JP2014052563A - Zoom lens, camera, and mobile information terminal device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zoom lens which is sufficiently wide-angle with a half view angle of no less than 38 degrees at the wide angle end, and yet offers a magnification ratio of no less than 7x, an F-number of less than 3 at the wide angle end, resolving power compatible with image sensors with 10 to 15 million pixels, and a compact size.SOLUTION: A zoom lens includes a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, and a fourth lens group G4 having positive refractive power arranged in order from the object side. The first lens group G1 comprises a negative lens and a positive lens cemented together, and the second lens group G2 comprises a first negative lens, a second negative lens, and a positive lens. A ratio of a distance along the optical axis between the first lens group G1 and the second lens group G2 at the wide angle end and a distance along the optical axis between the first lens group G1 and the second lens group G2 at a zoom position at which the total length becomes minimum is set within an appropriate range.

Description

  The present invention relates to a zoom lens improved as a photographing optical system, a camera having the zoom lens as a photographing optical system, and a portable information terminal device.

In recent years, the market for digital cameras has become very large, and the demands of users for digital cameras are also diverse. Among them, high image quality and miniaturization are always what users want, and the weight is large. Therefore, a zoom lens used as a photographing lens is also required to have both high performance and downsizing.
Here, in terms of miniaturization, it is first necessary to shorten the total lens length (distance from the lens surface closest to the object side to the image plane) during use, and reduce the thickness of each lens group. It is also important to reduce the overall length during storage. In addition, there is a strong demand to reduce the vertical and horizontal size of the camera by reducing the size of the lens in the radial direction. Furthermore, in terms of high performance, it is necessary to have a resolving power corresponding to an image sensor with about 10 million to 15 million pixels over the entire zoom range.
In addition, there are many users who desire a wider angle of view of the taking lens, and at least a half angle of view of about 38 degrees corresponding to a focal length of 28 mm equivalent to a 35 mm silver salt camera (so-called Leica version) is desired.
In addition, as large a zoom ratio as possible is desired. That is, it is considered that a zoom lens equivalent to about 28 to 200 mm (about 7.1 times) at a focal length equivalent to a 35 mm silver salt camera can cope with most of general photographing. In addition, it is desired that the release F number be as small as possible. In particular, there are an increasing number of users who want the F number to be less than 3 at the wide-angle end where the camera is activated and the imaging frequency is relatively high.

There are many types of zoom lenses for digital cameras, but as a type suitable for high zoom ratio, the positive focal length (in the case of "positive refractive power") in order from the object side to the image plane side A first lens group having a negative focal length (sometimes referred to as “negative refractive power”), a third lens group having a positive focal length, and a positive focus. A distance between the first lens group and the second lens group during zooming from the wide-angle end to the telephoto end, and the distance between the second lens group and the third lens group. In some cases, the distance decreases and the distance between the third lens group and the fourth lens group changes.
As a conventional example of this type of zoom lens, there is a type in which the first lens group is fixed at the time of zooming. In this case, if a large amount of movement of the second lens group that bears much of the zooming action is to be secured, The aperture stop disposed in the vicinity of the third lens group is separated from the first lens group even at the wide angle end, and the first lens group becomes very large for wide angle and high zooming. . Therefore, in order to realize a wide-angle, high-magnification, and compact zoom lens, it is desirable that the first lens unit be moved so that it is positioned closer to the object side at the telephoto end than at the wide-angle end. By making the total lens length at the wide angle end shorter than that at the telephoto end, it is possible to sufficiently widen the angle while suppressing an increase in size of the first lens group.

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 third lens group having a positive refractive power, and a fourth lens group having a positive refractive power. When the magnification is changed 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 decreased, and the first lens group and In the zoom lens in which the third lens group moves so as to be positioned closer to the object side at the telephoto end than at the wide-angle end, and the first lens group moves along a locus convex toward the image plane side, the second lens group includes: In order from the object side, the first negative lens, the second negative lens, and the positive lens are composed of three lenses: Patent Document 1 (Japanese Patent Laid-Open No. 2010-134081), Patent Document 2 (Japanese Patent Laid-Open No. 2009). No. 0-25366), Patent Document 3 (Japanese Patent Laid-Open No. 2007-21). 537 JP), Patent Document 4 (Japanese Patent No. 3977150), there like those disclosed in Patent Document 5 (Japanese Patent No. 4387505 Patent publication) and JP 6 (2008-145501 JP).
However, in the known example of Patent Document 1, both the zoom ratio and the maximum angle of view are secured to some extent, but the minimum F number is relatively dark as F3.6, and Patent Document 2, Patent Document 4 and Patent Document 5 As for the known example, although the minimum F number is secured to some extent, the maximum angle of view is relatively narrow at about 33 degrees, and for the known example of Patent Document 3, the minimum F number, zoom ratio, and maximum angle of view are somewhat. Although it can be ensured, it is difficult to say that the radial size of the first lens group is sufficiently small in any known example.

  The present invention has been made in view of the above-described circumstances, and the invention according to claim 1 has a half angle of view at a wide angle end of about 38 degrees or more and a sufficiently wide angle of view, and is 7 times or more. An object of the present invention is to provide a small zoom lens having a zoom ratio, an F number at the wide-angle end of less than 3, a resolution corresponding to an image sensor with 10 to 15 million pixels, and a small zoom lens.

In order to achieve the above object, a zoom lens according to claim 1 is provided.
In order from the object side to the image plane side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and positive refraction And a fourth lens group having power, and when changing the magnification 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 The distance between the first lens group and the third lens group is decreased, the first lens group and the third lens group are moved closer to the object side at the telephoto end than at the wide-angle end, and the first lens group is convex toward the image plane side. In the zoom lens that moves along such a locus, the first lens group is composed of a cemented lens of a negative lens and a positive lens, and the second lens group is an image in order from the object side toward the image plane side. A biconcave first negative lens having a concave surface with a larger curvature on the surface side than the object side surface; An aperture that is composed of a second negative lens having a concave surface facing the surface side and a positive lens having a convex surface facing the object side, and is movable between the second lens group and the third lens group during zooming. An optical axis of the first lens group and the second lens group at a zoom position having a stop, wherein the distance between the optical axes of the first lens group and the second lens group at the wide-angle end is L12W, and the total length is the shortest. The distance between them is L12M, the combined focal length of the first lens group and the second lens group at the zoom position where the total length is the shortest is fFm, the focal length of the entire system at the zoom position where the total length is the shortest is fm, Conditional expressions (1) and (2) below, with the length from the first surface of the lens closest to the object side of the first lens group to the image plane as the total length
0 ≦ (L12M−L12W) / L12W <0.15 (1)
1.00 <| fFm | / fm <1.55 (2)
It is characterized by satisfying.

According to the invention of claim 1,
In order from the object side to the image plane side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and positive refraction And a fourth lens group having power, and when changing the magnification 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 The distance between the first lens group and the third lens group is decreased, the first lens group and the third lens group are moved closer to the object side at the telephoto end than at the wide-angle end, and the first lens group is convex toward the image plane side. In the zoom lens that moves along such a locus, the first lens group is composed of a cemented lens of a negative lens and a positive lens, and the second lens group is an image in order from the object side toward the image plane side. A biconcave first negative lens having a concave surface with a larger curvature on the surface side than the object side surface; An aperture that is composed of a second negative lens having a concave surface facing the surface side and a positive lens having a convex surface facing the object side, and is movable between the second lens group and the third lens group during zooming. The distance between the first lens group and the second lens group at the wide-angle end is L12W, and the length from the first surface of the lens closest to the object side of the first lens group to the image plane is provided. The distance between the optical axes of the first lens group and the second lens group at the zoom position where the total length is the shortest is L12M, and the first lens group and the first lens at the zoom position where the total length is the shortest. Assuming that the combined focal length of the two lens groups is fFm and the focal length of the entire system at the zoom position where the total length is the shortest is fm, the following conditional expressions (1) and (2):
0 ≦ (L12M−L12W) / L12W <0.15 (1)
1.00 <| fFm | / fm <1.55 (2)
By satisfying the above, the half angle of view at the wide-angle end is a sufficiently wide angle of about 38 degrees or more, but has a zoom ratio of 7 times or more and the F number at the wide-angle end is less than 3, It is possible to provide a small zoom lens having a resolving power corresponding to an image pickup element of ˜15 million pixels.

