JP4439615B2 - Zoom lens - Google Patents

Description

【００４５】
なる式で表している。又「Ｄ−０ｘ」は「１０−ｘ」を意味している。
【００４６】

【００４７】
【表１】

【００４８】

【００４９】
【表２】

【００５０】

【００５１】
【発明の効果】
本発明によれば以上のように、フォーカスを適切に行うことにより、レンズ系全体の小型化を図りつつフォーカスの際の画角変化が少なく、無限遠物体から至近物体に至る物体距離全般にわたり高い光学性能を有したズームレンズを達成することができる。
【図面の簡単な説明】
【図１】 本発明の数値実施例１のレンズ断面図
【図２】 本発明の数値実施例２のレンズ断面図
【図３】 本発明に係るレンズ鏡筒の説明図
【図４】 本発明の数値実施例１のフォーカス方式の説明図
【図５】 本発明の数値実施例２のフォーカス方式の説明図
【図６】 本発明の数値実施例１のフォーカス方式における収差図
【図７】 本発明の数値実施例２のフォーカス方式における収差図
【図８】 本発明の数値実施例１の広角端の収差図
【図９】 本発明の数値実施例１の中間の収差図
【図１０】 本発明の数値実施例１の望遠端の収差図
【図１１】 本発明の数値実施例２の広角端の収差図
【図１２】 本発明の数値実施例２の中間の収差図
【図１３】 本発明の数値実施例２の望遠端の収差図
【図１４】 本発明のズームレンズの要部ブロック図
【符号の説明】
Ｌ１ 第１群
Ｌ２ 第２群
Ｌ３ 第３群
Ｌ４ 第４群
ＩＰ 像面
ＳＰ 絞り
ｄ ｄ線
ｇ ｇ線
ΔＳ サジタル像面
ΔＭ メリディオナル像面[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a zoom lens, and particularly suitable for an imaging apparatus such as a video camera, a film camera, and a digital camera having high optical performance over an entire object distance from an infinite object to a close object by appropriately focusing. It is a thing.
[0002]
[Prior art]
Conventionally, as a focusing method of a zoom lens, a method in which the first lens unit on the object side is focused is often used. This focusing method is characterized in that the amount of extension of the focus lens group is substantially constant regardless of the zoom position (zoom position), and it is easy to simplify the mechanism. Recently, for the purpose of improving the focus speed and reducing the front lens diameter, a so-called inner focus type (rear focus type) that moves the lens group other than the first lens group on the object side to perform focusing is adopted. Various proposals have been made.
[0003]
In general, an inner focus type zoom lens has a smaller effective diameter of the first lens unit than a zoom lens that focuses by moving the first lens unit, making it easy to downsize the entire lens system. In particular, close proximity photography is facilitated, and the relatively small and light lens group is moved, so that the driving force of the lens group is small and quick focusing is possible.
[0004]
This inner focus system has a helicoid bar or the like as a focus mechanism in addition to the cam means, and moves a focus lens group held there along the optical axis during focusing. The focus lens group is also called electronic zoom because it moves on the helicoid bar by zooming other than during focusing.
[0005]
On the other hand, in order to simplify the structure, a type in which a part of the zoom cam is used for the focus cam has been proposed. Since this method can move each group during focusing without the need to detect the zoom position in particular, it is possible to efficiently correct aberration fluctuation due to feeding with a simple configuration, and it has been increasingly used in recent years. Yes.
[0006]
[Problems to be solved by the invention]
There are various methods for focusing the zoom lens as described above, but each has the following problems.
[0007]
First, focusing by extending the first group as the focus lens group tends to increase the effective diameter of the first group in order to secure a peripheral light amount in photographing when the first group is extended. Further, as the effective diameter is increased, the focusing speed tends to be slowed because focusing is performed on the heavier first group. In addition, since only the first group is extended, there is a tendency for aberration fluctuations due to focusing to increase.
[0008]
Next, in the so-called focus method using electronic zoom, since the lens group used for focusing is usually only one specific lens group, fluctuations in aberrations during focusing generally increase. In addition, it is necessary to secure a certain distance in the optical axis direction between adjacent lens groups in the moving direction during focusing of the focus group. That is, a focus space is required.
[0009]
Further, both the pay-out method by the first group and the inner focus method by electronic zoom reduce the focal length of the entire system by focusing and change to the wide angle side. Therefore, the magnification may not increase as expected during close-up shooting.
[0010]
On the other hand, with regard to cam focus using a cam, since a part of the zoom cam is used as a focus cam, the focusable zoom positions are discrete. That is, the zoom position becomes a step-like multifocal camera, and particularly with respect to a zoom lens with a high zoom ratio, there may be a case where a desired angle of view cannot be obtained due to a large change in the angle of view with the adjacent zoom position.
[0011]
The present invention is a zoom that has high optical performance over the entire object distance from an infinite object to a close object, while reducing the angle of view at the time of focusing while reducing the size of the entire lens system by appropriately performing focusing. The purpose is to provide lenses.
[0012]
[Means for Solving the Problems]
