JP2017102173A - Imaging lens, camera, and inspection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging lens which has a wide view angle and large aperture and yet is compact, and offers sufficiently reduced astigmatism, field curvature, magnification chromatic aberration, color differences from coma aberration, distortion aberration and the like, and which provides desired resolving power and is capable of forming an undistorted image with high contrast from fully open aperture and with no distortion of a point image even at peripheral view angles.SOLUTION: An imaging lens comprises a first lens group G1 having negative power and a second lens group G2 having positive power in order from the object side. The second lens group G2 consists of a 2a lens group G2a having positive power, an aperture stop S, and a 2b lens group G2b having positive power. The 2b lens group G2b consists of a cemented lens comprising a negative lens L21b and a positive lens L22b, a negative lens L23b, a positive lens L24b, a negative lens L25b, and a positive lens L26b. A ratio (f2b/f) of a focal length f2b of the 2b lens group G2b to a focal length f of the entire system is set to be within a range defined by a predetermined conditional expression.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an imaging lens, a camera, and an inspection apparatus.

The imaging lens includes a so-called retrofocus type in which a lens group having a negative refractive power is disposed on the object side and a lens group having a positive refractive power is disposed on the image side as a single focus lens.
Examples of such retrofocus type imaging lenses include those described in Patent Document 1, Patent Document 2, and Patent Document 3.

However, the retrofocus type configured so that the principal point is behind the entire lens system has a large asymmetry in its refractive power arrangement, and correction of coma aberration, distortion aberration, lateral chromatic aberration, etc. tends to be incomplete. is there. Further, in the case of the retrofocus type, if focusing is simply performed with the entire extension, field curvature occurs due to focusing.
Further, since it is necessary to make the aperture large, it becomes difficult to sufficiently correct spherical aberration, coma aberration, and the like.
The imaging lenses disclosed in Patent Document 1 and Patent Document 2 do not have a resolution performance corresponding to 6 to 10 million pixels, and the reduction in the color difference between lateral chromatic aberration and coma is not sufficient. The imaging lens disclosed in Patent Document 3 is large and has not been sufficiently reduced in size.

  The present invention has been made in view of the above points, and its object is a wide angle of view and a large aperture but a small size, astigmatism, field curvature, lateral chromatic aberration, An object of the present invention is to provide a high-performance imaging lens having a high resolving power by sufficiently reducing the color difference of coma, distortion, and the like.

The imaging lens according to the first aspect of the present invention is an imaging lens including a first lens group having a negative power and a second lens group having a positive power in order from the object side. The second lens group includes, in order from the object side, a 2a lens group having a positive power, a stop, and a 2b lens group having a positive power. The second b lens group is in order from the object side, Consist of a negative lens L21b that is a concave surface and a positive lens L22b that is a convex surface on the image side, a negative lens L23b that is concave on the image side, a positive lens L24b, a negative lens L25b that is concave on the object side, and a positive lens L26b. The focal length of the second lens group is f2b, and the focal length of the entire system is f.
Conditional formula (1) below:
(1) 1.5 <f2b / f <3.0
It is characterized by satisfying.

  According to the present invention, it has a wide angle of view, a large aperture, and a small size. Astigmatism, field curvature, lateral chromatic aberration, coma color difference, distortion, etc. are sufficiently reduced, and the number of pixels is reduced. It is possible to provide a high-performance imaging lens having a resolving power corresponding to a large image sensor.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view along an optical axis showing a configuration of an imaging lens according to Example 1 (numerical example; the same applies hereinafter) according to a first embodiment of the present invention. FIG. 6 is a cross-sectional view along the optical axis showing the configuration of the imaging lens according to Example 2 according to the second embodiment of the present invention. FIG. 10 is a cross-sectional view along the optical axis showing a configuration of an imaging lens according to Example 3 according to the third embodiment of the present invention. FIG. 12 is a cross-sectional view along the optical axis showing a configuration of an imaging lens according to Example 4 according to a fourth embodiment of the present invention. FIG. 3 is an aberration curve diagram showing each aberration characteristic of spherical aberration, astigmatism, distortion aberration and coma aberration when the imaging lens according to Example 1 of the present invention shown in FIG. 1 is focused on an object at infinity. FIG. 1 shows an aberration curve showing the aberration characteristics of spherical aberration, astigmatism, distortion and coma when the imaging lens according to Example 1 of the present invention is focused on an object having a magnification of −0.05. FIG. FIG. 1 shows an aberration curve showing the aberration characteristics of spherical aberration, astigmatism, distortion aberration and coma aberration when the imaging lens according to Example 1 of the present invention is focused on an object having a magnification of −0.1. FIG. FIG. 5 is an aberration curve diagram showing each aberration characteristic of spherical aberration, astigmatism, distortion aberration and coma aberration when the imaging lens according to Example 2 of the present invention shown in FIG. 2 is focused on an object at infinity. FIG. 2 shows an aberration curve showing the aberration characteristics of spherical aberration, astigmatism, distortion aberration, and coma aberration when the imaging lens according to Example 2 of the present invention is focused on an object with a magnification of −0.05. FIG. FIG. 2 shows an aberration curve showing the spherical aberration, astigmatism, distortion aberration and coma aberration characteristics when the imaging lens according to Example 2 of the present invention is focused on an object having a magnification of −0.1. FIG. FIG. 6 is an aberration curve diagram showing each aberration characteristic of 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. 3 is focused on an object at infinity. FIG. 3 shows an aberration curve showing the aberration characteristics of spherical aberration, astigmatism, distortion aberration, and coma aberration when the imaging lens according to Example 3 of the present invention is focused on an object having a magnification of −0.05. FIG. FIG. 3 shows an aberration curve showing aberration characteristics of spherical aberration, astigmatism, distortion aberration and coma aberration when the imaging lens according to Example 3 of the present invention is focused on an object having a magnification of −0.1. FIG. FIG. 5 is an aberration curve diagram showing spherical aberration, astigmatism, distortion aberration, and coma aberration characteristics when the imaging lens according to Example 4 of the present invention shown in FIG. 4 is focused on an object at infinity. FIG. 4 shows an aberration curve showing spherical aberration, astigmatism, distortion aberration, and coma aberration characteristics when the imaging lens according to Example 4 of the present invention is focused on an object with a magnification of −0.05. FIG. FIG. 4 shows an aberration curve showing aberration characteristics of spherical aberration, astigmatism, distortion aberration, and coma aberration when the imaging lens according to Example 4 of the present invention is focused on an object with a magnification of −0.1. FIG. It is the perspective view seen from the to-be-photographed object side which shows typically the external appearance structure of the digital camera as a camera which concerns on the 5th Embodiment of this invention. It is the perspective view seen from the photographer side which shows typically the external appearance structure of the digital camera of FIG. FIG. 18 is a block diagram schematically illustrating a functional configuration of the digital camera in FIG. 17.

