JP6238103B2 - Imaging optical system, camera device, and portable information terminal device - Google Patents

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 for so-called digital cameras 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 are also diverse. Among them, the category of high-quality compact cameras equipped with an imaging lens composed of a high-performance single-focus optical system is highly expected by users. As a request from users, in addition to high performance, the F number is small, that is, a large diameter, excellent portability, that is, in addition to being small and light, a fast autofocus speed, It is also required that the operation sound be quiet.
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.
Furthermore, in terms of increasing the diameter, an F value of at least about F2.8 is required 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 downsizing during non-photographing, it is called a retractable type, and during non-photographing, the so-called lens length is shortened by shortening the air interval on the optical axis in the imaging optical system such as before and after the aperture and back focus. It is necessary to have a retracting mechanism.
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.
Also, since there are many users who want a certain wide angle of view of the imaging lens, the angle of view is equivalent to 28 mm at 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.
As a typical example of a focusing method for a wide-angle single focus lens, there are an overall feeding method for moving the entire optical system, and an inner focus method for moving the rear and center of the optical system. In any method, it is possible to combine a floating method in which the focusing unit moves while changing the distance on the optical axis between the moving groups.

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 portion increases, and the same problem as that of the entire extension tends to occur. In order to adopt the floating method, a mechanism for relating the movement ratios of at least two moving groups is required, and the load on the drive source may be further increased.
As conventional examples of the inner focus method 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), and Patent Document 3 (Japanese Patent No. 2518182). Publications), Patent Document 4 (Japanese Patent No. 4365922), Patent Document 5 (Japanese Patent No. 3735909), Patent Document 6 (Japanese Patent Laid-Open No. 2010-271669), and the like are known.

However, the optical systems disclosed in Patent Document 1 and Patent Document 2 are described in the public gazette that it is possible to perform focusing by moving a part of the rear group. Not shown in the example. In addition, the optical systems disclosed in Patent Documents 1 and 2 have a half angle of view of about 32.5 degrees and cannot be said to have a sufficiently wide angle of view. It is enough. 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 very large at 12 pieces. It is hard to say that it is sufficiently small and light. The optical system disclosed in Patent Document 4 performs a floating operation at the time of focusing, and requires a mechanism for defining the moving ratio of two moving groups that move at the time of focusing. In terms of reduction, it is insufficient. The optical system disclosed in Patent Document 5 has a configuration in which the aperture stop moves as a unit during focusing, and it is necessary to move a relatively large and heavy stop structure or shutter structure during focusing. There is a problem to be solved in terms of reducing the load. 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 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, an imaging optical system according to the present invention, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, an aperture stop, A third lens group having a positive refractive power and a fourth lens group having a negative refractive power,
The first lens group is composed of a negative lens having a concave surface facing the image side, the second lens group is composed of one cemented lens including a positive lens and a negative lens, and the third lens group is most object side. And a cemented lens in which a positive lens having a convex surface facing the image side and a negative lens are joined in order from the object side, and the fourth lens group is composed of a negative lens having a concave surface facing the object side. During the focusing, the fourth lens group moves in the optical axis direction ,
When the distance on the optical axis from the image plane to the exit pupil at the time of focusing on infinity is AP, and the radius of curvature of the leading surface of the fourth lens group is Rg41, the following conditional expression (6):
0.50 <| AP / Rg41 | <1.30 (6)
It is characterized by satisfying .

According to the first aspect of the present invention, in order from the object side, the first lens group having negative refractive power, the second lens group having positive refractive power, the aperture stop, and the third lens having positive refractive power. The first lens group includes a negative lens having a concave surface facing the image side, and the second lens group includes a positive lens and a negative lens. The third lens group includes a cemented lens in which a positive lens having a convex surface facing the image side in order from the object side and a negative lens are cemented on the most object side, The fourth lens group is composed of a negative lens having a concave surface facing the object side, and during focusing, the fourth lens group moves in the optical axis direction ,
When the distance on the optical axis from the image plane to the exit pupil at the time of focusing on infinity is AP, and the radius of curvature of the leading surface of the fourth lens group is Rg41, the following conditional expression (6):
0.50 <| AP / Rg41 | <1.30 (6)
By being configured so as to satisfy, yet large aperture F number of about 2.8 in wide angle of view angle of about 76 °, even inner focus type, the drive source during focusing Therefore, it is possible to realize an imaging optical system that is small in size and light in weight and can ensure very good image performance.

