JP2010039088A - Imaging lens, camera and personal digital assistant - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging lens which has a wide angle, a large diameter with an F-number of about 2.0, and also, which is relatively compact, wherein astigmatism, curvature of the field, transverse chromatic aberration, chromatic aberration of coma and distortion aberration, etc., are sufficiently reduced, and a resolution corresponding to an imaging element of 10 million to 20 million pixels is obtained. <P>SOLUTION: The imaging lens includes a first lens group G1 positioned in an object side, a second lens group G2 positioned in an image side, and an aperture diaphragm FA between the first lens group and the second lens group. The first lens group G1 includes, in order from the object side, an object-side first lens group GF1 comprising two negative lenses E1 and E2 and an image-side first lens group GR1 comprising a positive lens E3 that are positioned with the largest air distance therebetween in the first lens group G1 as a boundary. The second lens group G2 comprises an object-side second lens group GF2 comprising a fourth lens E4 to a seventh lens E7, and an image-side second lens group GR2 comprising an eighth lens E8. The fifth lens E5 and the sixth lens E6 are cemented to each other, the seventh lens E7 and the eighth lens E8 are cemented to each other. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to improvement of a single-focus imaging lens used as a photographing optical system in various cameras including a so-called silver salt camera, in particular, a digital camera and a video camera, and more particularly, a camera such as a digital camera and a video camera. In particular, the present invention relates to an imaging lens suitable for a camera, a camera using such an imaging lens, and a portable information terminal device.

In recent years, it is called a digital camera or an electronic camera, and a subject image is captured by a solid-state imaging device such as a CCD (charge coupled device) imaging device, and a still image (still image) or a moving image (movie image) of the subject is captured. The type of camera that obtains the image data and digitally records it in a nonvolatile semiconductor memory such as a flash memory has become common. The market for such digital cameras has become very large, and there are various demands for digital cameras by users. 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 F number (hereinafter sometimes simply referred to as “F”) is small, that is, the weight for the large diameter is high.
Here, in terms of high performance, in addition to having a resolution corresponding to at least 10 million to 20 million pixel image sensors, there is little coma flare from the wide open aperture, high contrast, and the periphery of the angle of view. It is necessary that the point image is not broken down to the portion, that no chromatic aberration is generated and unnecessary coloring is not generated even in a portion having a large luminance difference, that a straight line is drawn with little distortion.
Furthermore, in terms of increasing the diameter, it is necessary to be at least F2.4 or less, and there is a voice that desires to be F2.0 or less, because it is necessary to differentiate from a general compact camera equipped with a zoom lens. Not a few.

In addition, as for the angle of view of the photographing lens, there are many users who desire a certain wide angle, and it is desirable that the half angle of view of the imaging lens is 38 degrees or more. That is, the half angle of view of 38 degrees corresponds to 28 mm in terms of the focal length in terms of a 35 mm silver salt camera (so-called Leica version).
There are many types of imaging lenses for digital cameras, but typical configurations of wide-angle single focus lenses include a negative refractive power lens group on the object side and a positive refractive power lens group on the image side. A so-called retrofocus type in which is provided. Due to the characteristics of an area sensor that has a color filter and microlens for each pixel, there is a need for retrofocusing to move the exit pupil position away from the image plane so that the peripheral luminous flux is incident on the sensor at a near-perpendicular angle. This is the main reason why the type is adopted. However, the retrofocus type configured so that the principal point is behind the entire lens system has a large asymmetry in its refractive power arrangement, and correction of coma aberration, distortion aberration, lateral chromatic aberration, etc. tends to be incomplete. is there.
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 those disclosed in Patent Document 2 (Japanese Patent Laid-Open No. 09-218350) and Patent Document 3 (Japanese Patent Laid-Open No. 2006-349920).

However, although the imaging lens disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 06-308385) has a large aperture of F1.4, astigmatism and curvature of field are large, and the vicinity of the aperture is close to the open aperture. No, it does not have sufficient performance. In addition, the imaging lens disclosed in Patent Document 2 (Japanese Patent Laid-Open No. 09-218350) is inferior in terms of F2.8 and a large aperture, and has large astigmatism, field curvature, and lateral chromatic aberration. It cannot be said that this also has sufficient performance up to the peripheral part. In both cases, the distortion aberration exceeds 2% in absolute value.
In addition, the imaging lens disclosed in Patent Document 3 (Japanese Patent Laid-Open No. 2006-349920) is well corrected for astigmatism, field curvature, and distortion, but is not shown in the specification. The color difference of coma is large. Also, an embodiment with a small F number is insufficient in terms of miniaturization.

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

The present invention has been made in view of the above points, and the invention according to claim 1 has a wide angle with a half angle of view of about 38 degrees and an F number of about 2.0 or less. Although it is relatively small, astigmatism, curvature of field, lateral chromatic aberration, coma color difference, distortion, etc. are sufficiently reduced to support image sensors with 10 to 20 million pixels. High resolution with high resolving power, 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 It is an object of the present invention to provide an imaging lens.
The object of the present invention is to provide a high-performance imaging lens in which each aberration is corrected more satisfactorily.
A third object of the present invention is to provide a high-performance imaging lens in which a substantial manufacturing error sensitivity is reduced and stable performance is easily obtained.
An object of the present invention is to provide a higher performance imaging lens in which chromatic aberration is corrected in a balanced manner.
The object of the present invention is to provide a higher performance imaging lens with improved image plane flatness and the like.

An object of the present invention is to provide a higher-performance imaging lens that suppresses the occurrence of spherical aberration associated with an increase in aperture.
An object of the present invention is to provide a higher performance imaging lens in which chromatic aberration is corrected more favorably.
An object of the present invention is to provide a higher 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 is corrected more favorably without taking an unnecessarily complicated configuration.
The object of the present invention is to provide an appropriate method for performing focusing on a finite distance object.
The invention according to claim 11 is a relatively small size with a wide angle of about half an angle of view of about 38 degrees and a large aperture of F number of about 2.0 or less, astigmatism and field curvature, The chromatic aberration of magnification, the 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 at the periphery of the angle of view with a high contrast from the open aperture A small, high-quality image using a high-performance imaging lens as a photographic optical system that 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. The purpose is to provide a camera.

  The invention according to claim 12 is a comparatively small size with a half angle of view as wide as about 38 degrees and a large aperture with an F number of about 2.0 or less, astigmatism and field curvature, The chromatic aberration of magnification, the 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 at the periphery of the angle of view with a high contrast from the open aperture A high-performance imaging lens that can be drawn without distortion as a straight line without causing unnecessary coloration even in parts with large brightness differences, without causing point image distortion, An object of the present invention is to provide a small-sized and high-quality portable information terminal device.

