JP2012008347A - Imaging lens, imaging device, and information device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging lens that has a wide angle and a large diameter, is sufficiently compact, has sufficiently reduced aberration/color difference and so on, and high resolution, and achieves distortion-free depiction with high contrast even at full-open diaphragm without causing collapse of point images even in peripheral areas of a field angle or causing unnecessary coloring to a part with a large brightness difference.SOLUTION: A first lens group G1 is arranged on an object side of a diaphragm FA, and a second lens group G2 having positive diffractive power is arranged on an image side of the diaphragm FA. In the first lens group G1, a first F lens group S1F having a negative diffractive power and a first R lens group S1R are arranged in order from the object side. The first F lens group S1F is constituted by arranging a first negative lens E1 with its face of larger curvature directed toward the image side and a second negative lens E2 with its face of larger curvature directed toward the object side in order from the object side. The first R lens group S1R is constituted by positive lenses or by a cemented lens having a positive refractive power as a whole.

Description

  The present invention relates to an imaging lens that forms a subject image to capture a still image or a moving image, and can be used for a silver salt camera using a silver salt film. The present invention relates to an imaging lens suitable for an imaging apparatus using an electronic imaging means, an imaging apparatus using such an imaging lens, and an information device such as a portable information terminal device having an imaging function.

The market for so-called digital cameras is becoming increasingly large, and there are various requests for digital cameras from users. Among such digital cameras, the category of high-quality compact cameras using a relatively large image sensor with a diagonal length of about 20 mm to 45 mm and equipped with a high-performance single focus lens is highly expected by users. Collecting. As a request from users in this category, in addition to high performance, there is a high weight for being excellent in portability, that is, being small.
Here, in terms of performance enhancement, in addition to having a resolution that can accommodate at least an image sensor of about 10 million to 20 million pixels, 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, and that a straight line is drawn with little distortion.
Further, in terms of increasing the diameter, it is necessary to differentiate from a general compact camera equipped with a zoom lens, and therefore an open F value (F number) of at least less than F2.8 is required.

In terms of miniaturization, since the actual focal length becomes longer due to the relatively large image sensor, the overall length becomes shorter when normalized with the focal length or maximum image height than when using a small image sensor. It is necessary to be.
In addition, as for the angle of view of the taking 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 around 38 degrees. The half angle of view of 38 degrees corresponds to a focal length of 28 mm in terms of a 35 mm silver salt camera using a conventional 35 mm silver salt film (so-called Leica silver salt film).
Many types of imaging lenses for digital cameras can be considered, 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. Since the area sensor used as the image sensor has a characteristic of having a color filter and a micro lens for each pixel, the exit pupil position is kept away from the image plane, and the peripheral luminous flux is as close to the sensor as possible. The presence of a request to make the light incident on the main reason for adopting the retrofocus type is. However, the retrofocus type has a large asymmetry in refractive power arrangement, and tends to be incompletely corrected for coma, distortion, lateral chromatic aberration, and the like.

In addition, the retrofocus type was originally designed to ensure the back focus for using wide-angle lenses as interchangeable lenses for single-lens reflex (single-lens reflex) cameras. The distance from the side surface to the image plane) tends to be large.
Such a retrofocus type imaging lens, which has an open F value of less than 2.8 and a half angle of view of around 38 degrees, can correct various aberrations relatively well. Patent Document 1 (Japanese Patent Laid-Open No. 2010-39088), Patent Document 2 (Japanese Patent Laid-Open No. 9-96759), and the like.
The imaging lens disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 2010-39088) has a bright open F value of about F1.9, but the total lens length is very large, 9 times the maximum image height. Further, the imaging lens disclosed in Patent Document 2 (Japanese Patent Laid-Open No. 9-96759) has a wide angle of 41.5 degrees, but the total lens length is as large as 6 times or more of the maximum image height.

As described above, Patent Document 1 (Japanese Patent Application Laid-Open No. 2010-39088), Patent Document 2 (Japanese Patent Application Laid-Open No. 9-96759), and the like are retrofocus types having an open F value of less than 2.8, and An imaging lens is disclosed in which various aberrations are corrected relatively well while having a half angle of view of around 38 degrees.
However, the imaging lens disclosed in Patent Document 1 (Japanese Patent Application Laid-Open No. 2010-39088) has a sufficiently wide open F value of about F1.9, and is notable in terms of a large aperture. However, the total lens length is as large as 9 times the maximum image height, which is insufficient in terms of miniaturization. The imaging lens disclosed in Patent Document 2 (Japanese Patent Application Laid-Open No. 9-96759) has a wide angle of 41.5 degrees, but the total lens length is as large as 6 times or more of the maximum image height. In terms of miniaturization, it is insufficient.
The present invention has been made in view of the above-described circumstances. The half angle of view is as wide as about 38 degrees, the open F value is less than 2.8, and the aperture is sufficiently small, and is astigmatism. In addition to sufficiently reducing the curvature of field, chromatic aberration of magnification, color difference of coma aberration, distortion, etc., it has a resolution corresponding to an image sensor of 10 million to 20 million pixels, and from a wide aperture to high contrast The point image does not collapse to the periphery of the angle of view, no unnecessary coloring occurs even in areas with large luminance differences, and it is possible to draw straight lines without distortion, making it possible to obtain high performance It is an object to provide an imaging lens, an imaging device, and an information device.

The object of the present invention is to provide a wide angle, large aperture, sufficiently small size, sufficiently reduce aberration, color difference, etc., have high resolving power, and have a high contrast from the wide open aperture to the periphery of the angle of view. It is an object of the present invention to provide a high-performance imaging lens that does not cause a point image collapse to a portion, does not cause unnecessary coloring even in a portion having a large luminance difference, and enables depiction without distortion.
An object of claim 2 of the present invention is to provide an image forming lens that can be accommodated in a smaller size and that can achieve high performance by correcting each aberration better. .
The object of claim 3 of the present invention is to provide an image forming lens that can correct each aberration more satisfactorily and can achieve a small size and high performance by sufficiently moving the exit pupil position away from the image plane. There is to do.
A fourth object of the present invention is to provide an imaging lens that can improve the flatness of the image surface and obtain higher performance.
An object of claim 5 of the present invention is to provide an imaging lens that can more appropriately balance downsizing and high performance.
An object of claim 6 of the present invention is to provide an imaging lens that can suppress the generation of spherical aberration associated with an increase in diameter and obtain higher performance.
An object of claim 7 of the present invention is to provide an image forming lens that can correct chromatic aberration more satisfactorily and obtain even higher performance.

An object of an eighth aspect of the present invention is to provide, in particular, an imaging lens capable of suppressing the occurrence of chromatic aberration by a method different from that of the seventh aspect and obtaining even higher performance.
An object of claim 9 of the present invention is to provide an imaging lens that can obtain a small size and high performance by suppressing a change in imaging performance accompanying focusing on an object located at a finite distance. There is.
An object of claim 10 of the present invention is to provide an imaging lens that can achieve a smaller size and higher performance, in particular, by further suppressing a change in imaging performance associated with focusing on an object located at a finite distance. It is to provide.
The object of claim 11 of the present invention is a wide angle with a half angle of view of about 38 degrees and a large aperture with an F number of less than 2.8, sufficiently small, sufficiently reducing aberrations and color differences, It has a high resolving power corresponding to an image sensor with 10 million pixels, does not collapse the point image from the full aperture to the periphery of the angle of view with high contrast, and does not cause unnecessary coloring even in areas with large luminance differences. It is an object of the present invention to provide an image pickup apparatus that can perform high-quality image pickup with a small size by using a high-performance imaging lens that enables depiction without distortion as an image pickup optical system.

  The object of claim 12 of the present invention is wide angle, large aperture, sufficiently small size, sufficiently reducing aberration and color difference, etc., having high resolving power, and high contrast from the wide open to the periphery of the angle of view. An imaging optical system for imaging functions that does not cause point images to be lost, does not cause unnecessary coloring even in areas with large luminance differences, and enables depiction without distortion It is used to provide an information device that is capable of taking a small image with high image quality.

In order to achieve the above-described object, the imaging lens according to the present invention described in claim 1
A first lens group on the object side of the aperture stop, and a second lens group having a positive refractive power on the image side of the aperture stop, respectively.
In the imaging lens in which the first lens group is configured by arranging, in order from the object side, a first F lens group having a negative refractive power and a first R lens group having a positive refractive power,
The first F lens group includes, in order from the object side, a first negative lens having a large curvature surface facing the image side and a second negative lens having a large curvature surface facing the object side. ,
The first R lens group is configured with one of a positive lens and a cemented lens having a positive refractive power as a whole,
The distance from the surface closest to the object side of the first lens group to the image plane in a state focused on an object at infinity is L, the maximum image height is Y ′, and the radius of curvature of the object side surface of the second negative lens is r ₂₁ and the radius of curvature of the image-side surface of the second negative lens is r ₂₂ ,
Conditional expression:
[1] 2.8 <L / Y ′ <4.3
[2] −7.0 <(r ₂₁ + r ₂₂ ) / (r ₂₁ −r ₂₂ ) <− 0.7
It is characterized by satisfying.

An imaging lens according to the present invention described in claim 2 is the imaging lens of claim 1,
Bf is the distance from the surface closest to the image side of the second lens group in the state focused on the object at infinity, and the image height is Y ′.
Conditional expression:
[3] 0.8 <Bf / Y ′ <1.6
It is characterized by satisfying.
The imaging lens according to the present invention described in claim 3 is the imaging lens according to claim 1 or 2,
The distance from the most object-side surface of the first lens unit to the most image-side surface is L ₁ , and the distance from the most object-side surface of the first lens unit to the image surface in a state of focusing on an object at infinity. Let L be the distance
Conditional expression:
[4] 0.20 <L ₁ /L<0.32
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 focal length of the entire imaging lens system is f _A , and the focal length of the first lens group is f ₁ .
Conditional expression:
[5] 0.0 <f _A / f ₁ <0.6
It is characterized by satisfying.
An imaging lens according to the present invention described in claim 5 is the imaging lens of claim 4,
The focal length of the first F lens group is f _1F , and the focal length of the first R lens group is f _1R .
Conditional expression:
[6] -1.3 <f _1F / f _1R <−0.7
It is characterized by satisfying.

An 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 distance between the first F lens group and the first R lens group is A _1F-1R , and the distance from the most object side surface to the most image side surface of the first lens group is L ₁ .
Conditional expression:
[7] 0.0 <A _1F-1R / L ₁ <0.1
It is characterized by satisfying.
The imaging lens according to the present invention described in claim 7 is the imaging lens according to any one of claims 1 to 6,
The refractive index of the first negative lens or the second negative lens of the first F lens group is n _d , the Abbe number of the first negative lens or the second negative lens is ν _d , and the first negative lens or the _Let P _{g, F} be the partial dispersion ratio of the second negative lens,
The partial dispersion ratio _{P g, F} is the optical glass constituting the negative lens, g-line, F line and the refractive index, respectively _n g the C-line, as _{n F} and _{n C,
P g, F = (n g} -n F) / (n F -n C)
As
At least one of the first negative lens and the second negative lens of the first F lens group is
Conditional expression:
[8] 1.45 _<n d _<1.65
[9] 55.0 <ν _d <95.0
[10] 0.015 <P _{g, F} − (− 0.001802 × ν _d +0.6483) <0.050
It is characterized by satisfying.

