JPH08201696A - Zoom lens - Google Patents

Abstract

(57) [Summary] [Objective] To obtain a zoom lens having high optical performance by floating a plurality of lens units in the first lens unit in a four-unit zoom lens to perform focusing. A first lens unit having a positive refractive power, a second lens unit having a negative refractive power for zooming, and a third lens unit having a positive or negative refractive power for correcting an image plane variation due to zooming in order from the object side. A zoom lens having a group, and a fourth group having a fixed image forming action during zooming,
The first group is the negative refractive power group A, and the positive refractive power group B1.
Group, and three lens groups of a positive refractive power group B2, which moves the group A when focusing from an infinitely distant object to a short-distance object, and at the same time the group B1 and the group B2. Was moved to the object side with different movement amounts.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens suitable for a television camera, a video camera, a camera for photography, etc. F-number at the wide-angle end with a short object distance using so-called floating.
75, a zoom lens having a large aperture ratio of 14 times or more and a high zoom ratio.

[0002]

2. Description of the Related Art Conventionally, with the miniaturization of television cameras, zoom lenses for television cameras and the like have been required to have a compact overall lens system with a large aperture ratio and a high zoom ratio.

In a system in which focusing (focusing) is performed by a lens unit located closer to the object side than a variable power lens unit as a zoom lens, zooming (variable power) and focusing can be performed independently, so that a mechanism for movement is simplified. The advantage of this is that focusing does not occur due to zooming, and focusing can be performed with a constant amount of extension for a constant object distance regardless of the zoom position.

Among such zoom lenses, a first group (focusing lens group) having a positive refractive power for focusing and a second group (magnifying lens group having a negative refractive power for zooming) are arranged in order from the object side. ), A third group (correction lens group) having a positive or negative refractive power for correcting an image surface that varies with zooming, an aperture stop, and a fourth group (relay) having a positive refractive power for image formation. In a so-called four-group zoom lens composed of four lens groups (lens groups), a so-called inner focus type in which a part of the lens groups in the first group is moved for focusing is disclosed in, for example, Japanese Patent Publication No. Sho 59.
It is proposed in Japanese Patent No. 4686.

In the same publication, the first group is referred to as an eleventh lens having a negative refractive power.
Group consisting of three lens groups, a positive refractive power twelfth lens group and a positive refractive power thirteenth lens group, and moving the twelfth lens group toward the image plane side for focusing from an object at infinity to an object at a close range. I am doing it.

Further, JP-A-52-109952, JP-A-55-57815 and JP-A-55-11711.
9, Japanese Patent Publication No. 61-53696, Japanese Patent Publication No. 52
In the -41068 publication, etc., in a 4-group zoom lens, the first group is divided into a plurality of lens groups, and the lens group closest to the object side is fixed during focusing, and a part of the lens group on the image plane side behind that is fixed. Is the inner focusing that moves during focusing.

Further, in Japanese Unexamined Patent Publication No. 52-128153, the first lens unit is divided into two lens units, and the distance between the two lens units is increased when focusing from an object at infinity to an object at a finite distance. We are moving and focusing.

Generally, in an inner focus type zoom lens, the effective diameter of the first lens group is smaller than that of a zoom lens in which the entire first lens group is moved to perform focusing, which facilitates downsizing of the entire lens system and close-up photography. In particular, it is easy to perform extremely close-up photography, and since the relatively small and lightweight lens group is moved to perform the operation, the driving force of the lens group is small and quick focusing can be performed.

[0009]

The zoom lens has a large aperture ratio (for example, an F number of 1.75 to 3.3), a high zoom ratio (for example, a zoom ratio of 14 or more), and the entire zoom range and total zoom ratio. In order to obtain high optical performance over the focus range, it is necessary to appropriately set the refractive power (power) of each lens group, the lens configuration, and the achromatic share.

Generally, in order to obtain high optical performance with little aberration variation over the entire zoom range and the entire focus range, for example, the power of each lens group is reduced to reduce the aberration amount generated in each lens group, or each lens group is reduced. It becomes necessary to increase the degree of freedom in aberration correction by increasing the number of lenses in the group. Therefore, when trying to achieve a zoom lens with a large aperture ratio and a high zoom ratio, the air gap between the lens groups will inevitably increase, the number of lenses will increase, and so on.
There is a problem that the entire lens system becomes heavy and large.

In recent broadcast zoom lenses, there is a demand for wider angles and higher zoom ratios, and further improvements in short-distance performance and M.D. O. Shortening the D (shortest shooting distance) is becoming an important factor in terms of specifications and image effects.

However, in the zoom lens for broadcasting, variations in various aberrations due to focusing, particularly variations in spherical aberration, axial chromatic aberration, astigmatism, etc. are remarkable, and it is very difficult to maintain good optical performance. The aberration variation at this time is generally as the focal length becomes larger, the F number becomes smaller, and the aperture ratio becomes larger. O. The shorter D was, the larger the tendency was.

Regarding the focusing method described above, Japanese Patent Laid-Open Nos. 52-109952 and 55-5 are available.
In the zoom lenses of Japanese Patent No. 7815 and Japanese Patent Laid-Open No. 55-117119, the number of constituent lenses of the first lens group is large in terms of aberration correction, so that the entire lens system becomes large, complicated, and heavy.

In the zoom lens disclosed in Japanese Patent Publication No. 61-53696, the first lens group has a relatively simple structure.
The air gap between the first lens group and the zoom lens group at the time of focusing at infinity is wide, and the focus lens group having negative refractive power moves toward the image plane side at the time of focusing at a close distance, so that it is off-axis on the wide angle side. The height of the light beam becomes high in the first group, and the lens system becomes large.

