JP2010210883A - Imaging lens, camera and personal digital assistance device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging lens which has a wide angle, that is, a half angle of view of about 38°, a large aperture, that is, an F-number of about 2.0, and nonetheless is relatively compact and has sufficiently reduced aberrations, and high resolving power adaptive to an imaging device having from 10 million to 20 million pixels, and prevents unwanted coloring even in a portion where large brightness differences exist. <P>SOLUTION: A first lens group G1, an aperture stop FA, and a second lens group G2 are arranged in order from an object side to an image plane. The first lens group G1 comprises a lens group 1F which is positioned on a front side and has negative refractive power and a first lens group 1R which is positioned on a rear side and has positive refractive power, with the longest distance in the first lens group G1 as a boundary. The second lens group G2 comprises, in order from the object side, a second lens group 2F positioned on a front side and comprising a cemented lens of a first positive lens and a first negative lens and a cemented lens of a second negative lens and a second positive lens, and a second lens group 2R positioned on a rear side and comprising at least one lens. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an improvement of a single-focus imaging lens used as an imaging optical system in various cameras including a so-called silver salt camera, and more particularly to an imaging lens suitable for a camera such as a digital camera and a video camera and the like. The present invention relates to a camera having such an imaging lens as an imaging 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, the category of compact and high-quality compact cameras equipped with high-performance single focus lenses has gained a certain amount of support from users, and expectations are high. As a request from the user, in addition to high performance, the weight for the small F number, that is, the large diameter is high.
Here, in terms of performance enhancement, in addition to having a resolution corresponding to at least an image sensor of 10 million to 20 million pixels, from the full aperture to a high contrast and a peripheral portion of the angle of view with little coma flare. It is necessary that there is no distortion of the point image, that there is no chromatic aberration and that no unnecessary coloring is generated even in a portion with a large luminance difference, that there is little distortion and that a straight line can be drawn as a straight line.
Furthermore, in terms of increasing the diameter, at least F2.4 or less is necessary because of the need to differentiate from a general compact camera equipped with a zoom lens, and many people desire F2.0 or less.
In addition, there are many users who desire a certain wide angle as the angle of view of the photographing lens, and it is desirable that the half angle of view of the imaging lens is 38 degrees or more. A half angle of view of 38 degrees corresponds to a focal length of 28 mm in terms of a 35 mm silver salt camera (so-called Leica version).

There are many types of imaging lenses for digital cameras, but the typical configuration of a wide-angle single focus lens is a lens group with negative refractive power on the object side and a lens group with positive refractive power on the image side. A so-called retrofocus type in which is provided. This is because of the characteristics of an area sensor having a color filter and a microlens for each pixel, there is a need to move the exit pupil position away from the image plane so that the peripheral luminous flux is incident on the sensor at an angle close to vertical. This is the main reason why the retro focus type is adopted. However, the retrofocus type has a large asymmetry in its refractive power arrangement, and tends to be incompletely corrected for coma, distortion, lateral chromatic aberration, and the like.
Among the conventional examples of such a retrofocus type imaging lens, Patent Document 1 (Japanese Patent Laid-Open No. 06-308385), which has a relatively large aperture and a half field angle of about 38 degrees, There are some disclosed in Patent Document 2 (Japanese Patent Laid-Open No. 09-218350), Patent Document 3 (Japanese Patent Laid-Open No. 2006-349920), and the like.

However, although the imaging lens disclosed in Patent Document 1 has a large aperture of F1.4, it has large astigmatism and curvature of field, and has sufficient performance up to the periphery near the full aperture. I can't say that. In addition, the imaging lens disclosed in Patent Document 2 is inferior in terms of F2.8 and a large aperture, and has large astigmatism, curvature of field, and lateral chromatic aberration. In both cases, the distortion aberration is over 2% in absolute value, and even in this respect, dissatisfaction remains.
In addition, the imaging lens disclosed in Patent Document 3 is well corrected for astigmatism, curvature of field, and distortion, but has a large color difference of coma aberration not shown in the specification. In addition, an embodiment with a small F number is insufficient in terms of miniaturization.

The present invention has been made in view of the above circumstances, and the object of the invention according to claim 1 is that the half angle of view is a wide angle of about 38 degrees and the F number is about 2.0 or less. However, it is relatively small, and astigmatism, curvature of field, lateral chromatic aberration, coma color difference, distortion aberration, etc. are sufficiently reduced, and it can handle image sensors with 10 to 20 million pixels. High resolution, high contrast, high contrast, no distortion of the point image from the periphery of the angle of view, no unnecessary coloring even in areas with large luminance differences, and straight lines can be drawn without distortion. The object is to provide a performance imaging lens.
An object of the invention described in claim 2 is to provide a high-performance imaging lens in which substantial manufacturing error sensitivity is reduced and stable performance is easily obtained.
An object of the invention described in claim 3 is to provide a higher performance imaging lens in which monochromatic aberration and chromatic aberration are corrected in a well-balanced manner.
An object of the present invention is to provide a high-performance imaging lens in which each aberration is corrected more favorably.
An object of the invention described in claim 5 is to provide a higher performance imaging lens with improved flatness of the image surface.

An object of the invention described in claim 6 is to provide a higher performance imaging lens in which the generation of spherical aberration accompanying the increase in aperture is suppressed.
An object of the invention described in claim 7 is to provide a higher performance imaging lens in which chromatic aberration is corrected more favorably.
An object of the invention described in claim 8 is to provide a further high-performance imaging lens in which the generation of aberration is further suppressed, and particularly, distortion is favorably corrected.
An object of the present invention is to provide a high-performance imaging lens in which coma aberration is corrected more favorably without adopting an unnecessarily complicated configuration.
An object of the present invention is to provide a suitable means for performing focusing on a finite distance object.

The object of the invention of claim 11 is as wide as a half angle of view of about 38 degrees and a large aperture with an F number of about 2.0 or less, and is relatively small in size. Curvature, lateral chromatic aberration, coma color difference, distortion, etc. are sufficiently reduced to have a resolution corresponding to an image sensor of 10 to 20 million pixels, and high contrast and angle of view from wide aperture A compact, high-performance imaging lens that uses a high-performance imaging lens as a photographic optical system. The purpose is to provide a high-quality camera.
The object of the invention of claim 12 is a relatively small size with a wide angle of half field angle of about 38 degrees and a large aperture of F number of about 2.0 or less, astigmatism and image plane. Curvature, lateral chromatic aberration, coma color difference, distortion, etc. are sufficiently reduced to have a resolution corresponding to an image sensor of 10 to 20 million pixels, and high contrast and angle of view from wide aperture Uses a high-performance imaging lens as a photographic optical system for the camera function unit that does not cause point image distortion to the periphery, does not cause unnecessary coloring even in areas with large luminance differences, and allows straight lines to be drawn without distortion Another object of the present invention is to provide a small and high-quality portable information terminal device.

In order to achieve the above-mentioned object, the imaging lens according to the first aspect of the present invention includes a first lens group positioned on the object side with an aperture stop interposed therebetween, and a second lens group positioned on the image side. An imaging lens composed of: a front first lens group having a negative refractive power, in order from the object side toward the first lens group, with a widest air interval in the first lens group; And a rear first lens group having a refractive power, and the second lens group is sequentially arranged from the object side in the order of a first positive lens, a first negative lens, a second negative lens, and a second positive lens. The front second lens group is disposed and a rear second lens group including at least one lens, and the Abbe number of the first positive lens of the front second lens group is ν _dp1. the Abbe number of the first negative lens and [nu _dn1, the second deflection The Abbe number of's and _{[nu dn2,} the Abbe number of the second positive lens as _{[nu dp2,}
Conditional expression:
62.0 <ν _dp1 <98.0
20.0 <ν _dn1 <45.0
20.0 <ν _dn2 <45.0
35.0 <ν _dp2 <98.0
−20.0 <ν _dn1 −ν _dn2 <15.0
It is characterized by satisfying.

An imaging lens according to a second aspect of the present invention is the imaging lens according to the first aspect, wherein the first positive lens, the first negative lens, and the first lens constituting the front second lens group The second negative lens and the second positive lens are in close contact with each other and are integrally joined.
The imaging lens according to the present invention described in claim 3 is the imaging lens according to claim 2,
The radius of curvature of the cemented surface of the first positive lens and the first negative lens is r _S1, and the radius of curvature of the cemented surface of the second negative lens and the second positive lens is r _S2 , Let f _{A be} the focal length of the system,
Conditional expression:
−2.4 <r _S1 / f _A <−0.8
1.0 <r _S2 / f _A <2.6
It is characterized by satisfying.

The imaging lens according to the present invention described in claim 4 is the imaging lens according to any one of claims 1 to 3,
The total length of the front second lens group is L _2F, and the distance from the most object side surface of the imaging lens to the image plane is L,
Conditional expression:
0.1 <L _2F /L<0.25
It is characterized by satisfaction.
An imaging lens according to the present invention described in claim 5 is the imaging lens according to any one of claims 1 to 4,
The focal length of the entire system of the imaging lens is f _A, and the focal length of the first lens group is f ₁ ,
Conditional expression:
0.0 <f _A / f ₁ <0.8
It is characterized by satisfying.

The imaging lens according to the present invention described in claim 6 is the imaging lens according to any one of claims 1 to 5,
The interval between the front first lens group and the rear first lens group is A _1F-1R, and the total length of the first lens group is L ₁ .
Conditional expression:
0.35 <A _1F-1R / L ₁ <0.7
It is characterized by satisfying.
An imaging lens according to the present invention described in claim 7 is the imaging lens according to any one of claims 1 to 6,
When the Abbe number of the first positive lens is ν _d and the anomalous dispersion of the first positive lens is Δθ _{g, F} , the anomalous dispersion Δθ _{g, F} is the Abbe number ν _d on the horizontal axis. , Partial dispersion ratio θ _{g, F} = ( _ng -n _F ) / (n _F -n _C ) In the graph with the vertical axis, glass type K7 (Ohara glass type name NSL7) and glass type F2 (Ohara glass type) when a straight line connecting the name PBM2) a standard line, means a deviation from a standard line of the glass type, g-line, F-line, the refractive index for the C line, _{respectively,} n _g, n F, as _{n C,}
Conditional expression:
ν _d > 80.0
Δθ _{g, F} > 0.025
It is characterized by satisfying.