The zoom lens of the first aspect of the invention, in the zoom lens having a plurality of lens groups is driven in the optical axis direction by the first driving means, the lens unit F which is driven in the optical axis direction by a second drive means,
Based on the zoom position information and the object distance information, the zoom position detection means for obtaining the zoom position information, the object distance detection means for obtaining the object distance information, and the movement amount of the lens group F during focusing are obtained. Computing means;
When only the lens group F is driven and focused by the second driving means, the lens group F or a holding member that holds the lens group F, and the lens group R that is positioned in the moving direction of the lens group F or the lens group F are held. Determining means for determining whether or not the holding member to mechanically interfere,
When it is determined by the determining means that no mechanical interference occurs, focusing is performed by driving only the lens group F by the second driving means, and it is determined that mechanical interference is generated by the determining means. In this case, the plurality of lens groups are driven and zoomed by the first driving means, and the lens group F is driven and focused by the second driving means .
[0013]
According to a second aspect of the present invention, in the first aspect of the invention, in order from the object side to the image side, a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. And a fourth lens group having a negative refractive power, and during zooming from the wide-angle end to the telephoto end, the distance between the first lens group and the second lens group increases, and the second lens group and the second lens group Each lens group is moved to the object side so that the distance between the three lens groups increases and the distance between the third lens group and the fourth lens group decreases .
[0014]
According to a third aspect of the present invention, in the second aspect of the present invention, the second driving means drives the third lens group toward the object side during focusing from an object at infinity to a close object.
[0015]
According to a fourth aspect of the present invention, in the second or third aspect of the invention, the first driving means drives the first, second, and fourth lens groups toward the object side upon zooming from the wide-angle end to the telephoto end. It is characterized by.
[0016]
A fifth aspect of the invention is characterized in that, in the invention of any one of the second to fourth aspects, the third lens group moves in the optical axis direction on a helicoid bar extending from the second lens group.
[0017]
An imaging device according to a sixth aspect of the invention includes the zoom lens according to any one of the first to fifth aspects.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
1 and 2 are lens cross-sectional views of Numerical Examples 1 and 2 (to be described later) of the zoom lens of the present invention. In the lens cross-sectional view, (A) shows the wide-angle end, (B) shows the middle, and (C) shows the telephoto end.
[0021]
In the figure, L1 is a first group having a positive refractive power, and has a positive lens and a negative lens. L2 is a second lens unit having a positive refractive power and is composed of a meniscus positive lens having a convex surface directed toward the object side. L3 is a third group having a positive refractive power as the main focus lens group, and includes a lens having a concave surface facing the object side and a lens having an aspherical surface with the final lens surface facing the convex surface toward the image surface side. Yes. L4 is a fourth lens unit having a negative refractive power, and is composed of a negative lens having a concave surface directed toward the object side. SP is an aperture stop, which is disposed between the second group L2 and the third group L3. The stop SP moves integrally with the third lens unit L3. IP is the image plane.
[0022]
In the present embodiment, the distance between the first lens unit L1 and the second lens unit L2 increases with the zooming from the wide-angle end to the telephoto end, the interval between the second lens unit L2 and the third lens unit L3 increases, and the third lens unit. Each lens unit is moved to the object side as indicated by an arrow so that the distance between L3 and the fourth unit L4 decreases. At this time, the aperture stop SP is integrated with the third group.
[0023]
FIG. 3 is a schematic view for explaining the lens barrel structure of the present embodiment. L1 is the first group, L2 is the second group, L3 is the third group and the main focus group, L4 is the fourth group, 11, 12, and 14 are the cam pins of the first, second, and fourth groups, A part of one drive means is constituted. Reference numeral 13 denotes a helicoid bar coming out of the second group L2, which constitutes a part of the second drive means and is for driving the third group L3. Reference numeral 15 denotes a cam ring having a cam groove, and reference numeral 16 denotes a fixed cylinder having a rectilinear guide.