1 is a diagram illustrating a configuration of an optical system of a zoom lens according to a first embodiment of the present invention and a zoom locus associated with zooming, in which (a) is a short focal end (wide angle end, Wide), ( b) is an intermediate focal length (WM) between the short focal end (wide angle end) and the intermediate focal length, (c) is an intermediate focal length (Mean), and (d) is an intermediate focal length and a long focal end (telephoto). (E) is a cross-sectional view along the optical axis at each of the long focal ends (telephoto end, Tele). FIG. 2 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration (“lateral aberration”, hereinafter the same) at the short focal end (wide angle end) of the zoom lens according to Embodiment 1 of the present invention shown in FIG. 1. . FIG. 3 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration at the intermediate focal length of the zoom lens according to Example 1 of the present invention shown in FIG. 1. FIG. 3 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration at the long focal end (telephoto end) of the zoom lens according to Embodiment 1 of the present invention shown in FIG. 1. FIG. 6 is a diagram illustrating a configuration of an optical system of a zoom lens according to a second embodiment of the present invention and a zoom locus associated with zooming, in which (a) is a short focal end (wide angle end, Wide), ( b) is an intermediate focal length (WM) between the short focal end (wide angle end) and the intermediate focal length, (c) is an intermediate focal length (Mean), and (d) is an intermediate focal length and a long focal end (telephoto). (E) is a cross-sectional view along the optical axis at each of the long focal ends (telephoto end, Tele). FIG. 6 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma at the short focal end (wide angle end) of the zoom lens according to Embodiment 2 of the present invention shown in FIG. 5. FIG. 6 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration at the intermediate focal length of the zoom lens according to Example 2 of the present invention shown in FIG. 5. FIG. 6 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma at the long focal end (telephoto end) of the zoom lens according to Embodiment 2 of the present invention shown in FIG. 5. It is a figure which shows the zoom locus | trajectory accompanying the structure of the optical system of the zoom lens which concerns on the 3rd Embodiment of this invention, and Example 3, and zooming, (a wide-angle end, Wide), ( b) is an intermediate focal length (WM) between the short focal end (wide angle end) and the intermediate focal length, (c) is an intermediate focal length (Mean), and (d) is an intermediate focal length and a long focal end (telephoto). (E) is a cross-sectional view along the optical axis at each of the long focal ends (telephoto end, Tele). FIG. 10 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration at the short focal end (wide angle end) of the zoom lens according to Example 3 illustrated in FIG. 9; FIG. 10 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration at the intermediate focal length of the zoom lens according to Example 3 illustrated in FIG. 9. FIG. 10 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration at the long focal end (telephoto end) of the zoom lens according to Example 3 illustrated in FIG. 9; It is the perspective view seen from the to-be-photographed object side which shows typically the external appearance structure of the digital camera as an imaging device which concerns on the 4th Embodiment of this invention. It is the perspective view seen from the photographer side which shows typically the external appearance structure of the digital camera of FIG. It is a block diagram which shows typically the function structure of the digital camera of FIG. It is a schematic diagram of the imaging visual field for demonstrating the electronic correction | amendment of the distortion aberration by the image processing used by this invention.

Hereinafter, based on an embodiment of the present invention, a zoom lens, a camera, and a portable information terminal device according to the present invention will be described in detail with reference to the drawings. Before describing specific examples, first, a fundamental embodiment of the present invention will be described.
The zoom lens according to the first embodiment of the present invention includes a first lens group having a positive refractive power and a second lens group having a negative refractive power in order from the object side to the image plane side. A third lens group having a positive refractive power and a fourth lens group having a positive refractive power are arranged, and at the time of zooming from the short focal end (wide angle end) to the long focal end (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 decreased, and the first lens group and the third lens group are In the zoom lens which moves at the telephoto end so as to be positioned closer to the object side than at the wide-angle end, and moves along a locus such that the first lens group is convex toward the image plane side, further, as described below It has characteristics.
The zoom lens having four positive, negative, positive and positive lens groups as in the present invention is generally configured as a so-called variator in which the second lens group bears a main zooming action. However, in the present invention, the third lens group also shares the zooming action, reduces the burden on the second lens group, and provides the degree of freedom of aberration correction that becomes difficult with widening and high zooming. Secured. Further, at the time of zooming from the wide angle end (short focal length end) to the telephoto end (long focal length end), the light beam that passes through the first lens group at the wide angle end is largely moved to the object side. The height is reduced to suppress the enlargement of the first lens group due to the wide angle, and the distance between the first lens group and the second lens group is kept large at the telephoto end to achieve a long focal length. Yes.

During zooming from the wide-angle end to the telephoto end, the distance between the first lens group and the second lens group is increased, and the distance between the second lens group and the third lens group is decreased, so that the second lens group and the third lens group are Both magnifications (absolute values) of the lens group increase and share the zooming action.
Further, in the present invention, the first lens group is composed of a cemented lens of a negative lens and a positive lens, and the second lens group is arranged in order from the object side to the image plane side and toward the image plane side. The first negative lens having a biconcave shape with a concave surface having a curvature larger than the first surface, the second negative lens having the concave surface facing the image surface, and the positive lens having the convex surface facing the object side, An aperture stop movable at the time of zooming is provided between the second lens group and the third lens group. The distance between the optical axes of the first lens group and the second lens group at the wide-angle end is L12W. The distance between the optical axes of the first lens group and the second lens group at the zoom position where the shortest is the shortest is L12M, and the combined focal length of the first lens group and the second lens group at the zoom position where the total length is the shortest Is the shortest overall length The focal length of the entire system at over home position and fm, the first surface of the most object side lens of the first lens group, the total length of the length to the image plane, the following conditional expressions (1), (2):
0 ≦ (L12M−L12W) / L12W <0.15 (1)
1.00 <| fFm | / fm <1.55 (2)
(Corresponding to claim 1).

  By configuring the first lens group only with a cemented lens of a positive lens and a negative lens, the thickness of the first lens group is reduced, and the light ray height at the front surface of the first lens group is reduced. The effect of suppressing the increase in diameter of the first lens group can be obtained. In addition, the second lens group includes, in order from the object side, a first negative lens, a second negative lens, and a positive lens, thereby having a pair of a positive lens and a negative lens that is at least necessary for correcting chromatic aberration. However, the principal point position of the second lens group can be brought closer to the image plane side, and the effect of suppressing the total optical length especially at the telephoto end can be achieved with a small number of lenses of 3 while maintaining good aberration correction capability. can get. Further, by making the object side of the first negative lens of the second lens group a concave surface, the air space between the first lens group and the second lens group with respect to a light beam having a peripheral image height is reduced, and The effect of suppressing the light ray height of the first lens group can be obtained. By having a strong concave surface on the image side surface of the first negative lens of the second lens group and a convex surface on the object side surface of the positive lens, it is possible to obtain a favorable correction effect for spherical aberration, which tends to increase especially with a large aperture. In addition, since the concave surface is provided on the image plane side of the second negative lens, a good coma correction effect can be obtained. The following effects can be expected by satisfying conditional expressions (1) and (2) after adopting this configuration.

