JP5963040B2 - Imaging lens, imaging device, and information device - Google Patents

Description

  The present invention is used as an imaging optical system in various cameras including a so-called silver salt camera, in particular, a digital camera, a video camera, a surveillance camera, and the like, and is used to improve a single-focus imaging lens for imaging a subject image. In particular, an imaging lens suitable for an imaging apparatus using electronic imaging means such as a digital camera and a digital video camera, an imaging apparatus such as a camera using such an imaging lens, and a portable information terminal having an imaging function The present invention relates to an information device such as a device.

In recent years, digital still cameras and digital video cameras have been widely used as image pickup apparatuses using solid-state image pickup devices such as CCD (charge coupled device) image pickup devices and CMOS (complementary metal oxide semiconductor) image pickup devices. A digital camera used for capturing an image, that is, a still image, is widely used as an imaging apparatus that replaces a conventional silver salt camera using a so-called silver salt film.
Solid-state imaging devices used in this type of imaging apparatus have a higher number of pixels, and accordingly, higher optical performance is required for imaging lenses. In addition, the portability of imaging devices has been taken into account, and the downsizing has progressed, and the market has demanded imaging devices that have both high performance and compactness. It has been. Furthermore, the shooting speed required for shooting is also increasing, and the imaging lens is also required to be a brighter lens.
As for the angle of view of the imaging lens for digital cameras, a certain wide angle is preferred so that it can be easily photographed with a snapshot, etc., and a focal point equivalent to 35 mm in terms of 35 mm (so-called Leica) film photography. A half angle of view corresponding to the distance: 32 degrees is one of the guidelines for the required angle of view.

In recent years, wide-angle single focus lenses tend to be desired for large-diameter lenses. Therefore, when the focal length converted to a 35 mm film is made shorter than 50 mm to the wide angle side, coma aberration and field curvature increase, and it becomes more difficult to suppress them. Examples of such a lens having a large-diameter focal length wider than 50 mm in terms of 35 mm size are, for example, Patent Document 1 (Japanese Patent Laid-Open No. 08-313803), Patent Document 2 (Japanese Patent Laid-Open No. 2009-258157), and Patents. Document 3 (Japanese Patent Laid-Open No. 2010-39088) and the like are known.
The optical systems disclosed in Patent Document 1, Patent Document 2, and Patent Document 3 described above are inner focus type or rear focus type optical systems in which the total optical length does not change during focusing.
That is, the one disclosed in Patent Document 1 is an inner focus type optical system, which is a wide angle system in which an F value (so-called F number) is equivalent to F2.8, and a focal length in terms of 35 mm format is equivalent to 28 mm. The total length of the lens is about 3 times the maximum image height ratio. Further, since the number of lenses constituting the focus group driven during focusing is large, the focus speed during focusing tends to be slow. The one disclosed in Patent Document 2 is a rear focus type optical system, which has an F value equivalent to F2.8, a wide-angle system equivalent to a 35 mm equivalent focal length of 35 mm, and the total lens length is the maximum image height ratio. The peripheral light amount ratio is as dark as about 30%.
And what is shown in Patent Document 3 is an inner focus type optical system, which is a wide angle system equivalent to a focal length of 28 mm in 35 mm format, and the F value is notable in terms of F1.9 and a large aperture. However, the total lens length is 9 times or more in terms of the maximum image height ratio.

As described above, the one disclosed in Patent Document 1 is an inner focus type optical system, which has an F value (so-called F number) equivalent to F2.8 and a wide-angle system equivalent to a focal length equivalent to 28 mm in a 35 mm format. The total lens length is about three times as large as the maximum image height ratio. Further, since the number of lenses constituting the focus group driven during focusing is large, the focus speed during focusing tends to be slow. What is disclosed in Patent Document 2 is a rear focus type optical system, which is a wide-angle system with an F value equivalent to F2.8, a 35 mm equivalent focal length equivalent to 35 mm, and a maximum lens height with a maximum image height ratio. The peripheral light amount ratio is as dark as about 30%. And what was disclosed by patent document 3 is an optical system of an inner focus type | mold, and is a wide angle system whose focal distance of 35 mm size conversion is equivalent to 28 mm, and F value is notable in the surface of F1.9 and a large aperture. However, the total lens length is 9 times or more in terms of the maximum image height ratio. Thus, it cannot be said that the optical systems shown in any of Patent Document 1, Patent Document 2, and Patent Document 3 are mainly sufficient in terms of miniaturization.
The present invention has been made in view of the above-described circumstances, and is a so-called rear focus type optical system that can perform focusing without changing the entire length of the optical system, and has a wide angle of about 32 to 33 degrees. Thus, the F-number is as bright as about F2.5, the total length of the optical system is as small as about 2.2 times the image height, and distortion fluctuations during focusing are small, resulting in high performance. An object of the present invention is to provide an image lens and a small-sized and high-performance imaging device and information device using such an imaging lens.

In order to achieve the above-described object, an imaging apparatus according to the present invention provides
A first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power are sequentially arranged from the object side to the image plane side. In an imaging lens comprising an optical system that forms an optical image of an object,
An aperture stop is disposed in the first lens group,
The first lens group has at least four lenses,
The second lens group is composed of a single weak-power lens, and one negative lens having a concave surface on the object side,
The third lens group consists of one positive lens having a convex surface directed toward the image side,
Will constitute the optical system as a whole system for a total of 8 sheets or less of the lens,
In focusing, with the focusing from infinity to a finite distance object, the second lens group is moved from the object side to the image plane side direction,
The distance from a most object side surface of the first lens group to the image plane L, and most Daizo high Y ', and the focal length of the weak lens of said refractive power as _f 2weak,
Conditional expression:
[1] 2.2 <L / Y ′ <2.5
[4] | f _2weak |> 100
It is characterized by satisfying.

According to the present invention, it is a so-called rear focus type optical system that can perform focusing without changing the entire length of the optical system, a half angle of view is a wide angle of about 32 to 33 degrees, and an F value is equivalent to F2.5. Therefore, it is possible to provide an imaging lens that is as bright as possible, has a total length of the optical system as small as about 2.2 times the image height, and has a small variation in distortion during focusing and can achieve high performance.
That is, according to the invention described in claim 1,
A first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power are sequentially arranged from the object side to the image plane side. In an imaging lens comprising an optical system that forms an optical image of an object,
An aperture stop is disposed in the first lens group,
The first lens group has at least four lenses,
The second lens group is composed of a single weak-power lens, and one negative lens having a concave surface on the object side,
The third lens group consists of one positive lens having a convex surface directed toward the image side,
Will constitute the optical system as a whole system for a total of 8 sheets or less of the lens,
In focusing, with the focusing from infinity to a finite distance object, the second lens group is moved from the object side to the image plane side direction,
The distance from a most object side surface of the first lens group to the image plane L, and most Daizo high Y ', and the focal length of the weak lens of said refractive power as _f 2weak,
Conditional expression:
[1] 2.2 <L / Y ′ <2.5
[4] | f _2weak |> 100
By satisfying the above, it is possible to perform focusing without changing the entire length of the optical system, the half angle of view is a wide angle of about 32 degrees to about 33 degrees, the F value is equivalent to F2.5, a small size, and high performance. Can be obtained.

It is sectional drawing along the optical axis which shows the structure of the optical system of the imaging lens in Example 1 which concerns on the 1st Embodiment of this invention. FIG. 3 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration 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. Spherical aberration, astigmatism, distortion and coma aberration when the imaging lens according to Example 1 of the present invention shown in FIG. 1 is focused at an imaging magnification of about −1/20 times (imaging distance≈500 mm) are shown. FIG. It is sectional drawing along the optical axis which shows the structure of the optical system of the imaging lens in Example 2 which concerns on the 2nd Embodiment of this invention. FIG. 5 is an aberration curve diagram showing spherical aberration, astigmatism, distortion aberration, and coma aberration when the imaging lens according to Example 2 of the present invention shown in FIG. 4 is focused on an object at infinity. Spherical aberration, astigmatism, distortion, and coma aberration when the imaging lens according to Example 2 of the present invention shown in FIG. 4 is focused at an imaging magnification of about −1/20 times (an imaging distance≈500 mm). FIG. It is typical sectional drawing along the optical axis which shows the structure of the optical system of the imaging lens in Example 3 which concerns on the 3rd Embodiment of this 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. The spherical aberration, astigmatism, distortion and coma aberration in the state where the imaging lens according to Example 3 of the present invention shown in FIG. 7 is focused at an imaging magnification of about −1/20 times (imaging distance≈500 mm) are shown. FIG. It is sectional drawing along the optical axis which shows the structure of the optical system of the imaging lens in Example 4 which concerns on the 4th Embodiment of this invention. FIG. 11 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration in a state where the imaging lens according to Example 4 of the present invention shown in FIG. 10 is focused on an object at infinity. Spherical aberration, astigmatism, distortion and coma aberration in the state where the imaging lens according to Example 4 of the present invention shown in FIG. 10 is focused at an imaging magnification of about −1/20 times (imaging distance≈500 mm) are shown. FIG. It is sectional drawing along the optical axis which shows the structure of the optical system of the imaging lens in Example 5 which concerns on the 5th Embodiment of this invention. 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. 13 is focused on an object at infinity. Spherical aberration, astigmatism, distortion, and coma aberration when the imaging lens according to Example 5 of the present invention shown in FIG. 13 is focused at an imaging magnification of about −1/20 times (imaging distance≈500 mm) are shown. FIG. It is sectional drawing along the optical axis which shows the structure of the optical system of the imaging lens in Example 6 which concerns on the 6th Embodiment of this invention. FIG. 17 is an aberration curve diagram showing spherical aberration, astigmatism, distortion aberration, and coma aberration when the imaging lens according to Example 6 of the present invention shown in FIG. 16 is focused on an object at infinity. Spherical aberration, astigmatism, distortion, and coma aberration when the imaging lens according to Example 6 of the present invention shown in FIG. 16 is focused at an imaging magnification of about −1/20 times (imaging distance≈500 mm) are shown. FIG. It is sectional drawing along the optical axis which shows the structure of the optical system of the imaging lens in Example 7 which concerns on the 7th Embodiment of this invention. FIG. 20 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration in a state where the imaging lens according to Example 7 shown in FIG. 19 is focused on an object at infinity. Spherical aberration, astigmatism, distortion and coma aberration when the imaging lens according to Example 7 of the present invention shown in FIG. 19 is focused at an imaging magnification of about −1/20 (imaging distance≈500 mm) are shown. FIG. It is sectional drawing along the optical axis which shows the structure of the optical system of the imaging lens in Example 8 which concerns on the 8th Embodiment of this invention. FIG. 23 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration when the imaging lens according to Example 8 shown in FIG. 22 is focused on an object at infinity. Spherical aberration, astigmatism, distortion aberration, and coma aberration when the imaging lens according to Example 8 of the present invention shown in FIG. 22 is focused at an imaging magnification of about −1/20 times (shooting distance≈500 mm) are shown. FIG. It is the perspective view seen from the front side which shows typically the appearance composition of the digital camera as an image pick-up device concerning a 9th embodiment of the present invention, ie, the object side which is a photographic subject, (a). The imaging lens constructed using the imaging lens according to any of the first to eighth embodiments is retracted in the body of the digital camera, and (b) is the body of the digital camera. The state which protrudes from each is shown. It is the perspective view seen from the back side which shows the external appearance structure of the digital camera of FIG. 25, ie, a photographer side. FIG. 27 is a block diagram illustrating a functional configuration of the digital camera of FIGS. 25 and 26.

