JP2014219609A - Imaging optical system, camera device and portable information terminal device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging optical system that has various kinds of aberrations sufficiently reduced even if the imaging optical system is a wide-angle at 76° of an angle of view, has a large diameter of the F-number of about 2.8 or smaller and a small load to a driving source upon focusing, is a compact and light-weight inner focus type, and that exhibits resolving power coping with increase in the number of pixels and secures quite excellent image performance.SOLUTION: Across an aperture stop S, a first lens group 1G is arranged on an object side and a second lens group 2G is arranged on an image side, respectively. The first lens group 1G has a first lens L1 that is a negative lens on the most object side, and the second lens group 2G is composed of a positive second F lens group 2FG and a negative second R lens group 2RG. Upon focusing, the first lens group 1G, the aperture stop S and the second F lens group 2FG remain stationary, and only the second R lens group 2RG moves in an optical axis direction. A position of an image principal point with respect to the imaging optical system is fallen within a proper range, so that correction of various kinds of aberrations is facilitated, and miniaturization is attained.

Description

  The present invention relates to improvement of a single-focus imaging optical system for forming a subject image in various cameras including a so-called silver salt camera, in particular, a digital camera and a video camera, and more particularly to a digital camera, a digital video camera, and the like. The present invention relates to an imaging optical system in an imaging apparatus using electronic imaging means, a camera apparatus using such an imaging optical system, and a portable information terminal apparatus having an imaging function.

The market of so-called digital cameras and the like that acquire digital image data of a subject using a solid-state imaging device is a very large market, and the demands of users for this type of digital camera and the like are diverse. Among them, the category of a high-quality compact camera equipped with an imaging lens composed of a high-performance single-focus optical system has gained a certain level of support from users and is highly expected. As a request from the user, in addition to high performance, the F number is small, that is, it has a large diameter, but it has high portability, that is, a small weight and high weight. In addition to this, in recent years, a high autofocus speed and a quiet operation sound are also required.
Here, in terms of high performance, in addition to having a resolution corresponding to at least 10 million to 20 million pixel image sensors, there is little coma flare due to the wide open aperture, high contrast and the periphery of the angle of view. It is necessary that the point image is not deformed to a part, the chromatic aberration is small, no unnecessary coloring is generated even in a portion having a large luminance difference, the distortion is small, and a straight line can be drawn as a straight line.
Further, in terms of increasing the aperture, it is desired to have an F number of about 2.8 or less because it is necessary to differentiate from a general compact camera equipped with a zoom lens.

In terms of downsizing, it is necessary to keep the optical total length and lens diameter small. Furthermore, in terms of miniaturization during non-photographing, a retractable type is a mechanism that shortens the overall lens length by shortening the air gap on the optical axis in the photographic optical system such as before and after the aperture and back focus during non-photographing. It is necessary to have.
In terms of improving the speed and quietness during autofocus, it is desirable to reduce the amount of movement required for focusing and to minimize the load on the driving source of the focusing mechanism, and to optimize the refractive power of the optical system of the focusing unit It is also necessary to reduce the size, reduce the weight of the driven parts, and simplify the driving method.
In addition, since there are many users who want a certain wide angle of view, the angle of view equivalent to 28 mm is equivalent to 28 mm with a focal length converted to a 35 mm silver salt camera (so-called Leica version), that is, a half angle of view of 38 degrees. The above is desirable.
Typical examples of focusing methods for wide-angle single-focus lenses include an overall extension method that moves the entire optical system, and an inner focus method that moves the rear and center of the optical system. It is also possible to combine floating systems that move the focusing unit while changing the upper interval.

However, since the entire feeding system moves the entire optical system, the weight of the driven part is large, and it tends to be a disadvantageous problem for increasing the autofocus speed and quieting the operation sound. Even in the inner focus method, if the focus group includes an aperture mechanism or a shutter mechanism, the weight of the driven part increases, and as with the entire extension, disadvantageous problems arise in terms of speeding up and quieter operation noise. It's easy to do. In order to adopt the floating method, a mechanism for associating the movement ratios of at least two or more moving groups is required, and the load on the driving source may be increased.
As conventional examples of the inner focus type in a relatively wide angle single focus lens, Patent Document 1 (Japanese Patent Publication No. 61-138225), Patent Document 2 (Japanese Patent Laid-Open No. 03-265809), Patent Document 3 (Japanese Patent No. 2518182). Gazette), patent document 4 (Japanese Patent No. 3735909), patent document 5 (Japanese Patent No. 4365922), patent document 6 (Japanese Patent Laid-Open No. 2010-271669), and the like.
Further, as a conventional example of the entire payout method, there is one disclosed in Patent Document 7 (Japanese Patent Laid-Open No. 2011-59288).

  However, the optical systems disclosed in Patent Document 1 and Patent Document 2 have a description in the published text that a part of the rear group may be adopted as the focus group. In addition, the half angle of view is about 32.5 degrees, and it is difficult to say that the angle of view is sufficiently wide, and the imaging performance is insufficient as compared with the present invention. The optical system disclosed in Patent Document 3 is sufficiently bright and wide-angle, with an F number of about 2.8 and a half angle of view of about 47, but the optical total length is long, and the number of constituent lenses is 12 and very large. It is hard to say that it is sufficiently small and light. The optical system disclosed in Patent Document 4 has a configuration in which the aperture stop also moves as a unit during focusing, and it is necessary to move a relatively large and heavy stop structure or shutter structure during focusing. It is insufficient in terms of reducing the load. The optical system disclosed in Patent Document 5 performs a floating operation at the time of focusing, and requires a mechanism for defining the movement ratio of the two moving groups that move at the time of focusing. The load on the driving source at the time of focusing is also required. In terms of reduction, it is insufficient. The optical system disclosed in Patent Document 6 has a sufficient F number and angle of view, but has a large optical total length with respect to the image circle, and cannot be said to be a sufficiently small optical system. The imaging lens disclosed in Patent Document 7 has a small total lens length and total lens thickness, and the F number is sufficiently bright as F2.8. However, there is a shortage in imaging performance. The corner is slightly narrow. In addition, since the entire feeding system is adopted for focusing, it is not sufficient in terms of reducing the load on the driving source during focusing as compared with the inner focus type of the present invention.

  The present invention has been made in view of the above-described circumstances, and has a high performance, a wide field angle of about 76 °, a large aperture of about F number 2.8, and a load on a driving source during focusing. It is an object of the present invention to provide a small and lightweight inner focus type imaging optical system having a small size.

In order to achieve the above-described object, the imaging optical system according to the present invention provides:
The first lens group is located on the object side across the aperture stop, and the positive second lens group is located on the image side, and the first lens group has a negative lens closest to the object side, The second lens group includes, in order from the object side, a positive second F lens group and a negative second R lens group. During focusing, the first lens group, the aperture stop, and the second F lens group are Fixed, only the second R lens group moves in the optical axis direction,
The distance on the optical axis from the final surface of the second R lens group to the image side principal point position of the imaging optical system is PPi, and the second R lens group from the front surface of the first lens group at the time of focusing on infinity. When the distance on the optical axis to the final surface is TL,
Conditional formula (1) below:
0.15 <| PPi / TL | <0.55 (1)
It is characterized by satisfying.

According to the first aspect of the present invention, the first lens group is located on the object side across the aperture stop, and the positive second lens group is located on the image side. The second lens group includes, in order from the object side, a positive second F lens group and a negative second R lens group. In focusing, the first lens group, The aperture stop and the second F lens group are fixed, and only the second R lens group moves in the optical axis direction,
The distance on the optical axis from the final surface of the second R lens group to the image side principal point position of the imaging optical system is PPi, and the second R lens group from the front surface of the first lens group at the time of focusing on infinity. When the distance on the optical axis to the final surface is TL,
Conditional formula (1) below:
0.15 <| PPi / TL | <0.55 (1)
Even if it is a small and lightweight inner focus type that has a wide field angle of about 76 ° and a large aperture of about F2.8 or less, but has a small load on the driving source during focusing. Therefore, it is possible to realize an image pickup optical system that can ensure excellent image performance.

