JPH0894935A - In-focus zoom lens - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a focusing method suitable for a zoom lens. [Constitution] In order from the object side, a first lens group having a negative refracting power, a second lens group having a positive refracting power, a third lens group having a negative refracting power, and a positive refracting power. A fourth lens unit, which reduces an air gap between the first lens unit and the second lens unit during zooming from the wide-angle end to the telephoto end, and reduces the air gap between the second lens unit and the third lens unit. The air space between
In a zoom lens in which an air gap between the third lens group and the fourth lens group is reduced, and the fourth lens group moves in the object direction, the second lens group and the third lens group are integrated into an image. It is configured to focus from a long distance to a short distance by moving in the plane direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens, and more particularly to an internal focus wide-angle zoom lens suitable for an autofocus camera.

[0002]

2. Description of the Related Art Conventionally, many zoom lenses having a negative first lens group, a positive second lens group, a negative third lens group, and a positive fourth lens group have been proposed. And most of them move the first lens group for focusing.
The so-called first group extension focusing method was adopted.

[0003]

However, when the conventional zoom lens of the one-group extension focusing type is mounted on the autofocus camera, the largest and heaviest first lens group is driven by the motor. It was difficult to speed up. Therefore, a proposal for focusing with a lens group other than the first lens group is Japanese Patent Publication No. 5-6793.
No. 0, JP-A-2-296208, JP-A-4-
No. 235514, Japanese Patent Laid-Open No. 5-107476,
JP-A-5-173070, JP-A-5-17307
No. 1 publication.

The zoom lens of the second embodiment of Japanese Patent Publication No. 5-67930 comprises a negative first lens group, a positive second lens group, a negative third lens group, and a positive fourth lens group, Focusing is performed by moving the third lens group of these. However, the focusing movement amount with respect to the shooting distance of 1.5 m is 5.285 mm, which reaches 10% of the focal length (49 mm) at the telephoto end, and the zoom lens becomes large in size to secure a movement space for the focusing group. There was a problem. Further, the focusing magnification of the third lens group for focusing needs to be close to -1 at the wide-angle end, and the degree of freedom of power arrangement is limited, so that there is a problem that the design is difficult.

In the zoom lens of the embodiment disclosed in JP-A-2-296208, the negative first lens unit and the positive second lens unit are used.
It is composed of a lens unit, a negative third lens unit, and a positive fourth lens unit. The first lens unit is divided into two, and the image side lens unit is moved to perform focusing. However, since the first lens group is divided into two, it is substantially composed of five groups. For this reason, there has been a problem of cost increase due to an increase in the number of lens groups.

In the zoom lens of the embodiment disclosed in Japanese Patent Laid-Open No. 4-235514, a negative first lens group and a positive second lens group are used.
It is composed of a lens group, a negative third lens group, and a positive fourth lens group, and performs focusing by moving the third lens group or the third lens group and the fourth lens group. However, the amount of focusing movement with respect to the same shooting distance greatly differs depending on the focal length, and there is a problem in that a focus shift occurs when zooming is performed after the focusing operation.

In the zoom lens of the embodiment disclosed in JP-A-5-107476, the negative first lens group and the positive second lens group are used.
It consists of a lens group, a negative third lens group, a positive fourth lens group and a positive fifth lens group, and the fifth lens group is moved to perform focusing. However, similar to Japanese Patent Laid-Open No. 4-235514, there is a problem that the focusing movement amount with respect to the same shooting distance greatly varies depending on the focal length, and if zooming is performed after the focusing operation, a focus shift occurs.

In the zoom lenses of the embodiments disclosed in JP-A-5-173070 and JP-A-5-173071, the negative first lens group, the positive second lens group, the negative third lens group, and the positive lens group are positive. It is composed of a fourth lens group, the second lens group is divided into two, and the object side lens group is moved to perform focusing. However,
Since the second lens group is divided into two, it is substantially composed of five groups. For this reason, there has been a problem of cost increase due to an increase in the number of lens groups.

In view of the above-mentioned problems, the present invention provides an internal focusing method suitable for a wide-angle zoom lens, and in particular, the focusing movement amount with respect to the same shooting distance is substantially dependent on the focal length without increasing the number of lens groups due to internal focusing. It is an object to provide a new focusing method that becomes constant.