[0024]
By rotating the cam ring 15 with respect to the fixed cylinder 16 by the first driving means, the first, second and fourth groups are fed out while changing their relative intervals by the respective cams. At this time, since the cam pins are regulated in the rotational direction by the linear guide of the fixed cylinder 16, the first, second, and fourth groups do not rotate and are linearly extended. On the other hand, the third group L3 is electronically moved along the optical axis La by the second driving means by the helicoid bar 13 coming out of the second group L2, and the relative distance from the second group L2 is changed.
[0025]
In general, in order to reduce the size of the entire lens system, the air space between the second lens unit L2 and the third lens unit L3 is narrow on the wide-angle end side (intermediate zoom position from the wide-angle end). For this reason, there is a small space for extending the third lens unit L3 when focusing, and it may be impossible to focus from an object at infinity to an object at close range. Therefore, the present invention focuses as follows. FIG. 14 is a block diagram of the main part of the focus in the zoom lens according to the present invention, which will be described below with reference to FIG.
[0026]
Focusing in this embodiment is performed as follows. Focusing from an object at infinity to an object at a close distance is performed by moving the focusing lens group L3 (moving toward the object side). At this time, the current zoom position information (signal from the position sensor 21 as a zoom position detection means for detecting the position of the zoom lens group on the optical axis) and object distance information (from the AF means 22 as the object distance detection means). The movement amount of the lens unit L3 is obtained by the calculation means 23 from the above signal. When moving the third lens unit L3 on the optical axis according to the amount of movement obtained by the computing means 23,
(A-1) When it is determined by the determining means 24 that the third group L3 and the second group L2 do not mechanically interfere (for example, the lens holding frames are in contact) (for example, the object distance is very far) Sometimes when the amount of movement of the third lens unit L3 is small, or when there is a large gap between the second lens unit L2 and the third lens unit L3, such as a zooming range from the intermediate zoom position to the telephoto end). The driving unit 25 performs focusing by moving only the lens unit L3.
[0027]
(A-2) When the discriminating means 24 discriminates that the third group L3 and the second group L2 interfere mechanically, based on the degree of mechanical interference, the second group L2 and the third group L3 The first driving means 26 performs zooming based on the zooming locus when zooming is performed by moving the second lens unit L2 and the third lens unit L3 in the direction in which the air gap between the second lens group and the second lens group is increased. A predetermined amount of air space is created between the third group. Then, at the zoom position at which the magnification is changed, the third lens unit L3 is extended to perform focusing.
[0028]
At this time, the movement amount of the third lens unit L3 is obtained by the computing unit 23 from the zoom position information and the object distance information at the zoomed zoom position, and the third lens unit L3 is moved based on the computation result from the computing unit 23. Also good.
[0029]
In the present embodiment, in the predetermined zoom range from the wide-angle end to the intermediate zoom position, focusing may be performed by the first and second driving means based on data from the zoom position detecting means. .
[0030]
In the present embodiment, the air distance between the second lens unit L2 and the third lens unit L3 is compared based on the data from the zoom position detection means within a predetermined zooming range determined from the intermediate zoom position to the telephoto end. For this reason, the focus may be adjusted over the entire object distance range by moving only the third lens unit L3.
[0031]
In the present embodiment, a case has been described in which there are four lens groups as a whole, and the third group is moved to the object side to focus from an object at infinity to an object at a close distance. A zoom lens having a configuration can be similarly applied.
-Having a plurality of lens groups that move by zooming.
-At least one of the plurality of lens groups is a main focus lens group.
-When focusing is performed by moving the focusing lens group on the optical axis, the lens group mechanically interferes with the lens group (which is a zooming lens group) located in the moving direction.
