JP2006078979A - Zoom lens, camera, and personal digital terminal unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact zoom lens having a variable power ratio of 4.5 times or larger, while the half angle of view at the edge of a sufficiently wide angle is 35° or larger, and capable of obtaining the resolving power, coping an imaging device of 3 to 5 million pixels. <P>SOLUTION: The zoom lens satisfies 0.70<Y' max/fw<1.00, where fw is a focal length of all systems at the edge of a wide angle, and Y' max is the maximum image height. A second lens group I is composed of a negative lens L1 whose surface having the larger curvature faces the image side, a positive lens L2 whose surface having the larger curvature faces the image side, and a negative lens L3 whose surface having the larger curvature faces the object side, which are arranged successively from the object side with air space in between. The surface of the negative lens L6 of the closest second lens group II to the image is of aspheric shape, in which the negative refractive power becomes weaker as going farther away from the optical axis. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a zoom lens that can be used for various cameras such as a digital camera, a video camera, and a silver salt camera, a camera using the zoom lens, 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. Above all, 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 required to have both high performance and small size.

  Here, in terms of miniaturization, first, it is necessary to shorten the total lens length in use, that is, the distance from the lens surface closest to the object side to the image plane, and to reduce the thickness of each lens group. It is also important to reduce the overall length during storage. Furthermore, in terms of high performance, it is necessary to have a resolution corresponding to an image sensor with 3 to 5 million pixels at all zoom ranges.

  Especially in compact digital cameras, the diagonal size of the image sensor is as small as 6-9 mm, and in order to realize 3-5 million pixels, the pixel pitch is 3 μm or less, and so advanced aberration correction is required. Is done. For example, when the pixel pitch is 2.5 μm, the Nyquist frequency is 200 lines / mm, and the diffraction limit is also a problem. Therefore, the allowable amount of aberration is relatively small compared to the photographing lens for a silver salt camera. .

  In addition, there are many users who wish to widen the angle of view of the taking lens, and it is desirable that the half angle of view at the wide angle end of the zoom lens is at least 35 degrees or more, preferably 38 degrees or more. A half angle of view of 38 degrees corresponds to a focal length of 28 mm when converted to a 35 mm silver salt camera (so-called Leica version). In such a wide angle of view, the occurrence of off-axis aberrations such as distortion and lateral chromatic aberration increases, and coupled with the fact that the pixel pitch of the image sensor is small, the lens design becomes very difficult.

  Furthermore, a zoom lens having a zoom ratio as large as possible is desired. In terms of a 35mm silver salt camera, a zoom lens that can convert the focal length in a range corresponding to 28 to 135mm (zoom ratio is about 4.8 times) is considered to be able to handle most of general photography. It is done.

  Many types of zoom lenses for digital cameras are conceivable, but only those that can satisfy all of the above requirements are limited. In the zoom lens of about 3 times, as the most general type, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens having a positive refractive power. A lens group, and an aperture stop that moves integrally with the second group on the object side of the second lens group, and the second lens group is located on the image side during zooming from the short focal end to the long focal end. There is a lens that moves monotonically from the object side to the object side, and the first lens group moves so as to correct the fluctuation of the image plane position due to zooming. However, it is not suitable for high zoom ratio exceeding 4 times.

  What is known as a zoom lens of a type suitable for high zooming is, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a positive refractive power. When the zooming is performed 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 increased. Zoom lenses with a small value are known (see, for example, Patent Document 1, Patent Document 2, and Patent Document 3).

  Further, 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. A zoom lens in which 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 upon zooming from the wide-angle end to the telephoto end. Known (for example, see Patent Document 4, Patent Document 5, and Patent Document 6).

JP-A-11-109236 JP-A-11-142733 JP 11-242157 A Japanese Patent Laid-Open No. 04-190211 Japanese Patent Laid-Open No. 04-296809 JP 2001-056436 A

  However, in any of the conventional examples of the three-group configuration or the four-group configuration, although there are many cases where the zoom ratio exceeds 5 times, there is no half-field angle of 35 degrees or more at the wide-angle end. The widest angle of view is disclosed in the invention described in Patent Document 2, which has a zoom ratio of about 3 to 5 times and a half angle of view of about 25 to 34 degrees. is there. However, when the half angle of view is relatively wide at 34 degrees, the zoom ratio is only 3 times, which is not sufficient in terms of both wide angle of view and high zoom ratio.

  The present invention has been made in view of the above-mentioned problems of the prior art, and the invention according to claim 1 is such that the half angle of view at the wide-angle end is not less than 35 degrees and the angle of view is 4.5 times. An object of the present invention is to provide a zoom lens that has the above zoom ratio, is small, and has a resolving power corresponding to an image sensor with 3 to 5 million pixels.

An object of the present invention is to provide a high-performance zoom lens in which each aberration is corrected better.
A third object of the present invention is to provide a high-performance zoom lens in which distortion at the wide-angle end is corrected more satisfactorily.
An object of the present invention is to provide a high-performance zoom lens in which chromatic aberration is corrected better.
It is an object of the present invention to provide a high-performance zoom lens in which each aberration is corrected more satisfactorily.
The invention according to claim 9 has a zoom ratio of 4.5 times or more while the half angle of view at the wide-angle end is 35 degrees or more and a sufficiently wide angle of view, is small, and is 3 million to 5 million. Another object of the present invention is to provide another means for realizing a zoom lens having a resolving power corresponding to an image sensor of a pixel.