[0010]

To achieve the above object, in a zoom lens according to the present invention, a first lens group having a negative refractive power and a second lens group having a positive refractive power are arranged in order from the object side. And a third lens group having a negative refracting power and a fourth lens group having a positive refracting power, and at the time of zooming from the wide-angle end to the telephoto end, the first lens group and the second lens The air gap between the second lens group and the third lens group is increased, the air gap between the third lens group and the fourth lens group is reduced, and the fourth air gap is reduced. The lens group is a zoom lens that moves in the object direction. The second lens group and the third lens group are integrally moved in the image plane direction to perform focusing from a long distance to a short distance.

In the above basic structure, when the amount of movement of the fourth lens unit with respect to the image plane during zooming from the wide-angle end to the telephoto end is X4 and the focal length of the fourth lens unit is f4, A structure satisfying the condition of 1 <X4 / f4 <0.47 is preferable.

Alternatively, in the above basic structure, when the image forming magnification of the fourth lens group at the wide-angle end is B4W and the image forming magnification of the fourth lens group at the telephoto end is B4T, | B4W | <0.35 A structure satisfying the condition of | B4T | <0.35 is preferable.

Alternatively, in the above basic structure, when the image forming magnification of the fourth lens group at the wide-angle end is B4W and the image forming magnification of the fourth lens group at the telephoto end is B4T, −0.25 <| B4W A configuration satisfying the condition of |-| B4T | <0.25 is preferable. Alternatively, in the above basic configuration, the focal length of the fourth lens group is f4, the combined focal length from the first lens group to the third lens group at the wide angle end is f1-3W, and the first lens group at the telephoto end is from the first lens group. The combined focal length to the third lens group is f1-3T
Then, it is preferable that the structure satisfy the condition of | f4 / f1-3W | <0.4 | f4 / f1-3T | <0.25.

[0014]

In general, in a zoom lens having a negative first lens group, a positive second lens group, a negative third lens group and a positive fourth lens group, the second lens group and the third lens group are The lens diameter is smaller than the lens diameters of the first lens group and the fourth lens group, and it is preferable to move the second lens group or the third lens group when focusing with autofocus because the load on the motor is small.

However, if it is attempted to perform focusing by moving only the second lens group, the amount of focusing movement for the same shooting distance greatly changes depending on the focal length. Furthermore, when the focal length is such that the image forming magnification of the second lens group is −1, focusing becomes impossible in the vicinity of the focal length. Further, even when only the third lens group is moved to perform focusing, the focusing movement amount with respect to the same shooting distance largely changes depending on the focal length.

Therefore, in the present invention, the focusing is performed by moving the second lens group and the third lens group integrally, so that the focal length of the focusing movement amount with respect to the same shooting distance is different from the above two cases. It was possible to reduce the change. At that time, it is desirable that the axial light flux passing between the third lens group and the fourth lens group is close to afocal.

When the axial light flux that always passes between the third lens group and the fourth lens group from the wide-angle end to the telephoto end is completely afocal, the second lens group and the third lens group are integrally imaged. Moving the lens in the surface direction to perform focusing is substantially the same as moving the first lens unit to the object side to perform focusing, and the amount of focusing movement is constant regardless of the focal length. However, in this case, the position of the fourth lens unit does not change even when zooming is performed. Further, the fourth lens group has no zooming effect.
For this reason, it becomes difficult to reduce the size of the zoom lens and increase the zoom ratio.

Therefore, it is desirable that the axial light flux passing between the third lens group and the fourth lens group becomes a weak convergent light flux at the wide-angle end and a weak divergent light flux at the telephoto end. At this time, it is desirable that the fourth lens group be configured to move in the object direction during zooming from the wide-angle end to the telephoto end. In order to have such a configuration, at the time of zooming from the wide-angle end to the telephoto end, the air gap between the first lens group and the second lens group is reduced, and the second lens group and the third lens group are separated from each other. It is desirable to expand the air space and reduce the air space between the third lens group and the fourth lens group.

Further, in the case of the above configuration, in order to reduce the change of the focusing movement amount due to the focal length for the same photographing distance, the second lens unit and the third lens unit are moved integrally to perform focusing. It is desirable to satisfy any one of the conditions (1) to (6). (1) 0.1 <X4 / f4 <0.47 (2) | B4W | <0.35 (3) | B4T | <0.35 (4) -0.25 <| B4W |-| B4T | < 0.25 (5) | f4 / f1-3W | <0.4 (6) | f4 / f1-3T | <0.25 However, X4: 4th lens at the time of zooming from the wide-angle end to the telephoto end F4: focal length of the fourth lens group, B4W: imaging magnification of the fourth lens group at the wide-angle end, B4T: imaging magnification of the fourth lens group at the telephoto end, f1-3W: Composite focal length from the first lens group to the third lens group at the wide-angle end, f1-3T: Composite focal length from the first lens group to the third lens group at the telephoto end.

