JP2000028922A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the diameter of a front lens while making the viewing angle of a zoom lens constituted of 4 groups wide. SOLUTION: This zoom lens is provided with the 1st lens group I whose refractive power is positive, the 2nd lens group II whose refractive power is negative, the 3rd lens group III whose refractive power is positive and the 4th lens group IV whose refractive power is positive in turn from an object side. Then, when a variable power action is executed to a telephoto end from a wide angle end, the group II is moved to an image surface side and the group IV is moved so that the fluctuation of the position of an image surface occurring in accordance with the variable power action is corrected. Besides, the groups I and II are fixed. When the outside diameter of the lens set at the most object side is defined as ϕ1 and the focal distance of the whole system at the wide angle end is defined as Fw, the conditional expression of 0.145<Fw/ϕ1<0.182 is satisfied.

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 a zoom lens, which is suitable for a photograph or a video camera, and has a wide angle of view (wide angle end 2.omega..gtoreq.65.degree.) And a high zoom ratio (10 times or more). However, the present invention relates to a rear-focus type zoom lens that has a small front lens diameter and is compact as a whole.

[0002]

2. Description of the Related Art In recent years, as home video cameras have become smaller and lighter, remarkable progress has been made in miniaturization of imaging zoom lenses.
A great deal of effort has been put into simplifying the configuration.

As one means for achieving these objects, there is known a so-called rear focus type zoom lens which performs focusing by moving a lens group other than the first lens group on the object side.

In general, a rear focus type zoom lens has a smaller effective diameter of the first lens group than a zoom lens which performs focusing by moving the first lens group.
The size of the entire lens system can be easily reduced. In addition, close-up photography, particularly very close-up photography, is possible. Further, since the relatively small and lightweight lens group is moved, the driving force of the lens group is small, so that quick focusing can be performed.

[0005] As such a rear focus type zoom lens, for example, Japanese Patent Application Laid-Open Nos. 62-24213 and 63-247316 disclose a positive first lens group and a negative second lens in order from the object side. Group, positive third lens group,
A zoom lens having a positive fourth lens group, performing zooming by moving the second lens group, correcting the image plane variation due to zooming with the fourth lens group, and performing focusing is disclosed. .

JP-A-58-160913 discloses a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a positive refraction in order from the object side. It has four lens groups, a fourth lens group for power, and performs zooming by moving the first lens group and the second lens group, and performs image plane movement accompanying zooming by moving the fourth lens group. ing. Then, focusing is performed by moving one or more of these lens groups. However, in the above example, most of the zooming function is performed by the moving lens group on the object side of the aperture stop, so a large amount of space is required between the front lens and the aperture stop at the focal length at the wide-angle end. The entrance pupil position of the lens was likely to be deep, and the front lens diameter had to be huge.

On the other hand, the present applicant has disclosed in Japanese Patent Application Laid-Open No. 61-2963.
In Japanese Patent Publication No. 17 (1994), etc., the distance between the front lens and the aperture stop is shortened by making the lens group behind the aperture stop movable on the optical axis during zooming and sharing the variable power function, thereby reducing the diameter of the front lens. Is being planned. However, such conventional zoom lenses tend to be mechanically complex because the lens groups on both sides of the fixed aperture stop move during zooming. Also the first
Because the lens group focuses, the diameter of the front lens becomes large to secure the luminous flux to the peripheral angle of view at a close distance, and when trying to adapt it to the rear focus method for miniaturization, optimal refraction There is a problem that the arrangement is not the force arrangement or that the fluctuation of the focus aberration due to the rear focusing is not sufficiently corrected.

On the other hand, the present applicant has disclosed in Japanese Patent Application Laid-Open No. 56-48607.
In Japanese Patent Application Publication (JP-B-61-44288), a first lens unit having a positive refractive power for focusing and fixed during zooming in order from the object side, and a second lens unit having a negative refractive power which moves for zooming during zooming. A zoom lens having four lens groups, a lens group, a third lens group that moves to keep the image plane position constant, and a fourth lens group having a positive refractive power fixed during zooming is proposed. According to this proposal, it is advantageous to reduce the diameter of the front lens if the stop located on the front surface of the relay lens is closer to the first surface direction at the wide-angle end where the front lens diameter is the largest or at a position slightly zoomed from the wide-angle end. In the example, the aperture is moved. Furthermore, it has been proposed that the stop and the third lens group move integrally. However, since the first lens group focuses, the diameter of the front lens becomes large in order to secure a luminous flux to the peripheral angle of view at a close distance, and if this is to be adapted to the rear focus method for miniaturization, ,
There are problems that the refractive power is not optimally arranged and that the fluctuation of the focus aberration due to the rear focusing is not sufficiently corrected.