Hereinafter, the imaging lens of the present invention will be described in detail based on the first to fourth embodiments of the present invention with reference to FIGS.
Before describing specific numerical examples, first, a fundamental embodiment of the present invention will be described with reference to FIGS.
As a typical configuration of a wide-angle single focus lens as in the present invention, a lens group having a negative refractive power (power) is disposed on the object side, and a lens group having a positive refractive power (power) is disposed on the image side. Retro focus type is listed. Due to the characteristics of area sensors that have color filters and microlenses in each pixel, there is a need to keep the exit pupil position away from the image plane so that the peripheral luminous flux is incident at a near-perpendicular angle on the sensor. Is the main reason for adoption. However, the retrofocus type has a large asymmetry of the refractive power arrangement, and tends to be incompletely corrected for coma, distortion, lateral chromatic aberration, and the like. Furthermore, since it is necessary to make the aperture large, it becomes difficult to sufficiently correct spherical aberration, coma aberration, and the like.
In the case of the retrofocus type, if focusing is simply performed with the entire extension, an image surface curvature is generated by focusing.

In the present invention, as shown in FIGS. 1 to 4, in order to ensure high performance while having a large aperture, the first lens group G1 having negative power and the second lens group G2 having positive power are used. In the imaging lens configured, the second lens group G2 includes a second a lens group G2a having a positive power in order from the object side, an aperture stop S, and a second b lens group G2b having a positive power. The Further, the second-b lens group G2b includes, in order from the object side, a cemented lens of a negative lens L21b and a positive lens L22b, a negative lens L23b having a concave surface on the image side, a positive lens L24b, and a negative lens L25b having a concave surface on the object side. And a positive lens L26b.
Aberration correction is performed by canceling spherical aberration, coma, and the like generated on the object side surface of the negative lens L21b on the image side surface of the positive lens L22b. Therefore, a change in the distance from the object side surface of the negative lens L21b to the image side surface of the positive lens L22b and the influence of the eccentricity of the image side surface of the positive lens L22b on the object side surface of the negative lens L21b tend to increase. By joining L21b and the positive lens L22b, the combined thickness change of the negative lens L21b and the positive lens L22b and the decentering of the image side surface of the positive lens L22b with respect to the object side surface of the negative lens L21b can be reduced.

Further, in the configuration of the negative lens L23b having a concave image side surface, the positive lens L24b, and the negative lens L25b having a concave surface on the object side, off-axis rays are relatively low on the image side surface of the negative lens L23b, and the negative lens L25b. Both on-axis chromatic aberration and lateral chromatic aberration are effectively reduced by utilizing the fact that off-axis rays are relatively high on the object side.
The positive lens L26b of the second b lens group G2b serves to balance aberrations and control the exit pupil distance.
Furthermore, it is desirable that the following conditional expression (1) is satisfied (corresponding to claim 1).
(1) 1.5 <f2b / f <3.0
Here, f2b is the focal length of the second b lens group G2b, and f is the focal length of the entire system.
If the upper limit value of conditional expression (1) is exceeded, the focal length f2b of the second lens group G2b becomes too long, leading to an increase in the exchange of aberrations between the second lens group G2a and the second lens group G2b, and various aberrations. Correction becomes difficult. If the lower limit of conditional expression (1) is not reached, it will be difficult to correct various aberrations in the second lens group G2b.

More preferably, the following conditional expression should be satisfied.
(1 ′) 1.5 <f2b / f <2.5
In order to achieve higher performance, the following conditional expression (2) should be satisfied (corresponding to claim 2).
(2) 0.05 <(R24b2-R25b1) / (R24b2 + R25b1) <0.2
However, R24b2 is the radius of curvature of the image side surface of the positive lens L24b of the second b lens group G2b, and R25b1 is the radius of curvature of the object side surface of the negative lens L25b of the second b lens group G2b.
The coma aberration generated on the image side surface of the positive lens L24b is corrected on the object side surface of the negative lens L25b.
When the upper limit value of the conditional expression (2) is exceeded, the radius of curvature of the object side surface of the negative lens L25b becomes too small with respect to the image side surface of the positive lens L24b, and the aberration generated on the image side surface of the positive lens L24b is reduced. Overcorrection on the object side. If the lower limit value of the conditional expression (2) is not reached, the radius of curvature of the object side surface of the negative lens L25b becomes too large with respect to the image side surface of the positive lens L24b, and the aberration generated on the image side surface of the positive lens L24b is reduced. Correction is insufficient on the object side.

In order to achieve higher performance, the following conditional expression (3) should be satisfied (corresponding to claim 3).
(3) -0.2 <(R23b2 + R25b1) / (R23b2-R25b1) <0.2
However, R23b2 is the radius of curvature of the image side surface of the negative lens L23b of the second b lens group G2b, and R25b1 is the radius of curvature of the object side surface of the negative lens L25b of the second b lens group G2b.
The radius of curvature of the image side surface of the negative lens L23b of the second lens group G2b and the object side surface of the negative lens L25b of the second lens group G2b both have negative power, and the image side surface of the negative lens L23b is concave on the image side. Yes, the object side surface of the negative lens L25b is concave on the object side. By making these surfaces satisfy the conditional expression (3), it is possible to sufficiently correct axial chromatic aberration, lateral chromatic aberration, coma color difference, and the like.
In order to achieve higher performance, the following conditional expression (4) should be satisfied (corresponding to claim 4).
(4) -0.2 <f / fA <0.3
Here, fA is the combined focal length from the negative lens L23b to the negative lens L25b of the second b lens group G2b, and f is the focal length of the entire system.

Exceeding the upper limit of conditional expression (4) leads to the focal length of the positive lens L24b becoming too short, causing short wavelength chromatic aberration in the negative direction, and short wavelength axial chromatic aberration in the negative direction. Will lead to the occurrence. If the lower limit of conditional expression (4) is not reached, the focal lengths of the negative lens L23b and the negative lens L25b become too short, and short wavelength lateral chromatic aberration occurs in the positive direction and short wavelength axial chromatic aberration. Will occur in the positive direction.
In order to achieve higher performance, the following conditional expression (5) should be satisfied (corresponding to claim 5).
(5) 0.25 <DA / D2b <0.45
However, DA is the thickness of the cemented lens of the negative lens L21b and the positive lens L22b, and D2b is the thickness of the second b lens group G2b.
When the upper limit value of conditional expression (5) is exceeded, the cemented lens of the negative lens L21b and the positive lens L22b becomes too thick, and the degrees of freedom of the negative lens L23b, the positive lens L24b, the negative lens L25b, and the positive lens L26b are lost. The various aberrations cannot be corrected sufficiently. If the lower limit of conditional expression (5) is not reached, the cemented lens of the negative lens L21b and the positive lens L22b becomes too thin, and it becomes difficult to sufficiently correct spherical aberration and coma.