  Conditional expression (1) indicates that the distance between the optical axes of the first lens group and the second lens group at the wide-angle end and the optical axes of the first lens group and the second lens group at the zoom position where the total length is shortest. The ratio of the distance between the two lenses represents the appropriate range of the optical axis distance from the second lens group when the first lens group is moving in the image plane direction. Conditional expression (2) represents the ratio of the focal length of the entire system to the combined focal length of the system closer to the object side than the aperture stop at the zoom position where the total length is the shortest. It defines the appropriate range of the combined focal length of the system on the object side with respect to the aperture stop. Satisfying the conditional expression (1) and the conditional expression (2) is effective in suppressing the size of the first lens group in the radial direction particularly in a relatively wide field angle. When the upper limit of conditional expression (1) is exceeded, the first lens group and the second lens group are too far apart, and the height of the light beam passing through the first lens group at the zoom position where the total length is shortest becomes high. There is a possibility that the diameter of the first lens group is increased. If the lower limit of conditional expression (1) is not reached, the height of the light beam passing through the first lens group at the wide-angle end becomes high, and the first lens group may become large in diameter. If the upper limit of conditional expression (2) is exceeded, the refractive power of the system closer to the object side than the aperture stop becomes too weak, which is disadvantageous for high zooming, and the entire optical system may increase in the entire length direction.

If the lower limit value of conditional expression (2) is not reached, the height of the light beam that passes through the first lens group is particularly high, and the diameter of the first lens group may increase.
More preferably, the following conditional expressions (1) ′ and (2) ′ are satisfied.
0 ≦ (L12M−L12W) / L12W <0.125 (1) ′
1.1 <| fFm | / fm <1.4 (2) ′
For higher performance, the distance between the optical axes from the first surface of the lens closest to the object side to the aperture stop at the zoom position where the overall length is the shortest is LFm, and the overall length is the shortest. Conditional expression (3) below, where the combined focal length of the first lens group and the second lens group at the zoom position is fFm:
0.9 <LFm / | fFm | <1.65 (3)
Is preferably satisfied (corresponding to claim 2).

Conditional expression (3) represents the ratio of the distance from the head of the first lens group to the aperture stop with respect to the combined focal length of the system closer to the object side than the aperture stop at the zoom position where the total length is the shortest. An appropriate range of the position of the aperture stop with respect to the refractive power of the system closer to the object side than the stop is defined. Satisfying conditional expression (3) optimizes the position of the aperture stop, and is particularly effective in suppressing the size of the first lens group in the radial direction. If the upper limit value of conditional expression (3) is exceeded, the height of the light beam passing through the group on the object side from the aperture stop becomes high, and in particular, the diameter of the first lens group may increase. If the lower limit value of conditional expression (3) is not reached, there is a risk that the lower ray of the peripheral light beam will be cut too much and the peripheral light amount ratio will be significantly reduced.
More preferably, the following conditional expression (3) ′ should be satisfied.
1.0 <LFm / | fFm | <1.55 (3) ′
For higher performance, it is desirable that the second negative lens of the second lens group has at least one aspheric surface (corresponding to claim 3).
In this zoom lens type, among the second lens group serving as the main zooming group, the diameter is relatively small, and the width of the light beam passing through the wide-angle end and the telephoto end changes to some extent. By providing at least one aspherical surface in the second negative lens with a small overlapping width of high luminous flux, it is possible to maintain good correction of astigmatism and distortion that tend to increase with widening of the angle. Miniaturization can be promoted. Since it has a smaller diameter than the first negative lens in the second lens group, it is relatively easy to ensure aspheric accuracy, and there is an effect of suppressing image performance deterioration due to a shape error.

In order to achieve higher performance, from the viewpoint of correcting aberrations, the focal length of the second lens group is f2, and the focal length of the third lens group is f3. It is desirable to satisfy 4) (corresponding to claim 4).
0.50 <| f2 | / f3 <1.00 (4)
Conditional expression (4) represents the refractive power of the second lens group, which is the main zooming group in this zoom type, and the main image forming group, and the third lens group that also plays the role of the zooming group in an auxiliary manner. When the ratio falls below the lower limit of the conditional expression (4), the refractive power of the second lens group becomes too strong, and when the upper limit of the conditional expression (4) is exceeded, the third lens The refractive power of the group becomes too strong, and in any case, the aberration fluctuation during zooming tends to increase.
More preferably, the following conditional expression should be satisfied.
0.60 <| f2 | / f3 <0.90 (4) ′
For higher performance, the imaging magnification of the second lens group at the telephoto end is set to β2t, the imaging magnification of the second lens group at the wide-angle end is set to β2w, and the connection of the third lens group at the telephoto end is set. It is desirable that the image magnification is β3t, the image formation magnification of the third lens group at the wide angle end is β3w, and the following conditional expression (5) is satisfied (corresponding to claim 5).

0.5 <(β2t / β2w) / (β3t / β3w) <1.5 (5)
Conditional expression (5) is a conditional expression for appropriately setting the sharing of the zooming action of the second lens group having the zooming function and the third lens group. If the lower limit of conditional expression (5) is not reached, if the zooming action of the third lens group becomes too large, the third lens group may be enlarged or the number of components may be increased to compensate for the required aberration correction capability. Therefore, there is a risk of hindering the downsizing of the optical system.
Further, there is a risk that performance deterioration due to relative decentration with the second lens group increases. If the upper limit of conditional expression (5) is exceeded and the zooming action of the third lens group becomes too small, the zooming action of the second lens group becomes too large and the second lens group becomes large. In other words, it may be necessary to increase the number of components, which may hinder downsizing of the optical system.
More preferably, the following conditional expression should be satisfied.

0.7 <(β2t / β2w) / (β3t / β3w) <1.2 (5) ′
Further, in relation to the amount of movement of the first lens group, which is important for widening and increasing the focal length, the total amount of movement of the first lens group during zooming from the wide-angle end to the telephoto end is X1. When the focal length of the entire system at the telephoto end is ft and the following conditional expression (6) is satisfied, sufficient aberration correction can be performed (corresponding to claim 6).
0.15 <X1 / ft <0.45 (6)
If the lower limit of conditional expression (6) is not reached, the contribution of the second lens group to zooming will be reduced, increasing the burden on the third lens group, or the first lens group / second lens group. In any case, it causes deterioration of various aberrations. In addition, the total lens length at the wide-angle end is increased, and the height of light passing through the first lens group is increased, leading to an increase in size of the first lens group.
On the other hand, if the upper limit value of conditional expression (6) is exceeded, the total length at the wide-angle end becomes too short, or the total length at the telephoto end becomes too long. If the total length at the wide-angle end is too short, the moving space of the third lens group is limited, and the contribution to zooming of the third lens group is reduced, making it difficult to correct the entire aberration. If the total length at the telephoto end becomes too long, it will not only hinder downsizing in the full-length direction, but the radial direction will be enlarged to secure the amount of peripheral light at the telephoto end, and the lens barrel will be tilted. Degradation of image performance due to errors is also likely to occur.