  The invention according to claim 10 has a zoom ratio of 4.5 or more while having a sufficiently wide field angle of 35 degrees or more at the wide-angle end, is small, and is 3 million to 5 million. An object of the present invention is to provide a small and high-quality camera using a zoom lens having a resolving power corresponding to a pixel image sensor as a photographing optical system.

  The invention according to claim 11 has a zoom ratio of 4.5 times or more while having a sufficiently wide field angle of 35 degrees or more at the wide-angle end, is small, and has 3 to 5 million pixels. An object of the present invention is to provide a small-sized and high-quality portable information terminal device using a zoom lens having a resolving power corresponding to the image pickup device as a photographing optical system of a camera function unit.

  The zoom lens according to the first aspect of the present invention includes, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a positive refractive power. A third lens group having 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 in zooming from the wide-angle end to the telephoto end. The zoom lens further has the following characteristics.

In the zoom lens according to claim 1, when f _W is a focal length of the entire system at the wide angle end and _Y ′ _max is a maximum image height, the following conditional expression 0.70 <Y ′ _max / f _w <1.00
In addition, the second lens group is arranged in order from the object side with an air gap therebetween, a negative lens having a large curvature surface facing the image side, and a positive lens having a large curvature surface facing the image side , It is composed of three negative lenses having a large curvature surface facing the object side.

According to a second aspect of the present invention, in the zoom lens according to the first aspect, the negative refracting power becomes weaker as the image side surface of the negative lens disposed closest to the image side of the second lens group is separated from the optical axis. N _2I is the refractive index of the negative lens disposed closest to the image side of the second lens group, and X _2I (H _0.8 ) is the aspherical surface closest to the image side of the second lens group. When the aspherical amount is 80% of the maximum effective ray height at the following, the following conditional expression 0.0010 <(1-N _2I ) × X2I (H _0.8 ) / Y ′ _max <0.0500
It is characterized by satisfying. Here, the aspheric amount X (H) is the difference in the sag amount at the height H from the optical axis between the spherical surface defined by the paraxial curvature of the aspheric surface and the actual aspheric surface. The direction toward the side is positive.

According to a third aspect of the present invention, in the zoom lens according to the second aspect, in addition to the image side surface of the negative lens disposed closest to the image side of the second lens group, the zoom lens is disposed closest to the object side of the second lens group. The object side surface of the negative lens provided is aspheric, N _{2 O} is the refractive index of the negative lens disposed closest to the object side of the second lens group, and X _2O (H _0.8 ) is the second lens group. When the amount of aspherical surface is 80% of the maximum effective ray height on the most aspherical surface on the object side, the following conditional expression −0.0500 <((N ₂ O −1) × X _2O (H _0.8 )
+ (1-N _2I ) × X _2I (H _0.8 )) / Y ′ _max <0.1500
It is characterized by satisfying.

A zoom lens according to a fourth aspect is the zoom lens according to any one of the first to third aspects, wherein N _2i is counted from the object side in the second group, and the refractive index of the i-th lens is represented by ν _2i . When the Abbe number of the i-th lens is counted from the object side in the second group, the following conditional expression 1.75 <N ₂₁ <1.90, 35 <ν ₂₁ <50
1.65 <N ₂₂ <1.90, 20 <ν ₂₂ <35
1.75 <N ₂₃ <1.90, 35 <ν ₂₃ <50
It is characterized by satisfying.

The zoom lens according to claim 5, wherein, in the zoom lens according to any one of claims 1 to 4, the first lens group and the distance between the second lens at the wide-angle end to D _12W, the at the telephoto end of the D _12T When the distance between the first lens unit and the second lens, f _T is the focal length of the entire system at the telephoto end, the first lens unit monotonously moves to the object side during zooming from the wide-angle end to the telephoto end. the following conditional expression _{0.50 <(D 12T -D 12W)} / f T <0.85
It is characterized by satisfying.

A zoom lens according to a sixth aspect is the zoom lens according to any one of the first to fifth aspects, wherein _D23W is a distance between the first lens unit and the second lens at the wide angle end, and _D23T is a first distance at the telephoto end. When the distance between one lens group and the second lens, f _T is the focal length of the entire system at the telephoto end, the following conditional expression 0.25 <(D _23W −D _23T ) / f _T <0.65
It is characterized by satisfying.

The zoom lens according to claim 7, wherein, in the zoom lens according to any one of claims 1 to 6, when the a f ₂ the focal length of the second lens group, the focal length of the f ₃ third lens group , The following conditional expression 0.5 <| f ₂ | / f ₃ <1.0
It is characterized by satisfying.

The zoom lens according to claim 8 is the zoom lens according to any one of claims 1 to 7, wherein f ₁ is a focal length of the first lens unit, and f _w is a focal length of the entire system at the wide angle end. Then, the following conditional expression 6.0 <f ₁ / f _W <12.0
It is characterized by satisfying.

The zoom lens according to claim 9, 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 positive refraction. A fourth lens group having a force is provided, and the distance between the first lens group and the second lens group becomes large and the distance between the second lens group and the third lens group becomes large when zooming from the wide-angle end to the telephoto end. In a zoom lens in which at least the first lens unit and the third lens unit move to the object side so as to decrease, when f _W is the focal length of the entire system at the wide angle end and _Y ′ _max is the maximum image height, the following Conditional expression 0.70 < _{Y ′ max} / f _W <1.00
In addition, the second lens group is arranged in order from the object side with an air gap therebetween, a negative lens having a large curvature surface facing the image side, and a positive lens having a large curvature surface facing the image side , It is composed of three negative lenses having a large curvature surface facing the object side.