The imaging lens according to the present invention described in claim 8 is the imaging lens according to any one of claims 1 to 7,
The first R lens group is a cemented lens configured by sequentially arranging a positive lens and a negative lens from the object side.
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,
When focusing on an object at a short distance, the distance between the first lens group and the second lens group is shortened as compared with a state where an object at infinity is focused.
An imaging lens according to the present invention described in claim 10 is the imaging lens of claim 9,
The distance between the first lens group and the second lens group in a state focused on an object at infinity is A _1-2 , and the first lens in a state focused on a short distance object at an imaging magnification of −1/20 times. The distance from the surface closest to the image side of the second lens group to the image plane in a state where the distance between the second lens group and the second lens group is in the state of A _1-2M and an imaging magnification of −1 / 20 × Bf _M , and Bf is the distance from the most image side surface to the image plane of the second lens group in a state of focusing on an object at infinity,
Conditional expression:
[11] _{-0.5 <(A 1-2M -A 1-2)} / (Bf M -Bf) <- 0.2
It is characterized by satisfying.

An imaging device according to an eleventh aspect of the present invention includes the imaging lens according to any one of the first to tenth aspects as an imaging optical system.
An information device according to a twelfth aspect of the present invention has an imaging function, and the imaging lens according to any one of the first to tenth aspects is used as an imaging optical system.

  According to the present invention, the half angle of view is as wide as about 38 degrees, the open F value is less than 2.8 and the aperture is sufficiently small, and astigmatism, field curvature, lateral chromatic aberration, coma The color difference of aberration, distortion, etc. are sufficiently reduced to have a resolution corresponding to an image sensor with 10 to 20 million pixels, and point images from the full aperture to the periphery of the angle of view with high contrast. To provide a high-performance imaging lens, an imaging device, and an information device that do not collapse, do not cause unnecessary coloring even in a portion with a large luminance difference, and can draw a straight line without distortion as a straight line it can.

That is, according to the imaging lens of claim 1 of the present invention,
A first lens group on the object side of the aperture stop, and a second lens group having a positive refractive power on the image side of the aperture stop, respectively.
In the imaging lens in which the first lens group is configured by arranging, in order from the object side, a first F lens group having a negative refractive power and a first R lens group having a positive refractive power,
The first F lens group includes, in order from the object side, a first negative lens having a large curvature surface facing the image side and a second negative lens having a large curvature surface facing the object side. ,
The first R lens group is configured with one of a positive lens and a cemented lens having a positive refractive power as a whole,
The distance from the surface closest to the object side of the first lens group to the image plane in a state focused on an object at infinity is L, the maximum image height is Y ′, and the radius of curvature of the object side surface of the second negative lens is r ₂₁ and the radius of curvature of the image-side surface of the second negative lens is r ₂₂ ,
Conditional expression:
[1] 2.8 <L / Y ′ <4.3
[2] −7.0 <(r ₂₁ + r ₂₂ ) / (r ₂₁ −r ₂₂ ) <− 0.7
By satisfying
The half angle of view is as wide as 38 degrees, the F number is less than 2.8, and the aperture is sufficiently small and sufficiently small. It has a high resolving power 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 it is not necessary even in areas with large luminance differences. Therefore, a straight line can be drawn without distortion, and high performance can be obtained, and a compact and extremely high image quality imaging lens can be realized.

According to the imaging lens of claim 2 of the present invention, in the imaging lens of claim 1,
Bf is the distance from the surface closest to the image side of the second lens group in the state focused on the object at infinity, and the image height is Y ′.
Conditional expression:
[3] 0.8 <Bf / Y ′ <1.6
By satisfying
In particular, it can be housed in a smaller size, and moreover, it is possible to obtain a high performance by correcting each aberration better, thereby realizing a high-quality imaging lens that is more portable.
According to the imaging lens of claim 3 of the present invention, in the imaging lens of claim 1 or claim 2,
The distance from the most object-side surface of the first lens unit to the most image-side surface is L ₁ , and the distance from the most object-side surface of the first lens unit to the image surface in a state of focusing on an object at infinity. Let L be the distance
Conditional expression:
[4] 0.20 <L ₁ /L<0.32
By satisfying
In particular, each aberration is corrected better and the exit pupil position is far enough away from the image plane, making it possible to obtain a compact and high-performance lens that realizes a high-quality image-forming lens that does not lose light to the periphery of the screen. can do.

According to the imaging lens of claim 4 of the present invention, in the imaging lens of any one of claims 1 to 3,
The focal length of the entire imaging lens system is f _A , and the focal length of the first lens group is f ₁ .
Conditional expression:
[5] 0.0 <f _A / f ₁ <0.6
By satisfying
In particular, it is possible to improve the flatness of the image surface and obtain higher performance, and it is possible to realize a higher quality imaging lens having a high resolution from the full aperture to the entire screen.
According to the imaging lens of claim 5 of the present invention, in the imaging lens of claim 4,
The focal length of the first F lens group is f _1F , and the focal length of the first R lens group is f _1R .
Conditional expression:
[6] -1.3 <f _1F / f _1R <−0.7
By satisfying
In particular, it is possible to more appropriately balance downsizing and high performance, and it is possible to realize an imaging lens with a smaller size and higher image quality.

According to the imaging lens of claim 6 of the present invention, in the imaging lens of any one of claims 1 to 5,
The distance between the first F lens group and the first R lens group is A _1F-1R , and the distance from the most object side surface to the most image side surface of the first lens group is L ₁ .
Conditional expression:
[7] 0.0 <A _1F-1R / L ₁ <0.1
By satisfying
In particular, it is possible to obtain higher performance by suppressing the occurrence of spherical aberration associated with the increase in aperture, and realizing a high-quality imaging lens that can obtain images with higher sharpness from the wide open aperture. can do.

According to the imaging lens of claim 7 of the present invention, in the imaging lens of any one of claims 1 to 6,
The refractive index of the first negative lens or the second negative lens of the first F lens group is n _d , the Abbe number of the first negative lens or the second negative lens is ν _d , and the first negative lens or the _Let P _{g, F} be the partial dispersion ratio of the second negative lens,
The partial dispersion ratio _{P g, F} is the optical glass constituting the negative lens, g-line, F line and the refractive index, respectively _n g the C-line, as _{n F} and _{n C,
P g, F = (n g} -n F) / (n F -n C)
As
At least one of the first negative lens and the second negative lens of the first F lens group is
Conditional expression:
[8] 1.45 _<n d _<1.65
[9] 55.0 <ν _d <95.0
[10] 0.015 <P _{g, F} − (− 0.001802 × ν _d +0.6483) <0.050
By satisfying
In particular, it is possible to correct chromatic aberration more favorably to obtain even higher performance, and it is possible to realize a higher quality imaging lens that does not bother color shift and color blur.

According to the imaging lens of claim 8 of the present invention, in the imaging lens of any one of claims 1 to 7,
The first R lens group is a cemented lens configured by sequentially arranging a positive lens and a negative lens from the object side.
In particular, it is possible to suppress the occurrence of chromatic aberration by a method different from that of Claim 7 and to obtain even higher performance, realizing a higher quality imaging lens that does not bother color shift and color bleeding. can do.
According to the imaging lens of claim 9 of the present invention, in the imaging lens of any one of claims 1 to 8,
When focusing on a short-distance object, the distance between the first lens group and the second lens group is shorter than that in a state where the object is focused on an infinite object.
In particular, it is possible to obtain small size and high performance by suppressing changes in imaging performance due to focusing on an object located at a finite distance, and high resolution over the entire screen in all imaging areas from infinity to the shortest shooting distance. A compact and high-quality imaging lens having

According to the imaging lens of claim 10 of the present invention, in the imaging lens of claim 9,
The distance between the first lens group and the second lens group in a state focused on an object at infinity is A _1-2 , and the first lens in a state focused on a short distance object at an imaging magnification of −1/20 times. The distance from the surface closest to the image side of the second lens group to the image plane in a state where the distance between the second lens group and the second lens group is in the state of A _1-2M and an imaging magnification of −1 / 20 × Bf _M , and Bf is the distance from the most image side surface to the image plane of the second lens group in a state of focusing on an object at infinity,
Conditional expression:
[11] _{-0.5 <(A 1-2M -A 1-2)} / (Bf M -Bf) <- 0.2
By satisfying
In particular, it is possible to obtain a small size and higher performance by further suppressing changes in imaging performance due to focusing on an object located at a finite distance, and over the entire screen in the entire imaging area from infinity to the shortest imaging distance. A compact and higher quality imaging lens having a high resolution can be realized.

According to the imaging device of claim 11 of the present invention,
By including the imaging lens according to any one of claims 1 to 10 as an imaging optical system,
Although it has a wide half angle of view of about 38 degrees and a large aperture of F number less than 2.8, it is sufficiently small and has astigmatism, curvature of field, lateral chromatic aberration, distortion and coma, etc. With a high resolution corresponding to an image sensor with 10 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 a high contrast. In addition, it is possible to obtain a small and high-quality image by using a high-performance imaging lens as an imaging optical system that does not cause unnecessary coloring and enables straight lines to be drawn without distortion. The user can take a high-quality image with an imaging device having excellent portability.

And according to the information device of claim 12 of the present invention,
By using the imaging lens according to any one of claims 1 to 10 as an imaging optical system having an imaging function,
Although it has a wide half angle of view of about 38 degrees and a large aperture of F number less than 2.8, it is sufficiently small and has astigmatism, curvature of field, lateral chromatic aberration, distortion and coma, etc. With a high resolution corresponding to an image sensor with 10 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 a high contrast. High-quality imaging lens that uses a high-performance imaging lens as an imaging optical system for imaging functions, without causing unnecessary coloring, and allowing straight lines to be drawn without distortion The user can take a high-quality image with an information device having excellent portability and transmit the image to the outside.

It is a typical sectional view along an optical axis showing composition of an optical system of an imaging lens concerning Example 1 of the present invention. FIG. 3 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma in a state where the imaging lens according to Example 1 of the present invention shown in FIG. 1 is focused on an object at infinity. FIG. 2 is an aberration curve diagram showing spherical aberration, astigmatism, distortion aberration, and coma aberration in a state in which the imaging lens according to Example 1 of the present invention shown in FIG. It is a typical sectional view along an optical axis which shows composition of an optical system of an imaging lens concerning Example 2 of the present invention. FIG. 5 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma in a state where the imaging lens according to Example 2 of the present invention shown in FIG. 4 is focused on an object at infinity. FIG. 5 is an aberration curve diagram showing spherical aberration, astigmatism, distortion aberration and coma aberration in a state where the imaging lens according to Example 2 of the present invention shown in FIG. It is a typical sectional view along an optical axis which shows composition of an optical system of an imaging lens concerning Example 3 of the present invention. FIG. 8 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration in a state where the imaging lens according to Example 3 of the present invention shown in FIG. 7 is focused on an object at infinity. FIG. 9 is an aberration curve diagram showing spherical aberration, astigmatism, distortion aberration and coma aberration in a state where the imaging lens according to Example 3 of the present invention shown in FIG. It is a typical sectional view along an optical axis which shows composition of an optical system of an imaging lens concerning Example 4 of the present invention. FIG. 11 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration when the imaging lens according to Example 4 of the present invention shown in FIG. 10 is focused on an object at infinity. FIG. 11 is an aberration curve diagram showing spherical aberration, astigmatism, distortion aberration, and coma aberration in a state where the imaging lens according to Example 4 of the present invention shown in FIG. It is a typical sectional view along an optical axis showing composition of an optical system of an imaging lens concerning Example 5 of the present invention. FIG. 14 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma in the state where the imaging lens according to Example 5 of the present invention shown in FIG. 13 is focused on an object at infinity. FIG. 14 is an aberration curve diagram showing spherical aberration, astigmatism, distortion aberration and coma aberration when the imaging lens according to Example 5 of the present invention shown in FIG. It is the perspective view seen from the object side which shows typically the appearance composition of the digital camera as an imaging device concerning one embodiment of the present invention, among these, (a) uses the imaging lens concerning the present invention. (B) shows a state in which the image pickup lens protrudes from the body of the digital camera, partly omitted. It is the perspective view seen from the photographer side which shows typically the external appearance structure of the digital camera of FIG. It is a block diagram which shows typically the function structure of the digital camera of FIG.