It is an optical arrangement figure in the state where it focused on the object at infinity of the imaging optical system of Example 1 concerning the 1st embodiment of the present invention. FIG. 5 is an optical layout diagram in a state where an object in the short distance of the imaging optical system of Example 1 according to the first embodiment of the present invention is in focus (imaging magnification of 0.1). It is an optical arrangement | positioning state in the state which focused on the object at infinity of the imaging optical system of Example 2 which concerns on the 2nd Embodiment of this invention. FIG. 12 is an optical layout diagram in a state where an object in the imaging optical system of Example 2 according to the second exemplary embodiment of the present invention is focused on a short-distance object (imaging magnification is 0.1 times). It is an optical arrangement | positioning state in the state which focused on the object at infinity of the imaging optical system of Example 3 which concerns on the 3rd Embodiment of this invention. It is an optical arrangement | positioning state in the state (imaging magnification 0.1 time) which focused on the short-distance object of the imaging optical system of Example 3 which concerns on the 3rd Embodiment of this invention. It is an optical arrangement | positioning state in the state which focused on the object at infinity of the imaging optical system of Example 4 which concerns on the 4th Embodiment of this invention. It is an optical layout in the state (imaging magnification 0.1 time) which focused on the short-distance object of the imaging optical system of Example 4 which concerns on the 4th Embodiment of this invention. It is an optical arrangement | positioning in the state which focused on the object at infinity of the imaging optical system of Example 5 which concerns on the 5th Embodiment of this invention. It is an optical layout in the state (imaging magnification 0.1 time) which focused on the short-distance object of the imaging optical system of Example 5 which concerns on the 5th Embodiment of this invention. It is an optical arrangement | positioning in the state which focused on the object at infinity of the imaging optical system of Example 6 which concerns on the 6th Embodiment of this invention. It is an optical arrangement | positioning state in the state (imaging magnification 0.1 time) focused on the short-distance object of the imaging optical system of Example 6 which concerns on the 6th Embodiment of this invention. FIG. 3 is an aberration curve diagram showing spherical aberration, astigmatism, distortion aberration, and coma aberration when the imaging optical system according to Example 1 of the present invention shown in FIG. 1 is focused on an object at infinity. FIG. 3 is an aberration curve diagram showing spherical aberration, astigmatism, distortion aberration, and coma aberration when the imaging optical system according to the first embodiment of the present invention shown in FIG. 2 is focused on a short-distance object (magnification 0.1). FIG. 4 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration in a state where the imaging optical system according to Example 2 of the present invention shown in FIG. 3 is focused on an object at infinity. FIG. 5 is an aberration curve diagram showing spherical aberration, astigmatism, distortion aberration and coma aberration in a state where the imaging optical system according to Example 2 of the present invention shown in FIG. 4 is focused on a short-distance object (magnification 0.1 times). . FIG. 6 is an aberration curve diagram showing spherical aberration, astigmatism, distortion aberration, and coma aberration when the imaging optical system according to Example 3 of the present invention shown in FIG. 5 is focused on an object at infinity. FIG. 7 is an aberration curve diagram showing spherical aberration, astigmatism, distortion aberration, and coma aberration when the imaging optical system according to the third embodiment of the present invention shown in FIG. 6 is focused on a short-distance object (magnification 0.1 times). . FIG. 8 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration in a state where the imaging optical system according to Example 4 of the present invention shown in FIG. 7 is focused on an object at infinity. FIG. 9 is an aberration curve diagram showing spherical aberration, astigmatism, distortion aberration, and coma aberration in a state where the imaging optical system according to Example 4 of the present invention shown in FIG. 8 is focused on a short-distance object (magnification 0.1 times). . FIG. 10 is an aberration curve diagram showing spherical aberration, astigmatism, distortion aberration and coma aberration in a state where the imaging optical system according to Example 5 of the present invention shown in FIG. 9 is focused on an object at infinity. FIG. 11 is an aberration curve diagram showing spherical aberration, astigmatism, distortion aberration, and coma aberration when the imaging optical system according to the fifth embodiment of the present invention shown in FIG. 10 is focused on a short-distance object (magnification 0.1 times). . FIG. 12 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration in a state where the imaging optical system according to Example 6 of the present invention shown in FIG. 11 is focused on an object at infinity. FIG. 13 is an aberration curve diagram showing spherical aberration, astigmatism, distortion aberration, and coma aberration when the imaging optical system according to Example 6 of the present invention illustrated in FIG. 12 is focused on a short-distance object (magnification 0.1 times). . It is the perspective view which looked at the external appearance structure of the digital camera as a camera apparatus which concerns on the 7th Embodiment of this invention from the front side, ie, the object side which is a to-be-photographed object. It is the perspective view which looked at the external appearance structure of the digital camera of FIG. 25 from the back side, ie, a photographer side. FIG. 27 is a block diagram schematically illustrating a functional configuration of the digital camera of FIGS. 25 and 26.

Hereinafter, based on an embodiment of the present invention, an imaging optical system, a camera device, and a portable information terminal device according to the present invention will be described in detail with reference to the drawings.
Before describing specific numerical examples, first, an embodiment of the fundamental imaging optical system of the present invention will be described.
The first embodiment of the present invention is an embodiment of an imaging optical system that forms an optical image of an object, and the same applies to the second to sixth embodiments.
In general, coma aberration, astigmatism, curvature of field, and especially distortion are likely to increase as the angle of view increases, and coma aberration and especially spherical aberration increases as the aperture increases. In order to correct this aberration, the optical system tends to become longer. For faster autofocus operation and quiet operation noise, the amount of movement of the focus group required for focusing is somewhat small and light, and in addition, the drive mechanism is simple and the load on the drive source is small. An inner focus method in which only a part of the optical system is necessary and a focus group is desirable. However, when the inner focus method is adopted in a small-angle optical system having a wide angle and a large aperture, it is necessary to suppress or balance fluctuations in spherical aberration, curvature of field, and distortion due to focusing.

The present invention has been found that the following problems can be solved by correcting the aberrations and increasing the length of the optical system by adopting the following configuration.
That is, the present invention includes a first lens group located on the object side with an aperture stop interposed therebetween, and a positive second lens group located on the image side, and the first lens group is most negative on the object side. The second lens group includes, in order from the object side, a positive second F lens group and a negative second R lens group. During focusing, the first lens group, the aperture stop, The imaging optical system in which the second F lens group is fixed and only the second R lens group moves in the optical axis direction has the following characteristics.
In the imaging optical system according to claim 1, in addition to the above-described configuration, the distance on the optical axis from the final surface of the second R lens group to the image side principal point position of the imaging optical system is defined as PPi, and is at infinity. When the distance on the optical axis from the front surface of the first lens group to the final surface of the second R lens group at the time of focusing is TL,
Conditional formula (1) below:
0.15 <| PPi / TL | <0.55 (1)
Is satisfied (corresponding to claim 1).

First, in the imaging optical system of the present invention, a first lens group having a negative lens on the most object side and a negative second R lens group on the most image surface side with an aperture stop interposed therebetween, and a positive lens in the middle. Although it is not strict, the refractive power arrangement has symmetry, and the difficulty of correcting coma aberration, chromatic aberration of magnification, and distortion is reduced. In addition, since the negative second R lens group behind the positive second F lens group is used as the focus group, it moves in a direction away from the optical system at the time of short-distance focusing. It is not necessary to prepare a space for moving the group, and the degree of freedom in design is improved. In the point that it is not necessary to prepare a space for moving the focus group, the same effect can be obtained even if the group closest to the object side is used as the focus group.However, since the drive unit is exposed to the outside, Problems with external forces are likely to occur. Conditional expression (1) indicates an appropriate image-side principal point position with respect to the imaging optical system. When the upper limit of conditional expression (1) is exceeded, the imaging optical system approaches the telephoto type, the symmetry of the refractive power arrangement is lost, and the difficulty of correcting various aberrations increases, and it becomes difficult to ensure the peripheral light quantity ratio. Become. In addition, the maximum emission angle to the image plane (the angle formed by the optical axis of the principal ray with respect to the maximum image height) becomes too large, and there is a risk of causing problems such as false colors and shading on the individual image sensor.
If the lower limit of conditional expression (1) is not reached, the imaging optical system approaches a retrofocus type, and the symmetry of the refractive power arrangement is lost, increasing the difficulty of correcting various aberrations and increasing the back focus. As a result, the size of the entire imaging optical system may be increased.

According to the configuration of the imaging optical system of the present invention, as described above, it is possible to obtain a large effect on aberration correction, which is a wide angle of about 38 degrees half angle of view and a large aperture of about F number 2.8. It is possible to adopt an inner focus method that maintains high image performance even under severe conditions.
In order to achieve better performance, it is desirable to satisfy the following conditional expression.
0.20 <| PPi / TL | <0.50 (1A)
In order to further improve the balance between the aberration correction of the imaging optical system and the focusing performance as the inner focus, the following configuration may be satisfied.
That is, the first lens group includes, in order from the object side, a negative lens having a concave surface directed to the image side, and at least two cemented lenses of a random lens and an unordered positive lens, and the second lens group includes: In order from the object side, the positive second F lens group having a cemented lens of a positive lens and a negative lens having a concave surface facing the image side, and the negative second R lens group including a negative lens having a concave surface facing the object side When the magnification at the time of focusing on infinity of the second R lens group is M2R, the following conditional expression (2):
0.50 <| 1- (M2R) ² | <3.00 (2)
Is satisfied (corresponding to claim 2).

  First, in the imaging optical system of the present invention, the first lens group having a negative lens on the most object side and the negative second R lens group on the most image surface side are arranged with the aperture stop interposed therebetween, By giving positive refractive power to the lens, although it is not strict, symmetry of the refractive power arrangement is given, and the difficulty of correcting coma aberration, chromatic aberration of magnification, and distortion is lowered. Furthermore, the aberration described above is further increased by making both the image side surface of the negative lens closest to the object side of the first lens group and the object side surface of the negative lens in the second R lens group face each other as a concave shape. It is possible to correct by level. By making the image side surface of the negative lens located closest to the object side of the first lens group into a concave shape, it is particularly effective in correcting spherical aberration that increases with an increase in aperture. Further, by arranging a negative lens having a concave surface on the image side in the second F lens group, it is effective in correcting field curvature. Further, the image side component of the first lens group and the second F lens group are lens elements that are close to the aperture stop and perform large correction of spherical aberration, so that image performance is likely to deteriorate due to manufacturing errors. By reducing manufacturing errors to some extent as a lens, it is possible to suppress image performance degradation. The second R lens group that moves in the direction away from the aperture stop at the time of short-distance focusing is configured by a minimum number of one, thereby minimizing the thickness in the optical axis direction and reducing the radial direction of the second R lens group. There is an effect of suppressing enlargement.

Conditional expression (2) represents a paraxial image plane position movement amount per unit movement amount of the second R lens group, and defines an appropriate range of magnification of the second R lens group.
If the lower limit of conditional expression (2) is not reached, the amount of movement required for focusing increases, the autofocus speed decreases, and the focus group moves in the radial direction to ensure the peripheral light quantity ratio even when the focus group moves. There is a risk of upsizing.
If the upper limit value of conditional expression (2) is exceeded, the amount of movement required during focusing is reduced, which is advantageous for speeding up autofocusing, but there is a risk that excessive accuracy is required for the stop position of the focus group. In addition, the power of the second R lens group becomes large, and aberration fluctuations due to focusing become excessive, which may increase the closest shooting distance.
In order to achieve better performance,
Conditional formula (2A) below:
0.65 <| 1- (M2R) ² | <2.50 (2A)
It is desirable to satisfy

In order to exhibit the effect of the above configuration more appropriately, when the maximum image height of the imaging optical system is IY and the distance on the optical axis from the image plane to the exit pupil position of the imaging optical system is AP,
Conditional formula (3) below:
0.60 <| IY / AP | <0.85 (3)
(Corresponding to claim 3).
Conditional expression (3) defines an appropriate range of the exit pupil distance with which the effect of aberration correction is sufficiently exhibited with the configuration of the optical system described above with respect to the image height of the imaging optical system. If the upper limit of conditional expression (3) is exceeded, the optical system approaches the telephoto type, and the maximum exit angle to the image plane (the angle of the principal ray to the maximum image height with the optical axis) becomes too large. This may cause problems such as false color and shading on the individual image sensor. If the lower limit of conditional expression (3) is not reached, the optical system may approach a retrofocus type, the back focus may expand, and the overall size of the imaging optical system may be increased. In any case, if it falls outside the range of the conditional expression (3), the symmetry of refractive power is greatly lost, and in particular, the difficulty of correcting various aberrations such as coma and distortion that increase due to widening of the angle increases. .