  According to a tenth aspect of the present invention, there is provided a camera having the zoom lens according to any one of the first to ninth aspects as a photographing optical system.

  A portable information terminal device according to an eleventh aspect of the present invention includes the zoom lens according to any one of the first to ninth aspects as a photographing optical system of a camera function unit.

  According to the first aspect of the present invention, the half angle of view at the wide-angle end is 35 degrees or more and a sufficiently wide angle of view, but has a zoom ratio of 4.5 or more, a small size, and 3 million to 500 It is possible to provide a zoom lens having a resolving power corresponding to an image sensor with 10,000 pixels. By using such a zoom lens, it is possible to realize a camera or a portable information terminal device that is small and has high image quality and has a zooming range that sufficiently covers a normal shooting area.

  According to the second aspect of the present invention, it is possible to provide a high-performance zoom lens in which each aberration is corrected more favorably. By using this zoom lens, it is possible to provide a small, high-quality, normal photographing region. It is possible to realize a camera and a portable information terminal device having a zoom range that sufficiently covers the above.

  According to the third aspect of the present invention, it is possible to provide a high-performance zoom lens in which distortion at a wide-angle end is corrected more satisfactorily. Thus, it is possible to realize a camera or a portable information terminal device having a zooming range that sufficiently covers a normal shooting area.

  According to the fourth aspect of the present invention, a high-performance zoom lens in which chromatic aberration is corrected better can be provided. By using this zoom lens, it is possible to provide a small, high-quality, normal photographing region. It is possible to realize a camera or a portable information terminal device having a zoom range that sufficiently covers the above.

  According to the invention described in claims 5 to 8, since it is possible to provide a high-performance zoom lens in which each aberration is corrected more satisfactorily, the use of this zoom lens further increases the resolving power. A high-quality camera or a portable information terminal device can be realized.

  According to the ninth aspect of the present invention, the half angle of view at the wide-angle end is 35 degrees or more and a sufficiently wide angle of view, but has a zoom ratio of 4.5 times or more, a small size, and 3 million to 500 It is possible to provide another means for realizing a zoom lens having a resolving power corresponding to an image sensor with 10,000 pixels. By using this zoom lens, it is possible to realize a camera or a portable information terminal device that is small and has high image quality and has a zooming range that sufficiently covers a normal shooting area.

  According to the tenth aspect of the present invention, the half angle of view at the wide angle end is a wide angle of view of 38 degrees or more, while having a zoom ratio of 4.5 times or more, a small size, and 3 million to 500 It is possible to provide a small, high-quality camera using a zoom lens having a resolving power corresponding to an image sensor with 10,000 pixels as a photographing optical system. By using this camera, the user can take a high-quality image with a camera having excellent portability.

  According to the eleventh aspect of the present invention, the half angle of view at the wide-angle end is 35 degrees or more and a sufficiently wide angle of view, but has a zoom ratio of 4.5 times or more, is small, and has a zoom ratio of 3 to 500,000. It is possible to provide a small and high-quality portable information terminal device that uses a zoom lens having a resolving power corresponding to an image sensor with 10,000 pixels as a photographing optical system of a camera function unit. The user can take a high-quality image with a portable information terminal device excellent in portability and transmit the image to the outside.

  Among zoom lenses according to the present invention, a zoom lens having three lens groups of positive, negative, and positive in order from the object side is generally configured as a so-called variator in which the second lens group bears a main zooming action. Therefore, the configuration of the second lens group is very important. In particular, in a compact digital camera, the pixel pitch of the image sensor is small, and advanced aberration correction is required. Further, widening as intended by the present invention makes correction of off-axis aberrations more difficult. An unprecedented device is required for the configuration of the lens group.

The second lens group, which has been well known in the past, has, in order from the object side, a negative lens with a large curvature on the image side, a negative lens with a concave surface on the image side, and a convex surface on the object side. Some of them consist of three positive lenses. When the second group is constituted by three lenses, almost all conventional examples adopt this configuration. However, it is not an optimal configuration for realizing a zoom lens with a half angle of view exceeding 35 degrees at the wide-angle end for compact digital camera applications.
In many cases, the number of lenses in the second lens group is increased to improve performance. For example, in order from the object side, there are four lenses, a negative lens, a negative lens, a positive lens, and a negative lens having a surface with a large curvature facing the image side. However, as the number of lenses in the second lens group also increases, the second lens group becomes thicker, and the total length when the lens is accommodated increases, which impedes compactification and increases costs.

The present invention is optimal for realizing a zoom lens in which the half lens angle at the wide-angle end exceeds 35 degrees in a compact digital camera application, with the configuration of the second lens group being limited to three lenses. It was completed by finding the configuration of the two lens groups. The basic requirements are that the following conditional expression is satisfied, and the second lens group is arranged in order from the object side with an air gap between them, a negative lens with a large curvature surface facing the image side, and an image The object is to consist of three lenses: a positive lens having a surface with a large curvature on the side, and a negative lens having a surface with a large curvature on the object side.
0.70 <Y ′ _max / f _w <1.00
(Where f _w is the focal length of the entire system at the wide-angle end, and Y ′ _max is the maximum image height)
When _{Y'max /} f _w is 0.70 or less, in the state where sufficiently correct distortion, wide-angle more than 35 degrees half angle at the wide angle end can not be realized. On the other hand, if the _{Y'max /} f _w is 1.00 or more, the correction of the off-axial aberration becomes very difficult at the wide-angle end, also, the first lens group becomes large, it can not be made compact .

