JPH05288991A - Rear focus type zoom lens - Google Patents

Abstract

PURPOSE:To obtain the rear focus type zoom lens which has an 8 power variation ratio and an about 1.8 F number by providing four lens groups on the whole, performing focusing operation by a lens group behind a power variation system, and reducing the overall size of the lens system. CONSTITUTION:This zoom lens has 1st, 2nd, 3rd, and 4th groups 1, 2, 3, and 4 with positive, negative, positive, and positive refracting powers in order from the object side, and the 2nd group 2 is moved toward the image plane to perform power variation from the wide-angle end to the telephoto end; and image plane variation accompanying the power vairation is corrected by moving the 4th group 4 and the focusing operation is carried out by moving the 4th group 4. The 1st group 1 has three negative, positive, and positive lenses and the 2nd group 2 has three negative, negative, and positive lenses; and the 4th group 4 has a negative lens 4N on the most image plane side and a positive lens 4P on the object side of the lens 4N and satisfies -1.5<phia/phi4<0.5, where phia is the refracting power of the air lens formed between the lenses 4P and 4N and phi4 is the refracting power of the 4th group 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear focus type zoom lens, and more particularly to a photographic camera, a video camera,
Further, the present invention relates to a rear focus type zoom lens which is used for a broadcasting camera or the like and has a large aperture ratio such as an F number of about 1.8 and a high zoom ratio and is suitable for a compact zoom lens.

[0002]

2. Description of the Related Art With the recent reduction in size and weight of the entire camera in a photographic camera, a video camera or the like, there is a demand for a zoom lens attached to the camera to be small and lightweight.

In general, as a method for reducing the size of the entire lens system in a zoom lens, there is a so-called rear focus type method in which a lens group other than the first lens group on the object side is moved along the optical axis for focusing.

Generally, in a rear focus type zoom lens, the effective diameter of the first lens group is smaller than that of a zoom lens in which the first lens group is moved to perform focusing, which facilitates downsizing of the entire lens system and close-up photography. Especially, it is easy to perform very close-up photography, and since the relatively small and lightweight lens group is moved, the driving force of the lens group is small, and quick focusing is possible.

As such a rear focus type zoom lens, for example, JP-A-62-24213, JP-A-63-247316, and JP-A-63-29718.
JP-A-63-29719, JP-A-63-
No. 1,230,09 and Japanese Patent Laid-Open No. 2-48621 disclose a first group having a positive refractive power, a second group having a negative refractive power for zooming, a third group having a positive refractive power, and a positive group in order from the object side. 4 lens groups of the fourth lens group having a refracting power of, the first group and the third group are fixed, the second group is moved to perform zooming, and the fourth group is accompanied by zooming. Focusing is performed by moving the fourth lens unit while moving the fourth lens unit to correct the image plane variation.

[0006]

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

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

Particularly, in a zoom lens having a large aperture ratio and a high zoom ratio, it becomes very difficult to obtain high optical performance over the entire zoom range and over the entire object distance.

The present invention adopts the rear focus system, and at the time of achieving a large aperture ratio and a high zoom ratio, downsizing the entire lens system, and over the entire zoom range from the wide-angle end to the telephoto end. Another object of the present invention is to provide a rear focus type zoom lens having good optical performance over the entire object distance from an object at infinity to a near object.

[0010]

A rear focus type zoom lens according to the present invention comprises a first group having a positive refractive power, a second group having a negative refractive power, and a third group having a positive refractive power in order from the object side. , And a fourth lens unit of a fourth lens unit of positive refractive power,
The lens unit is moved to the image plane side to perform zooming from the wide-angle end to the telephoto end, and the image plane variation due to zooming is corrected by moving the fourth lens unit and moving the fourth lens unit to focus. The first group has three lenses, a negative eleventh lens, a positive twelfth lens, and a positive thirteenth lens, and the second group has a strong refractive power on the image plane side as compared to the object side. Negative 21st with concave face
A lens, a 22nd lens whose both lens surfaces are concave, and a 23rd positive lens with a convex surface having a stronger refractive power facing the object side than the image side.
The third lens group has three lenses, and the fourth lens group has a negative fourth N lens element closest to the image plane side and a positive fourth lens element side closer to the object side of the fourth N lens element.
When the refractive power of the air lens formed by the fourth P lens and the fourth N lens is φa, and the refractive power of the fourth lens group is φ4, then −1.5 <φa / φ4 <0.5 ... (1) It is characterized by satisfying the condition.