In the first-group extension type zoom lens, the first group has a relatively simple structure and is suitable for downsizing, but in particular, fluctuations in spherical aberration and axial chromatic aberration due to focusing become large. For example, as the focus becomes closer, spherical aberration falls to under, and axial chromatic aberration also becomes under.

The mechanism of aberration variation at this time will be described below. FIG. 18 shows that the first lens group has a negative refractive power of 11th.
Group (concave group) L11 and 12th group (convex group) L1 having positive refractive power
It is explanatory drawing of the thin-walled paraxial system when it comprised by 2. FIG.
FIG. 6 is a lens cross-sectional view of a representative first group L1 in a 4-group zoom lens.

In FIG. 18, the solid line indicates the position when the object at infinity is in focus, and the dotted line indicates the M.I. O. This is the position at D. The 11th group and the 1st group of paraxial rays at infinity focus shown by the solid line
The incident heights to the second group are ha and hb, the tilt angles between the 11th and 12th groups are α, and M. O. The incident heights of paraxial rays on the first and second groups at D are ha ′, hb ′, and 11th, respectively.
If the tilt angle between the group and the twelfth group is α ', then α'<α, and therefore hb-ha <hb'-ha '.

In the third-order aberration theory, the third-order aberration coefficient L of axial chromatic aberration is proportional to the square of the paraxial ray height h, and the third-order aberration coefficient I of spherical aberration is the fourth axis of the paraxial ray height h. Proportional. In this focusing method, the M.D. O. At the time of D, the coefficient L becomes larger in the plus direction, so the axial chromatic aberration becomes under, and the coefficient I also becomes larger in the plus direction.
Spherical aberration also changes to under.

In the zoom lens of Japanese Examined Patent Publication No. 52-41068, as shown in FIG. 21, the first group is divided into two lens groups, of which the eleventh group L11 on the object side has a weak negative refractive power of substantially no power. And is fixed during focusing, and focusing is performed by moving the twelfth lens unit L12 having a positive refractive power on the image side. This is shown in FIG. 20 as a thin-walled paraxial system of the 11th group and the 12th group. As shown in FIG. 20, the twelfth group is shown as the movement of its principal point.

The solid lines are paraxial rays when an object at infinity is focused, and the incident heights on the 11th group and the 12th group at this time are hf and hm, respectively. O. First paraxial ray at D
Assuming that the incident heights on the first group and the twelfth group are hf 'and hm' respectively, hb-ha <hm-hf hb'-ha'.apprxeq.hm'-compared with FIG. 18 (first group feeding method). hf '.

Therefore, according to the zoom lens of the above publication, compared with the first group moving-out method, the M.M. O. D
It is possible to reduce the amount of change in the third-order spherical aberration coefficient I and the axial chromatic aberration coefficient L until time. Therefore, spherical aberration due to focusing,
It is possible to reduce the fluctuation of the axial chromatic aberration. However, the variation is still unsatisfactory, and further improvement is desired.

In the zoom lens disclosed in Japanese Unexamined Patent Publication No. 52-128153, the first lens unit is divided into two lens units, both of which are moved during focusing, and the distance between the two lens units becomes shorter as the focus becomes closer. By increasing the size, the peripheral performance is mainly improved. However, according to the example, the spherical aberration is also under-corrected at the time of focusing at a short distance, and the central performance is deteriorated.

The present invention adopts a floating system in which the first group for focusing which constitutes the four-group zoom lens is composed of three lens groups, and each lens group is moved differently on the optical axis for focusing. However, when increasing the aperture and increasing the zoom ratio, by appropriately setting the lens configuration of each lens group, it is possible to reduce the fluctuations of various aberrations such as spherical aberration and chromatic aberration due to zooming and focusing, and to achieve total zoom. An object of the present invention is to provide a zoom lens having a wide-angle end F number of about 1.75, a large aperture ratio of 14 or more and a high zoom ratio, which has high optical performance over the zoom range and the entire focus range.

[0024]

The zoom lens of the present invention comprises:
From the object side, a first group having a positive refractive power, a second group having a negative refractive power for zooming, a third group having a positive or negative refractive power that corrects an image plane variation due to zooming, and In a zoom lens having a fourth group having a fixed image forming action during zooming, the first group includes a negative refractive power group A, a positive refractive power group B1, and a positive refractive power group B1. It has three lens groups of the B2 group, and moves the A group at the time of focusing from an object at infinity to a short-distance object, and moves the B1 group and the B2 group to the object side with different movement amounts. It is characterized by having been moved.

Others In the present invention, the above-mentioned B1 group and B2 group
When the moving amounts of the groups are MB1 and MB2, respectively, the following condition is satisfied: MB2 / MB1 <1 (1), and the infinite distance object from the focus position of the infinitely distant objects of the A group and the B1 group. When the distance to the focus position of is measured on the image plane side is positive, Δd, Δ
When X, the condition of -1.1 <Δd / ΔX <0.105 (2) is satisfied, and the refractive power and F number of the entire system at the telephoto end are φT, FNT, and Assuming that the refractive power and F number of the first group are φ1 and FN1, respectively, 1.05 <FN1 (3) However, FN1 = (φT / φ1) × FNT There is.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1, 2, 3 and 4 are lens sectional views at certain zoom positions according to Numerical Embodiments 1, 2, 3 and 4 of the present invention. FIG. 17 is an explanatory diagram of the paraxial refractive power arrangement of the first group of the zoom lens of the present invention.

In the figure, L1 is a positive refractive power focusing group (front lens group) as the first lens group, which has a negative refractive power focusing group A LA and a positive refractive power focusing group LA. It has a first lens group LB1 and a second lens group LB2 for focusing with a positive refractive power. Focusing from an object at infinity to an object at a close range is performed by moving the A-th group LA on the optical axis and independently moving the B1-th group LB1 and the B2-th group LB2 by different amounts to the object side.