An imaging lens according to an eighth aspect of the present invention is the imaging lens according to any one of the first to seventh aspects, wherein the front first lens group includes two object sides. Further, a negative meniscus lens having a convex surface is continuously arranged, and at least one of the lenses has an aspheric image side surface.
The imaging lens according to the present invention described in claim 9 is the imaging lens according to any one of claims 1 to 8, wherein the rear second lens group is a single lens. And is characterized by having an aspherical surface.
An imaging lens according to a tenth aspect of the present invention is the imaging lens according to any one of the first to ninth aspects, wherein the whole or a part of the second lens group is moved. And focusing on a finite distance object.
A camera according to the present invention described in claim 11 has the imaging lens according to any one of claims 1 to 10 as a photographing optical system.
A portable information terminal device according to a twelfth aspect of the present invention includes the imaging lens according to any one of the first to tenth aspects as a photographing optical system of a camera function unit. Yes.

According to the first aspect of the present invention, in the imaging lens including the first lens group located on the object side across the aperture stop and the second lens group located on the image side, the first lens In order from the object side, the front side first lens group having a negative refractive power and the rear side first lens group having a positive refractive power with the widest air interval in the first lens group as a boundary. And a second front lens group in which the second lens group is arranged in order from the object side in the order of the first positive lens, the first negative lens, the second negative lens, and the second positive lens, and at least one lens And the rear second lens group consisting of the above-mentioned lenses, the Abbe number of the first positive lens of the front second lens group is ν _dp1 , the Abbe number of the first negative lens is ν _dn1 , the Abbe number of the second negative lens and [nu _dn2, the second positive lens As _dp2 of the Abbe number _ν,
Conditional expression:
62.0 <ν _dp1 <98.0
20.0 <ν _dn1 <45.0
20.0 <ν _dn2 <45.0
35.0 <ν _dp2 <98.0
−20.0 <ν _dn1 −ν _dn2 <15.0
By satisfying
The half angle of view is as wide as about 38 degrees, and the F number is about 2.0 or less, but it is relatively small, and astigmatism, field curvature, lateral chromatic aberration, coma aberration color difference, and distortion. Aberrations are sufficiently reduced to have a resolution corresponding to an image sensor of 10 to 20 million pixels, and there is no distortion of the point image from the full aperture to the periphery of the angle of view with high contrast and brightness. It is possible to provide a high-performance imaging lens that does not cause unnecessary coloring even in areas with large differences and can draw straight lines without distortion. An information terminal device can be realized.

According to a second aspect of the present invention, in the imaging lens according to the first aspect, the first positive lens, the first negative lens, and the second negative lens constituting the front second lens group. And the second positive lens are intimately joined together,
It is possible to provide a high-performance imaging lens that can substantially reduce the sensitivity of manufacturing error, easily obtain stable performance, and realize a camera and a portable information terminal device that can obtain good depiction without variation. can do.
According to the invention described in claim 3, the imaging lens according to claim 2,
The radius of curvature of the cemented surface of the first positive lens and the first negative lens is r _S1, and the radius of curvature of the cemented surface of the second negative lens and the second positive lens is r _S2 , Let f _{A be} the focal length of the system,
Conditional expression:
−2.4 <r _S1 / f _A <−0.8
1.0 <r _S2 / f _A <2.6
By satisfying
Since a higher-performance imaging lens in which monochromatic aberration and chromatic aberration are corrected in a well-balanced manner can be provided, a higher-quality camera and a portable information terminal device can be realized.

According to invention of Claim 4, It is an imaging lens of any one of Claim 1 thru | or 3, Comprising:
The total length of the front second lens group is L _2F, and the distance from the most object side surface of the imaging lens to the image plane is L,
Conditional expression:
0.1 <L _2F /L<0.25
By being satisfied,
It is possible to provide a high-performance imaging lens in which each aberration is corrected more favorably. As a result, it is possible to realize a higher-quality camera and a portable information terminal device.
According to the invention described in claim 5, the imaging lens according to any one of claims 1 to 4,
The focal length of the entire system of the imaging lens is f _A, and the focal length of the first lens group is f ₁ ,
Conditional expression:
0.0 <f _A / f ₁ <0.8
By satisfying
It is possible to provide a higher-performance imaging lens with improved image plane flatness, etc. In addition, a higher-quality camera and portable information terminal device having a high resolution from the full aperture to the entire screen. Can be realized.

According to the invention described in claim 6, the imaging lens according to any one of claims 1 to 5,
The interval between the front first lens group and the rear first lens group is A _1F-1R, and the total length of the first lens group is L ₁ .
Conditional expression:
0.35 <A _1F-1R / L ₁ <0.7
By satisfying
It is possible to provide a higher-performance imaging lens that suppresses the occurrence of spherical aberration due to the increase in aperture, and in turn, a high-quality camera and portable information that can obtain a sharper image when the aperture is opened. A terminal device can be realized.

According to invention of Claim 7, It is an imaging lens of any one of Claim 1 thru | or 6, Comprising:
When the Abbe number of the first positive lens is ν _d and the anomalous dispersion of the first positive lens is Δθ _{g, F} , the anomalous dispersion Δθ _{g, F} is the Abbe number ν _d on the horizontal axis. , Partial dispersion ratio θ _{g, F} = ( _ng -n _F ) / (n _F -n _C ) In the graph with the vertical axis, glass type K7 (Ohara glass type name NSL7) and glass type F2 (Ohara glass type) when a straight line connecting the name PBM2) a standard line, means a deviation from a standard line of the glass type, g-line, F-line, the refractive index for the C line, _{respectively,} n _g, n F, as _{n C,}
Conditional expression:
ν _d > 80.0
Δθ _{g, F} > 0.025
By satisfying
It is possible to provide a higher-performance imaging lens with better chromatic aberration correction, and to realize higher-quality cameras and portable information terminal devices that do not bother color shift and color bleeding. Can do.

According to an eighth aspect of the present invention, in the imaging lens according to any one of the first to seventh aspects, the front first lens group has a convex surface facing two object sides. The negative meniscus lens is continuously arranged, and the image side surface of at least one of the lenses is aspheric.
It is possible to provide a higher-performance imaging lens that further suppresses the occurrence of aberrations, particularly corrects distortion aberrations, and even when photographing buildings etc., almost no distortion is felt. A higher-quality camera and a portable information terminal device can be realized.
According to the invention described in claim 9, in the imaging lens according to any one of claims 1 to 8, the rear second lens group is constituted by a single lens, By having an aspheric surface,
It is possible to provide a high-performance imaging lens that corrects coma better without adopting an unnecessarily complicated configuration, and as a result, a higher image quality that does not destroy the point image to the periphery. The camera and the portable information terminal device can be realized without increasing the size.

According to a tenth aspect of the present invention, in the imaging lens according to any one of the first to ninth aspects, the whole or a part of the second lens group is moved to move a finite distance object. By focusing on
An appropriate method for focusing on a finite distance object can be provided and the focus mechanism can be reduced in size, and thus a high-quality camera and a portable information terminal device can be realized more compactly. .
According to the invention described in claim 11, by having the imaging lens according to any one of claims 1 to 10 as a photographing optical system,
The half angle of view is as wide as about 38 degrees, and the F number is about 2.0 or less, but it is relatively small, with astigmatism, field curvature, lateral chromatic aberration, coma color difference, and distortion. Aberrations are sufficiently reduced to have resolution corresponding to an image sensor with 10 to 20 million pixels, and there is no distortion of the point image from the full aperture to the periphery of the angle of view with high contrast and brightness. Because it is possible to provide a small, high-quality camera that uses a high-performance imaging lens as a photographic optical system that does not cause unnecessary coloring even in large differences, and can draw straight lines without distortion as a straight line, The user can take a high-quality image with a camera having excellent portability.

According to the invention described in claim 12, by having the imaging lens according to any one of claims 1 to 10 as a photographing optical system of the camera function unit,
The half angle of view is as wide as about 38 degrees, and the F number is about 2.0 or less, but it is relatively small, and astigmatism, field curvature, lateral chromatic aberration, coma aberration color difference, and distortion. Aberrations are sufficiently reduced to have a resolution corresponding to an image sensor of 10 to 20 million pixels, and there is no distortion of the point image from the full aperture to the periphery of the angle of view with high contrast and brightness. A small, high-quality portable information terminal device that uses a high-performance imaging lens as a photographic optical system for the camera function unit that does not cause unnecessary coloring even in large differences, and can draw straight lines without distortion. Therefore, the user can take a high-quality image with a portable information terminal device excellent in portability and transmit the image to the outside.