The condition (1) defines the amount of movement of the fourth lens group during zooming. When the value exceeds the upper limit of the condition (1), the change in the focusing movement amount of the second lens unit and the third lens unit due to the focal length becomes large, which is not preferable. On the other hand, when the value goes below the lower limit of the condition (1), the change in the position of the fourth lens unit becomes small, and it becomes difficult to reduce the size of the zoom lens and increase the zoom ratio.

The condition (2) defines the imaging magnification of the fourth lens group at the wide-angle end. If the upper limit of condition (2) is exceeded,
The difference in the amount of focusing movement between the wide-angle end and the telephoto end becomes large, which is not preferable. The condition (3) defines the imaging magnification of the fourth lens group at the telephoto end. When the value exceeds the upper limit of the condition (3), the difference between the focusing movement amounts at the wide-angle end and the telephoto end becomes large, which is not preferable.

The condition (4) is the fourth condition at the wide-angle end and the telephoto end.
It defines the difference in absolute value of the imaging magnification of the lens group. If either the upper limit or the lower limit of the condition (4) is exceeded, the difference between the focusing movement amounts at the wide-angle end and the telephoto end becomes large, which is not preferable. The condition (5) defines the combined focal length from the first lens group to the third lens group at the wide-angle end. When the value exceeds the upper limit of the condition (5), the difference between the focusing movement amounts at the wide-angle end and the telephoto end becomes large, which is not preferable.

The condition (6) defines the combined focal length from the first lens group to the third lens group at the telephoto end. When the value exceeds the upper limit of the condition (6), the difference between the focusing movement amounts at the wide-angle end and the telephoto end becomes large, which is not preferable. In addition,
Needless to say, even if the first lens group is divided into two or more lens groups and the mutual distance is changed during zooming, the focusing method similar to that of the present invention is possible. The same applies to each of the second lens group, the third lens group, and the fourth lens group. Furthermore, it goes without saying that even if the fifth lens group is added to the image side of the fourth lens group, the focusing method similar to that of the present invention is possible.

[0024]

EXAMPLE 1 FIG. 1 is a lens configuration diagram of Example 1 of the present invention. Examples of the present invention will be described below. As shown in FIG. 1, the first embodiment includes a negative first lens group G1, a positive second lens group G2, a negative third lens group G3 and a positive fourth lens group G4, and the wide-angle end to the telephoto end. At the time of zooming to, the distance between the first lens group G1 and the second lens group G2 is reduced, the distance between the second lens group G2 and the third lens group G3 is increased, and the third lens group G3 and the fourth lens group. The interval of G4 is reduced, and at that time, the fourth lens group G4 moves toward the object. When focusing from a long distance to a short distance, the second lens group G2 and the third lens group G3 are moved integrally in the image plane direction.

The first negative lens group G1 is composed of, in order from the object side, a negative meniscus lens having a convex surface facing the object side, a negative meniscus lens, and a positive meniscus lens. The positive second lens group G2 is composed of, in order from the object side, a positive lens, a biconvex positive lens, and a cemented lens including a biconvex positive lens and a negative lens, and the negative third lens group G3 is , And a cemented lens including a positive lens and a negative lens in order from the object side. The positive fourth lens group G4 is composed of, in order from the object side, a negative lens and a cemented lens made up of a biconvex positive lens.

The values of the specifications and the numerical values corresponding to the conditions of the embodiment of the present invention are listed below. F in the specification table of the embodiment is the focal length,
F is the F number and 2ω is the angle of view. The leftmost number represents the order from the object side, r is the radius of curvature of the lens surface, d is the lens surface spacing, and n and ν are d lines (wavelength λ = 587.6
nm) and the Abbe number. The surface marked with * at the left end is an aspherical surface, and the aspherical shape is the distance along the optical axis from the tangent plane of the aspherical vertex at the height h in the vertical direction from the optical axis. Be A (h),
Assuming that the paraxial radius of curvature is r, the conic constant is k, and the aspherical coefficient of the nth order is Cn, A (h) = (h ² / r) / [1+ (1-kh ² / r ² ) ^1/2 ] + C4 is expressed by ^{h 4 + C6 h 6 + C8} h 8 + C10h 10. In the table of focusing movement amounts, R is a photographing distance, and FW, FM, and FT are focusing movement amounts of the second lens unit and the third lens unit at the wide-angle end, the intermediate focal length, and the telephoto end, respectively. In the table of the amount of image plane deviation, the amount of image plane deviation at each focal length when the focusing movement amount at the telephoto end is given, R is the shooting distance, F is the focusing movement amount, ΔW, ΔM and ΔT are image plane shift amounts at the wide-angle end, the intermediate focal length, and the telephoto end, respectively. The sign of the amount of image plane deviation is positive, but the direction in which the back focus increases,
Negative is the direction in which the back focus becomes shorter.