L2 is a variator of negative refracting power for zooming as the second lens unit, which is monotonically moved to the image plane side on the optical axis to move from the wide-angle end (wide) to the telephoto end (tele). We are changing the magnification. In the second group L2, the image-forming magnification is changed within a region including the same magnification (−1 ×) when the magnification is changed.

L3 is a compensator for positive or negative refracting power as the third lens unit, which corrects the image plane variation due to zooming, and has a convex locus on the object side in the case of negative refracting power. To move. In the case of positive refracting power, it moves monotonically to the object side.
SP is a stop, and L4 is a relay group having a positive refractive power as the fourth group. P is a color separation prism, an optical filter, or the like, and is shown as a glass block in FIG.

Generally, in the so-called front lens focus system, in which focusing is performed on the entire first group closest to the object in the four-group zoom lens, the amount of extension of the first group is constant for the same object distance at each focal length. Therefore, it has a feature that the lens barrel structure is simple.

However, if there is a change in the object distance at the telephoto end, the optical performance, in particular the spherical aberration and the axial chromatic aberration, will fluctuate greatly. O. It becomes difficult to shorten D and it becomes difficult to obtain a good image.

Therefore, in the present invention, in the zoom lens having the above-described structure, focusing is performed from the object at infinity to the object at the closest distance by moving the A lens unit LA on the optical axis and the B1 lens unit LB1 and the B2 lens unit LB2. We adopted a floating focus method by moving the lens to the object side by different amounts, and obtained good optical performance.

That is, in the present invention, light rays pass by using a floating that expands or contracts an arbitrary air space in the lens group that moves when the object distance changes and the object is focused. Aberration variation is corrected well by changing the angle and height.

In particular, when focusing from an object at infinity to a near object, the moving amounts of the B1 group and the B2 group are respectively set to MB.
1, MB2, M. O. The moving distances of the group A and the group B1 when focusing on D are Δd and Δ, respectively.
The refractive power and F number of the entire system at X and the telephoto end are respectively φ
T, FNT, the refracting power and F number of the first group are φ
1, FN1, the above conditional expressions (1), (2),
Each element is set so as to satisfy the condition (3), whereby variation in aberration is reduced over the entire focus range and high optical performance is obtained.

Next, in the zoom lens of the present invention,
A group LA of the group L1, a B1 group LB1 and a B2 group LB2
The optical action when focusing is performed using and will be described with reference to FIG.

The first lens unit L1 is, in order from the object side, the A lens unit LA that moves during focusing, the B lens unit LB1 that moves during focusing, and the B lens unit LB that moves during focusing.
2 are arranged. The paraxial ray at an object at infinity is shown by a solid line, and the positions on the optical axis of the A group, the B1 group, and the B2 group at this time are a, b1, b2, and the intervals between b1 and b2 are t, respectively. The paraxial ray heights are shown as Ha, Hb1, and Hb2.

On the other hand, the paraxial ray at a certain finite distance object is shown by the dotted line, and the positions on the optical axis of the A group, the B1 group and the B2 group at this time are a ', b1', b2 ', b1. ′ And b2 ′ is T (when t <T), and each paraxial ray height is H
It is shown as a ', Hb1', Hb2 '.

When the group A is fixed with respect to the same finite distance object and the distance t between the groups B1 and B2 arranged in the same positional relationship as that of the object at infinity is maintained (when t = T). The position on the optical axis of the second optical axis is a position b1 ″ on the image plane side from the position b1 ′ for the B1th group, and a position b2 ″ on the object side from the position b2 ′ for the B2th group. The ray heights are Ha ″, Hb1 ″, and Hb2 ″.

In the present invention, the A-th group and the B1-th group at the time of an object at infinity
By separating the distance from the group, the difference between Hb1-Ha and, for example, Hb1'-Ha 'when the object is at a finite distance is reduced, and fluctuations in spherical aberration and axial chromatic aberration are reduced to some extent.

Next, focusing on changes in paraxial ray heights of the B1 and B2 groups when t <T and when t = T, Hb1 ′> Hb1 ″ Hb2 ′ <Hb2 ″.

Therefore, as described above, the change of the third-order aberration coefficient of spherical aberration and axial chromatic aberration is t = T when t <T.
From the time of, the B1 group and the B2 group are (a) B1 group: the third-order aberration coefficient I of spherical aberration changes in the positive direction, and the third-order aberration coefficient L of axial chromatic aberration also changes in the positive direction. Aberration changes to under and axial chromatic aberration also changes to under.

(B) Group B2: The third-order aberration coefficient I of the spherical aberration changes in the negative direction, and the third-order aberration coefficient L of the axial chromatic aberration also changes in the negative direction. Change to over. The action occurs.

Further, paying attention to the change in paraxial ray height of the A-th group LA, when the A-th group LA is moved to the image plane side and moved to the object side, (c) movement to the image plane side; Since Ha 'becomes large, the third-order aberration coefficient I of spherical aberration changes in the negative direction, the third-order aberration coefficient L of axial chromatic aberration also changes in the negative direction, spherical aberration changes to over, and axial chromatic aberration changes to over. .

(D) Moving to the object side: Since Ha 'becomes smaller, the third-order aberration coefficient I of spherical aberration changes in the positive direction, and the third-order aberration coefficient L of axial chromatic aberration also changes in the positive direction, and the spherical aberration Under, the axial chromatic aberration also changes to under. The action occurs.

In the present invention, the above-mentioned group A, group B1 and group B2
The aberration variation due to the movement of the three lens groups, which is a group, is skillfully used to suppress the aberration variation due to focusing.

M. O. At an object distance in the vicinity of D, the distance between the A group and the B1 group is narrowed because the B1 group moves toward the object side, and the difference between Hb1 ′ and Ha ′ when t <T, Hb
The difference between 1'-Ha 'and Hb1 "-Ha" at t = T, that is, Hb1 "-Ha" is approximately equal, and Hb1'-Ha'≈Hb1 "-Ha".