The first drive means for zooming and the second drive means for focus are provided.
[0032]
In the present invention, in order to obtain high optical performance over the entire zoom range and the entire object distance, each lens group is preferably configured as follows.
[0033]
The first lens unit L1 having a positive refractive power is composed of two lenses, a positive lens having both convex surfaces and a negative lens having a concave surface facing the object side, and the second lens unit L2 having a positive refractive power is disposed on the object side. Consists of a single meniscus positive lens with a convex surface, and a positive third lens L3 having a positive refractive power and a meniscus negative lens with the convex surface facing the image surface, and a convex lens with both lens surfaces convex The fourth lens unit L4 having a negative refractive power is composed of one lens of a meniscus negative lens having a convex surface facing the image surface side. As a result, aberration fluctuations associated with zooming are corrected well while ensuring a predetermined zooming ratio, and high optical performance is obtained over the entire zooming range.
[0034]
The third group has at least one aspheric surface. As a result, aberration fluctuations during zooming and focusing are corrected satisfactorily.
[0035]
The fourth group is composed of a single negative lens having a concave surface facing the object side, and at least one lens surface of the negative lens has a shape in which the negative refractive power becomes weaker from the lens center to the lens periphery. And aberration variation due to zooming is corrected, and particularly off-axis aberrations such as curvature of field and distortion are favorably corrected.
[0036]
FIG. 4 and FIG. 5 are explanatory views of the optical action by the focusing method in the zoom lens of the present invention. 4B and 5B correspond to Numerical Examples 1 and 2 of the present invention. 4A, 4B, 5A, and 5B are optical path diagrams when focusing on a subject distance of 60 cm at the wide angle end when the numerical example is expressed in mm. FIGS. 4A and 5A show the case where focusing is performed only with the third lens group (integrated with the diaphragm). 4 (B) and 5 (B) show a state where the third group is moved and focused while moving the cam ring slightly to the telephoto side, that is, the third group and other lens groups are moved and focused. 1 represents an embodiment according to the present invention.
[0037]
In FIGS. 4A and 5A, the stop SP mechanically interferes with the front group (second group), whereas in FIGS. 4B and 5B, the second and second apertures. There is a space between the three groups. Further, in FIGS. 4A and 5A, the peripheral light beam is considerably thin, whereas in FIGS. 4B and 5B, a relatively large amount of the peripheral light beam passes.
[0038]
In FIGS. 4 (B) and 5 (B), 5% of the cam rotation angle from the wide-angle end to the telephoto end when assuming a cam ring in which the fourth group is linearly moved in both the first and second embodiments is shown. While rotating, the third group is moved along the helicoid bar like an electronic cam and focused.
[0039]
Further, the focal length is 31.2 mm in the state of FIG. 4A, but is 33.6 mm in the state of FIG. 4B, that is, Embodiment 1 of the present invention. This is close to the focal length fw = 34.0 mm at the wide-angle end when the subject distance of the first embodiment is infinity. In other words, according to the embodiment of the present invention, the problem that the wider the angle of the lens group, the wider the angle becomes, and the image does not appear large while approaching the subject is solved.
[0040]
Incidentally, the focal length in FIG. 5 (A) is 26.9 mm, whereas in FIG. 5 (B), it is 29.4 mm, and this is also the focal length fw = 28.9 mm at the wide-angle end at the subject distance infinite in the second embodiment. It is close to.
[0041]
FIGS. 6B and 7B are aberration diagrams corresponding to Embodiments 1 and 2, respectively. FIGS. 6A and 7A show a case where focusing is performed only in the third group. FIGS. 6B and 7B are longitudinal aberration diagrams at a subject distance of 60 cm when each lens group is moved and focused in the same manner as in FIGS. 4B and 5B described above. In both cases, the curvature of field is particularly well corrected as compared with FIGS. 6A and 7A focused on only the third group.
[0042]
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 spacing from the object side, and Ni and νi are respectively the i-th lens in order from the object side. Refractive index and Abbe number of glass.
[0043]
The aspheric shape is the X axis in the optical axis direction, the H axis in the direction perpendicular to the optical axis, the light traveling direction is positive, R is the paraxial radius of curvature, and k, B, C, D, and E are the aspheric coefficients. When
[0044]
[Expression 1]