For higher performance, when the focal length of the entire system is f and the focal length of the second R lens group is F2R,
Conditional formula (4) below:
0.30 <| f / f2R | <1.30 (4)
(Corresponding to claim 4).
Conditional expression (4) defines an appropriate range of the focal length of the second R lens group with respect to the focal length of the entire system. If the lower limit value of conditional expression (4) is not reached, the image plane position fluctuation amount per unit movement amount of the second R lens group that is the focus group becomes too small, and the speed at the time of autofocus is reduced, or the peripheral light amount The second R lens group may be enlarged in the radial direction for securing.
If the upper limit of conditional expression (4) is exceeded, the amount of image plane position fluctuation per unit movement amount of the second R lens group, which is the focus group, increases, which is advantageous for improving the speed during autofocus. However, there is a possibility that excessive accuracy is required for the stop position of the focus group. Also, it approaches the telephoto type, which is advantageous for downsizing of the entire optical system, but the exchange of aberration correction between the second F lens group and the second R lens group becomes excessive, and the image performance is greatly deteriorated due to manufacturing errors. There is a fear.

In order to achieve better performance,
Conditional formula (4A) below:
0.40 <| f / f2R | <1.20 (4A)
It is desirable to satisfy
For higher performance, when the focal length of the entire system is f and the focal length of the second F lens group is f2F,
Conditional formula (5) below:
0.90 <f / f2F <2.30 (5)
Is satisfied (corresponding to claim 5).
Conditional expression (5) defines an appropriate range of the focal length of the second F lens group with respect to the focal length of the entire system. If the lower limit value of conditional expression (5) is not reached, it is necessary to increase the positive power of the first lens unit, and the symmetry of the refractive power arrangement of the optical system is greatly lost, and in particular, coma aberration and chromatic aberration of magnification. The degree of difficulty in correcting distortion and the like increases. In order to correct it, the entire optical system may be lengthened. If the upper limit value of the conditional expression (5) is exceeded, the exchange of aberration correction between the second F lens group and the second R lens group becomes excessive, and there is a possibility that image performance deterioration due to manufacturing errors becomes large.

In order to achieve better performance,
The following conditional expression (5A)
1.00 <f / f2F <2.20 (5A)
It is desirable to satisfy
For higher performance, when the focal length of the entire system is f and the focal length of the first lens group is f1,
Conditional formula (6) below:
0.01 <f / | f1 | <0.50 (6)
Is satisfied (corresponding to claim 6).
Conditional expression (6) defines an appropriate range of the focal length of the first lens group with respect to the focal length of the entire system. If the lower limit of conditional expression (6) is not exceeded or the upper limit is exceeded, the symmetry of the refractive power arrangement of the optical system is greatly lost, and in particular, the degree of difficulty in correcting coma, chromatic aberration of magnification, distortion, etc. May increase, and the entire optical system may be lengthened to correct it.
In order to perform better aberration correction,
Conditional formula (6A) below:
0.01 <f / | f1 | <0.35 (6A)
It is desirable to satisfy

To achieve higher performance, when the distance on the optical axis from the final surface of the first lens group to the aperture stop at the time of focusing on infinity is Ls and the focal length of the entire system is f,
Conditional formula (7) below:
0.00 <Ls / f <0.10 (7)
Is satisfied (corresponding to claim 7).
Conditional expression (7) defines an appropriate range of the distance on the optical axis between the first lens group and the aperture stop with respect to the focal length of the entire system. If the lower limit of conditional expression (7) is not reached, the upper light beam passing through the second lens group becomes too high, and the second lens group may become large in diameter. If the upper limit value of conditional expression (7) is exceeded, the lower ray passing through the first lens group becomes too low, and the first lens group may become large in diameter.
In order to achieve higher performance, the distance on the optical axis from the first surface of the first lens unit to the final surface of the second R lens unit at the time of focusing on infinity is TL, and the focal length of the entire system is f. When
Conditional formula (8) below:
0.80 <TL / f <1.30 (8)
Is satisfied (corresponding to claim 8).

Conditional expression (8) defines an appropriate range of the total lens length when focusing on infinity with respect to the focal length of the entire system. If the lower limit of conditional expression (8) is not reached, the symmetry of the refractive power arrangement is greatly lost, and in particular, the difficulty of correcting coma aberration, chromatic aberration of magnification, distortion, etc. is increased. There is a risk that the entire optical system may become longer. In addition, in order to increase the refractive power of each surface, it is necessary to use an expensive high refractive index glass material, which leads to high costs or excessive exchange of aberrations, resulting in increased image performance degradation due to manufacturing errors. There is a fear. When the upper limit value of conditional expression (8) is exceeded, it is necessary to dispose a lens at a position far from the entrance pupil or exit pupil, and the optical system may be increased in diameter.
In order to perform better aberration correction,
The following conditional expression (8A):
0.90 <TL / f <1.20 (8A)
It is desirable to satisfy
For higher performance, the distance on the optical axis from the first surface of the first lens group to the image plane is AL, and the distance on the optical axis from the image plane to the exit pupil at the time of focusing on infinity is AP. When
Conditional formula (9) below:
0.40 <| AP / AL | <0.90 (9)
Is satisfied (corresponding to claim 9).

Conditional expression (9) defines an appropriate range of the total optical length with respect to the exit pupil distance. When the lower limit value of conditional expression (9) is not reached, the first lens group is too far from the aperture stop and the first lens group is enlarged in the radial direction, or the first lens group has a strong negative power. Therefore, the symmetry of the refractive power arrangement of the entire optical system is greatly broken. In particular, the difficulty of correcting coma, chromatic aberration of magnification, distortion and the like increases, and the entire optical system may be lengthened to correct it. If the upper limit value of conditional expression (9) is exceeded, excessive aberrations will be exchanged in the first lens group, and image performance deterioration due to manufacturing errors will increase. There is a possibility that the symmetry of the arrangement is greatly broken and the same adverse effect as that of falling below the lower limit value may occur.
In order to perform better aberration correction,
The following conditional expression (9A):
0.50 <| AP / AL | <0.80 (9A)
It is desirable to satisfy
The second R lens group is preferably composed of a single negative lens. By configuring the second R lens group that moves in the direction away from the aperture stop at the time of short-distance focusing with a minimum number of one, the thickness in the optical axis direction is minimized, and the radial direction of the second R lens group Has the effect of suppressing the increase in size. Further, it is desirable that the image side of the first negative lens in the first lens group has a concave shape. This is because it is particularly effective for correcting spherical aberration that increases as the diameter increases.

By configuring the imaging optical system in a camera device such as a so-called digital camera by the imaging optical system described above,
It has a wide angle of view of about 76 degrees (half angle of view is 38 degrees) and a large aperture with an F value of about F2.8, but it is small enough in terms of total lens length, total lens thickness, and lens diameter. Even in the focus type, various aberrations can be sufficiently reduced to ensure very good image performance, and a high-quality imaging lens as an imaging optical system can be used as a compact and high-quality camera device ( Corresponding to claim 10).
In addition, the camera device may have a function of using a captured image as digital information (corresponding to claim 11).
In addition, the imaging optical system described above constitutes an imaging optical system in an information device such as a portable information terminal device having an imaging function,
Similarly, a small and high performance imaging optical system may be used as the imaging optical system of the imaging function unit, and a small portable information terminal device capable of obtaining high image quality may be used (corresponding to claim 12).

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, and Example 6 described below are the first embodiment, second embodiment, and third embodiment of the present invention. It is an Example by the specific numerical example of the imaging optical system which concerns on form, 4th Embodiment, 5th Embodiment, and 6th Embodiment. The seventh embodiment is an embodiment of a camera device or a portable information terminal device using the imaging optical system shown in Examples 1 to 6 as an imaging lens.
1 and 2 are diagrams for explaining an imaging lens as an imaging optical system in Example 1 according to the first embodiment of the present invention. FIG. 3 and FIG. 4 are for explaining the imaging lens in Example 2 according to the second embodiment of the present invention. FIG. 5 and FIG. 6 are for explaining the imaging lens in Example 3 according to the third embodiment of the present invention. 7 and 8 are for explaining the imaging lens in Example 4 according to the fourth embodiment of the present invention. FIGS. 9 and 10 are for explaining the imaging lens in Example 5 according to the fifth embodiment of the present invention. FIG. 11 and FIG. 12 are for explaining the imaging lens in Example 6 according to the sixth embodiment of the present invention.

In all of Examples 1 to 6, the maximum image height is 14.3 mm.
In the imaging lens as the imaging optical system of each of the first to sixth embodiments, the parallel plate F disposed on the image side of the second R lens group includes various filters such as an optical low-pass filter and an infrared cut filter. In addition, a cover glass (seal glass) of a light receiving element such as a CMOS sensor is assumed.
In addition, the glass type of the optical glass used in each Example of these Examples 1 to 6 is the optical glass type of the products of HOYA Corporation (HOYA), Ohara Corporation (OHARA), and Shot Japan Corporation (SCHOTT). It is shown by name.
Aberrations in Examples 1 to 6 are corrected at a high level, and spherical aberration and axial chromatic aberration are very small. Astigmatism, curvature of field and lateral chromatic aberration are also sufficiently small, and coma and disturbance of the color difference are suppressed to the outermost periphery. By forming an imaging lens as an imaging optical system as in the present invention, the angle of view is 76 degrees (half angle of view is 38 degrees) and a wide angle, and the F value is about F2.8 and a large aperture. Moreover, it is clear from Examples 1 to 6 that the lens overall length, the total lens thickness, and the lens diameter are sufficiently reduced in size and have a very good image performance. is there.