Therefore, the total sum of spherical aberration and axial chromatic aberration generated in the A-th group and the B1-th group becomes substantially equal, but when t <T, the aberration generation in the B2 group occurs due to the action of (b). It is possible to reduce the amount of M. O. Under spherical aberration and under axial chromatic aberration at an object distance near D are corrected.

Further, when an object at infinity is used, the M. O. When the group A is located closer to the object side than the group D,
Compared with the conventional method of 0, Hb1-Ha>hm-hf> hb-ha, so the value of Hb1-Ha at infinity object and M. O.
It is possible to reduce the difference between the value of Hb1'-Ha 'of D. Therefore, the object at infinity and M. O. The changes in the spherical aberration coefficient I and the chromatic aberration coefficient L at D are also small, and the object distance fluctuations of the spherical aberration and the axial chromatic aberration can be corrected.

On the other hand, when the object distance is small in the vicinity of the infinitely distant object and the distance between the A group and the B1 group is relatively large, both the effects of (a) and (b) are used. The aberration correction can be performed.

For example, when the aberration variation due to focusing from an object at infinity to an object at a certain finite distance causes spherical aberration to be over and axial chromatic aberration to be under, axial aberration and axial chromatic aberration due to the above (a) and (b) are respectively caused. By taking advantage of the difference in effectiveness, spherical aberration is corrected to under and axial chromatic aberration is corrected to over. Also, at the zoom position on the telephoto side, the M. O. When both spherical aberration and axial chromatic aberration monotonously change from overcorrection to undercorrection upon focusing on D, it is preferable to mainly apply the action (C) of moving the A-th group. That is, from an object at infinity to M. O. When focusing on D, the A-th group is monotonically moved to the image plane side.

On the telephoto side, an M. O. When the spherical aberration fluctuates so as to have an inflection point when focusing on D, for example, when a change is made from under → over → under, a correction effect is mainly given by the movement of the A group ( It is better to apply both of (c) and (d). That is, it is preferable to move the group A toward the object side so as to have a convex locus with the inflection point as a boundary.

According to the present invention, when focusing on a change in the object distance, by moving the group A, the group B1 and the group B2 so that their relative positional relationship changes, the spherical aberration and the axis are mainly changed. The variation of the upper chromatic aberration is well corrected.

At this time, the moving directions of the first and second lens groups B1 and B2 are M. O. D When the object is focused, the object side is moved monotonously so as to satisfy the conditional expression (1), and the increase in the total lens length of the first group is prevented, while suppressing the complication of the moving mechanism. There is.

When MB2 / MB1 <1 is t in the above description.
<Corresponding to T, and when MB2 / MB1 = 1 corresponds to t = T. When MB2 / MB1> 1, the movement amount of the B2 group becomes larger than the movement amount of the B1 group, so that it becomes necessary to additionally set an interval between the B1 group and the B2 group at the time of an object at infinity. The overall length and size of the first lens group increase.

Further, by making the movement of the A group satisfy the conditional expression (2), the spherical aberration and the axial chromatic aberration are corrected, and the total lens length of the first group is prevented from increasing. If the upper limit is exceeded, M. O. The effect of correcting the spherical aberration and the axial chromatic aberration by the A group in D disappears, and the burden of the aberration correction by the B2 group increases, and when the lower limit is exceeded, the spherical aberration and the axial chromatic aberration by the A group are reduced. The correction effect increases, but it is not good because the total lens length becomes longer.

The zoom lens of the present invention uses a bright lens system that satisfies the conditional expression (3) for the first lens unit, and
It has a zoom ratio of about 4 to 44 times, and realizes a large aperture ratio in the entire zoom range.

In the present invention, high optical performance is obtained by setting each element as described above, but in order to obtain high optical performance over the entire object distance and the entire zoom range, the following various conditions are required. Is good to satisfy.

The group A has at least two independent lenses, a negative first lens A1 and a positive second lens A2. The refractive power of the group A is φA, and the refractive power of the Ai lens is φAi. The sum of the ratios of Abbe number νAi is ΣA = φAi / νA
i, said group B1 comprises at least one positive group B1,1
A lens having a refracting power of the B1 group of φB1, B1,1
The sum of the ratio of the lens refracting power φB1, i and the Abbe number νB1, i of the material is ΣB1 = φB1, i / νB1, i,
The group is a positive meniscus B2,1 with the convex surface facing the object side.
A lens having a refracting power of B2, B2,1
When the ratio of the refractive power of the lens to φB2,1 and the Abbe number νB2,1 of the material is ΣB2 = φB2,1 / νB2,1, then −0.30 <φA / φ1 <−0.02 (4 ) −0.02 <ΣA / φ1 <−0.0095 (5) −1.30 <ΣA / (ΣB1 + ΣB2) <− 0.80 (6) 0.25 <φB2 / φB1 <0 .90 (7) 0.25 <ΣB2 / ΣB1 <1.30 (8).

In the zoom lens according to the present invention, the height of the axial ray passing through the first lens group is highest at the telephoto end. And the second
Since the aberration generated in the first lens group is magnified by the magnification after the lens group, the spherical aberration and the axial chromatic aberration at the telephoto end largely depend on the amount of aberration generated in the first lens group. In particular, the zoom lens for broadcasting is required to have high specifications and high performance, and it is necessary to increase the focal length at the telephoto end and increase the aperture ratio.

Therefore, it becomes difficult to correct various aberrations such as spherical aberration and chromatic aberration due to zooming and focusing. On the other hand, if the power of each lens is reduced by design or the number of lenses is increased to cope with the problem, the entire lens system becomes large, and the weight and the manufacturing cost increase.