[0011]

1 is a schematic view of an embodiment showing the paraxial refractive power arrangement of a rear focus type zoom lens according to the present invention.

2 to 6 are lens cross-sectional views of Numerical Examples 1 to 5 described later of the present invention, and FIGS. 7 to 21 are various aberration diagrams of Numerical Examples 1 to 5 described later of the present invention. In the aberration diagrams, FIGS. 7, 10, 13, 16, and 19 are wide-angle ends, FIGS. 8, 11, 14, 17, and 20 are intermediate, and FIGS. 9, 12, 15, and 18, FIG. 21 shows the telephoto end.

In the figure, 1 is a first group having a positive refractive power, 2 is a second group having a negative refractive power, 3 is a third group having a positive refractive power, and 4 is a fourth group having a positive refractive power. .. SP is an aperture stop, which is arranged in front of the third group 3. G is a glass block such as a face plate.

In this embodiment, the second lens unit is moved to the image plane side as indicated by the arrow when the magnification is changed from the wide-angle end to the telephoto end, and the image plane variation due to the magnification change is corrected by moving the fourth lens unit. ing.

Further, a rear focus type in which focusing is performed by moving the fourth lens unit on the optical axis is adopted. The solid curve 4a and the dotted curve 4b of the fourth group shown in the same figure show the image plane variation during zooming from the wide-angle end to the telephoto end when focusing on an object at infinity and a near object, respectively. The movement locus for correction is shown. The first and third groups are fixed during zooming and focusing.

In the present embodiment, the fourth lens unit is moved to correct the image plane variation due to zooming, and the fourth lens unit is moved to perform focusing. Curve 4 in the figure
As shown in a and 4b, when the magnification is changed from the wide-angle end to the telephoto end, the object side is moved so as to have a convex locus.
As a result, the space between the third group and the fourth group is effectively used, and the total lens length is effectively shortened.

In the present embodiment, for example, when focusing from an object at infinity to a near object at the telephoto end, the fourth lens unit is moved forward as indicated by a straight line 4c in the figure.

The zoom lens in this embodiment adopts a zoom system in which a virtual image formed by a combined system of the first group and the second group is formed on the photosensitive surface by the third group and the fourth group.

In this embodiment, as compared with the conventional so-called four-group zoom lens in which the first group is extended and focused, the rear focus system as described above is employed, thereby preventing performance deterioration due to the eccentricity error of the first group. At the same time, the effective lens diameter of the first lens group is effectively prevented from increasing.

By arranging the aperture stop immediately before the third lens unit, variation in aberration due to the movable lens unit is reduced, and by shortening the distance between the lens units in front of the aperture stop, the diameter of the front lens is reduced. Achieved easily.

In particular, in this embodiment, the negative fourth N lens is arranged on the most image side of the fourth lens unit, and the entire lens system is of the telephoto type, which facilitates downsizing of the entire lens system.

Further, the positive fourth P lens of the fourth group and the negative fourth P lens
A predetermined air gap is secured by the N lens so that the principal point position of the entire system can be easily moved to the object side, and the overall size of the lens system is reduced.

Further, according to the present invention, the second lens group is composed of three lenses which are separated from each other and has a predetermined shape as described above, and the variation of the aberration is increased to about 8 and the variation of the aberration caused by the variation of the magnification when the magnification is increased is improved. Has been corrected to.

Generally, for example, in a rear focus type zoom lens as proposed in Japanese Patent Laid-Open No. 62-24213, a negative lens and a positive lens are bonded to a part of the second lens unit for zooming. A lens is provided.

The cemented lens surface of this cemented lens mainly corrects axial chromatic aberration, spherical aberration, and off-axis coma aberration in a well-balanced manner.

In such a lens system, it is effective to increase the negative refracting power of the second lens group in order to reduce the size of the entire lens system and achieve a high zoom ratio. However, if the refracting power of the second group is increased, the burden of aberration correction on the cemented lens surface of the cemented lens becomes too large, and it becomes difficult to obtain high optical performance over the entire zoom range.

Therefore, in the present invention, the second group is composed of three independent lenses, and is constructed so as to have an appropriately shaped air lens instead of the cemented lens surface, whereby the aberration correction is balanced over the entire zoom range. I'm doing well.