It is an optical arrangement | positioning figure which shows the movement locus | trajectory of the imaging optical system in Example 1 which concerns on the 1st Embodiment of this invention, (a) is at the time of infinity focusing of an imaging optical system (focusing on an object at infinity) (B) is an optical layout diagram at the time of focusing on a short distance of the imaging optical system (when focusing on a short distance object with a shooting magnification of 0.05 times; the same applies below). is there. FIG. 3 is an aberration curve diagram showing various aberrations of spherical aberration, astigmatism, distortion, and coma aberration for the d line and the g line when the imaging optical system according to Example 1 shown in FIG. 1 is focused at infinity. FIG. 3 is an aberration curve diagram showing various aberrations of spherical aberration, astigmatism, distortion aberration, and coma aberration for d-line and g-line when the imaging optical system according to Example 1 shown in FIG. It is an optical arrangement | positioning figure which shows the movement locus | trajectory of the imaging optical system in Example 2 which concerns on the 2nd Embodiment of this invention, (a) is at the time of infinity focusing of an imaging optical system (focusing on an object at infinity) (B) is an optical arrangement diagram at the time of focusing on a short distance of the imaging optical system (at the time of focusing on a short distance object with a shooting magnification of 0.05 times). FIG. 5 is an aberration curve diagram showing various aberrations of spherical aberration, astigmatism, distortion, and coma aberration with respect to the d-line and the g-line when the imaging optical system according to Example 2 shown in FIG. 4 is focused at infinity. 5 is an aberration curve diagram showing various aberrations of spherical aberration, astigmatism, distortion aberration, and coma aberration for d-line and g-line when the imaging optical system according to Example 2 shown in FIG. It is an optical arrangement | positioning figure which shows the movement locus | trajectory of the imaging optical system in Example 3 which concerns on the 3rd Embodiment of this invention, (a) is at the time of infinity focusing of an imaging optical system (focusing on an object at infinity) (B) is an optical arrangement diagram at the time of focusing on a short distance of the imaging optical system (at the time of focusing on a short distance object with a shooting magnification of 0.05 times). FIG. 9 is an aberration curve diagram showing various aberrations of spherical aberration, astigmatism, distortion and coma aberration for d line and g line when the imaging optical system according to Example 3 shown in FIG. 7 is focused at infinity. FIG. 10 is an aberration curve diagram showing various aberrations of spherical aberration, astigmatism, distortion aberration, and coma aberration for d-line and g-line when the imaging optical system according to Example 3 shown in FIG. 7 is focused at a short distance. It is an optical arrangement | positioning figure which shows the movement locus | trajectory of the imaging optical system in Example 4 which concerns on the 4th Embodiment of this invention, (a) is at the time of infinity focusing of an imaging optical system (focusing on an object at infinity) (B) is an optical arrangement diagram at the time of focusing on a short distance of the imaging optical system (at the time of focusing on a short distance object with a shooting magnification of 0.05 times). FIG. 11 is an aberration curve diagram showing various aberrations of spherical aberration, astigmatism, distortion, and coma aberration for the d line and the g line when the imaging optical system according to Example 4 shown in FIG. 10 is focused at infinity. FIG. 11 is an aberration curve diagram showing various aberrations of spherical aberration, astigmatism, distortion aberration, and coma aberration for d-line and g-line when the imaging optical system according to Example 4 shown in FIG. It is an optical arrangement | positioning figure which shows the movement locus | trajectory of the imaging optical system in Example 5 which concerns on the 5th Embodiment of this invention, (a) is at the time of infinity focusing of an imaging optical system (focusing on an object at infinity) (B) is an optical arrangement diagram at the time of focusing on a short distance of the imaging optical system (at the time of focusing on a short distance object with a shooting magnification of 0.05 times). FIG. 14 is an aberration curve diagram showing various aberrations of spherical aberration, astigmatism, distortion, and coma aberration with respect to the d-line and the g-line when the imaging optical system according to Example 5 shown in FIG. 13 is focused at infinity. FIG. 14 is an aberration curve diagram showing spherical aberration, astigmatism, distortion aberration, and various aberrations of coma aberration when the imaging optical system according to Example 5 shown in FIG. It is an optical arrangement | positioning figure which shows the movement locus | trajectory of the imaging optical system in Example 6 which concerns on the 6th Embodiment of this invention, (a) is at the time of infinity focusing of an imaging optical system (focusing on an object at infinity) (B) is an optical arrangement diagram at the time of focusing on a short distance of the imaging optical system (at the time of focusing on a short distance object with a shooting magnification of 0.05 times). FIG. 17 is an aberration curve diagram showing spherical aberration, astigmatism, distortion aberration, and coma aberration for d-line and g-line when the imaging optical system according to Example 6 shown in FIG. 16 is focused at infinity. FIG. 17 is an aberration curve diagram showing various aberrations of spherical aberration, astigmatism, distortion aberration, and coma aberration with respect to the d-line and the g-line when the imaging optical system according to Example 6 shown in FIG. 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. 19 from the back side, ie, a photographer side. It is a block diagram which shows typically the function structure of the digital camera of FIG. 19 and FIG.