Hereinafter, based on an embodiment 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 specific numerical examples, first, a fundamental embodiment of the present invention will be described.
The first embodiment of the present invention is an embodiment as an imaging lens constituting an optical system that forms an optical image of an object.
The imaging lens according to the first embodiment of the present invention is an optical system configured as a so-called rear focus type in which the optical total length does not change with focusing, and the half angle of view is about 32 degrees to about 32 degrees. High-performance imaging with a wide angle of 33 degrees, a bright F value equivalent to about F2.5, a small overall optical system length of about 2.2 times the image height, and a small change in distortion due to focusing. It is a lens system.

That is, the imaging lens according to the first embodiment of the present invention is
A first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power are sequentially arranged from the object side to the image plane side. An imaging lens comprising an optical system for forming an optical image of an object,
An aperture stop is disposed in the first lens group,
The first lens group has at least four lenses,
The second lens group is composed of a single weak-power lens, and one negative lens having a concave surface on the object side,
The third lens group consists of one positive lens having a convex surface directed toward the image side,
Will constitute the optical system as a whole system for a total of 8 sheets or less of the lens,
In focusing, with the focusing from infinity to a finite distance object, the second lens group is moved from the object side to the image plane side direction,
By adopting a configuration that satisfies the following conditional expression [1], a compact and high-performance imaging lens is obtained .
[1] 2.2 <L / Y ′ <2.5
[4] | f _2weak |> 100
Here, L represents the distance from the most object side surface of the first lens group to the image surface , Y ′ represents the maximum image height , and f _2weak represents the focal length of the lens having a weak refractive power .

Conditional expression [1] defines the total length of the imaging lens that best exhibits the effects of the present invention. If L / Y ′ in the conditional expression [1] exceeds the upper limit, the total length of the optical system becomes large, which is advantageous in terms of optical performance, but such a configuration is not desirable in terms of compactness. Further, if L / Y ′ in conditional expression [1] is below the lower limit, in the case of the configuration according to the present invention, particularly, chromatic aberration and coma aberration are greatly generated and the optical performance is deteriorated. Absent.
If the conditional expression [4] is not satisfied, the refractive power of the lens becomes strong, (1) the fluctuation of aberration caused by focusing becomes large, and (2) large astigmatism occurs. Is not desirable.
The imaging lens according to the present invention is
A first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power are sequentially arranged from the object side to the image plane side. An imaging lens comprising an optical system for forming an optical image of an object,
An aperture stop is disposed in the first lens group,
The first lens group has at least four lenses,
The second lens group includes a lens having a weak refractive power and a negative lens having a concave surface facing the object side,
The third lens group is composed of one positive lens having a convex surface facing the image surface side,
Will constitute the optical system as a whole system for a total of 8 sheets or less of the lens,
In focusing, only the second lens group is moved along the optical axis direction,
By configuring so as to satisfy the following condition (1) to (4), a small, but it may also as a high-performance imaging lens.

[1] 2.2 <L / Y ′ <2.5
[2] 0.3 <f1 / f3 <0.8
[3] -0.5> f2 / f> -0.8
[4] | f _2weak |> 100
Here, similarly to the above, L is the distance from the most object side surface of the first lens group to the image plane, Y ′ is the maximum image height, f1 is the focal length of the first lens group, and f2 is the first lens group. 2 represents the focal length of the second lens group, f3 represents the focal length of the third lens group , f represents the focal length of the entire optical system at infinity , and _f2weak represents the focal length of the lens having a weak refractive power. Yes.
As described above, the conditional expression [1] defines the total length of the imaging lens in which the effect of the present invention is best exhibited. If L / Y ′ in the conditional expression [1] exceeds the upper limit, the total length of the optical system becomes large, which is advantageous in terms of optical performance, but such a configuration is not desirable in terms of compactness. If L / Y ′ in the conditional expression [1] is below the lower limit, in the case of the configuration according to the present invention, particularly chromatic aberration and coma aberration are greatly generated and the optical performance is deteriorated.

Conditional expression [2] gives an optimum condition regarding the focal length between the first lens group and the third lens group. If f1 / f3 in conditional expression [2] is below the lower limit, the refractive power of the third lens group will increase, or the refractive power of the first lens group will decrease, and astigmatism will occur. Such a configuration is not desirable because it occurs greatly. If f1 / f3 in conditional expression [2] exceeds the upper limit, lateral chromatic aberration is greatly generated, and such a configuration is not desirable.
Conditional expression [3] gives an optimum condition for the focal length between the second lens group and the entire optical system at infinity. When f2 / f in conditional expression [3] is below the lower limit, the astigmatic difference becomes large, and axial chromatic aberration tends to occur greatly in the g-line versus d-line, so such a configuration is not desirable. . If f2 / f in conditional expression [3] exceeds the upper limit, the focal length increases and the optical total length increases, so that compactness cannot be secured, and such a configuration is disadvantageous in terms of portability. It becomes.
If the conditional expression [4] is not satisfied, the refractive power of the lens becomes strong, (1) the fluctuation of aberration caused by focusing becomes large, and (2) large astigmatism occurs. Is not desirable.

And the imaging lens according to the present invention is:
A first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power are sequentially arranged from the object side to the image plane side. An imaging lens comprising an optical system for forming an optical image of an object,
An aperture stop is disposed in the first lens group,
The first lens group includes any one of four and five lenses,
The second lens group is composed of a single weak-power lens, and one negative lens having a concave surface on the object side,
The third lens group consists of one positive lens having a convex surface directed toward the image side,
Focusing is performed by moving only the second lens group along the optical axis direction,
Ri name and a total of eight or less of the lens of the optical system as a whole system,
Let f _{2weak be} the focal length of the lens with weak refractive power ,
Conditional expression:
[4] | f _2weak |> 100
By satisfying the above, a compact and high-performance imaging lens may be obtained.

As described above, by disposing an aperture stop in the first lens group and by disposing lenses before and after the aperture stop, in particular, spherical aberration correction, tangential coma aberration and axial chromatic aberration are corrected, The lens having a weak refractive power in the second lens group particularly contributes to correction of lateral chromatic aberration and correction of astigmatism, and a negative lens having a concave surface facing the object side serves as a field lens. At first glance, even if there is no lens with weak refractive power, it is apt to be judged that aberration correction is established. It is. In addition, by disposing at least one positive lens having a convexity with the convex surface facing the image surface side in the third lens group, aberrations occurring in the front lens, that is, the object side lens, In particular, it serves to correct axial chromatic aberration and lateral chromatic aberration.
If the conditional expression [4] is not satisfied, the refractive power of the lens becomes strong, (1) fluctuations in aberrations caused by focusing increase, and (2) large astigmatism occurs. Not desirable.
Further, in the imaging lens described above, by adopting a configuration that performs focusing by moving only the second lens group along the optical axis direction, but it may also the higher performance imaging lens.

When focusing, only the second lens group consisting of the lens having a weak refractive power and the negative lens having a concave shape on the object side is moved to effectively suppress aberration fluctuations due to focusing. It becomes possible to do. In addition, since the number of lenses in the moving lens group can be reduced during focusing, it is possible to improve the focusing speed and reduce the burden on the driving mechanism when moving the lens group.
In the imaging lens described above, the second lens group is moved from the object side toward the image plane side without moving the first lens group in accordance with focusing from infinity to a finite distance object. by the, not to want to be a higher-performance imaging lens.
That is, since the focusing group has a negative refractive power, it is a feature of the imaging lens in this case that the focusing group is moved from the object side to the image plane side during focusing. When the focusing operation is performed, the first lens group is fixed without being moved, so that the total lens length becomes constant. Therefore, when the imaging operation is performed while holding the lens barrel, the lens barrel expands and contracts. There is no complication.

The imaging lens according to the first embodiment of the present invention includes:
An optical system constituting the optical system total system at eight following lens,
An aperture stop is arranged between the lenses of the optical system,
The object side of the aperture stop has at least two lenses,
On the image plane side of the aperture stop, there is one single lens having a weak refractive power, one negative single lens having a concave shape on the object side, and two positive lenses having a convex shape on the image side. Having
By configured to perform focusing by moving the negative single lens having a concave surface on the object side and a weak single lens having a refractive power on the optical axis, but it may also as a high-performance imaging lens.
As described above, it is particularly preferable to dispose at least two lenses in front of the aperture stop, that is, on the object side, and to dispose a lens having a positive refractive power behind the aperture stop, that is, on the image surface side. It is effective for correction. The imaging lens according to the present invention is a wide-angle imaging lens, and it is desirable to make it a negative lens preceding type in order to achieve both compactness and high performance, but even a positive lens preceding type is sufficiently compact, Aberration correction is also possible (see Example 4 below). In addition, by moving a part of the lens behind the aperture stop, that is, the object side lens during the focusing, it is possible to minimize the aberration variation due to the focusing.

In the imaging lens according to the present invention, the focusing group is composed of a lens having a weak refractive power and a negative lens having a concave shape facing the object side, and aberration fluctuations caused by the movement of these two lenses To consider. Therefore, paying attention to the change in astigmatism at a short distance (FIGS. 2, 3, 5, 6, 8, 9, 11, 11, 12, 14, 15, 15, 17, FIG. 18, see FIG. 20, FIG. 21, FIG. 23, and FIG. 24), the astigmatic difference is suppressed to a small extent until the image height is about 0.8 Y ′, and the configuration according to the present invention is at a short distance. Is also high performance. In order to obtain a bright, compact, and high-performance imaging lens, it is desirable that the entire optical system is composed of 7 to 8 lenses.
The imaging lens according to the first embodiment of the present invention is
An optical system comprising the entire optical system with eight or fewer lens elements,
An aperture stop is arranged between the lenses of the optical system,
The object side of the aperture stop has at least two lenses,
The image plane side from the aperture stop includes a lens having a weak refractive power, a negative lens having a concave shape on the object side, and a positive lens having a convex shape on the image side, and a total of five or less. Made up of lenses
In focusing, without moving the lens on the object side than the lens having a weak refractive power, the lens having a weak refractive power and the negative lens having a concave shape on the object side are moved on the optical axis. by be configured to perform focusing, but it may also as a high-performance imaging lens.