By specifying the lens configuration of each lens group and satisfying conditional expression (1) as described above, the overall lens length can be shortened, and good optical performance can be obtained over the entire zoom range and over the entire object distance. We have obtained a zoom lens with a high zoom ratio.

When the upper limit of conditional expression (1) is exceeded and the refractive power φa of the air lens becomes too strong, the telephoto type becomes weak and it becomes difficult to downsize the entire lens system. If the lower limit value is exceeded and the refractive power φa of the air lens becomes too weak, various aberrations, particularly spherical aberration, increase, and further, the aberration variation accompanying the change of the object distance at the time of focusing with the fourth lens unit increases. It's not good because it comes.

The rear focus type zoom lens which is the object of the present invention can be achieved by satisfying the above-mentioned various conditions, but it is more preferable to satisfy the following various conditions.

(B) The fourth lens group is composed of three lenses, a positive lens, a positive lens, and a negative lens in order from the object side, or two lenses, a positive lens and a negative lens. It is preferable to maintain good optical performance while achieving good performance.

(B) It is preferable that the third lens unit is composed of a single positive lens having at least one aspherical surface in order to satisfactorily correct spherical aberration generated in the third lens unit close to the stop.

(C) When the imaging magnifications at the wide-angle end and the telephoto end of the second lens unit are β2W and β2T, respectively | 1 / β2W | ≦ | β2T | (2) The condition (2) is satisfied.

Generally, in order to reduce the size of the entire lens system, it is preferable that the distance from the fourth lens unit to the image plane is longer at the wide-angle end than at the telephoto end. This is to use a region in which the image forming magnification of the second lens unit is equal to or larger than that in accordance with the magnification change.

Conditional expression (2) is for satisfying this condition. In the conditional expression (2), the equal sign indicates that the fourth lens group makes a complete reciprocating motion for the purpose of correcting the image plane variation accompanying the magnification change.

(D) The distance from the final lens surface to the exit pupil at the wide-angle end is Tkw ', the distance from the first lens surface to the final lens surface at the wide-angle end is ΣDw, the back focus at the wide-angle end is bfw, and the back focus at the wide-angle end. Fw the focal length of the entire system, the maximum image height Y _max, when the focal length of the i-th group and fi 0.5 <(| Tkw' | + bfw) / (ΣDw + bfw) <0.8 ‥ (3) 0 .5 <bfw / f4 <0.75 ‥‥‥‥ (4) 4.0 <| Tkw' | / Y max <10 ‥‥‥‥ (5) 4.0 <(| Tkw' | + bfw) / Fw <8.0 ... (6) 0.5 <| Tkw '| / f4 <2.5 ... (7) The following condition must be satisfied.

Conditional expressions (3), (5), (6) and (7) are expressions relating to the total lens length (ΣDw + bfw) and the exit pupil position. If any of the conditional expressions deviates from the upper limit value, the total lens length becomes large. Also, when the value goes below the lower limit, the light flux reaching the imaging surface deviates from telecentricity and becomes an oblique light flux, and the imaging surface position deviates on the optical axis (for example, wobbling of the imaging surface for autofocus (modulation method, etc.)). It looks like the imaging magnification has changed, or CC
When a device such as D is used for the image pickup surface, so-called shading is conspicuous, which is not suitable. Conditional expression (4) also relates to the total length of the lens. If the upper limit is exceeded, the entire system becomes large, and if the lower limit is exceeded, dust or the like attached to the final lens tends to be reflected on the imaging surface, which is not appropriate.

(E) The focal length of the entire system at the telephoto end is F
t, when the moving amount of the second lens unit associated with zooming is M2 0.7 <| f2 | / Fw <0.9 (8) 2.5 <f4 / Fw <4.0 (9) 0.2 <| M2 | / (Ft-Fw) <0.4 ... (10) 0.3 <f1 / (ΣDw + bfw) <0.6 ... (11) ) The following conditions must be satisfied.

Conditional expression (8) represents the balance of the refracting power of the second group of the main variator of the zoom lens with respect to the entire system. If the value exceeds the upper limit, it is necessary to increase the amount of movement of the second lens unit in order to obtain a desired zoom ratio, which is not appropriate because the entire lens system becomes large. On the other hand, if the lower limit is exceeded, the Petzval sum will increase with a positive value, and the image plane will be over, which is not appropriate.