Therefore, the first group A is a negative group A1 having at least a negative refractive power surface and having a relatively small air space.
It is composed of two lenses, a positive A2 lens. By providing this air space, the degree of freedom in design is increased, variations in various aberrations are reduced, and various aberrations can be easily controlled in a well-balanced manner. Furthermore, by pushing out the rear principal point of the first lens group, the entire lens system The miniaturization of

Both the B1 group for focus and the B2 group for focus are constructed so as to have at least one positive lens to reduce the amount of various aberrations and at the same time cancel the residual aberration in the A group. In particular, the second lens group B2 includes a positive meniscus second lens B1 having a convex surface directed toward the object side, which reduces the amount of spherical aberration generated by itself and at the same time corrects distortion and astigmatism well. There is. still,
It is preferable to provide a concave lens in the B1 group or the B2 group because various aberrations can be easily corrected.

Next, the technical meaning of the conditional expressions (4) to (8) will be described. Conditional expression (4) limits the power of the A-th group in the first group. When the value goes below the lower limit of conditional expression (4), the power becomes large, so that high-order aberrations such as spherical aberration and coma easily occur, and the moving lens groups B1 and B2 are used to correct the residual higher-order aberrations. Power must also be increased and the radius of curvature must be reduced, which makes it difficult to correct aberration fluctuations due to zooming and focusing. Further, when the upper limit is exceeded, the power becomes almost no power, so that the difference in paraxial ray height between the A group and the B1 group at the time of an object at infinity becomes small, and fluctuations in spherical aberration and axial chromatic aberration due to focusing are reduced. It becomes difficult to correct it well.

Conditional expression (5) defines the achromatic condition of the A-th group as the first condition.
It is standardized by the power of the group. Conditional expression (6) is defined by the first group A, which is fixed, and the first group B1, which is moved during focusing.
This is defined as the shared value of the achromatic condition when divided into two lens groups, that is, the first lens group and the second lens group B2. Conditional expression (5),
(6) is for keeping the variation of axial chromatic aberration due to focusing in good balance.

The achromatic condition of the first group A, the second group B1 and the second group B2 is preferably Σa≅Σb1 + Σb2≅0, but the focus moving group is usually compact and lightweight. Considering this, since only the convex lens is used, the achromatic condition of the focus moving group is always a positive value.

In order to cancel this, conditional expression (5) has a slightly negative value. Conditional expressions (5), (6)
If the lower limit value is exceeded, overcorrection occurs, and over-axial chromatic aberration remains over the entire focus range. If the upper limit value is exceeded, undercorrection occurs, and under-axial chromatic aberration remains.

The conditional expressions (7) and (8) define the power sharing and the achromatizing sharing of the B1 group and the B2 group that move during focusing, respectively.

If the lower limit value of conditional expression (7) is exceeded, the power of the second lens group B2 becomes relatively weak, so that the effect of (B) is lost, and the spherical aberration and the axial chromatic aberration due to focusing fluctuate. Is difficult to correct satisfactorily. When the value exceeds the upper limit, the power of the B1 group becomes relatively weaker this time, so that the effect of the above (a) is lost, and it is difficult to satisfactorily correct the fluctuations of the spherical aberration and the axial chromatic aberration due to focusing. That is, the amount of focus movement of the first lens group B1 increases, and the total lens length or lens system of the first lens group increases, which is not good.

If the lower limit of conditional expression (8) is exceeded, the amount of change in axial chromatic aberration to under will increase due to the action of (a), and the amount of change to over will decrease in the action of (b). Therefore, the amount of change in the axial chromatic aberration to under is increased as a whole, which is not good. On the other hand, if the upper limit is exceeded, the amount of change in the axial chromatic aberration to the contrary increases, which is not good.

As described above, in the present invention, the first group is divided into three lens groups so as to suppress the aberration variation due to focusing, the movement amount is limited, and the lens arrangement, the power sharing, the achromatic sharing, etc. are specified. By doing so, the fluctuations of the spherical aberration and the axial chromatic aberration are mainly corrected well.

Numerical Examples 1 to 1 of the present invention shown in FIGS.
The lens configuration of No. 4 will be described. 1 is a lens cross-sectional view of Numerical Embodiment 1 of the present invention, in which an object distance is infinity,
Aberration diagrams at the telephoto end for 3.0 m and 0.9 m (M.O.D.) are shown in FIGS.

In this embodiment, the zoom ratio is 14 times and R
1 to R8 are a first group having a positive refractive power. Of these, R1
R4 is a group A having a negative refractive power, R5 and R6 are a group B1 having a positive refractive power, and R7 and R8 are a group B2 having a positive refractive power.

R9 to R15 are a second lens unit having a negative refracting power, which moves monotonically toward the image plane side from the wide-angle end to the telephoto end due to zooming and passes lateral magnification -1 × on the way. R16 to R18
Is a third lens group that compensates for image plane variation due to zooming, and moves in a convex shape toward the object side from the wide-angle end to the telephoto end. R19 (SP)
Is an aperture. R20 to R37 are the fourth having an image forming action
In the group, R38 and R39 are glass blocks P equivalent to a color separation prism, a trimming filter and the like.

In this embodiment, when the F number of the first lens group is defined as FN1 = (φT / φ1) × FNT as a target for increasing the aperture, FN1 = 1.145. On the other hand, the first
In order to correct spherical aberration and axial chromatic aberration within the group, the A group is composed of one positive and one negative lens respectively, and the B1 group and the B2 group are composed of one positive lens respectively to correct the aberration. It is shared.