The imaging lens according to any one of claims 1 to 10 of the present invention includes an image forming unit including 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 lens further has the following characteristics.
The imaging lens according to claim 1, wherein the first lens group is arranged in order from the object side, and includes at least two negative lenses positioned on the object side with the widest air interval in the first lens group as a boundary. An object-side first lens group, and an image-side first lens group having at least one positive lens located on the image side, and the second lens group in order from the object side, the first positive lens, An object-side second lens group in which a negative lens, a second negative lens, and a second positive lens are continuously arranged, and an image-side second lens group including at least one lens located on the image side. It is characterized by that.
In the imaging lens according to claim 2, when L _2F is the total length of the second lens unit on the object side and L is a distance from the most object side surface of the imaging lens to the image plane, the following conditional expression is satisfied. It is characterized by satisfaction.
0.1 <L _2F /L<0.25

The imaging lens according to claim 3 is the imaging lens according to claim 1 or 2, wherein the first positive lens, the first negative lens, and the second negative lens of the object side second lens. And the second positive lens are joined together.
The imaging lens according to claim 4 is the imaging lens according to claim 3, wherein a cemented surface of the first positive lens and the first negative lens of the object-side second lens is convex toward the image side. The cemented surface of the second negative lens and the second positive lens has a convex shape on the object side.
The imaging lens according to claim 5 is the imaging lens according to any one of claims 1 to 4, wherein f _A is a focal length of the entire system, and f ₁ is a focal point of the first lens group. When the distance is used, the following conditional expression is satisfied.
0.0 <f _A / f ₁ <0.8
The imaging lens according to claim 6 is the imaging lens according to any one of claims 1 to 5, wherein A _1F-1R is _replaced with the object side first lens group and the image side first. distance between the lens group, when the L ₁ and the entire length of the first lens group, and satisfies the following conditional expression.
0.35 <A _1F-1R / L ₁ <0.7

The imaging lens according to claim 7 is the imaging lens according to any one of claims 1 to 6, wherein ν _d is an Abbe number of the first positive lens and Δθ _{g, F} is When the anomalous dispersibility of the first positive lens is satisfied, the following conditional expression is satisfied.
ν _d > 80.0
Δθ _{g, F} > 0.025
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.
The imaging lens according to claim 8 is the imaging lens according to any one of claims 1 to 7, wherein the object-side first lens group has a convex surface facing two object sides. Further, the negative meniscus lens is continuously arranged, and at least one of the lenses has an aspheric image side surface.
An imaging lens according to a ninth aspect is the imaging lens according to any one of the first to eighth aspects, wherein the second lens group on the image side includes a single lens. It is characterized by having a spherical surface.

An imaging lens according to a tenth aspect 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 to a finite distance object. It is characterized by performing focusing.
A camera according to an eleventh aspect of the present invention includes the imaging lens according to any one of the first to tenth aspects 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.

According to the first aspect of the present invention, in the imaging lens constituted by the first lens group positioned on the object side with the aperture stop interposed therebetween and the second lens group positioned on the image side,
In order from the object side to the first lens group, an object-side first lens group having at least two negative lenses positioned on the object side with the widest air interval in the first lens group as a boundary, and the image side And an image-side first lens group having at least one positive lens located in the first lens group, and the second lens group in order from the object side, a first positive lens, a first negative lens, a second negative lens, and a second lens In particular, the half angle of view is 38 degrees by including the second lens group on the object side in which the positive lenses are continuously arranged and the second lens group on the image side including at least one lens located on the image side. It is relatively small in size and wide angle, and its F number is about 2.0 or less, but it is relatively small and sufficiently reduces astigmatism, curvature of field, lateral chromatic aberration, coma color difference, distortion, etc. An image sensor with 10 to 20 million pixels It has the corresponding resolving power, does not collapse the point image from the wide open to the periphery of the angle of view with high contrast, does not cause unnecessary coloring even in areas with large luminance differences, and can draw straight lines without distortion. A high-performance imaging lens can be provided, and thus a small and very high-quality camera or portable information terminal device can be realized.

According to a second aspect of the present invention, in the imaging lens according to the first aspect, L _2F is the total length of the second lens group on the object side, and L is the surface from the most object side of the imaging lens to the image plane. When expressing the distance of
0.1 <L _2F /L<0.25
By satisfying the conditional expression
A high-performance imaging lens in which each aberration is corrected better can be provided.
According to a third aspect of the present invention, in the imaging lens according to the first or second aspect, the first positive lens, the first negative lens, and the second negative lens of the object side second lens group. Since the lens and the second positive lens are respectively joined, it is possible to provide a high-performance imaging lens that reduces substantial manufacturing error sensitivity and easily obtains stable performance. It is possible to realize a camera and a portable information terminal device that can obtain good depiction without variation.
According to a fourth aspect of the present invention, in the imaging lens according to the third aspect, the cemented surface of the first positive lens and the first negative lens of the object side second lens group is convex on the image side. The present invention provides a high-performance imaging lens that is particularly well-balanced and corrects chromatic aberration by having a shape, and the cemented surface of the second negative lens and the second positive lens is convex on the object side. As a result, it is possible to realize a camera (personal digital assistant device) that further suppresses color misregistration, color blurring, and the like of an image and has excellent resolution and contrast.

According to a fifth aspect of the present invention, in the imaging lens according to any one of the first to fourth aspects, f _A is the focal length of the entire system, and f ₁ is the _first lens. When the focal length of the lens group
0.0 <f _A / f ₁ <0.8
By satisfying the following conditional expression, it is possible to provide a high-performance imaging lens that improves the flatness of the image surface in particular, and thus has a high resolution from the full aperture to the entire screen. A higher quality camera (personal digital assistant device) can be realized.
According to the invention described in claim 6, in the imaging lens according to any one of claims 1 to 5,
When A _1F-1R is the distance between the object side first lens group and the image plane side first lens group, and L ₁ is the total length of the first lens group,
0.35 <A _1F-1R / L ₁ <0.7
By satisfying the following conditional expression, it is possible to provide a higher-performance imaging lens that suppresses the occurrence of spherical aberrations particularly with an increase in aperture, and thus has a higher degree of sharpness from the opening of the aperture. A high-quality camera (personal digital assistant device) capable of obtaining an image can be realized.

According to the invention described in claim 7, in the imaging lens according to any one of claims 1 to 6,
ν _d is the Abbe number of the first positive lens of the second lens group, Δθ _{g, F} is the anomalous dispersion of the first positive lens,
The anomalous dispersion Δθ _{g, F} is a graph in which the Abbe number ν _d is the horizontal axis and the partial dispersion ratio θ _{g, F} = ( _ng− n _F ) / (n _F −n _C ) is the vertical axis. K7 a straight line connecting (OHARA glass type name NSL7) and glass type F2 (OHARA glass type name PBM2) when a standard line, and a deviation from the standard line of the glass _type, n _g, n F, the _{n C} , And the refractive index for g-line, F-line, and C-line, respectively.
ν _d > 80.0
Δθ _{g, F} > 0.025
By satisfying the following conditional expression, it is possible to provide a higher-performance imaging lens that corrects the chromatic aberration more satisfactorily. Camera (personal digital assistant device) can be realized.