Conditional expression (9) relates to the refracting power of the fourth lens unit used for focusing. When the upper limit is exceeded, the focal length of the focus lens becomes long, and the fourth lens unit moves toward the desired shortest shooting distance. The amount is too large to be suitable.
On the other hand, if the value goes below the lower limit, the sensitivity of the image plane due to the position of the fourth lens unit becomes large, control becomes difficult, and the back focus tends to become short, which is not suitable.

Conditional expression (10) defines an appropriate refractive power arrangement of the second group of variators. When the value exceeds the upper limit, the amount of movement of the second lens unit becomes large and the lens system becomes large, or the zoom ratio becomes small, which is not suitable. If the lower limit is exceeded, the moving amount of the second lens unit cannot be obtained to obtain a desired zoom ratio, the refractive power of the second lens unit becomes strong, the Petzval sum increases to a negative value, and the image surface becomes unsuitable. ..

Conditional expression (11) relates to the refractive power of the first lens group. When the value exceeds the upper limit, the magnification of the second lens unit becomes considerably low at the wide-angle end, and it becomes large to obtain a desired zoom ratio, which is not suitable. On the other hand, when the value goes below the lower limit, the moving range of the second lens unit for zooming cannot be secured and a desired zoom ratio cannot be secured.

(F) At least one of the positive lenses in the fourth lens unit.
It is preferable to dispose aspherical surfaces to maintain better optical performance.

(G) If the Abbe number of the glass that constitutes the positive lens in the third and fourth groups is ν _p and the Abbe number of the glass that constitutes the negative lens of the fourth group is ν _n , then ν Satisfy the condition of _p > 45 (12) ν _n <35 (13).

Conditional expressions (12) and (13) are for satisfactorily correcting chromatic aberration while achieving downsizing of the entire lens system. If it deviates from this range, the g-line chromatic aberration of magnification becomes under-corrected and the axial chromatic aberration becomes insufficiently corrected, which is not appropriate.

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

The aspherical shape has the X axis in the optical axis direction, the Y axis in the direction perpendicular to the optical axis, the traveling direction of light is positive, the intersection of the apex of the lens and the X axis is taken as the origin, and r is the lens surface. When paraxial radius of curvature of a ₁ , a ₂ , a ₃ , a ₄ , a ₅ is aspherical

[0048]

[Equation 1] It is represented by the following formula.

R in the numerical embodiments 1, 2, 3, and 4
Reference numerals 19 and R20 and R21 and R22 in Numerical Embodiment 5 indicate parallel plane plates such as a face plate and a filter. Table 1 shows the relationship with each conditional expression in each numerical example. Numerical Example 1 f = 1.0 to 7.97 FNO = 1: 1.85 to 2.73 2ω = 56.1 ° to 7.6 ° R 1 = 4.289 D 1 = 0.17 N 1 = 1.84666 ν 1 = 23.8 R 2 = 2.631 D 2 = 0.74 N 2 = 1.51633 ν 2 = 64.2 R 3 = -30.429 D 3 = 0.03 R 4 = 2.866 D 4 = 0.42 N 3 = 1.71300 ν 3 = 53.8 R 5 = 10.497 D 5 = variable R 6 = 7.448 D 6 = 0.08 N 4 = 1.80610 ν 4 = 41.0 R 7 = 1.062 D 7 = 0.33 R 8 = -1.918 D 8 = 0.08 N 5 = 1.71300 ν 5 = 53.8 R 9 = 1.333 D 9 = 0.08 R10 = 1.408 D10 = 0.28 N 6 = 1.78472 ν 6 = 25.7 R11 = 6.437 D11 = Variable R12 = (Aperture) D12 = 0.18 R13 = 2.075 D13 = 0.54 N 7 = 1.48749 ν 7 = 70.2 R14 = -4.119 D14 = Variable R15 = 3.074 D15 = 0.55 N 8 = 1.51633 ν 8 = 64.2 R16 = -1.269 D16 = 0.02 R17 = -1.227 D17 = 0.08 N 9 = 1.84666 ν 9 = 23.8 R18 = -1.953 D18 = 0.50 R19 = ∞ D19 = 0.83 N10 = 1.51633 ν10 = 64.2 R20 = ∞

[0050]