With regard to the floating of the present invention, the moving amount MB1 of the B1 group and the moving amount MB2 of the B2 group, and the moving amount MB1 of the B1 group and the moving of the A group from the object at infinity to a certain finite object. The relationship of the amount MA is given by MB2 = 0.83035 MB1 + 0.11110 MB1 ² +0.00966 MB1 ³ MA = -1.48735 MB1 + 0.00331 MB1 ² +0.00535 MB1 ³ , and the parameters at 3.0 m and 0.9 m are shown in Table 1. Shown in. At this time, the maximum value of MB2 / MB1 is 0.830 near infinity, and the minimum value is MB1 = -5.
It is 0.511 at the time of 751.

In this embodiment, from 3 m to M. O. By reducing the relative movement amount of the B2 group with respect to the B1 group to about 0.6, the Δd / ΔX is set to -1.096 while effectively using the action of (b) above. ,
By increasing the moving distance of the group A toward the image plane side and moving it monotonically, the effect of the above (c) is effectively used to correct the fluctuations of the spherical aberration and the axial chromatic aberration.

Further, by increasing the Abbe number difference between the positive lens and the negative lens in the group A to be about 70, φA / φ1 = −0.02 while favoring correction of chromatic aberration in the first group.
The refracting powers of the third lens group and the third lens group A are relatively small. B1
Constituting one positive lens element with a large Abbe number and one positive lens element with a high refractive index for the second lens group B2 makes it advantageous to correct chromatic aberration, spherical aberration, etc., while sharing power to compensate for the degree of freedom in aberration correction. , ΦB2 / φB1 = 0.83 in terms of achromatization
4, ΣB2 / ΣB1 = 1.240.

As shown in the aberration diagrams of FIGS. 5 to 7, the spherical aberration and the axial chromatic aberration are corrected particularly well.

FIG. 2 is a lens cross-sectional view of Numerical Embodiment 2 of the present invention, in which the object distances are infinity, 3.0 m and 0.8 m.
Aberration diagrams at the telephoto end of (MOD) are shown in FIGS.
Shown in 10.

In this embodiment, although the lens configuration is substantially the same as in Numerical Embodiment 1, the F-number at the telephoto end is 1.9 as compared with that.
With a large diameter, in addition to M. O. D is very short at 0.8m. In the first group, FN1 = 1.069, which is very bright, and spherical aberration and axial chromatic aberration are corrected,
The A group is composed of one positive and one negative lens, the B1 group is composed of two positive lenses, and the B2 group is composed of one positive lens to share the aberration correction.

Regarding the floating of the present invention, the moving amount MB1 of the B1st group, the moving amount MB2 of the B2th group, and the moving amount MB1 of the B1st group and the moving amount of the Ath group from the object at infinity to a certain finite object. The relationship of MA is given by MB2 = 0.66467 MB1 + 0.11372 MB1 ² +0.01025 MB1 ³ MA = 0.14832 MB1-0.09759 MB1 ² -0.00897 MB1 ³ and the parameters at 3.0 m and 0.8 m are shown in Table 2. At this time, the maximum value of MB2 / MB1 is M.M. O. D is 0.696, and the minimum value is MB1 =-
It is 0.349 at the time of 5.547.

Therefore, in this embodiment, M. O. The action of (b) is used while the change rate of the relative movement amount of the B2 group with respect to the B1 group has a minimum value from small to large as it becomes D. Also Δd / ΔX = 0.099
And group A with M. O. In the case of D, the object is located closer to the object side than at infinity, but the movement locus is convex toward the object side. O. In the vicinity of D, the action of (c) above is used. Then, the variation of the axial chromatic aberration in the entire focus area is corrected.

Further, the F number, M. O. In order to make it compact with respect to D, the group A is made to have a strong divergence system and the rear principal point of the first group is pushed out. Therefore, the B1 group is composed of two positive lenses and the B2 group is composed of one positive lens to increase the degree of freedom of aberration correction. At this time, φA / φ1 = −0.294, ΣA / φ1 = −0.019, ΣA / (ΣB1 + ΣB2) = − 1.247.

As shown in the aberration diagrams of FIGS. 8 to 10, not only the axial chromatic aberration is well corrected, but the M.M. O. Despite D, the spherical aberration is well corrected.

FIG. 3 is a lens sectional view of Numerical Embodiment 3 of the present invention, in which the object distance is infinity, 10.0 m and 1.7 m.
Aberration diagrams at the telephoto end of (MOD) are shown in FIGS.
2 and 13.

In this embodiment, the zoom ratio is 44 times, and R
1 to R10 are the first group having a positive refractive power. Of these, R1
˜R4 are fixed and have a negative refractive power during the focusing and zooming, and R5 to R8 are the positive B1 group, R9 and R10.
Is a positive group B2.

Since R11 to R17 are for zooming, they move monotonically toward the image side from the wide-angle end to the telephoto end, and the lateral magnification -1 on the way.
It is the second group of negative refracting power that passes double. R18-R2
Reference numeral 7 denotes a third lens unit having a positive refracting power that compensates for image plane variation as well as the zooming action, moves monotonically toward the object side, and passes lateral magnification -1 × on the way. R28 (SP) is a diaphragm. R29 to R
A fourth group 44 has an image forming action, and R45 and R46 are glass blocks P equivalent to a color separation prism, a trimming filter and the like.

In this embodiment, the focal length at the wide angle end is 9.0 m.
Despite being widened to m, the focal length at the telephoto end is 396.0 mm with a very high zoom ratio of 44 times. On the other hand, in order to correct spherical aberration and axial chromatic aberration in the first group, the A group is composed of one positive lens and one negative lens, the B1 group is two positive lenses, and the B2 group is one positive lens. In this configuration, the aberration correction is shared.