More preferably, the following conditional expression should be satisfied.
0.20 <X1 / fT <0.40 (6) ′
Regarding the movement amount of the third lens group that shares the zooming action with the second lens group, the total movement amount of the third lens group during zooming from the wide-angle end to the telephoto end is X3, and the telephoto end It is desirable to satisfy the following conditional expression (7), where ft is the focal length of the entire system at (corresponding to claim 7).
0.10 <X3 / ft <0.50 (7)
If the lower limit of conditional expression (7) is not reached, the contribution of the third lens group to zooming will be reduced, increasing the burden on the second lens group, or increasing the refractive power of the third lens group itself. In any case, it causes deterioration of various aberrations. On the other hand, if the upper limit value of conditional expression (7) is exceeded, the total lens length at the wide-angle end becomes long, the height of light passing through the first lens group increases, and the size of the first lens group may increase. There is.
It is more desirable to satisfy the following conditional expression (7) ′.
0.20 <X3 / ft <0.40 (7) ′

In addition, regarding the amount of movement of the third lens group that shares the zooming action with the second lens group, the total amount of movement of the second lens group during zooming from the wide-angle end to the telephoto end is X2. The total movement amount of the third lens group during zooming from the wide-angle end to the telephoto end is X3, and the following conditional expression (8) is satisfied as a ratio to the movement amount of the second lens group. Is desirable (corresponding to claim 8).
0.05 <| X2 | / X3 <0.50 (8)
If the lower limit of conditional expression (8) is not reached, the contribution of the second lens group to zooming will be reduced, increasing the burden on the third lens group, or the refractive power of the second lens group itself. In any case, there is a risk of deteriorating various aberrations and decentration sensitivity. On the other hand, when the upper limit value of the expression (8) is exceeded, the contribution of the third lens group to the zooming is reduced, and the burden on the second lens group is increased, or the refractive power of the third lens group itself is increased. In any case, there is a risk of deteriorating various aberrations and decentration sensitivity. Alternatively, the amount of movement of the second lens group becomes large and the optical total length at the wide-angle end increases, which may hinder downsizing the entire camera and shortening the start-up time of the camera.

The first lens group may be composed of, in order from the object side, a negative meniscus lens having a convex surface facing the object side, and a positive lens having a convex surface having a larger curvature than the image side surface on the object side. desirable.
In order to increase the zoom ratio, in particular, to increase the focal length at the telephoto end, it is necessary to increase the combined magnification of the second lens group, the third lens group, and the fourth lens group at the telephoto end. The aberration generated in the first lens group is magnified on the image plane. For this reason, in order to advance the zooming ratio, it is necessary to sufficiently reduce the amount of aberration generated in the first lens group. For this purpose, the first lens group is preferably configured as described above.
The third lens group includes, in order from the object side to the image surface side, a biconvex positive lens, a positive lens having a convex surface on the object side, and a negative lens having a concave surface on the image side. It is desirable. By arranging the positive lens, the positive lens, and the negative lens in order from the object side, the principal point of the third lens group can be raised to the object side, which can contribute to shortening the total length of the optical system at the telephoto end. . Further, by making the final surface of the third lens group a concave surface on the image side, it is effective for good correction of coma and sagittal field curvature.

In the zoom lens according to the embodiment of the present invention, the fourth lens group is provided mainly for securing an exit pupil distance (telecentricity) and focusing by movement thereof. In order to reduce the size of the lens system, the fourth lens group needs to be as simple as possible, and is preferably composed of one positive lens. In addition, the use of a relatively lightweight resin material is effective in speeding up the focusing operation and suppressing the operating volume.
The zoom lens according to the present invention is not limited to the four-group configuration. Since it is necessary to increase the degree of freedom in order to ensure performance, such as suppressing fluctuations in aberrations during zooming, the fifth lens group may be configured on the image plane side of the fourth lens group.
An aspheric surface is indispensable for further miniaturization while maintaining good aberration correction, and it is desirable that at least the second lens group and the third lens group each have one or more aspheric surfaces.
In addition, as an aspherical lens, optical glass or optical plastic molded (glass molded aspherical surface, plastic molded aspherical surface), or a thin resin layer is molded on the surface of the glass lens, and the surface is aspherical. A thing (it is called a hybrid aspherical surface, a replica aspherical surface, etc.) etc. can be used.

It may be simplified in terms of mechanism that the aperture diameter of the aperture stop is constant regardless of zooming. However, by changing the aperture diameter of the aperture stop from the vicinity of the telephoto end as compared with the wide-angle end, it is possible to reduce the change in the F number accompanying zooming. In addition, it is possible to obtain better optical performance by preparing a plurality of types of open apertures according to the focal length range. When it is necessary to reduce the amount of light reaching the image plane, the aperture stop diameter may be reduced. However, if the amount of light is reduced by inserting an ND filter or the like without greatly changing the stop diameter, it is caused by the diffraction phenomenon. It is preferable because a decrease in resolution can be prevented.
Specific numerical examples of the zoom lens of the present invention are shown below. In all the examples, the maximum image height is 4.78 mm. However, at the wide-angle end, in order to apply distortion-corrected image processing for enlarging and generating an image corresponding to the generated negative distortion, the maximum image height is set to a small 4.14 in consideration of the amount of distortion. It is.
Examples 1 to 3 according to the first to third embodiments have a four-group configuration of positive, negative, positive, and positive.

In each embodiment, the parallel plate FG disposed on the image plane side of the fourth lens group is a cover glass (seal) of various filters such as an optical low-pass filter and an infrared cut filter, and a light receiving element such as a CMOS or CCD sensor. Glass).
The lens material is optical glass except for the case where the positive lens of the fourth lens group is optical plastic in all the embodiments.
Embodiments and specific numerical examples of the zoom lens according to the present invention will be described below. In all the examples, the maximum image height is 4.78 mm. However, at the wide-angle end, the maximum image height is set to a small 4.14 in consideration of the distortion aberration amount in order to apply distortion correction image processing for generating an image by magnifying the generated negative distortion aberration. It is.
In the zoom lenses of Examples 1 to 3, aberration correction is performed by image processing for distortion as described above. That is, in the zoom lenses of Examples 1 to 3, FIG. 16 shows that the imaging range (imaging range at the intermediate focal length and the long focal end (telephoto end)) of the light receiving element is TF, and the short focal end (wide angle end). ), The barrel-shaped distortion like the imaging range WF is generated at the short focal point on the light receiving surface TF of the rectangular light receiving element.

16 represents an image circle that covers the imaging range at the intermediate focal length and the long focal end (telephoto end), and WFC represents an image circle that covers the imaging range near the short focal end (wide angle end). Represent.
On the other hand, the occurrence of distortion is suppressed in the intermediate focal length, the vicinity thereof, and the long focal end. In order to electrically correct distortion, the effective imaging range is a barrel shape (WF) at the short focal end and a rectangular shape (TF) at the intermediate focal length or the long focal end. Then, the effective imaging range (WF) at the short focal end is image-converted by image processing and converted into rectangular image information with reduced distortion. Therefore, in Embodiments 1 to 3, the image height at the short focal end is made smaller than the image height at the intermediate focal length and the image height at the long focal end. As a result, the aberrations of the respective examples are sufficiently corrected, and it is possible to deal with light receiving elements with 10 to 15 million pixels. It is clear from Examples 1 to 3 that by configuring the zoom lens as in the present invention, it is possible to ensure very good image performance while achieving sufficient size reduction.

In addition, the meaning of the symbol in Example 1- Example 3 is as follows.
f: Focal length of the entire system F: F value (F number)
omega: half field angle R: curvature radius D: surface interval Nd: refractive index at d-line [nu] d: Abbe number K: aspherical conic constant A _4: 4-order aspherical coefficients A _6: 6-order aspheric coefficients A ₈ : 8th-order aspheric coefficient A ₁₀ : 10th-order aspheric coefficient However, for the aspheric surface used here, the reciprocal of the paraxial radius of curvature (paraxial curvature) is C, and the height from the optical axis is H In this case, the amount of displacement in the optical axis direction from the surface vertex is A _2i , and the aspherical surface is defined by the following equation.