  As described above, by arranging at least two lenses in front of the aperture stop, that is, on the object side, positive spherical aberration is generated on the third-order aberration surface, but on the rear side of the aperture stop, that is, on the image plane side. Thus, a negative spherical aberration is generated and corrected. The number of lenses on the rear side of the aperture stop and on the image plane side is five or less, and various aberrations are efficiently corrected. By moving the lens having a weak refractive power on the image plane side behind the aperture stop and the negative lens having a concave shape on the object side to perform focusing, the aberration variation due to focusing is minimized. Yes. When focusing, by fixing the lens on the object side rather than the lens having a weak refractive power so as not to move, the troublesomeness of the photographer during operation is reduced. Further, the focusing speed can be improved by forming the focusing lens group with two lenses.

Furthermore, the imaging lens according to the first embodiment of the present invention includes:
An optical system constituting the optical system total system at eight following lens,
An aperture stop is arranged between the lenses of the optical system,
The object side of the aperture stop has at least two lenses,
From the object side to the image surface side, the image plane side of the aperture stop is sequentially composed of one of a cemented lens and a single lens, has a positive refractive power, a lens having a weak refractive power, and an object. A negative lens having a concave shape on the side and a positive lens having a convex shape on the image plane side are arranged and configured,
In focusing, the lens on the object side and the negative lens having a concave surface on the object side are moved together on the optical axis without moving the lens on the object side than the lens having a weak refractive power. by configured to perform focusing by, but it may also as a high-performance imaging lens.

As described above, the lens arrangement on the image plane side from the aperture stop is sequentially changed from the object side to the image plane side, “a cemented lens or a single lens having a positive refractive power, a lens having a weak refractive power, and an object. A negative lens having a concave shape on the side and a positive lens having a convex shape on the image side are arranged in a “positive-weak refractive power-negative-positive” arrangement, so-called triplet type first lens The lens is a modified triplet type in which an aberration correction lens is disposed between the first lens and the second lens, and an aberration change accompanying the movement of the lens due to focusing in the configuration of the imaging lens according to the present invention is effectively corrected. In addition, aberrations generated by the lens on the object side of the aperture stop, in this case, spherical aberration, in particular, are corrected by a positive lens on the image side of the aperture stop.
The imaging lens according to the first embodiment of the present invention is
In the optical system constituting the optical system total system at eight following lens described above,
By adopting a configuration that satisfies the following condition (1), but it may also be set as the high-performance imaging lens.
[1] 2.2 <L / Y ′ <2.5
Here, L represents the distance from the most object-side surface of the first lens group to the image plane, and Y ′ represents the maximum image height.

As described above, the conditional expression [1] defines the total length of the imaging lens in which the effect of the present invention is best exhibited. If L / Y ′ in the conditional expression [1] exceeds the upper limit, the total length of the optical system becomes large, which is advantageous in terms of optical performance, but such a configuration is not desirable in terms of compactness. Further, if L / Y ′ in conditional expression [1] is below the lower limit, in the case of the configuration according to the present invention, particularly, chromatic aberration and coma aberration are greatly generated and the optical performance is deteriorated. Absent.
Further, in the optical system constituting the optical system total system at eight following lens described above,
By adopting a configuration that satisfies the following condition (4), but it may also be set as the high-performance imaging lens.
[4] | f _2weak |> 100
Here, f _2weak represents the focal length of the lens having a weak refractive power among the lenses that move on the optical axis during focusing. If this conditional expression [4] is not satisfied, the refractive power of the lens becomes strong, (1) the fluctuation of aberration caused by focusing becomes large, and (2) the astigmatic difference is greatly generated. Is not desirable.

In the imaging lens that performs focusing by moving the lens having a weak refractive power and the lens having a concave shape on the object side on the optical axis,
By adopting a configuration that satisfies the following condition: [5], but it may also be set as the high-performance imaging lens.
[5] 2.1 <| ff / fAir | <3.7
Here, ff is the combined focal length of the lens group that moves during focusing, and fAir is the distance between the lens having a weak refractive power in the lens group that moves during focusing and the lens having a concave shape on the object side. It represents the air gap.
When | ff / fAir | in conditional expression [5] is below the lower limit, the refractive power increases and the air space between the lenses also increases, so that various aberrations increase and the configuration is not realized. If | ff / fAir | of the conditional expression [5] exceeds the upper limit, the longitudinal chromatic magnification chromatic aberration is greatly generated, and the variation of the spherical aberration at the time of focusing is increased.

Furthermore, in the imaging lens described above,
By adopting a configuration that satisfies the following condition (6), but it may also be set as the high-performance imaging lens.
[6] 11.7 <| ΔD _1-2 /β|<15.7
Here, ΔD _1-2 represents the distance to which the focusing lens group is moved when focusing to focus on a finite short distance object from the infinity state, and β represents the photographing magnification at the time of focusing on the short distance object. Yes.
If | ΔD _1-2 / β | in conditional expression [6] is below the lower limit, the amount of variation in magnification due to focusing increases, so the amount of movement during focusing from infinity to a finite short distance object decreases. Although the focusing speed is improved and works advantageously, (1) it is necessary to finely control the resolution, and such a configuration is not desirable. Further, if | ΔD _1-2 / β | in conditional expression [6] exceeds the upper limit, the amount of variation in magnification due to focusing becomes small. Therefore, when focusing from infinity to a finite short distance object, (1) Such a configuration is undesirable because the amount of movement is large and (2) the focusing speed is slow.

In the imaging lens described above,
By adopting a configuration in which satisfy the following condition (7), but it may also be set as the high-performance imaging lens.
[7] -0.8 <fen / fep <-0.4
Here, fen represents the focal length of the lens having the negative refractive power located closest to the image plane side, and fep represents the focal length of the lens having the positive refractive power located closest to the image plane side. If fen / fep in conditional expression [7] is below the lower limit, the focal length of the negative lens is large, the focal length of the positive lens is large, and the lateral chromatic aberration and coma aberration are large. Absent. And if fen / fep of conditional expression [7] exceeds an upper limit, since a sagittal coma aberration will generate | occur | produce largely, such a structure is not desirable. In addition, when the fen / fep in the conditional expression [7] is outside the range between the upper limit and the lower limit, the variation of the spherical aberration at the time of focusing increases, so such a configuration is not desirable.

In the imaging lens described above,
By adopting a configuration that satisfies the following condition: [8], but it may also be set as the high-performance imaging lens.
[8] 0.4 <LD1 / LD3 <0.8
Here, LD1 is the maximum effective diameter of the lens having the largest diameter in front of the aperture stop, that is, the lens on the object side, and LD3 is the maximum of the lens having the largest diameter in the rear of the aperture stop, that is, the lens on the image plane side. The effective diameter is shown.
Conditional expression [8] defines the lens diameter of the imaging lens that best exhibits the effect of the configuration of the present invention. When LD1 / LD3 in conditional expression [8] exceeds the upper limit or falls below the lower limit, the lens diameter of the first lens group or the third lens group becomes large. Therefore, (1) the lens barrel of the imaging lens Such a configuration is not desirable because the diameter is increased, (2) the lens diameter of the lens constituting the imaging lens is increased, and (3) it is difficult to make the lens compact.

And in the imaging lens described above,
By adopting a configuration that satisfies the following condition (9), but it may also be set as the high-performance imaging lens.
[9] SD> 3.1 [mm]
Here, SD represents the size of the shutter space on the optical axis between the lenses. In the configuration of the imaging lens according to this embodiment, a shutter space is formed between the lenses before and after the aperture stop. ing. It is most efficient to place the shutter before and after the aperture stop at the position where the light flux becomes the largest in the entire optical system, and it is an imaging lens that secures a shutter space of at least 3.1 mm (each implementation) See example).
The ninth embodiment of the present invention is an embodiment as an imaging apparatus such as a so-called digital camera or an information apparatus having an imaging function.
That is, an imaging apparatus according to a ninth embodiment of the present invention, the imaging lens described above, that make up used as an imaging optical system.
With such a configuration, a small and high-performance imaging device can be realized.
The information device according to a ninth embodiment of the present invention has an imaging function, an imaging lens as described above, that make up used as an imaging optical system.
With such a configuration, a small and high-performance information device having an imaging function can be realized.

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, Example 5, Example 6, Example 7, and Example 8 described below are the first, second, third, and fourth examples of the present invention. , Examples of specific configurations of the imaging lenses according to the fifth, sixth, seventh and eighth embodiments by specific numerical examples, and the ninth embodiment includes Examples 1 to Examples. 8 is a specific example of an imaging apparatus or information apparatus according to the ninth embodiment of the present invention in which a lens unit having an imaging lens as shown in FIG. 8 is used as an imaging optical system.
1 to 3 are diagrams for explaining an imaging lens in Example 1 according to the first embodiment of the present invention, and FIGS. 4 to 6 illustrate a second embodiment of the present invention. FIG. 7 to FIG. 9 are for explaining the imaging lens in Example 3 according to the third embodiment of the present invention. FIGS. 10 to 12 are for explaining the imaging lens in Example 4 according to the fourth embodiment of the present invention, and FIGS. 13 to 15 illustrate the fifth embodiment of the present invention. FIG. 16 to FIG. 18 are for explaining the imaging lens in Example 6 according to the sixth embodiment of the present invention. FIGS. 19 to 21 show the results in Example 7 according to the seventh embodiment of the present invention. Lens is intended to explain and FIGS. 22 to 24 are diagrams for explaining the imaging lens of Example 8 according to the eighth embodiment of the present invention.