[Table 1] Aspheric surface R13 surface R15 surface a ₁ = 0 a ₁ = 0 a ₂ = -2.87 x 10 ^-2 a ₂ = -3.26 x 10 ^-2 a ₃ = 3.02 x 10 ^-2 a ₃ = 7.38 x 10 ^-3 a ₄ = -5.28 x 10 ^-2 a ₄ = 5.24 x 10 ^-3 a ₅ = 1.16 x 10 ^-2 a ₅ = -6.23 x 10 ^-3 Numerical Example 2 f = 1.0 to 7.99 FNO = 1: 1.85 to 2.65 2ω = 56.1 ° to 7.6 ° R 1 = 4.150 D 1 = 0.17 N 1 = 1.84666 ν 1 = 23.8 R 2 = 2.556 D 2 = 0.76 N 2 = 1.51633 ν 2 = 64.2 R 3 = -25.070 D 3 = 0.03 R 4 = 2.866 D 4 = 0.41 N 3 = 1.71300 ν 3 = 53.8 R 5 = 9.998 D 5 = Variable R 6 = 8.825 D 6 = 0.08 N 4 = 1.80610 ν 4 = 41.0 R 7 = 0.973 D 7 = 0.36 R 8 = -1.724 D 8 = 0.08 N 5 = 1.71300 ν 5 = 53.8 R 9 = 1.538 D 9 = 0.08 R10 = 1.541 D10 = 0.29 N 6 = 1.78472 ν 6 = 25.7 R11 = 33.375 D11 = Variable R12 = (Aperture) D12 = 0.18 R13 = 3.829 D13 = 0.62 N 7 = 1.48749 ν 7 = 70.2 R14 = -2.176 D14 = Variable R15 = 3.037 D15 = 0.55 N 8 = 1.51633 ν 8 = 64.2 R16 =- 1.299 D16 = 0.02 R17 = -1.211 D17 = 0.08 N 9 = 1.84666 ν 9 = 23.8 R18 = -2.089 D18 = 0.50 R19 = ∞ D19 = 0.83 N10 = 1.51633 ν10 = 64.2 R20 = ∞

[0051]

[Table 2] Aspheric surface R14 surface R15 surface a ₁ = 0 a ₁ = 0 a ₂ = 2.87 × 10 ^-2 a ₂ = 1.72 × 10 ^-2 a ₃ = -1.37 × 10 ^-2 a ₃ = -1.07 × 10 ^-2 a ₄ = 2.22 × 10 ^-3 a ₄ = 1.79 × 10 ^-2 a ₅ = 2.12 × 10 ^-2 a ₅ = 7.39 × 10 ^-2 Numerical example 3 f = 1.0 to 7.97 FNO = 1: 1.85 to 2.75 2ω = 56.1 ° ~ 7.6 ° R 1 = 4.305 D 1 = 0.17 N 1 = 1.80518 ν 1 = 25.4 R 2 = 2.459 D 2 = 0.80 N 2 = 1.51633 ν 2 = 64.2 R 3 = -693.37 D 3 = 0.03 R 4 = 2.801 D 4 = 0.48 N 3 = 1.69680 ν 3 = 55.5 R 5 = 13.956 D 5 = Variable R 6 = 5.392 D 6 = 0.08 N 4 = 1.80610 ν 4 = 41.0 R 7 = 0.943 D 7 = 0.36 R 8 = -1.458 D 8 = 0.08 N 5 = 1.69680 ν 5 = 55.5 R 9 = 1.486 D 9 = 0.07 R10 = 1.592 D10 = 0.26 N 6 = 1.84666 ν 6 = 23.8 R11 = 17.094 D11 = Variable R12 = (Aperture) D12 = 0.18 R13 = 1.815 D13 = 0.44 N 7 = 1.48749 ν 7 = 70.2 R14 = -4.608 D14 = Variable R15 = 2.247 D15 = 0.55 N 8 = 1.51633 ν 8 = 64.2 R16 = -1.198 D16 = 0.01 R17 = -1.531 D17 = 0.08 N 9 = 1.84666 ν 9 = 23.8 R18 = -4.557 D18 = 0.50 R19 = ∞ D19 = 0.83 N10 = 1.51633 ν10 = 64.2 R20 = ∞

[0052]

