large, and it is difficult to achieve the miniaturization of the lens system. If the lower limit is exceeded, the magnification of the second lens unit becomes large, making it difficult to achieve a high magnification.

(2-2) The second lens unit is a negative twenty-first lens having a concave surface having a stronger refractive power on the image surface side than the object side in order from the object side. The lens is composed of three single lenses, that is, a positive 23rd lens having a convex surface having a stronger refractive power directed toward the object side than the image plane side.

As a result, the position of the front principal point of the second group is set closer to the object side, and the distance between the principal points with the first group is shortened. Thus, the height of the off-axis light beam entering the first group from the optical axis is reduced, and the lens diameter of the first group is reduced.

(2-3) The first group includes, in order from the object side, a negative eleventh lens, a positive twelfth lens, and a positive thirteenth lens. The second lens group includes a negative twenty-first lens.
3 of lens, negative 22nd lens and positive 23rd lens
The third group includes two lenses, a positive 31a lens and a negative 32a lens or a negative 31b lens and a positive 32b lens, and the fourth group includes a positive 41a lens. The negative 42a lens and the positive 4th lens
Three lenses of the 3a lens or the positive 41b lens, the negative 42b lens, the positive 43b lens and the positive 4th lens
4b lens.

As a result, high optical performance is obtained over the entire zoom range and over the entire screen.

(2-4) The radius of curvature of the lens surface on the image plane side of the 21st lens in the second group is R _{21, R} , the radius of curvature of the lens surface on the object side of the 22nd lens is R _{22, F} , when the focal length of the entire system at the telephoto end FT, the focal length of the composite from the first group at the telephoto end to the third group was FT _{1, 3}

[0041]

(Equation 1) Satisfy the following conditions.

Here, conditional expression (5) relates to the air lens and the focal length of the second lens unit. If the lower limit is exceeded, the distortion at the wide-angle end tends to be a barrel type.

On the other hand, if the value exceeds the upper limit, distortion at the telephoto end tends to be pincushion.

Conditional expression (6) relates to an on-axis light beam emitted from the third lens unit at the telephoto end. If the lower limit value is exceeded, the divergence of the axial luminous flux emitted from the third lens group becomes strong, and the lens diameter of the fourth lens group becomes large. In addition, there is a problem that the fluctuation of spherical aberration due to focusing becomes large.

On the other hand, when the value exceeds the upper limit, the convergence of the axial light beam emitted from the third lens unit becomes strong, and a problem arises in that a sufficient back focus and an exit pupil cannot be obtained.

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. The last three lens surfaces in the numerical examples are glass blocks such as a color separation prism and a filter. 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 a direction perpendicular to the optical axis, a positive traveling direction of light, R represents a paraxial radius of curvature, and A, B, C, D, and E represent aspherical shapes. Spherical coefficient

[0048]

(Equation 2) It is represented by the following expression. "E-0X" means "10- ^X ".

<Numerical Example 1> f = 1 to 8.0 Fno = 1: 1.65 2ω = 56.4 ° to 7.3 ° R 1 = 9.760 D 1 = 0.305 N 1 = 1.80518 ν 1 = 25.4 R 2 = 5.255 D 2 = 0.915 N 2 = 1.60311 ν 2 = 60.7 R 3 = 57.424 D 3 = 0.033 R 4 = 5.401 D 4 = 0.559 N 3 = 1.69680 ν 3 = 55.5 R 5 = 14.080 D 5 = Variable R 6 = 6.644 D 6 = 0.152 N 4 = 1.88300 ν 4 = 40.8 R 7 = 1.421 D 7 = 0.593 R 8 = -7.409 D 8 = 0.135 N 5 = 1.69680 ν 5 = 55.5 R 9 = 3.188 D 9 = 0.169 R10 = 2.673 D10 = 0.423 N 6 = 1.84666 ν 6 = 23.8 R11 = 19.594 D11 = Variable R12 = (Aperture) D12 0.254 R13 = 16.349 D13 = 0.152 N 7 = 1.80400 ν 7 = 46.6 R14 = 1.863 D14 = 0.644 N 8 = 1.60342 ν 8 = 38.0 R15 = -5.937 D15 = Variable R16 = -90.332 D16 = 0.423 N 9 = 1.48749 ν 9 = 70.2 R17 = -4.286 D17 = 0.025 R18 = 8.585 D18 = 0.169 N10 = 1.80518 ν10 = 25.4 R19 = 2.706 D19 = 0.576 N11 = 1.48749 ν11 = 70.2 R20 =- 19.124 D20 = 0.025 R21 = 3.892 D21 = 0.542 N12 = 1.48749 ν12 = 70.2 R22 = -5.134 D22 = 0.678 R23 = ∞ D23 = 0.423 N13 = 1.51633 ν13 = 64.2 R24 = ∞ D24 = 3.389 N14 = 1.60342 ν14 = 38.0 R25 =