Similarly, Japanese Patent Application Laid-Open No. 57-111507 also discloses a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a positive lens having a positive refractive power. The zoom lens has a third lens group. The second lens group and the third lens group move in opposite directions during zooming. The third lens group includes two positive lens groups. A positive four-group zoom lens is proposed. In this proposal, an aperture stop (aperture stop) is positioned in the third lens group. However, in this configuration, since the second lens group and the third lens group move in opposite directions, it is necessary to widen the interval between the second and third lens groups at the wide-angle end, and the stop is in the third lens group. Therefore, the entrance pupil position at the wide-angle end is closest to the image plane, which is not suitable for downsizing the front lens diameter and the entire system. Also in this case, since the first lens group focuses, the diameter of the front lens becomes large to secure the luminous flux to the peripheral angle of view at a close distance, and this is adapted to the rear focus method for downsizing. If this is attempted, there is a problem that the refractive power arrangement is not optimal, and the fluctuation of the focus aberration due to the rear focusing is not sufficiently corrected.

In Japanese Patent Application Laid-Open No. 3-200113, a positive first lens unit fixed during zooming in order from the object side and a negative second lens unit moving back and forth for zooming are similarly constructed from the object side.
A zoom lens including a lens group, a positive third lens group that moves in association with the movement of the second lens group, and a positive fourth lens group that moves a part or all of the focal position accompanying zooming. Has been proposed. According to this proposal, the movement of the positive third lens group that moves in relation to the movement of the second lens group is performed to reduce the amount of image plane movement correction performed by the fourth lens group, and the correction function Are movements for sharing a part of the third lens group with the third lens group. Specifically, it is desirable to move from the image side to the object side from the intermediate focal length to the telephoto end. However, in this configuration, the second lens group and the third lens group move in opposite directions, as in the above-described known example, so that it is necessary to widen the interval between the second and third lens groups on the wide-angle side. The entrance pupil position is closest to the image plane, which is not suitable for downsizing the front lens diameter and the entire system.

[0011] Similarly, in Japanese Patent Application Laid-Open No. 3-15813, the lens system is composed of a positive first lens group, a negative second lens group, a positive third lens group, and a positive fourth lens group in this order from the object side. Discloses a zoom lens in which the second lens group and the third lens group are moved along the optical axis to perform zooming, and the aperture stop is moved integrally with the third lens group. According to this proposal, the distance between the second lens group and the third lens group decreases with zooming from the wide-angle end to the telephoto end. Also in the embodiment, the third lens group having the aperture stop is located closest to the image at the wide-angle end, and at the wide-angle end where the front lens diameter is the largest or at a position slightly zoomed from the wide-angle end, the third lens group with the stop is provided. The vicinity of the three lens groups is closest to the image side, and the entrance pupil position is deep. This is disadvantageous for reducing the front lens diameter, and also has large distortion, which is suitable for reducing the front lens diameter and miniaturizing the entire system. There was a disadvantage that it was not.

On the other hand, the present applicant has disclosed in
In the publication No. 215810, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a stop, a third lens group having a positive refractive power, and a positive fourth lens The zoom lens has a lens group, and moves the second lens group toward the image plane when zooming from the wide-angle end to the telephoto end.
A rear focus zoom lens has been proposed in which the third lens group and the fourth lens group are independently moved so as to have a locus convex toward the object side, and the fourth lens group is moved in accordance with the distance. According to this proposal, it is necessary to secure a certain distance between the diaphragm and the third lens group, and the second lens group, the diaphragm, the third lens group, and the fourth lens group move significantly differently independently of each other. Therefore, there is a drawback that the mechanism tends to be complicated. Also, since the third lens group and the aperture move differently during zooming and the position of the pupil changes with respect to the third lens group, spherical aberration, coma aberration, and on-axis aberration which suppress the fluctuation with the third lens group. Chromatic aberration
It is not suitable because it fluctuates greatly. In addition, this configuration is still insufficient for widening the angle (2ω ≧ 60 °), and the power arrangement and group movement are not optimal for widening the angle.

[0013]

As described above, generally, in a zoom lens, in order to achieve the miniaturization of the front lens diameter and the entire system, rather than the distance adjustment by the first lens group, a so-called rear focus system is used. Is more suitable.