The meanings of symbols common to the first to sixth embodiments are as follows.
f: Focal length of the entire optical system F: F value (F number)
ω: Half field angle Y: Maximum image height R: Radius of curvature (Paraxial radius of curvature for aspheric surfaces)
D: Distance between surfaces Nd: Refractive index νd: Abbe number In Examples 1 to 6, some lens surfaces are aspherical. In order to form an aspherical surface, there is a configuration in which each lens surface is directly aspherical like a so-called molded aspherical lens.

In addition, there is a configuration in which an aspheric surface is obtained by laying a resin thin film that forms an aspheric surface on the lens surface of a spherical lens, such as a so-called hybrid aspheric lens. Any of them may be used. In such an aspherical shape, the displacement in the optical axis direction (that is, the amount of aspherical surface in the optical axis direction) X at the position of the height H from the optical axis with respect to the vertex of the surface is an aspherical cone. The constant is K, the fourth-order aspheric coefficient is A ₄ , the sixth-order aspheric coefficient is A ₆ , the eighth-order aspheric coefficient is A ₈ , the tenth-order aspheric coefficient is A ₁₀ , and the paraxial radius of curvature is It is defined by the following formula (10) where the reciprocal of R is C.

FIG. 1 shows an optical arrangement diagram in a state where an object at infinity is in focus in the imaging optical system of Example 1 according to the first embodiment of the present invention.
FIG. 2 shows an optical arrangement diagram in the state where the short-distance object of the imaging optical system of Example 1 according to the first embodiment of the present invention is in focus (imaging magnification of 0.1).
That is, as shown in FIGS. 1 and 2, the optical system of the imaging lens according to Example 1 of the present invention sequentially includes a first lens L1, a second lens L2, and a second lens from the object side to the image side. A third lens L3, a fourth lens L4, an aperture stop S, a fifth lens L5, a sixth lens L6, a seventh lens L7, and an eighth lens L8 are arranged. The second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6 each constitute a cemented lens, and has a so-called five-group eight-lens configuration.
Focusing on the lens group configuration, the first lens group 1G is configured by the first lens L1 to the fourth lens L4. The fifth lens L5 to the eighth lens L8 constitute a second lens group 2G. The fifth lens L5, the sixth lens L6, and the seventh lens L7 constitute a second F lens group 2FG having a positive refractive power, and the eighth lens L8 constitutes a second R lens group 2RG having a negative refractive power. ing. That is, the optical system of the imaging lens shown in FIGS. 1 and 2 moves the first lens group 1G, aperture stop S, second F lens group 2FG, and second R lens group 2RG from the object side to the image side. The arrangement is sequentially arranged.

Specifically, the first lens group 1G is formed of a negative lens having a negative meniscus shape in which an aspherical surface is formed on the image side sequentially from the object side to the image side and a concave surface is directed to the image side. One lens L1, a second lens L2 made of a positive lens having a convex surface with a larger curvature than the object side on the image side, and a biconcave shape with a concave surface having a larger curvature on the image side than the object side A third lens L3 made of a negative lens and a fourth lens L4 made of a positive lens having a positive meniscus shape with a convex surface facing the object side are arranged so as to exhibit positive refractive power. Note that the three lenses of the second lens L2, the third lens L3, and the fourth lens L4 are closely bonded to each other and are integrally joined to form a cemented lens composed of three lenses.
An aperture stop S is disposed between the first lens group 1G and the second lens group 2G.
The second F lens group 2FG includes, from the object side to the image side, a fifth lens L5 including a positive lens having a biconvex shape with a convex surface having a larger curvature than the object side surface in order from the object side; A sixth lens L6 made of a negative lens having a biconcave shape with a concave surface having a larger curvature than the image side surface and a seventh lens L7 made of a positive lens having a positive meniscus shape with the convex surface facing the image side. Thus, it is configured to exhibit a positive refractive power. The two lenses of the fifth lens L5 and the sixth lens L6 of the second F lens group 2FG are closely bonded to each other and are integrally joined to form a cemented lens composed of two lenses. The second R lens group 2RG is arranged with a biconcave eighth lens L8 having a concave surface with a larger curvature than the image side surface on the object side and an aspheric surface on the image side, and has a negative refractive power. It is configured as shown.

Further, behind the second lens group 2G, that is, on the image side, various filters such as an optical low-pass filter and an infrared cut filter, and a cover glass (seal glass) of the light receiving element are shown as equivalent parallel plates. A filter glass F is disposed.
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, the filter glass F described above as a representative of these is equivalently shown as two parallel flat plates. In Examples 2 to 6, the filter glass F is equivalently shown as two parallel flat plates. Similarly to the filter glass F in this example, the back insertion glass, the low-pass filter, and the infrared cut It represents at least one of glass and cover glass.
At the time of focusing, the first lens group 1G, the aperture stop S, and the second F lens group 2FG are fixed, and only the second R lens group 2RG moves in the optical axis direction to perform focusing.
In the above embodiment, the second R lens group 2RG is constituted by one negative lens. Although there is no denying that the lens is composed of a plurality of lenses, by configuring the second R lens group 2RG with a minimum number of one lens, the thickness in the optical axis direction is minimized, and the second R lens group 2RG There is an effect of suppressing enlargement in the radial direction.

When focusing on a short distance, the second R lens group 2RG is positioned at the position shown in FIG. 1 when focused at infinity (when focused on an object at infinity). When focusing on an object (imaging magnification, 0.1 times), it moves in the direction away from the aperture stop S (the direction indicated by the arrow shown in FIG. 1) and moves to the position shown in FIG.
At the time of short distance focusing, it is narrowed down in a direction away from the optical system, so that it is not necessary to prepare a space for moving the focus group in the optical system in advance, and the degree of freedom in design is improved.
FIG. 1 also shows the surface numbers of the optical surfaces in the imaging optical system. 1 and FIG. 2 are used independently for each embodiment in order to avoid complicated explanation due to an increase in the number of digits of the reference code. Common reference numerals are attached.
In Example 1, the focal length f, the open F value Fno, and the half angle of view ω [degrees] of the entire optical system are f = 18.30, Fno = 2.88, and ω = 38.26, respectively. The optical characteristics of each optical element in Example 1, such as the radius of curvature of the optical surface (paraxial radius of curvature for an aspheric surface) R, the spacing between adjacent optical surfaces D, the refractive index Nd, the Abbe number νd, and the glass type are as follows: Table 1 is as follows.

In Table 1, the lens surface with the surface number indicated by adding “* (asterisk)” to the surface number is an aspherical surface.
That is, in Table 1, the optical surfaces of the second surface, the twelfth surface, and the fourteenth surface marked with “*” are aspheric surfaces, and the parameters of each aspheric surface in the equation (10) are It is.
In addition, after the glass type name of the glass material of the optical glass lens, the manufacturer name is abbreviated as OHARA (Ohara Corporation) or HOYA (HOYA Corporation). Although these are the same also about another Example, in Example 3, SCHOTT (Shot Japan Co., Ltd.) is used in the 1st lens L1.
○ Aspherical surfaces (surfaces with * symbol on surface numbers)
Second side K = 1.30506
A ₄ = 2.33754E-04,
A ₆ = 6.99258E-06
A ₈ = −1.86192E-07,
A ₁₀ = 4.48314E-09

12th surface K = -11.52411,
A ₄ = −5.09057E-04,
A ₆ = 1.33373E-05,
A ₈ = −2.19326E-07,
A ₁₀ = 2.14888E-09
14th surface K = 0.0,
A ₄ = −2.69198E-05,
A ₆ = 1.56982E-06
A ₈ = −1.09430E−08
In Example 1, the variable distance DA between the seventh lens L7 of the second F lens group 2FG and the eighth lens L8 of the second R lens group 2RG shown in FIGS. 1 and 2 and the eighth lens L8 and the filter are used. The variable distance DB between the glass F changes as shown in Table 2 when the object distance changes to infinity and the imaging magnification changes to a short distance of 0.1 times.

  In this case, values corresponding to the conditional expressions (1) to (9) are as shown in Table 3 below, which satisfy the conditional expressions (1) to (9), respectively.

FIG. 13 shows various aberrations in the d-line and g-line in the state where the imaging optical system according to Example 1 is focused on an object at infinity, that is, spherical aberration, astigmatism, distortion aberration, and coma aberration. An aberration curve diagram is shown.
FIG. 14 shows various aberrations in the d-line and g-line in a state where the imaging optical system according to Example 1 is focused on a short-distance object (magnification 0.1 times), that is, spherical aberration, astigmatism, Each aberration curve figure of a distortion aberration and a coma aberration is shown.
In the aberration curve diagrams of FIGS. 13 and 14, a broken line in spherical aberration represents a sine condition, a solid line in astigmatism represents sagittal, and a broken line represents meridional. Further, d and g in the respective aberration diagrams of spherical aberration, astigmatism, and coma aberration represent d-line and g-line, respectively. The same applies to the aberration curve diagrams according to other examples.

FIG. 3 shows an optical arrangement diagram in a state where an object at infinity is in focus in the imaging optical system of Example 2 according to the second embodiment of the present invention.
FIG. 4 shows an optical layout diagram in the state where the short-distance object of the imaging optical system of Example 2 according to the second embodiment of the present invention is in focus (imaging magnification 0.1 times).
In other words, the optical system of the imaging lens according to Example 2 of the present invention, as shown in FIGS. 3 and 4, sequentially from the object side to the image side, the first lens L1, the second lens L2, and the second lens A third lens L3, a fourth lens L4, an aperture stop S, a fifth lens L5, a sixth lens L6, a seventh lens L7, and an eighth lens L8 are arranged, and the second lens L2, the third lens L3, and the third lens L3 are arranged. The four lenses L4, the fifth lens L5, and the sixth lens L6 each constitute a cemented lens and have a so-called five-group eight-lens configuration.
Focusing on the lens group configuration, the first lens group 1G is configured by the first lens L1 to the fourth lens L4. The fifth lens L5 to the eighth lens L8 constitute a second lens group 2G. The fifth lens L5, the sixth lens L6, and the seventh lens L7 constitute a second F lens group 2FG having a positive refractive power, and the eighth lens L8 constitutes a second R lens group 2RG having a negative refractive power. ing. That is, the optical system of the imaging lens shown in FIGS. 3 and 4 moves the first lens group 1G, the aperture stop S, the second F lens group 2FG, and the second R lens group 2RG from the object side to the image side. The arrangement is sequentially arranged.