It is sectional drawing which shows the structure of the imaging lens which concerns on the numerical Example 1 of this invention. It is sectional drawing which shows the structure of the imaging lens which concerns on numerical Example 2 of this invention. It is sectional drawing which shows the structure of the imaging lens which concerns on the numerical Example 3 of this invention. It is sectional drawing which shows the structure of the imaging lens which concerns on Numerical Example 4 of this invention. It is sectional drawing which shows the structure of the imaging lens which concerns on the numerical Example 5 of this invention. It is sectional drawing which shows the structure of the imaging lens which concerns on numerical Example 6 of this invention. It is sectional drawing which shows the structure of the imaging lens which concerns on numerical Example 7 of this invention. FIG. 3 is an aberration curve diagram of the imaging lens according to Numerical Example 1 of the present invention. FIG. 6 is an aberration curve diagram of an imaging lens according to Numerical Example 2 of the present invention. It is an aberration curve diagram of the imaging lens according to Numerical Example 3 of the present invention. FIG. 9 is an aberration curve diagram of an imaging lens according to Numerical Example 4 of the present invention. FIG. 10 is an aberration curve diagram of the imaging lens according to Numerical Example 5 of the present invention. FIG. 10 is an aberration curve diagram of the imaging lens according to Numerical Example 6 of the present invention. FIG. 10 is an aberration curve diagram of the imaging lens according to Numerical Example 7 of the present invention. It is the perspective view which looked at the external appearance structure of the camera which concerns on Example 8 of this invention from the object side, among these, (a) is the state in which the photographic lens is retracted in the camera body, (b) is FIG. 3 shows a state in which the photographing lens protrudes from the camera body. It is the perspective view seen from the photographer side which shows typically the external appearance structure of the camera of FIG. FIG. 16 is a block diagram schematically illustrating a functional configuration of the camera in FIG. 15.

Hereinafter, based on the embodiment and the example concerning the present invention, with reference to drawings, the imaging lens, camera, and personal digital assistant device of the present invention are explained in detail. Before describing specific embodiments and examples, the basic configuration of the present invention will be described first.
In general, a retrofocus type imaging lens like the present invention has a negative refractive power on the object side and a positive refractive power on the image side. Due to its asymmetry, distortion aberration and lateral chromatic aberration Etc. are likely to occur, and the reduction of these aberrations becomes a major issue. Further, with the increase in diameter, it becomes difficult to correct coma aberration and the color difference of coma aberration, and further problems are accumulated. The present invention has been found that these aberration correction problems can be solved by adopting the following configuration.
That is, in an imaging lens composed of a first lens group located on the object side with an aperture stop interposed therebetween and a second lens group located on the image side, the first lens group is arranged in order from the object side. A first lens group having a negative refractive power (positionally on the object side, but hereinafter referred to as “front side”) having a positive refractive power, with the widest air interval in the group as a boundary. A first lens group having a rear side (positionally on the image side, but hereinafter referred to as “rear side”), and a second lens group in order from the object side. The first positive lens includes a front second lens group in which a negative lens, a second negative lens, and a second positive lens are continuously arranged, and a rear second lens group including at least one lens. And the first negative lens, the second negative lens and the second positive lens are in close contact with each other. Body is bonded to, and so as to satisfy the following condition (corresponding to claim 1).

62.0 <ν _dp1 <98.0
20.0 <ν _dn1 <45.0
20.0 <ν _dn2 <45.0
35.0 <ν _dp2 <98.0
20.0 <ν _dn1 −ν _dn2 <15.0
Where ν _dp1 is the Abbe number of the first positive lens, ν _dn1 is the Abbe number of the first negative lens, ν _dn2 is the Abbe number of the second negative lens, and ν _dp2 is the Abbe number of the second positive lens.
First, in the imaging lens of the present invention, it can be considered that the first lens group plays a role like a wide converter added to the second lens group. Here, the first lens group is configured such that a negative refractive power (front first lens group) and a positive refractive power (rear first lens group) are arranged in this order from the object side, and the interval therebetween. By taking a relatively large value, it is possible to secure both a sufficient angle of view and correction of various aberrations including spherical aberration. Here, the rear first lens group faces the front second lens group with the aperture stop in between, and a coma aberration is controlled by a balance of positive refractive powers of both. is there.

The most characteristic of the present invention is the role and configuration of the front second lens group. In the imaging lens according to the present invention, the front second lens group has a main imaging function and can be said to be the most important lens group in terms of aberration correction. Here, the front second lens group is based on a so-called triplet having a positive, negative, and positive refractive power arrangement, but the central negative refractive power is divided into two, and positive, negative, negative, A positive four-sheet configuration was adopted. Since the aperture stop is disposed on the object side of the front second lens group, the first positive lens, the first negative lens pair, the second negative lens, the second positive lens pair, However, the height of off-axis rays is different, and this can be used to effectively reduce both axial chromatic aberration and lateral chromatic aberration. Furthermore, the color difference of coma aberration can be reduced by utilizing the degree of freedom of the second negative lens.
The conditional expression is for satisfactorily correcting various chromatic aberrations. When ν _dp1 is 62 or less or ν _dn1 is 45 or more, axial chromatic aberration and, secondarily, lateral chromatic aberration are insufficiently corrected. On the other hand, the condition that ν _dp1 is 98 or more or ν _dn1 is 20 or less is not practical because there is no optical material that can be used or even if it is present. When [nu _dn2 45 or greater or [nu _dp2 is 35 or less, mainly lateral chromatic aberration, secondary to the unfavorably axial chromatic aberration sufficiently corrected. On the other hand, the condition that ν _dn2 is 20 or less or ν _dp2 is 98 or more is not practical because there is no optical material that can be used or even if it is present. Further, the difference in Abbe number between the first negative lens and the second negative lens; (ν _dn1 −ν _dn2 ) is set in the range of more than −20.0 and less than 15.0, whereby the color difference of coma aberration Can be sufficiently reduced.

More preferably, each of the following conditional expressions should be satisfied.
67.0 <ν _dp1 <85.0
20.0 <ν _dn1 <40.0
20.0 <ν _dn2 <40.0
40.0 <ν _dp2 <85.0
−15.0 <ν _dn1 −ν _dn2 <10.0
The rear second lens group serves to balance aberrations and control the exit pupil distance. Needless to say, having positive refracting power is effective in securing the exit pupil distance, but if the exit pupil distance can be short, giving negative refracting power contributes to shortening the overall lens length. It is also possible.
According to the configuration of the imaging lens of the present invention, as described above, it is possible to obtain a great effect on aberration correction, a wide angle of about half a field angle of about 38 degrees, and a large aperture of about F number of about 2.0 or less. Even under such severe conditions, extremely high image performance can be achieved.
In the front second lens group, it is desirable that the first positive lens and the first negative lens, and the second negative lens and the second positive lens are closely and integrally joined. 2).

In each lens surface in the front second lens group, in order to reduce the final aberration amount, each aberration is greatly exchanged, and the manufacturing error sensitivity tends to be high. By joining the first positive lens and the first negative lens, and the second negative lens and the second positive lens, the substantial manufacturing error sensitivity is reduced, and stable performance is easily obtained. It also leads to a reduction in the parts of the lens barrel that actually holds the lens.
Note that the chromatic aberration correction in the rear second lens group is mainly performed to correct axial chromatic aberration in the pair of the first positive lens and the first negative lens close to the aperture stop, and away from the aperture stop. This is a design concept in which a pair of the second negative lens and the second positive lens mainly has a role of correcting lateral chromatic aberration. When the first positive lens and the first negative lens, and the second negative lens and the second positive lens are cemented, the cemented surfaces of the first positive lens and the first negative lens are convex on the image side. The cemented surface of the second negative lens and the second positive lens is preferably convex toward the object side, so that the entire chromatic aberration can be corrected more effectively.

It is desirable that the front second lens group having the above-described configuration satisfy the following conditional expression (corresponding to claim 3).
−2.4 <r _S1 / f _A <−0.8
1.0 <r _S2 / f _A <2.6
Where r _S1 is the radius of curvature of the cemented surface of the first positive lens and the first negative lens, r _S2 is the radius of curvature of the cemented surface of the second negative lens and the second positive lens, and f _A is It represents the focal length of the entire imaging lens system.
The conditional expression is for correcting the chromatic aberration in a well-balanced manner while keeping the monochromatic aberration sufficiently small. When r _S1 / f _A is −2.4 or less or r _S2 / f _A is 2.6 or more, spherical aberration is insufficiently corrected when chromatic aberration correction is prioritized, or introverted coma remains. It is not preferable. On the other hand, when r _S1 / f _A is −0.8 or more or r _S2 / f _A is 1.0 or less, spherical aberration is overcorrected when chromatic aberration correction is prioritized, or outward coma is It is not preferable because it remains.

The front second lens group preferably satisfies the following conditional expression (corresponding to claim 4).
0.1 <L _2F /L<0.25
Here, L _2F represents the total length of the front second lens group, and L represents the distance from the most object-side surface of the imaging lens to the image plane.
As a mechanism that enables both axial chromatic aberration and lateral chromatic aberration to be effectively reduced, the aperture stop is disposed on the object side of the front second lens group, so that the first positive lens, As described above, the first negative lens pair, the second negative lens, and the second positive lens pair utilize the fact that the height of the off-axis ray is different. The total length of the front second lens group for the mechanism to work most effectively is regulated. When L _2F / L is 0.1 or less, the difference in height of off-axis rays in the front second lens group becomes small, the above-described mechanism becomes difficult to work, and correction of chromatic aberration is not possible. May be enough. On the other hand, if L _2F / L is 0.25 or more, the front second lens group unnecessarily occupies space, and the relationship with other lens groups is lost, so that field curvature and astigmatism There is a risk that coma may not be balanced.

For better aberration correction, the following conditional expression should be satisfied.
0.1 <L _2F /L<0.2
The refractive power arrangement of the entire imaging lens preferably satisfies the following conditional expression (corresponding to claim 5).
0.0 <f _A / f ₁ <0.8
Here, f _A represents the focal length of the entire imaging lens system, and f ₁ represents the focal length of the first lens group.
In the imaging lens of the present invention, it has been described above that the first lens group can be considered to play a role like a wide converter added to the second lens group. Above, it is not best that the first lens group be completely afocal. If f _A / f ₁ is 0.0 or less, the refractive power of the second lens group has to be increased, and the curvature of the image surface becomes large, or negative distortion is likely to occur greatly. It is not preferable. On the other hand, if f _A / f ₁ is 0.8 or more, the contribution of the second lens group to the image forming action is reduced, and it is difficult to realize the concept of aberration correction as described above. A relatively large aberration occurs in the first lens group, and the manufacturing error sensitivity increases more than necessary, which is not preferable.