Hereinafter, based on first to sixth embodiments 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, a fundamental embodiment 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, but the same applies to the second to sixth embodiments.

Currently, there is a strong need for higher quality, smaller size, wider angle, and larger aperture for digital cameras, and it is necessary to develop to meet these demands. In addition, in recent years, in addition to this, there has been an increasing need for high-speed autofocus operation and quiet operation noise, and an optical design that satisfies both of these needs is required.
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.
In order from the object side to the image plane side, a first lens group having negative refractive power, a second lens group having positive refractive power, an aperture stop, and a third lens group having positive refractive power And a fourth lens group having negative refractive power. The first lens group includes a negative lens having a concave surface facing the image side. The second lens group includes one cemented lens including a positive lens and a negative lens. The third lens group includes a cemented lens in which a positive lens having a convex surface facing the image side in order from the object side and a negative lens are arranged on the most object side. The fourth lens group is configured by a negative lens having a concave surface directed toward the object side, and during focusing, the fourth lens group moves in the optical axis direction ,
When the distance on the optical axis from the image plane to the exit pupil at the time of focusing on infinity is AP, and the radius of curvature of the leading surface of the fourth lens group is Rg41, the following conditional expression (6):
0.50 <| AP / Rg41 | <1.30 (6)
Is satisfied (corresponding to claim 1).
First, in the imaging optical system of the present invention, the first lens group having negative power on the most object side and the fourth lens group having negative power on the most image side are disposed with the aperture stop interposed therebetween. However, by providing the second lens group and the third lens group in the middle with positive refractive power, it is not strict, but the refractive power arrangement has symmetry, coma aberration, chromatic aberration of magnification, distortion. The difficulty of correcting aberrations is lowered. Further, by making both the image side surface of the first lens group and the object side surface of the fourth lens group face each other as a concave shape, it is possible to correct the aberration correction at a higher level. .

In addition to this, the negative lens at the head of the first lens group has a concave surface on the image surface side, which is particularly effective in correcting spherical aberration that increases with an increase in aperture. Further, by arranging at least one combination of positive lens and negative lens in the second lens group and the third lens group having positive power, respectively, correction of axial chromatic aberration and coma aberration color difference can be achieved. It has been effective.
In addition, by focusing the fourth lens group having a negative refractive power behind the third lens group having a positive refractive power as a focus group, focusing from the infinity side to the short distance side is performed. Therefore, it is not necessary to prepare a space for moving the focus group in advance in the optical system, and the degree of freedom in design is improved. Further, the third lens group includes a positive lens having a convex surface on the image side, and the fourth lens group includes a negative lens having a concave surface on the object side, so that the two lenses are paired with each other. In particular, this is effective for correcting curvature of field. In addition, there is an effect of suppressing the amount of variation in spherical aberration and field curvature due to focusing, or balancing the amount of variation in spherical aberration and field curvature.
Conditional expression (6) defines an appropriate range of the radius of curvature of the front surface of the fourth lens group with respect to the exit pupil distance. When the lower limit value of conditional expression (6) is not reached, the refractive power of the image side surface of the fourth lens group becomes excessive, and when the upper limit value is exceeded, the refractive power of the object side surface of the fourth lens group becomes excessive. Aberration correction is insufficient, and the manufacturing error sensitivity of the fourth lens group may increase. If the lower limit of conditional expression (6) is not reached, the edge thickness of the fourth lens group increases, and the substantial thickness of the entire optical system increases. When the upper limit value of conditional expression (6) is exceeded, the air space between the final surface of the third lens group and the leading surface of the fourth lens group increases, and the length on the optical axis of the optical system increases. When the optical system is retracted and stored in the camera body, the camera thickness may increase.
In order to perform better aberration correction, the following conditional expression should be satisfied.
0.60 <| AP / Rg41 | <1.20 (6A)