[0027]

[Table 1] Specifications of Example 1 f = 28.80 to 82.50 F = 3.71 to 4.90 2ω = 77.3 to 28.5 ° r d ν n 1 61.0224 1.0000 46.53 1.80411 2 25.8275 9.5991 3 * 179.6222 1.0000 70.45 1.48749 4 32.4922 2.8439 5 34.3796 4.3782 23.01 1.86074 6 53.2985 (d6) 7 49.2121 2.8044 70.45 1.48749 8 354.5410 0.1000 9 48.1226 4.2785 70.45 1.48749 10 -62.2580 0.1000 11 33.8694 4.5046 70.45 1.48749 12 -56.7505 1.0000 23.01 1.86074 13 257.2868 (d13) 23.29. 1.86074 16 371.7484 1.0000 40.75 1.58144 17 27.7177 1.3386 18 114.6883 1.0000 39.61 1.80454 19 25.2292 (d19) 20 * 74.2932 1.0000 23.01 1.86074 21 41.2352 7.5636 57.03 1.62280 22 -44.8827 (Bf) The third aspherical shape is shown below.

K = 1.000 C4 = 0.2596 × 10 ^-5 C6 = 0.2166 × 10 ^-8 C8 = -0.4935 × 10 ^-11 C10 = 0.1401 × 10 ^-13 The aspherical shape of the 20th surface is shown below. k = 1.000 C4 = -0.2644 × 10 ^-5 C6 = 0.2816 × 10
^-8 C8 = -0.1579 × 10 ^-11 C10 = -0.3620 × 10 ^{-14 The} following shows the change in the interval during zooming. f 28.7984 50.0048 82.4996 d6 53.2968 17.5403 1.0000 d13 0.5000 5.7138 12.3317 d19 20.4000 16.9199 4.0561 Bf 42.6975 52.7059 65.8936 The focusing movement amount is shown below.

R FW FM FT ∞ 0.0000 0.0000 0.0000 10000 0.2443 0.2303 0.2369 5000 0.4943 0.4648 0.4775 3000 0.8368 0.7842 0.8045 2000 1.2803 1.1945 1.2232 1500 1.7420 1.6177 1.6536 1200 2.2229 2.0544 2.0961 1000 2.7243 2.5053 2.5512 Image deviation amount R F ΔW ΔM ΔT ∞ 0.0000 0.0000 0.0000 0.0000 10000 0.2369 0.0025 -0.0072 0.0000 5000 0.4775 0.0057 -0.0139 0.0000 3000 0.8045 0.0110 -0.0223 0.0000 2000 1.2232 0.0194 -0.0316 0.0000 1500 1.6536 0.0300 -0.0416 0.0000 1200 2.0961 0.0429 -0.0459 0.0000 1000 2.5512 0.0585 -0.0506 0.0000 Condition corresponding value (1 ) X4 / f4 = 0.447 (2) | B4W | = 0.144 (3) | B4T | = 0.303 (4) | B4W |-| B4T | = -0.159 (5) | f4 / f1 -3W | = 0.260 (6) | f4 / f1-3T | = 0.191 FIG. 2 is a diagram of various types of aberration at the wide angle end of Example 1, and FIG.
4A is a diagram of various types of aberration at the intermediate focal length of Example 1, and FIG.
6A is a diagram of various types of aberration at the telephoto end of Example 1. FIG. In each aberration diagram, H is the incident ray height, Y is the image height, and d is the d line (λ = 58
7.6 nm) and g indicate the g-line (λ = 435.8 nm). In the astigmatism diagram, the dotted line indicates the meridional image plane and the solid line indicates the sagittal image plane.

From each aberration diagram, it is clear that various aberrations are satisfactorily corrected and that the embodiment of the present invention has excellent imaging performance. In addition, from the table of the amount of image plane deviation, the amount of image plane deviation is small even if focusing is performed at other focal lengths due to the amount of focusing movement at the telephoto end. You can see that it can be kept constant.