For better aberration correction, the following conditional expression should be satisfied.
0.0 <f _A / f ₁ <0.7
Among these, the most desirable range is to satisfy the following conditional expression.
0.0 <f _A / f ₁ <0.4
The first lens group preferably satisfies the following conditional expression (corresponding to claim 6).
0.35 <A _1F-1R / L ₁ <0.7
However, A _1F-1R is a spacing between the rear side first lens group and the front-side first lens group, L ₁ represents the full length of the first lens group.
For better aberration correction, it is preferable to appropriately set the distance between the front first lens group and the rear first lens group. If A _1F-1R / L ₁ is 0.35 or less, the spherical aberration is likely to be undercorrected, and if A _1F-1R / L ₁ is 0.7 or more, the correction tends to be overcorrected. It is not preferable.

It is desirable that the material of the first positive lens satisfies the following conditional expression (corresponding to claim 7).
ν _d > 80.0
Δθ _{g, F} > 0.025
Where ν _d is the Abbe number of the first positive lens, and Δθ _{g, F} is the anomalous dispersion of the first positive lens.
Here, anomalous dispersion [Delta] [theta] _g, and _F, graph the Abbe number [nu _d horizontal axis, the partial dispersion ratio theta _{g, F} = a _{(n g -n F) / (} n F -n C) and the vertical axis , The deviation from the standard line of the glass type when the straight line connecting the glass type K7 (Ohara Glass Type Name NSL7) and the glass type F2 (Ohara Glass Type Name PBM2) is used as the standard line. _{Incidentally,} n _g, n F, _{n C,} respectively, g-line, F-line, the refractive index for the C line.
By configuring the first positive lens with so-called special low dispersion glass that satisfies this conditional expression, it is possible to effectively reduce the secondary spectrum of chromatic aberration and realize a better correction state. .

It is desirable that the front first lens group has a configuration in which two negative meniscus lenses having convex surfaces facing the object side are continuously arranged, and at least one of the lenses has an aspheric image side surface. (Corresponding to claim 8).
By dividing the negative refractive power of the front first lens group into two meniscus lenses and preventing excessive aberrations from occurring on specific surfaces, the entire lens system can be corrected more appropriately for astigmatism. it can. Further, by making the image side surface having a large curvature an aspherical surface, a large effect can be obtained in correcting distortion, and a role of correcting coma aberration and the like can be provided.
The rear second lens group is preferably composed of a single lens and has an aspherical surface (corresponding to claim 9).
Since the front second lens group has a sufficient degree of freedom, a simple configuration is sufficient for the rear second lens group, and it is appropriate to use one lens for miniaturization. . In addition, by providing an aspherical surface in the rear second lens group, coma aberration can be corrected mainly better.
The aspheric surfaces of the front first lens group and the rear second lens group complement each other in the role of aberration correction and work more effectively, so it is desirable to provide them simultaneously.

In the imaging lens according to the present invention, focusing on a finite distance object can be performed by moving all or part of the second lens group (corresponding to claim 10).
According to such a focusing method, the weight of the moving portion can be reduced compared to a method in which the entire imaging lens is moved for focusing, which is advantageous for speeding up focusing and power saving. In addition, when the imaging lens according to the present invention is incorporated in a camera as a photographing optical system, the second lens is provided when the lens group has a mechanism for shortening the distance between the lens groups and the back focus portion when not in use and storing them in a compact manner. The storage mechanism for the group can be shared with the focusing mechanism, which is convenient.

Next, specific examples based on the above-described embodiment of the present invention will be described in detail.
Examples 1 to 7 described below are also embodiments of the imaging lens according to the present invention, and also show examples of specific configurations based on specific numerical examples.
Embodiments of a camera and a portable information terminal device according to the present invention using an imaging lens as shown in Examples 1 to 7 as a photographing optical system will be described later with reference to FIGS.
Specific examples of the imaging lens of the present invention are shown below. In all the examples, the maximum image height is 4.80 mm.
In each embodiment, the parallel plate MF disposed on the image plane side of the rear second lens group 2R is made of various filters such as an optical low-pass filter and an infrared cut filter, and a cover glass of a light receiving element such as a CCD sensor ( Seal glass).
The aberration in each example is corrected at a high level, and the spherical aberration and the axial chromatic aberration are so small that they do not cause a problem. Astigmatism, curvature of field, and lateral chromatic aberration are sufficiently small, coma and disturbance of the color difference are well suppressed to the outermost periphery, and distortion aberration is 2.0% or less in absolute value. By constructing an imaging lens as in the present invention, a very wide image with a half angle of view of about 38 degrees and an F number of about 2.0 or less ensures a very good image performance. It is clear from the examples that this can be done.

The meanings of the symbols in this embodiment are as follows.
f: focal length of the image forming lens system F: 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 following Aspheric coefficient A ₆ : 6th-order aspheric coefficient A ₈ : 8th-order aspheric coefficient A ₁₀ : 10th-order aspheric coefficient where the reciprocal of the paraxial radius of curvature (paraxial curvature) is C, When the height is H, the amount of displacement in the optical axis direction from the surface vertex is X, the aspheric coefficient is A _2i , and the aspheric surface is defined by the following equation.

FIG. 1 shows the configuration of an imaging lens according to Example 1 of the present invention, and schematically shows a longitudinal section along the optical axis.
The optical system shown in FIG. 1 has, in order from the object side to the image surface, a first lens E1 composed of a negative meniscus negative lens having a convex surface facing the object side, and a strong concave surface formed with an aspheric surface on the image surface side. The second lens E2 made of a negative meniscus negative lens, the third lens E3 that is a biconvex positive lens, the aperture stop FA, the fourth lens E4 that is a biconvex positive lens, and the negative meniscus negative. A cemented lens obtained by closely bonding a fifth lens E5 that is a lens, a sixth lens E6 that is a negative meniscus negative lens, and a seventh lens E7 that is a biconvex positive lens are closely bonded. A cemented lens and an eighth lens E8, which is a negative meniscus negative lens having an aspheric surface on the object side, are arranged.
The first lens E1 to the third lens E3 constitute the first lens group G1, and the fourth lens E4 to the eighth lens E8 constitute the second lens group G2.
In the first lens group G1, the front first lens group 1F is constituted by the first lens E1 and the second lens E2 which are located on the object side having negative refractive power with the widest air interval as a boundary, The third lens E3 located on the image side having positive refractive power constitutes the rear first lens group 1R.

The second lens group G2 includes, in order from the object side, a fourth lens E4 as a first positive lens, a fifth lens E5 as a first negative lens, a sixth lens E6 as a second negative lens, and a second positive lens. The seventh lens E7 as a lens constitutes the front second lens group 2F, and the eighth lens E8 constitutes the rear second lens group 2R. In the imaging lens L1, the whole or part of the second lens group G2 is moved to perform focusing on a finite distance object.
For example, in an imaging lens of a camera that uses a solid-state image sensor such as a CCD image sensor, such as a digital still camera, a low-pass filter or an infrared cut filter is provided between the final surface of the eighth lens E8 and the image plane FS. It constitutes at least one of cover glass (hereinafter referred to as “optical filter FS”) for protecting the light receiving surface of the filter and the CCD image pickup device.
In FIG. 1, surface numbers of the respective optical surfaces are also given. Each reference numeral for FIG. 1 is used independently for each example (embodiment) in order to avoid complicating the description. Therefore, even if a common reference numeral is attached, it is common to other embodiments. It is not a configuration of.
FIG. 8 is an aberration curve diagram showing the respective aberration characteristics of spherical aberration, astigmatism, distortion and coma aberration of the imaging lens according to Example 1 of the present invention shown in FIG.
In Example 1, the focal length f = 6.00 mm, the F number = 1.92, and the half angle of view ω = 39.0 °. The characteristics of each optical surface are as shown in the following table.

In Table 1, each optical surface of the fourth surface and the fourteenth surface with an asterisk “*” attached to the surface number is an aspheric surface, and the parameters in the equations for each aspheric surface are as follows.
Aspheric surface; 4th surface
K = -0.82391, A ₄ = 1.51453 × 10 ^-4 , A ₆ = -8.03748 × 10 ^-6 , A ₈ = 2.33697 × 10 ^-7 , A ₁₀ = -1.16222 × 10 ^-8
Aspheric surface: 14th surface
K = -26.92849, A ₄ = 9.33931 × 10 ^-5 , A ₆ = -1.79865 × 10 ^-5 , A ₈ = 3.06532 × 10 ^-7 , A ₁₀ = -3.57164 × 10 ^-9
In addition, each numerical value related to the conditional expression described in the first embodiment is as follows.
Conditional expression numerical value:
ν _dp1 = 81.54
ν _dn1 = 26.29
ν _dn2 = 28.46
ν _dp2 = 54.82
ν _dn1 −ν _dn2 = −2.17
r _S1 / f _A = −1.36
r _S2 / f _A = 1.76
L _2F /L=0.164
f _A / f ₁ = 0.192
A _1F-1R / L ₁ = 0.580
Accordingly, the numerical values related to the conditional expressions of the present invention described in the first embodiment are all within the range of the conditional expressions.

FIG. 8 is an aberration curve diagram showing each aberration characteristic of each aberration spherical aberration, astigmatism, distortion aberration and coma aberration of the imaging lens L1 of the present invention shown in FIG. 1 according to Example 1 described above.
In each aberration curve, a broken line in spherical aberration represents a sine condition, a solid line in astigmatism represents sagittal, and a broken line represents meridional.
According to the imaging lens L1 having the configuration shown in FIG. 1 according to the first embodiment of the present invention described above, the aberration is corrected at a high level as shown in FIG. 8, and spherical aberration and longitudinal chromatic aberration are problematic. Small enough not to become. Astigmatism, curvature of field, and lateral chromatic aberration are sufficiently small, coma and disturbance of the color difference are well suppressed to the outermost periphery, and distortion aberration is 2.0% or less in absolute value. By forming the imaging lens L1 as in Example 1 according to the present invention, the half angle of view is as wide as about 39 degrees, and the F number is about 1.92 or less, but the aperture is very large. It is clear that good image performance can be ensured.