  While satisfying the above conditional expression range, in order from the object side, the second lens group is a negative lens having a large curvature surface facing the image side, a positive lens having a large curvature surface facing the image side, and the object side. If it is composed of three negative lenses having a surface with a large curvature, off-axis aberrations at the wide-angle end, particularly lateral chromatic aberration, can be corrected satisfactorily. The structural point is that both the image side surface of the second lens from the object side and the object side surface of the third lens (most image side) from the object side have a convex shape on the image side. . By adopting such a configuration, off-axis light beams near the wide-angle end are incident on these surfaces at a large angle, so that a necessary and sufficient amount of aberration can be generated with a high degree of freedom. By appropriately canceling out aberrations with aberrations generated on other surfaces, it becomes possible to correct aberrations at a higher level than before.

The second lens group is composed of a negative lens having a large curvature surface on the image side, a negative lens having a concave surface on the image side, and a positive lens having a convex surface on the object side. In this case, the image side surface of the second lens from the object side and the object side surface of the third lens (most image side) from the object side both have a convex shape on the object side. In such a configuration, when the angle of the off-axis light beam with respect to the optical axis is increased in widening the angle, the incident angle of the off-axis light beam on these surfaces becomes very small, and the amount of aberration generated is limited. Thus, a sufficient effect for correcting off-axis aberrations cannot be obtained.
The second lens from the object side and the third lens (most image side) from the object side may be cemented together so that the cemented surface has the above-described aberration correction effect. However, it is possible to control the aberration with a higher degree of freedom when separated.

In the zoom lens of the present invention, in order to realize better aberration correction, the negative refractive power becomes weaker as the image side surface of the negative lens arranged closest to the image side of the second lens group moves away from the optical axis. It is desirable that the aspherical surface has such a shape. Furthermore, it is desirable that this aspherical surface satisfy the following conditional expression.
0.0010 <(1-N _2I ) × X _2I (H _0.8 ) / Y ′ _max <0.0500
Where N _2I is the refractive index of the negative lens disposed closest to the image side of the second lens group, and X _2I (H _0.8 ) is the maximum ray effective height on the aspherical surface closest to the image side of the second lens group. Represents the amount of aspherical surface at 80% of. Here, the aspheric amount X (H) is the difference in the sag amount at the height H from the optical axis between the spherical surface defined by the paraxial curvature of the aspheric surface and the actual aspheric surface. The direction toward the side is positive. If (1-N _2I ) × X _2I (H _0.8 ) is 0.0010 or less, or 0.0500 or more, distortion aberration and astigmatism / coma aberration cannot be corrected in a well-balanced manner. In particular, this is an obstacle to securing higher imaging performance at the wide-angle end.

In order to better correct distortion at the wide-angle end, in addition to the image side surface of the negative lens arranged closest to the image side of the second lens group, it is arranged closest to the object side of the second lens group. It is desirable that the object side surface of the negative lens be an aspherical surface. Furthermore, it is desirable that this aspherical surface satisfy the following conditional expression.
−0.0500 <((N ₂ O −1) × X ₂ O (H _0.8 )
+ (1-N _2I ) × X _2I (H _0.8 )) / Y ′ _max <0.1500
Where N _{2 O} is the refractive index of the negative lens disposed closest to the object side of the second lens group, and X _2O (H _0.8 ) is the maximum effective ray height on the aspherical surface closest to the object side of the second lens group. Represents the amount of aspherical surface at 80% of. When ((N _{2 O} −1) × X _{2 O} (H _0.8 ) + (1-N _2I ) × X _2I (H _0.8 )) / Y ′ _max is −0.0500 or less, at the wide angle end. This is not preferable because the distortion aberration is insufficiently corrected or an unnatural shape having an inflection point. On the other hand, when ((N _{2 O} −1) × X _{2 O} (H _0.8 ) + (1−N _2I ) × X _2I (H _0.8 )) / Y ′ _max is set to 0.1500 or more, the distortion is reduced. In addition to being overcorrected, it becomes difficult to correct other off-axis aberrations well.

It is desirable that each lens in the second lens group satisfies the following conditional expression.
1.75 <N ₂₁ <1.90, 35 <ν ₂₁ <50
1.65 <N ₂₂ <1.90, 20 <ν ₂₂ <35
1.75 <N ₂₃ <1.90, 35 <ν ₂₃ <50
N ₂₁ represents the refractive index of the i-th lens counted from the object side in the second group, and ν ₂₁ represents the Abbe number of the i-th lens counted from the object side in the second group. By selecting such a glass type, it is possible to correct chromatic aberration better.

  In the present invention, in order to achieve higher zooming, when zooming from the wide-angle end to the telephoto end, the third lens unit is moved toward the object side, so that the zooming action is also exerted on the third lens unit. It is desirable to share it and reduce the burden on the second lens group to ensure the degree of freedom of aberration correction. Further, at the time of zooming from the wide-angle end to the telephoto end, the first lens unit is moved to the object side, so that the height of the light beam passing through the first lens unit is reduced at the wide-angle end, and the first lens accompanying the widening of the angle. The enlargement of the group can be suppressed, and at the telephoto end, a long distance can be achieved by ensuring a large interval between the first lens group and the second lens group.