In order to correct chromatic aberration while correcting monochromatic aberration, the positive lens L24b preferably satisfies the following conditional expressions (6), (7), and (8) (corresponding to claim 6).
_{(6) 1.45 <n d <} 1.65
(7) 65.0 <ν _d <95.0
(8) 0.009 <P _{g, F} − (− 0.001802 × ν _d +0.6483) <0.050
However, _{n d} is the refractive index of the positive lens L24b, [nu _d is Abbe number of the positive lens _{L24b, P g, F} represents a partial dispersion ratio of the positive lens L24b.
Here, the partial dispersion ratio P _{g, F} = ( _ng− n _F ) / (n _F −n _C ), and _ng , n _F and n _C are the g line and F line of the positive lens L24b, respectively. , The refractive index for the C line.
By using a glass material having anomalous dispersion characteristics, it is possible to sufficiently correct axial chromatic aberration, lateral chromatic aberration, and coma color difference.
The second a lens group includes, in order from the object side, a negative lens having a concave surface on the image side, and a cemented lens of a positive lens and a negative lens. The focal length of the second a lens group is f2a, and the second b lens group Let the focal length be f2b.
Conditional formula (9) below:
(9) 0.5 <f2a / f2b <1.5
Is satisfied (corresponding to claim 7).
Since the generation of aberration can be suppressed and a higher-performance imaging lens can be provided, a camera (inspection apparatus) with higher image quality can be realized.
When focusing from an object at infinity to an object at a short distance, it is desirable that the second lens group G2 moves to the object side (corresponding to claim 8). This is because it is possible to suppress the curvature of field that occurs due to focusing accompanying the change in the object distance.

When focusing from an object at infinity to a near object, the first lens group G1 is preferably fixed with respect to the image plane. As a result, it is possible to sufficiently reduce the curvature of field caused by the change in the object distance while having a simple configuration.
Next, embodiments of the present invention and specific examples (numerical examples) will be described in detail. Example 1, Example 2, Example 3 and Example 4 described below are the first embodiment, the second embodiment, the third embodiment and the fourth embodiment of the present invention. It is an Example of the specific structure by the specific numerical example of the imaging lens which concerns on. The fifth embodiment is an embodiment of an inspection apparatus using the imaging lens shown in Examples 1 to 4 as an imaging optical system or an imaging optical system of a camera function unit. .
FIG. 1 is a view for explaining an imaging lens in Example 1 according to the first embodiment of the present invention. FIG. 2 is a view for explaining an imaging lens in Example 2 according to the second embodiment of the present invention. FIG. 3 is a view for explaining an imaging lens in Example 3 according to the third embodiment of the present invention. FIG. 4 is a view for explaining an imaging lens in Example 4 according to the fourth embodiment of the present invention.

In all of Examples 1 to 4, the maximum image height is 8.0 mm.
In the imaging lenses of the first to fourth embodiments, the parallel flat plate disposed on the image side of the second lens group G2 includes various filters such as an optical low-pass filter and an infrared cut filter, and a CMOS sensor. A cover glass (seal glass) of a light receiving element such as the above is assumed. Here, these are collectively referred to as various filters MF.
In addition, the glass material of the optical glass used in each Example of these Examples 1-4 is shown with the optical glass type name of the product of OHARA Co., Ltd. (OHARA).
In a usual imaging lens, some lens surfaces may be aspherical surfaces. However, in the embodiment according to the present invention, it is desirable that all lens surfaces are composed of only spherical lenses.
This is because it can be configured at low cost while having high performance.
The aberrations of Examples 1 to 4 described below are corrected at a high level, and the spherical aberration and the longitudinal chromatic aberration are so small that they do not cause a problem. The number of lenses is about 11, and astigmatism, field curvature, and chromatic aberration of magnification are sufficiently small, coma and disturbance of color difference are well suppressed to the outermost periphery, and distortion is also magnification of -0.05. In absolute magnification, the absolute value is 3% or less, and it has a resolving power corresponding to an image sensor with 6 to 10 million pixels. By configuring the imaging lens as in the present invention, it is possible to ensure a very good image performance while the half field angle is about 68 degrees and the F number is about 2.0. Is apparent from the following examples.

The meanings of symbols common to the first to fourth embodiments are as follows.
f: Focal length of the entire system F: F value (F number)
ω: Half angle of view (°)
R: radius of curvature D: surface spacing N: refractive index ν: Abbe number φ: effective beam diameter

FIG. 1 shows a lens configuration of a longitudinal section along the optical axis of the optical system of the imaging lens according to the first embodiment of the present invention and Example 1 (corresponding to claim 1).
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 L11, a second lens L12, and a third lens from the object side to the image surface side. L21a, fourth lens L22a, fifth lens L23a, fixed aperture FS, aperture stop S, sixth lens L21b, seventh lens L22b, eighth lens L23b, ninth lens L24b, tenth lens L25b, and eleventh lens L26b It is arranged. The fourth lens L22a and the fifth lens L23a, the sixth lens 21b and the seventh lens L22b, and the eighth lens L23b and the ninth lens L24b respectively constitute a cemented lens.
Focusing on the lens group configuration, the first lens group G1 having negative refractive power (power) is configured by the first lens L11 and the second lens L12 located on the object side. The third lens L21a, the fourth lens 22a, and the fifth lens L23a constitute a second a lens group G2a having a positive refractive power. Further, the sixth lens L21b, the seventh lens L22b, the eighth lens L23b, the ninth lens L24b, the tenth lens 25b, and the eleventh lens 26b constitute a second b lens group G2b having a positive refractive power.

That is, the optical system of the imaging lens shown in FIG. 1 has the first lens group G1, the second lens group G2a, the fixed stop FS, the aperture stop S, and the second b lens group G2b from the object side to the image plane side. The configuration is arranged sequentially. The second lens group G2 is composed of the second a lens group G2a and the second b lens group G2b.
Specifically, the first lens group G1 includes, in order from the object side to the image side, a first lens L11 including a negative lens having a negative meniscus shape with a convex surface facing the object side, and a convex surface on the image side. A second lens L12 made of a positive lens having a positive meniscus shape is disposed so as to exhibit negative refractive power. The second-a lens group G2a has a biconcave shape in which a concave surface having a larger curvature than the object side is sequentially directed to the image surface side sequentially from the object side to the image surface side. A third lens L21a composed of a negative lens, a fourth lens L22a composed of a positive lens having a biconvex shape with a convex surface having a larger curvature on the image surface side than the object side, and a negative meniscus shape having a convex surface directed to the image surface side And a fifth lens L23a made of a negative lens is arranged so as to exhibit positive refractive power.