[Table 3] Aspheric surface R13 surface R16 surface a ₁ = 0 a ₁ = 0 a ₂ = -4.64 x 10 ^-2 a ₂ = 9.79 x 10 ^-2 a ₃ = 2.94 x 10 ^-2 a ₃ = 4.11 x 10 ^-2 a ₄ = -4.41 x 10 ^-2 a ₄ = -2.50 x 10 ^-2 a ₅ = 3.41 x 10 ^-3 a ₅ = 3.11 x 10 ^-2 Numerical Example 4 f = 1.0 to 7.98 FNO = 1: 1.85 to 2.67 2ω = 56.1 ° ~ 7.6 ° R 1 = 3.424 D 1 = 0.17 N 1 = 1.80518 ν 1 = 25.4 R 2 = 2.260 D 2 = 0.70 N 2 = 1.51633 ν 2 = 64.2 R 3 = 33.150 D 3 = 0.03 R 4 = 2.801 D 4 = 0.43 N 3 = 1.69680 ν 3 = 55.5 R 5 = 10.004 D 5 = Variable R 6 = 4.847 D 6 = 0.08 N 4 = 1.80518 ν 4 = 25.4 R 7 = 0.781 D 7 = 0.32 R 8 = -1.218 D 8 = 0.08 N 5 = 1.69680 ν 5 = 55.5 R 9 = 1.418 D 9 = 0.04 R10 = 1.487 D10 = 0.31 N 6 = 1.84666 ν 6 = 23.8 R11 = -5.766 D11 = Variable R12 = (Aperture) D12 = 0.18 R13 = 2.209 D13 = 0.37 N 7 = 1.58313 ν 7 = 59.4 R14 = -15.937 D14 = Variable R15 = 1.960 D15 = 0.63 N 8 = 1.58313 ν 8 = 59.4 R16 = -1.257 D16 = 0.00 R17 = -2.293 D17 = 0.08 N 9 = 1.84666 ν 9 = 23.8 R18 = 17.522 D18 = 0.50 R19 = ∞ D19 = 0.83 N10 = 1.51633 ν10 = 64.2 R20 = ∞

[0053]

[Table 4] Aspherical surface R13 surface R16 surface a ₁ = 0 a ₁ = 0 a ₂ = -3.55 × 10 ^-2 a ₂ = 1.48 × 10 ^-1 a ₃ = 1.23 × 10 ^-2 a ₃ = 3.61 × 10 ^-2 a ₄ = -5.41 x 10 ^-3 a ₄ = -4.42 x 10 ^-2 a ₅ = -1.58 x 10 ^-2 a ₅ = 3.57 x 10 ^-2 Numerical Example 5 f = 1.0 to 8.00 FNO = 1: 1.85 to 2.61 2ω = 56.1 ° ~ 7.6 ° R 1 = 3.061 D 1 = 0.17 N 1 = 1.84666 ν 1 = 23.8 R 2 = 2.085 D 2 = 0.75 N 2 = 1.51633 ν 2 = 64.2 R 3 = 13.994 D 3 = 0.03 R 4 = 2.866 D 4 = 0.44 N 3 = 1.71300 ν 3 = 53.8 R 5 = 11.512 D 5 = Variable R 6 = 6.420 D 6 = 0.08 N 4 = 1.80610 ν 4 = 41.0 R 7 = 0.803 D 7 = 0.39 R 8 = -1.412 D 8 = 0.08 N 5 = 1.71300 ν 5 = 53.8 R 9 = 2.511 D 9 = 0.03 R10 = 1.989 D10 = 0.25 N 6 = 1.78472 ν 6 = 25.7 R11 = -8.325 D11 = Variable R12 = (Aperture) D12 = 0.18 R13 = 2.277 D13 = 0.43 N 7 = 1.58313 ν 7 = 59.4 R14 = -7.975 D14 = Variable R15 = 5.647 D15 = 0.38 N 8 = 1.58313 ν 8 = 59.4 R16 = -3.202 D16 = 0.03 R17 = 3.648 D17 = 0.47 N 9 = 1.48749 ν 9 = 70.2 R18 = -1.446 D18 = 0.03 R19 = -2.531 D19 = 0.12 N10 = 1.84666 ν10 = 23.8 R20 = 6.987 D20 = 0.50 R21 = ∞ D21 = 0.8 3 N11 = 1.51633 ν11 = 64.2 R22 = ∞

[0054]