FIG. 1 shows the configuration of the optical system of the zoom lens according to the first embodiment of the present invention and the long focal end (telephoto end) through a predetermined intermediate focal length from the short focal end (wide angle end). FIG. 5A shows a stage of movement of the optical system during zooming, wherein (a) is a sectional view along the optical axis at the wide angle end (Wide), and (b) is an intermediate focal length between the wide angle end and the intermediate focal length ( (C) is a cross-sectional view along the optical axis at the intermediate focal length (Mean), and (d) is an intermediate focal length between the intermediate focal length and the telephoto end (M). (T) is a cross-sectional view along the optical axis and (e) is a cross-sectional view along the optical axis at the telephoto end (Tele). In FIG. 1 showing the lens group arrangement of Example 1, the left side in the figure is the object (subject) side.
The zoom lens shown in FIG. 1 includes a first lens group G1 having a positive refractive power and a second lens group G2 having a negative refractive power in order from the object side to the image plane side along the optical axis. A third lens group G3 having a positive refractive power and a fourth lens group G4 having a positive refractive power, and an aperture stop AD between the second lens group G2 and the third lens group G3. Is arranged. The first lens group G1 includes a first lens L1 and a second lens L2, and the second lens group G2 includes a third lens L3, a fourth lens L4, and a fifth lens L5. The third lens group G3 includes a sixth lens L6, a seventh lens L7, and an eighth lens L8, and the fourth lens group G4 includes a single ninth lens L9.

The first lens group G1 to the fourth lens group G4 are supported by a common support frame or the like that is appropriate for each group, and operate integrally for each group during zooming or the like. Works independently. FIG. 1 also shows the surface numbers of the optical surfaces. Note that each reference symbol in FIG. 1 is used independently for each embodiment in order to avoid complication of explanation due to an increase in the number of digits of the reference symbol. Therefore, a reference symbol common to the drawings according to the other embodiments. Even if attached, they are not necessarily a common configuration with other embodiments.
When zooming from the short focal end (wide angle end) to the long focal end (telephoto end), the first lens group G1 to the fourth lens group G4 are moved, and the first lens group G1 and the second lens group are moved. The distance between the group G2 increases, the distance between the second lens group G2 and the third lens group G3 decreases, and the first lens group G1 and the third lens group G3 have their long focal ends (telephoto ends). Is moved so that the position at is closer to the object side than the position at the short focal end (wide angle end).
The first lens group G1 includes, in order from the object side to the image surface side, a first lens (negative lens) L1 including a negative meniscus lens having a convex surface directed toward the object side, and a positive meniscus having a convex surface directed toward the object side. A second lens (positive lens) L2 made of a lens is disposed. The two lenses of the first lens L1 and the second lens L2 are closely bonded to each other and bonded together to form a cemented lens composed of two lenses.

The second lens group G2 includes, from the object side to the image side, a third lens L3 composed of a biconcave lens with a concave surface having a larger curvature than the object side surface toward the image surface side, and an object side surface on the image surface side. A biconcave lens having a concave surface having a larger curvature than the surface, and comprising a fourth lens L4 made of an aspherical lens forming an aspheric surface on both sides thereof, and a positive meniscus lens having a convex surface facing the object side A fifth lens L5 is arranged.
The aperture stop AD is interposed between the second lens group G2 and the third lens group G3.
The third lens group G3 is a biconvex lens in which a convex surface having a larger curvature than the image side surface is directed to the object side sequentially from the object side, and a sixth lens L6 composed of an aspheric lens having both surfaces formed with aspheric surfaces. A seventh lens L7 made of a biconvex lens having a convex surface having a larger curvature than the image side surface on the object side, and an eighth lens L8 made of a biconcave lens having a concave surface having a larger curvature than the object side surface on the image side The two lenses of the seventh lens L7 and the eighth lens L8 on the object side are closely bonded to each other and integrally joined to form a cemented lens composed of two lenses.
The fourth lens group G4 is a positive meniscus lens having a convex surface with a larger curvature on the object side than the image-side surface, and is composed of a single positive lens including an aspheric lens having an aspheric surface on the object side. Nine lenses L9 are arranged.
The optical characteristics of each optical element in Example 1 are as shown in Table 1 below.

In Table 1, the lens surface with the surface number indicated by “* (asterisk)” attached to the surface number is an aspheric surface, and after the glass name, the manufacturer name of the glass material is HOYA (HOYA Corporation). ) And OHARA (Ohara Inc.).
That is, in Table 1, the optical surfaces of the sixth surface, the seventh surface, the eleventh surface, the twelfth surface, and the sixteenth surface marked with “*” are aspheric surfaces, and The spherical parameters are as follows.
6th page
K = 0.0, A4 = 1.73151E-04, A6 = 1.50341E-05, A8 = -6.43287E-07, A10 = 5.37742E-09

7th page
K = 0.0, A6 = 1.24471E-05, A8 = -6.56585E-07
11th page
K = -3.96583, A4 = 8.13536E-04, A6 = -1.39829E-05, A8 = -1.68224E-08, A10 = 1.37134E-08
12th page
K = -5.01861, A4 = -2.08540E-04, A6 = 1.71516E-05, A8 = -9.14917E-07, A10 = 2.89450E-08
16th page
K = 0.0, A4 = -2.17184E-05, A6 = 1.96470E-07, A8 = 4.52101E-08, A10 = -8.69735E-10
In Example 1, the focal length f of the entire optical system, the variable distance DA between the first lens group G1 and the second lens group G2, and the variable distance DB between the second lens group G2 and the aperture stop AD. , The variable distance DC between the aperture stop AD and the third lens group G3, the variable distance DD between the third lens group G3 and the fourth lens group G4, and the fourth lens group G4 and the parallel plate FG, etc. The variable interval DE is changed as shown in Table 2 along with zooming.

The image height Y ′ at the wide angle end (Tele) is as described above. Referring to FIG. 16, as described above, in order to perform aberration correction by image processing of distortion aberration, the imaging range at the telephoto end (and the intermediate focal length) is substantially matched with the imaging range of the light receiving element, so that the rectangular shape is obtained. At the wide-angle (Wide) end, Y ′ generates a distortion aberration such that the image-capturing range at the wide-angle end has a barrel shape. Then, the barrel-shaped effective imaging range at the wide-angle end is image-converted by image processing and converted into rectangular image information with reduced distortion.
The values corresponding to the conditional expressions (1) to (8) in Example 1 described above are as shown in Table 3 below, and satisfy the conditional expressions (1) to (8), respectively.

  2, FIG. 3 and FIG. 4 show respective aberration diagrams of spherical aberration, astigmatism, distortion aberration and coma aberration (lateral aberration) at the wide-angle end, intermediate focal length and telephoto end of Example 1. ing. In these drawings, a broken line in spherical aberration represents a sine condition, a solid line in astigmatism represents sagittal, and a broken line represents meridional. Further, g and d in the respective aberration diagrams of spherical aberration, astigmatism, and coma aberration (lateral aberration) represent g-line and d-line, respectively. The same applies to the aberration diagrams of the other examples.