Regarding the movement of the first lens group, it is desirable to satisfy the following conditional expression.
_{0.50 <(D 12T -D 12W)} / f T <0.85
Here, D _12W represents the distance between the first lens group and the second lens at the wide angle end, D _12T represents the distance between the first lens group and the second lens at the telephoto end, and f _T represents the focal length of the entire system at the telephoto end. If (D _12T −D _12W ) is 0.50 or less, the contribution of the second lens group to the zooming is reduced and the load on the third lens group is increased, or the first lens group / second lens group The refractive power must be increased, and in any case, various aberrations are deteriorated. In addition, the total lens length at the wide-angle end increases, and the height of the light beam passing through the first lens group increases, leading to an increase in size of the first group. On the other hand, if (D _12T −D _12W ) is 0.85 or more, 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 becomes too short, the moving space of the third lens group is limited, and the contribution of the third lens group to zooming becomes small, 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 total length direction, but also the radial direction will be enlarged to ensure the amount of peripheral light at the telephoto end, and manufacturing errors such as tilting of the lens barrel will occur. Degradation of the image performance due to is likely to be caused.
More preferably, the following conditional expression should be satisfied.
_{0.60 <(D 12T -D 12W)} / f T <0.75

Regarding the change in the distance between the second lens group and the third lens group, it is desirable to satisfy the following conditional expression.
_{0.25 <(D 23W -D 23T)} / f T <0.65
However, _D23W represents the distance between the second lens group and the third lens at the wide-angle end, and _D23T represents the distance between the second lens group and the third lens at the telephoto end. If (D _23W −D _23T ) / f _T is 0.25 or less, the contribution of the third lens group to zooming is reduced, and the burden on the second lens group increases, or the third lens group itself The refractive power must be increased, and in any case, various aberrations are deteriorated. On the other hand, if (D _23W −D _23T ) / f _{T is set} to 0.65 or more, the total lens length at the wide angle end becomes longer, the height of the light beam passing through the first lens group increases, and the size of the first group increases. Invite.
More preferably, the following conditional expression should be satisfied.
_{0.30 <(D 23W -D 23T)} / f T <0.60

It is desirable to satisfy the following conditional expression regarding aberration correction.
0.5 <| f ₂ | / f ₃ <1.0
6.0 <f ₁ / f _W <12.0
Here, f ₁ is the focal length of the first lens group, f ₂ is the focal length of the second lens group, f ₃ is the focal length of the third lens group, and f _W is the focal length of the entire system at the wide angle end. If | f ₂ | / f ₃ is 0.5 or less, the refractive power of the second lens group becomes too strong. If | f ₂ | / f ₃ is 1.0 or more, the refractive power of the third lens group is In any case, the aberration variation during zooming tends to increase. If f ₁ / f _W is 6.0 or less, the imaging magnification of the second lens unit approaches to the same magnification and the zooming efficiency is improved, which is advantageous for high zooming. The lens requires a large refracting power, which not only has adverse effects such as worsening chromatic aberration at the telephoto end, but is also disadvantageous for downsizing especially in the storage state because the first group becomes thicker and larger in diameter. It becomes. On the other hand, if f ₁ / f _{W is set} to 12.0 or more, the contribution of the second lens group to zooming becomes small, and high zooming becomes difficult. Desirably, f ₁ / f _W is preferably 10.0 or more.

The object of the present invention can also be achieved by the following configuration. That is, 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. Are arranged in a four-group configuration, 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 is increased, and the distance between the second lens group and the third lens group is decreased. Thus, a zoom lens in which at least the first lens group and the third lens group move to the object side is used. Thus, the following conditional expression is satisfied, and the second lens group is arranged in order from the object side, a negative lens having a surface with a large curvature on the image side, a positive lens having a surface with a large curvature on the image side, It consists of three negative lenses with a large curvature facing the object side.
0.70 < _{Y ′ max} / f _W <1.00
However, f _W represents the focal length of the entire system at the wide angle end, and _Y ′ _max represents the maximum image height.

  In the zoom lens of the present invention, an aperture stop is disposed between the second lens group and the third lens group, and the aperture stop moves independently of the adjacent lens group, and the aperture stop and the third lens group are moved. It is desirable that the distance from the lens group be the widest at the wide-angle end and the narrowest at the telephoto end. By widening the distance between the aperture stop and the third lens group at the wide-angle end, it is possible to bring the aperture stop closer to the first lens group at the wide-angle end and to lower the height of the light beam passing through the first lens group. Thus, further downsizing of the first group can be achieved.

The following describes the conditions for better aberration correction within a range that does not hinder downsizing. It is desirable that the first lens group has at least one negative lens and at least one positive lens from the object side. More specifically, either a negative meniscus lens having a convex surface facing the object side and a positive lens having a strong convex surface facing the object side are arranged in order from the object side, or the object side is arranged in order from the object side. Negative meniscus lens with convex surface, positive lens with strong convex surface on object side,
It is preferable to use three positive lenses having a strong convex surface on the object side.

  When the entire system is composed of only three groups of positive, negative, and positive, it is desirable that the third lens group is composed of four lenses in order from the object side: a positive lens, a positive lens, a negative lens, and a positive lens. Here, the second lens and the third lens from the object side may be appropriately joined. When the entire system is composed of four groups of positive, negative, positive, and positive, it is desirable that the third lens group is composed of three lenses in order from the object side: a positive lens, a positive lens, and a negative lens. Here, the second lens and the third lens from the object side may be appropriately joined.