The second lens group G2b has a sixth lens L21b formed of a biconcave negative lens with a concave surface having a larger curvature than the image surface side facing the object side, and a convex surface having a larger curvature than the object side facing the image surface side. A seventh lens L22b composed of a positive lens having a biconvex shape, an eighth lens L23b composed of a negative lens having a negative meniscus shape with a concave surface facing the image surface, and a curvature larger on the object side than the surface on the image surface A ninth lens L24b made of a positive lens having a biconvex lens shape with a convex surface facing, a tenth lens L25b made of a negative lens having a negative meniscus shape with a concave surface facing the object side, and a surface on the image side from the object side An eleventh lens L26b, which is a positive lens having a biconvex shape with a convex surface having a large curvature, is disposed so as to exhibit positive refractive power.
Note that the two lenses of the fourth lens L22a and the fifth lens L23a, the two lenses of the sixth lens L21b and the seventh lens L22b, and the two lenses of the eighth lens L23b and the ninth lens L24b are respectively The two lenses are bonded together so as to be bonded together to form a cemented lens composed of two lenses.
That is, the second lens group G2 includes a second a lens group G2a having a positive refractive power and a second b lens group G2b having a positive refractive power.

Further, behind the second lens group G2, that is, on the image side, there are various filters such as an optical low-pass filter and an infrared cut filter, and a filter glass showing a cover glass (seal glass) of the light receiving element as an equivalent parallel plate. Be placed.
As in the so-called digital still camera, in an imaging optical system using a solid-state imaging device such as a CCD (charge coupled device) sensor or a CMOS (complementary metal oxide semiconductor) sensor, a back insertion glass, a low-pass filter, an infrared cut At least one of glass and a cover glass for protecting the light receiving surface of the solid-state imaging device is inserted. In this embodiment, these are represented as various filters MF, equivalently as a single parallel plate. Show. In addition, in Examples 2 to 4, various filters MF are equivalently shown as one parallel flat plate. However, similar to the various filters MF in the present embodiment, a back insertion glass, a low-pass filter, an infrared cut It represents at least one of glass and cover glass.
The first lens group G1 and the second lens group G2 are supported by an appropriate support frame or the like, and the first lens group G1 is fixed and the second lens group G2 is in focus for focusing on a target object. , And focusing is performed by changing the distance A between the first lens group G1 and the second a lens group G2a.

FIG. 1 also shows the surface number of each optical surface in the optical system of the imaging lens. Note that each reference symbol shown in FIG. 1 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. 2, FIG. 3, FIG. Even if a common reference symbol is attached, it is not necessarily a common configuration with the corresponding embodiments.
In Example 1, the focal length f, the open F value F, and the field angle 2ω [°] of the entire optical system are f = 12.0 mm, F = 1.99, field angle 2, ω = 68. The optical characteristics of each optical element in the first embodiment are 5 degrees, and the optical characteristics such as the curvature radius R of the optical surface, the surface interval D between adjacent optical surfaces, the refractive index N, the Abbe number ν, the aperture φ, and the lens material are as follows. It is as Table 1.

  The variable distance A between the second lens L12 in the first lens group G1 and the third lens L21a in the second lens group G2, the 26th lens L26b in the second lens group G2, and various filters MF The variable interval B between the first and second intervals in the state of focusing on an object at infinity (Inf) during focusing and the state of focusing on an object having a magnification of 0.05 times and a magnification of 0.10 times [Table 2] It can be changed as follows.

That is, as shown in [Table 2] above, it can be seen that the distance A between the first lens group G1 and the second a lens group G2a is reduced during focusing from a long distance object to a short distance object.
The values corresponding to the conditional expressions (1) to (9) described in the first embodiment are as shown in [Table 3].

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.
Further, FIG. 5 shows respective aberration curve diagrams of spherical aberration, astigmatism, distortion aberration, and coma aberration when the imaging lens according to Example 1 is focused on an object at infinity. FIG. 6 is a diagram illustrating aberration curves of spherical aberration, astigmatism, distortion aberration, and coma aberration when the imaging lens according to Example 1 is focused on an object with a magnification of −0.05. ing.
Further, FIG. 7 shows respective aberration curve diagrams of spherical aberration, astigmatism, distortion aberration and coma aberration in a state where the imaging lens according to Example 1 is focused on an object having a magnification of −0.1. ing.
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. 2 shows a lens configuration of a longitudinal section along the optical axis of the optical system of the imaging lens according to Example 2 of the second embodiment of the present invention.
That is, as shown in FIG. 2, the optical system of the imaging lens according to Example 2 of the present invention sequentially includes a first lens L11, a second lens L12, and a third lens from the object side to the image surface side. L21a, fourth lens L22a, fifth lens L23a, fixed aperture FS, aperture stop S, sixth lens L21b, seventh lens L22b, eighth lens L23b, ninth lens L24b, tenth lens L25b, and eleventh lens L26b The fourth lens L22a and the fifth lens L23a, the sixth lens L21b and the seventh lens L22b, and the eighth lens L23b and the ninth lens L24b respectively constitute a cemented lens.
Focusing on the lens group configuration, the first lens group G1 having negative refractive power (power) is configured by the first lens L11 and the second lens L12 located on the object side. The third lens L21a, the fourth lens L22a, and the fifth lens L23a constitute a second a lens group G2a having a positive refractive power. Further, the sixth lens L21b, the seventh lens L22b, the eighth lens L23b, the ninth lens L24b, the tenth lens L25b, and the eleventh lens L26b constitute a second b lens group G2b having a positive refractive power.

That is, the optical system of the imaging lens shown in FIG. 2 moves these first lens group G1, 2a lens group G2a, fixed aperture FS, aperture stop S, and 2b lens group G2b from the object side to the image plane side. The configuration is arranged sequentially. The second lens group G2 is composed of the second a lens group G2a and the second b lens group G2b.
Specifically, the first lens group G1 includes, in order from the object side to the image side, a first lens L11 including a negative lens having a negative meniscus shape with a convex surface facing the object side, and a convex surface on the image side. A second lens L12 made of a positive lens having a positive meniscus shape is disposed so as to exhibit negative refractive power.

  The second-a lens group G2a includes, from the object side to the image surface side, a third lens L21a including a negative lens having a biconcave shape in which a concave surface having a larger curvature than the object side is directed to the image surface side, and an image surface A fourth lens L22a formed of a positive lens having a biconvex shape with a convex surface having a larger curvature than the object side, and a fifth lens L23a formed of a negative lens having a negative meniscus shape having a convex surface directed to the image surface side. It arrange | positions and it is comprised so that positive refractive power may be shown. The second lens group G2b has a sixth lens L21b formed of a biconcave negative lens with a concave surface having a larger curvature than the image surface side facing the object side, and a convex surface having a larger curvature than the object side facing the image surface side. A seventh lens L22b composed of a positive lens having a biconvex shape, an eighth lens L23b composed of a negative lens having a negative meniscus shape with a concave surface facing the image surface, and a curvature larger on the object side than the surface on the image surface A ninth lens L24b made of a positive lens having a biconvex lens shape with a convex surface facing, a tenth lens L25b made of a negative lens having a negative meniscus shape with a concave surface facing the object side, and a surface on the image side from the object side An eleventh lens L26b, which is a positive lens having a biconvex shape with a convex surface having a large curvature, is disposed so as to exhibit positive refractive power.