[Table 5] Aspherical surface R13 surface R16 surface a ₁ = 0 a ₁ = 0 a ₂ = -2.43 x 10 ^-2 a ₂ = 7.80 x 10 ^-2 a ₃ = 7.06 x 10 ^-3 a ₃ = 3.58 x 10 ^-2 a ₄ = 1.08 x 10 ^-2 a ₄ = 2.20 x 10 ^-2 a ₅ = -3.57 x 10 ^-2 a ₅ = 2.05 x 10 ^-2

[0055]

[Table 6]

[0056]

According to the present invention, as described above, the refractive powers and lens configurations of the four lens groups and the refractive power of the air lens in the fourth lens group are set, and the fourth lens group is moved during focusing. By adopting the above-mentioned lens system, it is possible to reduce the size of the entire lens system, achieve a good aberration correction over a zoom ratio of about 8 and the entire zoom range, and to have high optical performance with little aberration fluctuation during focusing. A rear focus type zoom lens with a number 1.8 and a large aperture ratio can be achieved.

[Brief description of drawings]

FIG. 1 is a schematic view of an embodiment showing a paraxial refractive power arrangement of the present invention.

FIG. 2 is a lens cross-sectional view of Numerical Example 1 of the present invention.

FIG. 3 is a lens cross-sectional view of Numerical Example 2 of the present invention.

FIG. 4 is a lens sectional view of Numerical Example 3 of the present invention.

FIG. 5 is a lens cross-sectional view of Numerical Example 4 of the present invention.

FIG. 6 is a lens cross-sectional view of Numerical Example 5 of the present invention.

FIG. 7 is an aberration diagram at the wide-angle end according to Numerical Example 1 of the present invention.

FIG. 8 is an intermediate aberration diagram of Numerical Example 1 of the present invention.

FIG. 9 is an aberration diagram at a telephoto end according to Numerical Example 1 of the present invention.

FIG. 10 is an aberration diagram at a wide-angle end according to Numerical Example 2 of the present invention.

FIG. 11 is an intermediate aberration diagram of Numerical example 2 of the present invention.

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

FIG. 13 is an aberration diagram at a wide-angle end according to Numerical Example 3 of the present invention.

FIG. 14 is an intermediate aberration diagram of Numerical Example 3 of the present invention.

FIG. 15 is an aberration diagram at a telephoto end according to 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 intermediate aberration diagram of Numerical Example 4 of the present invention.

FIG. 18 is an aberration diagram at a telephoto end according to Numerical Example 4 of the present invention.

FIG. 19 is an aberration diagram at a wide-angle end according to Numerical Example 5 of the present invention.

FIG. 20 is an intermediate aberration diagram of Numerical example 5 of the present invention.

FIG. 21 is an aberration diagram at a telephoto end according to Numerical Example 5 of the present invention.

[Explanation of symbols]

 1 1st group 2 2nd group 3 3rd group 4 4th group SP stop d d line g g line ΔS sagittal image plane ΔM meridional image plane

Claims (3)

[Claims] 1. Four lens groups, a first group having a positive refractive power, a second group having a negative refractive power, a third group having a positive refractive power, and a fourth group having a positive refractive power, in order from the object side. And moving the second lens unit toward the image side to perform zooming from the wide-angle end to the telephoto end, and moving the fourth lens unit to correct the image surface variation due to zooming and The group is moved to perform focusing, and the first group includes a negative eleventh lens, a positive twelfth lens, and a positive thirteenth lens.
A negative 21st lens having three lenses, the second group of which has a concave surface having a stronger refractive power toward the image side than toward the object side;
It has three lenses, a 22nd lens whose both lens surfaces are concave and a 23rd positive lens with a convex surface having a stronger refracting power toward the object side than the image side, and the 4th group is the most negative on the image side. The fourth
It has an N lens and a positive fourth P lens on the object side of the fourth N lens, the refractive power of the air lens formed by the fourth P lens and the fourth N lens is φa, and the refraction of the fourth group is A rear focus type zoom lens which satisfies the condition of −1.5 <φa / φ4 <0.5 when the force is φ4. 2. The fourth lens group, in order from the object side, is a positive lens,
The rear focus type zoom lens according to claim 1, wherein the rear focus type zoom lens comprises three lenses of a positive lens and a negative lens, or two lenses of a positive lens and a negative lens. 3. The rear focus type zoom lens according to claim 1, wherein the third lens unit is composed of a single positive lens having at least one aspherical surface.