According to the configuration of the photographic 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 a small inner focus method that maintains high image performance even under severe conditions.
In order to achieve better performance, the air lens formed by the final surface of the second lens group and the leading surface of the third lens group has a shape with a concave surface facing the image side, and is positive. It is sufficient to have a refractive power of (corresponding to claim 2).
With this configuration, the Petzval sum is easily balanced, the difficulty of controlling the field curvature is reduced, and the flatness of the image plane performance is effective. Further, since the convex shape of the lens exists in the shutter space, the utilization efficiency of the space is increased, which is effective in reducing the size of the optical system.
In order to achieve higher performance, f is the focal length of the entire system, and f4 is the focal length of the fourth lens group. The following conditional expression (1):
0.30 <| f / f4 | <1.20 (1)
Is preferably satisfied (corresponding to claim 3).

Conditional expression (1) defines an appropriate range of the focal length of the fourth lens group with respect to the focal length of the entire system. If the lower limit of conditional expression (1) is not reached, the image plane position fluctuation amount per unit movement amount of the fourth lens group, which is the focus group, becomes too small, and the speed at the time of autofocus is reduced, and the peripheral light amount is secured. For this reason, the fourth lens group may be enlarged in the radial direction. If the upper limit value of conditional expression (1) is exceeded, the image plane position fluctuation amount per unit movement amount of the fourth lens group as the focus group becomes large, which is advantageous for improving the speed during autofocusing. Excessive accuracy may be required for the stop position of the focus group. Also, it approaches the telephoto type, which is advantageous for downsizing the entire optical system, but the aberration correction exchange between the third lens group and the fourth lens group becomes excessive, and the image performance deteriorates due to manufacturing errors. May grow.
In order to obtain better performance, it is desirable to satisfy the following conditional expression (1A).
0.45 <| f / f4 | <1.10 (1A)
In order to achieve higher performance, let f be the focal length of the entire system, f3 be the focal length of the third lens group, and the following conditional expression (2):
0.90 <f / f3 <1.80 (2)
Is satisfied (corresponding to claim 4).

The conditional expression (2) defines an appropriate range of the focal length of the third lens group with respect to the focal length of the entire system. If the lower limit value of conditional expression (3) is not reached, it is necessary to increase the positive power of the second lens group, 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, and there is a risk that the entire optical system will become longer in order to correct it. If the upper limit value of conditional expression (2) is exceeded, there will be excessive exchange of aberration correction between the third lens group and the fourth lens group, and there is a risk that image performance will be degraded due to manufacturing errors.
In order to obtain better performance, it is desirable to satisfy the following conditional expression (2A).
1.05 <f / f3 <1.65 (2A)
For higher performance, the focal length of the entire system is f, and the combined focal length of the second lens group is f12. Conditional expression (3) below:
0.01 <f / | f12 | <0.50 (3)
Is satisfied (corresponding to claim 5).

The conditional expression (3) defines an appropriate range of the focal length of the first lens group with respect to the focal length of the entire system. Regardless of whether the lower limit value of conditional expression (3) is exceeded or the upper limit value 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, it is preferable that the following conditional expression (3A) is satisfied.
0.05 <f / | f1 | <0.40 (3A)
In order to achieve higher performance, the distance on the optical axis from the head surface of the first lens group to the aperture stop is Ls, and the fourth lens is moved from the head surface of the first lens group when focusing on infinity. Conditional expression (4) below, where TL is the distance on the optical axis to the final surface of the group:
0.35 <Ls / TL <0.65 (4)
Is satisfied (corresponding to claim 6).

Conditional expression (4) defines an appropriate range of the aperture stop position with respect to the length on the optical axis of the optical system. If the lower limit value of conditional expression (4) 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 (4) is exceeded, the lower ray passing through the first lens group becomes too low, and the first lens group may become large in diameter. Moreover, even if the lower limit value is exceeded or the upper limit value is exceeded, the position of the aperture stop blades in the air gap including the aperture stop is too biased, and the space utilization efficiency in configuring the aperture stop and shutter mechanism May decrease.
For higher performance, let TL be the distance on the optical axis from the first surface of the first lens group to the final surface of the fourth lens group when focusing on infinity, and let f be the focal length of the entire system. The following conditional expression (5):
0.50 <TL / f <1.30 (5)
Is satisfied (corresponding to claim 7).