Note that the two lenses of the fourth lens L22a and the fifth lens L23a, the two lenses of the sixth lens L21b and the seventh lens L22b, and the two lenses of the eighth lens L23b and the ninth lens L24b are respectively The two lenses are bonded together so as to be bonded together to form a cemented lens composed of two lenses.
That is, the second lens group G2 includes a second a lens group G2a having a positive refractive power and a second b lens group G2b having a positive refractive power.
Further, behind the second lens group G2, that is, on the image side, there are various filters such as an optical low-pass filter and an infrared cut filter, and a filter glass showing a cover glass (seal glass) of the light receiving element as an equivalent parallel plate. Be placed.
As in the so-called digital still camera, in an imaging optical system using a solid-state imaging device such as a CCD (charge coupled device) sensor or a CMOS (complementary metal oxide semiconductor) sensor, a back insertion glass, a low-pass filter, an infrared cut At least one of glass and a cover glass for protecting the light receiving surface of the solid-state image sensor is inserted, but in this embodiment, these are representatively shown as various filters MF and equivalently shown as one parallel plate. ing.

In addition, in Examples 2 to 4, various filters MF are equivalently shown as one parallel flat plate. However, similar to the various filters MF in the present embodiment, a back insertion glass, a low-pass filter, an infrared cut It represents at least one of glass and cover glass.
The first lens group G1 and the second lens group G2 are supported by an appropriate support frame or the like, and the first lens group G1 is fixed and the second lens group G2 is in focus for focusing on a target object. , And the focusing is performed by changing the distance between the first lens group G1 and the second a lens group G2a.

FIG. 2 also shows the surface numbers of the optical surfaces in the optical system of the imaging lens. 2 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. Therefore, FIG. 1, FIG. 3, FIG. Even if a common reference symbol is attached, it is not necessarily a common configuration with the corresponding embodiments.
In Example 2, the focal length f, the open F value F, and the field angle 2ω [°] of the entire optical system are f = 12.0 mm, F = 2.00, and 2ω = 68.5 degrees, respectively. The optical characteristics of each optical element in Example 2 are as shown in Table 4 below, including the radius of curvature R of the optical surface, the distance D between adjacent optical surfaces, the refractive index N, the Abbe number ν, the aperture φ, and the lens material. It is.

  The variable distance A between the second lens L12 in the first lens group G1 and the third lens L21a in the second lens group G2, and the eleventh lens L26b in the second b lens group in the second lens group G2. And the variable distance B between the various filters MF are focused on an object at infinity (Inf) during focusing and on an object with a magnification of 0.05 times and a magnification of 0.10 times, respectively. The state is changed as shown in [Table 5].

That is, as shown in [Table 5] above, it can be seen that the distance A between the first lens group G1 and the second a lens group G2a is reduced during focusing from a long distance object to a short distance object.
The values corresponding to the conditional expressions (1) to (9) described in the second embodiment are as shown in [Table 6].

Therefore, 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. 8 shows respective aberration curve diagrams of spherical aberration, astigmatism, distortion aberration, and coma aberration when the imaging lens according to Example 2 is focused on an object at infinity. FIG. 9 is a graph showing aberration curves of spherical aberration, astigmatism, distortion aberration, and coma aberration when the imaging lens according to Example 2 is focused on an object with a magnification of −0.05. ing.
Further, FIG. 10 shows respective aberration curve diagrams of spherical aberration, astigmatism, distortion aberration, and coma aberration in a state where the imaging lens according to Example 2 is focused on an object having a magnification of −0.1. ing.
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. 3 shows a lens configuration of a longitudinal section along the optical axis of the optical system of the imaging lens according to Example 3 of the third embodiment of the present invention.
That is, as shown in FIG. 3, the optical system of the imaging lens according to Example 3 of the present invention sequentially has a first lens L11, a second lens L12, and a third lens from the object side to the image plane side. L21a, fourth lens L22a, fifth lens L23a, fixed aperture FS, aperture stop S, sixth lens L21b, seventh lens L22b, eighth lens L23b, ninth lens L24b, tenth lens L25b, and eleventh lens L26b The fourth lens L22a and the fifth lens L23a, and the sixth lens L21b and the seventh lens L22b each constitute a cemented lens. Unlike Example 1 and Example 2, the eighth lens L23b and the ninth lens L24b are not cemented lenses and are configured separately.
Focusing on the lens group configuration, the first lens group G1 having negative refractive power (power) is configured by the first lens L11 and the second lens L12 located on the object side. The third lens L21a, the fourth lens L22a, and the fifth lens L23a constitute a second a lens group G2a having a positive refractive power.

Further, the sixth lens L21b, the seventh lens L22b, the eighth lens L23b, the ninth lens L24b, the tenth lens L25b, and the eleventh lens L26b constitute a second b lens group G2b having a positive refractive power. That is, the optical system of the imaging lens shown in FIG. 3 moves these first lens group G1, 2a lens group G2a, fixed aperture FS, aperture stop S, and 2b lens group G2b from the object side to the image plane side. The configuration is arranged sequentially. The second lens group G2 is composed of the second a lens group G2a and the second b lens group G2b.
Specifically, the first lens group G1 includes, in order from the object side to the image side, a first lens L11 that is a negative lens having a negative meniscus shape with a convex surface facing the object side, and an object side on the image side. A second lens L12 made of a positive lens having a biconvex shape with a convex surface having a larger curvature is disposed so as to exhibit negative refractive power. The second-a lens group G2a includes, from the object side to the image surface side, a third lens L21a including a negative lens having a biconcave shape in which a concave surface having a larger curvature than the object side is directed to the image surface side, and an image surface A fourth lens L22a formed of a positive lens having a biconvex shape with a convex surface having a larger curvature than the object side, and a fifth lens L23a formed of a negative lens having a negative meniscus shape having a convex surface directed to the image surface side. It arrange | positions and it is comprised so that positive refractive power may be shown.