  When the entire system is composed of four groups of positive, negative, positive, and positive, it is desirable that the fourth lens group be composed of one positive lens. Further, when focusing to a finite distance, the method of moving only the fourth lens group may minimize the weight of the object to be moved. The fourth lens group has a small movement amount at the time of zooming, and there is an advantage that a moving mechanism for zooming can be used as a moving mechanism for focusing.

  An aspherical surface is indispensable for further downsizing while maintaining good aberration correction, and it is desirable that at least the third lens unit has at least one aspherical surface other than the second lens unit. The aspherical surface of the third lens group is mainly effective in correcting spherical aberration and coma aberration.

  As an aspheric lens, an optical glass or plastic is molded, that is, a glass mold aspheric surface or a plastic mold aspheric surface, or a thin resin layer is molded on the surface of the glass lens, and the surface is aspherical. For example, what is called a hybrid aspherical surface, a replica aspherical surface, or the like can be used.

  Considering the adoption of a glass mold aspherical lens on the most image side of the second lens group, if the most image side lens in the second lens group is a positive lens, the lens material is used for correcting chromatic aberration. However, a heavy flint glass type is required, but there is a problem that few heavy flint type glass materials are suitable for molding. As in the present invention, when the lens on the most image side of the second lens group is a negative lens, a lanthanum crown type to tantalum flint type glass material is used as a lens material for chromatic aberration correction, which is suitable for a mold. There are many glass types.

  In addition, when considering using a hybrid aspherical lens on the most image side of the second lens group, a slightly larger lens outer diameter is required for the purpose of applying a mold for molding the resin layer. If the lens on the most image side of the second lens group is a positive lens, the edge thickness of the lens becomes small, which causes a problem that it cannot be processed. As in the present invention, when the lens closest to the image side of the second lens group is a negative lens, the edge thickness is increased, so that no processing problems occur.

  It may be simplified in terms of the mechanism that the aperture diameter of the aperture is constant regardless of zooming. However, the change in the F number accompanying zooming can be reduced by increasing the length of the long focal point compared to the short focal length. In addition, when it is necessary to reduce the amount of light reaching the image plane, the diameter of the diaphragm may be reduced. However, if the amount of light is reduced by inserting an ND filter or the like without greatly changing the diameter of the diaphragm, 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. 1 to 4 are sectional views showing different embodiments of the zoom lens according to the present invention. FIGS. 1 and 2 show examples of a three-group configuration, and FIGS. 3 and 4 show examples of a four-group configuration. In these drawings, the surface numbers of the respective surfaces are shown as “01”, “02”, “03”,... In order from the object side, and the respective lenses are indicated by “L1”, “L2”, “L3”,.・ Indicates like The first lens group is indicated by “I”, the second lens group is indicated by “II”, the third lens group is indicated by “III”, and the fourth lens group is indicated by “IV”. 1 to 4, the upper diagram shows the lens arrangement at the time of non-use or carrying, the middle diagram shows the lens arrangement at the wide angle end, and the lower diagram shows the lens arrangement at the telephoto end. The maximum image height is 3.50 mm in Numerical Example 1 and 3.70 mm in Numerical Example 2 to Numerical Example 4. In each embodiment, the parallel plate disposed on the image plane side of the lens system is assumed to be various filters such as an optical low-pass filter and an infrared cut filter, and a cover glass (seal glass) of a light receiving element such as a CCD sensor. Is. The materials of the lenses are all optical glass except that the ninth lens (fourth group) of Example 3 is an optical plastic.

The aberration in each example is sufficiently corrected, and can correspond to a light receiving element having 3 to 5 million pixels. 5 to 16 show aberration curves of the respective numerical examples. In these aberration curves, broken lines in the diagrams showing spherical aberration indicate sine conditions. In the diagram showing astigmatism, the solid line indicates sagittal and the broken line indicates meridional. It is clear from the embodiment that by configuring the zoom lens as in the present invention, a very good image performance can be secured while achieving a sufficiently small size.
The meanings of the symbols in the examples are as follows.
f: the focal length F of the entire system: F number omega: half field angle R: curvature radius D: surface interval N _d: refractive index [nu _d: Abbe number K: aspherical conic constant A _4: 4-order aspheric coefficients A ₆ : 6th-order aspheric coefficient A ₈ : 8th-order aspheric coefficient A ₁₀ : 10th-order aspheric coefficient However, the aspheric surface used here represents the reciprocal of the paraxial radius of curvature (paraxial curvature) as C When the height from the optical axis is H, it is defined by the following equation.

Numerical example 1

  FIG. 5 shows an aberration curve at the short focal point of the zoom lens according to Numerical Example 1, FIG. 6 shows an aberration curve at the intermediate focal length, and FIG. 7 shows an aberration curve at the long focal point.

Numerical example 2

  FIG. 8 shows an aberration curve at the short focal point of the zoom lens according to Numerical Example 2, FIG. 9 shows an aberration curve at the intermediate focal length, and FIG. 10 shows an aberration curve at the long focal point.

Numerical Example 3

FIG. 11 shows an aberration curve at the short focal end of the zoom lens according to Numerical Example 3, FIG. 12 shows an aberration curve at the intermediate focal length, and FIG. 13 shows an aberration curve at the long focal end.