FIG. 2 shows the configuration of the imaging lens according to Example 2 of the present invention, and schematically shows a longitudinal section along the optical axis.
The imaging lens L2 shown in FIG. 2 includes, in order from the object side to the image surface, a first lens E1 composed of a negative meniscus negative lens having a convex surface facing the object side, and a strong concave surface forming an aspheric surface. A second lens E2 composed of a negative meniscus negative lens toward the side, a cemented lens formed by closely bonding a third lens E3, which is a biconvex positive lens, and a negative meniscus negative lens E4, and an aperture A stop lens, a cemented lens obtained by closely bonding a fifth lens E5, which is a biconvex positive lens, and a sixth lens E6, which is a negative meniscus negative lens, and a seventh lens which is a biconcave negative lens. A cemented lens obtained by closely bonding a lens E7 and an eighth lens E8, which is a biconvex positive lens, a biconvex positive lens having a strong convex surface on the image side and an aspheric surface on the object side It has a configuration in which the ninth lens E9 is arranged at.
The first lens E1 to the fourth lens E4 constitute the first lens group G1, and the fifth lens E5 to the ninth lens E9 constitute the second lens group G2.

In the first lens group G1, the front first lens group 1F is composed of a first lens E1 and a second lens E2 which are located on the object side (front side) having negative refractive power with the widest air interval as a boundary. The rear first lens group 1R is configured by the third lens E3 and the fourth lens E4 that are configured and located on the image surface side (rear side) having positive refractive power.
Further, in the second lens group G2, in order from the object side, a fifth lens E5 as a first positive lens, a sixth lens E6 as a first negative lens, a seventh lens E7 as a second negative lens, and a second positive lens. The eighth lens E8 as a lens constitutes the front second lens group 2F, and the ninth lens E9 constitutes the rear second lens group 2R. In the imaging lens L2, the whole or part of the second lens group G2 is moved to perform focusing on a finite distance object.
For example, in an imaging lens of a camera that uses a solid-state imaging device such as a CCD imaging device, such as a digital still camera, a low-pass filter or an infrared cut is provided between the final surface of the ninth lens E9 and the image plane FS. It constitutes at least one of cover glass (hereinafter referred to as “optical filter MF”) for protecting the filter and the light receiving surface of the CCD image sensor.

In FIG. 2, the surface number of each optical surface is also given. Each reference numeral for FIG. 2 is used independently for each example (embodiment) in order to avoid complicating the description. Therefore, even if a common reference numeral is attached, it is common to other embodiments. It is not a configuration.
FIG. 9 is an aberration curve diagram showing the respective aberration characteristics of spherical aberration, astigmatism, distortion and coma aberration of the imaging lens according to Example 2 of the present invention shown in FIG.
In Example 2, the focal length f = 5.90 mm, the F number = 2.04, and the half angle of view ω = 39.2 °. The characteristics of each optical surface are as shown in the following table.

In Table 2, each optical surface of the fourth surface and the fifteenth surface with an asterisk “*” attached to the surface number is an aspheric surface, and parameters in the respective aspheric surface equations are as follows.
Aspheric surface; 4th surface
K = -0.41935, A ₄ = -5.42080 × 10 ^-5 , A ₆ = -2.48263 × 10 ^-5 , A ₈ = 7.57412 × 10 ^-7 , A ₁₀ = -2.30755 × 10 ^-8
Aspheric surface: 15th surface
K = 0.0, A ₄ = -3.94481 × 10 ^-4 , A ₆ = 7.14419 × 10 ^-7 , A ₈ = 6.43089 × 10 ^-8 , A ₁₀ = -2.58953 × 10 ^-9
In addition, each numerical value related to the conditional expression described in the second embodiment is as follows.

Conditional expression numerical value:
ν _dp1 = 81.54
ν _dn1 = 31.07
ν _dn2 = 29.52
ν _dp2 = 42.71
ν _dn1 −ν _dn2 = 1.55
r _S1 / f _A = −1.16
r _S2 / f _A = 2.17
L _2F /L=0.143
f _A / f ₁ = 0.604
A _1F-1R / L ₁ = 0.628
Therefore, the numerical values related to the conditional expressions of the present invention described in the second embodiment are all within the range of the conditional expressions.

FIG. 9 is an aberration curve diagram showing the respective aberration characteristics of spherical aberration, astigmatism, distortion and coma aberration of the imaging lens L2 of the present invention shown in FIG. 2 according to Example 2 described above.
In each aberration curve diagram, a broken line in spherical aberration represents a sine condition, a solid line in astigmatism represents sagittal, and a broken line represents meridional.
According to the imaging lens L2 having the configuration shown in FIG. 2 according to the second embodiment of the present invention described above, the aberration is corrected at a high level as shown in FIG. Small enough not to become. Astigmatism, curvature of field, and lateral chromatic aberration are sufficiently small, coma and disturbance of the color difference are well suppressed to the outermost periphery, and distortion aberration is 2.0% or less in absolute value. By forming the imaging lens L2 as in Example 2 according to the present invention, the half angle of view is as wide as 39 degrees and the F number is as large as about 2.04 or less. It is clear that good image performance can be ensured.

FIG. 3 shows a configuration of an imaging lens according to Example 3 of the present invention, and schematically shows a longitudinal section along the optical axis.
The imaging lens L3 shown in FIG. 3 includes, in order from the object side to the image surface, a first lens E1 composed of a negative meniscus negative lens having a convex surface facing the object side, and a strong concave surface forming an aspheric surface. A second lens E2 composed of a negative meniscus negative lens facing the side, a third lens E3 that is a biconvex positive lens, an aperture stop FA, a fourth lens E4 that is a biconvex positive lens, and a negative meniscus type A cemented lens obtained by closely bonding a fifth lens E5 that is a negative lens, a sixth lens E6 that is a negative meniscus negative lens, and a seventh lens E7 that is a biconvex positive lens. The eighth lens E8, which is a positive meniscus type positive lens having a strong convex surface facing the object side and an aspherical surface, is disposed.

The first lens E1 to the third lens E3 constitute the first lens group G1, and the fourth lens E4 to the eighth lens E8 constitute the second lens group G2.
In the first lens group G1, the front first lens group 1F is composed of a first lens E1 and a second lens E2 that are located on the object side (front side) having negative refractive power with the widest air interval as a boundary. The rear first lens group 1R is configured by the third lens E3 that is configured and located on the image surface side (rear side) having positive refractive power.
The second lens group G2 includes, in order from the object side, a fourth lens E4 as a first positive lens, a fifth lens E5 as a first negative lens, a sixth lens E6 as a second negative lens, and a second positive lens. The seventh lens E7 as a lens constitutes the front second lens group 2F, and the eighth lens E8 constitutes the rear second lens group 2R. In the imaging lens L3, the whole or a part of the second lens group G2 is moved to perform focusing on a finite distance object.
For example, in an imaging lens of a camera that uses a solid-state imaging device such as a CCD imaging device, such as a digital still camera, a low-pass filter or an infrared cut is provided between the final surface of the eighth lens E8 and the image surface FS. It constitutes at least one of cover glasses (hereinafter referred to as “optical filter MF”) for protecting the filter and the light receiving surface of the CCD image sensor.

In FIG. 3, surface numbers of the respective optical surfaces are also given. Each reference numeral with respect to FIG. 3 is used independently for each example (embodiment) in order to avoid complication of the explanation. Therefore, even if a common reference numeral is attached, it is common to other embodiments. It is not a configuration.
FIG. 10 is an aberration curve diagram showing respective aberration characteristics of spherical aberration, astigmatism, distortion and coma aberration of the imaging lens according to Example 3 of the present invention shown in FIG.
In Example 3, the focal length f is 6.00 mm, the F number is 1.95, and the half angle of view ω is 39.1 °. The characteristics of each optical surface are as shown in the following table.

In Table 3, the optical surfaces of the fourth surface, the sixth surface, and the fourteenth surface with an asterisk “*” attached to the surface number are aspherical surfaces, and the parameters in the respective aspherical expressions are as follows.
Aspheric surface; 4th surface
K = -0.82391, A ₄ = 7.26169 × 10 ^-5 , A ₆ = -5.10959 × 10 ^-6 , A ₈ = 4.38244 × 10 ^-8 , A ₁₀ = -6.97612 × 10 ^-9
Aspheric surface; 6th surface
K = 0.0, A ₄ = 2.05935 × 10 ^-5 , A ₆ = -1.04777 × 10 ^-6 , A ₈ = 8.84156 × 10 ^-8 , A ₁₀ = -2.25119 × 10 ^-9
Aspheric surface: 14th surface
K = -26.92849, A ₄ = 5.11073 × 10 ^-4 , A ₆ = -2.92185 × 10 ^-5 , A ₈ = 7.49033 × 10 ^-7 , A ₁₀ = -1.06280 × 10 ^-8
In addition, each numerical value related to the conditional expression described in the third embodiment is as follows.

Conditional expression numerical value:
ν _dp1 = 81.54
ν _dn1 = 27.79
ν _dn2 = 30.13
ν _dp2 = 65.44
ν _dn1 −ν _dn2 = −2.34
r _S1 / f _A = −1.50
r _S2 / f _A = 1.66
L _2F /L=0.142
f _A / f ₁ = 0.243
A _1F-1R / L ₁ = 0.637
Accordingly, the numerical values related to the conditional expressions of the present invention described in the third embodiment are all within the range of the conditional expressions.