The second lens group G2b has a sixth lens L21b formed of a biconcave negative lens with a concave surface having a larger curvature than the image surface side facing the object side, and a convex surface having a larger curvature than the object side facing the image surface side. A seventh lens L22b made of a positive lens having a biconvex shape, an eighth lens L23b made of a negative lens having a negative meniscus shape with a concave surface facing the image surface side, and a curvature larger than that of the object side surface on the image surface side A ninth lens L24b composed of a positive lens having a biconvex lens shape facing the convex surface, a tenth lens L25b composed of a negative lens having a negative meniscus shape facing the concave surface to the object side, and a surface on the object side from the object side surface An eleventh lens L26b, which is a positive lens having a biconvex shape with a convex surface having a large curvature, is disposed so as to exhibit positive refractive power.
The two lenses, the fourth lens L22a and the fifth lens L23a, and the two lenses, the sixth lens L21b and the seventh lens L22b, respectively constitute a cemented lens. Unlike the first and second embodiments, the two lenses of the eighth lens L23b and the ninth lens L24b are not joined to each other and are configured separately.
That is, the second lens group G2 includes a second a lens group G2a having a positive refractive power and a second b lens group G2b having a positive refractive power.

Further, behind the second lens group G2, that is, on the image side, there are various filters such as an optical low-pass filter and an infrared cut filter, and a filter glass showing a cover glass (seal glass) of the light receiving element as an equivalent parallel plate. Be placed.
The first lens group G1 and the second lens group G2 are supported by an appropriate support frame or the like, and the first lens group G1 is fixed and the second lens group G2 is in focus for focusing on a target object. , And the focusing is performed by changing the distance between the first lens group G1 and the second a lens group G2a.
In Example 3, the focal length f, the open F value F, and the field angle 2ω [°] of the entire optical system are f = 12.0 mm, F = 2.01, and 2ω = 68.9 degrees, respectively. The optical characteristics of each optical element in Example 3 are as shown in Table 7 below, including the radius of curvature R of the optical surface, the distance D between adjacent optical surfaces, the refractive index N, the Abbe number ν, the aperture φ, and the lens material. It is.

  The variable distance A between the second lens L12 in the first lens group G1 and the third lens L21a in the second lens group G2, and the eleventh lens L26b in the second b lens group in the second lens group G2. And the variable distance B between the various filters MF are focused on an object at infinity (Inf) during focusing and on an object with a magnification of 0.05 times and a magnification of 0.10 times, respectively. The state is changed as shown in [Table 8].

That is, as shown in [Table 8] above, it can be seen that the distance A between the first lens group G1 and the second a lens group G2a decreases during focusing from a long distance object to a short distance object.
The values corresponding to the conditional expressions (1) to (9) described in the third embodiment are as shown in [Table 9].

Therefore, the numerical values related to the conditional expressions (1) to (9) described in the third embodiment are within the range of each conditional expression, and satisfy the conditional expressions (1) to (9). doing.
FIG. 11 is a diagram illustrating aberration curves of spherical aberration, astigmatism, distortion, and coma aberration when the imaging lens according to Example 3 is focused on an object at infinity. FIG. 12 shows spherical aberration, astigmatism, distortion aberration, and coma aberration curve diagrams when the imaging lens according to Example 3 is focused on an object with a magnification of −0.05. ing.
Further, FIG. 13 shows respective aberration curve diagrams of spherical aberration, astigmatism, distortion aberration and coma aberration when the imaging lens according to Example 3 is focused on an object having a magnification of −0.1. ing.
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 shows a lens configuration of a longitudinal section along the optical axis of the optical system of the imaging lens according to the fourth embodiment of the present invention and Example 4.
That is, as shown in FIG. 4, the optical system of the imaging lens according to Example 4 of the present invention sequentially has a first lens L11, a second lens L12, and a third lens from the object side to the image surface side. L21a, fourth lens L22a, fifth lens L23a, fixed aperture FS, aperture stop S, sixth lens L21b, seventh lens L22b, eighth lens L23b, ninth lens L24b, tenth lens L25b, and eleventh lens L26b The fourth lens L22a and the fifth lens L23a, and the sixth lens L21b and the seventh lens L22b each constitute a cemented lens. Unlike the first and second embodiments, the eighth lens L23b and the ninth lens L24b are not cemented lenses and are configured separately.

  Focusing on the lens group configuration, the first lens group G1 having negative refractive power (power) is configured by the first lens L11 and the second lens L12 located on the object side. The third lens L21a, the fourth lens L22a, and the fifth lens L23a constitute a second a lens group G2a having a positive refractive power. Further, the sixth lens L21b, the seventh lens L22b, the eighth lens L23b, the ninth lens L24b, the tenth L lens 25b, and the eleventh lens L26b constitute a second b lens group G2b having a positive refractive power. That is, the optical system of the imaging lens shown in FIG. 4 has the first lens group G1, the second a lens group G2a, the fixed stop FS, the aperture stop S, and the second b lens group G2b from the object side to the image plane side. The configuration is arranged sequentially. The second lens group G2 is composed of the second a lens group G2a and the second b lens group G2b.

  Specifically, the first lens group G1 includes, in order from the object side to the image side, a first lens L11 that is a negative lens having a negative meniscus shape with a convex surface facing the object side, and an image surface side on the object side. A second lens L12 made of a positive lens having a biconvex shape with a convex surface having a larger curvature is disposed so as to exhibit negative refractive power. The second-a lens group G2a includes a third lens L21a formed of a negative meniscus lens having a concave surface facing the image surface side from the object side toward the image surface side, and a larger image surface side than the object side. Positive refraction by disposing a fourth lens L22a made of a positive lens having a biconvex shape with a convex surface of curvature and a fifth lens L23a made of a negative lens having a negative meniscus shape having a convex surface facing the image surface side. It is configured to show power. The second lens group G2b has a sixth lens L21b formed of a biconcave negative lens with a concave surface having a larger curvature than the image surface side facing the object side, and a convex surface having a larger curvature than the object side facing the image surface side. A seventh lens L22b made of a positive lens having a biconvex shape, an eighth lens L23b made of a negative lens having a negative meniscus shape with a concave surface facing the image surface side, and a curvature larger than that of the object side surface on the image surface side A ninth lens L24b composed of a positive lens having a biconvex lens shape facing the convex surface, a tenth lens L25b composed of a negative lens having a negative meniscus shape facing the concave surface to the object side, and a surface on the object side from the object side surface An eleventh lens L26b, which is a positive lens having a biconvex shape with a convex surface having a large curvature, is disposed so as to exhibit positive refractive power.

Note that the two lenses, the fourth lens L22a and the fifth lens L23a, and the two lenses, the sixth lens L21b and the seventh lens L22b, are closely bonded to each other and integrally joined. A cemented lens made of cement is formed.
That is, the second lens group G2 includes a second a lens group G2a having a positive refractive power and a second b lens group G2b having a positive refractive power.
Further, behind the second lens group G2, that is, on the image side, there are various filters such as an optical low-pass filter and an infrared cut filter, and a filter glass showing a cover glass (seal glass) of the light receiving element as an equivalent parallel plate. Be placed.
As in the so-called digital still camera, in an imaging optical system using a solid-state imaging device such as a CCD (charge coupled device) sensor or a CMOS (complementary metal oxide semiconductor) sensor, a back insertion glass, a low-pass filter, an infrared cut At least one of glass and a cover glass for protecting the light receiving surface of the solid-state image sensor is inserted, but in this embodiment, these are representatively shown as various filters MF and equivalently shown as one parallel plate. ing. In addition, in Examples 2 to 4, various filters MF are equivalently shown as one parallel flat plate. However, similar to the various filters MF in the present embodiment, a back insertion glass, a low-pass filter, an infrared cut It represents at least one of glass and cover glass.