Regarding the floating of the present invention, the moving amount MB1 of the B1st group, the moving amount MB2 of the B2th group, the moving amount MB1 of the B1st group, and the moving amount of the Ath group from the object at infinity to a certain finite object. The relationship of MA is given by MB2 = 0.47921 MB1 + 0.05718 MB1 ² +0.00351 MB1 ³ MA = 0.08385 MB1-0.04012 MB1 ² −0.00207 MB1 ³ and the parameters at 10.0 m and 1.7 m are shown in Table 3. At this time, the maximum value of MB2 / MB1 is M.M. O. D is 0.987, and the minimum value is MB1 =-
It is 0.246 at the time of 8.145.

Therefore, in this embodiment, M. O. As it becomes D, the change rate of the relative movement amount of the B2 group with respect to the B1 group has a minimum value from small to large. Especially 1
In the vicinity of 0.0 m, MB2 / MB1 = 0.285, which is a small value, is used. O. MB / MB1 = at D (1.7m)
The value is as large as 0.987. Further, Δd / ΔX = −0.071 is set while moving the group A in a convex shape toward the object side. This is for the following reason.

MB2 / MB1 = 0.0.0m near 10.0 m.
285 from the infinite object peculiar to the long focal length zoom lens.
The fluctuations of spherical aberration and axial chromatic aberration near 0 m are over and under, respectively, by boldly correcting the effects of both (a) and (b) and (d) of the A group. There is.

M. O. MB / MB of D (2.0m)
1 = 0.987 In order to suppress the increase in the lens diameter of the first group due to the widening of the angle within the allowable range, M.I. O. While controlling the movement amount MB1 of the B1st lens group on the D side, spherical aberration and axial chromatic aberration are corrected to the over side by utilizing the action of (C) of the Ath lens group.

Generally, the larger the zoom ratio and the longer the focal length at the telephoto end, the more difficult it becomes to correct spherical aberration and axial chromatic aberration. Therefore, in the present embodiment, the first group includes one positive lens and one negative lens for the first group, two positive lenses for the B1 side, and the second lens for the second group.
The two groups are composed of a total of five positive lenses, and all the positive lenses have Abbe numbers of 90 or more. At this time, φB2 / φB1 = 0.260 in terms of power sharing and achromatization,
ΣB2 / ΣB1 = 0.259.

As shown in the aberration diagrams of FIGS. 11 to 13, the spherical aberration is well corrected, and the axial chromatic aberration is M.I. O. D
Although it is slightly undercorrected, it is corrected well overall.

FIG. 4 is a lens cross-sectional view of Numerical Embodiment 4 of the present invention, in which the object distance is infinity, 10.0 m and 2.0 m.
Aberration diagrams at the telephoto end of (MOD) are shown in FIGS.
5,16.

In this embodiment, the zoom ratio is 44 times and the configuration is substantially the same as that of the numerical embodiment 3, but the focal length at the telephoto end is 440.0.
Despite shifting to the telephoto side by mm, the F number at the telephoto end became brighter at 3.0. On the other hand, in order to correct spherical aberration and axial chromatic aberration in the first group, the A group is composed of one positive lens and one negative lens, the B1 group is two positive lenses, and the B2 group is one positive lens. In this configuration, the aberration correction is shared.

Regarding the floating of the present invention, the moving amount MB1 of the B1st group, the moving amount MB2 of the B2th group, and the moving amount MB1 of the B1st group and the moving amount of the Ath group from an object at infinity to a certain finite object. The relationship of MA is given by MB2 = 0.58265 MB1 + 0.05363 MB1 ² +0.00368 MB1 ³ MA = -0.19904 MB1-0.05107 MB1 ² -0.00450 MB1 ³ and the parameters at 10.0 m and 2.0 m are shown in Table 4. . At this time, the maximum value of MB2 / MB1 is M.M. O. D is 0.949, and the minimum value is MB1 =-
It is 0.387 at 7.287.

Therefore, in this embodiment, M. O. As it becomes D, the change rate of the relative movement amount of the B2 group with respect to the B1 group has a minimum value from small to large. Especially 1
The reason why MB2 / MB1 = 0.407 is set to a small value in the vicinity of 0.0 m is for the same reason as in Numerical Example 3 but the group A is not substantially immobile. M.
O. At D (2.0 m), MB2 / MB1 = 0.949, and the groups B1 and B2 are not operated, but Δd /
ΔX = −0.930 and the group A is largely moved to the image plane side, whereby spherical aberration and axial chromatic aberration are corrected by using the effect of (C).

Correction of spherical aberration and axial chromatic aberration becomes difficult even if the F number becomes small. Therefore, in this embodiment, the first group includes one positive lens and one negative lens, each of the B1 group includes two positive lenses, and the second lens group includes one positive lens, for a total of five lenses.
The positive lenses of the A group and the B1 group all have Abbe numbers of 90 or more, and the positive lenses of the B2 group have a higher refractive index than other positive lenses. And at this time, ΣA
/Φ1=−0.010, ΣA / (ΣB1 + ΣB2) = −
It is set to 0.839.

As shown in the aberration diagrams of FIGS. 14 to 16, the spherical aberration and the axial chromatic aberration are well corrected as a whole.

In each of the above embodiments, the relational expressions of floating MB1 and MB2 are used up to the third order term of MB1. However, it is not necessary to pay attention to this and higher order terms may be used. According to the method, it is possible to increase the degree of freedom in correcting aberration variation.

[0102]

[Table 1] Next, numerical examples of the present invention will be shown. In the numerical example, r
i is the radius of curvature of the i-th lens surface in order from the object side, d
i is the i-th lens thickness and air gap from the object side, ni
And νi are the refractive index and Abbe number of the glass with respect to the i-th lens d-line in order from the object side. In the numerical examples, the last two lens surfaces are glass blocks such as face plates and filters. Table 5 shows the relationship between the above-mentioned conditional expressions and various numerical values in the numerical examples.