[0050]

[Table 1] <Numerical Example 2> f = 1 to 12.65 Fno = 1: 1.65 to 2 2ω = 60.0 ° to 5.2
° R 1 = 15.833 D 1 = 0.346 N 1 = 1.80518 ν 1 = 25.4 R 2 = 6.746 D 2 = 1.500 N 2 = 1.60311 ν 2 = 60.7 R 3 = -38.377 D 3 = 0.038 R 4 = 6.039 D 4 = 0.730 N 3 = 1.69680 ν 3 = 55.5 R 5 = 15.975 D 5 = Variable R 6 = 7.024 D 6 = 0.173 N 4 = 1.88300 ν 4 = 40.8 R 7 = 1.692 D 7 = 0.786 R 8 = -3.073 D 8 = 0.153 N 5 = 1.69680 ν 5 = 55.5 R 9 = 2.791 D 9 = 0.192 R10 = 3.248 D10 = 0.423 N 6 = 1.84666 ν 6 = 23.8 R11 = -36.211 D11 = Variable R12 = (Aperture) D12 0.288 R13 = 7.387 D13 = 0.807 N 7 = 1.62588 ν 7 = 35.7 R14 = -2.053 D14 = 0.173 N 8 = 1.77250 ν 8 = 49.6 R15 = -13.939 D15 = Variable R16 = 84.254 D16 = 0.480 N 9 = 1.51633 ν 9 = 64.2 R17 = -4.349 D17 = 0.028 R18 = 8.629 D18 = 0.192 N10 = 1.80518 ν10 = 25.4 R19 = 2.482 D19 = 0.769 N11 = 1.48749 ν11 = 70.2 R20 = -22.864 D20 = 0.028 R21 = 2.808 D21 = 0.538 N12 = 1.48749 ν12 = 70.2 R22 = 47.595 D22 = 0.769 R23 = ∞ D23 = 0.480 N13 = 1.51633 ν13 = 64.2 R24 = ∞ D24 = 3.461 N14 = 1.60342 ν14 = 38.0 R25 = ∞

[0051]

[Table 2] <Numerical Example 3> f = 1 to 10.0 Fno = 1: 1.65 to 1.85 2ω = 56.4 ° ~
6.1 ° R 1 = 13.935 D 1 = 0.321 N 1 = 1.80518 ν 1 = 25.4 R 2 = 6.199 D 2 = 1.160 N 2 = 1.60311 ν 2 = 60.7 R 3 = -46.242 D 3 = 0.035 R 4 = 6.062 D 4 = 0.642 N 3 = 1.69680 ν 3 = 55.5 R 5 = 18.709 D 5 = Variable R 6 = 5.215 D 6 = 0.142 N 4 = 1.88300 ν 4 = 40.8 R 7 = 1.640 D 7 = 0.653 R 8 = -2.610 D 8 = 0.142 N 5 = 1.69680 ν 5 = 55.5 R 9 = 2.588 D 9 = 0.178 R10 = 3.060 D10 = 0.392 N 6 = 1.84666 ν 6 = 23.8 R11 = -19.876 D11 = Variable R12 = (Aperture) D12 0.267 R13 = 8.618 D13 = 0.714 N 7 = 1.60342 ν 7 = 38.0 R14 = -1.616 D14 = 0.142 N 8 = 1.77250 ν 8 = 49.6 R15 = -19.460 D15 = Variable R16 = -104.168 D16 = 0.446 N 9 = 1.51633 ν 9 = 64.2 R17 = -4.034 D17 = 0.026 R18 = 8.573 D18 = 0.178 N10 = 1.84666 ν10 = 23.8 R19 = 2.919 D19 = 0.714 N11 = 1.48749 ν11 = 70.2 R20 = -11.679 D20 = 0.026 R21 = 3.431 D21 = 0.500 N12 = 1.51633 ν12 = 64.2 R22 = -22.410 D22 = 0.714 R23 = ∞ D23 = 0.446 N13 = 1.51633 ν13 = 64.2 R24 = ∞ D24 = 3.571 N14 = 1.60342 ν14 = 38.0 R25 = ∞