Conditional expression (5) defines an appropriate range of the entire lens length when focusing on infinity with respect to the focal length of the entire system. If the lower limit value of conditional expression (5) is not reached, the symmetry of the refractive power arrangement is greatly lost, and in particular, the degree of difficulty in correcting coma aberration, lateral chromatic aberration, distortion aberration, 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. If the upper limit value of conditional expression (5) 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 become large in diameter.
In order to perform better aberration correction, the following conditional expression (5A) should be satisfied.
0.60 <TL / f <1.20 (5A )

To performance in of al, the second lens group has a cemented lens of a biconcave negative lens and a positive lens, the third lens group, both a double convex positive lens What is necessary is just to set it as the structure which has a cemented lens with a concave negative lens (corresponding to claim 8 ).

By arranging positive and negative cemented lenses on both sides of the aperture stop, it is possible to effectively correct axial chromatic aberration while maintaining the symmetry of refractive power arrangement to some extent. In addition, it is close to the aperture stop and is a lens element that greatly corrects spherical aberration, so it tends to cause image performance degradation due to manufacturing errors. However, it can suppress image performance degradation by reducing manufacturing errors to some extent as a cemented lens. Is possible. By having the biconcave negative lens in both the second lens group and the third lens group, it is particularly effective in correcting coma aberration while maintaining the object of aberration correction.
In order to achieve higher performance, the third lens group is composed of a cemented lens of a biconvex positive lens and a biconcave negative lens, and a positive meniscus lens having a convex surface facing the image side. (Corresponding to claim 9 ).
By arranging a positive lens having a convex surface on the image side in the third lens group and a negative lens having a concave surface on the object side in the fourth lens group, the two lenses are paired with each other. In particular, this is effective for correcting curvature of field. In addition, there is an effect of suppressing the amount of variation in spherical aberration and field curvature due to focusing, or balancing the amount of variation in spherical aberration and field curvature.
The fourth lens group is preferably composed of a single negative lens. In short-distance focusing, the fourth lens group moving in the direction away from the aperture stop is set to a minimum number of one to minimize the thickness in the optical axis direction, thereby increasing the size of the fourth lens group in the radial direction. There is an inhibitory effect.

And, by configuring the imaging optical system in a camera device such as a so-called digital camera by the imaging optical system described above,
Although the half angle of view is as wide as 38 degrees and the F-number is as large as F2.8, it is small enough to ensure very good image performance and the number of pixels. May be a small and high-quality camera device using a high-performance imaging lens having a resolving power corresponding to an imaging element of 10 million to 20 million pixels as an imaging optical system (corresponding to claim 10 ). .
Further, the camera device may be provided with a function of using the 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 portable information terminal device that uses a small and high-performance image pickup optical system as an image pickup optical system of the image pickup function unit and can obtain high image quality may be used (corresponding to claim 12 ).

  Next, embodiments of the present invention and specific examples (numerical examples) based thereon will be described in detail. Example 1, Example 2, Example 3, Example 4, Example 5, and Example 6 described below are the first embodiment, the second embodiment, and the 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.

In all of Examples 1 to 6, the maximum image height is 14.3 mm.
In the imaging lenses of the first to sixth embodiments, the parallel plate MF disposed on the image plane side of the fourth lens group includes various filters such as an optical low-pass filter and an infrared cut filter, and a CMOS sensor. A cover glass (seal glass) of a light receiving element such as is assumed.
In addition, the glass material of the optical glass used in each Example of these Examples 1-Example 6 is shown by the optical glass type name of the product of HOYA Corporation (HOYA) and OHARA Corporation.
The aberrations of the first to sixth embodiments are corrected at a high level, the half angle of view is about 38 degrees and a wide angle, the F value is about F2.8 and a large aperture, and It is apparent from the first to sixth embodiments that the present invention is a small and lightweight inner focus type imaging optical system with a small load on the driving source during lens focusing.

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 The reciprocal of R is defined as C by the following equation (7).