FIG. 10 is an aberration curve diagram showing the respective aberration characteristics of spherical aberration, astigmatism, distortion and coma aberration of the imaging lens L3 of the present invention shown in FIG. 3 according to Example 3 described above.
In each aberration curve diagram, a broken line in spherical aberration represents a sine condition, a solid line in astigmatism represents sagittal, and a broken line represents meridional.
According to the imaging lens L3 having the configuration shown in FIG. 3 according to the third embodiment of the present invention described above, the aberration is corrected at a high level as shown in FIG. 10, and spherical aberration and axial chromatic aberration are problematic. Small enough not to become. Astigmatism, curvature of field, and lateral chromatic aberration are sufficiently small, coma and disturbance of the color difference are well suppressed to the outermost periphery, and distortion aberration is 2.0% or less in absolute value. By forming the imaging lens L3 as in Example 3 according to the present invention, the half angle of view is as wide as 39 degrees, and the F number is as large as about 1.95 or less. It is clear that good image performance can be ensured.

FIG. 4 shows a configuration of an imaging lens according to Example 4 of the present invention, and schematically shows a longitudinal section along the optical axis.
The imaging lens L4 shown in FIG. 4 includes, in order from the object side to the image surface, a first lens E1 composed of a negative meniscus negative lens having a convex surface facing the object side, and a strong concave surface formed with an aspheric surface. A second lens E2 composed of a negative meniscus negative lens facing the side, a third lens E3 which is a positive meniscus type positive lens, a fourth lens E4 which is a biconvex positive lens, an aperture stop FA, a biconvex type A fifth lens E5 which is a positive lens and a sixth lens E6 which is a negative meniscus negative lens are closely bonded together, a seventh lens E7 which is a negative meniscus negative lens and a positive meniscus type A cemented lens obtained by closely bonding an eighth lens E8, which is a positive lens, and a biconvex positive lens in which a strong convex surface is directed to the object side and an aspheric surface is formed on the object side. And it has a configuration of arranging the ninth lens E9.
The first lens E1 to the fourth lens E4 constitute the first lens group G1, and the fifth lens E5 to the ninth lens E9 constitute the second lens group G2.

In the first lens group G1, the first lens E1, the second lens E2, and the third lens E3 located on the object side (front side) having negative refractive power with the widest air interval as a boundary, The first lens group 1R is configured, and the rear first lens group 1R is configured by the fourth lens E4 positioned on the image plane side (rear side) having a positive refractive power.
The second lens group G2 includes, in order from the object side, a fifth lens E5 as a first positive lens, a sixth lens E6 as a first negative lens, a seventh lens E7 as a second negative lens, and a second positive lens. The eighth lens E8 as a lens constitutes the front second lens group 2F, and the ninth lens E9 constitutes the rear second lens group 2R. In the imaging lens L4, the whole or part of the second lens group G2 is moved to perform focusing on a finite distance object.
For example, in an imaging lens of a camera that uses a solid-state imaging device such as a CCD imaging device, such as a digital still camera, a low-pass filter or an infrared cut is provided between the final surface of the ninth lens E9 and the image plane FS. It constitutes at least one of cover glass (hereinafter referred to as “optical filter MF”) for protecting the filter and the light receiving surface of the CCD image sensor.

In FIG. 4, the surface number of each optical surface is also given. Each reference numeral with respect to FIG. 4 is used independently for each example (embodiment) in order to avoid complication of explanation, and therefore, even if a common reference numeral is attached, it is common to other embodiments. It is not a configuration of.
FIG. 11 is an aberration curve diagram showing the respective aberration characteristics of spherical aberration, astigmatism, distortion and coma aberration of the imaging lens according to Example 4 of the present invention shown in FIG.
In Example 4, the focal length f = 6.00 mm, the F number = 1.96, and the half angle of view ω = 39.1 °. The characteristics of each optical surface are as shown in the following table.

In Table 4, each optical surface of the fourth surface and the sixteenth surface with an asterisk “*” attached to the surface number is an aspheric surface, and the parameters in the respective aspheric surface equations are as follows.
Aspheric surface; 4th surface
K = -0.40687, A ₄ = -3.60864 × 10 ^-4 , A ₆ = -2.38402 × 10 ^-5 , A ₈ = 6.28983 × 10 ^-7 , A ₁₀ = -2.42525 × 10 ^-8
Aspherical surface: 16th surface
K = 0.0, A ₄ = -4.01894 × 10 ^-4 , A ₆ = 3.25574 × 10 ^-6 , A ₈ = -2.41480 × 10 ^-7 , A ₁₀ = 3.20689 × 10 ^-9
In addition, each numerical value related to the conditional expression described in the fourth embodiment is as follows.

Conditional expression numerical value:
ν _dp1 = 81.54
ν _dn1 = 34.71
_νdn2 = 27.51
ν _dp2 = 81.54
ν _dn1 −ν _dn2 = 7.20
r _S1 / f _A = −1.68
r _S2 / f _A = 1.33
L _2F /L=0.154
f _A / f ₁ = 0.183
A _1F-1R / L ₁ = 0.424
Therefore, the numerical values related to the conditional expressions of the present invention described in the fourth embodiment are all within the range of the conditional expressions.

FIG. 11 is an aberration curve diagram showing the respective aberration characteristics of spherical aberration, astigmatism, distortion and coma aberration of the imaging lens L4 of the present invention shown in FIG. 4 according to Example 4 described above.
In each aberration curve diagram, a broken line in spherical aberration represents a sine condition, a solid line in astigmatism represents sagittal, and a broken line represents meridional.
According to the imaging lens L4 having the configuration shown in FIG. 4 according to the fourth embodiment of the present invention described above, the aberration is corrected at a high level as shown in FIG. 11, and spherical aberration and longitudinal chromatic aberration are problematic. Small enough not to become. Astigmatism, curvature of field, and lateral chromatic aberration are sufficiently small, coma and disturbance of the color difference are well suppressed to the outermost periphery, and distortion aberration is 2.0% or less in absolute value. By forming the imaging lens L4 as in Example 4 according to the present invention, the half angle of view is as wide as 39 degrees and the F number is as large as about 1.96 or less. It is clear that good image performance can be ensured.

FIG. 5 shows a configuration of an imaging lens according to Example 5 of the present invention, and schematically shows a longitudinal section along the optical axis.
An imaging lens L5 shown in FIG. 5 includes, in order from the object side to the image surface, a first lens E1 composed of a negative meniscus negative lens having a convex surface directed toward the object side, and a strong concave surface formed with an aspheric surface. A second lens E2 composed of a negative meniscus negative lens toward the side, a third lens E3 which is a biconvex positive lens, a fourth lens E4 which is a biconvex positive lens, an aperture stop FA, a biconvex type A fifth lens E5 which is a positive lens and a sixth lens E6 which is a negative meniscus negative lens are closely bonded together, a seventh lens E7 which is a negative meniscus negative lens and a positive meniscus type A positive meniscus type positive lens in which a strong convex surface is directed to the object side and an aspheric surface is formed on the object side. And it has a configuration of arranging the ninth lens E9.

  The first lens E1 to the fourth lens E4 constitute the first lens group G1, and the fifth lens E5 to the ninth lens E9 constitute the second lens group G2.

In the first lens group G1, the first lens E1, the second lens E2, and the third lens E3, which are located on the object side (front side) with the widest air interval as a boundary, have a negative refractive power. The first lens group 1 </ b> F is configured, and the rear first lens group 1 </ b> R is configured by the fourth lens E <b> 4 positioned on the image plane side (rear side) having a positive refractive power.
The second lens group G2 includes, in order from the object side, a fifth lens E5 as a first positive lens, a sixth lens E6 as a first negative lens, a seventh lens E7 as a second negative lens, and a second positive lens. The eighth lens E8 as a lens constitutes the front second lens group 2F, and the ninth lens E9 constitutes the rear second lens group 2R. In the imaging lens L5, the whole or part of the second lens group G2 is moved to perform focusing on a finite distance object.
For example, in an imaging lens of a camera that uses a solid-state imaging device such as a CCD imaging device, such as a digital still camera, a low-pass filter or an infrared cut is provided between the final surface of the ninth lens E9 and the image plane FS. It constitutes at least one of cover glass (hereinafter referred to as “optical filter MF”) for protecting the filter and the light receiving surface of the CCD image sensor.

In FIG. 5, surface numbers of the respective optical surfaces are also given. Each reference numeral with respect to FIG. 5 is used independently for each example (embodiment) in order to avoid complication of explanation, and therefore, even if a common reference numeral is attached, it is common to other embodiments. It is not a configuration of.
12 is an aberration curve diagram showing the respective aberration characteristics of spherical aberration, astigmatism, distortion and coma aberration of the imaging lens according to Example 5 of the present invention shown in FIG.
In the fifth embodiment, the focal length f = 6.00 mm, the F number = 1.95, and the half angle of view ω = 39.1 °. The characteristics of each optical surface are as shown in the following table.

In Table 5, each optical surface of the fourth surface and the sixteenth surface with an asterisk “*” attached to the surface number is an aspheric surface, and the parameters in the equations for each aspheric surface are as follows.
Aspheric surface; 4th surface
K = -0.85535, A ₄ = 3.24166 × 10 ^-6 , A ₆ = -2.56520 × 10 ^-6 , A ₈ = -3.63511 × 10 ^-8 , A ₁₀ = -1.39606 × 10 ^-9
Aspherical surface: 16th surface
K = 0.0, A ₄ = -3.27966 × 10 ^-4 , A ₆ = 3.00723 × 10 ^-6 , A ₈ = -2.59822 × 10 ^-7 , A ₁₀ = 4.26578 × 10 ^-9
In addition, each numerical value related to the conditional expression described in the fifth embodiment is as follows.

Conditional expression numerical value:
ν _dp1 = 81.54
ν _dn1 = 29.23
ν _dn2 = 23.78
ν _dp2 = 81.54
ν _dn1 −ν _dn2 = 5.45
r _S1 / f _A = -1.91
r _S2 / f _A = 1.33
L _2F /L=0.132
f _A / f ₁ = 0.238
A _1F-1R / L ₁ = 0.469
Therefore, the numerical values related to the conditional expressions of the present invention described in the fifth embodiment are all within the range of the conditional expressions.