FIG. 5 shows the configuration of the optical system of the zoom lens according to the second embodiment of the present invention and Example 2, and the long focal end (telephoto end) through a predetermined intermediate focal length from the short focal end (wide angle end). FIG. 5A shows a stage of movement of the optical system during zooming, wherein (a) is a sectional view along the optical axis at the wide angle end (Wide), and (b) is an intermediate focal length between the wide angle end and the intermediate focal length ( (C) is a cross-sectional view along the optical axis at the intermediate focal length (Mean), and (d) is an intermediate focal length between the intermediate focal length and the telephoto end (M). (T) is a cross-sectional view along the optical axis and (e) is a cross-sectional view along the optical axis at the telephoto end (Tele). In FIG. 5 showing the lens group arrangement of Example 2, the left side in the figure is the object (subject) side.
The zoom lens shown in FIG. 5 has a first lens group G1 having a positive refractive power and a second lens group G2 having a negative refractive power sequentially from the object side to the image plane side along the optical axis. A third lens group G3 having a positive refractive power and a fourth lens group G4 having a positive refractive power, and an aperture stop AD between the second lens group G2 and the third lens group G3. Is arranged. The first lens group G1 includes a first lens L1 and a second lens L2, and the second lens group G2 includes a third lens L3, a fourth lens L4, and a fifth lens L5. The third lens group G3 includes a sixth lens L6, a seventh lens L7, and an eighth lens L8, and the fourth lens group G4 includes a single ninth lens L9.

The first lens group G1 to the fourth lens group G4 are supported by a common support frame or the like that is appropriate for each group, and operate integrally for each group during zooming or the like. Works independently. FIG. 5 also shows the surface numbers of the optical surfaces. In addition, in order to avoid complication of explanation due to an increase in the number of digits of the reference code, each reference code in FIG. 5 is used independently for each embodiment. Therefore, the same reference numerals as those in the drawings according to the other embodiments are used. Even if attached, they are not necessarily a common configuration with other embodiments.
When zooming from the short focal end (wide angle end) to the long focal end (telephoto end), the first lens group G1 to the fourth lens group G4 are moved, and the first lens group G1 and the second lens group are moved. The distance between the group G2 increases, the distance between the second lens group G2 and the third lens group G3 decreases, and the first lens group G1 and the third lens group G3 have their long focal ends (telephoto ends). Is moved so that the position at is closer to the object side than the position at the short focal end (wide angle end).
The first lens group G1 includes, in order from the object side to the image surface side, a first lens (negative lens) L1 including a negative meniscus lens having a convex surface directed toward the object side, and a positive meniscus having a convex surface directed toward the object side. A second lens (positive lens) L2 made of a lens is disposed. The two lenses of the first lens L1 and the second lens L2 are closely bonded to each other and bonded together to form a cemented lens composed of two lenses.

The second lens group G2 includes, in order from the object side to the image side, a third lens L3 composed of a biconcave lens having a concave surface having a larger curvature than the object side surface on the image surface side, and the object side on the image surface side. A biconcave lens having a concave surface with a larger curvature than that of the first lens L4, a fourth lens L4 made of an aspheric lens having an aspheric surface on both sides thereof, and a positive meniscus lens having a convex surface facing the object side The fifth lens L5 is arranged.
The aperture stop AD is interposed between the second lens group G2 and the third lens group G3.
The third lens group G3 is a biconvex lens in which a convex surface having a larger curvature than the image side surface is directed to the object side from the object side to the image surface side, and an aspheric lens having aspheric surfaces on both surfaces. A sixth lens L6, a seventh lens L7 composed of a biconvex lens having a convex surface having a larger curvature than the image side surface on the object side, and a biconcave lens having a concave surface having a curvature larger than the object side surface on the image side An eighth lens L8 made of The two lenses of the seventh lens L7 and the eighth lens L8 are closely bonded to each other and bonded together to form a cemented lens composed of two lenses.
The fourth lens group G4 is a positive meniscus lens having a convex surface with a larger curvature on the object side than the image-side surface, and is composed of a single positive lens including an aspheric lens having an aspheric surface on the object side. Nine lenses L9 are arranged.
The optical characteristics of the optical elements in Example 2 are as shown in Table 4 below.

In Table 4, the lens surface with the surface number indicated by adding “* (asterisk)” to the surface number is an aspheric surface, and after the glass name, the manufacturer name of the glass material is HOYA (HOYA Corporation). ) And OHARA (Ohara Inc.).
That is, in Table 4, the optical surfaces of the sixth surface, the seventh surface, the eleventh surface, the twelfth surface, and the sixteenth surface marked with “*” are aspheric surfaces, and The spherical parameters are as follows.
6th page
K = 0.0, A4 = 1.93747E-04, A6 = 1.10916E-05, A8 = -4.22903E-07, A10 = 3.51388E-09
7th page
K = 0.0, A6 = 9.64823E-06, A8 = -4.62147E-07
11th page
K = -3.93078, A4 = 8.38196E-04, A6 = -1.43109E-05, A8 = -1.02115E-08, A10 = 1.60177E-08

12th page
K = -5.32878, A4 = -1.91560E-04, A6 = 1.82242E-05, A8 = -9.73696E-07, A10 = 3.29795E-08
16th page
K = 0.0, A4 = -2.73951E-05, A6 = 1.36005E-06, A8 = 2.69391E-08, A10 = -6.00656E-10
In the second embodiment, the focal length f of the entire optical system, the variable distance DA between the first lens group G1 and the second lens group G2, and the variable distance DB between the second lens group G2 and the aperture stop AD. , The variable distance DC between the aperture stop AD and the third lens group G3, the variable distance DD between the third lens group G3 and the fourth lens group G4, and the fourth lens group G4 and the parallel plate FG, etc. The variable interval DE is changed as shown in Table 5 along with zooming.

The image height Y ′ at the wide angle end (Tele) is as described above. Referring to FIG. 16, as described above, in order to perform aberration correction by image processing of distortion aberration, the imaging range at the telephoto end (and the intermediate focal length) is substantially matched with the imaging range of the light receiving element, so that the rectangular shape is obtained. At the wide-angle (Wide) end, Y ′ generates a distortion aberration such that the image-capturing range at the wide-angle end has a barrel shape. Then, the barrel-shaped effective imaging range at the wide-angle end is image-converted by image processing and converted into rectangular image information with reduced distortion.
The values corresponding to the conditional expressions (1) to (8) in Example 2 described above are as shown in Table 6 below, and satisfy the conditional expressions (1) to (8), respectively.

  FIGS. 6, 7, and 8 show aberration diagrams of spherical aberration, astigmatism, distortion, and coma aberration (lateral aberration) at the wide-angle end, intermediate focal length, and telephoto end, respectively, in Example 2. ing. In these drawings, a broken line in spherical aberration represents a sine condition, a solid line in astigmatism represents sagittal, and a broken line represents meridional. Further, g and d in the respective aberration diagrams of spherical aberration, astigmatism, and coma aberration (lateral aberration) represent g-line and d-line, respectively. The same applies to the aberration diagrams of the other examples.

FIG. 9 shows the configuration of the optical system of the zoom lens according to the third embodiment of the present invention and Example 3, and the long focal point (telephoto end) through a predetermined intermediate focal length from the short focal point (wide angle end). FIG. 5A shows a stage of movement of the optical system during zooming, wherein (a) is a sectional view along the optical axis at the wide angle end (Wide), and (b) is an intermediate focal length between the wide angle end and the intermediate focal length ( (C) is a cross-sectional view along the optical axis at the intermediate focal length (Mean), and (d) is an intermediate focal length between the intermediate focal length and the telephoto end (M). (T) is a cross-sectional view along the optical axis and (e) is a cross-sectional view along the optical axis at the telephoto end (Tele). In FIG. 9 showing the lens group arrangement of the third embodiment, the left side in the figure is the object (subject) side.
The zoom lens shown in FIG. 9 includes a first lens group G1 having a positive refractive power and a second lens group G2 having a negative refractive power sequentially from the object side to the image plane side along the optical axis. A third lens group G3 having a positive refractive power and a fourth lens group G4 having a positive refractive power, and an aperture stop AD between the second lens group G2 and the third lens group G3. Is arranged. The first lens group G1 includes a first lens L1 and a second lens L2, and the second lens group G2 includes a third lens L3, a fourth lens L4, and a fifth lens L5. The third lens group G3 includes a sixth lens L6, a seventh lens L7, and an eighth lens L8, and the fourth lens group G4 includes a single ninth lens L9.