Numerical Example 4

FIG. 14 shows an aberration curve at the short focal end of the zoom lens according to Numerical Example 4, FIG. 15 shows an aberration curve at the intermediate focal length, and FIG. 16 shows an aberration curve at the long focal end.

Next, embodiments of a camera and a portable information terminal device using the zoom lens according to the present invention will be described with reference to FIGS.
A portable information terminal device such as a camera or a mobile phone with a camera has a light receiving element including a photographing lens and an area sensor, and is configured to read an image of a photographing object formed on the light receiving element by the photographing lens with the light receiving element. Has been. As the photographing lens, the zoom lens according to each of the embodiments described so far is used.

  In FIG. 19, the image information of the subject output from the light receiving element 34 is processed by the signal processing device 36 under the control of the central processing unit 40 and converted into digital information. The image information digitized by the signal processing device 36 is recorded in the semiconductor memory 42 after undergoing predetermined image processing in the image processing device 38 under the control of the central processing unit 40. An image being shot can be displayed on the liquid crystal monitor 46, and an image recorded in the semiconductor memory 42 can be displayed. The image information recorded in the semiconductor memory 42 can also be transmitted to the outside using a communication card 44 or the like.

  As shown in FIGS. 17 and 18, the taking lens 30 is in the retracted state as shown in FIG. 17A when the camera is carried, and when the user operates the power switch 58 to turn on the power, FIG. ), The lens barrel of the taking lens 30 is extended. At this time, each group of zoom lenses in the lens barrel has an arrangement of, for example, a short focal point, and the arrangement of each group is changed by operating the zoom lever 52 and zooming to the long focal point is performed. be able to. At this time, the viewfinder 32 is also scaled in conjunction with the change in the angle of view of the photographic lens 30.

  Focusing is performed by half-pressing the shutter button 50. In the zoom lens according to each of the embodiments described above, focusing can be performed by moving the second group or the fourth group, or moving the light receiving element. When the shutter button 50 is further pressed from the half-pressed state, photographing is performed, and thereafter, the above-described processing is performed. When the image information recorded in the semiconductor memory 42 is displayed on the liquid crystal monitor 46 or transmitted to the outside using the communication card 44 or the like, the appropriate operation button 60 is used. The semiconductor memory 42 and the communication card 44 are used by being inserted into dedicated or general-purpose slots 62 and 64, respectively.

  When the photographing lens 30 is in the retracted state, each group of zoom lenses does not necessarily have to be aligned on the optical axis. For example, if the mechanism is such that the third lens group is retracted from the optical axis and stored in parallel with the other lens groups, the camera can be made thinner. FIGS. 17 and 18 show an example in which the zoom lens according to the embodiment is incorporated in a camera. The zoom lens according to the present invention is used as a photographing lens for a camera incorporated in a portable information terminal device such as a cellular phone. It can also be incorporated.

  By using the zoom lens according to Numerical Example 1 to Numerical Example 4 as a photographic lens in the camera or the portable information terminal device as described above, a light receiving element of 3 to 5 million pixel class is used. A small camera or a portable information terminal device with high image quality can be realized.

  The zoom lens according to the present invention can be used as a shooting lens for digital cameras, silver halide photography cameras, video cameras, and other various cameras. In particular, it is possible to realize a high-definition zoom lens that is compatible with a digital camera having a large number of pixels while being compact and having a high zoom ratio. In addition, by adopting such a zoom lens, it is possible to obtain a high-performance camera or a camera-equipped portable information terminal device that is compact and has a high zoom ratio.

1 shows a configuration of a zoom lens according to Numerical Example 1, wherein (a) is a non-use state, (b) is a short focal end, and (c) is a cross sectional view showing a long focal end. 2 shows a configuration of a zoom lens according to Numerical Example 2, in which (a) is a non-use state, (b) is a short focal end, and (c) is a cross sectional view showing a long focal end. 9 shows a configuration of a zoom lens according to Numerical Example 3, in which (a) shows a non-use state, (b) shows a short focal end, and (c) shows a long focal end. 9 shows a configuration of a zoom lens according to Numerical Example 4, in which (a) is a non-use state, (b) is a short focal end, and (c) is a cross sectional view showing a long focal end. 6 is an aberration curve diagram at a short focal end of the zoom lens according to Numerical Example 1. FIG. 6 is an aberration curve diagram at an intermediate focal length of the zoom lens according to Numerical Example 1. FIG. 6 is an aberration curve diagram at the long focal end of the zoom lens according to Numerical Example 1. FIG. FIG. 10 is an aberration curve diagram at the short focal point of the zoom lens according to Numerical Example 2. FIG. 9 is an aberration curve diagram at an intermediate focal length of the zoom lens according to Numerical Example 2. FIG. 6 is an aberration curve diagram at the long focal end of the zoom lens according to Numerical Example 2. 10 is an aberration curve diagram at the short focal point of the zoom lens according to Numerical Example 3. FIG. 10 is an aberration curve diagram at an intermediate focal length of the zoom lens according to Numerical Example 3. FIG. FIG. 10 is an aberration curve diagram at the long focal end of the zoom lens according to Numerical Example 3. FIG. 9 is an aberration curve diagram at the short focal point of the zoom lens according to Numerical Example 4; FIG. 10 is an aberration curve diagram at an intermediate focal length of the zoom lens according to Numerical Example 4; FIG. 10 is an aberration curve diagram at the long focal end of the zoom lens according to Numerical Example 4; 1A and 1B show an external appearance of an embodiment of a camera according to the present invention, in which FIG. 1A is an overall perspective view showing a state where a taking lens is retracted, and FIG. 2B is a perspective view of a part of the camera showing a state where the taking lens is advanced. It is. It is the whole perspective view which looked at the camera concerning the above-mentioned example from the back side. It is a block diagram which shows the processing circuit example of the part relevant to the imaging | photography function of the camera concerning this invention or a portable information terminal device.