Aberrations in the imaging lenses of Examples 1 to 8 are corrected at a high level, and spherical aberration, astigmatism, field curvature, and lateral chromatic aberration are sufficiently corrected. By configuring the imaging lens as in Examples 1 to 8, the half angle of view is 32 to 33 degrees and the F value (F number) is about F2.5, which is a large aperture. It is clear from each example that good imaging performance can be secured.
The meanings of symbols common to Examples 1 to 8 are as follows.
f: Focal length of the entire optical system F: F value (F number)
R: radius of curvature (paraxial radius of curvature for aspheric surfaces)
D: Surface interval Nd: Refractive index νd: Abbe number SD: Shutter space [mm]
ω: Half angle of view [degree]
In Examples 1 to 8, 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. In such an aspherical shape, the displacement X in the optical axis direction at the position of the height H from the optical axis when the vertex of the surface is used as a reference, the cone coefficient is k, fourth order, sixth order, eighth order, The aspherical coefficients of the 10th order, 12th order, 14th order, 16th order, 18th order,... Are C4, C6, C8, C10, C12, C14, C16, C18, ..., respectively, and the reciprocal of the paraxial radius of curvature R is C. Is defined by the following equation [10].

FIG. 1 is a first embodiment of the present invention, and shows a lens configuration of a longitudinal section when an optical system of an imaging lens according to Example 1 is focused at infinity.
That is, as shown in FIG. 1, the optical system of the imaging lens according to Example 1 of the present invention sequentially has a first lens L1, a second lens L2, and a third lens from the object side to the image surface side. L3, an aperture stop AD, a fourth lens L4, a fifth lens L5, a sixth lens L6, a seventh lens L7, and an eighth lens L8 are arranged. The second lens L2 and the third lens L3 are L2- An L3 cemented lens is configured, and the fourth lens L4 and the fifth lens L5 configure an L4-L5 cemented lens. The lens configuration is a so-called six-group, eight-lens configuration.
On the other hand, in the optical system of the imaging lens according to Example 1 of the present invention shown in FIG. 1, when focusing on the lens group driven integrally, the first lens group Gr1 having a positive refractive index, the negative refractive index A second lens group Gr2 having a positive refractive index and a third lens group Gr3 having a positive refractive index are sequentially arranged from the object side to the image plane side. The first lens group Gr1 and the second lens group Gr2 The third lens group Gr3 is supported by an appropriate common support frame or the like for each lens group, and the second lens group Gr2 operates integrally during focusing or the like. In this case, the aperture stop AD is disposed in the first lens group Gr1, and operates integrally with the first lens group Gr1.

The first lens group Gr1 has a first lens L1 formed of a biconcave negative lens formed with an aspheric surface on the image surface side and a strong concave surface on the object side, and a slightly strong convex surface on the image surface side. L2- is a two-piece cemented lens in which a second lens L2 made of a biconvex positive lens and a third lens L3 made of a negative meniscus negative lens having a convex surface facing the image surface are in close contact with each other. The L3 cemented lens, the fourth lens L4 composed of a biconcave negative lens with a strong concave surface facing the image surface side, and the fifth lens L5 composed of a biconvex positive lens with a strong convex surface facing the object side are in close contact with each other. And an L4-L5 cemented lens that is a two-lens cemented lens, and an aperture stop AD is provided between the third lens L3 and the fourth lens L4 in the first lens group Gr1. Arranged integrally with the group Gr1.
The second lens group Gr2 includes a sixth lens L6 including a positive meniscus positive lens having a convex surface formed with an aspheric surface on the object side and a negative meniscus shape having a concave surface on the object side. The seventh lens L7 is a negative lens.
The third lens group Gr3 includes an eighth lens L8 including a positive meniscus positive lens having a concave surface formed with an aspheric surface on the object side.
A back insertion glass BG is disposed behind the first lens group Gr1, the second lens group Gr2, and the third lens group Gr3, that is, on the image plane side.

In an imaging optical system using a solid-state imaging device such as a CCD (charge coupled device) imaging device or a CMOS (complementary metal oxide semiconductor) imaging device like a digital still camera, a back insertion glass, a low-pass filter, infrared At least one of a cut glass and a cover glass for protecting the light-receiving surface of the solid-state imaging device is inserted, but in the present embodiment, these are shown as the above-described back insertion glass BG, and equivalently Treat as one parallel plane plate. In addition, in Example 2 to Example 8, the back insertion glass BG is equivalently shown as one plane parallel plate, but the back insertion glass, low pass filter, It represents at least one of infrared cut glass and cover glass.
In the focusing operation, that is, focusing in this imaging lens, when focusing from infinity to a finite distance object, the first lens group Gr1 is fixed, and the second lens group Gr2 is moved to the image plane side along the optical axis. And move it.

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. For this reason, FIGS. 4, 7, 10, and 13 are used. 16, FIG. 19, and FIG. 22, the reference numerals common to those in FIG. 16, FIG. 19, and FIG.
In the first embodiment, the focal length f, the half angle of view ω [degrees], and the open F value F of the entire system are f = 22.9 mm, ω = 32.7 degrees, and F = 2.57 (that is, Fno). 2.57), and the radius of curvature (paraxial radius of curvature for an aspheric surface) R of each optical element in Example 1, R between adjacent optical surfaces, refractive index Nd, and Abbe number νd The optical characteristics are as shown in Table 1 below.

In Table 1, the lens surface with the surface number indicated by adding “* (asterisk)” to the surface number is an aspherical surface. “INF” represents infinity (∞). The same applies to the other Examples 2 to 8.
That is, in Table 1, the second surface which is the optical surface on the image plane side of the first lens L1 marked with “*”, the tenth surface which is the optical surface on the object side of the sixth lens L6, and the eighth surface. The 14th surface which is the object side optical surface of the lens L8 is an aspheric surface, and the aspheric parameter (aspheric coefficient) in the equation [10] is as shown in Table 2 below. In the aspheric parameter, “En” represents “power of 10”, that is, “× 10 ⁿ ”, for example, “E-05” represents “× 10 ⁻⁵ ”. The same applies to the other embodiments.

  In Example 1, the variable distance D9 between the fifth lens L5 of the first lens group Gr1 and the sixth lens L6 of the second lens group Gr2 shown in Table 1 and the seventh of the second lens group Gr2 are shown. The variable distance D13 between the lens L7 and the eighth lens L8 of the third lens group Gr3 is changed so that the imaging magnification changes and the object distance is infinite and the imaging magnification is −1/20 (object distance≈500 mm). In this case, it changes as shown in Table 3 below.

The values corresponding to the conditional expressions [1] to [9] described in the first embodiment are as shown in Table 4 below.

Therefore, the numerical values related to the conditional expressions [1] to [9] described in the first embodiment are within the ranges of the conditional expressions, respectively, and satisfy the conditional expressions [1] to [9]. doing.
FIG. 2 shows various aberrations in the d-line and g-line when the imaging lens according to Example 1 is focused on an object at infinity, that is, each of spherical aberration, astigmatism, distortion aberration, and coma aberration. FIG. 3 shows aberration curves, and FIG. 3 shows various d-line and g-line conditions when the imaging lens according to Example 1 is focused on an object at an imaging magnification of about −1/20 times (object distance≈500 mm). Each aberration curve diagram of aberration, that is, spherical aberration, astigmatism, distortion and coma is shown.
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 is a second embodiment of the present invention, and shows a lens configuration of a longitudinal section when the optical system of the imaging lens according to Example 2 is focused at infinity.
That is, as shown in FIG. 4, the optical system of the imaging lens according to Example 2 of the present invention sequentially has a first lens L1, a second lens L2, and a third lens from the object side to the image plane side. L3, an aperture stop AD, a fourth lens L4, a fifth lens L5, a sixth lens L6, a seventh lens L7, and an eighth lens L8 are arranged. The second lens L2 and the third lens L3 are L2- An L3 cemented lens is configured, and the fourth lens L4 and the fifth lens L5 configure an L4-L5 cemented lens. The lens configuration is a so-called six-group, eight-lens configuration.
On the other hand, the optical system of the imaging lens according to Example 2 of the present invention shown in FIG. 4 is focused on the lens group that is driven integrally, the first lens group Gr1 having a positive refractive index, and the negative refractive index. A second lens group Gr2 having a positive refractive index and a third lens group Gr3 having a positive refractive index are sequentially arranged from the object side to the image plane side. The first lens group Gr1 and the second lens group Gr2 The third lens group Gr3 is supported by an appropriate common support frame or the like for each lens group. Also in this case, the aperture stop AD is disposed in the first lens group Gr1, and operates integrally with the first lens group Gr1.

The first lens group Gr1 includes a first lens L1 composed of a negative meniscus negative lens having a convex surface formed with an aspheric surface on the object side, and a biconvex shape with a slightly strong convex surface facing the object side. An L2-L3 cemented lens which is a two-lens cemented lens in which a second lens L2 composed of a positive lens and a third lens L3 composed of a biconcave negative lens having a slightly strong concave surface facing the object side are in close contact with each other; The fourth lens L4 made of a negative meniscus negative lens having a convex surface facing the object side and the fifth lens L5 made of a biconvex positive lens having a slightly strong convex surface facing the object side are in close contact with each other. L4-L5 cemented lens which is a two-lens cemented lens, and an aperture stop AD is integrated with the first lens group Gr1 between the third lens L3 and the fourth lens L4 in the first lens group Gr1. Is placed in
The second lens group Gr2 includes a sixth lens L6 made of a negative meniscus negative lens with a slightly strong concave surface formed with an aspheric surface on the object side and a negative meniscus with a concave surface facing the object side. And a seventh lens L7 made of a negative lens.
The third lens group Gr3 is composed of an eighth lens L8 made of a positive meniscus positive lens having a convex surface formed with an aspheric surface on the image surface side.
A back insertion glass BG substantially the same as that of the first embodiment (FIG. 1) is arranged behind the first lens group Gr1, the second lens group Gr2, and the third lens group Gr3, that is, on the image plane side.

In the focusing operation, that is, focusing in this imaging lens, when focusing from infinity to a finite distance object, the first lens group Gr1 is fixed, and the second lens group Gr2 is moved to the image plane side along the optical axis. And move it.
FIG. 4 also shows the surface numbers of the optical surfaces. 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 code. For this reason, FIG. 1, FIG. 7, FIG. 10, FIG. 16, FIG. 19, and FIG. 22, the reference numerals common to those in FIG. 16, FIG. 19, and FIG.
In Example 2, the focal length f, the half angle of view ω [degrees], and the open F value F of the entire system are f = 22.9 mm, ω = 22.9 degrees, and F = 2.56 (that is, Fno), respectively. 2.56), the radius of curvature of the optical surface in each optical element in Example 2 (paraxial radius of curvature for an aspherical surface) R, the distance between adjacent optical surfaces D, the refractive index Nd, and the Abbe number νd The optical characteristics are as shown in Table 5 below.

In Table 5, the lens surface with the surface number indicated by adding “*” to the surface number is an aspherical surface. “INF” represents infinity (∞). The same applies to the other embodiments.
That is, in Table 5, the first surface that is the object-side optical surface of the first lens L1 marked with “*”, the tenth surface that is the object-side optical surface of the sixth lens L6, and the eighth lens. The fifteenth surface, which is the optical surface on the image surface side of L8, is an aspheric surface, and the aspheric parameter (aspheric coefficient) in equation [10] is as shown in Table 6 below.