According to an eighth aspect of the present invention, in the imaging lens according to any one of the first to seventh aspects, the object-side first lens group has a convex surface on the two object sides. The negative meniscus lens is continuously arranged, and the image side surface of at least one of the lenses is aspherical. In particular, the occurrence of aberration is further suppressed, and distortion is corrected particularly well. In addition, it is possible to provide a higher-performance imaging lens, and to realize a higher-quality camera (portable information terminal device) that can hardly feel distortion even when a building is photographed. it can.
According to the invention described in claim 9, in the imaging lens according to any one of claims 1 to 8, the image-side second lens group includes one lens, By having an aspherical surface, it is possible to provide a high-performance imaging lens that corrects coma aberration better without adopting an unnecessarily complicated configuration. Therefore, a higher-quality camera (personal digital assistant device) that does not collapse 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. In particular, it is possible to provide an appropriate method for performing focusing on a finite distance object, and it becomes possible to reduce the size of the focus mechanism, thereby improving the image quality. A camera (personal digital assistant device) can be realized more compactly.
According to the eleventh aspect of the present invention, by including the imaging lens according to any one of the first to tenth aspects as a photographing optical system, in particular, the half angle of view is 38 degrees. It is relatively small in size and wide angle, and its F number is about 2.0 or less, but it is relatively small and sufficiently reduces astigmatism, curvature of field, lateral chromatic aberration, coma color difference, distortion, etc. In addition, it has resolving power corresponding to an image sensor of 10 million to 20 million pixels, and there is no collapse of the point image from the full aperture to the periphery of the angle of view with high contrast, even in a portion with a large luminance difference 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 and can be drawn without distortion as a straight line. Shoot high-quality images with a portable camera Rukoto can.

  According to the twelfth aspect of the present invention, by including the imaging lens according to any one of the first to eleventh aspects as a photographing optical system of the camera function unit, in particular, a 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 has astigmatism, curvature of field, lateral chromatic aberration, coma color difference, distortion, etc. The resolution is sufficiently reduced to have a resolution corresponding to an image sensor with 10 to 20 million pixels, and the point image does not collapse from the full aperture to the periphery of the angle of view, and the luminance difference is large. To provide a small and high-quality portable information terminal device that includes a high-performance imaging lens that can be drawn without distortion in a portion without generating unnecessary coloring, and a straight line as a straight line, including a photographing optical system of a camera function unit And, by extension, users are highly portable Taking a high-quality image in a portable information terminal apparatus, or can send the image to the outside.

Hereinafter, based on an embodiment of the present invention, an imaging lens, a camera, and a portable information terminal device of the present invention will be described in detail with reference to the drawings.
Before describing specific embodiments, first, the basic configuration of the present invention will be described.
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. In addition, as the diameter increases, it becomes difficult to correct coma and coma aberration color differences, 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. An object-side first lens group having at least two negative lenses positioned on the object side and an image-side first lens having at least one positive lens positioned on the image side with the widest air interval in the group as a boundary. An object-side second lens group including a lens group, and the second lens group in which the first positive lens, the first negative lens, the second negative lens, and the second positive lens are sequentially arranged from the object side. The image-side second lens group including at least one lens located on the image side from these (corresponding to claim 1).

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 (object-side first lens group) and a positive refractive power (image-side 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 image-side first lens group faces the object-side second lens group with the aperture stop interposed therebetween, and there is also an aspect in which coma aberration is controlled by the balance of the positive refractive powers of both.
What characterizes the present invention most is the role and configuration of the second lens unit on the object side. In the imaging lens of the present invention, the object-side 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 second lens group on the object side is based on a so-called triplet of positive, negative, and positive as the refractive power arrangement, but the central negative refractive power is divided into two to be positive, negative, negative, and positive. The four-sheet configuration. Since the aperture stop is disposed on the object side of the object side second lens group, the first positive lens and first negative lens pair and the second negative lens and second positive lens pair transmit off-axis rays. The height is different, and it is possible to effectively reduce both the longitudinal chromatic aberration and the lateral chromatic aberration by using this. Furthermore, the color difference of coma aberration can be reduced by utilizing the degree of freedom of the second negative lens.

The image-side second lens group has a function of balancing aberration and controlling 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 imaging lens of the present invention, it is desirable that the object side second lens group satisfies the following conditional expression (corresponding to claim 2).
0.1 <L _2F /L<0.25
However, L _2F represents the total length of the object-side 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 can effectively reduce both axial chromatic aberration and lateral chromatic aberration, the aperture stop is disposed on the object side of the second lens group on the object side. Therefore, the first positive lens and the first negative lens are arranged. We have already mentioned that the height of off-axis rays is different between the lens pair, the second negative lens, and the second positive lens pair, but this conditional expression is the most effective mechanism. The total length of the object side second lens group for working is regulated. Here, if L _2F / L is 0.1 or less, the difference in height of off-axis rays in the second lens group on the object side becomes small, the above-described mechanism becomes difficult to work, and chromatic aberration is reduced. There is a risk that the correction will be insufficient. On the other hand, if L _2F / L is 0.25 or more, the object-side second lens group unnecessarily occupies space, and the relationship with the other lens groups is lost, so that field curvature, 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
In the object-side 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 cemented (corresponding to claim 3).
On each lens surface in the object side 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.

In the object-side second lens group, when the first positive lens and the first negative lens, and the second negative lens and the second positive lens are cemented, the cemented surface of the first positive lens and the first negative lens is the image side. It is desirable that the cemented surface of the second negative lens and the second positive lens be convex toward the object side (corresponding to claim 4).
By configuring the object-side second lens group in this way, the cemented surface of the first positive lens and the first negative lens mainly has a role of correcting axial chromatic aberration, and the second negative lens and the second positive lens are corrected. The cemented surface of the lens can mainly have a role of correcting chromatic aberration of magnification, and the entire chromatic aberration can be corrected effectively.
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
However, f _A represents the focal length of the entire 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. 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 must 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 imaging action is reduced, making it difficult to establish 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
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 the distance between the first lens group and the image side a first lens unit object side, 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 object-side first lens group and the image-side 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.

The material of the first positive lens preferably 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.
The object side first lens group has a configuration in which two negative meniscus lenses having a convex surface facing the object side are continuously arranged, and it is desirable that the image side surface of at least one of the lenses is aspherical ( Corresponding to claim 8).