The first lens group G1 to the fourth lens group G4 are supported by a common support frame or the like that is appropriate for each group, and operate integrally for each group during zooming or the like. Works independently. FIG. 9 also shows the surface numbers of the optical surfaces. In addition, in order to avoid complication of explanation due to an increase in the number of digits of the reference code, each reference code in FIG. 9 is used independently for each embodiment. Therefore, the same reference numerals as those in the drawings according to other embodiments. Even if attached, they are not necessarily a common configuration with other embodiments.
When zooming from the short focal end (wide angle end) to the long focal end (telephoto end), the first lens group G1 to the fourth lens group G4 are moved, and the first lens group G1 and the second lens group are moved. The distance between the group G2 increases, the distance between the second lens group G2 and the third lens group G3 decreases, and the first lens group G1 and the third lens group G3 have their long focal ends (telephoto ends). Is moved so that the position at is closer to the object side than the position at the short focal end (wide angle end).
The first lens group G1 includes, in order from the object side to the image surface side, a first lens (negative lens) L1 including a negative meniscus lens having a convex surface directed toward the object side, and a positive meniscus having a convex surface directed toward the object side. A second lens (positive lens) L2 made of a lens is disposed. The two lenses of the first lens L1 and the second lens L2 are closely bonded to each other and bonded together to form a cemented lens composed of two lenses.

The second lens group G2 includes, in order from the object side to the image surface side, a third lens L3 composed of a biconcave lens having a concave surface having a larger curvature than the object side surface on the image surface side, and an object on the image surface side. A biconcave lens having a concave surface with a larger curvature than the side surface, a fourth lens L4 made of an aspherical lens forming an aspheric surface on both sides thereof, and a positive meniscus lens having a convex surface facing the object side And a fifth lens L5.
The aperture stop AD is interposed between the second lens group G2 and the third lens group G3.
The third lens group G3 is a biconvex lens in which a convex surface having a larger curvature than the image side surface is directed to the object side sequentially from the object side, and a sixth lens L6 composed of an aspheric lens having both surfaces formed with aspheric surfaces. A seventh lens L7 made of a biconvex lens having a convex surface with a larger curvature than the image side surface on the object side, and an eighth lens L8 made of a biconcave lens with a concave surface having a larger curvature than the object side surface on the image side. It is arranged. The two lenses of the seventh lens L7 and the eighth lens L8 are closely bonded to each other and bonded together to form a cemented lens composed of two lenses.
The fourth lens group G4 is a positive meniscus lens having a convex surface with a larger curvature on the object side than the image-side surface, and is composed of a single positive lens including an aspheric lens having an aspheric surface on the object side. Nine lenses L9 are arranged.
The optical characteristics of the optical elements in Example 3 are as shown in Table 7 below.

In Table 7, the surface number indicated by adding “* (asterisk)” to the surface number is an aspherical surface. The glass name is followed by the name of the glass manufacturer, HOYA (HOYA Corporation). ) And OHARA (Ohara Inc.).
That is, in Table 7, the optical surfaces of the sixth surface, the seventh surface, the eleventh surface, the twelfth surface, and the sixteenth surface marked with “*” are aspheric surfaces, and The spherical parameters are as follows.
6th page
K = 0.0, A4 = 8.03455E-05, A6 = 1.26234E-05, A8 = -4.98977E-07, A10 = 3.22726E-09
7th page
K = 0.0, A6 = 1.26328E-05, A8 = -5.55414E-07
11th page
K = -3.92324, A4 = 8.19635E-04, A6 = -1.29178E-05, A8 = -2.11428E-07, A10 = 1.76794E-08

12th page
K = -4.28532, A4 = -1.99201E-04, A6 = 2.04979E-05, A8 = -1.22552E-06, A10 = 3.47302E-08
16th page
K = 0.0, A4 = -3.16993E-05, A6 = 8.67083E-07, A8 = 1.32703E-08, A10 = -4.25625E-10
In Example 3, the focal length f of the entire optical system, the variable distance DA between the first lens group G1 and the second lens group G2, and the variable distance DB between the second lens group G2 and the aperture stop AD. , The variable distance DC between the aperture stop AD and the third lens group G3, the variable distance DD between the third lens group G3 and the fourth lens group G4, and the fourth lens group G4 and the parallel plate FG, etc. The variable interval DE is changed as shown in Table 8 along with zooming.

The image height Y ′ at the wide angle end (Tele) is as described above. Referring to FIG. 16, as described above, in order to perform aberration correction by image processing of distortion aberration, the imaging range at the telephoto end (and the intermediate focal length) is substantially matched with the imaging range of the light receiving element, so that the rectangular shape is obtained. At the wide-angle (Wide) end, Y ′ generates a distortion aberration such that the image-capturing range at the wide-angle end has a barrel shape. Then, the barrel-shaped effective imaging range at the wide-angle end is image-converted by image processing and converted into rectangular image information with reduced distortion.
Values corresponding to the conditional expressions (1) to (8) in Example 3 described above are as shown in Table 9 below, and satisfy the conditional expressions (1) to (8), respectively.

10, FIG. 11, and FIG. 12 show aberration diagrams of spherical aberration, astigmatism, distortion aberration, and coma aberration (lateral aberration) at the wide-angle end, intermediate focal length, and telephoto end, respectively, in Example 3. ing. In these drawings, a broken line in spherical aberration represents a sine condition, a solid line in astigmatism represents sagittal, and a broken line represents meridional. Further, g and d in the respective aberration diagrams of spherical aberration, astigmatism, and coma aberration (lateral aberration) represent g-line and d-line, respectively. The same applies to the aberration diagrams of the other examples.
Next, as an imaging apparatus according to the fourth embodiment of the present invention, which is configured by adopting the zoom lens according to the first to third embodiments of the present invention described above as an imaging optical system. The digital camera will be described with reference to FIGS. FIG. 13 is a perspective view schematically showing the external appearance of the digital camera viewed from the front side that is the object side, that is, the subject side, and FIG. 14 is a schematic external view of the digital camera viewed from the back side that is the photographer side. FIG. 15 is a schematic block diagram showing a functional configuration of a digital camera. Here, the image pickup apparatus is described taking a digital camera as an example, but the zoom lens according to the present invention may be employed in a silver salt film camera using a silver salt film as a conventional image recording medium.

In addition, an information device such as a so-called PDA (personal data assistant) or a portable information terminal device such as a cellular phone in which a camera function is incorporated is widely used. Although such an information device also has a slightly different appearance, it includes substantially the same functions and configuration as a digital camera, and the zoom lens according to the present invention is adopted as an imaging optical system in such an information device. May be.
As shown in FIGS. 13 and 14, the digital camera includes a photographing lens 101, an optical viewfinder 102, a strobe (flash light) 103, a shutter button 104, a camera body 105, a power switch 106, a liquid crystal monitor 107, an operation button 108, and a memory. A card slot 109 and a zoom switch 110 are provided. Further, as shown in FIG. 15, the digital camera includes a central processing unit (CPU) 111, an image processing device 112, a light receiving element 113, a signal processing device 114, a semiconductor memory 115, a communication card 116 and the like.
The digital camera includes a photographing lens 101 as an imaging optical system and a light receiving element 113 configured as an image sensor using a CMOS (complementary metal oxide semiconductor) imaging element or a CCD (charge coupled device) imaging element. The light receiving element 113 reads an optical image of a subject (object) formed by the photographing lens 101.