Specifically, the first lens group 1G is formed of a negative lens having a negative meniscus shape in which an aspherical surface is formed on the image side sequentially from the object side to the image side and a concave surface is directed to the image side. One lens L1, a second lens L2 made of a positive lens having a convex surface with a larger curvature than the object side on the image side, and a biconcave shape with a concave surface having a larger curvature on the image side than the object side A third lens L3 made of a negative lens and a fourth lens L4 made of a positive lens having a positive meniscus shape with a convex surface facing the object side are arranged so as to exhibit positive refractive power. Note that the three lenses of the second lens L2, the third lens L3, and the fourth lens L4 are closely bonded to each other and are integrally joined to form a cemented lens composed of three lenses.
An aperture stop S is disposed between the first lens group 1G and the second lens group 2G.
The second F lens group 2FG includes, from the object side to the image side, a fifth lens L5 including a positive lens having a biconvex shape with a convex surface having a larger curvature than the object side surface in order from the object side; A positive lens having a positive meniscus shape having a convex surface facing the image side and an aspherical surface facing the image side. A seventh lens L7 made of a lens is arranged so as to exhibit positive refractive power. The two lenses of the fifth lens L5 and the sixth lens L6 of the second F lens group 2FG are closely bonded to each other and are integrally joined to form a cemented lens composed of two lenses. The second R lens group 2RG is arranged with a biconcave eighth lens L8 having a concave surface with a larger curvature than the image side surface on the object side and an aspheric surface on the image side, and has a negative refractive power. It is configured as shown.

Further, behind the second lens group 2G, that is, on the image side, various filters such as an optical low-pass filter and an infrared cut filter, and a cover glass (seal glass) of the light receiving element are shown as equivalent parallel plates. A filter glass F is disposed.
During focusing, the first lens group 1G, the aperture stop S, and the second F lens group 2FG are fixed, and only the second R lens group 2RG is moved in the optical axis direction for focusing.
In the above embodiment, the second R lens group 2RG is constituted by one negative lens. Although there is no denying that the lens is composed of a plurality of lenses, by configuring the second R lens group 2RG with a minimum number of one lens, the thickness in the optical axis direction is minimized, and the second R lens group 2RG There is an effect of suppressing enlargement in the radial direction.
When the second R lens group 2RG is at the position shown in FIG. 3 at the time of focusing on an object at infinity (when focused on an object at infinity), the object at a short distance (imaging magnification, 0. When focusing to (1 ×), the lens moves in the direction away from the aperture stop S (the direction indicated by the arrow shown in FIG. 3) and moves to the position shown in FIG.
At the time of short distance focusing, it is narrowed down in a direction away from the optical system, so that it is not necessary to prepare a space for moving the focus group in the optical system in advance, and the degree of freedom in design is improved.

FIG. 3 also shows the surface numbers of the optical surfaces in the imaging optical system. Note that each reference symbol shown in FIG. 3 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, the reference symbol common to FIGS. The code | symbol is attached | subjected.
In Example 2, the focal length f, the open F value Fno, and the half angle of view ω [degrees] of the entire optical system are f = 18.31, Fno = 2.88, and ω = 38.22, respectively. The optical characteristics of each optical element in Example 2, such as the radius of curvature of the optical surface (paraxial radius of curvature for an aspheric surface) R, the distance between adjacent optical surfaces D, the refractive index Nd, the Abbe number νd, and the glass type are as follows: Table 4 is as follows.

In Table 4, the lens surface with the surface number indicated by adding “* (asterisk)” to the surface number is an aspherical surface.
That is, in Table 4, the optical surfaces of the second surface, the twelfth surface, and the fourteenth surface marked with “*” are aspheric surfaces, and the parameters of each aspheric surface in the equation (10) are as follows. It is.
○ Aspherical surfaces (surfaces with * symbol on surface numbers)
Second surface K = −0.34160,
A ₄ = 2.48255E-04,
A ₆ = 6.37217E-06
A ₈ = −1.72004E-07,
A ₁₀ = 4.441760E-09

12th surface K = -11.13558,
A ₄ = −4.40431E-04,
A ₆ = 1.20261E-05,
A ₈ = -1.93275E-07,
A ₁₀ = 2.45001E-09
14th surface K = 0.0,
A ₄ = −2.229209E-05,
A ₆ = 1.28403E-06
A ₈ = −1.11975E-08,
A ₁₀ = 3.55281E-11
In Example 2, the variable distance DA between the seventh lens L7 of the second F lens group 2FG and the eighth lens L8 of the second R lens group 2RG shown in FIGS. 3 and 4 and the eighth lens L8 and the filter are used. The variable distance DB between the glass F changes as shown in Table 5 when the imaging magnification changes to change the object distance to infinity and the imaging magnification to a short distance of 0.1.

  In this case, values corresponding to the conditional expressions (1) to (9) are as shown in Table 6 below, which satisfy the conditional expressions (1) to (9), respectively.

FIG. 15 shows various aberrations in the d-line and g-line in a state where the imaging optical system according to Example 2 is focused on an object at infinity, that is, spherical aberration, astigmatism, distortion aberration, and coma aberration. An aberration curve diagram is shown.
FIG. 16 shows various aberrations in the d-line and g-line in a state where the imaging optical system according to Example 2 is focused on a short-distance object (magnification 0.1 times), that is, spherical aberration, astigmatism, Each aberration curve figure of a distortion aberration and a coma aberration is shown.
In the aberration curve diagrams of FIGS. 15 and 16, the broken line in spherical aberration represents the sine condition, the solid line in astigmatism represents sagittal, and the broken line represents meridional. Further, d and g in the respective aberration diagrams of spherical aberration, astigmatism, and coma aberration represent d-line and g-line, respectively. The same applies to the aberration curve diagrams according to other examples.

FIG. 5 shows an optical arrangement diagram in a state where an object at infinity is in focus in the imaging optical system of Example 3 according to the third embodiment of the present invention.
FIG. 6 shows an optical arrangement diagram in a state where the short distance object of the imaging optical system of Example 3 according to the third embodiment of the present invention is in focus (imaging magnification of 0.1).
In other words, the optical system of the imaging lens according to Example 3 of the present invention, as shown in FIGS. 5 and 6, sequentially from the object side to the image side, the first lens L1, the second lens L2, the first lens A third lens L3, a fourth lens L4, an aperture stop S, a fifth lens L5, a sixth lens L6, a seventh lens L7, and an eighth lens L8 are arranged, and the second lens L2, the third lens L3, The four lenses L4, the fifth lens L5, and the sixth lens L6 each constitute a cemented lens and have a so-called five-group eight-lens configuration.
Focusing on the lens group configuration, the first lens group 1G is configured by the first lens L1 to the fourth lens L4. The fifth lens L5 to the eighth lens L8 constitute a second lens group 2G. The fifth lens L5, the sixth lens L6, and the seventh lens L7 constitute a second F lens group 2FG having a positive refractive power, and the eighth lens L8 constitutes a second R lens group 2RG having a negative refractive power. ing. That is, the optical system of the imaging lens shown in FIG. 5 sequentially arranges the first lens group 1G, the aperture stop S, the second F lens group 2FG, and the second R lens group 2RG from the object side to the image side. The configuration is as follows.

Specifically, the first lens group 1G is formed of a negative lens having a negative meniscus shape in which an aspherical surface is formed on the image side sequentially from the object side to the image side and a concave surface is directed to the image side. One lens L1, a second lens L2 made of a positive lens having a convex surface with a larger curvature than the object side on the image side, and a biconcave shape with a concave surface having a larger curvature on the image side than the object side A third lens L3 made of a negative lens and a fourth lens L4 made of a positive lens having a positive meniscus shape with a convex surface facing the object side are arranged so as to exhibit positive refractive power. Note that the three lenses of the second lens L2, the third lens L3, and the fourth lens L4 are closely bonded to each other and are integrally joined to form a cemented lens composed of three lenses.
An aperture stop S is disposed between the first lens group 1G and the second lens group 2G.
The second lens group 2FG includes, from the object side to the image side, a fifth lens L5 composed of a positive lens having a biconvex shape with a convex surface having a larger curvature than the object-side surface sequentially toward the image side, A negative lens having a biconcave shape with a concave surface having a larger curvature than the image side surface and a positive meniscus shape having a convex surface on the image side and an aspheric surface on the image side is formed. A seventh lens L7 made of a positive lens is arranged so as to exhibit positive refractive power. The two lenses of the fifth lens L5 and the sixth lens L6 of the second F lens group 2FG are closely bonded to each other and are integrally joined to form a cemented lens composed of two lenses. The second R lens group 2RG is configured to have a negative refracting power by disposing a negative meniscus eighth lens L8 having a concave surface on the object side and an aspheric surface on the image side.

Further, behind the second lens group 2G, that is, on the image side, various filters such as an optical low-pass filter and an infrared cut filter, and a cover glass (seal glass) of the light receiving element are shown as equivalent parallel plates. A filter glass F is disposed.
During focusing, the first lens group 1G, the aperture stop S, and the second F lens group 2FG are fixed, and only the second R lens group 2RG is moved in the optical axis direction for focusing.
In the above embodiment, the second R lens group 2RG is constituted by one negative lens. Although there is no denying that the lens is composed of a plurality of lenses, by configuring the second R lens group 2RG with a minimum number of one lens, the thickness in the optical axis direction is minimized, and the second R lens group 2RG There is an effect of suppressing enlargement in the radial direction.
When focusing on a short distance, the second R lens group 2RG is positioned at the position shown in FIG. 5 when focused at infinity (when focused on an object at infinity). When focusing on an object (imaging magnification, 0.1 times), it moves in the direction away from the aperture stop S (the direction indicated by the arrow shown in FIG. 5) and moves to the position shown in FIG.
At the time of short distance focusing, it is narrowed down in a direction away from the optical system, so that it is not necessary to prepare a space for moving the focus group in the optical system in advance, and the degree of freedom in design is improved.
In Example 3, the focal length f, the open F value Fno, and the half angle of view ω [degrees] of the entire optical system are f = 18.30, Fno = 2.88, and ω = 38.27, respectively. The optical characteristics of each optical element in Example 3, such as the radius of curvature of the optical surface (paraxial radius of curvature for an aspherical surface) R, the surface spacing D of adjacent optical surfaces, the refractive index Nd, the Abbe number νd, and the glass type are as follows: Table 7 below.