By dividing the negative refractive power of the first lens unit on the object side into two meniscus lenses and preventing excessive aberrations from occurring on specific surfaces, the entire lens system can be corrected more appropriately. 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 image-side second lens group is preferably composed of a single lens and has an aspherical surface (corresponding to claim 9).
Since the object-side second lens group has a sufficient degree of freedom, a simple configuration is sufficient for the image-side second lens group, and it is appropriate to use a single lens for miniaturization. Further, by providing an aspherical surface in the image side second lens group, coma aberration can be mainly corrected more satisfactorily.
The aspheric surfaces of the object-side first lens group and the image-side second lens group complement each other's role of aberration correction and work more effectively, so it is desirable to provide them simultaneously.
In the imaging lens of 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 of the present invention is incorporated in a camera as a photographing optical system, when it has a mechanism for shortening the interval between the lens groups and the back focus portion when not in use and storing them in a compact manner, it relates to the second lens group. The storage mechanism can be shared with the focusing mechanism, which is convenient.
In the imaging lens, by changing the position of the first lens group on the optical axis with respect to the image plane, it is possible to control the tilt of the image plane while suppressing the influence on other aberrations. During focusing, the whole or part of the second lens group is moved, and the first lens group is moved by a small amount in the opposite direction to compensate for the tilting of the image plane caused by focusing. It is also possible to always maintain high imaging performance over a very short distance.

Next, specific numerical examples will be described in detail as examples of the present invention.
Numerical examples 1 to 5 described below are numerical examples of specific configurations according to specific numerical examples of the imaging lens according to the present invention.
After that, an embodiment of a camera and a portable information terminal device according to the present invention in which an imaging lens according to the present invention as shown in Numerical Example 1 to Numerical Example 5 is employed in a photographing optical system will be described.
In Numerical Example 1 to Numerical Example 5 showing the imaging lens according to the present invention, the configuration of the imaging lens and specific numerical examples are shown.
The aberration of each numerical 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 the imaging lens as in the present invention, it is possible to ensure a very good image performance while the half angle of view is as wide as about 38 degrees and the F number is about 2.0 or less. It is apparent from each numerical example that this can be done.

Hereinafter, the meanings of symbols in Numerical Example 1 to Numerical Example 5 are as follows.
f: Focal length of entire system F: F number ω: Half angle of view R: Radius of curvature D: Surface interval (lens thickness or lens interval)
N _d : Refractive index of d-line ν _d : Abbe number of d-line K: Aspherical conic constant A ₄ : Fourth-order aspheric coefficient A ₆ : Sixth-order aspheric coefficient A ₈ : Eighth-order aspheric coefficient A ₁₀ : 10th-order aspheric coefficient However, the aspheric surface used here has the following when the reciprocal (paraxial curvature) of the paraxial radius of curvature (R) is C and the height from the optical axis is H: It is defined by an expression.

FIG. 1 shows the configuration of an imaging lens according to Numerical Example 1 (corresponding to the first embodiment) of the present invention, and schematically shows a longitudinal section along the optical axis.
The optical system (imaging lens) shown in FIG. 1 is a negative meniscus type negative having a strong concave surface in order from the object side to the image surface (in other words, a convex surface facing the object side). A first lens E1 composed of a lens, a second lens E2 composed of a negative meniscus negative lens with a strong concave surface directed toward the image surface side, a third lens E3 that is a biconvex positive lens, an aperture stop FA, a biconvex type A fourth lens E4 that is a positive lens, a fifth lens E5 that is a negative meniscus negative lens with a strong concave surface facing the object side, and a sixth lens that is a negative meniscus negative lens with a strong concave surface facing the image side A lens E6, a seventh lens E7 made of a biconvex positive lens with a strong convex surface facing the object side, and an eighth lens E8 made of a negative meniscus negative lens with a strong concave surface facing the image surface side Become That.
The first lens E1, the second lens E2, and the third lens E3 located on the object side with the aperture stop FA interposed therebetween constitute the first lens group G1, and the fourth lens located on the image side with the stop FA interposed therebetween. E4, the fifth lens E5, the sixth lens E6, the seventh lens E7, and the eighth lens E8 constitute a second lens group G2.

Further, the first lens group G1 includes two negative lenses positioned on the object side, that is, the first lens E1 and the second lens E2, with the widest air interval in the first lens group G1 as a boundary. And an image side first lens group GR1 including a third lens E3 which is a positive lens located on the image side of the object side first lens group GF1.
The second lens group G2 includes, in order from the object side, a first 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. A seventh lens E7 as a lens is composed of an object-side second lens group GF2 arranged continuously, and an eighth lens E8 as a negative lens located on the image side of the object-side second lens group GF2. Image side second lens group GR2.
An aspheric surface is formed on each of the image side surface 4 of the second lens E2 of the object side first lens group GF1 and the object side surface 14 of the eighth lens E8 of the image side second lens group GR2.
The fourth lens E4 and the fifth lens E5 of the object-side second lens group GF2 are closely bonded and bonded, and the sixth lens E6 and the seventh lens E7 are closely bonded and bonded. It is said that.

Then, in a photographing optical system of a camera using 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 is provided between the final surface of the eighth lens E8 and the image plane FS. At least one of a cover glass for protecting the filter and the light receiving surface of the CCD image sensor is inserted. For example, one parallel flat glass P1 is inserted.
In the first embodiment, focusing on a finite distance object is performed by moving all or part of the second lens group G2.
In FIG. 1, the surface numbers of the respective optical surfaces are shown. The reference numerals for FIG. 1 are used independently for each embodiment in order to avoid complication of the description, and therefore, even if a common reference numeral is used, it is not a configuration common to the other embodiments.
FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, distortion aberration, and coma aberration when the object distance in the imaging lens of FIG. 1 is infinity.
In this numerical example 1, the focal length f = 6.00, 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 (Table 1).

In Table 1, the optical surfaces of the fourth surface and the fourteenth surface with an asterisk “*” attached to the surface number are aspherical surfaces, and the parameters in the equation (1) for each aspherical 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
The numerical values of the conditional expressions [L _2F / L], [f _A / f ₁ ], and [A _1F-1R / L ₁ ] described above in the numerical example 1 are as follows.
Conditional expression numerical value L _2F /L=0.164
f _A / f ₁ = 0.192
A _1F-1R / L ₁ = 0.580
Therefore, all the numerical values related to the conditional expressions of the present invention described in the numerical example 1 are within the range of the conditional expressions.

FIG. 6 shows aberration curves of spherical aberration, astigmatism, distortion aberration and coma aberration formed by the imaging lens shown in FIG. 1 according to Numerical Example 1 described above. A broken line represents a sine condition, a solid line in astigmatism represents sagittal, and a broken line represents meridional.
As shown in FIG. 6, according to the imaging lens according to the first embodiment and numerical example 1 described above, each aberration is corrected at a high level, and spherical aberration and axial chromatic aberration do not become a problem. Astigmatism, curvature of field, lateral chromatic aberration are sufficiently small, coma and disturbance of color difference are well suppressed to the outermost part, and distortion is 2.0% or less in absolute value. ing.
By forming the imaging lens as in the present invention, a very good image performance can be ensured while the half field angle is about 38 degrees and the wide number and the F number is about 2.0 or less. This is clear from Numerical Example 1.
FIG. 2 shows a configuration of an imaging lens according to Numerical Example 2 (corresponding to the second embodiment) of the present invention, and schematically shows a longitudinal section along the optical axis.