Hereinafter, based on an embodiment and an example of the present invention, an imaging lens, an imaging device, and an information device concerning the present invention are explained in detail with reference to drawings. Before describing examples including specific numerical values, first, in order to explain the principle embodiments of the present invention, configurations defined in the claims of the claims will be described.
In the imaging lens according to the first to tenth aspects of the present invention, a first lens group is disposed on the object side of the aperture stop, and a second lens group having a positive refractive power is disposed on the image side of the aperture stop. The first lens group is an imaging lens configured by arranging, in order from the object side, a first F lens group having a negative refractive power and a first R lens group having a positive refractive power. Furthermore, each has the following characteristics. Here, the first F lens group refers to a lens group positioned in the front of the first lens group, and the first R lens group refers to a lens group positioned in the rear of the first lens group.

According to a first aspect of the present invention, there is provided an imaging lens in which the first F lens group is arranged in order from the object side, a first negative lens having a large curvature surface facing the image side, and a first curvature lens having a large curvature surface facing the object side. The first lens in a state in which the first R lens group is configured with a negative lens and the first R lens group is a positive lens or a cemented lens having a positive refractive power as a whole and is focused on an object at infinity. The distance from the most object-side surface of the group to the image surface is L, the maximum image height is Y ′, the radius of curvature of the object-side surface of the second negative lens is r ₂₁ , and the image side of the second negative lens is When the radius of curvature of the surface is r ₂₂ , the following conditional expression is satisfied.
Conditional expression:
[1] 2.8 <L / Y ′ <4.3
[2] −7.0 <(r ₂₁ + r ₂₂ ) / (r ₂₁ −r ₂₂ ) <− 0.7
An imaging lens according to a second aspect is the imaging lens according to the first aspect, wherein the distance from the surface closest to the image side to the image plane of the second lens group in a state in which an object at infinity is in focus is Bf, and the maximum When the image height is Y ′, the following conditional expression is satisfied.
Conditional expression:
[3] 0.8 <Bf / Y ′ <1.6
The imaging lens according to claim 3 is the imaging lens according to claim 1 or 2, wherein the distance from the most object-side surface to the most image-side surface of the first lens group is L ₁ , and infinity. When the distance from the most object-side surface of the first lens group to the image plane in the state of focusing on the object is L, the following conditional expression is satisfied.

Conditional expression:
[4] 0.20 <L ₁ /L<0.32
The imaging lens according to claim 4 is the imaging lens according to any one of claims 1 to 3, wherein the focal length of the entire imaging lens system is f _A , and the focal length of the first lens group. When f ₁ is satisfied, the following conditional expression is satisfied.
Conditional expression:
[5] 0.0 <f _A / f ₁ <0.6
An imaging lens according to a fifth aspect of the present invention is the imaging lens of the fourth aspect, wherein when the focal length of the first F lens group is f _1F and the focal length of the first R lens group is f _1R , the following condition is satisfied. Satisfies the equation.
Conditional expression:
[6] -1.3 <f _1F / f _1R <−0.7
An imaging lens according to a sixth aspect is the imaging lens according to any one of the first to fifth aspects, wherein an interval between the first F lens group and the first R lens group is A _1F-1R , and when the distance from the most object side surface of the first lens group to the surface of the most image side is L _1, satisfying the following condition.

Conditional expression:
[7] 0.0 <A _1F-1R / L ₁ <0.1
The imaging lens according to a seventh aspect is the imaging lens according to any one of the first to sixth aspects, wherein the refractive index of the first negative lens or the second negative lens of the first F lens group is n. _d , where the Abbe number of the first negative lens or the second negative lens is ν _d , and the partial dispersion ratio of the first negative lens or the second negative lens is P _{g, F} , the partial dispersion ratio P _{g, F} is the optical glass constituting the negative lens, g-ray, the refractive index, respectively _n g for the F line and C line, if _{n F} and _{n C, P g, F =} (n g -n F) / (N _F −n _C ), at least one of the first negative lens and the second negative lens in the first F lens group satisfies the following conditional expression.
Conditional expression:
[8] 1.45 _<n d _<1.65
[9] 55.0 <ν _d <95.0
[10] 0.015 <P _{g, F} − (− 0.001802 × ν _d +0.6483) <0.050
The imaging lens according to claim 8 is the imaging lens according to any one of claims 1 to 7, wherein the first R lens group is a cemented lens, and the cemented lens is formed from the object side. Sequentially, a positive lens and a negative lens are arranged.
An imaging lens according to a ninth aspect is the imaging lens according to any one of the first to eighth aspects, wherein the first lens group and the second lens group are subjected to focusing on a short-distance object. The interval is configured to be shorter than that in a state in which an object at infinity is in focus.
An imaging lens according to a tenth aspect is the imaging lens according to the ninth aspect, wherein an interval between the first lens group and the second lens group in a state in which an object at infinity is in focus is A _1-2 , and an imaging magnification. The distance between the first lens group and the second lens group in a state in which a short distance object is focused at −1/20 times is A _1-2M and the near distance object is focused at an imaging magnification of −1/20 times. The distance from the most image side surface of the second lens group to the image plane in the state is Bf _M , and the distance from the most image side surface of the second lens group to the image plane in the state of focusing on the object at infinity When Bf is satisfied, the following conditional expression is satisfied.
Conditional expression:
[11] _{-0.5 <(A 1-2M -A 1-2)} / (Bf M -Bf) <- 0.2
An imaging device according to an eleventh aspect uses the imaging lens according to any one of the first to tenth aspects as an imaging optical system.

An information device according to a twelfth aspect has an imaging function, and uses the imaging lens according to any one of the first to tenth aspects as an imaging optical system.
Next, the embodiments defined in the claims of the above-described claims of the present invention will be described in more detail.
A so-called retrofocus type imaging lens, such as the imaging lens according to the present invention, generally has a lens system having a negative refractive power on the object side and a lens system having a positive refractive power on the image side. In view of this asymmetry, distortion, lateral chromatic aberration, and the like are likely to occur, and reducing these aberrations is a major issue. Further, when an attempt is made to increase the diameter, it becomes difficult to correct coma aberration and the color difference of coma aberration, and more problems are accumulated. Furthermore, since the retro-focus type lens system is originally developed for the purpose of ensuring the back focus by moving the principal point to the rear side (that is, the image side), the above-mentioned aberration correction is performed. Coupled with difficulties, the total lens length tends to be large. In the present invention, it is possible to solve these problems by adopting the configuration described below.

That is, a first lens group is disposed on the object side of the aperture stop, and a second lens group having a positive refractive power is disposed on the image side of the aperture stop. In an imaging lens configured by sequentially arranging a first F lens group having a negative refractive power and a first R lens group having a positive refractive power from the side, the first F lens group is moved from the object side. In order, a first negative lens having a surface with a large curvature facing the image side and a second negative lens having a surface with a large curvature facing the object side are arranged, and the first R lens group is a positive lens. Or a cemented lens having a positive refractive power as a whole, and satisfying the following conditional expression (corresponding to claim 1).
Conditional expression:
[1] 2.8 <L / Y ′ <4.3
[2] −7.0 <(r ₂₁ + r ₂₂ ) / (r ₂₁ −r ₂₂ ) <− 0.7
However, the distance from the most object-side surface of the first lens group to the image plane in a state in which an object at infinity is in focus is L, the maximum image height is Y ′, and the curvature of the object-side surface of the second negative lens is The radius is r ₂₁ , and the radius of curvature of the image side surface of the second negative lens is r ₂₂ .

First, in the imaging lens according to the present invention, a lens group (first R lens group) having a positive refractive power is disposed on the image side of the first lens group, and a positive refractive power is sandwiched between an aperture stop. It is easy to control off-axis aberrations by confronting the second lens group having
Further, the point is the shape of the second negative lens arranged second from the object side in the first F lens group. The first lens group includes a lens group (first F lens group) having negative refractive power on the object side, and a lens group (first R lens group) having positive refractive power on the image side. However, in a similar example in the past, there are many cases in which ensuring of the angle of view and correction of various aberrations such as spherical aberration are made compatible by making these intervals relatively large. However, it is not possible to achieve sufficient miniaturization. A means for solving this is to configure the second negative lens so that a surface with a large curvature is directed to the object side. Specifically, the total lens length that falls within the range of the conditional expression [1] is set. As a premise, a shape that satisfies conditional expression [2] is good. If the conditional expression [2] is −7.0 or less, the refractive power of the second negative lens becomes small, and aberrations are easily canceled between the object side surface and the image side surface of the second negative lens. Thus, the exchange of aberrations with other lenses is reduced, the role played by the second negative lens in correcting aberrations is limited, and the overall aberration level is not reduced.

On the other hand, if the conditional expression [2] is −0.7 or more, the axial aberration (spherical aberration) and the off-axis aberration (particularly astigmatism and coma aberration of the lower ray) cannot be balanced, and It becomes difficult to make the peripheral image quality compatible.
Furthermore, in the imaging lens according to the present invention, it is desirable that the following conditional expression is satisfied (corresponding to claim 2).
Conditional expression:
[3] 0.8 <Bf / Y ′ <1.6
However, the distance from the surface closest to the image side of the second lens group to the image plane in the state of focusing on an object at infinity is Bf, and the maximum image height is Y ′.
If the conditional expression [3] is 0.8 or less, it is impossible to efficiently store the camera when a retractable camera is assumed, or scratches or dirt on the lens surface of the second lens group. Etc. are not preferable because they tend to affect the image. On the other hand, if the conditional expression [3] is 1.6 or more, the space in which the lens group can be disposed substantially becomes narrow, and it is difficult to perform sufficient aberration correction.

In the imaging lens according to the present invention, it is preferable that the following conditional expression is satisfied (corresponding to claim 3).
Conditional expression:
[4] 0.20 <L ₁ /L<0.32
However, the distance from the most object-side surface of the first lens group to the most image-side surface is L ₁ , and the image plane from the most object-side surface of the first lens group in a state of focusing on an object at infinity Let the distance to be L.
If conditional expression [4] is 0.20 or less, three lenses in three groups or four lenses in three groups arranged as the first lens group correct aberrations with a sufficient degree of freedom. There is a risk that the shape will not be suitable. On the other hand, if the conditional expression [4] is 0.32 or more, the stop is too close to the image plane, and it becomes difficult to move the exit pupil position away from the image plane. This is not preferable because the refractive power arrangement in the two lens groups lacks balance.

Furthermore, it is desirable that the refractive power arrangement of the entire imaging lens satisfies the following conditional expression (corresponding to claim 4).
Conditional expression:
[5] 0.0 <f _A / f ₁ <0.6
Here, the focal length of the entire imaging lens system is f _A , and the focal length of the first lens group is f ₁ .
In the imaging lens according to 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. However, in terms of actual aberration correction, it is not optimal that the first lens group is completely afocal. If f _A / f ₁ is 0.0 or less, the refractive power of the second lens group must be increased, resulting in large curvature of the image surface and large negative distortion. It becomes easy and it is not preferable. On the other hand, if f _A / f ₁ is 0.6 or more, the contribution of the second lens group to the image forming action decreases, and the first lens group shares this. A relatively large aberration is exchanged between the first lens group and the second lens group, and the manufacturing error sensitivity is increased more than necessary, which is not preferable.