[0031]

As described above, according to the present invention, there is no increase in the number of lens groups due to an internal focusing method suitable for a wide-angle zoom lens, in particular, internal focusing, and the focusing movement amount with respect to the same shooting distance varies depending on the focal length. It is possible to provide a focusing method that is substantially constant.

[Brief description of drawings]

FIG. 1 is a lens configuration diagram of a first embodiment according to the present invention.

FIG. 2 is a diagram of various types of aberration at the wide-angle end according to the first exemplary embodiment of the present invention.

FIG. 3 is a diagram of various types of aberration in an intermediate focal length state of Example 1 according to the present invention.

FIG. 4 is a diagram of various types of aberration at the telephoto end of Embodiment 1 according to the present invention.

[Explanation of the sign of the main part]

 G1 ... First lens group G2 ... Second lens group G3 ... Third lens group G4 ... Fourth lens group

Claims (4)

[Claims] 1. A first lens element having a negative refractive power in order from the object side.
It has a lens group, a second lens group having a positive refracting power, a third lens group having a negative refracting power, and a fourth lens group having a positive refracting power, and has a wide-angle end to a telephoto end. When doubling the first
An air gap between the lens group and the second lens group is reduced, an air gap between the second lens group and the third lens group is expanded, and an air gap between the third lens group and the fourth lens group is reduced. In the zoom lens in which the fourth lens group moves in the object direction, the second lens group and the third lens group are moved integrally in the image plane direction to change the distance from the long distance to the short distance. Focusing is performed, and the amount of movement of the fourth lens group with respect to the image plane during zooming from the wide-angle end to the telephoto end is X4,
An inner-focus type zoom lens which satisfies the following conditions when the focal length of the fourth lens unit is f4. 0.1 <X4 / f4 <0.47 2. A first lens element having a negative refractive power in order from the object side.
It has a lens group, a second lens group having a positive refracting power, a third lens group having a negative refracting power, and a fourth lens group having a positive refracting power, and has a wide-angle end to a telephoto end. When doubling the first
An air gap between the lens group and the second lens group is reduced, an air gap between the second lens group and the third lens group is expanded, and an air gap between the third lens group and the fourth lens group is reduced. In the zoom lens in which the fourth lens group moves in the object direction, the second lens group and the third lens group are moved integrally in the image plane direction to change the distance from the long distance to the short distance. And the fourth at the wide-angle end
An internal focus type zoom lens which satisfies the following conditions when the image forming magnification of the lens unit is B4W and the image forming magnification of the fourth lens unit at the telephoto end is B4T. ｜ B4W ｜ <0.35 ｜ B4T ｜ <0.35 3. A first lens element having a negative refractive power in order from the object side.
It has a lens group, a second lens group having a positive refracting power, a third lens group having a negative refracting power, and a fourth lens group having a positive refracting power, and has a wide-angle end to a telephoto end. When doubling the first
An air gap between the lens group and the second lens group is reduced, an air gap between the second lens group and the third lens group is expanded, and an air gap between the third lens group and the fourth lens group is reduced. In the zoom lens in which the fourth lens group moves in the object direction, the second lens group and the third lens group are moved integrally in the image plane direction to change the distance from the long distance to the short distance. And the fourth at the wide-angle end
An internal focus type zoom lens which satisfies the following conditions when the image forming magnification of the lens unit is B4W and the image forming magnification of the fourth lens unit at the telephoto end is B4T. -0.25 <| B4W |-| B4T | <0.25 4. A first lens element having a negative refractive power in order from the object side.
It has a lens group, a second lens group having a positive refracting power, a third lens group having a negative refracting power, and a fourth lens group having a positive refracting power, and has a wide-angle end to a telephoto end. When doubling the first
An air gap between the lens group and the second lens group is reduced, an air gap between the second lens group and the third lens group is expanded, and an air gap between the third lens group and the fourth lens group is reduced. In the zoom lens in which the fourth lens group moves in the object direction, the second lens group and the third lens group are moved integrally in the image plane direction to change the distance from the long distance to the short distance. Focusing is performed, the focal length of the fourth lens unit is f4, the combined focal length from the first lens unit to the third lens unit at the wide-angle end is f1-3W, and the first lens unit from the first lens unit at the telephoto end to the first lens unit. An in-focus type zoom lens characterized by satisfying the following conditions when the combined focal length to the three lens groups is f1-3T. | F4 / f1-3W | <0.4 | f4 / f1-3T | <0.25