The optical system (imaging lens) shown in FIG. 2 is a negative meniscus type negative having a strong concave surface in order from the object side to the image surface (in other words, a convex surface facing the object side). A first lens E1 composed of a lens, a second lens E2 composed of a negative meniscus negative lens with a strong concave surface facing the image surface side, a third lens E3 which is a biconvex positive lens, and a strong concave surface facing the object side A fourth lens E4 consisting of a negative meniscus negative lens facing the lens, an aperture stop FA, a fifth lens E5 being a biconvex positive lens, and a negative meniscus negative lens having a strong concave surface facing the object side. 6 lens E6, 7th lens E7 consisting of a biconcave negative lens with a strong concave surface facing the object side, 8th lens E8 consisting of a biconvex positive lens with a strong convex surface facing the object side, an image of a strong convex surface To face side And it has a configuration of arranging the ninth lens E9 consisting of a biconvex type positive lens.
The first lens E1, the second lens E2, the third lens E3, and the fourth lens E4 that are located on the object side with the aperture stop FA interposed therebetween constitute the first lens group G1, and on the image side with the stop FA interposed therebetween. The fifth lens E5, the sixth lens E6, the seventh lens E7, the eighth lens E8, and the ninth lens E9 that are positioned constitute a second lens group G2.

Further, the first lens group G1 includes two negative lenses positioned on the object side, that is, the first lens E1 and the second lens E2, with the widest air interval in the first lens group G1 as a boundary. An image-side first lens group GF1, a third lens E3 that is a positive lens located on the image side of the object-side first lens group GF1, and a fourth lens E4 that is a negative lens. It consists of one lens group GR1.
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. An object side second lens group GF2 in which an eighth lens E8 as a lens is continuously arranged, and a ninth lens E9 as a positive lens located on the image side from the object side second lens group GF2 are configured. Image side second lens group GR2.
An aspherical surface is formed on each of the image side surface 4 of the second lens E2 of the object side first lens group GF1 and the object side surface 15 of the ninth lens E9 of the image side second lens group GR2.
The third lens E3 and the fourth lens E4 of the image side first lens group GR1 are closely bonded to form a cemented lens, and the fifth lens E5 and the sixth lens E6 of the object side second lens group GF2. Are closely bonded to form a cemented lens, and the seventh lens E7 and the eighth lens E8 are closely bonded to be a cemented lens.

Then, in a photographing optical system of a camera using 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 is provided between the final surface of the ninth lens E9 and the image plane FS. At least one of a cover glass for protecting the filter and the light receiving surface of the CCD image sensor is inserted. For example, one parallel flat glass P1 is inserted.
In the second embodiment, focusing on a finite distance object is performed by moving all or part of the second lens group G2.
In FIG. 2, the surface numbers of the respective optical surfaces are given. The reference numerals for FIG. 2 are used independently for each embodiment in order to avoid complication of the description. Therefore, even if a common reference numeral is used, it is not a configuration common to the other embodiments.
FIG. 7 is an aberration diagram showing spherical aberration, astigmatism, distortion aberration, and coma aberration of the imaging lens of FIG. 2 (when the object distance is infinity).
In this numerical value example 2, the focal length f = 5.90, 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 (Table 2).

In Table 2, the optical surfaces of the fourth surface and the fifteenth surface with an asterisk “*” attached to the surface number are aspheric surfaces, and the parameters in the expression (1) of each aspheric surface 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
Further, the numerical values of the conditional expressions [L _2F / L], [f _A / f ₁ ], and [A _1F-1R / L ₁ ] described above in the numerical example 2 are as follows.

Conditional expression numerical value L _2F /L=0.143
f _A / f ₁ = 0.604
A _1F-1R / L ₁ = 0.628
Therefore, all the numerical values related to the conditional expressions of the present invention described in the numerical example 2 are within the range of the conditional expressions.

FIG. 7 shows aberration curves of spherical aberration, astigmatism, distortion aberration, and coma aberration formed by the imaging lens shown in FIG. 2 according to Numerical Example 2 described above. A broken line represents a sine condition, a solid line in astigmatism represents sagittal, and a broken line represents meridional.
As shown in FIG. 7, according to the imaging lens according to the second embodiment and numerical example 2 described above, each aberration is corrected at a high level, and spherical aberration and axial chromatic aberration are not a problem. Astigmatism, curvature of field, lateral chromatic aberration are sufficiently small, coma and disturbance of color difference are well suppressed to the outermost part, and distortion is 2.0% or less in absolute value. ing.
By forming the imaging lens as in the present invention, a very good image performance can be ensured while the half angle of view is as wide as 38 degrees and the F number is as large as 2.0. This is also clear from Numerical Example 2.

FIG. 3 shows a configuration of an imaging lens according to Numerical Example 3 (corresponding to the third embodiment) of the present invention, and schematically shows a longitudinal section along the optical axis.
The optical system (imaging lens) shown in FIG. 3 includes a first lens E1 composed of a negative meniscus type negative lens with a strong concave surface facing the image surface in order from the object side to the image surface, and a strong concave surface on the image surface. A second lens E2 composed of a negative meniscus negative lens facing the side, a third lens E3 which is a biconvex positive lens, an aperture stop FA, a fourth lens E4 which is a biconvex positive lens, and a strong concave surface A fifth lens E5 made of a negative meniscus negative lens facing the object side, a sixth lens E6 made of a negative meniscus negative lens having a strong concave surface directed to the image side, and a biconvex having a strong convex surface directed to the object side A seventh lens E7 composed of a positive lens of the type and an eighth lens E8 composed of a positive meniscus positive lens with a strong convex surface facing the object side are arranged.
The first lens E1, the second lens E2, and the third lens E3 located on the object side with the aperture stop FA interposed therebetween constitute the first lens group G1, and the fourth lens located on the image side with the stop FA interposed therebetween. E4, the fifth lens E5, the sixth lens E6, the seventh lens E7, and the eighth lens E8 constitute a second lens group G2.

Further, the first lens group G1 includes two negative lenses positioned on the object side, that is, the first lens E1 and the second lens E2, with the widest air interval in the first lens group G1 as a boundary. And an image side first lens group GR1 including a third lens E3 which is a positive lens located on the image side of the object side first lens group GF1.
The second lens group G2 includes, in order from the object side, a first 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. A seventh lens E7 as a lens is composed of an object-side second lens group GF2 arranged continuously, and an eighth lens E8 as a single positive lens located on the image side of the object-side second lens group GF2. Image side second lens group GR2.
On the image side surface 4 of the second lens E2 of the object side first lens group GF1, the image side surface 6 of the image side first lens group GR1, and the object side surface 14 of the eighth lens E8 of the image side second lens group GR2, Each has an aspherical surface.
The fourth lens E4 and the fifth lens E5 of the object side second lens group GF2 are closely bonded to form a cemented lens, and the sixth lens E6 and the seventh lens E7 are closely bonded to be cemented. It is considered as a lens.