[0045]
It is expressed by the following formula. “D-0x” means “10-x”.
[0046]

[0047]
[Table 1]

[0048]

[0049]
[Table 2]

[0050]

[0051]
【The invention's effect】
As described above, according to the present invention, by appropriately performing focusing, the entire lens system is reduced in size, and there is little change in the angle of view during focusing, and the entire object distance from an infinite object to a close object is high. A zoom lens with optical performance can be achieved.
[Brief description of the 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 an explanatory diagram of a lens barrel according to the present invention. FIG. 5 is an explanatory diagram of a focus system according to Numerical Example 1 of the present invention. FIG. 5 is an explanatory diagram of a focus system according to Numerical Example 2 of the present invention. FIG. 6 is an aberration diagram of the focus system according to Numerical Example 1 of the present invention. FIG. 8 is an aberration diagram at the wide-angle end of Numerical Example 1 of the present invention. FIG. 9 is an aberration diagram in the middle of Numerical Example 1 of the present invention. FIG. 11 is an aberration diagram at the telephoto end of Numerical Example 1 of the invention. FIG. 11 is an aberration diagram at the wide-angle end of Numerical Example 2 of the invention. FIG. 12 is an aberration diagram at the middle of Numerical Example 2 of the invention. FIG. 14 is an aberration diagram at the telephoto end according to Numerical Example 2 of the invention. Description of the code]
L1 1st group L2 2nd group L3 3rd group L4 4th group IP Image plane SP Aperture d d line g g line ΔS Sagittal image plane ΔM Meridional image plane

Claims (6)

In a zoom lens having a plurality of lens groups driven in the optical axis direction by the first driving means and a lens group F driven in the optical axis direction by the second driving means,
Based on the zoom position information and the object distance information, the zoom position detection means for obtaining the zoom position information, the object distance detection means for obtaining the object distance information, and the movement amount of the lens group F during focusing are obtained. Computing means;
When only the lens group F is driven and focused by the second driving means, the lens group F or a holding member that holds the lens group F, and the lens group R that is positioned in the moving direction of the lens group F or the lens group F are held. Determining means for determining whether or not the holding member to mechanically interfere,
When it is determined by the determining means that no mechanical interference occurs, focusing is performed by driving only the lens group F by the second driving means, and it is determined that mechanical interference is generated by the determining means. In this case, the zoom lens is characterized in that the first driving means drives the plurality of lens groups to change the magnification, and the second driving means drives the lens group F to perform focusing . In order from the object side to the image side, the lens unit includes a first lens unit having a positive refractive power, a second lens unit having a positive refractive power, a third lens unit having a positive refractive power, and a fourth lens group having a negative refractive power. When zooming from the wide-angle end to the telephoto end, the distance between the first lens group and the second lens group is increased, the distance between the second lens group and the third lens group is increased, and the third lens is increased. 2. The zoom lens according to claim 1 , wherein each lens unit moves toward the object side so that a distance between the first lens unit and the fourth lens unit is reduced . 3. The zoom lens according to claim 2, wherein the second driving unit drives the third lens group toward the object side during focusing from an object at infinity to a close object . 4. The zoom lens according to claim 2, wherein the first driving unit drives the first, second, and fourth lens groups toward the object side during zooming from the wide-angle end to the telephoto end . The zoom lens according to any one of claims 2 to 4, wherein the third lens group moves in a direction of an optical axis on a helicoid bar extending from the second lens group . An image pickup apparatus comprising the zoom lens according to claim 1 .

Images