[0052]

[Table 3] <Numerical Example 4> f = 1 to 10.0 Fno = 1: 1.65 to 1.85 2ω = 56.4 ° ~
7.3 ° R 1 = 10.876 D 1 = 0.321 N 1 = 1.80518 ν 1 = 25.4 R 2 = 5.631 D 2 = 1.160 N 2 = 1.60311 ν 2 = 60.7 R 3 = -32.694 D 3 = 0.035 R 4 = 6.601 D 4 = 0.571 N 3 = 1.69680 ν 3 = 55.5 R 5 = 15.120 D 5 = Variable R 6 = 6.050 D 6 = 0.142 N 4 = 1.88300 ν 4 = 40.8 R 7 = 1.679 D 7 = 0.703 R 8 = -2.707 D 8 = 0.142 N 5 = 1.69680 ν 5 = 55.5 R 9 = 2.918 D 9 = 0.178 R10 = 3.235 D10 = 0.392 N 6 = 1.84666 ν 6 = 23.8 R11 = -23.215 D11 = Variable R12 = (Aperture) D12 0.267 R13 = 112.150 D13 = 0.714 N 7 = 1.60342 ν 7 = 38.0 R14 = -1.888 D14 = 0.142 N 8 = 1.80400 ν 8 = 46.6 R15 = -6.647 D15 = Variable R16 = 3.724 D16 = 0.642 N 9 = 1.48749 ν 9 = 70.2 R17 = -7.678 D17 = 0.026 R18 = 5.683 D18 = 0.178 N10 = 1.84666 ν10 = 23.8 R19 = 2.652 D19 = 0.821 N11 = 1.48749 ν11 = 70.2 R20 = -4.896 D20 = 0.714 R21 = ∞ D21 = 0.446 N12 = 1.51633 ν12 = 64.2 R22 = ∞ D22 = 3.571 N13 = 1.60342 ν13 = 38.0 R23 = ∞

[0053]

[Table 4] <Numerical Example 5> f = 1 to 10.0 Fno = 1: 1.65 to 1.8 2ω = 56.4 ° ~
7.3 ° R 1 = 9.706 D 1 = 0.321 N 1 = 1.80518 ν 1 = 25.4 R 2 = 5.409 D 2 = 1.160 N 2 = 1.51633 ν 2 = 64.2 R 3 = 1713.793 D 3 = 0.035 R 4 = 6.342 D 4 = 0.625 N 3 = 1.69680 ν 3 = 55.5 R 5 = 31.759 D 5 = Variable R 6 = 4.624 D 6 = 0.142 N 4 = 1.88300 ν 4 = 40.8 R 7 = 1.649 D 7 = 0.722 R 8 = -2.569 D 8 = 0.142 N 5 = 1.69680 ν 5 = 55.5 R 9 = 2.896 D 9 = 0.178 R10 = 3.254 D10 = 0.392 N 6 = 1.84666 ν 6 = 23.8 R11 = -34.333 D11 = Variable R12 = (Aperture) D12 0.267 R13 = 121.593 D13 = 0.714 N 7 = 1.61293 ν 7 = 37.0 R14 = -1.968 D14 = 0.142 N 8 = 1.77250 ν 8 = 49.6 R15 = -6.912 D15 = Variable R16 = 3.821 D16 = 0.642 N 9 = 1.51633 ν 9 = 64.2 R17 = -5.790 D17 = 0.026 R18 = 5.124 D18 = 0.178 N10 = 1.84666 ν10 = 23.8 R19 = 2.187 D19 = 0.535 R20 = 2.335 D20 = 0.821 N11 = 1.48749 ν11 = 70.2 R21 = -4.801 D21 = 0.714 R22 = ∞ D22 = 0.446 N12 = 1.51633 ν12 = 64.2 R23 = ∞ D23 = 3.571 N13 = 1.60342 ν13 = 38.0 R24 = ∞