Then, in a photographing optical system of a camera using 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 is provided between the final surface of the eighth lens E8 and the image plane FS. At least one of a cover glass for protecting the filter and the light receiving surface of the CCD image sensor is inserted. For example, one parallel flat glass P1 is inserted.
In the third embodiment, focusing on a finite distance object is performed by moving all or part of the second lens group G2.
In FIG. 3, surface numbers of the respective optical surfaces are given. The reference numerals for FIG. 3 are used independently for each embodiment in order to avoid complicating the description. Therefore, even if a common reference numeral is used, it is not a configuration common to other embodiments.
FIG. 8 is an aberration diagram showing spherical aberration, astigmatism, distortion aberration, and coma aberration when the object distance in the imaging lens of FIG. 3 is infinity.
In Numerical Example 3, the focal length f = 6.00, 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 (Table 3).

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 aspheric surfaces, and the parameters in the equation (1) for each aspheric surface are as follows. It is.
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
Further, the numerical values of the conditional expressions [L _2F / L], [f _A / f ₁ ], and [A _1F-1R / L ₁ ] described above in the numerical example 3 are as follows.
Conditional expression numerical value 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 numerical example 3 are all within the range of the conditional expressions.

FIG. 8 shows aberration curves of spherical aberration, astigmatism, distortion aberration, and coma aberration formed by the imaging lens shown in FIG. 3 according to Numerical Example 3 described above. A broken line represents a sine condition, a solid line in astigmatism represents sagittal, and a broken line represents meridional.
As shown in FIG. 8, according to the imaging lens according to the first embodiment and Numerical Example 3 described above, each aberration is corrected at a high level, and spherical aberration and axial chromatic aberration do not become a problem. Astigmatism, curvature of field, lateral chromatic aberration are sufficiently small, coma and disturbance of color difference are well suppressed to the outermost part, and distortion is 2.0% or less in absolute value. ing.
By constructing the imaging lens as in the present invention, it is possible to ensure a very good image performance while having a wide angle of about 39 degrees and a large aperture with an F number of about 2.0 or less. It is clear from this Numerical Example 3 that it is obtained.
FIG. 4 shows a configuration of an imaging lens according to Numerical Example 4 (corresponding to the fourth embodiment) of the present invention, and schematically shows a longitudinal section along the optical axis.

The optical system (imaging lens) shown in FIG. 4 includes a first lens E1 composed of a negative meniscus type negative lens in which a strong concave surface is directed toward the image surface in order from the object side to the image surface, and the strong concave surface is an image surface. A second lens E2 made of a negative meniscus negative lens facing the side, a third lens E3 made of a positive meniscus type positive lens, a fourth lens E4 made of a biconvex positive lens, an aperture stop FA, a biconvex type A fifth lens E5, a sixth lens E6 composed of a negative meniscus negative lens with a strong concave surface facing the object side, and a seventh lens composed of a negative meniscus negative lens with a strong concave surface directed to the image side E7, an eighth lens E8 composed of a positive meniscus type positive lens with a strong convex surface facing the object side, and a ninth lens E9 composed of a biconvex positive lens with a strong convex surface directed to the object side And it has a configuration.
The first lens E1, the second lens E2, the third lens E3, and the fourth lens E4 located on the object side with the aperture stop FA interposed therebetween constitute the first lens group G1, and on the image side with the stop FA interposed therebetween. The fifth lens E5, the sixth lens E6, the seventh lens E7, the eighth lens E8, and the ninth lens E9 that are positioned constitute a second lens group G2.
Further, the first lens group G1 includes two negative lenses located on the object side with the widest air interval in the first lens group G1, that is, the first lens E1, the second lens E2, and the positive lens. An image-side first lens that is configured by an object-side first lens group GF1 configured with the third lens E3 and a fourth lens E4 that is a positive lens positioned closer to the image side than the object-side first lens group GF1. It consists of group GR1.

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. An object side second lens group GF2 in which an eighth lens E8 as a lens is continuously arranged, and a ninth lens E9 as a positive lens located on the image side from the object side second lens group GF2 are configured. Image side second lens group GR2.
An aspherical surface is formed on each of the image side surface 4 of the second lens E2 of the object side first lens group GF1 and the object side surface 16 of the ninth lens E9 of the image side second lens group GR2.
The fifth lens E5 and the sixth lens E6 of the object-side second lens group GF2 are closely bonded to form a cemented lens, and the seventh lens E7 and the eighth lens E8 are closely bonded to be cemented. It is considered as a lens.
Then, in a photographing optical system of a camera using a solid-state image pickup device such as a CCD image pickup device like a digital still camera, a low-pass filter, an infrared ray is provided between the final surface 17 of the ninth lens E9 and the image surface FS. At least one of a cover glass for protecting the cut filter and the light receiving surface of the CCD image sensor is inserted. For example, one parallel flat glass P1 is inserted.
In the fourth embodiment, the whole or part of the second lens group G2 is moved to perform focusing on a finite distance object.

In FIG. 4, surface numbers of the respective optical surfaces are given. The reference numerals for FIG. 4 are used independently for each embodiment in order to avoid complication of the description, and therefore, even if a common reference numeral is used, it is not a configuration common to the other embodiments.
FIG. 9 is an aberration diagram showing spherical aberration, astigmatism, distortion aberration, and coma aberration when the object distance in the imaging lens of FIG. 4 is infinity.
In Numerical Example 4, the focal length f = 6.00, 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 (Table 4).

In Table 4, each of the fourth and sixteenth optical surfaces with an asterisk “*” attached to the surface number is an aspheric surface, and the parameters in the expression (1) for each aspheric surface 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
Aspheric 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
The numerical values of the conditional expressions [L _2F / L], [f _A / f ₁ ], and [A _1F-1R / L ₁ ] described above in the numerical example 4 are as follows.
Conditional expression numerical value L _2F /L=0.154
f _A / f ₁ = 0.183
A _1F-1R / L ₁ = 0.424
Therefore, all the numerical values related to the conditional expressions of the present invention described in the numerical example 4 are within the range of the conditional expressions.

FIG. 9 shows aberration curves of spherical aberration, astigmatism, distortion aberration, and coma aberration formed by the imaging lens shown in FIG. 4 according to Numerical Example 4 described above. A broken line represents a sine condition, a solid line in astigmatism represents sagittal, and a broken line represents meridional.
As shown in FIG. 9, according to the imaging lens according to the fourth embodiment and Numerical Example 2 described above, each aberration is corrected at a high level, and spherical aberration and axial chromatic aberration do not matter. Astigmatism, curvature of field, lateral chromatic aberration are sufficiently small, coma and disturbance of color difference are well suppressed to the outermost part, and distortion is 2.0% or less in absolute value. ing.
By configuring the imaging lens as in the present invention, a very good image performance can be ensured while the half angle of view is as wide as 39 degrees and the F number is as large as 2.0. This is also clear from Numerical Example 4.
FIG. 5 shows a configuration of an imaging lens according to Numerical Example 5 (corresponding to the fifth embodiment) of the present invention, and schematically shows a longitudinal section along the optical axis.