[0103]

[Outside 1]

[0104]

[Outside 2]

[0105]

[Outside 3]

[0106]

[Outside 4]

[0107]

[Table 2]

[0108]

As described above, according to the present invention, the first lens group for focusing which constitutes the four-group zoom lens is divided into three lens groups, and each lens group is moved on the optical axis to focus. When increasing the aperture and increasing the magnification while adopting the floating focus method, by appropriately setting the lens configuration of each lens group, various aberrations such as spherical aberration and chromatic aberration associated with the magnification and focusing can be reduced. A wide-angle end F-number of about 1.75 with a wide-angle end and a high aperture ratio and a high zoom ratio that has high optical performance over the entire zoom range and the entire focus range. be able to.

[Brief description of drawings]

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

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

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

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

FIG. 5 is an aberration diagram of an object at infinity at the telephoto end according to Numerical Example 1 of the present invention.

FIG. 6 is an aberration diagram at 3 m at the telephoto end according to Numerical Example 1 of the present invention.

FIG. 7 is an aberration diagram of the numerical example 1 of the present invention at the telephoto end at 0.9 m.

FIG. 8 is an aberration diagram of a numerical example 2 of the present invention when an object at infinity is located at the telephoto end.

FIG. 9 is an aberration diagram at 3 m at the telephoto end according to Numerical Example 2 of the present invention.

FIG. 10 is an aberration diagram of Numerical example 2 of the present invention at the telephoto end at 0.8 m.

FIG. 11 is an aberration diagram of a numerical example 3 of the present invention when an object at infinity is at the telephoto end.

FIG. 12 is an aberration diagram at 10 m at the telephoto end according to Numerical Example 3 of the present invention.

FIG. 13 is an aberration diagram of Numerical example 3 of the present invention at the telephoto end at 1.7 m.

FIG. 14 is an aberration diagram of an infinite object at the telephoto end according to Numerical Example 4 of the present invention.

FIG. 15 is an aberration diagram of Numerical example 4 of the present invention at the telephoto end at 10 m.

FIG. 16 is an aberration diagram of Numerical example 4 of the present invention at the telephoto end at 2.0 m.

FIG. 17 is an explanatory diagram of a paraxial refractive power arrangement of the first group of the zoom lens of the present invention.

FIG. 18 is an explanatory diagram of the paraxial refractive power arrangement of the first group of the conventional four-group zoom lens.

FIG. 19 is a lens sectional view of a first group of a conventional four-group zoom lens.

FIG. 20 is an explanatory diagram of the paraxial refractive power arrangement of the first group of the conventional four-group zoom lens.

FIG. 21 is a lens cross-sectional view of a first group of a conventional four-group zoom lens.

[Explanation of symbols]

 L1 1st group L2 2nd group L3 3rd group L4 4th group LA 4th group LA 1st group LB1 1st group 1st group LB2 2nd group 2nd SP SP diaphragm P glass block e e line g g line S sagittal image surface M meridional image surface

Claims (8)

[Claims] 1. A first group of positive refracting powers, a second group of negative refracting powers for zooming, and a positive or negative refracting powers for correcting image plane fluctuations associated with zooming in order from the object side. In a zoom lens having a third lens unit and a fourth lens unit having a fixed image-forming action during zooming, the first lens unit has a negative refractive power group A and a positive refractive power group B.
It has three lens groups, a first lens group and a second lens group B2 having a positive refractive power, and moves the first lens group A upon focusing from an object at infinity to a short distance object and at the same time, the first lens group B1 and the second lens group B2. The zoom lens is characterized in that and are moved to the object side by different movement amounts. 2. The zoom lens according to claim 1, wherein the condition that MB2 / MB1 <1 is satisfied, where MB1 and MB2 are the movement amounts of the B1 and B2 groups, respectively. 3. When the distance from the focus position of the infinitely distant object to the focus position of the closest object of the A-th group and the B1-th group is measured on the image plane side is positive, and Δd and ΔX are set, −1 2. The zoom lens according to claim 1, wherein the condition of 1 <Δd / ΔX <0.105 is satisfied. 4. When the refractive power and F number of the entire system at the telephoto end are φT and FNT, respectively, and the refractive power and F number of the first group are φ1 and FN1, respectively, 1.05 <FN1 where FN1 = The zoom lens according to claim 1, wherein a condition of (φT / φ1) × FNT is satisfied. 5. The group A has at least two independent lenses, a negative A1 lens and a positive A2 lens,
The refractive power of the A-th group is φA, and the refractive power of the Ai-th lens is φAi.
And the Abbe number νAi of the material are summed up ΣA = φAi / ν
Ai, and said group B1 is at least one positive group B
It has a 1,1 lens and the refracting power of the B1 group is φB1,
1, i Lens refractive power φB1, i and material Abbe number νB1, i
The total sum of the ratios is ΣB1 = φB1, i / νB1, i, and the B2 group is a meniscus-shaped positive B-side lens with a convex surface facing the object side.
It has a 2,1 lens and the refractive power of the B2 group is φB2,
Refractive power of 2,1 lens φB2,1 and Abbe number of material νB2,1
When the ratio of is ΣB2 = φB2,1 / νB2,1, then −0.30 <φA / φ1 <−0.02 −0.02 <ΣA / φ1 <−0.0095 −1.30 <ΣA / ( The zoom lens according to claim 1, wherein a condition of ΣB1 + ΣB2) <− 0.80 0.25 <φB2 / φB1 <0.90 0.25 <ΣB2 / ΣB1 <1.30 is satisfied. 6. The position on the optical axis in the focus of the A-th group is such that the focus position of a near object is located closer to the image plane side than the focus position of an object at infinity. Zoom lens. 7. The zoom lens according to claim 5, wherein the A-th group moves monotonically toward the image plane when focusing from an object at infinity to a near object. 8. The zoom lens according to claim 5, wherein the A-th group moves while having a convex locus on the object side when focusing from an infinitely distant object to a close-up object.