In Table 7, the lens surface with the surface number indicated by adding “* (asterisk)” to the surface number is an aspherical surface.
That is, in Table 7, the optical surfaces of the second surface, the twelfth surface, and the fourteenth surface marked with “*” are aspheric surfaces, and the parameters of each aspheric surface in the equation (10) are as follows. It is.
○ Aspherical surfaces (surfaces with * symbol on surface numbers)
Second surface K = −0.52519,
A ₄ = 2.40446E-04,
A ₆ = 6.103331E-06
A ₈ = −1.19767E-07,
A ₁₀ = 3.66663E-09

12th surface K = -11.824,
A ₄ = -3.97190E-04,
A ₆ = 1.18087E-05,
A ₈ = −1.650402E-07,
A ₁₀ = 2.03608E-09
14th surface K = 0.0,
A ₄ = −4.009017E-05,
A ₆ = 1.31296E-06,
A ₈ = −7.48800E−09,
A ₁₀ = 4.32750E-12
In Example 3, the variable distance DA between the seventh lens L7 of the second F lens group 2FG and the eighth lens L8 of the second R lens group 2RG shown in FIGS. 5 and 6 and the eighth lens L8 and the filter are used. The variable distance DB between the glass F changes as shown in Table 8 when the imaging magnification changes and the object distance changes to infinity and the imaging magnification changes to a short distance of 0.1.

  In this case, values corresponding to the conditional expressions (1) to (9) are as shown in Table 9 below, which satisfy the conditional expressions (1) to (9), respectively.

FIG. 17 shows various aberrations in the d-line and g-line in the state in which the imaging optical system according to Example 3 is focused on an object at infinity, that is, spherical aberration, astigmatism, distortion aberration, and coma aberration. An aberration curve diagram is shown.
FIG. 18 shows various aberrations in the d-line and g-line in a state where the imaging optical system according to Example 3 is focused on a short-distance object (magnification 0.1 times), that is, spherical aberration, astigmatism, Each aberration curve figure of a distortion aberration and a coma aberration is shown.
In the aberration curve diagrams of FIGS. 17 and 18, a broken line in spherical aberration represents a sine condition, a solid line in astigmatism represents sagittal, and a broken line represents meridional. Further, d and g in the respective aberration diagrams of spherical aberration, astigmatism, and coma aberration represent d-line and g-line, respectively. The same applies to the aberration curve diagrams according to other examples.

FIG. 7 shows an optical arrangement diagram in a state where an object at infinity is in focus in the imaging optical system of Example 4 according to the fourth embodiment of the present invention.
Further, FIG. 8 shows an optical layout diagram in a state where an object in the short distance of the imaging optical system of Example 4 according to the fourth embodiment of the present invention is in focus (imaging magnification of 0.1).
In the imaging optical system of Example 4 according to the fourth embodiment, the configuration of the first lens group 1G includes three configurations of a negative lens, a positive lens, and a negative lens. Unlike the other embodiments, the fourth embodiment does not have a fourth lens (positive lens).
That is, as shown in FIGS. 7 and 8, 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, a first lens from the object side to the image side. A third lens L3, an aperture stop S, a fourth lens L4, a fifth lens L5, a sixth lens L6, and a seventh lens L7 are disposed. The second lens L2, the third lens L3, and the fourth lens L4 and the fourth lens L4 are arranged. Each of the five lenses L5 constitutes a cemented lens, and has a so-called five-group seven-element configuration.
Focusing on the lens group configuration, the first lens group 1G is constituted by the first lens L1 to the third lens L3. The fourth lens L4 to the seventh lens L7 constitute a second lens group 2G. The fourth lens L4, the fifth lens L5, and the sixth lens L6 constitute a second F lens group 2FG having a positive refractive power, and the seventh lens L7 constitutes a second R lens group 2RG having a negative refractive power. ing. That is, the optical system of the imaging lens shown in FIG. 7 and FIG. 8 moves the first lens group 1G, aperture stop S, second F lens group 2FG, and second R lens group 2RG from the object side to the image side. The arrangement is sequentially arranged.

Specifically, the first lens group 1G is formed of a negative lens having a negative meniscus shape in which an aspherical surface is formed on the image side sequentially from the object side to the image side and a concave surface is directed to the image side. 1 lens L1, a second lens L2 made of a positive lens having a convex surface with a larger curvature than the image side on the object side, and a biconcave shape with a concave surface having a larger curvature on the image side than the object side The third lens L3 is a negative lens. Note that the two lenses, the second lens L2 and the third lens L3, are closely bonded to each other and integrally joined to form a cemented lens composed of two lenses.
An aperture stop S is disposed between the first lens group 1G and the second lens group 2G.
The second lens group 2FG includes, from the object side to the image side, a fourth lens L4 including a positive lens having a biconvex shape with a convex surface having a larger curvature than the object side surface facing the image side, and the object side A fifth lens L5 comprising a negative lens having a biconcave shape with a concave surface having a larger curvature than the image side surface, and a convex surface having a larger curvature than the object side on the image side and an aspheric surface on the image side. A sixth lens L6 made of a positive lens having a biconvex shape is arranged so as to exhibit a positive refractive power. The two lenses, the fourth lens L4 and the fifth lens L5, of the second F lens group 2FG are closely bonded to each other and integrally joined to form a cemented lens composed of two lenses. The second R lens group 2RG has negative refractive power by disposing a biconcave seventh lens L7 having a concave surface having a larger curvature than the image side surface on the object side and aspheric surfaces on both sides. It is configured as follows.

Further, behind the second lens group 2G, that is, on the image side, various filters such as an optical low-pass filter and an infrared cut filter, and a cover glass (seal glass) of the light receiving element are shown as equivalent parallel plates. A filter glass F is disposed.
During focusing, the first lens group 1G, the aperture stop S, and the second F lens group 2FG are fixed, and only the second R lens group 2RG is moved in the optical axis direction for focusing.
In the above embodiment, the second R lens group 2RG is constituted by one negative lens. Although there is no denying that the lens is composed of a plurality of lenses, by configuring the second R lens group 2RG with a minimum number of one lens, the thickness in the optical axis direction is minimized, and the second R lens group 2RG There is an effect of suppressing enlargement in the radial direction.
When focusing on a short distance, the second R lens group 2RG is positioned at the position shown in FIG. 7 when focused at infinity (when focused on an object at infinity). When focusing on an object (imaging magnification, 0.1 times), the lens moves in a direction away from the aperture stop S (a direction indicated by an arrow in FIG. 7) and moves to a position shown in FIG.

At the time of short distance focusing, it is narrowed down in a direction away from the optical system, so that it is not necessary to prepare a space for moving the focus group in the optical system in advance, and the degree of freedom in design is improved.
In Example 4, the focal length f, the open F value Fno, and the half angle of view ω [degrees] of the entire optical system are f = 18.30, Fno = 2.88, and ω = 38.27, respectively. The optical characteristics of each optical element in Example 4, such as the radius of curvature of the optical surface (paraxial radius of curvature for an aspherical surface) R, the surface spacing D of adjacent optical surfaces, the refractive index Nd, the Abbe number νd, and the glass type are as follows: Table 10 is shown below.

In Table 10, the lens surface with the surface number indicated by adding “* (asterisk)” to the surface number is an aspherical surface.
That is, in Table 10, the optical surfaces of the second surface, the eleventh surface, the twelfth surface, and the thirteenth surface marked with “*” are aspherical surfaces. It is as follows.
○ Aspherical surfaces (surfaces with * symbol on surface numbers)
Second side K = −0.50027,
A ₄ = 2.63913E-04,
A ₆ = 4.001323E-06
A ₈ = −3.32741E-08,
A ₁₀ = 2.64457E-09
11th surface K = −5.88863
A ₄ = -5.00729E-04,
A ₆ = 9.73446E-06
A ₈ = −1.84289E-07,
A ₁₀ = 1.77095E-09

12th surface K = -1.42501,
A ₄ = 5.37431E-05,
A ₆ = −2.15186E-06
A ₈ = 2.08751E-08
13th surface K = 0.0,
A ₄ = -3.80354E-05,
A ₆ = 1.69297E-06
A ₈ = −1.09924E−08
In Example 4, the variable distance DA between the sixth lens L6 of the second F lens group 2FG and the seventh lens L7 of the second R lens group 2RG shown in FIGS. 7 and 8, and the seventh lens L7 and the filter The variable distance DB between the glass F changes as shown in Table 11 when the imaging magnification changes to change the object distance to infinity and the imaging magnification to a short distance of 0.1.

  In this case, values corresponding to the conditional expressions (1) to (9) are as shown in the following table 12, which satisfy the conditional expressions (1) to (9), respectively.

FIG. 19 shows various aberrations in the d-line and g-line in the state in which the imaging optical system according to Example 4 is focused on an object at infinity, that is, spherical aberration, astigmatism, distortion aberration, and coma aberration. An aberration curve diagram is shown.
FIG. 20 shows various aberrations in the d-line and g-line in a state where the imaging optical system according to Example 4 is focused on a short-distance object (magnification 0.1 times), that is, spherical aberration, astigmatism, Each aberration curve figure of a distortion aberration and a coma aberration is shown.
In the aberration curve diagrams of FIGS. 19 and 20, the broken line in spherical aberration represents the sine condition, the solid line in astigmatism represents sagittal, and the broken line represents meridional. Further, d and g in the respective aberration diagrams of spherical aberration, astigmatism, and coma aberration represent d-line and g-line, respectively. The same applies to the aberration curve diagrams according to other examples.