The first lens group G1 and the second lens group G2 are supported by an appropriate support frame or the like, and the first lens group G1 is fixed and the second lens group G2 is in focus for focusing on a target object. , And focusing is performed by changing the distance A between the first lens group G1 and the second a lens group G2a.
In Example 4, the focal length f, the open F value F, and the field angle 2ω [°] of the entire optical system are f = 12.0 mm, F = 2.01, and 2ω = 68.9 degrees, respectively. The optical characteristics of each optical element in Example 4 are as shown in Table 10 below, such as the radius of curvature R of the optical surface, the distance D between adjacent optical surfaces, the refractive index N, the Abbe number ν, the aperture φ, and the lens material. It is.

  The variable distance A between the second lens L12 in the first lens group G1 and the third lens L21a in the second lens group G2, and the eleventh lens L26b in the second b lens group in the second lens group G2. And the variable distance B between the various filters MF are focused on an object at infinity (Inf) during focusing and on an object with a magnification of 0.05 times and a magnification of 0.10 times, respectively. The state is changed as shown in [Table 11].

That is, as shown in [Table 11] above, it can be seen that the distance A between the first lens group G1 and the second a lens group G2a decreases during focusing from a long distance object to a short distance object.
The values corresponding to the conditional expressions (1) to (9) described in the fourth embodiment are as shown in [Table 12].

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.
Further, FIG. 14 shows respective aberration curve diagrams of spherical aberration, astigmatism, distortion aberration and coma aberration when the imaging lens according to Example 4 is focused on an object at infinity. FIG. 15 is a graph showing aberration curves of spherical aberration, astigmatism, distortion aberration, and coma aberration when the imaging lens according to Example 4 is focused on an object with a magnification of −0.05. ing.
Further, FIG. 16 shows respective aberration curve diagrams of spherical aberration, astigmatism, distortion aberration and coma aberration in a state where the imaging lens according to Example 4 is focused on an object having a magnification of −0.1. ing.
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.

[Fifth Embodiment]
Next, a digital camera as a camera according to the fifth embodiment of the present invention configured by employing the imaging lens according to the first to fourth embodiments of the present invention described above will be described. This will be described with reference to FIGS. FIG. 17 is a perspective view schematically showing the external appearance of the digital camera viewed from the front side which is the object side, that is, the subject side, and FIG. 18 is a schematic external view of the digital camera viewed from the back side which is the photographer side. FIG. 19 is a schematic block diagram showing a functional configuration of a digital camera. Here, the camera apparatus is described taking a digital camera as an example, but the imaging lens according to the present invention may be employed in a silver salt film camera using a silver salt film as a conventional image recording medium.
In addition, an information device such as a so-called PDA (personal data assistant) or a portable information terminal device such as a mobile phone or an inspection device incorporating a camera function is widely used. Such an information device also has substantially the same functions and configuration as a digital camera, although the appearance is slightly different, and may be employed as an imaging optical system in such an information device inspection device.

As shown in FIGS. 17 to 19, the digital camera includes an imaging lens 1 as an imaging lens, an optical finder 2, a strobe (flashlight) 3, a shutter button 4, a camera body 5, a power switch 6, a liquid crystal monitor 7, An operation button 8, a memory card slot 9 and the like are provided. Further, as shown in FIG. 19, the digital camera includes a central processing unit (CPU) 11, an image processing device 12, a light receiving element 13, a signal processing device 14, a semiconductor memory 15 and a communication card 16.
The digital camera includes an imaging lens 1 as an imaging optical system and a light receiving element 13 configured as an image sensor using a CMOS (complementary metal oxide semiconductor) imaging element or a CCD (charge coupled device) imaging element. The light receiving element 13 reads a subject (object) optical image formed by the imaging lens 1. As the imaging lens 1, the imaging lens according to the present invention as described in the first to fourth embodiments is used (corresponding to claim 9 or claim 10).
The output of the light receiving element 13 is processed by a signal processing device 14 controlled by the central processing unit 11 and converted into digital image information. That is, such a digital camera includes means for converting a captured image (subject image) into digital image information, which substantially controls the light receiving element 13, the signal processing device 14, and these. And a central processing unit (CPU) 11 or the like.

The image information digitized by the signal processing device 14 is subjected to predetermined image processing in the image processing device 12 which is also controlled by the central processing unit 11 and then recorded in the semiconductor memory 15 such as a nonvolatile memory. In this case, the semiconductor memory 15 may be a memory card loaded in the memory card slot 9 or a semiconductor memory built in the camera body (onboard). The liquid crystal monitor 7 can display an image being shot, and can display an image recorded in the semiconductor memory 15. The image recorded in the semiconductor memory 15 can also be transmitted to the outside via a communication card 16 or the like loaded in a communication card slot (not shown).
When the camera is carried, the objective surface of the imaging lens 1 is covered with a lens barrier (not shown). When the user operates the power switch 6 to turn on the power, the lens barrier is opened and the objective surface is The structure is exposed.
In many cases, focusing is performed by half-pressing the shutter button 4. Focusing in the image forming lens according to the present invention (the image forming lens defined in claims 1 to 8 or shown in the first to fourth embodiments described above) is a part of the plurality of optical systems. This can be done by moving the two lens group G2. When the shutter button 4 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 15 is displayed on the liquid crystal monitor 7 or transmitted to the outside via the communication card 16 or the like, the operation button 8 is operated in a predetermined manner. The semiconductor memory 15 and the communication card 16 are used by being loaded into dedicated or general-purpose slots such as the memory card slot 9 and the communication card slot.
As described above, in the digital camera (imaging device) or the portable information terminal device or the inspection device as described above, the imaging lens as shown in the first to fourth embodiments is used as the imaging optical system. Can be used.
As can be seen from the detailed description of the embodiments and examples, the present invention provides various effects.