[0014] However, for example, Japanese Patent Application Laid-Open No.
In Japanese Patent Application Laid-Open Nos. 24213 and 63-247316, when an attempt is made to further increase the angle of view, the incident height of the off-axis light beam to the first lens group increases at the intermediate zoom position near the wide-angle end. The effective lens diameter of one lens group increases. In order to reduce the effective diameter of the first lens group, there is a method of shortening the distance between the first lens group and the stop.
However, the second lens group, which is the main zoom lens group, is located between the first lens group and the aperture, and if the distance between the first lens group and the aperture is reduced, the moving space for zooming the second lens group is insufficient. Therefore, a desired zoom ratio, particularly a zoom ratio of 10 or more, cannot be secured. If an attempt is made to obtain a desired zoom ratio in a state where the distance between the first lens unit and the aperture is reduced, the negative refractive power of the second lens unit becomes strong, the Petzval sum increases negatively, and the image plane becomes over. It is unsuitable because it tends to collapse. In addition, the sensitivity of the second lens group to the focal plane increases, and the manufacturing accuracy becomes severe, which is not appropriate.

An object of the present invention is to improve the drawbacks of the above-mentioned conventional example, and particularly to the improvement of Japanese Patent Application Laid-Open No. 3-215810 proposed by the present applicant.
> 65 °), high zoom ratio (10 times or more), small size and wide angle with good performance over the entire zoom range and all object distances while simplifying and reducing the size and weight including the mechanism. It is an object of the present invention to provide a zoom lens that is designed to have a small distortion.

[0016]

In order to achieve the above object, a zoom lens according to the present invention comprises, in order from the object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, and a positive lens unit. The zoom lens has a third lens unit having a refractive power and a fourth lens unit having a positive refractive power. When zooming from the wide-angle end to the telephoto end, the second lens unit is moved toward the image plane and the fourth lens unit is moved. A zoom lens in which the first lens group and the third lens group are fixed and the outer diameter of the lens closest to the object is φ ₁ and the wide angle is When the focal length of the whole system at the end is Fw, the following conditional expression is satisfied: 0.145 <Fw / φ ₁ <0.173 (1)

[0017]

1 to 3 are a lens sectional view and various aberration diagrams of a numerical example according to the present invention. In the figures, (B), (C), and (D) show various aberration diagrams at the wide-angle end, the intermediate zoom position, and the telephoto end, respectively.

I is a first lens group having a positive refractive power, I
I is a second lens group having a negative refractive power, III is a third lens group having a positive refractive power, IV is a fourth lens group having a positive refractive power, and S is fixed in front of the third lens group. It is the aperture that is being done. Zooming from the wide-angle end to the telephoto end is performed by moving the second lens group II and the fourth lens group IV as shown by arrows, while performing the focusing by moving the fourth lens group IV. The first lens group and the third lens group are stationary during zooming. Then, the above-mentioned conditional expression is satisfied.

In general, when the focal length Fw at the wide-angle end becomes short, the front lens diameter φ ₁ tends to become large. If the focal length Fw of the wide-angle end becomes longer Conversely, it depends but front lens diameter phi ₁ becomes smaller in the brightness of the telephoto end of the lens. Equation (1) is a condition that defines an appropriate balance between the front lens diameter and the focal length at the wide-angle end in order to achieve a small and wide-angle zoom lens. Deviating from either the upper limit or the lower limit of (1) makes it impossible to provide a small and wide-angle zoom lens. Specifically, if you deviate from the upper limit, it becomes a telephoto zoom lens,
Beyond the lower limit, it tends to be a large zoom lens.

The front lens diameter (outer diameter) φ ₁ discussed here
Is equivalent to the optical effective diameter of the first lens, and is the actual lens outer diameter. The front lens diameter φ1 is about 0 to 6% larger than the optical effective diameter of the first lens.

In general, a so-called front lens focus method in which the first lens group is moved on the optical axis to adjust the distance is known, but in order to secure a luminous flux on a peripheral screen at the time of close-up shooting on the wide angle side. Ball diameter tends to be large. For this reason, in this focus method, downsizing, which is one of the objects of the present invention, becomes difficult. Therefore, focusing is performed by the entire lens unit or a part of the lens unit disposed after the third lens unit.