[0054]

[Table 5] <Numerical example 6> f = 1 to 10.0 Fno = 1: 1.65 to 1.95 2ω = 56.4 ° to 7.
3 ° R 1 = 12.257 D 1 = 0.285 N 1 = 1.80518 ν 1 = 25.4 R 2 = 5.953 D 2 = 0.267 R 3 = 7.776 D 3 = 0.803 N 2 = 1.49700 ν 2 = 81.6 R 4 = -246.325 D 4 = 0.035 R 5 = 5.666 D 5 = 0.928 N 3 = 1.69680 ν 3 = 55.5 R 6 = 226.941 D 6 = Variable R 7 = 5.144 D 7 = 0.142 N 4 = 1.88300 ν 4 = 40.8 R 8 = 1.664 D 8 = 0.667 R 9 = -2.600 D 9 = 0.142 N 5 = 1.69680 ν 5 = 55.5 R10 = 2.617 D10 = 0.178 R11 = 3.115 D11 = 0.392 N 6 = 1.84666 ν 6 = 23.8 R12 = -21.490 D12 = Variable R13 = (Aperture) D13 = 0.267 R14 = 8.690 D14 = 0.714 N 7 = 1.61293 ν 7 = 37.0 R15 = -1.618 D15 = 0.142 N 8 = 1.77250 ν 8 = 49.6 R16 = -17.470 D16 = Variable R17 = -80.048 D17 = 0.446 N 9 = 1.48749 ν 9 = 70.2 R18 = -4.119 D18 = 0.026 R19 = 8.509 D19 = 0.178 N10 = 1.84666 ν10 = 23.8 R20 = 2.945 D20 = 0.714 N11 = 1.48749 ν11 = 70.2 R21 = -11.983 D21 = 0.026 R22 = 3.435 D22 = 0.500 N12 = 1.51633 ν12 = 64.2 R23 = -25.034 D23 = 0.714 R24 = ∞ D24 = 0.446 N13 = 1.51633 ν13 = 64.2 R25 = ∞ D25 = 3.571 N14 = 1.60342 ν14 = 38.0 R26 = ∞

[0055]

[Table 6] <Numerical example 7> f = 1 to 10.0 Fno = 1: 1.65 to 1.96 2ω = 56.4 ° to 7.
3 ° R 1 = 12.989 D 1 = 0.285 N 1 = 1.80518 ν 1 = 25.4 R 2 = 6.175 D 2 = 0.257 R 3 = 7.871 D 3 = 0.803 N 2 = 1.49700 ν 2 = 81.6 R 4 = -80.049 D 4 = 0.089 R 5 = 5.647 D 5 = 0.857 N 3 = 1.69680 ν 3 = 55.5 R 6 = 85.989 D 6 = Variable R 7 = 4.788 D 7 = 0.142 N 4 = 1.88300 ν 4 = 40.8 R 8 = 1.628 D 8 = 0.691 R 9 = -2.589 D 9 = 0.142 N 5 = 1.69680 ν 5 = 55.5 R10 = 2.635 D10 = 0.178 R11 = 3.131 D11 = 0.357 N 6 = 1.84666 ν 6 = 23.8 R12 = -21.153 D12 = Variable R13 = (Aperture) D13 = 0.267 R14 = 8.729 D14 = 0.678 N 7 = 1.61293 ν 7 = 37.0 R15 = -1.896 D15 = 0.046 R16 = -1.765 D16 = 0.142 N 8 = 1.77250 ν 8 = 49.6 R17 = -12.326 D17 = Variable R18 = -28.412 D18 = 0.464 N 9 = 1.48749 ν 9 = 70.2 R19 = -4.142 D19 = 0.026 R20 = 8.004 D20 = 0.160 N10 = 1.84666 ν10 = 23.8 R21 = 2.872 D21 = 0.678 N11 = 1.48749 ν11 = 70.2 R22 = -12.333 D22 = 0.026 R23 = 3.713 D23 = 0.535 N12 = 1.51633 ν12 = 64.2 R24 = -11.186 D24 = 0.714 R25 = ∞ D25 = 0.446 N13 = 1.51633 ν13 = 64.2 R26 = ∞ D26 = 3.571 N14 = 1.60342 ν14 = 38.0 R27 = ∞