At this time, it is desirable that the refractive power arrangement of the first lens group satisfies the following conditional expression (corresponding to claim 5).
Conditional expression:
[6] -1.3 <f _1F / f _1R <−0.7
However, the focal length of the first F lens group is f _1F , and the focal length of the first R lens group is f _1R .
Here, if the conditional expression [6] is −1.3 or less, the first lens group has a relatively strong positive refractive power, and it becomes difficult to satisfy the conditional expression [5]. End up. On the other hand, when the conditional expression [6] is −0.7, the first lens group becomes large in order to satisfy the conditional expression [5], or aberration correction becomes difficult if the size is forcibly reduced. It is not preferable.

It should be noted that if conditional formula [5] and conditional formula [6] satisfy the following conditions, better aberration correction can be performed.
[5 ′] 0.0 <f _A / f ₁ <0.3
[6 ′] −1.0 <f _1F / f _1R <−0.7
In addition, it is desirable that the first lens group satisfies the following conditional expression (corresponding to claim 6).
Conditional expression:
[7] 0.0 <A _1F-1R / L ₁ <0.1
However, the distance between the first F lens group and the first R lens group is A _1F-1R , and the distance from the most object side surface to the most image side surface of the first lens group is L ₁ .

In the configuration of the imaging lens according to the present invention, it is better that the numerical value of the conditional expression [7] is small.
It is desirable that at least one material of the first negative lens and the second negative lens of the first F lens group satisfies the following conditional expression (corresponding to claim 7).
Conditional expression:
[8] 1.45 _<n d _<1.65
[9] 55.0 <ν _d <95.0
[10] 0.015 <P _{g, F} − (− 0.001802 × ν _d +0.6483) <0.050
However, the refractive index of the first negative lens or the second negative lens of the first F lens group is n _d , the Abbe number of the first negative lens or the second negative lens is ν _d , and the first negative lens Or, _{let Pg, F} be the partial dispersion ratio of the second negative lens. The partial dispersion ratio _{P g, F} is the optical glass constituting the negative lens, g-line, F line and the refractive index, respectively _n g the C-line, as _{n F} and _{n C,
P g, F = (n g} -n F) / (n F -n C)
It is expressed.

By configuring at least one of the first negative lens and the second negative lens of the first F lens group with so-called anomalous dispersion glass satisfying conditional expressions [8] to [10], chromatic aberration can be reduced. It is possible to effectively reduce the secondary spectrum and realize a better correction state.
The first R lens group is a cemented lens, and is preferably configured by sequentially arranging a positive lens and a negative lens from the object side (corresponding to claim 8).
As described above, by making the first R lens group a cemented lens in which a positive lens and a negative lens are sequentially arranged from the object side, it is possible to correct axial chromatic aberration better. It becomes.
In the imaging lens according to the present invention, when focusing on an object at a short distance, it is desirable to shorten the distance between the first lens group and the second lens group than when the object is focused on an object at infinity. (Corresponding to claim 9).
When focusing on a short-distance object with a simple entire extension of the imaging lens, a positive curvature of field (a curvature of field in a direction away from the lens in the periphery) is likely to occur, but the first is accompanied by the extension. By appropriately shortening the distance between the lens group and the second lens group, occurrence of field curvature can be suppressed.

At this time, it is more preferable to satisfy the following conditional expression (corresponding to claim 10).
Conditional expression:
[11] _{-0.5 <(A 1-2M -A 1-2)} / (Bf M -Bf) <- 0.2
However, the distance between the first lens group and the second lens group in a state of focusing on an object at infinity is A _1-2 and the first lens group in the state of focusing on a short-distance object at an imaging magnification of −1/20 times. The distance between the first lens group and the second lens group is A _1-2M , and the imaging magnification is −1/20 times, and the distance from the most image side surface to the image plane of the second lens group in the state of focusing on a short-distance object. Is the distance Bf _M , and the distance from the most image-side surface to the image plane of the second lens group in the state of focusing on the object at infinity is Bf.
When the conditional expression [11] is −0.5 or less, the change in the distance between the first lens group and the second lens group becomes excessive, and is smaller at a short distance than at infinity. Field curvature is likely to occur. On the other hand, if the conditional expression [11] is −0.2 or more, the change in the distance between the first lens group and the second lens group becomes insufficient, and a positive image plane is obtained at a short distance compared to infinity. Bending is likely to occur.

The second lens group includes a second F lens group having a positive refractive power, a second M lens group having a negative refractive power, and a second R lens group having a positive refractive power in order from the object side. It is desirable to arrange them.
The second F lens group may be a cemented lens having a meniscus shape with a convex surface facing the object as a whole. The second M lens group may be a negative meniscus lens having a concave surface facing the object side, or a cemented lens having a negative meniscus shape having a concave surface facing the object side as a whole. The second R lens group may be a positive lens having a convex surface facing the image side.
In order to correct distortion and the like better, it is desirable to provide an aspherical surface in the second R lens group. In addition, in order to suppress various aberrations that tend to increase with downsizing, it is desirable to provide an aspherical surface also in the first F lens group. The aspherical surfaces of the first F lens and the second R lens group complement each other in the role of aberration correction and work more effectively, so it is desirable to provide them simultaneously.
Furthermore, the imaging apparatus according to the present invention is an imaging apparatus such as a digital camera, and is configured using the imaging lens as described above for an imaging optical system.
The information device according to the present invention is an information device such as a portable information terminal device, and has an imaging function, and is configured using the imaging lens as described above for an imaging optical system.

Next, specific examples based on the above-described embodiment of the present invention will be described in detail. Example 1, Example 2, Example 3, Example 4 and Example 5 described below are examples of specific configurations based on specific numerical examples of the imaging lens according to the present invention, and Example 6 is 5 is a specific example of an imaging apparatus or information apparatus according to the present invention in which a lens unit having a zoom lens as shown in Examples 1 to 5 is used as an imaging optical system.
In the first to fifth embodiments of the imaging lens according to the present invention, the configuration of the imaging lens and specific numerical examples thereof are shown. In all of Examples 1 to 5, the maximum image height is 14.2 mm.
In the first to fifth embodiments, the optical element formed of a parallel plate disposed on the image plane side of the second lens group includes various optical filters such as an optical low-pass filter and an infrared cut filter, and CMOS (complementary metal). Oxide semiconductor) This is assumed to be a cover glass (seal glass) of a light receiving element such as an image sensor, and is here referred to as various filters MF. The parallel plate optical element is disposed so that the image side surface is located at a position of about 0.5 mm from the image forming surface to the object side. However, the present invention is not limited to this and may be divided into a plurality of pieces. .

In the first to fifth embodiments, some lens surfaces are aspherical. In order to form an aspherical surface, each lens surface is directly aspherical like a so-called molded aspherical lens, and a resin that forms an aspherical surface on the lens surface of a spherical lens like a so-called hybrid aspherical lens. There is a configuration in which an aspheric surface is obtained by laying a thin film, any of which may be used.
The aberrations in Examples 1 to 5 are corrected at a high level, and the spherical aberration and the longitudinal chromatic aberration are so small that they do not cause a problem. In addition, 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 is sufficiently low at 2.0% or less in absolute value. It is getting smaller. By configuring the imaging lens as in the first to fifth embodiments of the present invention, the half angle of view is as wide as about 38 degrees, and the open F number (F number) is less than 2.8, which is a large aperture. In addition, it is clear from Examples 1 to 5 that very good image performance can be secured.

  The meanings of symbols common to the first to fifth embodiments are as follows.

f: Focal length of the entire system F: F value (F number)
ω: Half angle of view [degree]
R: radius of curvature (paraxial radius of curvature for aspheric surfaces)
D: Surface spacing N _d : Refractive index ν _d : Abbe number 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 A ₁₂ : 12th-order aspheric coefficient A ₁₄ : 14th-order aspheric coefficient A ₁₆ : 16th-order aspheric coefficient A ₁₈ : 18th-order aspheric coefficient The spherical surface is defined by the following equation [12], where C is the reciprocal of the paraxial radius of curvature (paraxial curvature) and H is the height from the optical axis.

図１は、本発明の実施例１に係る結像レンズの光学系の縦断面の構成を模式的に示している。
図１に示す結像レンズは、第１レンズＥ１、第２レンズＥ２、第３レンズＥ３、第４レンズＥ４、第５レンズＥ５、第６レンズＥ６、第７レンズＥ７、開口絞りＦＡおよび各種フィルタＭＦを具備している。第１レンズＥ１〜第３レンズＥ３は、第１レンズ群Ｇ１を構成して、開口絞り、すなわち絞り、ＦＡの物体側に配置し、そして第４レンズＥ４〜第７レンズＥ７は、第２レンズ群Ｇ２を構成して、絞りＦＡの像面側に配置しており、それぞれ各群毎に適宜なる共通の支持枠等によって支持され、フォーカシング等に際しては各群毎に一体的に動作する。絞りＦＡは、この場合、第２レンズ群Ｇ２と一体的に動作する。図１には、各光学面の面番号も示している。なお、図１に対する各参照符号は、参照符号の桁数の増大による説明の煩雑化を避けるため、各実施例毎に独立に用いており、そのため、図４、図７、図１０および図１３と共通の参照符号を付していてもそれらに対応する実施例とはかならずしも共通の構成ではない。 [12]

FIG. 1 schematically shows a configuration of a longitudinal section of an optical system of an imaging lens according to Embodiment 1 of the present invention.
The imaging lens shown in FIG. 1 includes a first lens E1, a second lens E2, a third lens E3, a fourth lens E4, a fifth lens E5, a sixth lens E6, a seventh lens E7, an aperture stop FA, and various filters. MF is provided. The first lens E1 to the third lens E3 constitute the first lens group G1, and are arranged on the object side of the aperture stop, that is, the stop, FA. The fourth lens E4 to the seventh lens E7 are the second lens. The group G2 is configured and arranged on the image plane side of the stop FA, and is supported by a common support frame or the like that is appropriate for each group. The focusing unit operates integrally for each group. In this case, the aperture FA operates integrally with the second lens group G2. FIG. 1 also shows the surface numbers of the optical surfaces. 1 are used independently for each embodiment in order to avoid complication of explanation due to an increase in the number of digits of the reference code, and therefore FIG. 4, FIG. 7, FIG. 10, and FIG. Even if the same reference numerals are attached, they are not necessarily in a common configuration with the corresponding embodiments.

In FIG. 1, each optical element constituting the optical system of the imaging lens includes, for example, in order from the object side such as a subject, a first lens E1, a second lens E2, a third lens E3, an aperture FA, and a fourth lens E4. The fifth lens E5, the sixth lens E6, the seventh lens E7, and the various filters MF are arranged in this order, and an image of an object is formed behind the various filters MF.
The first lens E1 is a negative meniscus lens having a surface with a larger curvature than the object side (that is, a surface with a smaller radius of curvature) convex toward the object side. The second lens E2 is a negative meniscus lens in which a surface having a larger curvature than the image side is directed toward the object side and the surface is aspherical so as to be convex toward the image side. The first lens E1 and the second lens E2 constitute a first F lens group S1F having negative refractive power as a whole, the first lens E1 corresponds to the first negative lens, and the second lens E2 This corresponds to the second negative lens.
The third lens E3 is a positive lens composed of a biconvex lens with a surface having a curvature larger than that of the image side facing the object side. In this case, the third lens E3 is a first R lens group having a positive refractive power alone. Configure S1R.