Explanation of symbols

I 1st group lens II 2nd group lens III 3rd group lens IV 4th group lens L1-L10 Lens 01, 02, 03 ... Surface number

Claims (11)

In order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power are arranged to change from the wide-angle end to the telephoto end. When zooming, in a zoom lens in which the distance between the first lens group and the second lens group is large and the distance between the second lens group and the third lens group is small, the following conditional expression 0.70 < _{Y ′ max} / f _W <1.00
(Where f _W is the focal length of the entire system at the wide-angle end, and _Y ′ _max is the maximum image height)
In addition, the second lens group is arranged in order from the object side with an air gap therebetween, a negative lens having a large curvature surface facing the image side, and a positive lens having a large curvature surface facing the image side A zoom lens comprising three negative lenses having a surface with a large curvature facing the object side. 2. The zoom lens according to claim 1, wherein the image side surface of the negative lens disposed closest to the image side of the second lens group is an aspherical surface having a shape in which the negative refractive power decreases as the distance from the optical axis increases. Conditional expression 0.0010 <(1-N _2I ) × X _2I (H _0.8 ) / Y ′ _max <0.0500
(Where N _2I is the refractive index of the negative lens disposed closest to the image side of the second lens group, and X _2I (H _0.8 ) is the maximum effective ray height on the aspherical surface closest to the image side of the second lens group. The aspherical amount in 80% of the aspherical amount X (H) is the sag amount at the height H from the optical axis between the spherical surface defined by the paraxial curvature of the aspherical surface and the actual aspherical surface. This is the difference, and the direction from the object side to the image side is positive)
A zoom lens characterized by satisfying 3. The zoom lens according to claim 2, wherein, in addition to the image side surface of the negative lens disposed closest to the image side of the second lens group, the object side surface of the negative lens disposed closest to the object side of the second lens group includes: It is an aspherical surface, and the following conditional expression −0.0500 <((N ₂ O −1) × X ₂ O (H _0.8 )
+ (1-N _2I ) × X _2I (H _0.8 )) / Y ′ _max <0.1500
(Where N _{2 O} is the refractive index of the negative lens disposed closest to the object side of the second lens group, and X _2O (H _0.8 ) is the maximum effective ray height on the aspherical surface closest to the object side of the second lens group. Aspheric amount in 80% of the above)
A zoom lens characterized by satisfying 4. The zoom lens according to claim 1, wherein the following conditional expressions: 1.75 <N ₂₁ <1.90, 35 <ν ₂₁ <50
1.65 <N ₂₂ <1.90, 20 <ν ₂₂ <35
1.75 <N ₂₃ <1.90, 35 <ν ₂₃ <50
(Where N _2i is the refractive index of the i-th lens counted from the object side in the second group, and ν _2i is the Abbe number of the i-th lens counted from the object side in the second group)
A zoom lens characterized by satisfying 5. The zoom lens according to claim 1, wherein the first lens unit monotonously moves toward the object side upon zooming from the wide-angle end to the telephoto end, and the following conditional expression 0.50 < _{(D 12T -D 12W) / f} T <0.85
(Where D _12W is the distance between the first lens group and the second lens at the wide angle end, D _12T is the distance between the first lens group and the second lens at the telephoto end, and f _T is the focal length of the entire system at the telephoto end).
A zoom lens characterized by satisfying 6. The zoom lens according to claim 1, wherein the third lens unit monotonously moves toward the object side upon zooming from the wide-angle end to the telephoto end, and the following conditional expression 0.25 < _{(D 23W -D 23T) / f} T <0.65
(Where D _23W is the distance between the second lens group and the third lens at the wide-angle end, and D _23T is the distance between the second lens group and the third lens at the telephoto end)
A zoom lens characterized by satisfying 7. The zoom lens according to claim 1, wherein the following conditional expression: 0.5 <| f ₂ | / f ₃ <1.0
(Where f ₂ is the focal length of the second lens group, f ₃ is the focal length of the third lens group)
A zoom lens characterized by satisfying In the zoom lens according to any one of claims 1 to 7, the following conditional expression 6.0 <f ₁ / f _W <12.0
(Where f ₁ is the focal length of the first lens group, and f _W is the focal length of the entire system at the wide-angle end)
A zoom lens characterized by satisfying 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 are arranged. And at the time of zooming from the wide-angle end to the telephoto end, at least the first lens so that 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. In the zoom lens in which the first lens unit and the third lens unit are moved toward the object side, the following conditional expression 0.70 < _{Y ′ max} / f _W <1.00
(Where f _W is the focal length of the entire system at the wide-angle end, and _Y ′ _max is the maximum image height)
In addition, the second lens group is arranged in order from the object side with an air gap therebetween, a negative lens having a large curvature surface facing the image side, and a positive lens having a large curvature surface facing the image side A zoom lens comprising three negative lenses having a surface with a large curvature facing the object side.   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.

Images