FIG. 9 shows an optical arrangement diagram in a state where an object at infinity is in focus in the image pickup optical system of Example 5 according to the fifth embodiment of the present invention.
FIG. 10 shows an optical layout diagram in the state where the short-distance object of the imaging optical system of Example 5 according to the fifth embodiment of the present invention is in focus (imaging magnification 0.1 times).
That is, the optical system of the imaging lens according to Example 5 of the present invention, as shown in FIGS. 9 and 10, sequentially from the object side to the image side, the first lens L1, the second lens L2, the first lens A third lens L3, a fourth lens L4, an aperture stop S, a fifth lens L5, a sixth lens L6, a seventh lens L7, and an eighth lens L8 are arranged. The second lens L2, the third lens L3, and the fourth lens L8 are arranged. The lens L4, the fifth lens L5, and the sixth lens L6 each constitute a cemented lens, which is a so-called five-group eight-lens configuration.
Focusing on the lens group configuration, the first lens group 1G is configured by the first lens L1 to the fourth lens L4. The fifth lens L5 to the eighth lens L8 constitute a second lens group 2G. The fifth lens L5, the sixth lens L6, and the seventh lens L7 constitute a second F lens group 2FG having a positive refractive power, and the eighth lens L8 constitutes a second R lens group 2RG having a negative refractive power. ing. That is, the optical system of the imaging lens shown in FIGS. 9 and 10 moves the first lens group 1G, the aperture stop S, the second F lens group 2FG, and the second R lens group 2RG from the object side to the image side. The arrangement is sequentially arranged.

Specifically, the first lens group 1G is formed with an aspheric surface on both sides in order from the object side to the image side, and has a biconcave shape with a concave surface having a larger curvature than the object side on the image side. A first lens L1 made of a negative lens, a second lens L2 made of a positive lens having a biconvex shape with a convex surface having a larger curvature on the image side than the object side, and a concave surface having a larger curvature on the image side than the object side. A third lens L3 made of a negative lens having a biconcave shape and a fourth lens L4 made of a positive lens having a positive meniscus shape with a convex surface facing the object side are arranged to show a positive refractive power. ing. Note that the three lenses of the second lens L2, the third lens L3, and the fourth lens L4 are closely bonded to each other and are integrally joined to form a cemented lens composed of three lenses.
An aperture stop S is disposed between the first lens group 1G and the second lens group 2G.
The second F lens group 2FG includes, from the object side to the image side, a fifth lens L5 including a positive lens having a biconvex shape with a convex surface having a larger curvature than the object side surface in order from the object side; A negative lens having a biconcave shape with a concave surface having a larger curvature than the image side surface, and a positive lens having a positive meniscus shape with a convex surface having an aspheric surface formed on the image side. The seventh lens L7 is arranged so as to exhibit positive refractive power. The two lenses of the fifth lens L5 and the sixth lens L6 of the second F lens group 2FG are closely bonded to each other and are integrally joined to form a cemented lens composed of two lenses. The second R lens group 2RG includes a biconcave eighth lens L8 having a concave surface with a larger curvature than the image side surface on the object side and an aspheric surface on both sides, and has a negative refractive power. It is configured as shown.

Further, behind the second lens group 2G, that is, on the image side, various filters such as an optical low-pass filter and an infrared cut filter, and a cover glass (seal glass) of the light receiving element are shown as equivalent parallel plates. A filter glass F is disposed.
During focusing, the first lens group 1G, the aperture stop S, and the second F lens group 2FG are fixed, and only the second R lens group 2RG is moved in the optical axis direction for focusing.
In the above embodiment, the second R lens group 2RG is constituted by one negative lens. Although there is no denying that the lens is composed of a plurality of lenses, by configuring the second R lens group 2RG with a minimum number of one lens, the thickness in the optical axis direction is minimized, and the second R lens group 2RG There is an effect of suppressing enlargement in the radial direction.
When the second R lens group 2RG is in the position shown in FIG. 9 at the time of focusing on an object at infinity (when focused on an object at infinity), the object at a short distance (imaging magnification, 0. When focusing to (1 ×), the lens moves in a direction away from the aperture stop S (a direction indicated by an arrow shown in FIG. 9) and moves to a position shown in FIG.
At the time of short distance focusing, it is narrowed down in a direction away from the optical system, so that it is not necessary to prepare a space for moving the focus group in the optical system in advance, and the degree of freedom in design is improved.

FIG. 9 also shows the surface numbers of the optical surfaces in the imaging optical system. Note that each reference code shown in FIG. 9 is used independently for each embodiment in order to avoid complication of explanation due to an increase in the number of digits of the reference code.
In Example 5, the focal length f, the open F value Fno, and the half angle of view ω [degrees] of the entire optical system are f = 18.30, Fno = 2.88, and ω = 38.27, respectively. The optical characteristics of each optical element in Example 5, such as the radius of curvature of the optical surface (paraxial radius of curvature for an aspherical surface) R, the spacing between adjacent optical surfaces D, the refractive index Nd, the Abbe number νd, and the glass type, are as follows: Table 13 is shown below.

In Table 13, the lens surface with the surface number indicated by adding “* (asterisk)” to the surface number is an aspherical surface.
That is, in Table 13, the optical surfaces of the first surface, the second surface, the twelfth surface, the thirteenth surface, and the fourteenth surface marked with “*” are aspherical surfaces. The spherical parameters are as follows.
○ Aspherical surfaces (surfaces with * symbol on surface numbers)
First side K = 0.0,
A ₄ = 1.76870E-04,
A ₆ = 1.68011E-06
A ₈ = −1.13764E-07,
A ₁₀ = 1.42623E-09
Second side K = 4.775611
A ₄ = 3.28558E-04,
A ₆ = 7.51936E-06
A ₈ = -2.81870E-07,
A ₁₀ = 4.22711E-09

12th surface K = -14.050727,
A ₄ = −5.1048E-04,
A ₆ = 1.21288E-05,
A ₈ = −2.000645E-07,
A ₁₀ = 2.52302E-09
13th surface K = 3.67111,
A ₄ = −1.45430E-04,
A ₆ = −2.667616E-06
A ₈ = 8.38187E-08
14th surface K = 0.0,
A ₄ = −2.25985E-04,
A ₆ = 2.55267E-06
A ₈ = -4.28860E-09
In Example 5, the variable distance DA between the seventh lens L7 of the second F lens group 2FG shown in FIG. 9 and the eighth lens L8 of the second R lens group 2RG and the eighth lens L8 and the filter glass F When the imaging magnification changes and the object distance changes to infinity and the imaging magnification changes to a short distance of 0.1, the variable interval DB between changes as shown in Table 14 below.

  In this case, values corresponding to the conditional expressions (1) to (9) are as shown in Table 15 below, which satisfy the conditional expressions (1) to (9), respectively.

FIG. 21 shows various aberrations in the d-line and g-line in the state in which the imaging optical system according to Example 5 is focused on an object at infinity, that is, spherical aberration, astigmatism, distortion aberration, and coma aberration. An aberration curve diagram is shown.
FIG. 22 shows various aberrations in the d-line and g-line in a state where the imaging optical system according to Example 5 is focused on a short-distance object (magnification 0.1 times), that is, spherical aberration, astigmatism, Each aberration curve figure of a distortion aberration and a coma aberration is shown.
In the aberration curve diagrams of FIGS. 21 and 22, the broken line in spherical aberration represents the sine condition, the solid line in astigmatism represents sagittal, and the broken line represents meridional. Further, d and g in the respective aberration diagrams of spherical aberration, astigmatism, and coma aberration represent d-line and g-line, respectively. The same applies to the aberration curve diagrams according to other examples.

FIG. 11 shows an optical arrangement diagram in a state in which an object at infinity is in focus in the imaging optical system of Example 6 according to the sixth embodiment of the present invention.
FIG. 12 shows an optical arrangement diagram in a state where an imaging optical system of Example 6 according to the sixth embodiment of the present invention is focused on a short-distance object (imaging magnification of 0.1).
That is, as shown in FIGS. 11 and 12, the optical system of the imaging lens according to Example 6 of the present invention sequentially includes a first lens L1, a second lens L2, and a second lens from the object side to the image side. A third lens L3, a fourth lens L4, an aperture stop S, a fifth lens L5, a sixth lens L6, a seventh lens L7, and an eighth lens L8 are arranged, and the second lens L2, the third lens L3, and the third lens L3 are arranged. The four lenses L4, the fifth lens L5, and the sixth lens L6 each constitute a cemented lens and have a so-called five-group eight-lens configuration.
Focusing on the lens group configuration, the first lens group 1G is configured by the first lens L1 to the fourth lens L4. The fifth lens L5 to the eighth lens L8 constitute a second lens group 2G. The fifth lens L5, the sixth lens L6, and the seventh lens L7 constitute a second F lens group 2FG having a positive refractive power, and the eighth lens L8 constitutes a second R lens group 2RG having a negative refractive power. ing. That is, the imaging lens optical system shown in FIGS. 11 and 12 moves the first lens group 1G, aperture stop S, second F lens group 2FG and second R lens group 2RG from the object side to the image side. The arrangement is sequentially arranged.

Specifically, the first lens group 1G is formed with an aspheric surface on both sides in order from the object side to the image side, and has a biconcave shape with a concave surface having a larger curvature than the image side on the object side. A first lens L1 made of a negative lens, a second lens L2 made of a positive lens having a biconvex shape with a convex surface having a larger curvature on the image side than the object side, and a concave surface having a larger curvature on the image side than the object side. A third lens L3 made of a negative lens having a biconcave shape and a fourth lens L4 made of a positive lens having a positive meniscus shape having a convex surface facing the object side are disposed. Note that the three lenses of the second lens L2, the third lens L3, and the fourth lens L4 are closely bonded to each other and are integrally joined to form a cemented lens composed of three lenses.
An aperture stop S is disposed between the first lens group 1G and the second lens group 2G.
The second F lens group 2FG includes, from the object side to the image side, a fifth lens L5 including a positive lens having a biconvex shape with a convex surface having a larger curvature than the object side surface in order from the object side; A negative lens having a biconcave shape with a concave surface having a larger curvature than the image side surface and a positive meniscus shape having a convex surface on the image side and an aspheric surface on the image side is formed. A seventh lens L7 made of a positive lens is arranged so as to exhibit positive refractive power. The two lenses of the fifth lens L5 and the sixth lens L6 of the second F lens group 2FG are closely bonded to each other and are integrally joined to form a cemented lens composed of two lenses. The second R lens group 2RG is configured such that a negative meniscus eighth lens L8 is disposed with the concave surface facing the object side and exhibits negative refractive power.