[0056]

[Table 7] <Numerical example 8> f = 1 to 8.0 Fno = 1: 1.65 to 22Ω = 53.1 ° to 7.
2 ° R 1 = 14.585 D 1 = 0.300 N 1 = 1.80518 ν 1 = 25.4 R 2 = 4.950 D 2 = 1.000 N 2 = 1.60311 ν 2 = 60.7 R 3 = -12.965 D 3 = 0.033 R 4 = 3.950 D 4 = 0.500 N 3 = 1.69680 ν 3 = 55.5 R 5 = 9.147 D 5 = Variable R 6 = 7.777 D 6 = 0.150 N 4 = 1.88300 ν 4 = 40.8 R 7 = 1.459 D 7 = 0.538 R 8 = -1.730 D 8 = 0.133 N 5 = 1.69680 ν 5 = 55.5 R 9 = 2.114 D 9 = 0.383 N 6 = 1.84666 ν 6 = 23.8 R10 = -8.785 D10 = Variable R11 = (Aperture) D11 = 0.250 R12 = 7.249 D12 = 0.666 N 7 = 1.62588 ν 7 = 35.7 R13 = -1.513 D13 = 0.150 N 8 = 1.77250 ν 8 = 49.6 R14 = -8.358 D14 = Variable R15 = -107.336 D15 = 0.416 N 9 = 1.51633 ν 9 = 64.2 R16 = -3.600 D16 = 0.025 R17 = 7.512 D17 = 0.166 N10 = 1.80518 ν10 = 25.4 R18 = 2.098 D18 = 0.666 N11 = 1.48749 ν11 = 70.2 R19 = -12.762 D19 = 0.025 R20 = 3.046 D20 = 0.550 N12 = 1.48749 ν12 = 70.2 R21 = -7.730 D21 = 0.666 R22 = ∞ D22 = 0.416 N13 = 1.51633 ν13 = 64.2 R23 = ∞ D23 = 3.000 N14 = 1.60342 ν14 = 38.0 R24 = D

[0057]

[Table 8]

[0058]

According to the present invention, as described above, the lens unit is constituted by four lens units as a whole, the refractive power of each lens unit is set, and the fourth unit is moved during focusing. Achieving good aberration correction over the entire zoom range while miniaturizing the entire lens system, and achieving a large aperture ratio rear focus zoom lens with a sufficiently long back focus with little aberration fluctuation during focusing can do.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a paraxial refractive power arrangement according to the present invention.

FIG. 2 is a sectional view of a lens according to a numerical example 1 of the present invention.

FIG. 3 is a sectional view of a lens according to a numerical example 2 of the present invention.

FIG. 4 is a sectional view of a lens according to a numerical example 3 of the present invention.

FIG. 5 is a sectional view of a lens according to a numerical example 4 of the present invention.

FIG. 6 is a sectional view of a lens according to a numerical example 5 of the present invention.

FIG. 7 is a sectional view of a lens according to a numerical example 6 of the present invention.

FIG. 8 is a sectional view of a lens according to a numerical example 7 of the present invention.

FIG. 9 is a sectional view of a lens according to a numerical example 8 of the present invention.

FIG. 10 is an aberration diagram at a wide-angle end according to Numerical Embodiment 1 of the present invention.