As the photographing lens 101, the zoom lens according to the present invention as described in the first to third embodiments is used (corresponding to claim 9 or claim 10).
The output of the light receiving element 113 is processed by a signal processing device 114 controlled by the central processing unit 111 and converted into digital image information. That is, such a digital camera includes means for converting a captured image (subject image) into digital image information. This means substantially controls the light receiving element 113, the signal processing device 114, and these. Central processing unit (CPU) 111 and the like.
The image information digitized by the signal processing device 114 is recorded in a semiconductor memory 115 such as a nonvolatile memory after being subjected to predetermined image processing in the image processing device 112 which is also controlled by the central processing unit 111. In this case, the semiconductor memory 115 may be a memory card loaded in the memory card slot 109 or a semiconductor memory built in the camera body (on-board). The liquid crystal monitor 107 can display an image being photographed, or can display an image recorded in the semiconductor memory 115. The image recorded in the semiconductor memory 115 can also be transmitted to the outside via a communication card 116 or the like loaded in a communication card slot (not shown).

When the camera is carried, the objective surface of the photographic lens 101 is covered with a lens barrier (not shown). When the user operates the power switch 106 to turn on the power, the lens barrier is opened and the objective surface is The structure is exposed. At this time, in the lens barrel of the photographing lens 101, the optical systems of the respective groups constituting the zoom lens are arranged at, for example, a short focal end (wide angle end). The arrangement of the group optical system is changed, and the zooming operation to the long focal end (telephoto end) can be performed via the intermediate focal length. It is desirable that the optical system of the optical finder 102 is also scaled in conjunction with the change in the angle of view of the photographing lens 101.
In many cases, focusing is performed by half-pressing the shutter button 104. Focusing in the zoom lens according to the present invention (the zoom lens defined in claims 1 to 8 or shown in the first to third embodiments described above) is one of a plurality of optical systems constituting the zoom lens. This can be done by moving a group of parts or moving a light receiving element. When the shutter button 104 is further pushed down to the fully depressed state, photographing is performed, and then the processing as described above is performed.

When the image recorded in the semiconductor memory 115 is displayed on the liquid crystal monitor 107 or transmitted to the outside via the communication card 116 or the like, the operation button 108 is operated as specified. The semiconductor memory 115 and the communication card 116 are used by being loaded into dedicated or general-purpose slots such as the memory card slot 109 and the communication card slot, respectively.
As described above, the above-described digital camera (imaging device) or portable information terminal device captures the photographic lens 101 configured using the zoom lens as described in the first to third embodiments. It can be used as an optical system. Therefore, it is possible to realize a small digital camera (imaging device) or a portable information terminal device with high image quality using light receiving elements having 10 million to 15 million pixels or more.
Also, it can be applied as a zoom photographing lens of a silver salt camera and a projection lens of a projector.

G1 first lens group (positive)
G2 Second lens group (negative)
G3 Third lens group (positive)
G4 4th lens group (positive)
L1, L2, L3, L4, L5, L6, L7, L8, L9 1st lens, 2nd lens, 3rd lens, 4th lens, 5th lens, 6th lens, 7th lens, 8th lens, 1st lens 9 lenses AD aperture stop FG parallel plate 101 photographic lens 102 optical viewfinder 103 strobe (flash light)
104 Shutter button 105 Camera body 106 Power switch 107 Liquid crystal monitor 108 Operation button 109 Memory card slot 110 Zoom switch 111 Central processing unit (CPU)
112 Image processing device 113 Light receiving element 114 Signal processing device 115 Semiconductor memory 116 Communication card, etc.

JP 2010-140881 A JP 2009-025366 A JP 2007-212537 A Japanese Patent No. 3777150 (Japanese Patent Laid-Open No. 2004-12638) Japanese Patent No. 4387505 (Japanese Patent Laid-Open No. 2001-42215) JP 2008-145501 A

Claims (11)

In order from the object side to the image plane side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and positive refraction And a fourth lens group having power, and when changing the magnification 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 The distance between the first lens group and the third lens group is decreased, the first lens group and the third lens group are moved closer to the object side at the telephoto end than at the wide-angle end, and the first lens group is convex toward the image plane side. In the zoom lens that moves along such a locus, the first lens group is composed of a cemented lens of a negative lens and a positive lens, and the second lens group is an image in order from the object side toward the image plane side. A biconcave first negative lens having a concave surface with a larger curvature on the surface side than the object side surface; An aperture that is composed of a second negative lens having a concave surface facing the surface side and a positive lens having a convex surface facing the object side, and is movable between the second lens group and the third lens group during zooming. A zoom lens having an aperture and satisfying the following conditional expression:
0 ≦ (L12M−L12W) / L12W <0.15 (1)
1.00 <| fFm | / fm <1.55 (2)
Where L12W is the distance between the optical axes of the first lens group and the second lens group at the wide-angle end, and L12M is the optical axis of the first lens group and the second lens group at the zoom position where the total length is the shortest. The distance between the first lens group and the second lens group at the zoom position where the total length is the shortest, and fm represents the focal length of the entire system at the zoom position where the total length is the shortest. The total length represents the length from the first surface of the lens closest to the object side of the first lens group to the image plane. 2. The zoom lens according to claim 1, wherein the following conditional expression is satisfied.
0.90 <LFm / | fFm | <1.65 (3)
However, LFm is the distance between the optical axes from the first surface of the lens closest to the object side to the aperture stop in the zoom position where the total length is the shortest, and fFm is the zoom position where the total length is the shortest. It represents the combined focal length of the first lens group and the second lens group.   3. The zoom lens according to claim 1, wherein the second negative lens of the second lens group has at least one aspheric surface. 4. 4. The zoom lens according to claim 1, wherein the zoom lens satisfies the following conditional expression. 5.
0.50 <| f2 | / f3 <1.00 (4)
However, f2 represents the focal length of the second lens group, and f3 represents the focal length of the third lens group. 5. The zoom lens according to claim 1, wherein the following conditional expression is satisfied: 5.
0.5 <(β2t / β2w) / (β3t / β3w) <1.5 (5)
Where β2t is the imaging magnification of the second lens group at the telephoto end, β2w is the imaging magnification of the second lens group at the wide-angle end, β3t is the imaging magnification of the third lens group at the telephoto end, and β3w is the wide-angle The imaging magnification of the third lens group at the end is represented. 6. The zoom lens according to claim 1, wherein the following conditional expression is satisfied.
0.15 <X1 / ft <0.45 (6)
Here, X1 represents the total amount of movement of the first lens group upon zooming from the wide-angle end to the telephoto end, and ft represents the focal length of the entire system at the telephoto end. The zoom lens according to any one of claims 1 to 6, wherein the following conditional expression is satisfied.
0.10 <X3 / ft <0.50 (7)
X3 represents the total amount of movement of the third lens group during zooming from the wide-angle end to the telephoto end, and ft represents the focal length of the entire system at the telephoto end. 8. The zoom lens according to claim 1, wherein the following conditional expression is satisfied.
0.05 <| X2 | / X3 <0.50 (8)
Where X2 is the total amount of movement of the second lens group during zooming from the wide-angle end to the telephoto end, and X3 is the total amount of movement of the third lens group during zooming from the wide-angle end to the telephoto end. Represents.   9. The zoom lens according to claim 1, wherein the zoom lens is used in an information device that reads an image obtained by the zoom lens by an image pickup device, and the distortion aberration is obtained electronically from data converted into information by the image pickup device. Zoom lens, which is allowed within a range that can be corrected by simple processing.   A camera comprising the zoom lens according to claim 1 as a photographing optical system.   A portable information terminal device comprising the zoom lens according to claim 1 as a photographing optical system of a camera function unit.

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