Further, behind the second lens group 2G, that is, on the image side, various filters such as an optical low-pass filter and an infrared cut filter, and a cover glass (seal glass) of the light receiving element are shown as equivalent parallel plates. A filter glass F is disposed.
During focusing, the first lens group 1G, the aperture stop S, and the second F lens group 2FG are fixed, and only the second R lens group 2RG is moved in the optical axis direction for focusing.
In the above embodiment, the second R lens group 2RG is constituted by one negative lens. Although there is no denying that the lens is composed of a plurality of lenses, by configuring the second R lens group 2RG with a minimum number of one lens, the thickness in the optical axis direction is minimized, and the second R lens group 2RG There is an effect of suppressing enlargement in the radial direction.
When the second R lens group 2RG is in the position shown in FIG. 11 at the time of focusing at infinity (when focused on an object at infinity), it is assumed that the second R lens group 2RG is at a short distance object (shooting magnification, 0. When focusing to (1 time), the lens moves in a direction away from the aperture stop S (a direction indicated by an arrow shown in FIG. 11) and moves to a position shown in FIG.
At the time of short distance focusing, it is narrowed down in a direction away from the optical system, so that it is not necessary to prepare a space for moving the focus group in the optical system in advance, and the degree of freedom in design is improved.

FIG. 11 also shows the surface numbers of the optical surfaces in the imaging optical system. In addition, in order to avoid complication of explanation due to an increase in the number of digits of the reference code, each reference code shown in FIG. 11 is used independently for each embodiment, and is given a common reference code.
In Example 6, the focal length f, the open F value Fno, and the half angle of view ω [degrees] of the entire optical system are f = 18.30, Fno = 2.88, and ω = 38.27, respectively. The optical characteristics of each optical element in Example 6, such as the radius of curvature of the optical surface (paraxial radius of curvature for an aspherical surface) R, the distance between adjacent optical surfaces D, the refractive index Nd, the Abbe number νd, and the glass type, are as follows. Table 16 is shown below.

In Table 16, the lens surface with the surface number indicated by adding “* (asterisk)” to the surface number is an aspherical surface.
That is, in Table 16, the optical surfaces of the first surface, the second surface, and the twelfth surface marked with “*” are aspheric surfaces, and the parameters of each aspheric surface in Equation (10) are as follows. It is.
○ Aspherical surfaces (surfaces with * symbol on surface numbers)
First side K = 0.0,
A ₄ = 8.03113E-04,
A ₆ = −1.69298E-05,
A ₈ = 2.40464E-07,
A ₁₀ = −1.35280E−09
Second side K = 0.0,
A ₄ = 9.35043E-04,
A ₆ = -1.00109E-05,
A ₈ = −1.69465E−08,
A ₁₀ = 4.006348E-09

Twelfth surface K = -23.00732,
A ₄ = −4.66866E-04,
A ₆ = 1.68716E-05,
A ₈ = -2.99500E-07,
A ₁₀ = 3.51261E-09
In Example 6, the variable distance DA between the seventh lens L7 of the second F lens group 2FG and the eighth lens L8 of the second R lens group 2RG shown in FIG. When the imaging magnification changes to change the object distance to infinity and the imaging magnification to a short distance of 0.1 times, the variable interval DB between changes as shown in Table 17 below.

  In this case, values corresponding to the conditional expressions (1) to (9) are as shown in Table 18 below, which satisfy the conditional expressions (1) to (9), respectively.

FIG. 23 shows various aberrations in the d-line and g-line in the state in which the imaging optical system according to Example 6 is focused on an object at infinity, that is, spherical aberration, astigmatism, distortion aberration, and coma aberration. An aberration curve diagram is shown.
FIG. 24 shows various aberrations in the d-line and g-line in a state where the imaging optical system according to Example 6 is focused on a short-distance object (magnification 0.1 times), that is, spherical aberration, astigmatism, Each aberration curve figure of a distortion aberration and a coma aberration is shown.
In the aberration curve diagrams of FIGS. 23 and 24, a broken line in spherical aberration represents a sine condition, a solid line in astigmatism represents sagittal, and a broken line represents meridional. Further, d and g in the respective aberration diagrams of spherical aberration, astigmatism, and coma aberration represent d-line and g-line, respectively. The same applies to the aberration curve diagrams according to other examples.

[Seventh Embodiment]
Next, a digital camera as a camera device according to the seventh embodiment of the present invention configured by employing the imaging optical system according to the first to sixth embodiments of the present invention described above. Will be described with reference to FIGS. FIG. 25 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. 26 is a schematic external view of the digital camera viewed from the back side which is the photographer side. FIG. 27 is a schematic block diagram showing a functional configuration of a digital camera. Here, the camera apparatus has been described by taking a digital camera as an example, but the imaging optical system according to the present invention may be employed in a silver salt film camera that uses 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 cellular phone in which a camera function is incorporated is widely used. Although such an information device has a slightly different appearance, it includes substantially the same functions and configuration as a digital camera, and may be employed as an imaging optical system in such an information device.

As shown in FIGS. 25 to 27, the digital camera includes an imaging lens 1 as an imaging optical system, 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. 27, 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 optical system according to the present invention as described in the first to sixth embodiments is used (corresponding to claim 10 or claim 12).
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 (corresponding to claim 11).

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 pickup optical system according to the present invention (the image pickup optical system defined in claims 1 to 9 or shown in the first to sixth embodiments described above) is a partial lens group of the image pickup optical system, That is, it can be performed by moving the second R lens group. 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, the digital camera (camera device) or the portable information terminal device as described above includes the imaging lens 1 configured using the imaging optical system as described in the first to sixth embodiments. It can be used as an imaging optical system. Therefore, it is possible to realize a small camera (camera device) or a portable information terminal device with a large aperture with an F number of about 2.8 or less, while having a sufficiently wide angle of view of 76 degrees or more, and a high image quality. be able to.
In addition to the technical field described above, the present invention can be applied to an optical system used for an optical sensor, a projection optical system used for a projection optical system, and the like.

1G 1st lens group 2G 2nd lens group 2FG 2F lens group 2RG 2R lens group L1 1st lens L2 2nd lens L3 3rd lens L4 4th lens L5 5th lens L6 6th lens L7 7th lens L8 1st lens 8 lenses S aperture stop F filter glass 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.

Japanese Examined Patent Publication No. 61-138225 Japanese Patent Laid-Open No. 03-265809 Japanese Patent No. 2518182 Japanese Patent No. 3735909 Japanese Patent No. 4365922 JP 2010-271669 A JP 2011-059288 A

Claims (12)

The first lens group is located on the object side across the aperture stop, and the positive second lens group is located on the image side, and the first lens group has a negative lens closest to the object side, The second lens group includes, in order from the object side, a positive second F lens group and a negative second R lens group. During focusing, the first lens group, the aperture stop, and the second F lens group are An imaging optical system characterized in that only the second R lens group is fixed and moves in the optical axis direction, and satisfies the following conditional expression:
0.15 <| PPi / TL | <0.55 (1)
Where PPi is the distance on the optical axis from the final surface of the second R lens group to the image side principal point position of the imaging optical system, and TL is the distance from the top surface of the first lens group when focusing on infinity. This represents the distance on the optical axis to the final surface of the second R lens group. 2. The imaging optical system according to claim 1, wherein the first lens group includes, in order from the object side, a negative lens having a concave surface facing the image side, and at least two cemented lenses of a random lens and a random lens that are out of order. The second lens group includes, in order from the object side, the positive second F lens group having a cemented lens of a positive lens and a negative lens having a concave surface facing the image side, and a negative lens having a concave surface facing the object side. An imaging optical system comprising the negative second R lens group consisting of: and satisfying the following conditional expression:
0.50 <| 1- (M2R) ² | <3.00 (2)
However, M2R represents the magnification at the time of focusing on infinity of the second R lens group. The imaging optical system according to claim 1, wherein the following conditional expression is satisfied.
0.60 <| IY / AP | <0.85 (3)
However, IY represents the maximum image height of the imaging optical system, and AP represents the distance on the optical axis from the image plane to the exit pupil position of the imaging optical system. The imaging optical system according to any one of claims 1 to 3, wherein the following conditional expression is satisfied.
0.30 <| f / f2R | <1.30 (4)
Here, f represents the focal length of the entire system, and F2R represents the focal length of the second R lens group. 5. The imaging optical system according to claim 1, wherein the following conditional expression is satisfied: 5.
0.90 <f / f2F <2.30 (5)
However, f represents the focal length of the entire system, and f2F represents the focal length of the second F lens group. 6. The imaging optical system according to claim 1, wherein the following conditional expression is satisfied.
0.01 <f / | f1 | <0.50 (6)
However, f represents the focal length of the entire system, and f1 represents the focal length of the first lens group. The imaging optical system according to claim 1, wherein the following conditional expression is satisfied.
0.00 <Ls / f <0.10 (7)
However, Ls is the distance on the optical axis from the final surface of the first lens group to the aperture stop at the time of focusing on infinity, and f is the focal length of the entire system. 8. The imaging optical system according to claim 1, wherein the following conditional expression is satisfied.
0.80 <TL / f <1.30 (8)
Here, TL represents the distance on the optical axis from the first surface of the first lens group to the final surface of the second R lens group when focusing on infinity. 9. The imaging optical system according to claim 1, wherein the imaging optical system satisfies the following conditional expression.
0.40 <| AP / AL | <0.90 (9)
Here, AL represents the distance on the optical axis from the head surface of the first lens group to the image plane, and AP represents the distance on the optical axis from the image plane to the exit pupil at the time of focusing on infinity.   A camera apparatus comprising the imaging optical system according to claim 1.   The camera apparatus according to claim 10, wherein the camera apparatus has a function of using a captured image as digital information.   A portable information terminal device comprising the imaging optical system according to any one of claims 1 to 9.

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