In an imaging lens composed of a first lens group G1 having negative power and a second lens group G2 having positive power in order from the object side, the second lens group G2 is positive in order from the object side. The second a lens group G2a having power, a stop (fixed stop FS, aperture stop S), and a second b lens group G2b having positive power, the second b lens group G2b in order from the object side, Consist of a negative lens L21b that is a concave surface and a positive lens L22b that is a convex surface on the image side, a negative lens L23b that is concave on the image side, a positive lens L24b, a negative lens L25b that is concave on the object side, and a positive lens L26b. The focal length of the second lens group G2b is f2b, and the focal length of the entire system is f.
Conditional formula (1) below:
(1) 1.5 <f2b / f <3.0
By satisfying the above, the angle of view is about 68 degrees, the F number is about 2.0, and the size is small, but the size is small, the number of lenses is about 11, and astigmatism, field curvature, and magnification. Chromatic aberration, color difference of coma aberration, distortion, etc. are sufficiently reduced to have a resolution corresponding to an image sensor with 6 to 10 million pixels, and the point image collapses from the wide aperture to the periphery of the angle of view with high contrast. In addition, it is possible to provide a high-performance imaging lens that can describe a straight line as a straight line without distortion.

In addition, according to the inventions described in claims 2 to 5 and claim 7, it is possible to provide a high-performance imaging lens that suppresses the occurrence of aberration more.
According to the invention described in claim 6, since it is possible to provide a high-performance imaging lens that suppresses the occurrence of chromatic aberration and has less color blur, a high-quality camera (inspection apparatus) with less color blur. Can be realized.
Further, according to the invention described in claim 8, since focusing can be achieved with a simple configuration while ensuring high performance, a compact and high-performance imaging lens can be provided.
According to the ninth aspect of the present invention, the angle of view is about 68 degrees, the F number is about 2.0, which is a large aperture and is small, the number of lenses is about 11, and the astigmatism. Aberration, curvature of field, lateral chromatic aberration, coma color difference, distortion, etc. are sufficiently reduced to have a resolution corresponding to an image sensor with 6 to 10 million pixels, and around the angle of view with high contrast from wide open aperture Providing a compact, high-quality camera that uses a high-performance imaging lens from infinity to near-distance objects that can be drawn without distortion as a straight line without distortion of the point image. Therefore, the user can take a high-quality image with a small camera.

Furthermore, according to the invention described in claim 10, the angle of view is about 68 degrees, the F number is about 2.0, which is a large aperture and is small, the number of lenses is about 11, and astigmatism. Aberration, curvature of field, lateral chromatic aberration, coma color difference, distortion, etc. are sufficiently reduced to have a resolution corresponding to an image sensor with 6 to 10 million pixels, and around the angle of view with high contrast from wide open aperture A compact, high-quality image using a high-performance imaging lens from infinity to short-distance objects that can be drawn without distortion as a straight line without distortion of the point image. Therefore, the user can take a high-quality image with a small inspection device.
In addition, the imaging lens shown in the above-described embodiment can be used for image processing with high-definition inspection of an object at a finite distance, and can also be applied as an imaging lens for a silver salt camera. Is possible.

G1 first lens group (negative)
G2 Second lens group (positive)
G2a 2a lens group (positive)
G2b 2b lens group (positive)
L11, L12, L21a, L22a, L23a, L21b, L22b, L23b, L24b, L25b, L26b First lens, second lens, third lens, fourth lens, fifth lens, sixth lens, seventh lens, 8 lens, 9th lens, 10th lens, 11th lens FS Fixed stop S Aperture stop MF Various filters 1 Imaging lens 2 Optical viewfinder 3 Strobe (flash light)
4 Shutter button 5 Camera body 6 Power switch 7 LCD monitor 8 Operation button 9 Memory card slot 11 Central processing unit (CPU)
DESCRIPTION OF SYMBOLS 12 Image processing apparatus 13 Light receiving element 14 Signal processing apparatus 15 Semiconductor memory 16 Communication card etc.

JP 2014-174234 A JP 2006-171285 A JP 2004-354405 A

Claims (10)

In an imaging lens including a first lens group having a negative power and a second lens group having a positive power in order from the object side, the second lens group has a positive power in order from the object side. The second lens group includes a 2a lens group, a stop, and a 2b lens group having a positive power. The second b lens group is, in order from the object side, a negative lens L21b having a concave surface on the object side and a positive lens L22b having a convex surface on the image side. A negative lens L23b having a concave surface on the image side, a positive lens L24b, a negative lens L25b having a concave surface on the object side, and a positive lens L26b. The focal length of the second lens group is f2b, and the focal point of the entire system. Let distance be f
Conditional formula (1) below:
(1) 1.5 <f2b / f <3.0
An imaging lens characterized by satisfying The radius of curvature of the image side surface of the positive lens L24b of the second lens group is R24b2, and the radius of curvature of the object side surface of the negative lens L25b of the second lens group is R25b1.
Conditional expression (2) below:
(2) 0.05 <(R24b2-R25b1) / (R24b2 + R25b1) <0.30
The imaging lens according to claim 1, wherein: The radius of curvature of the image side surface of the negative lens L23b of the second lens group is R23b2, and the radius of curvature of the object side surface of the negative lens L25b of the second lens group is R25b1.
Conditional formula (3) below:
(3) -0.2 <(R23b2 + R25b1) / (R23b2-R25b1) <0.2
The imaging lens according to claim 1, wherein the imaging lens is satisfied. The combined focal length from the negative lens L23b of the second lens group to the negative lens L25b is fA, and the focal length of the entire system is f.
Conditional formula (4) below:
(4) -0.2 <f / fA <0.3
The imaging lens according to any one of claims 1 to 3, wherein the imaging lens is satisfied. The axial thickness of the cemented lens of the negative lens L21b and the positive lens L22b of the second b lens group is DA, and the axial thickness of the second b lens group is D2b.
Conditional formula (5) below:
(5) 0.25 <DA / D2b <0.45
5. The imaging lens according to claim 1, wherein the imaging lens is satisfied. The refractive index of the positive lens L24b of the 2b lens and _{n d,} Abbe number and [nu _d, and g-line, F-line, the refractive index for the C line _{n g,} n F, and _{n C,} the partial dispersion ratio P _{g, F}
P _{g, F} = (n _g -n _F ) / (n _F -n _C )
The following conditional expressions (6), (7), (8):
_{(6) 1.45 <n d <} 1.65
(7) 65.0 <ν _d <95.0
(8) 0.009 <P _{g, F} − (− 0.001802 × ν _d +0.6483) <0.050
The imaging lens according to claim 1, wherein the imaging lens is satisfied. The second a lens group includes, in order from the object side, a negative lens having a concave surface on the image side, and a cemented lens of a positive lens and a negative lens. The focal length of the second a lens group is f2a, and the second b lens group Let the focal length be f2b.
Conditional formula (9) below:
(9) 0.5 <f2a / f2b <1.5
The imaging lens according to claim 1, wherein the imaging lens is satisfied.   8. The structure according to claim 1, wherein the first lens unit is fixed and the second lens unit moves toward the object side when focusing from an infinite object to a close object. The imaging lens according to any one of the above.   A camera comprising the imaging lens according to claim 1 as a photographing optical system.   An inspection apparatus comprising the imaging lens according to claim 1 as a photographing optical system of a camera function unit.

Images