  In Example 2, the variable distance D9 between the fifth lens L5 of the first lens group Gr1 and the sixth lens L6 of the second lens group Gr2 shown in Table 5 and the seventh distance of the second lens group Gr2 are shown. The variable distance D13 between the lens L7 and the eighth lens L8 of the third lens group Gr3 is changed so that the imaging magnification changes and the object distance is infinite and the imaging magnification is −1/20 (object distance≈500 mm). In this case, it changes as shown in Table 7 below.

  Further, values corresponding to the conditional expressions [1] to [9] described in the second embodiment are as shown in Table 8 below.

Accordingly, the numerical values related to the conditional expressions [1] to [9] described in the second embodiment are within the range of the conditional expressions, respectively, and satisfy the conditional expressions [1] to [9]. doing.
FIG. 5 shows various aberrations in d-line and g-line when the imaging lens according to Example 2 is focused on an object at infinity, that is, spherical aberration, astigmatism, distortion aberration, and coma aberration. FIG. 6 shows aberration curves, and FIG. 6 shows various d-line and g-line conditions when the imaging lens according to Example 2 is focused on an object at an imaging magnification of about −1/20 times (object distance≈500 mm). Each aberration curve diagram of aberration, that is, spherical aberration, astigmatism, distortion and coma is shown.
As in the aberration curve diagrams according to the other examples, in these aberration curve diagrams, the broken line in spherical aberration represents the sine condition, the solid line in astigmatism represents sagittal, and the 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 is a third embodiment of the present invention, and schematically shows a lens configuration of a longitudinal section when the optical system of the imaging lens according to Example 3 is focused at infinity.
That is, as shown in FIG. 7, the optical system of the imaging lens according to Example 3 of the present invention sequentially has a first lens L1, a second lens L2, and a third lens from the object side to the image surface side. L3, an aperture stop AD, a fourth lens L4, a fifth lens L5, a sixth lens L6, a seventh lens L7, and an eighth lens L8 are arranged. The second lens L2 and the third lens L3 are L2- An L3 cemented lens is configured, and the fourth lens L4 and the fifth lens L5 configure an L4-L5 cemented lens. The lens configuration is a so-called six-group, eight-lens configuration.
On the other hand, in the optical system of the imaging lens according to Embodiment 3 of the present invention shown in FIG. 7, when focusing on the lens group driven integrally, the first lens group Gr1 having a positive refractive index, the negative refractive index A second lens group Gr2 having a positive refractive index and a third lens group Gr3 having a positive refractive index are sequentially arranged from the object side to the image plane side. The first lens group Gr1 and the second lens group Gr2 The third lens group Gr3 is supported by an appropriate common support frame or the like for each lens group. Also in this case, the aperture stop AD is disposed in the first lens group Gr1, and operates integrally with the first lens group Gr1.

The first lens group Gr1 includes both a first lens L1 formed of a negative meniscus negative lens having a convex surface facing the object side and an aspheric surface formed on the image surface side, and a strong concave surface facing the image surface side. L2-L3 cemented lens which is a two-lens cemented lens in which a second lens L2 composed of a negative negative lens and a third lens L3 composed of a biconvex positive lens with a strong convex surface facing the object side are in close contact with each other. The lens and the fourth lens L4, which is a positive meniscus positive lens having a convex surface facing the image surface, and the fifth lens L5, which is a negative meniscus negative lens having a convex surface facing the image surface, are closely bonded. And an L4-L5 cemented lens, which is a two-lens cemented lens, and an aperture stop AD between the third lens L3 and the fourth lens L4 in the first lens group Gr1, and the first lens group Gr1. They are arranged integrally.
The second lens group Gr2 includes a sixth lens L6 including a positive meniscus positive lens having a convex surface formed with an aspheric surface on the object side and a negative meniscus shape having a concave surface on the object side. The seventh lens L7 is a negative lens.
The third lens group Gr3 is composed of an eighth lens L8 made of a positive meniscus positive lens having a convex surface formed with an aspheric surface on the image surface side.
A back insertion glass BG substantially the same as in the first embodiment (FIG. 1) and the like is arranged behind the first lens group Gr1, the second lens group Gr2, and the third lens group Gr3, that is, on the image plane side.

In the focusing operation, that is, focusing in this imaging lens, when focusing from infinity to a finite distance object, the first lens group Gr1 is fixed, and the second lens group Gr2 is moved to the image plane side along the optical axis. And move it.
FIG. 7 also shows the surface numbers of the optical surfaces. 7 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. 1, FIG. 4, FIG. 10, FIG. 16, FIG. 19, and FIG. 22, the reference numerals common to those in FIG. 16, FIG. 19, and FIG.
In Example 3, the focal length f, the half angle of view ω [degrees], and the open F value F of the entire system are f = 22.9 mm, ω = 32.8 degrees, and F = 2.56 (that is, Fno). 2.56), the radius of curvature of the optical surface (paraxial radius of curvature for an aspherical surface) R in each optical element in Example 3, R between adjacent optical surfaces, refractive index Nd, and Abbe number νd The optical characteristics are as shown in Table 9 below.

In Table 9, as in the other examples, the lens surface with the surface number indicated by adding “*” to the surface number is an aspherical surface. “INF” represents infinity (∞).
That is, in Table 9, the second surface which is the optical surface on the image plane side of the first lens L1 marked with “*”, the tenth surface which is the optical surface on the object side of the sixth lens L6, and the eighth surface. The fifteenth surface that is the optical surface on the image plane side of the lens L8 is an aspheric surface, and the aspheric parameters (aspheric coefficients) in Equation [10] are as shown in the following table.

  In Example 3, the variable distance D9 between the fifth lens L5 of the first lens group Gr1 and the sixth lens L6 of the second lens group Gr2 shown in Table 9 and the seventh distance of the second lens group Gr2 are shown. The variable distance D13 between the lens L7 and the eighth lens L8 of the third lens group Gr3 is changed so that the imaging magnification changes and the object distance is infinite and the imaging magnification is −1/20 (object distance≈500 mm). In this case, it changes as shown in Table 11 below.

Further, values corresponding to the conditional expressions [1] to [9] described in the third embodiment are as shown in Table 12 below.

Therefore, the numerical values related to the conditional expressions [1] to [9] described in the third embodiment are within the range of the conditional expressions, respectively, and satisfy the conditional expressions [1] to [9]. doing.
FIG. 8 shows various aberrations in the d-line and g-line when the imaging lens according to Example 3 is focused on an object at infinity, that is, spherical aberration, astigmatism, distortion aberration, and coma aberration. FIG. 9 shows aberration curves, and FIG. 9 shows various d-line and g-line conditions when the imaging lens according to Example 3 is focused on an object at an imaging magnification of about −1/20 times (object distance≈500 mm). Each aberration curve diagram of aberration, that is, spherical aberration, astigmatism, distortion and coma is shown.
As in the aberration curve diagrams according to the other examples, in these aberration curve diagrams, the broken line in spherical aberration represents the sine condition, the solid line in astigmatism represents sagittal, and the 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 is a fourth embodiment of the present invention, and schematically shows a longitudinal cross-sectional lens configuration of the optical system of the imaging lens according to Example 4 when focusing on infinity.
That is, as shown in FIG. 10, the optical system of the imaging lens according to Example 4 of the present invention sequentially has a first lens L1, a second lens L2, and a third lens from the object side to the image surface side. L3, aperture stop AD, fourth lens L4, fifth lens L5, sixth lens L6, seventh lens L7, and eighth lens L8 are arranged. The fourth lens L4 and the fifth lens L5 are L4- The L5 cemented lens is configured, and the so-called 7 group 8 lens configuration is used.
On the other hand, in the optical system of the imaging lens according to Embodiment 4 of the present invention shown in FIG. 10, when focusing on the lens group driven integrally, the first lens group Gr1 having a positive refractive index, the negative refractive index A second lens group Gr2 having a positive refractive index and a third lens group Gr3 having a positive refractive index are sequentially arranged from the object side to the image plane side. The third lens group Gr3 is supported by an appropriate common support frame or the like for each lens group. Also in this case, the aperture stop AD is disposed in the first lens group Gr1, and operates integrally with the first lens group Gr1.

The first lens group Gr1 includes a first lens L1 including a positive meniscus positive lens having a convex surface formed with an aspheric surface on the object side, and a negative meniscus negative lens having a convex surface facing the object side. A second lens L2 comprising: a third lens L3 comprising a positive meniscus positive lens having a convex surface facing the object side; and a fourth lens L4 comprising a biconvex positive lens having a strong convex surface facing the image side. And a L4-L5 cemented lens which is a two-lens cemented lens in which a fifth lens L5 composed of a negative meniscus negative lens having a convex surface facing the image surface side is closely adhered and cemented. An aperture stop AD is disposed integrally with the first lens group Gr1 between the third lens L3 and the fourth lens L4 in the group Gr1.
The second lens group Gr2 includes a sixth lens L6 including a positive meniscus positive lens having a convex surface formed with an aspheric surface on the object side and a negative meniscus shape having a concave surface on the object side. The seventh lens L7 is a negative lens.
The third lens group Gr3 is composed of an eighth lens L8 made of a positive meniscus positive lens having a convex surface formed with an aspheric surface on the image surface side.
A back insertion glass BG substantially the same as in the first embodiment (FIG. 1) and the like is arranged behind the first lens group Gr1, the second lens group Gr2, and the third lens group Gr3, that is, on the image plane side.

In the focusing operation, that is, focusing in this imaging lens, when focusing from infinity to a finite distance object, the first lens group Gr1 is fixed, and the second lens group Gr2 is moved to the image plane side along the optical axis. And move it.
FIG. 10 also shows the surface number of each optical surface. Note that 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 numerals. Therefore, FIGS. 1, 4, 7, and 13 are used. 16, FIG. 19, and FIG. 22, the reference numerals common to those in FIG. 16, FIG. 19, and FIG.
In Example 4, the focal length f of the entire system, the half angle of view ω [degrees], and the open F value F are f = 22.9 mm, ω = 22.9 degrees, and F = 2.56 (that is, Fno). 2.56), the radius of curvature of the optical surface in each optical element in Example 4 (paraxial radius of curvature for an aspherical surface) R, the surface spacing D of adjacent optical surfaces, the refractive index Nd, and the Abbe number νd The optical characteristics such as are as shown in Table 13 below.