FIG. 12 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration characteristics of the imaging lens L5 of the present invention shown in FIG. 5 according to Example 5 described above.
In each aberration curve diagram, a broken line in spherical aberration represents a sine condition, a solid line in astigmatism represents sagittal, and a broken line represents meridional.
According to the imaging lens L5 having the configuration shown in FIG. 5 according to the fifth embodiment of the present invention described above, the aberration is corrected at a high level as shown in FIG. 12, and spherical aberration and axial chromatic aberration are problematic. Small enough not to become. Astigmatism, curvature of field, and lateral chromatic aberration are sufficiently small, coma and disturbance of the color difference are well suppressed to the outermost periphery, and distortion aberration is 2.0% or less in absolute value. By forming the imaging lens L5 as in the fifth embodiment of the present invention, the half angle of view is as wide as 39 degrees and the F number is as large as about 1.95 or less. It is clear that good image performance can be ensured.

FIG. 6 shows a configuration of an imaging lens according to Example 6 of the present invention, and schematically shows a longitudinal section along the optical axis.
An imaging lens L6 shown in FIG. 6 includes, in order from the object side to the image surface, a first lens E1 composed of a negative meniscus negative lens having a convex surface facing the object side, and a strong concave surface forming an aspheric surface. A second lens E2 composed of a negative meniscus negative lens facing the side, a third lens E3 that is a biconvex positive lens, an aperture stop FA, a fourth lens E4 that is a biconvex positive lens, and a negative meniscus type A fifth lens E5, which is a negative lens, and a sixth lens E6, which is a negative meniscus negative lens, and a seventh lens E7, which is a biconvex positive lens. The eighth lens E8, which is a positive meniscus type positive lens having a strong convex surface facing the object side and an aspherical surface, is disposed.
The first lens E1 to the third lens E3 constitute the first lens group G1, and the fourth lens E4 to the eighth lens E8 constitute the second lens group G2.

In the first lens group G1, the front first lens group 1F is composed of a first lens E1 and a second lens E2 that are located on the object side (front side) having negative refractive power with the widest air interval as a boundary. The rear first lens group 1R is configured by the third lens E3 that is configured and located on the image surface side (rear side) having positive refractive power.
The second lens group G2 includes, in order from the object side, a fourth lens E4 as a first positive lens, a fifth lens E5 as a first negative lens, a sixth lens E6 as a second negative lens, and a second positive lens. The seventh lens E7 as a lens constitutes the front second lens group 2F, and the eighth lens E8 constitutes the rear second lens group 2R. In the imaging lens L6, the whole or part of the second lens group G2 is moved to perform focusing on a finite distance object.
For example, in an imaging lens of a camera that uses a solid-state imaging device such as a CCD imaging device, such as a digital still camera, a low-pass filter or an infrared cut is provided between the final surface of the eighth lens E8 and the image surface FS. It constitutes at least one of cover glasses (hereinafter referred to as “optical filter MF”) for protecting the filter and the light receiving surface of the CCD image sensor.
In FIG. 6, surface numbers of the respective optical surfaces are also given. Each reference numeral with respect to FIG. 6 is used independently for each example (embodiment) in order to avoid complication of explanation, and therefore, even if a common reference numeral is attached, it is common to other embodiments. It is not a configuration of.
FIG. 13 is an aberration curve diagram showing each aberration characteristic of spherical aberration, astigmatism, distortion and coma aberration of the imaging lens according to Example 6 of the present invention shown in FIG.
In the sixth embodiment, the focal length f = 6.00 mm, the F number = 1.95, and the half angle of view ω = 39.1 °. The characteristics of each optical surface are as shown in the following table.

In Table 6, each optical surface of the fourth surface and the fourteenth surface with an asterisk “*” attached to the surface number is an aspheric surface, and the parameters in the equations for each aspheric surface are as follows.
Aspheric surface; 4th surface
K = -0.83616, A ₄ = 1.06538 × 10 ^-4 , A ₆ = -2.50034 × 10 ^-6 , A ₈ = 9.83448 × 10 ^-9 , A ₁₀ = -1.85737 × 10 ^-9
Aspheric surface: 14th surface
K = 0.0, A ₄ = -2.40864 × 10 ^-4 , A ₆ = 3.17695 × 10 ^-6 , A ₈ = -1.91600 × 10 ^-7 , A ₁₀ = 2.94310 × 10 ^-9
In addition, each numerical value related to the conditional expression described in the sixth embodiment is as follows.

Conditional expression numerical value:
ν _dp1 = 81.54
ν _dn1 = 30.13
ν _dn2 = 33.79
ν _dp2 = 81.54
ν _dn1 −ν _dn2 = −3.66
r _S1 / f _A = −1.36
r _S2 / f _A = 1.63
L _2F /L=0.137
f _A / f ₁ = 0.049
A _1F-1R / L ₁ = 0.621
Therefore, the numerical values related to the conditional expressions of the present invention described in the sixth embodiment are all within the range of the conditional expressions.

FIG. 13 is an aberration curve diagram showing the respective aberration characteristics of spherical aberration, astigmatism, distortion and coma aberration of the imaging lens L6 of the present invention shown in FIG. 6 according to Example 6 described above.
In each aberration curve diagram, a broken line in spherical aberration represents a sine condition, a solid line in astigmatism represents sagittal, and a broken line represents meridional.
According to the imaging lens L6 having the configuration shown in FIG. 6 according to the sixth embodiment of the present invention described above, the aberration is corrected at a high level as shown in FIG. Small enough not to become. Astigmatism, curvature of field, and lateral chromatic aberration are sufficiently small, coma and disturbance of the color difference are well suppressed to the outermost periphery, and distortion aberration is 2.0% or less in absolute value. By forming the imaging lens L6 as in Example 6 according to the present invention, the half angle of view is as wide as 39 degrees and the F number is as large as about 1.95 or less. It is clear that good image performance can be ensured.

FIG. 7 shows a configuration of an imaging lens according to Example 7 of the present invention, and schematically shows a longitudinal section along the optical axis.
The imaging lens L7 shown in FIG. 7 includes, in order from the object side to the image surface, a first lens E1 composed of a negative meniscus negative lens having a convex surface facing the object side, and a strong concave surface forming an aspheric surface. A second lens E2 composed of a negative meniscus negative lens facing the side, a third lens E3 that is a biconvex positive lens, an aperture stop FA, a fourth lens E4 that is a positive meniscus positive lens, and a negative meniscus type A fifth lens E5, which is a negative lens, and a sixth lens E6, which is a negative meniscus negative lens, and a seventh lens E7, which is a biconvex positive lens. The eighth lens E8, which is a biconvex positive lens with a strong convex surface facing the object side and an aspheric surface, is disposed.
The first lens E1 to the third lens E3 constitute the first lens group G1, and the fourth lens E4 to the eighth lens E8 constitute the second lens group G2.

In the first lens group G1, the front first lens group 1F is composed of a first lens E1 and a second lens E2 that are located on the object side (front side) having negative refractive power with the widest air interval as a boundary. The rear first lens group 1R is configured by the third lens E3 that is configured and located on the image surface side (rear side) having positive refractive power.
The second lens group G2 includes, in order from the object side, a fourth lens E4 as a first positive lens, a fifth lens E5 as a first negative lens, a sixth lens E6 as a second negative lens, and a second positive lens. The seventh lens E7 as a lens constitutes the front second lens group 2F, and the eighth lens E8 constitutes the rear second lens group 2R. In the imaging lens L7, the whole or a part of the second lens group G2 is moved to perform focusing on a finite distance object.
For example, in an imaging lens of a camera that uses a solid-state imaging device such as a CCD imaging device, such as a digital still camera, a low-pass filter or an infrared cut is provided between the final surface of the eighth lens E8 and the image surface FS. It constitutes at least one of cover glasses (hereinafter referred to as “optical filter MF”) for protecting the filter and the light receiving surface of the CCD image sensor.
In FIG. 7, surface numbers of the respective optical surfaces are also given. Each reference numeral with respect to FIG. 7 is used independently for each example (embodiment) in order to avoid complication of explanation, and therefore, even if a common reference numeral is attached, it is common to other embodiments. It is not a configuration.
FIG. 14 is an aberration curve diagram showing the respective aberration characteristics of spherical aberration, astigmatism, distortion and coma aberration of the image forming lens according to Example 7 shown in FIG.
In the seventh embodiment, the focal length f = 6.00 mm, the F number = 1.96, and the half angle of view ω = 39.1 °. The characteristics of each optical surface are as shown in the following table.

In Table 7, each optical surface of the fourth surface and the fourteenth surface with an asterisk “*” attached to the surface number is an aspheric surface, and the parameters in the equations for each aspheric surface are as follows.
Aspheric surface; 4th surface
K = -0.82970, A ₄ = 6.46605 × 10 ^-5 , A ₆ = -2.89248 × 10 ^-6 , A ₈ = 1.03022 × 10 ^-8 , A ₁₀ = -1.71499 × 10 ^-9
Aspheric surface: 14th surface
K = 0.0, A ₄ = -2.57760 × 10 ^-4 , A ₆ = 1.76756 × 10 ^-6 , A ₈ = -1.22031 × 10 ^-7 , A ₁₀ = 1.59466 × 10 ^-9
In addition, each numerical value related to the conditional expression described in the seventh embodiment is as follows.

Conditional expression numerical value:
ν _dp1 = 70.24
ν _dn1 = 28.30
ν _dn2 = 39.68
ν _dp2 = 81.54
ν _dn1 −ν _dn2 = −11.38
r _S1 / f _A = −1.13
r _S2 / f _A = 1.48
L _2F /L=0.158
f _A / f ₁ = 0.073
A _1F-1R / L ₁ = 0.594
Accordingly, all the numerical values related to the conditional expressions of the present invention described in the seventh embodiment are within the range of the conditional expressions.