That is, the first lens group G1 includes a first F lens group S1F having a negative refractive power composed of the first lens E1 and the second lens E2, and a first R lens group SIR having a positive refractive power composed of the third lens E3. And it consists of.
The fourth lens E4 is a positive lens made up of a biconvex lens, and the fifth lens E5 is a negative lens made up of a biconcave lens. The four lenses E4 and E5 are in close contact with each other. The two lenses are bonded together to form a two-piece cemented lens. The cemented lens composed of the fourth lens E4 and the fifth lens E5 has a second meniscus shape S2F having a convex meniscus shape on the object side as a whole with the image side surface having a larger curvature than the object side surface facing the object side. Configure.
The sixth lens E6 is a negative meniscus lens in which a surface having a larger curvature than the image side is directed to the object side and the image side surface is aspherical so as to be convex toward the image side. The sixth lens E6 alone constitutes the second M lens group S2M.
The seventh lens E7 is a positive meniscus lens having a surface with a larger curvature than the object side facing the image side and the image side surface aspherical, and is convex on the image side. The seventh lens E7 alone constitutes the second R lens group S2R.

That is, the second lens group G2 includes a second F lens group S2F composed of a cemented lens of the fourth lens E4 and the fifth lens E5, a second M lens group S2M composed of a sixth lens E6 and having negative refractive power, And a second R lens group S2R having a positive refractive power.
Note that in the imaging lens according to the present invention, the first lens group G1 in a state of focusing on an object at infinity is not a simple whole extension of the imaging lens for focusing but focusing on a close object. The distance between the first lens group G1 and the second lens group G2 is made shorter than the distance between the first lens group G2 and the second lens group G2. In the case of the configuration of Example 1, since the aperture FA operates integrally with the second lens group G2, the distance between the first lens group G1 and the second lens group G2 is set to be the first lens group G1. And the fixed distance from the aperture FA to the object side surface of the fourth lens E4 of the second lens group G2.
That is, as the entire imaging lens is extended by focusing from infinity to a close object (increasing the variable distance DB between the second lens group G2 and the various filters MF), the first lens group G1 and the stop FA During focusing on a short-distance object, the variable interval DA between is moved so as to be smaller than that in the state of focusing on an object at infinity.
In Example 1, the focal length f, the open F value F, and the half field angle ω of the entire system are f = 18.28, F = 2.51, and ω = 38.3, respectively. The optical characteristics are as shown in the following table.

In Table 1, the lens surface with the surface number indicated by “* (asterisk)” in the surface number is an aspherical surface, and the glass manufacturer name is the name of the glass material before the name of the glass type. OHARA) and HOYA (HOYA Corporation) (in Example 1, the glass material of HOYA Corporation is not used). The same applies to the other Examples 2 to 5.
That is, in Table 1, the optical surfaces of the third surface, the twelfth surface, and the fourteenth surface marked with “*” are aspherical surfaces. It is.

Aspherical parameters Aspherical surface: Third surface K = 0.0
A ₄ = 9.888622 × 10 ⁻⁶
A ₆ = −1.42073 × 10 ⁻⁷
A ₈ = −3.18066 × 10 ⁻⁹
A ₁₀ = 1.97408 × 10 ⁻¹¹
Aspherical surface: 12th surface K = −0.16558
A ₄ = 1.59985 × 10 ⁻⁴
A ₆ = 1.84355 × 10 ⁻⁶
A ₈ = −2.66581 × 10 ⁻⁸
A ₁₀ = 1.97333 × 10 ⁻¹⁰
Aspheric surface: 14th surface K = −0.21279
A ₄ = 1.80877 × 10 ⁻⁵
A ₆ = 1.25436 × 10 ⁻⁷
A ₈ = 5.41982 × 10 ⁻¹⁰
A ₁₀ = 1.54602 × 10 ⁻¹¹
The variable distance DA between the first lens group G1 and the stop FA, and the variable distance DB between the second lens group G2 and the various filters MF are in focus on the object at infinity and the imaging magnification during focusing. It is changed as shown in the following table in the state of focusing on a short-distance object at -1/20 times.

The values corresponding to the conditional expressions [1] to [11] described in the first embodiment are as follows.
Conditional expression numerical value [1] L / Y '= 3.28
[2] (r ₂₁ + r ₂₂ ) / (r ₂₁ −r ₂₂ ) = − 1.538
[3] Bf / Y ′ = 1.165
[4] _L 1 /L=0.260
[5] f _A / f ₁ = 0.532
[6] f _1F / f _1R = −1.189
[7] A _1F-1R / L ₁ = 0.0108
[8] n _d = 1.497
[9] ν _d = 81.5
[10] P _{g, F} − (− 0.001802 × ν _d +0.6483) = 0.0361
[11] _{(A 1-2M -A 1-2) / (} Bf M -Bf) = - 0.226
Therefore, the numerical values related to the conditional expressions [1] to [11] described in the first embodiment are within the ranges of the conditional expressions, respectively, and satisfy the conditional expressions [1] to [11]. is doing.

  Also, FIG. 2 shows spherical aberration, astigmatism, distortion, and coma aberration curve diagrams in the state where the imaging lens according to Example 1 is focused on an object at infinity, and FIG. FIG. 9 shows respective aberration curve diagrams of spherical aberration, astigmatism, distortion aberration and coma aberration in a state where the imaging lens according to Example 1 is focused on a short distance object at −1/20 times. In these aberration curve diagrams, a broken line in spherical aberration represents a sine condition, a solid line in astigmatism represents sagittal, and a broken line represents meridional. In addition, g and d in the respective aberration diagrams of spherical aberration, astigmatism, and coma aberration represent g-line and d-line, respectively. The same applies to the aberration curve diagrams according to other examples.

FIG. 4 schematically shows the configuration of the longitudinal section of the optical system of the imaging lens according to Example 2 of the present invention.
The imaging lens shown in FIG. 4 includes a first lens E1, a second lens E2, a third lens E3, a fourth lens E4, a fifth lens E5, a sixth lens E6, a seventh lens E7, an aperture stop FA, and various filters. MF is provided. In this case, the first lens E1 to the third lens E3 constitute the first lens group G1, and are arranged on the object side of the aperture stop, that is, the stop, FA. The fourth lens E4 to the seventh lens E7 are The second lens group G2 is configured and disposed on the image plane side of the stop FA, and is supported by a common support frame or the like that is appropriate for each group, and operates integrally for each group during focusing or the like. To do. In this case, the aperture FA operates integrally with the first lens group G1. FIG. 4 also shows the surface numbers of the optical surfaces. As described above, the reference numerals for FIG. 4 are used independently for each embodiment in order to avoid complication of explanation due to an increase in the number of digits of the reference numerals. 10 and FIG. 13, the reference numerals common to those in FIGS. 10 and 13 are not necessarily in common with the corresponding embodiments.

In FIG. 4, each optical element constituting the optical system of the imaging lens includes, for example, a first lens E1, a second lens E2, a third lens E3, an aperture FA, a fourth lens E4, in this order from the object side such as a subject. The fifth lens E5, the sixth lens E6, the seventh lens E7, and the various filters MF are sequentially arranged, and an image of the object is formed behind the various filters MF.
The first lens E1 is a negative meniscus lens in which a surface having a curvature larger than that of the object side is directed to the image side, is convex toward the object side, and both surfaces thereof are aspheric surfaces. The second lens E2 is a negative lens composed of a biconcave lens formed with a surface having a larger curvature than the image side facing the object side. The first lens E1 and the second lens E2 constitute a first F lens group S1F having negative refractive power as a whole, the first lens E1 corresponds to the first negative lens, and the second lens E2 This corresponds to the second negative lens.
The third lens E3 is a positive lens composed of a biconvex lens with a surface having a curvature larger than that of the image side facing the object side. In this case, the third lens E3 is a first R lens group having a positive refractive power alone. Configure S1R.
That is, the first lens group G1 includes a first F lens group S1F having a negative refractive power composed of the first lens E1 and the second lens E2, and a first R lens group SIR having a positive refractive power composed of the third lens E3. And it consists of.

The fourth lens E4 is a positive lens made up of a biconvex lens, and the fifth lens E5 is a negative lens made up of a biconcave lens. The four lenses E4 and E5 are in close contact with each other. The two lenses are bonded together to form a two-piece cemented lens. The cemented lens including the fourth lens E4 and the fifth lens E5 constitutes a second F lens group S2F having a meniscus shape that is convex on the object side as a whole.
The sixth lens E6 is a negative meniscus lens that is formed convex toward the image side with the surface having a larger curvature than the image side facing the object side. The sixth lens E6 alone constitutes the second M lens group S2M.
The seventh lens E7 is a positive meniscus lens having a surface with a larger curvature than the object side facing the image side and the image side surface aspherical, and is convex on the image side. The seventh lens E7 alone constitutes the second R lens group S2R.
That is, the second lens group G2 includes a second F lens group S2F composed of a cemented lens of the fourth lens E4 and the fifth lens E5, a second M lens group S2M composed of a sixth lens E6 and having negative refractive power, And a second R lens group S2R having a positive refractive power.

As described above, in the imaging lens according to the present invention, in focusing, it is not a simple whole extension of the imaging lens, but in focusing on a short distance object, it is in a state of focusing on an object at infinity. The distance between the first lens group G1 and the second lens group G2 is made shorter than the distance between the first lens group G1 and the second lens group G2. In the case of the configuration of Example 2, since the aperture FA operates integrally with the first lens group G1, the interval between the first lens group G1 and the second lens group G2 is set to be the first lens group G1. This is the sum of the fixed distance from the image side surface of the third lens E3 to the stop FA and the variable distance DA between the stop FA and the first lens group G1.
That is, as the entire imaging lens is extended by focusing from infinity to a close object (increasing the variable distance DB between the second lens group G2 and the various filters MF), the stop FA and the second lens group G2 During focusing on a short-distance object, the variable interval DA between is moved so as to be smaller than that in the state of focusing on an object at infinity.
In Example 2, the focal length f, the open F value F, and the half angle of view ω of the entire system are f = 18.29, F = 2.52, and ω = 38.2, respectively. The optical characteristics are as shown in the following table.

Also in Table 3, the lens surface with the surface number indicated by “* (asterisk)” is an aspherical surface, and the name of the glass material manufacturer is the OHARA (stock) before the glass type name. Company Ohara) and HOYA (HOYA Corporation).
That is, in Table 3, the optical surfaces of the first surface, the second surface, and the fourteenth surface marked with “*” are aspheric surfaces, and the parameters of each aspheric surface in the equation [12] are as follows. It is.

Aspherical parameters Aspherical surface: first surface K = 0.0
A ₄ = −1.15383 × 10 ⁻⁴
A ₆ = 2.38416 × 10 ⁻⁷
A ₈ = −1.86497 × 10 ⁻⁹
Aspheric surface: second surface K = −0.71833
A ₄ = −1.17671 × 10 ⁻⁵
A ₆ = 9.43499 × 10 ⁻⁷
A ₈ = −4.664708 × 10 ⁻⁹
A ₁₀ = 7.05861 × 10 ⁻¹¹
Aspherical surface: 14th surface K = −0.28312
A ₄ = 6.41382 × 10 ⁻⁵
A ₆ = 2.15787 × 10 ⁻⁷
A ₈ = −6.004112 × 10 ⁻¹⁰
A ₁₀ = 5.13609 × 10 ⁻¹²
The variable distance DA between the aperture FA and the second lens group G2 and the variable distance DB between the second lens group G2 and the various filters MF are in focus on the object at infinity and the imaging magnification during focusing. It is changed as shown in the following table in a state in which a short distance object is focused at -1/20 times.