In Table 13, the lens surface with the surface number indicated by adding “*” to the surface number is an aspherical surface as in the other examples. “INF” represents infinity (∞).
That is, in Table 13, the first surface that is the object-side optical surface of the first lens L1 marked with “*”, the eleventh surface that is the object-side optical surface of the sixth lens L6, and the eighth lens. The sixteenth surface that is the optical surface on the image surface side of L8 is an aspheric surface, and the aspheric parameter (aspheric coefficient) in Equation [10] is as shown in Table 14 below.

  In Example 4, the variable distance D10 between the fifth lens L5 of the first lens group Gr1 and the sixth lens L6 of the second lens group Gr2 shown in Table 13 and the seventh distance of the second lens group Gr2 are shown. The variable distance D14 between the lens L7 and the eighth lens L8 of the third lens group Gr3 is changed from an imaging magnification to an infinite distance and an imaging magnification of −1/20 (object distance≈500 mm). At this time, the values change as shown in Table 15 below.

  Further, values corresponding to the conditional expressions [1] to [9] described in the fourth embodiment are as shown in Table 16 below.

Therefore, the numerical values related to the conditional expressions [1] to [9] described in the fourth embodiment are within the ranges of the conditional expressions, respectively, and satisfy the conditional expressions [1] to [9]. doing.
FIG. 11 shows various aberrations in d-line and g-line in the state where the imaging lens according to Example 4 is focused on an object at infinity, that is, spherical aberration, astigmatism, distortion aberration, and coma aberration. FIG. 12 shows aberration curves, and FIG. 12 shows various d-line and g-line conditions when the imaging lens according to Example 4 is focused on an object at an imaging magnification of about −1/20 times (object distance≈500 mm). Each aberration curve diagram of aberration, that is, spherical aberration, astigmatism, distortion and coma is shown.
As in the aberration curve diagrams according to the other examples, in these aberration curve diagrams, the broken line in spherical aberration represents the sine condition, the solid line in astigmatism represents sagittal, and the 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 is a fifth embodiment of the present invention, and schematically shows a lens configuration in a longitudinal section when the optical system of the imaging lens according to Example 5 is focused at infinity.
That is, as shown in FIG. 13, the optical system of the imaging lens according to Example 5 of the present invention sequentially forms the first lens L1, the second lens L2, and the aperture stop AD from the object side to the image surface side. A third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, and a seventh lens L7. The third lens L3 and the fourth lens L4 constitute an L3-L4 cemented lens. In terms of the lens configuration, a so-called 6-group 7-lens configuration is employed.
On the other hand, the optical system of the imaging lens according to Example 5 of the present invention shown in FIG. 13 focuses on the lens group that is driven integrally, the first lens group Gr1 having a positive refractive index, and the negative refractive index. A second lens group Gr2 having a positive refractive index and a third lens group Gr3 having a positive refractive index are sequentially arranged from the object side to the image plane side. The first lens group Gr1 and the second lens group Gr2 The third lens group Gr3 is supported by an appropriate common support frame or the like for each lens group. Also in this case, the aperture stop AD is disposed in the first lens group Gr1, and operates integrally with the first lens group Gr1.

The first lens group Gr1 has a first lens L1 formed of a biconcave negative lens formed with an aspheric surface on the image surface side and a strong concave surface on the object side, and a slightly strong convex surface on the image surface side. A second lens L2 made of a biconvex positive lens, a third lens L3 made of a biconvex positive lens with a strong convex surface facing the image surface side, and a negative meniscus negative with a convex surface facing the image surface side An L3-L4 cemented lens that is a two-lens cemented lens formed by closely joining a fourth lens L4 composed of a lens, and the second lens L2 and the third lens L3 in the first lens group Gr1. The aperture stop AD is disposed integrally with the first lens group Gr1.
The second lens group Gr2 includes a negative lens with a negative meniscus shape and a negative meniscus shape with a concave surface facing the object side. The sixth lens L6 is a negative lens.
The third lens group Gr3 includes a seventh lens L7 formed of a positive meniscus positive lens having a convex surface formed with an aspheric surface on the image surface side.
A back insertion glass BG substantially the same as in the first embodiment (FIG. 1) and the like is arranged behind the first lens group Gr1, the second lens group Gr2, and the third lens group Gr3, that is, on the image plane side.

In the focusing operation, that is, focusing in this imaging lens, when focusing from infinity to a finite distance object, the first lens group Gr1 is fixed, and the second lens group Gr2 is moved to the image plane side along the optical axis. And move it.
FIG. 13 also shows the surface numbers of the optical surfaces. In addition, in order to avoid the complicated description by the increase in the number of digits of a reference code, each reference code with respect to FIG. 13 is used independently for each Example, Therefore, FIG.1, FIG.4, FIG.7, FIG.10 is used. 16, FIG. 19, and FIG. 22, the reference numerals common to those in FIG. 16, FIG. 19, and FIG.
In Example 5, the focal length f of the entire system, the half angle of view ω [degrees], and the open F value F are f = 22.9 mm, ω = 22.9 degrees, and F = 2.53 (that is, Fno). 2.53), and the radius of curvature of the optical surface (paraxial radius of curvature for an aspheric surface) R in each optical element in Example 5, R between adjacent optical surfaces, refractive index Nd, and Abbe number νd The optical characteristics are as shown in Table 17 below.

In Table 17, as in the other examples, the lens surface with the surface number indicated by adding “*” to the surface number is an aspherical surface. “INF” represents infinity (∞).
That is, in Table 17, the second surface which is the optical surface on the image plane side of the first lens L1 marked with “*”, the ninth surface which is the optical surface on the object side of the fifth lens L5, and the seventh surface. The fourteenth surface, which is the optical surface on the image surface side of the lens L7, is an aspheric surface, and the aspheric parameter (aspheric coefficient) in Equation [10] is as shown in Table 18 below.

  In Example 5, the variable distance D8 between the fourth lens L4 of the first lens group Gr1 and the fifth lens L5 of the second lens group Gr2 shown in Table 17 and the sixth distance of the second lens group Gr2 are shown. The variable distance D12 between the lens L6 and the seventh lens L7 of the third lens group Gr3 is changed so that the imaging magnification is changed and the object distance is infinity and the imaging magnification is −1/20 (object distance≈500 mm). In this case, the value changes as shown in Table 19 below.

  The values corresponding to the conditional expressions [1] to [9] described in the fifth embodiment are as shown in Table 20 below.

Therefore, the numerical values related to the conditional expressions [1] to [9] described in the fifth embodiment are within the ranges of the conditional expressions, respectively, and satisfy the conditional expressions [1] to [9]. doing.
FIG. 14 shows various aberrations in d-line and g-line when the imaging lens according to Example 5 is focused on an object at infinity, that is, spherical aberration, astigmatism, distortion aberration, and coma aberration. FIG. 15 shows aberration curves, and FIG. 15 shows various d-line and g-line conditions when the imaging lens according to Example 5 is focused on an object at an imaging magnification of about −1/20 times (object distance≈500 mm). Each aberration curve diagram of aberration, that is, spherical aberration, astigmatism, distortion and coma is shown.
As in the aberration curve diagrams according to the other examples, in these aberration curve diagrams, the broken line in spherical aberration represents the sine condition, the solid line in astigmatism represents sagittal, and the 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. 16 is a sixth embodiment of the present invention, and schematically shows a lens configuration in a longitudinal section when the optical system of the imaging lens according to Example 6 is focused at infinity.
That is, the optical system of the imaging lens according to Example 6 of the present invention, as shown in FIG. 16, sequentially from the object side to the image surface side, the first lens L1, the second lens L2, and the aperture stop AD. A third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, and a seventh lens L7. The third lens L3 and the fourth lens L4 constitute an L3-L4 cemented lens. In terms of the lens structure, a so-called 6-group 7-element structure is adopted.
On the other hand, the optical system of the imaging lens according to Example 6 of the present invention shown in FIG. 16 focuses on the lens group that is driven integrally, the first lens group Gr1 having a positive refractive index, and the negative refractive index. A second lens group Gr2 having a positive refractive index and a third lens group Gr3 having a positive refractive index are sequentially arranged from the object side to the image plane side. The first lens group Gr1 and the second lens group Gr2 The third lens group Gr3 is supported by an appropriate common support frame or the like for each lens group. Also in this case, the aperture stop AD is disposed in the first lens group Gr1, and operates integrally with the first lens group Gr1.

The first lens group Gr1 has a first lens L1 formed of a biconcave negative lens formed with an aspheric surface on the image surface side and a strong concave surface on the object side, and a slightly strong convex surface on the image surface side. A second lens L2 composed of a positive biconvex lens, a third lens L3 composed of a positive meniscus positive lens having a convex surface facing the image surface side, and a negative meniscus negative lens facing the convex surface toward the image surface side The L3-L4 cemented lens is a two-lens cemented lens in which the fourth lens L4 made of is closely joined and is composed of a second lens L2 and a third lens L3 in the first lens group Gr1. An aperture stop AD is integrally disposed with the first lens group Gr1 therebetween.
The second lens group Gr2 includes a negative lens with a negative meniscus shape and a negative meniscus shape with a concave surface facing the object side. The sixth lens L6 is a negative lens.
The third lens group Gr3 includes a seventh lens L7 formed of a positive meniscus positive lens having a convex surface formed with an aspheric surface on the image surface side.
A back insertion glass BG substantially the same as in the first embodiment (FIG. 1) and the like is arranged behind the first lens group Gr1, the second lens group Gr2, and the third lens group Gr3, that is, on the image plane side.
In the focusing operation, that is, focusing in this imaging lens, when focusing from infinity to a finite distance object, the first lens group Gr1 is fixed, and the second lens group Gr2 is moved to the image plane side along the optical axis. And move it.

FIG. 16 also shows the surface numbers of the optical surfaces. In addition, in order to avoid the complicated description by the increase in the number of digits of a reference code, each reference code with respect to FIG. 16 is used independently for each Example, Therefore, FIG.1, FIG.4, FIG.7, FIG.10 is used. 13, 19, and 22, reference numerals common to those in FIGS. 13, 19, and 22 are not necessarily in common with the corresponding embodiments.
In Example 6, the focal length f, the half angle of view ω [degrees], and the open F value F of the entire system are f = 22.9 mm, ω = 32.5 degrees, and F = 2.50 (that is, Fno), respectively. 2.50), and the radius of curvature (paraxial radius of curvature for an aspheric surface) R of each optical element in Example 6, R between adjacent optical surfaces, refractive index Nd, and Abbe number νd The optical characteristics are as shown in Table 21 below.