FIG. 14 is an aberration curve diagram showing each aberration characteristic of spherical aberration, astigmatism, distortion and coma aberration of the imaging lens L7 of the present invention shown in FIG. 7 according to Example 7 described above.
In each aberration curve diagram, a broken line in spherical aberration represents a sine condition, a solid line in astigmatism represents sagittal, and a broken line represents meridional.
According to the imaging lens L7 having the configuration shown in FIG. 7 according to the seventh embodiment of the present invention described above, the aberration is corrected at a high level as shown in FIG. 14, and spherical aberration and longitudinal chromatic aberration are problematic. Small enough not to become. Astigmatism, curvature of field, and lateral chromatic aberration are sufficiently small, coma and disturbance of the color difference are well suppressed to the outermost periphery, and distortion aberration is 2.0% or less in absolute value. By forming the imaging lens L7 as in Example 7 according to the present invention, the half angle of view is as wide as 39 degrees and the F number is as large as about 1.96 or less. It is clear that good image performance can be ensured.

Next, the seventh embodiment of the present invention in which the imaging lens L1 to the imaging lens L7 according to the present invention as shown in the above-described first to seventh embodiments is employed as a photographing optical system to constitute a camera. Examples (embodiments) will be described with reference to FIGS. FIG. 15 is a perspective view showing an appearance of an object, that is, a camera viewed from the front side that is the subject side, in which (a) shows a state in which the lens barrel is retracted, and (b) shows that the lens barrel is in the retracted state. Indicates the extended state. FIG. 16 is a perspective view showing the appearance of the camera as seen from the back side that is the photographer side, and FIG. 17 is a block diagram showing the functional configuration of the camera. Although a camera is described here, a camera in which a camera function is incorporated in a personal digital assistant such as a so-called PDA (personal data assistant) or a mobile phone has recently appeared. Such a portable information terminal device also includes substantially the same function and configuration as a camera, although the appearance is slightly different. Even if the zoom lens according to the present invention is adopted in such a portable information terminal device, Good.
As shown in FIGS. 15 and 16, the camera includes a photographing lens 101, a shutter button 102, a viewfinder 104, a strobe 105, a liquid crystal monitor 106, an operation button 107, a power switch 108, a memory card slot 109, a communication card slot 110, and the like. I have. Furthermore, as shown in FIG. 17, the camera also includes a light receiving element 201, a signal processing device 202, an image processing device 203, a central processing unit (CPU) 204, a semiconductor memory 205, a communication card 206, and the like.

The camera includes a photographing lens 101 and a light receiving element 201 as an area sensor such as a CCD (Charge Coupled Device) imaging element, and is an object to be photographed, that is, a subject formed by the photographing lens 101 that is a photographing optical system. These images are read by the light receiving element 201. As the photographing lens 101, an imaging lens according to the present invention (that is, defined in claims 1 to 10) as described in the first to seventh embodiments is used (claims 11 and 12). Corresponding to).
The output of the light receiving element 201 is processed by the signal processing device 202 controlled by the central processing unit 204 and converted into digital image information. The image information digitized by the signal processing device 202 is subjected to predetermined image processing in the image processing device 203 which is also controlled by the central processing unit 204 and then recorded in the semiconductor memory 205 such as a nonvolatile memory. In this case, the semiconductor memory 205 may be a memory card loaded in the memory card slot 109 or a semiconductor memory built in the camera body. The liquid crystal monitor 106 can display an image being shot, and can also display an image recorded in the semiconductor memory 205. The image recorded in the semiconductor memory 205 can also be transmitted to the outside via a communication card 206 or the like loaded in the communication card slot 110.

When the camera is carried, the taking lens 101 is in the retracted state and buried in the body of the camera as shown in FIG. 15A. When the user operates the power switch 108 to turn on the power, (B), the lens barrel is extended and protrudes from the camera body.
In many cases, focusing is performed by half-pressing the shutter button 102. Focusing in the imaging lenses L1 to L7 as described in the first to seventh embodiments is performed by moving all or part of the second lens group G2, but is performed by moving the light receiving element 201. You can also When the shutter button 102 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 205 is displayed on the liquid crystal monitor 106 or transmitted to the outside via the communication card 206 or the like, the operation button 107 is operated in a predetermined manner. The semiconductor memory 205 and the communication card 206 are used by being loaded into dedicated or general-purpose slots such as the memory card slot 109 and the communication card slot 110, respectively.

  According to the present invention described above, the half angle of view is as wide as about 38 degrees, and the F number is about 2.0 or less, but it is relatively small in size, astigmatism, field curvature, and magnification. Chromatic aberration, color difference of coma aberration, distortion, etc. are sufficiently reduced to have a resolution corresponding to an image sensor of 10 million to 20 million pixels, and from the wide open aperture to the periphery of the angle of view with high contrast. Small size that uses a high-performance imaging lens as a photographic optical system for the camera function unit, which does not cause point image distortion, does not cause unnecessary coloring even in areas with large luminance differences, and can draw straight lines without distortion. Can provide a high-quality camera and a portable information terminal device, so that a user can take a high-quality image with a highly portable camera and portable information terminal device and transmit the image to the outside. it can.

1-19 Surface number E1-E9 1st lens-9th lens 1F Front side 1st lens group 1R Rear side 1st lens group 2F Front side 2nd lens group 2R Rear side 2nd lens group G1 1st lens group G2 2nd lens Group FA Aperture stop MF Optical filter FS Image surface 101 Shooting lens 102 Shutter button 104 Viewfinder 105 Strobe 106 Liquid crystal monitor 107 Operation button 108 Power switch 109 Memory card slot 110 Communication card slot 201 Light receiving element 202 Signal processing device 203 Image processing device 204 Central Arithmetic unit 205 Semiconductor memory 206 Communication card, etc.

Japanese Patent Laid-Open No. 06-308385 JP 09-218350 A JP 2006-349920 A

Claims (12)

In an imaging lens composed of a first lens group located on the object side with an aperture stop interposed therebetween and a second lens group located on the image side, the first lens group is arranged in order from the object side. A front first lens group having a negative refractive power and a rear first lens group having a positive refractive power at the widest air interval in the group, and the second lens group is formed on the object side Sequentially from the front second lens group in which the first positive lens, the first negative lens, the second negative lens, and the second positive lens are continuously arranged, and the rear second lens group including at least one lens; And an imaging lens characterized by satisfying the following conditional expression:
62.0 <ν _dp1 <98.0
20.0 <ν _dn1 <45.0
20.0 <ν _dn2 <45.0
35.0 <ν _dp2 <98.0
−20.0 <ν _dn1 −ν _dn2 <15.0
Where ν _dp1 is the Abbe number of the first positive lens of the front second lens group, ν _dn1 is the Abbe number of the first negative lens, ν _dn2 is the Abbe number of the second negative lens, and ν _dp2 is the first 2 represents the Abbe number of a positive lens. 2. The imaging lens according to claim 1, wherein the first positive lens, the first negative lens, the second negative lens, and the second positive lens constituting the front second lens group are in close contact with each other. An imaging lens characterized by being cemented. 3. The imaging lens according to claim 2, wherein the following conditional expression is satisfied.
−2.4 <r _S1 / f _A <−0.8
1.0 <r _S2 / f _A <2.6
Where r _S1 is the radius of curvature of the cemented surface of the first positive lens and the first negative lens, r _S2 is the radius of curvature of the cemented surface of the second negative lens and the second positive lens, and f _A is the image formation. This represents the focal length of the entire lens system. 4. The imaging lens according to claim 1, wherein the imaging lens satisfies the following conditional expression: 5.
0.1 <L _2F /L<0.25
Where L _2F is the total length of the front second lens group, and L is the distance from the most object-side surface of the imaging lens to the image plane. 5. The imaging lens according to claim 1, wherein the following conditional expression is satisfied: 5.
0.0 <f _A / f ₁ <0.8
However, f _A represents the focal length of the entire system of the imaging lens, and f ₁ represents the focal length of the first lens group. The imaging lens according to claim 1, wherein the following conditional expression is satisfied.
0.35 <A _1F-1R / L ₁ <0.7
However, A _1F-1R, the distance between the front-side first lens group and the rear-side first lens group, L ₁ represents a length of said first lens group. 7. The imaging lens according to claim 1, wherein the following conditional expression is satisfied.
ν _d > 80.0
Δθ _{g, F} > 0.025
Where ν _d is the Abbe number of the first positive lens, and Δθ _{g, F} is the anomalous dispersion of the first positive lens.
Here, the anomalous dispersion Δθ _{g, F} is the Abbe number ν _d on the horizontal axis, the partial dispersion ratio θ _{g, F} = (n _g −n _F ) / (n _F −n _C ) on the vertical axis. In the graph, the deviation from the standard line of the glass type when the straight line connecting the glass type K7 (Ohara Glass Type Name NSL7) and the glass type F2 (Ohara Glass Type Name PBM2) is taken as the standard line. _{Incidentally,} n _g, n F, _{n C,} respectively, g-line, F-line, the refractive index for the C line. 8. The imaging lens according to claim 1, wherein the front first lens group has a configuration in which negative meniscus lenses having convex surfaces facing the object side are continuously arranged. An imaging lens comprising: an image spherical side surface of at least one of the lenses. 9. The imaging lens according to claim 1, wherein the second rear lens group includes one lens and has an aspherical surface. 10. 10. The imaging lens according to claim 1, wherein focusing to a finite distance object is performed by moving all or a part of the second lens group. . A camera comprising the imaging lens according to any one of claims 1 to 10 as a photographing optical system. 11. A portable information terminal device comprising the imaging lens according to claim 1 as a photographing optical system of a camera function unit.

Images