Further, the values corresponding to the conditional expressions [1] to [11] described in the second embodiment are as follows.
Conditional expression numerical value [1] L / Y '= 3.95
[2] (r ₂₁ + r ₂₂ ) / (r ₂₁ −r ₂₂ ) = − 0.877
[3] Bf / Y ′ = 1.374
[4] L ₁ /L=0.291
[5] f _A / f ₁ = 0.265
[6] f _1F / f _1R = −0.861
[7] A _1F-1R / L ₁ = 0.0061
[8] n _d = 1.553
[9] ν _d = 71.7
[10] P _{g, F} − (− 0.001802 × ν _d +0.6483) = 0.0211
[11] _{(A 1-2M -A 1-2) / (} Bf M -Bf) = - 0.374
Therefore, the numerical values related to the conditional expressions [1] to [11] in Example 2 are within the ranges of the conditional expressions, respectively, and satisfy the conditional expressions [1] to [11].

  FIG. 5 shows spherical aberration, astigmatism, distortion, and coma aberration curve diagrams when the imaging lens according to Example 2 is focused on an object at infinity, and FIG. FIG. 9 shows respective aberration curve diagrams of spherical aberration, astigmatism, distortion aberration and coma aberration in a state where the imaging lens according to Example 2 is focused on a short distance object at −1/20 times. In these aberration curve diagrams, a broken line in spherical aberration represents a sine condition, a solid line in astigmatism represents sagittal, and a broken line represents meridional. In addition, g and d in the respective aberration diagrams of spherical aberration, astigmatism, and coma aberration represent g-line and d-line, respectively.

FIG. 7 schematically shows the configuration of the longitudinal section of the optical system of the imaging lens according to Example 3 of the present invention.
The imaging lens shown in FIG. 7 includes a first lens E1, a second lens E2, a third lens E3, a fourth lens E4, a fifth lens E5, a sixth lens E6, a seventh lens E7, an eighth lens E8, and an aperture. A diaphragm FA and various filters MF are provided. The first lens E1 to the fourth lens E4 constitute the first lens group G1, and are arranged on the object side of the aperture stop, that is, the stop, FA. The fifth lens E5 to the eighth lens E8 are the second lens. The group G2 is configured and arranged on the image plane side of the stop FA, and is supported by a common support frame or the like that is appropriate for each group. The focusing unit operates integrally for each group. In this case, the aperture FA operates integrally with the first lens group G1. FIG. 7 also shows the surface numbers of the optical surfaces. As described above, each reference numeral for FIG. 7 is used independently for each embodiment in order to avoid complication of explanation due to an increase in the number of digits of the reference code. 4, even if reference numerals common to FIGS. 10 and 13 are given, they are not necessarily in common with the embodiments corresponding thereto.

In FIG. 7, each optical element constituting the optical system of the imaging lens includes, in order from the object side, a first lens E1, a second lens E2, a third lens E3, a fourth lens E4, an aperture FA, and a fifth lens. E5, sixth lens E6, seventh lens E7, eighth lens E8, and various filters MF are arranged in this order, and an object image is formed behind the various filters MF.
The first lens E1 is a negative meniscus lens in which a surface having a curvature larger than that of the object side is directed to the image side, is convex toward the object side, and both surfaces thereof are aspheric surfaces. The second lens E2 is a negative meniscus lens that is formed convex toward the image side with the surface having a larger curvature than the image side facing the object side. The first lens E1 and the second lens E2 constitute a first F lens group S1F having negative refractive power as a whole, the first lens E1 corresponds to the first negative lens, and the second lens E2 This corresponds to the second negative lens.
The third lens E3 is a positive lens composed of a biconvex lens with a surface having a larger curvature than the object side facing the image side, and the fourth lens E4 has a surface having a larger curvature than the image side directed toward the object side. A negative meniscus lens convexly formed on the side, and the two lenses, the third lens E3 and the fourth lens E4, are closely bonded to each other and integrally joined to form a two-piece cemented lens. . The cemented lens including the third lens E3 and the fourth lens E4 has a biconvex shape as a whole, and constitutes a first R lens group S1R having a positive refractive power.

That is, the first lens group G1 has a first F lens group S1F having a negative refractive power composed of the first lens E1 and the second lens E2, and a positive refractive power composed of the third lens E3 and the fourth lens E4. And a first R lens group SIR.
The fifth lens E5 is a positive lens made up of a biconvex lens, and the sixth lens E6 is a negative lens made up of a biconcave lens. The two lenses of the fifth lens E5 and the sixth lens E6 are in close contact with each other. The two lenses are bonded together to form a two-piece cemented lens. The cemented lens including the fifth lens E5 and the sixth lens E6 constitutes a second F lens group S2F having a negative meniscus shape on the object side as a whole.
The seventh lens E7 is a negative meniscus lens formed convexly on the image side with the surface having a larger curvature than the image side facing the object side. The seventh lens E7 alone constitutes the second M lens group S2M.
The eighth lens E8 is a positive lens composed of a biconvex lens in which a surface having a larger curvature than the object side is directed to the image side and the image side surface is aspheric. The eighth lens E8 alone constitutes the second R lens group S2R.

That is, the second lens group G2 includes a second F lens group S2F composed of a cemented lens of the fifth lens E5 and the sixth lens E6, a second M lens group S2M composed of a seventh lens E7 and having negative refractive power, And a second R lens unit S2R having a positive refractive power and including eight lenses E8.
As described above, in the imaging lens according to the present invention, in focusing, it is not a simple whole extension of the imaging lens, but in focusing on a short distance object, it is in a state of focusing on an object at infinity. The distance between the first lens group G1 and the second lens group G2 is made shorter than the distance between the first lens group G1 and the second lens group G2. In the case of the configuration of Example 3, since the aperture FA operates integrally with the first lens group G1, the interval between the first lens group G1 and the second lens group G2 is set to be the first lens group G1. This is the sum of the fixed distance from the image side surface of the fourth lens E4 to the stop FA and the variable distance DA between the stop FA and the first lens group G1.
That is, as the entire imaging lens is extended by focusing from infinity to a close object (increasing the variable distance DB between the second lens group G2 and the various filters MF), the stop FA and the second lens group G2 During focusing on a short-distance object, the variable interval DA between is moved so as to be smaller than that in the state of focusing on an object at infinity.
In Example 3, the focal length f, the open F value F, and the half angle of view ω of the entire system are f = 18.30, F = 2.52, and ω = 38.2, respectively. The optical characteristics are as shown in the following table.

Also in Table 5, the surface number indicated by “* (asterisk)” attached to the surface number is an aspherical surface, and the name of the glass material manufacturer is designated OHARA (stock) before the glass type name. Company Ohara) and HOYA (HOYA Corporation).
That is, in Table 5, the optical surfaces of the first surface, the second surface, and the fifteenth surface marked with “*” are aspherical surfaces, and the parameters of each aspherical surface in the equation [12] are as follows. is there.
Aspherical parameters Aspherical surface: first surface K = 0.0
A ₄ = −3.996377 × 10 ⁻⁵
A ₆ = 9.21553 × ^{10 -8}
Aspherical surface: second surface K = −0.59156
A ₄ = −8.337359 × 10 ⁻⁶
A ₆ = 3.49291 × 10 ⁻⁷
A ₈ = −5.31443 × 10 ⁻⁹
A ₁₀ = 5.50904 × 10 ⁻¹¹
Aspherical surface: 15th surface K = −0.56176
A ₄ = 7.57070 × 10 ⁻⁵
A ₆ = 3.27942 × 10 ⁻⁷
A ₈ = −1.51207 × 10 ⁻⁹
A ₁₀ = 9.93156 × 10 ⁻¹²
The variable distance DA between the aperture FA and the second lens group G2 and the variable distance DB between the second lens group G2 and the various filters MF are in focus on the object at infinity and the imaging magnification during focusing. It is changed as shown in the following table in the state of focusing on a short-distance object at -1/20 times.

The values corresponding to the conditional expressions [1] to [11] described in the third embodiment are as follows.
Conditional expression numerical value [1] L / Y ′ = 3.97
[2] (r ₂₁ + r ₂₂ ) / (r ₂₁ −r ₂₂ ) = − 4.268
[3] Bf / Y '= 1. 211
[4] L ₁ /L=0.264
[5] f _A / f ₁ = 0.163
[6] f _1F / f _1R = −0.867
[7] A _1F-1R / L ₁ = 0.0067
[8] n _d = 1.497
[9] ν _d = 81.5
[10] P _{g, F} − (− 0.001802 × ν _d +0.6483) = 0.0361
[11] _{(A 1-2M -A 1-2) / (} Bf M -Bf) = - 0.476
Therefore, the numerical values related to the conditional expressions [1] to [11] in Example 3 are within the range of the conditional expressions, respectively, and satisfy the conditional expressions [1] to [11].

  Also, FIG. 8 shows spherical aberration, astigmatism, distortion aberration, and coma aberration curve diagrams when the imaging lens according to Example 3 is focused on an object at infinity, and FIG. FIG. 7 shows respective aberration curve diagrams of spherical aberration, astigmatism, distortion aberration and coma aberration in a state where the imaging lens according to Example 3 is focused on an object at a short distance of −1/20 times. In these aberration curve diagrams, a broken line in spherical aberration represents a sine condition, a solid line in astigmatism represents sagittal, and a broken line represents meridional. In addition, g and d in the respective aberration diagrams of spherical aberration, astigmatism, and coma aberration represent g-line and d-line, respectively.

FIG. 10 schematically shows the configuration of the longitudinal section of the optical system of the imaging lens according to Example 4 of the present invention.
The imaging lens shown in FIG. 10 includes a first lens E1, a second lens E2, a third lens E3, a fourth lens E4, a fifth lens E5, a sixth lens E6, a seventh lens E7, an eighth lens E8, and an aperture. A diaphragm FA and various filters MF are provided. The first lens E1 to the fourth lens E4 constitute the first lens group G1, and are arranged on the object side of the aperture stop, that is, the stop, FA. The fifth lens E5 to the eighth lens E8 are the second lens. The group G2 is configured and arranged on the image plane side of the stop FA, and is supported by a common support frame or the like that is appropriate for each group. The focusing unit operates integrally for each group. Also in this case, the aperture FA operates integrally with the first lens group G1. FIG. 10 also shows the surface number of each optical surface. As described above, each reference numeral for FIG. 10 is used independently for each embodiment in order to avoid complication of explanation due to an increase in the number of digits of the reference code. 4, FIG. 7 and FIG. 13, the reference numerals common to those in FIG.

In FIG. 10, each optical element constituting the optical system of the imaging lens includes, in order from the object side, a first lens E1, a second lens E2, a third lens E3, a fourth lens E4, an aperture FA, and a fifth lens. E5, sixth lens E6, seventh lens E7, eighth lens E8, and various filters MF are arranged in this order, and an object image is formed behind the various filters MF.
The first lens E1 is a negative meniscus lens in which a surface having a curvature larger than that of the object side is directed to the image side, is convex toward the object side, and both surfaces thereof are aspheric surfaces. The second lens E2 is a negative meniscus lens that is formed convex toward the image side with the surface having a larger curvature than the image side facing the object side. The first lens E1 and the second lens E2 constitute a first F lens group S1F having negative refractive power as a whole, the first lens E1 corresponds to the first negative lens, and the second lens E2 This corresponds to the second negative lens.
The third lens E3 is a positive lens composed of a biconvex lens with a surface having a larger curvature than the object side facing the image side, and the fourth lens E4 has a surface having a larger curvature than the image side directed toward the object side. A negative meniscus lens convexly formed on the side, and the two lenses, the third lens E3 and the fourth lens E4, are closely bonded to each other and integrally joined to form a two-piece cemented lens. . The cemented lens including the third lens E3 and the fourth lens E4 has a biconvex shape as a whole, and constitutes a first R lens group S1R having a positive refractive power.