In Table 21, the lens surface with the surface number indicated by adding “*” to the surface number is an aspherical surface as in the other examples. “INF” represents infinity (∞).
That is, in Table 21, the second surface which is the optical surface on the image plane side of the first lens L1 marked with “*”, the ninth surface which is the optical surface on the object side of the fifth lens L5, and the seventh surface. The 14th surface, which is the optical surface on the image plane side of the lens L7, is an aspherical surface. The aspherical parameters (aspherical coefficients) in equation [10] are as shown in Table 22 below.

  In Example 6, the variable distance D8 between the fourth lens L4 of the first lens group Gr1 and the fifth lens L5 of the second lens group Gr2 shown in Table 21, and the sixth of the second lens group Gr2 are shown. The variable distance D12 between the lens L6 and the seventh lens L7 of the third lens group Gr3 is changed so that the imaging magnification is changed and the object distance is infinity and the imaging magnification is −1/20 (object distance≈500 mm). At this time, the values change as shown in Table 23 below.

  The values corresponding to the conditional expressions [1] to [9] described in the sixth embodiment are as shown in Table 24 below.

Therefore, the numerical values related to the conditional expressions [1] to [9] described in the sixth embodiment are within the ranges of the conditional expressions, respectively, and satisfy the conditional expressions [1] to [9]. doing.
FIG. 17 shows various aberrations in d-line and g-line in the state where the imaging lens according to Example 6 is focused on an object at infinity, that is, spherical aberration, astigmatism, distortion aberration, and coma aberration. FIG. 18 shows aberration curves, and FIG. 18 shows various d-line and g-line conditions when the imaging lens according to Example 6 is focused on an object at an imaging magnification of about −1/20 times (object distance≈500 mm). Each aberration curve diagram of aberration, that is, spherical aberration, astigmatism, distortion and coma is shown.
As in the aberration curve diagrams according to the other examples, in these aberration curve diagrams, the broken line in spherical aberration represents the sine condition, the solid line in astigmatism represents sagittal, and the 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. 19 is a seventh embodiment of the present invention, and shows a lens configuration of a longitudinal section when the optical system of the imaging lens according to Example 7 is focused at infinity.
That is, the optical system of the imaging lens according to Example 7 of the present invention has a first lens L1, a second lens L2, and a third lens sequentially from the object side to the image surface side as shown in FIG. L3, aperture stop AD, fourth lens L4, fifth lens L5, sixth lens L6, seventh lens L7, and eighth lens L8 are disposed. The fourth lens L4 and the fifth lens L5 are L4- The L5 cemented lens is configured, and the so-called 7 group 8 lens configuration is used.
On the other hand, in the optical system of the imaging lens according to Example 7 of the present invention shown in FIG. 19, when focusing on the lens group driven integrally, the first lens group Gr1 having a positive refractive index, the negative refractive index A second lens group Gr2 having a positive refractive index and a third lens group Gr3 having a positive refractive index are sequentially arranged from the object side to the image plane side. The first lens group Gr1 and the second lens group Gr2 The third lens group Gr3 is supported by an appropriate common support frame or the like for each lens group. Also in this case, the aperture stop AD is disposed in the first lens group Gr1, and operates integrally with the first lens group Gr1.

The first lens group Gr1 forms a first lens L1 composed of a negative meniscus negative lens having a strong concave surface on the image side and an aspheric surface on the object side, and an aspheric surface on the image side. A second lens L2 composed of a biconcave negative lens having a slightly strong concave surface, a third lens L3 composed of a biconvex positive lens formed with equal curvature on both surfaces, and a convex surface on the image surface side. Is a two-lens cemented lens in which a fourth lens L4 made of a positive meniscus shape positive lens facing the lens and a fifth lens L5 made of a negative meniscus shape negative lens having a convex surface facing the image surface are in close contact with each other. L4-L5 cemented lens, and an aperture stop AD is disposed integrally with the first lens group Gr1 between the third lens L3 and the fourth lens L4 in the first lens group Gr1.
The second lens group Gr2 includes an aspheric surface on the object side and a sixth lens L6 formed of a negative meniscus negative lens having a weak refractive power and having an aspheric surface on both sides and a convex surface facing the object side. And a seventh lens L7 made of a negative meniscus negative lens having a concave surface.
The third lens group Gr3 includes an eighth lens L8 including a positive meniscus positive lens having a convex surface directed toward the image side.
A back insertion glass BG substantially the same as in the first embodiment (FIG. 1) and the like is arranged behind the first lens group Gr1, the second lens group Gr2, and the third lens group Gr3, that is, on the image plane side.
In the focusing operation, that is, focusing in this imaging lens, when focusing from infinity to a finite distance object, the first lens group Gr1 is fixed, and the second lens group Gr2 is moved to the image plane side along the optical axis. And move it.

FIG. 19 also shows the surface numbers of the optical surfaces. Note that each reference symbol for FIG. 19 is used independently for each embodiment in order to avoid complication of explanation due to an increase in the number of digits of the reference symbol. Therefore, FIG. 1, FIG. 4, FIG. 7, FIG. Even though the same reference numerals as those in FIGS. 13, 16 and 22 are given, they are not necessarily in a common configuration with the corresponding embodiments.
In Example 7, the focal length f of the entire system, the half angle of view ω [degrees], and the open F value F are f = 22.9 mm, ω = 32.2 degrees, and F = 2.57 (that is, Fno). 2.57), and the radius of curvature of the optical surface (paraxial radius of curvature for an aspheric surface) R in each optical element in Example 7, R between adjacent optical surfaces, refractive index Nd, and Abbe number νd The optical characteristics are as shown in Table 25 below.

In Table 25, as in the other examples, the lens surface with the surface number indicated by adding “*” to the surface number is an aspherical surface. “INF” represents infinity (∞).
That is, in Table 25, the first surface that is the object-side optical surface of the first lens L1 marked with “*”, the fourth surface that is the optical surface on the image plane side of the second lens L2, and the sixth lens. The eleventh surface and the twelfth surface that are optical surfaces on both sides of L6, and the thirteenth surface that is the optical surface on the object side of the seventh lens L7 are aspherical surfaces. ) Is as shown in Table 26 below.

  In Example 7, the variable distance D10 between the fifth lens L5 of the first lens group Gr1 and the sixth lens L6 of the second lens group Gr2 shown in Table 25, and the seventh distance of the second lens group Gr2 are shown. The variable distance D14 between the lens L7 and the eighth lens L8 of the third lens group Gr3 is changed from an imaging magnification to an infinite distance and an imaging magnification of −1/20 (object distance≈500 mm). At this time, the values change as shown in Table 27 below.

The values corresponding to the conditional expressions [1] to [9] described in the seventh embodiment are as shown in Table 28 below.

Therefore, the numerical values related to the conditional expressions [1] to [9] described in the seventh embodiment are within the range of the conditional expressions, respectively, and satisfy the conditional expressions [1] to [9]. doing.
FIG. 20 shows various aberrations in d-line and g-line when the imaging lens according to Example 7 is focused on an object at infinity, that is, spherical aberration, astigmatism, distortion aberration, and coma aberration. FIG. 21 is an aberration curve diagram, and FIG. 21 shows various graphs of the d-line and g-line when the imaging lens according to Example 7 is focused on an object at an imaging magnification of about −1/20 times (object distance≈500 mm). Each aberration curve diagram of aberration, that is, spherical aberration, astigmatism, distortion and coma is shown.
As in the aberration curve diagrams according to the other examples, in these aberration curve diagrams, the broken line in spherical aberration represents the sine condition, the solid line in astigmatism represents sagittal, and the 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. 22 is an eighth embodiment of the present invention, and shows a lens configuration of a longitudinal section when the optical system of the imaging lens according to Example 8 is focused at infinity.
That is, the optical system of the imaging lens according to Example 8 of the present invention, as shown in FIG. 22, sequentially from the object side to the image plane side, the first lens L1, the second lens L2, and the third lens. L3, an aperture stop AD, a fourth lens L4, a fifth lens L5, a sixth lens L6, and a seventh lens L7 are arranged, and a so-called seven-group seven-element configuration is used.
On the other hand, the optical system of the imaging lens according to Example 8 of the present invention shown in FIG. 22 focuses on the lens group that is driven integrally, the first lens group Gr1 having a positive refractive index, and the negative refractive index. A second lens group Gr2 having a positive refractive index and a third lens group Gr3 having a positive refractive index are sequentially arranged from the object side to the image plane side. The first lens group Gr1 and the second lens group Gr2 The third lens group Gr3 is supported by an appropriate common support frame or the like for each lens group. Also in this case, the aperture stop AD is disposed in the first lens group Gr1, and operates integrally with the first lens group Gr1.

The first lens group Gr1 has a first lens L1 formed of a negative meniscus negative lens formed with a concave surface facing the image surface and an aspheric surface formed on the object side, and an aspheric surface formed on the image surface side. A second lens L2 made of a biconcave negative lens with a slightly stronger concave surface, a third lens L3 made of a biconvex positive lens with a slightly stronger convex surface facing the object side, and a convex surface on the image surface side. And a fourth lens L4 composed of a positive meniscus positive lens directed to the first lens group Gr1, and an aperture stop AD is provided between the third lens L3 and the fourth lens L4 in the first lens group Gr1. Are arranged in one piece.
The second lens group Gr2 includes a fifth lens L5 formed of a negative meniscus negative lens having a weak refractive power and having an aspheric surface on the object side, and an aspheric surface on the object side. And a sixth lens L6 made of a negative meniscus negative lens having a concave surface.
The third lens group Gr3 includes a seventh lens L7 including a positive meniscus positive lens having a convex surface directed toward the image surface side.
A back insertion glass BG substantially the same as in the first embodiment (FIG. 1) and the like is arranged behind the first lens group Gr1, the second lens group Gr2, and the third lens group Gr3, that is, on the image plane side.
In the focusing operation, that is, focusing in this imaging lens, when focusing from infinity to a finite distance object, the first lens group Gr1 is fixed, and the second lens group Gr2 is moved to the image plane side along the optical axis. And move it.

FIG. 22 also shows the surface numbers of the optical surfaces. Note that each reference symbol for FIG. 22 is used independently for each embodiment in order to avoid complication of explanation due to an increase in the number of digits of the reference symbol. Therefore, FIG. 1, FIG. 4, FIG. 7, FIG. Although the same reference numerals as those in FIGS. 13, 16 and 19 are attached, the embodiments corresponding to those are not necessarily in a common configuration.
In Example 8, the focal length f of the entire system, the half angle of view ω [degrees], and the open F value F are f = 22.9 mm, ω = 32.2 degrees, and F = 2.56 (that is, Fno). 2.56), the radius of curvature of the optical surface (paraxial radius of curvature for an aspheric surface) R in each optical element in Example 8, the surface spacing D of adjacent optical surfaces, the refractive index Nd, and the Abbe number νd The optical characteristics are as shown in Table 29 below.