FIG. 11 is an aberration diagram at a telephoto end in Numerical Example 1 of the present invention;

FIG. 12 is an aberration diagram at a wide-angle end according to Numerical Example 2 of the present invention.

FIG. 13 is an aberration diagram at a telephoto end in Numerical Example 2 of the present invention.

FIG. 14 is an aberration diagram at a wide angle end according to Numerical Example 3 of the present invention.

FIG. 15 is an aberration diagram at a telephoto end in Numerical Example 3 of the present invention.

FIG. 16 is an aberration diagram at a wide angle end according to Numerical Example 4 of the present invention.

FIG. 17 is an aberration diagram at a telephoto end in Numerical Example 4 of the present invention.

FIG. 18 is an aberration diagram at a wide angle end according to Numerical Example 5 of the present invention.

FIG. 19 is an aberration diagram at a telephoto end in Numerical Example 5 of the present invention.

FIG. 20 is an aberration diagram at a wide angle end according to Numerical Example 6 of the present invention.

FIG. 21 is an aberration diagram at a telephoto end in Numerical Example 6 of the present invention.

FIG. 22 is an aberration diagram at a wide angle end according to Numerical Example 7 of the present invention.

FIG. 23 is an aberration diagram at a telephoto end in Numerical Example 7 of the present invention;

FIG. 24 is an aberration diagram at a wide-angle end according to Numerical Example 8 of the present invention.

FIG. 25 is an aberration diagram at a telephoto end in Numerical Example 8 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 d d-line g g-line ΔS Sagittal image plane ΔM Meridional image plane

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02B 15/16 G02B 13/18

Claims (7)

(57) [Claims] 1. A first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power. Moving the second lens unit to the image plane side to perform zooming from the wide-angle end to the telephoto end, and correcting and correcting the image plane fluctuation caused by zooming by moving the fourth lens unit. The lens system according to claim 1, wherein a focus is moved by moving the zoom lens, and a condition of 3.5 <F3 / F4 is satisfied when the focal length of the i-th lens unit is Fi. 2. The second group is composed of a negative twenty-first lens having a concave surface having a stronger refractive power on the image surface side than the object side in order from the object side, a negative twenty-second lens having both lens surfaces concave, and A positive second lens with a convex surface having a stronger refractive power facing the object side than the image surface side
2. A rear focus type zoom lens according to claim 1, wherein said zoom lens comprises three single lenses. 3. The first lens unit includes a negative eleventh lens element in order from the object side.
3 of lens, positive twelfth lens and positive thirteenth lens
The second group is a negative 21st lens,
The third lens unit includes three lenses, a negative twenty-second lens and a positive twenty-third lens, and the third group includes two lenses, that is, a positive 31a lens and a negative 32a lens or a negative 31b lens and a positive 32b lens. The fourth group is a positive 41st lens
a lens, a negative 42a lens and a positive 43a lens, or a positive 41b lens and a negative 42th lens.
2. The rear focus type zoom lens according to claim 1, wherein the zoom lens comprises four lenses, a b lens, a positive 43b lens, and a positive 44b lens. 4. The rear focus type zoom lens according to claim 2, wherein a stop is arranged on the object side of said third group. 5. The focal length of the entire system at the wide-angle end is Fw,
5. The condition of 3 <bfw / Fw <5-0.8 <Fw / F2 <-0.45 <F1 / Fw <12 when the back focus at the wide angle end is bfw. Rear focus zoom lens. 6. The radius of curvature of the lens surface on the image plane side of the 21st lens in the second group is R _{21, R} , the radius of curvature of the object side lens surface of the 22nd lens is R _{22, F} , and the telephoto end. Where FT is the focal length of the entire system at, and FT _1,3 is the combined focal length of the first to third units at the telephoto end. 1 <(1 / R _{22, F} −1 / R _{21, R} ) 2. The rear focus type zoom lens according to claim 1, wherein a condition of F2 <2-0.55 <FT / FT _1,3 <0 is satisfied. 7. The refill according to claim 1, wherein:
It is characterized by having a short focus zoom lens
Camera.