The optical system (imaging lens) shown in FIG. 5 is a first lens E1 composed of a negative meniscus type negative lens with a strong concave surface facing the image surface side in order from the object side to the image surface, and a strong concave surface as the image surface. A second lens E2 composed of a negative meniscus negative lens facing the side, a third lens E3 which is a biconvex positive lens, a fourth lens E4 composed of a biconvex positive lens, an aperture stop FA, a biconvex type A fifth lens E5 that is a positive lens, a sixth lens E6 that is a negative meniscus negative lens with a strong concave surface facing the object side, and a seventh lens that is a negative meniscus negative lens with a strong concave surface facing the image side A lens E7, an eighth lens E8 composed of a positive meniscus type positive lens with its strong convex surface facing the object side, and a ninth lens E9 composed of a positive meniscus type positive lens with its strong convex surface facing the object side And has a configuration was.
The first lens E1, the second lens E2, the third lens E3, and the fourth lens E4 that are located on the object side with the aperture stop FA interposed therebetween constitute the first lens group G1, and on the image side with the stop FA interposed therebetween. The fifth lens E5, the sixth lens E6, the seventh lens E7, the eighth lens E8, and the ninth lens E9 that are positioned constitute a second lens group G2.

Further, the first lens group G1 includes two negative lenses positioned on the object side with the widest air interval in the first lens group G1, that is, a first lens E1 and a second lens E2, and a positive lens. An image-side first lens group GF1 composed of a third lens E3 composed of a lens and a fourth lens E4 which is a positive lens located on the image side of the object-side first lens group GF1. It consists of one lens group GR1.
The second lens group G2 includes, in order from the object side, a first 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. An object side second lens group GF2 in which an eighth lens E8 as a lens is continuously arranged, and a ninth lens E9 as a positive lens located on the image side from the object side second lens group GF2 are configured. Image side second lens group GR2.
An aspherical surface is formed on each of the image side surface 4 of the second lens E2 of the object side first lens group GF1 and the object side surface 16 of the ninth lens E9 of the image side second lens group GR2.
The fifth lens E5 and the sixth lens E6 of the object-side second lens group GF2 are closely bonded to form a cemented lens, and the seventh lens E7 and the eighth lens E8 are closely bonded to be cemented. It is considered as a lens.

Then, in a photographing optical system of a camera using a solid-state image pickup device such as a CCD image pickup device like a digital still camera, a low-pass filter, an infrared ray is provided between the final surface 17 of the ninth lens E9 and the image surface FS. At least one of a cover glass for protecting the cut filter and the light receiving surface of the CCD image sensor is inserted. For example, one parallel flat glass P1 is inserted.
In the fifth embodiment, focusing on a finite distance object is performed by moving all or part of the second lens group G2.
In FIG. 5, the surface numbers of the respective optical surfaces are shown. The reference numerals for FIG. 5 are used independently for each embodiment in order to avoid complication of description, and therefore, even if a common reference numeral is used, it is not a configuration common to the other embodiments.
FIG. 10 is an aberration diagram showing spherical aberration, astigmatism, distortion aberration, and coma aberration when the object distance in the imaging lens of FIG. 5 is infinity.
In this numerical value example 5, the focal length f = 6.00, 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 (Table 5).

In Table 5, the fourth and sixteenth optical surfaces with an asterisk “*” in the surface number are aspherical surfaces, and the parameters in the expression (1) for each aspherical 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
Aspheric surface: 14th 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

Further, the numerical values of the conditional expressions [L _2F / L], [f _A / f ₁ ], and [A _1F-1R / L ₁ ] described above in the numerical example 5 are as follows.
Conditional expression numerical value L _2F /L=0.132
f _A / f ₁ = 0.238
A _1F-1R / L ₁ = 0.469
Accordingly, the numerical values related to the conditional expressions of the present invention described above in the numerical value example 5 are all within the range of the conditional expressions.

FIG. 10 shows aberration curves of spherical aberration, astigmatism, distortion aberration, and coma aberration formed by the imaging lens shown in FIG. 5 according to Numerical Example 5 described above. A broken line represents a sine condition, a solid line in astigmatism represents sagittal, and a broken line represents meridional.
As shown in FIG. 10, according to the imaging lens according to the fifth embodiment and numerical example 5 described above, each aberration is corrected at a high level, and spherical aberration and axial chromatic aberration do not become a problem. Astigmatism, curvature of field, lateral chromatic aberration are sufficiently small, coma and disturbance of color difference are well suppressed to the outermost part, and distortion is 2.0% or less in absolute value. ing.
By configuring the imaging lens as in the present invention, a very good image performance can be ensured while the half angle of view is as wide as 39 degrees and the F number is as large as 2.0. This is also clear from Numerical Example 5.
Next, an imaging lens as a zoom lens according to the present invention as shown in Numerical Example 1 to Numerical Example 5 (first to fifth embodiments) described above is employed (portable information). An embodiment of the present invention that includes a terminal device will be described with reference to FIGS.

FIG. 11A is a perspective view schematically showing the appearance of the retracted state of the camera as viewed from the front side, that is, the object, that is, the subject side, and FIG. 11B is a state of use of the camera as viewed from the front side. FIG. 11C is a perspective view schematically showing the appearance of the camera as seen from the back side that is the photographer side, and FIG. 12 shows the functional configuration of the camera. It is a block diagram. 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, and the imaging lens or camera according to the present invention is included in such a portable information terminal device. It may be adopted.
As shown in FIGS. 11A, 11B, and 11C, the camera 1 includes a photographing lens 2, a shutter button 3, a zoom lever 4, a finder 5, a strobe 6, a liquid crystal monitor 7, an operation button 8, and a power switch. 9. A memory / communication card slot 10 is provided. Further, as shown in FIG. 12, the camera 1 also includes a light receiving element 12, a signal processing device 13, an image processing device 14, a central processing unit (CPU) 15, a semiconductor memory 16, a communication card 17 and the like.