Specifically, some of the zoom lenses shown in FIGS. 1 to 3 have, in order from the object side, a first lens unit I having a positive refractive power, a second lens unit II having a negative refractive power, and a positive refractive power. Power third
Lens group III, and fourth lens group IV having a positive refractive power
The first and third lens groups are always stationary, and when zooming from the wide-angle end to the telephoto end, the second lens group is moved to the image plane side and the fourth lens group is zoomed. Is moved so as to correct the image plane position fluctuation accompanying the
Focusing is performed by moving the fourth lens group.

As described above, the so-called front lens focus method in which the first lens group is moved on the optical axis to adjust the distance is a so-called front lens focus method in which the front lens diameter is large in order to secure a luminous flux on a peripheral screen during close-up shooting on the wide angle side. It tends to be. For this reason, in this focusing method, downsizing, which is one of the objects of the present invention, becomes difficult. Therefore, the fourth lens group as described above particularly has a focusing function.

In order to make the front lens diameter small and to have a simple mechanical structure during zooming while increasing the magnification width, it is preferable that the zoom lens has a stop in front of the third lens unit.

In order to set a wide angle of view at the wide-angle end, if the principal point distance e1 between the first positive lens unit and the second negative lens unit at the wide-angle end is short, the focal length of the entire system can be further reduced. Is possible. However, a minimum air gap is required between the first lens group and the second lens group, and it is not appropriate to collide with each other. Therefore, it is preferable that the image-side principal point of the first lens group is set closer to the second lens group, or that the object-side principal point of the second lens group is set closer to the first lens group. In particular, in the first lens group, it is preferable to satisfy the following conditional expression because the size of the front lens is also involved.

−0.1 <H ₁ ′ / F ₁ <0.1 (2) Here, H ₁ ′ is the vertex of the most image side surface of the first lens unit and the image side of the first lens unit. interval in the main point (- the object side, + the image side) in, F ₁ represents the focal length of the first lens group. This equation is necessary to shorten the distance between the principal points of the first lens group and the second lens group as described above. If the lower limit value is exceeded, the principal point position of the first lens group goes too far to the object side, and the above-mentioned e1 cannot be shortened, and the desired wide angle cannot be obtained.
When the value exceeds the upper limit, the distance between the first lens unit and the second lens unit increases, and the diameter of the front lens becomes large, which is not appropriate.

Further, when miniaturizing the entire system, it is preferable to satisfy the following conditions.

2.5 <Bfw / Fw <4.0 (3) where Bfw is the back focus at the infinity of the object distance at the wide-angle end (“G” in the embodiment such as a glass block and a filter). Excluding). Equation (3) is an equation necessary to effectively reduce the size of the entire system. If the lower limit value is exceeded, not only is it impossible to insert a block such as a filter, but also the exit pupil becomes short. However, the image formation on the image sensor is shifted from the telecentric system, which is inappropriate. On the other hand, if the ratio exceeds the upper limit, the size becomes large, which is not suitable.

In order to reduce the diameter of the front lens, it is preferable to satisfy the following expression.

5.7 <F ₁ /Fw<9.0 (4) This equation relates to the object point for the second lens group, that is, the magnification. In order to set the entire system to be small, it is preferable that the second lens group has the same magnification during zooming.
When the same magnification is interposed, the locus of zooming of the fourth lens group is substantially reciprocating, and high zooming is possible with the most effective space efficiency. Specifically, if the upper limit of the equation (4) is exceeded, the second
The object point with respect to the lens group becomes far, the imaging magnification of the second lens group becomes low, and it is difficult to effectively reduce the size. Furthermore,
The distance between the first lens group and the second lens group increases, and it is difficult to achieve miniaturization. If the lower limit value is exceeded, the magnification of the second lens group becomes large, and it is difficult to achieve high magnification, and the object of the present invention cannot be achieved.

In particular, as described in the expression (2),
One of the important points is how the principal point interval e1 between the first lens unit and the second lens unit can be reduced at the wide-angle end for widening the angle. For this purpose, the first lens group preferably has the following specific configuration.

In order from the object side of the first lens group, a negative meniscus lens L11 having a convex surface on the object side, a positive lens L12 having a convex surface on the object side with an air gap, and a positive lens L13 having a convex surface on the object side L1
1. The air lens constituted by L12 has a negative refractive power.

As another configuration, in order from the object side,
Biconcave lens L11, positive lens L1 bonded to it
2, and at least one positive lens may be arranged.

With such a configuration, the image-side principal point of the first lens group is set closer to the second lens group, and the principal point distance e1 between the first lens group and the second lens group at the wide-angle end is short. This is effective for widening the angle.