In Table 29, as in the other examples, the lens surface with the surface number indicated by adding “*” to the surface number is an aspherical surface. “INF” represents infinity (∞).
That is, in Table 29, the first surface that is the object-side optical surface of the first lens L1 marked with “*”, the fourth surface that is the optical surface on the image plane side of the second lens L2, and the fifth lens. The tenth and eleventh surfaces, which are the optical surfaces on both sides of L6, and the twelfth surface, which is the optical surface on the object side of the sixth lens L6, are aspherical surfaces. ) Is as shown in Table 30 below.

  In Example 8, the variable distance D9 between the fourth lens L4 of the first lens group Gr1 and the fifth lens L5 of the second lens group Gr2 shown in Table 29, and the sixth of the second lens group Gr2 are shown. The variable distance D13 between the lens L6 and the seventh lens L7 of the third lens group Gr3 is changed so that the imaging magnification is changed and the object distance is infinity and the imaging magnification is −1/20 (object distance≈500 mm). In this case, it changes as shown in Table 31 below.

  The values corresponding to the conditional expressions [1] to [9] described in the eighth embodiment are as shown in Table 32 below.

Therefore, the numerical values related to the conditional expressions [1] to [9] described in Example 8 are within the range of the conditional expressions, respectively, and satisfy the conditional expressions [1] to [9]. doing.
FIG. 23 shows various aberrations in the d-line and g-line when the imaging lens according to Example 8 is focused on an object at infinity, that is, spherical aberration, astigmatism, distortion aberration, and coma aberration. FIG. 24 shows aberration curves, and FIG. 24 shows various values for the d-line and g-line when the imaging lens according to Example 8 is focused on an object at an imaging magnification of about −1/20 times (object distance≈500 mm). Each aberration curve diagram of aberration, that is, spherical aberration, astigmatism, distortion and coma is shown.
As in the aberration curve diagrams according to the other examples, in these aberration curve diagrams, the broken line in spherical aberration represents the sine condition, the solid line in astigmatism represents sagittal, and the 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.
[Ninth Embodiment]

Next, the ninth embodiment of the present invention configured by adopting an imaging lens such as the first to eighth embodiments of the present invention described above as an imaging optical system. An imaging apparatus according to the embodiment will be described with reference to FIGS.
FIG. 25 is a perspective view showing an appearance of a digital camera viewed from the front side that is the object, that is, the subject side, and FIG. 26 is a perspective view showing an appearance of the digital camera viewed from the back side that is the photographer side. FIG. 27 is a block diagram showing a functional configuration of the digital camera. Although a digital camera as an imaging device is described here, 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 in 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 configurations as a digital camera or the like, and the imaging lens according to the present invention may be employed in such an information device. .

25 and 26, the digital camera includes an imaging lens 101, a shutter button 102, a zoom button 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 communication. A card slot 110 and the like are provided. Further, as shown in FIG. 27, the digital camera also includes a light receiving element 111, a signal processing device 112, an image processing device 113, a central processing unit (CPU) 114, a semiconductor memory 115, a communication card 116, and the like.
The digital camera includes an imaging lens 101 and a light receiving element 111 as an area sensor such as a CMOS (complementary metal oxide semiconductor) imaging device or a CCD (charge coupled device) imaging device, and is an imaging optical system. An optical image of an object to be imaged, that is, a subject is formed by the lens 101, and this optical image is read by the light receiving element 111. As the imaging lens 101, the imaging lens according to the first to eighth embodiments of the present invention described in Examples 1 to 8 is used.
The output of the light receiving element 111 is processed by the signal processing device 112 controlled by the central processing unit 114 and converted into digital image information. The image information digitized by the signal processing device 112 is subjected to predetermined image processing in the image processing device 113 which is also controlled by the central processing unit 114 and then recorded in the semiconductor memory 115 such as a nonvolatile memory. In this case, the semiconductor memory 115 may be a memory card loaded in the memory card slot 109 or a semiconductor memory built in the digital camera body. The liquid crystal monitor 106 can display an image being shot, or can display an image recorded in the semiconductor memory 115.

The image recorded in the semiconductor memory 115 can also be transmitted to the outside via a communication card 116 or the like loaded in the communication card slot 110.
When the digital camera is carried, the imaging lens 101 is retracted and buried in the body of the digital camera as shown in FIG. 25A. When the user operates the power switch 108 to turn on the power, As shown in FIG. 25B, the lens barrel is extended so as to protrude from the body of the digital camera. By operating the zoom button 103, it is possible to perform so-called digital zoom type zooming in which the cut-out range of the subject image is changed and pseudo zooming is performed. 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.
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 115 is displayed on the liquid crystal monitor 106 or transmitted to the outside via the communication card 116 or the like, the operation button 107 is operated in a predetermined manner. The semiconductor memory 115 and the communication card 116 are used by being loaded into dedicated or general-purpose slots such as the memory card slot 109 and the communication card slot 110, respectively.
When the imaging lens 101 is in the retracted state, each group of imaging lenses does not necessarily have to be aligned on the optical axis. For example, if the mechanism is such that 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.

Gr1 First lens group Gr2 Second lens group Gr3 Third lens group L1 to L8 Lens AD Aperture stop BG Back insertion glass, etc. 101 Imaging lens 102 Shutter button 103 Zoom button 104 Viewfinder 105 Strobe 106 Liquid crystal monitor 107 Operation button 108 Power switch 109 Memory card slot 110 Communication card slot 111 Light receiving element (area sensor)
112 signal processing device 113 image processing device 114 central processing unit (CPU)
115 Semiconductor memory 116 Communication card, etc.

Japanese Patent Laid-Open No. 08-313803 (Japanese Patent No. 3541983) JP 2009-258157 A JP 2010-39088 A

Claims (10)

A first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power are sequentially arranged from the object side to the image plane side. In an imaging lens comprising an optical system that forms an optical image of an object,
An aperture stop is disposed in the first lens group,
The first lens group has at least four lenses,
The second lens group includes one lens having a weak refractive power and one negative lens having a concave surface facing the object side.
The third lens group includes one positive lens having a convex surface on the image side,
The entire optical system consists of a total of 8 or less lenses.
In focusing, with the focusing from infinity to a finite distance object, the second lens group is moved from the object side to the image plane side direction,
The distance from the most object-side surface of the first lens group to the image plane is L, the maximum image height is Y ′, and the focal length of the lens with weak refractive power is f _2weak .
Conditional expression:
[1] 2.2 <L / Y ′ <2.5
[4] | f _2weak |> 100
An imaging lens characterized by satisfying A first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power are sequentially arranged from the object side to the image plane side. In an imaging lens comprising an optical system that forms an optical image of an object,
An aperture stop is disposed in the first lens group,
The first lens group has at least four lenses,
The second lens group includes a lens having a weak refractive power and a negative lens having a concave surface facing the object side,
The third lens group is composed of one positive lens having a convex surface facing the image surface side,
The entire optical system consists of a total of 8 or less lenses.
In focusing, only the second lens group moves along the optical axis direction,
The distance from the most object side surface of the first lens unit to the image plane is L, the maximum image height is Y ′, the focal length of the first lens unit is f1, the focal length of the second lens unit is f2, The focal length of the third lens group is f3, the focal length of the entire optical system at infinity is f, and the focal length of the lens having a weak refractive power is _f2weak .
Conditional expression:
[1] 2.2 <L / Y ′ <2.5
[2] 0.3 <f1 / f3 <0.8
[3] -0.5> f2 / f> -0.8
[4] | f _2weak |> 100
An imaging lens characterized by satisfying An optical system comprising the entire optical system with eight or fewer lenses,
An aperture stop is arranged between the lenses of the optical system,
The object side of the aperture stop has at least two lenses,
From the object side to the image surface side, the image plane side of the aperture stop is sequentially composed of one of a cemented lens and a single lens, has a positive refractive power, a lens having a weak refractive power, and an object. A negative lens having a concave shape on the side and a positive lens having a convex shape on the image plane side are arranged and configured,
In focusing, the lens on the object side and the negative lens having a concave surface on the object side are moved together on the optical axis without moving the lens on the object side than the lens having a weak refractive power. It is a configuration that performs focusing by
The focal length of the lens with weak refractive power is f _2weak , the combined focal length of the lens group that can be moved on the optical axis during focusing is ff, and the refractive power of the lens group that is moved on the optical axis during focusing is weak The air gap between the lens and the lens having a concave shape on the object side is defined as fAir ,
Conditional expression:
[4] | f _2weak |> 100
[5] 2.1 <| ff / fAir | <3.7
An imaging lens characterized by satisfying The combined focal length of the lens group moved on the optical axis during focusing is ff, and the lens having a low refractive power in the lens group moved on the optical axis during focusing and the lens having a concave shape on the object side The air interval between them is fAir,
Conditional expression:
[5] 2.1 <| ff / fAir | <3.7
The imaging lens according to claim 1 , wherein the imaging lens is satisfied. The distance that the lens group can be moved during focusing to focus from infinity to a finite short distance object is ΔD _1-2 , and the imaging magnification when focusing on a finite short distance object is β,
Conditional expression:
[6] 11.7 <| ΔD _1-2 /β|<15.7
An imaging lens according to any one of claims 1 to 4, characterized by satisfying the. The focal length of the lens having the negative refractive power located closest to the image plane side as f n and the focal length of the lens having the positive refractive power located closest to the image plane side as f p e
Conditional expression:
[7] -0.8 <fen / fep <-0.4
An imaging lens according to any one of claims 1 to 5, characterized by satisfying the. LD1 is the maximum effective diameter of the lens having the largest diameter in the lens on the object side from the aperture stop, and LD3 is the maximum effective diameter of the lens having the largest diameter in the lens on the image plane side from the aperture stop.
Conditional expression:
[8] 0.4 <LD1 / LD3 <0.8
An imaging lens according to any one of claims 1 to 6, characterized by satisfying the. A shutter space for providing a mechanical shutter is formed between the lenses before and after the aperture stop, and the dimension in the optical axis direction of the shutter space is SD,
[9] SD> 3.1 [mm]
The imaging lens according to any one of claims 1 to 7 , wherein the imaging lens is satisfied. As an imaging optical system, an imaging apparatus characterized by comprising any one of the imaging lens of claims 1 to 8. An information device having an imaging function and using the imaging lens according to any one of claims 1 to 8 as an imaging optical system.

Images