The camera 1 includes a photographic lens 2 that is a photographic optical system and a light receiving element 12 as an area sensor such as a CCD (charge coupled device) imaging element. An image is read by the light receiving element 12. As the photographic lens 2, the photographic optical system according to the present invention as described in Numerical Examples 1 to 5 is used. Specifically, a lens unit is configured using a lens or the like that is an optical element constituting the photographing optical system. This lens unit has a mechanism for holding each lens or the like so that it can be moved and operated at least for each lens group. The photographing lens 2 incorporated in the camera is usually incorporated in the form of this lens unit.
The output of the light receiving element 12 is processed by the signal processing device 13 controlled by the central processing unit 15 and converted into digital image information. The image information digitized by the signal processing device 13 is subjected to predetermined image processing in the image processing device 14 which is also controlled by the central processing unit 15 and then recorded in the semiconductor memory 16 such as a nonvolatile memory. In this case, the semiconductor memory 16 may be a memory card loaded in the memory / communication card slot 10 or a semiconductor memory built in the camera body.
On the liquid crystal monitor 7, an image being photographed can be displayed, and an image recorded in the semiconductor memory 16 can be displayed. The image recorded in the semiconductor memory 16 can also be transmitted to the outside via a communication card 17 or the like loaded in the memory / communication card slot 10.

When the camera 1 is carried, the taking lens 2 is retracted and buried in the body of the camera 1 as shown in FIG. 11A. When the user operates the power switch 9 to turn on the power, As shown in FIG. 11B, the lens barrel is extended and protrudes from the body of the camera 1. Since the present invention is a single focus lens, when the zoom lever 4 is operated, zooming by so-called digital zoom is performed in which the cutout range of the image is changed and pseudo-displacement is performed. At this time, it is desirable that the optical system of the finder 5 is also scaled in conjunction with the change in the angle of view of the photographing lens 2.
In many cases, focusing is performed by half-pressing the shutter button. In the imaging lens according to any one of claims 1 to 10, focusing can be performed by moving the whole or a part of the second lens group G2, as described above, and the movement of the first lens group G1, It can also be performed by moving the light receiving element 12, and can also be performed by a combination of a plurality of methods if necessary. When the shutter button is further pressed, shooting is performed, and thereafter, the processing described above is performed.
When the image recorded in the semiconductor memory 16 is displayed on the liquid crystal monitor 7 or transmitted to the outside using the communication card 17 or the like, the operation button 8 is used. The semiconductor memory 16 and the communication card 17 are inserted into dedicated or general-purpose slots 10 for use.

When the photographing lens 2 is in the retracted state, the lens groups of the imaging lens are not necessarily arranged on the optical axis. For example, if the mechanism is such that the object-side second lens group GF2 and / or the image-side second lens group GR2 are retracted from the optical axis and housed in parallel with other lens groups, the camera can be made thinner. Can be realized. In addition, if the distance between the object-side first lens group GF1 and the image-side first lens group GR1 is shortened in the retracted state, a further reduction in thickness can be achieved.
In the camera (personal digital assistant device) as described above, the imaging lens of Numerical Example 1 to Numerical Example 5 can be used as a photographing lens. Therefore, a small camera (personal digital assistant device) with high image quality using a light receiving element of 10 million to 20 million pixel class can be realized.

2 is a cross-sectional view illustrating a configuration of an imaging lens of Numerical Example 1. FIG. 6 is a cross-sectional view illustrating a configuration of an imaging lens of Numerical Example 2. FIG. 10 is a cross-sectional view illustrating a configuration of an imaging lens of Numerical Example 3. FIG. 6 is a cross-sectional view illustrating a configuration of an imaging lens of Numerical Example 4. FIG. 10 is a cross-sectional view illustrating a configuration of an imaging lens of Numerical Example 5. FIG. 3 is an aberration curve diagram of the imaging lens of Numerical Example 1. FIG. 10 is an aberration curve diagram of the imaging lens of Numerical Example 2. FIG. 10 is an aberration curve diagram of the imaging lens of Numerical Example 3. FIG. FIG. 9 is an aberration curve diagram of the imaging lens of Numerical Example 4. 10 is an aberration curve diagram of the imaging lens of Numerical Example 5. FIG. BRIEF DESCRIPTION OF THE DRAWINGS It is an external view of the digital camera which shows one Embodiment as a camera (portable information terminal device) which concerns on this invention, (a) is the perspective view seen from the front side at the time of carrying (when retracted), (b) is The perspective view which shows a part of the front side at the time of use (at the time of lens extension), (c) is a perspective view of the back side. It is a block diagram which shows the outline of the system structure of the camera which concerns on this invention of this invention.

Explanation of symbols

G1 First lens group G2 Second lens group GF1 Object side first lens group GR1 Image side first lens group GF2 Object side second lens group GR2 Image side second lens group E1 to E9 First lens to ninth lens FA aperture Aperture P1 Parallel plate FS Image plane 1 Camera 2 Shooting lens 3 Shutter button 4 Zoom lever 5 Viewfinder 6 Strobe 7 Liquid crystal monitor 8 Operation button 9 Power switch 10 Memory / communication card slot 12 Light emitting element 13 Signal processing device 14 Image processing device 15 Center Arithmetic unit 16 Semiconductor memory 17 Communication card, etc.

Claims (12)

In an imaging lens composed of a first lens group located on the object side across the aperture stop and a second lens group located on the image side,
In order from the object side to the first lens group, an object-side first lens group having at least two negative lenses positioned on the object side with the widest air interval in the first lens group as a boundary, and the image side And an image-side first lens group having at least one positive lens located in the first lens group, and the second lens group in order from the object side, a first positive lens, a first negative lens, a second negative lens, and a second lens An imaging lens comprising: an object-side second lens group in which a positive lens is continuously arranged; and an image-side second lens group including at least one lens located on the image side. 2. The imaging lens according to claim 1, wherein the following conditional expression is satisfied.
0.1 < _L2F / L <0.25
However, L _2F represents the total length of the object side second lens group, and L represents the distance from the most object side surface of the imaging lens to the image plane.   3. The imaging lens according to claim 1, wherein the first positive lens and the first negative lens, and the second negative lens and the second positive lens of the object-side second lens group are cemented. An imaging lens characterized by having   4. The imaging lens according to claim 3, wherein a cemented surface of the first positive lens and the first negative lens of the object-side second lens group has a convex shape toward the image side, and the second negative lens and the An imaging lens, wherein the cemented surface of the second positive lens has a convex shape on the object side. 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, 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 is a spacing between the image plane-side first lens group and the object-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: 7.
ν _d > 80.0
Δθ _{g, F} > 0.025
Where ν _d is the Abbe number of the first positive lens in the second lens group, 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 and the partial dispersion ratio θ _{g, F} = (
In n _g -n _{F) / (graph} with n F -n _C) a longitudinal axis, and the standard line a straight line connecting the glass type K7 (OHARA glass type name NSL7) and glass type F2 (OHARA glass type name PBM2) This is the deviation from the standard line of the glass type. _{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 object-side first lens group includes two negative meniscus lenses having a convex surface facing the object side. An imaging lens having the configuration described above, wherein at least one of the lenses has an aspheric image side surface.   9. The imaging lens according to claim 1, wherein the image-side second lens group includes one lens and has an aspherical surface. .   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. Image lens.   A camera comprising the imaging lens according to claim 1 as a photographing optical system.   A portable information terminal device comprising the imaging lens according to any one of claims 1 to 11 as a photographing optical system of a camera function unit.

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