Also, in the second lens group, it is desirable for widening the angle of view that the object side principal point of the second lens group is set to the object side in order to shorten e1 at the wide angle end. .

More specifically, in order from the object side of the second lens group, a negative meniscus lens L21 having a convex surface on the object side,
Biconcave negative lens L21, positive lens L2 with air spacing
3 in that order. Due to this air space, the object-side principal point of the second lens group is closer to the first lens, and e1 on the wide-angle side can be easily shortened, which is effective for widening the angle of view.

By configuring as described above,
The front lens diameter is small, the angle of view is wide (2ω> 65 °), and a high zoom ratio is ensured (10 times or more).
It has become possible to provide a rear-focus type zoom lens that is compact and lightweight and has good performance over the entire zoom range and all object distances.

Hereinafter, embodiments of the present invention will be described.

In the numerical examples, ri is the radius of curvature of the i-th lens surface in the order from the object side, di is the i-th lens thickness and air gap in the order from the object side, and ni and νi are those in the order from the object side. The refractive index and Abbe number of the i-th lens.

The aspherical shape has an X-axis in the optical axis direction, a Y-axis in a direction perpendicular to the optical axis, a positive traveling direction of light, a point of intersection between the vertex of the lens and the X-axis taken as an origin, and r as a lens surface. When the paraxial radius of curvature, k, A2, A3, A4, and A5 are aspheric coefficients,

[0041]

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

For example, "D-03" is displayed as "1".
0 ^-3 ].

G in the numerical examples indicates an optical filter, a face plate and the like.

For reference, the values of the corresponding conditions in each embodiment are shown in Table 1, in which the movement parameters a, b, c
There is, when the amount of movement of the second lens group has a M _2, this parameter denotes _{M 2 = ax (0 ≦ x} ≦ 1) and consisting coefficient (a> 0), respectively.

[0045]

[Table 1]

[0046]

[Outside 2]

[0047]

[Outside 3]

[0048]

[Outside 4]

[0049]

As described above, according to the present invention, while the angle of view is wide (2.omega..gtoreq.60.degree.) And a high zoom ratio is secured (10 times or more), the diameter of the front lens is small, and it is easy to make. It has become possible to provide a compact zoom lens.

[Brief description of the drawings]

FIG. 1 is a lens cross-sectional view and various aberration diagrams of Numerical Example 1 according to the present invention, (A) is a lens cross-sectional view, (B) is a wide-angle end,
(C) is an intermediate zoom position, (D) is a diagram of various aberrations at the telephoto end.

2A and 2B are a lens cross-sectional view and various aberration diagrams of Numerical Example 2 according to the present invention, FIG. 2A is a lens cross-sectional view, FIG.
(C) is an intermediate zoom position, (D) is a diagram of various aberrations at the telephoto end.

3A and 3B are a lens cross-sectional view and various aberration diagrams of Numerical Example 3 relating to the present invention, FIG. 3A is a lens cross-sectional view, FIG.
(C) is an intermediate zoom position, (D) is a diagram of various aberrations at the telephoto end.

[Explanation of symbols]

 I First lens group II Second lens group III Third lens group IV Fourth lens group S Sagittal image plane M Meridional image plane d d line g g line

Claims (4)

[Claims] 1. A first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power are arranged in order from the object side. Upon zooming from the wide-angle end to the telephoto end, the second lens group is positioned on the image side,
A zoom lens in which the fourth lens group is moved so as to correct a change in the image plane position caused by zooming, and wherein the first lens group and the third lens group are fixed; The outer diameter is φ ₁ , and the focal length of the entire system at the wide-angle end is Fw
Wherein the following conditional expression is satisfied: 0.145 <Fw / φ ₁ <0.173. 2. The distance between the vertex of the most image-side surface of the first lens unit and the image-side principal point of the first lens unit (-is the object side,
+ Is the image side) H ₁ ′, and the focal length of the first lens group is F ₁
When _{a, -0.1 <H 1 '/ F} 1 < zoom lens according to claim 1, characterized by satisfying 0.1 conditional expression. 3. The conditional expression 2.5 <Bfw / Fw <4.0 when the back focus at the object distance infinity at the wide angle end is Bfw. Zoom lens. When wherein the focal length of the first lens group and F _1, 5.7 <of claims 1 to 3, wherein satisfies the F ₁ /Fw<9.0 following condition threshold Zoom lens.