That is, the first lens group G1 includes the first lens E1 and the second lens E2, and includes the first F lens group S1F having negative refractive power, the third lens E3, and the fourth lens E4, and has positive refractive power. And a first R lens group SIR.
The fifth lens E5 is a positive lens made up of a biconvex lens, and the sixth lens E6 is a negative lens made up of a biconcave lens. The two lenses of the fifth lens E5 and the sixth lens E6 are in close contact with each other. The two lenses are bonded together to form a two-piece cemented lens. The cemented lens including the fifth lens E5 and the sixth lens E6 constitutes a second F lens group S2F having a meniscus shape that is convex on the object side as a whole.
The seventh lens E7 is a negative meniscus lens formed convexly on the image side with the surface having a larger curvature than the image side facing the object side. The seventh lens E7 alone constitutes the second M lens group S2M.
The eighth lens E8 is a positive lens composed of a biconvex lens in which a surface having a larger curvature than the object side is directed to the image side and the image side surface is aspheric. The eighth lens E8 alone constitutes the second R lens group S2R.

That is, the second lens group G2 includes a second F lens group S2F composed of a cemented lens of the fifth lens E5 and the sixth lens E6, a second M lens group S2M composed of the seventh lens E7 and having negative refractive power, The second R lens unit S2R is composed of eight lenses E8 and has a positive refractive power.
As described above, in the imaging lens according to the present invention, in focusing, it is not a simple whole extension of the imaging lens, but in focusing on a short distance object, it is in a state of focusing on an object at infinity. The distance between the first lens group G1 and the second lens group G2 is made shorter than the distance between the first lens group G1 and the second lens group G2. In the configuration of the fourth embodiment, since the aperture FA operates integrally with the first lens group G1, the distance between the first lens group G1 and the second lens group G2 is set to be the first lens group G1. This is the sum of the fixed distance from the image side surface of the fourth lens E4 to the stop FA and the variable distance DA between the stop FA and the first lens group G1.
That is, as the entire imaging lens is extended by focusing from infinity to a close object (increasing the variable distance DB between the second lens group G2 and the various filters MF), the stop FA and the second lens group G2 During focusing on a short-distance object, the variable interval DA between is moved so as to be smaller than that in the state of focusing on an object at infinity.
In Example 4, the focal length f, the open F value F, and the half angle of view ω of the entire system are f = 18.29, F = 2.55, and ω = 38.3, respectively. The optical characteristics are as shown in the following table.

Also in Table 7, the lens surface with the surface number indicated by “* (asterisk)” is an aspheric surface, and the name of the glass material manufacturer is the OHARA (stock) before the glass type name. Company Ohara) and HOYA (HOYA Corporation).
That is, in Table 7, the optical surfaces of the first surface, the second surface, and the fifteenth surface marked with “*” are aspheric surfaces, and the parameters of each aspheric surface in the equation [12] are as follows. is there.
Aspherical parameters Aspherical surface: first surface K = 0.0
A ₄ = 5.513535 × 10 ⁻⁶
A ₆ = −2.266669 × 10 ⁻⁷
Aspherical surface: second surface K = 0.50663
A ₄ = −4.996155 × 10 ⁻⁵
A ₆ = 9.77362 × 10 ⁻⁷
A ₈ = −3.889927 × 10 ⁻⁸
A ₁₀ = −3.82203 × 10 ⁻¹⁰
A ₁₂ = 1.87953 × 10 ⁻¹¹
A ₁₄ = −2.16473 × 10 ⁻¹³
Aspheric surface: 15th surface K = 0.0
A ₄ = 1.07649 × 10 ⁻⁴
A ₆ = −1.45102 × 10 ⁻⁶
A ₈ = 6.57063 × 10 ⁻⁸
A ₁₀ = −1.20942 × 10 ⁻⁹
A ₁₂ = 9.40772 × 10 ⁻¹²
A ₁₄ = 2.04652 × 10 ⁻¹⁴
A ₁₆ = −7.56483 × 10 ⁻¹⁶
A ₁₈ = 3.26908 × 10 ⁻¹⁸
The variable distance DA between the aperture FA and the second lens group G2 and the variable distance DB between the second lens group G2 and the various filters MF are in focus on the object at infinity and the imaging magnification during focusing. It is changed as shown in the following table in the state of focusing on a short-distance object at -1/20 times.

The values corresponding to the conditional expressions [1] to [11] described in the fourth embodiment are as follows.
Conditional expression numerical value [1] L / Y ′ = 3.42
[2] (r ₂₁ + r ₂₂ ) / (r ₂₁ −r ₂₂ ) = − 1.970
[3] Bf / Y ′ = 1.068
[4] L ₁ /L=0.245
[5] f _A / f ₁ = 0.217
[6] f _1F / f _1R = −0.928
[7] A _1F-1R / L ₁ = 0.0084
[8] n _d = 1.497
[9] ν _d = 81.5
[10] P _{g, F} − (− 0.001802 × ν _d +0.6483) = 0.0361
[11] _{(A 1-2M -A 1-2) / (} Bf M -Bf) = - 0.334
Therefore, the numerical values related to the conditional expressions [1] to [11] in Example 4 are within the range of the conditional expressions, respectively, and satisfy the conditional expressions [1] to [11].

  Also, FIG. 11 shows spherical aberration, astigmatism, distortion aberration, and coma aberration curve diagrams in a state where the imaging lens according to Example 4 is focused on an object at infinity, and FIG. FIG. 7 shows respective aberration curve diagrams of spherical aberration, astigmatism, distortion aberration and coma aberration in a state where the imaging lens according to Example 4 is focused on an object at a short distance of −1/20 times. In these aberration curve diagrams, a broken line in spherical aberration represents a sine condition, a solid line in astigmatism represents sagittal, and a broken line represents meridional. In addition, g and d in the respective aberration diagrams of spherical aberration, astigmatism, and coma aberration represent g-line and d-line, respectively.

FIG. 13 schematically shows the configuration of the longitudinal section of the optical system of the imaging lens according to Example 5 of the present invention.
The imaging lens shown in FIG. 13 includes a first lens E1, a second lens E2, a third lens E3, a fourth lens E4, a fifth lens E5, a sixth lens E6, a seventh lens E7, an eighth lens E8, 9 lens E9, aperture stop FA, and various filters MF. The first lens E1 to the fourth lens E4 constitute the first lens group G1, and are arranged on the object side of the aperture stop, that is, the stop, FA. The fifth lens E5 to the ninth lens E9 are the second lens. The group G2 is configured and arranged on the image plane side of the stop FA, and is supported by a common support frame or the like that is appropriate for each group. The focusing unit operates integrally for each group. Also in this case, the aperture FA operates integrally with the first lens group G1.
In FIG. 13, each optical element constituting the optical system of the imaging lens includes, in order from the object side, a first lens E1, a second lens E2, a third lens E3, a fourth lens E4, an aperture FA, and a fifth lens. E5, sixth lens E6, seventh lens E7, eighth lens E8, ninth lens E9, and various filters MF are arranged in this order, and an image of an object is formed behind the various filters MF.

The first lens E1 is a negative meniscus lens in which a surface having a larger curvature than the object side is directed toward the image side, is convex toward the object side, and the image side surface is aspheric. The second lens E2 is a negative meniscus lens that is formed convex toward the image side with the surface having a larger curvature than the image side facing the object side. The first lens E1 and the second lens E2 constitute a first F lens group S1F having negative refractive power as a whole, the first lens E1 corresponds to the first negative lens, and the second lens E2 This corresponds to the second negative lens.
The third lens E3 is a positive lens composed of a biconvex lens with a surface having a larger curvature than the object side facing the image side, and the fourth lens E4 has a surface having a larger curvature than the image side directed toward the object side. A negative meniscus lens convexly formed on the side, and the two lenses, the third lens E3 and the fourth lens E4, are closely bonded to each other and integrally joined to form a two-piece cemented lens. . The cemented lens including the third lens E3 and the fourth lens E4 has a biconvex shape as a whole, and constitutes a first R lens group S1R having a positive refractive power.

That is, the first lens group G1 includes the first lens E1 and the second lens E2, and includes the first F lens group S1F having negative refractive power, the third lens E3, and the fourth lens E4, and has positive refractive power. And a first R lens group SIR.
The fifth lens E5 is a positive lens made up of a biconvex lens, and the sixth lens E6 is a negative lens made up of a biconcave lens. The two lenses of the fifth lens E5 and the sixth lens E6 are in close contact with each other. The two lenses are bonded together to form a two-piece cemented lens. The cemented lens including the fifth lens E5 and the sixth lens E6 constitutes a second F lens group S2F having a meniscus shape that is convex on the object side as a whole.
The seventh lens E7 is a negative lens composed of a biconcave lens with a surface having a larger curvature than the image side facing the object side, and the eighth lens E8 is a biconvex lens having a surface having a larger curvature than the object side directed toward the image side These two lenses, the seventh lens E7 and the eighth lens E8, are closely bonded and bonded together to form a two-lens cemented lens. The cemented lens including the seventh lens E7 and the eighth lens E8 has a negative meniscus shape having a convex surface facing the image as a whole, and constitutes a second M lens group S2M having negative refractive power.

The ninth lens E9 is a positive meniscus lens formed with a surface having a larger curvature than the object side facing the image side and the image side surface aspherical, and convex toward the image side. The ninth lens E9 alone constitutes the second R lens group S2R.
That is, the second lens group G2 includes a second F lens group S2F composed of a cemented lens of the fifth lens E5 and the sixth lens E6, and a cemented lens of the seventh lens E7 and the eighth lens E8, and has a negative refractive power. The second M lens group S2M includes the second lens group S2R including the ninth lens E9 and has a positive refractive power.
As described above, in the imaging lens according to the present invention, in focusing, it is not a simple whole extension of the imaging lens, but in focusing on a short distance object, it is in a state of focusing on an object at infinity. The distance between the first lens group G1 and the second lens group G2 is made shorter than the distance between the first lens group G1 and the second lens group G2. In the case of the configuration of Example 5, since the aperture FA operates integrally with the first lens group G1, the distance between the groups of the first lens group G1 and the second lens group G2 is the first lens group G1. This is the sum of the fixed distance from the image side surface of the fourth lens E4 to the stop FA and the variable distance DA between the stop FA and the first lens group G1.

That is, as the entire imaging lens is extended by focusing from infinity to a close object (increasing the variable distance DB between the second lens group G2 and the various filters MF), the stop FA and the second lens group G2 During focusing on a short-distance object, the variable interval DA between is moved so as to be smaller than that in the state of focusing on an object at infinity.
In Example 5, the focal length f, the open F value F, and the half angle of view ω of the entire system are f = 18.30, F = 2.56, and ω = 38.2, respectively. The optical characteristics are as shown in the following table.

Also in Table 9, the lens surface with the surface number indicated with “* (asterisk)” attached to the surface number is an aspheric surface, and the name of the glass material manufacturer is designated OHARA (stock) before the glass type name. Company Ohara) and HOYA (HOYA Corporation).
That is, in Table 9, the optical surfaces of the second surface and the sixteenth surface to which “*” is attached are aspheric surfaces, and the parameters of each aspheric surface in Equation [12] are as follows.
Aspheric parameters Aspheric surface: second surface K = −0.19254
A ₄ = 2.29237 × 10 ⁻⁵
A ₆ = 1.87839 × 10 ⁻⁷
A ₈ = 1.99882 × 10 ⁻⁸
A ₁₀ = −4.093939 × 10 ⁻¹⁰
A ₁₂ = 5.19254 × 10 ⁻¹²
Aspherical surface: 16th surface K = 0.0
A ₄ = 8.53049 × 10 ⁻⁵
A ₆ = −1.665776 × 10 ⁻⁷
A ₈ = 1.06167 × 10 ⁻⁸
A ₁₀ = −1.01522 × 10 ⁻¹⁰
A ₁₂ = 4.07983 × 10 ⁻¹³
The variable distance DA between the aperture FA and the second lens group G2 and the variable distance DB between the second lens group G2 and the various filters MF are in focus on the object at infinity and the imaging magnification during focusing. It is changed as shown in the following table in the state of focusing on a short-distance object at -1/20 times.

  Further, the values corresponding to the conditional expressions [1] to [11] described in the fifth embodiment are as follows.

Conditional expression numerical value [1] L / Y ′ = 3.43
[2] (r ₂₁ + r ₂₂ ) / (r ₂₁ −r ₂₂ ) = − 1.119
[3] Bf / Y ′ = 1.136
[4] L ₁ /L=0.223
[5] f _A / f ₁ = 0.0183
[6] f _1F / f _1R = −0.836
[7] A _1F-1R / L ₁ = 0.0092
[8] n _d = 1.497
[9] ν _d = 81.5
[10] P _{g, F} − (− 0.001802 × ν _d +0.6483) = 0.0361
[11] _{(A 1-2M -A 1-2) / (} Bf M -Bf) = - 0.361
Therefore, the numerical values related to conditional expression [1] to conditional expression [11] in Example 5 are within the range of the conditional expressions, respectively, and satisfy conditional expression [1] to conditional expression [11].

  FIG. 14 is a diagram illustrating spherical aberration, astigmatism, distortion, and coma aberration curves when the imaging lens according to Example 5 is focused on an object at infinity, and FIG. FIG. 10 shows respective aberration curve diagrams of spherical aberration, astigmatism, distortion aberration and coma aberration in a state where the imaging lens according to Example 5 is focused on an object at a short distance of −1/20 times. In these aberration curve diagrams, a broken line in spherical aberration represents a sine condition, a solid line in astigmatism represents sagittal, and a broken line represents meridional. Further, g and d in the respective aberration diagrams of spherical aberration, astigmatism, and coma aberration represent g-line and d-line, respectively.

  Next, one of the present inventions in which an imaging lens according to the present invention as shown in the first to fifth embodiments described above is employed as an imaging optical system to form an imaging apparatus, for example, a so-called digital camera. The embodiment will be described with reference to FIGS. FIGS. 16A and 16B are views showing the external appearance of the digital camera 100 as viewed from the front side that is the object, that is, the subject side. FIG. 16A is a state in which the photographing lens is retracted in the camera body, and FIG. FIG. 17 is a perspective view showing the external appearance of the digital camera 100 as seen from the back side that is the photographer side, and FIG. 18 is a block diagram showing the functional configuration of the digital camera 100. is there. Here, although the digital camera 100 as an imaging device is described, it is called not only an imaging device mainly for imaging including a video camera and a film camera but also a mobile phone, a personal data assistant (PDA), and the like. In many cases, an imaging function corresponding to a digital camera or the like is incorporated into various information devices including a portable information terminal device and a portable terminal device called a smartphone that combines these functions. Although such an information device also has a slightly different appearance, it includes substantially the same functions and configuration as a digital camera or the like, and the imaging lens according to the present invention may be employed in such an information device. .

As shown in FIGS. 16 and 17, the digital camera 100 includes a photographing lens 101, a shutter button 102, a zoom lever 103, a finder 104, a strobe 105, a liquid crystal monitor 106, an operation button 107, a power switch 108, a memory card slot 109, and A communication card slot 110 and the like are provided. Furthermore, as shown in FIG. 18, the digital 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 digital camera includes a photographing lens 101 and a light receiving element 201 as an area sensor such as a CMOS (complementary metal oxide semiconductor) imaging element or a CCD (charge coupled device) imaging element, and is an imaging optical system. An image of an object to be imaged, that is, a subject formed by the lens 101 is read by the light receiving element 201. As the photographing lens 101, the imaging lens according to the present invention described in the first to fifth embodiments is used (corresponding to claim 11 or claim 12).

  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 digital camera body. The liquid crystal monitor 106 can display an image being photographed, or can 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 digital camera 100 is carried, the photographing lens 101 is in a retracted state and buried in the body of the digital camera as shown in FIG. 16A. When the user operates the power switch 108 to turn on the power. As shown in FIG. 16B, the lens barrel is extended and protrudes from the body of the digital camera 100. By operating the zoom lever 103, zooming of a so-called digital zoom method can be performed in which the cutout range of the subject image is changed to perform pseudo scaling. At this time, it is desirable that the optical system of the finder 104 is also scaled in conjunction with the change in the effective field angle.
In many cases, focusing is performed by half-pressing the shutter button 102. Focusing in the imaging lens according to the present invention (imaging lens defined in claims 1 to 10) can be performed by moving the entire lens system, but can also be performed by moving the light receiving element 201. (Mainly the structure of claims 1 to 8). In addition, when focusing is performed by moving the entire lens system (or moving the light receiving element 201), the first lens group G1 and the second lens group G2 and the second lens group are more focused than when focused on an object at infinity. By shortening the distance to the lens group G2, it is possible to cancel the change in the curvature of field and minimize the degradation of the imaging performance at a finite distance (configurations of claims 9 to 10). Further, focusing can be performed by moving only the second lens group G2.

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.
Note that when the photographing lens 101 is in the retracted state, the groups of the imaging lenses are not necessarily arranged on the optical axis. For example, if the second lens group G2 is retracted from the optical axis and retracted in parallel with the first lens group G1 when retracted, the digital camera can be made thinner.
As described above, in the imaging apparatus or information apparatus as described above, the photographing lens 101 configured using the imaging lens as shown in the first to fifth embodiments is used as an imaging optical system. Can do. Accordingly, it is possible to realize a small image pickup apparatus or information apparatus with high image quality using a light receiving element of 10 million pixels to 20 million pixels.

G1 1st lens group G2 2nd lens group S1F 1F lens group S1R 1R lens group S2F 2F lens group S2M 2M lens group S2R 2R lens group E1 to E9 Lens FA Aperture stop MF Various filters 100 Digital camera 101 Shooting Lens 102 Shutter button 103 Zoom lever 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 (area sensor)
202 Signal Processing Unit 203 Image Processing Unit 204 Central Processing Unit (CPU)
205 Semiconductor memory 206 Communication card, etc.

JP 2010-39088 A JP 9-96759 A (Patent No. 3625923)

Claims (12)

A first lens group on the object side of the aperture stop, and a second lens group having a positive refractive power on the image side of the aperture stop, respectively.
In the imaging lens in which the first lens group is configured by arranging, in order from the object side, a first F lens group having a negative refractive power and a first R lens group having a positive refractive power,
The first F lens group includes, in order from the object side, a first negative lens having a large curvature surface facing the image side and a second negative lens having a large curvature surface facing the object side. ,
The first R lens group is configured with one of a positive lens and a cemented lens having a positive refractive power as a whole,
The distance from the surface closest to the object side of the first lens group to the image plane in a state focused on an object at infinity is L, the maximum image height is Y ′, and the radius of curvature of the object side surface of the second negative lens is r ₂₁ and the radius of curvature of the image-side surface of the second negative lens is r ₂₂ ,
Conditional expression:
[1] 2.8 <L / Y ′ <4.3
[2] −7.0 <(r ₂₁ + r ₂₂ ) / (r ₂₁ −r ₂₂ ) <− 0.7
An imaging lens characterized by satisfying Bf is the distance from the surface closest to the image side of the second lens group in the state focused on the object at infinity, and the image height is Y ′.
Conditional expression:
[3] 0.8 <Bf / Y ′ <1.6
The imaging lens according to claim 1, wherein: The distance from the most object-side surface of the first lens unit to the most image-side surface is L ₁ , and the distance from the most object-side surface of the first lens unit to the image surface in a state of focusing on an object at infinity. Let L be the distance
Conditional expression:
[4] 0.20 <L ₁ /L<0.32
The imaging lens according to claim 1, wherein the imaging lens is satisfied. The focal length of the entire imaging lens system is f _A , and the focal length of the first lens group is f ₁ .
Conditional expression:
[5] 0.0 <f _A / f ₁ <0.6
The imaging lens according to any one of claims 1 to 3, wherein the imaging lens is satisfied. The focal length of the first F lens group is f _1F , and the focal length of the first R lens group is f _1R .
Conditional expression:
[6] -1.3 <f _1F / f _1R <−0.7
The imaging lens according to claim 4, wherein: The distance between the first F lens group and the first R lens group is A _1F-1R , and the distance from the most object side surface to the most image side surface of the first lens group is L ₁ .
Conditional expression:
[7] 0.0 <A _1F-1R / L ₁ <0.1
The imaging lens according to claim 1, wherein the imaging lens is satisfied. The refractive index of the first negative lens or the second negative lens of the first F lens group is n _d , the Abbe number of the first negative lens or the second negative lens is ν _d , and the first negative lens or the _Let P _{g, F} be the partial dispersion ratio of the second negative lens,
The partial dispersion ratio _{P g, F} is the optical glass constituting the negative lens, g-line, F line and the refractive index, respectively _n g the C-line, as _{n F} and _{n C,
P g, F = (n g} -n F) / (n F -n C)
As
At least one of the first negative lens and the second negative lens of the first F lens group is
Conditional expression:
[8] 1.45 _<n d _<1.65
[9] 55.0 <ν _d <95.0
[10] 0.015 <P _{g, F} − (− 0.001802 × ν _d +0.6483) <0.050
The imaging lens according to claim 1, wherein the imaging lens is satisfied.   8. The first lens group according to claim 1, wherein the first R lens group is a cemented lens configured by sequentially arranging a positive lens and a negative lens from the object side. Imaging lens.   The structure in which the distance between the first lens group and the second lens group is shortened when focusing on a short-distance object as compared with a state where an object at infinity is focused. Item 9. The imaging lens according to any one of items 8 to 9. The distance between the first lens group and the second lens group in a state focused on an object at infinity is A _1-2 , and the first lens in a state focused on a short distance object at an imaging magnification of −1/20 times. The distance from the surface closest to the image side of the second lens group to the image plane in a state where the distance between the second lens group and the second lens group is in the state of A _1-2M and an imaging magnification of −1 / 20 × Bf _M , and Bf is the distance from the most image side surface to the image plane of the second lens group in a state of focusing on an object at infinity,
Conditional expression:
[11] _{-0.5 <(A 1-2M -A 1-2)} / (Bf M -Bf) <- 0.2
The imaging lens according to claim 9, wherein:   An imaging apparatus comprising the imaging lens according to any one of claims 1 to 10 as an imaging optical system.   11. An information device having an imaging function and using the imaging lens according to claim 1 as an imaging optical system.

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