FIG. 1 is an optical arrangement diagram showing the movement trajectory of the image pickup optical system according to the first embodiment of the present invention and Example 1. FIG. FIG. 7B is an optical layout diagram when focusing on an object), and FIG. 8B shows an optical layout diagram when focusing on a short distance of the imaging optical system (when focusing on a near distance object with a shooting magnification of 0.05 times). Yes.
That is, as shown in FIG. 1, the imaging optical system according to Example 1 of the present invention sequentially includes a first lens L1, a second lens L2, a third lens L3, and a first lens from the object side to the image plane side. 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 L1 constitutes a first lens group G1 having negative refractive power. The second lens L2 to the fourth lens L4 constitute a second lens group G2 having a positive refractive power. The fifth lens L5 to the seventh lens L7 constitute a third lens group G3 having positive refractive power. The eighth lens L8 constitutes a fourth lens group G4 having a negative refractive power. In other words, the imaging optical system shown in FIG. 1 moves the first lens group G1, the second lens group G2, the aperture stop S, the third lens group G3, and the fourth lens group G4 from the object side to the image plane side. Thus, the arrangement is sequentially arranged.

Specifically, the first lens group G1 is formed by sequentially forming aspheric surfaces on both sides from the object side to the image plane side, and both concave surfaces having a curvature larger than the object side surface are directed to the image plane side. A first lens L1 made of a negative lens having a concave shape is arranged so as to exhibit negative refractive power. The second lens group G2 includes a second lens L2 composed of a positive lens having a biconvex shape with a convex surface having a larger curvature than the object-side surface facing the image surface side, and a concave surface having a larger curvature than the object-side surface. A third lens L3 made of a negative lens having a biconcave shape directed toward the side, and a fourth lens L4 made of a positive lens having a positive meniscus shape having a convex surface directed toward the object side are arranged to have a positive refractive power It is configured to show. 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 second lens group G2 and the third lens group G3.
The third lens group G3 includes, from the object side to the image surface side, a fifth lens L5 made of a positive lens having a convex surface having a curvature larger than that of the object side surface toward the image surface side. A sixth lens L6 formed of a negative lens having a biconcave shape with a concave surface having a curvature larger than that of the image side surface directed toward the object side, and a positive meniscus formed with a concave surface directed toward the object side and aspheric surfaces formed on both sides A seventh lens L7 made of a positive lens having a shape is arranged so as to exhibit positive refractive power.

The two lenses of the third lens group G3, that is, the fifth lens L5 and the sixth lens L6, are closely bonded to each other and joined together to form a cemented lens composed of two lenses. The fourth lens group G4 includes a seventh lens L7 made of a negative meniscus negative lens having a concave surface facing the object side, and is configured to exhibit negative refractive power.
Further, behind the fourth lens group G4, that is, on the image plane 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 formed as equivalent parallel plates. The filter glass BF shown is arranged.
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 the present embodiment, the above-described filter glass BF is representatively shown as two parallel flat plates. In Examples 2 to 6, the filter glass BF is equivalently shown as two parallel flat plates. Similarly to the filter glass BF 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. An image plane is located further on the image side of the filter glass BF. This image plane matches the light receiving surface of the image sensor.

The first lens group G1, the second lens group G2, the aperture stop S, and the third lens group G3 are substantially integrally supported by an appropriate support frame or the like at least during use, and during focusing to focus on the subject. The fourth lens group G4 is moved along the optical axis direction for focusing. That is, the eighth lens L8 of the fourth lens group G4 is in focus at a short distance from the position shown in FIG. 1A when focused at infinity (when focused at a shooting magnification of 0.05). First, it moves in the direction shown in FIG.
FIG. 1 also shows the surface numbers of the optical surfaces in the optical system of the imaging lens. 1 is used independently for each embodiment in order to avoid complication of explanation due to an increase in the number of digits of the reference code. Therefore, FIG. 4, FIG. 7, FIG. 10, FIG. 13 and 16 and the like are attached with the same reference numerals.
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 = 38.27, 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, It is as shown in Table 1 below.

In Table 1, the lens surface with the surface number indicated by adding “* (asterisk)” to the surface number is an aspherical surface. 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). The same applies to the other embodiments.
That is, in Table 1, the optical surfaces of the first surface, the second surface, the eleventh surface, and the twelfth surface marked with “*” are aspheric surfaces, and the parameters of each aspheric surface in Equation (7) are It is as follows.
Aspheric parameter 1st surface K = 0.0
A4 = 1.76932E-04
A6 = 8.84366E-07
A8 = −730590E−08
A10 = 8.51752E-10
Second side K = 0.0
A4 = 3.63704E-04
A6 = 7.84486E-06
A8 = -2.38441E-07
A10 = 3.74467E-09

11th surface K = 0.0
A4 = -1.35804E-04
A6 = −8.27909E-07
A8 = 1.09620E-07
Twelfth surface K = −9.06451
A4 = −7.339515E−04
A6 = 1.66524E-05
A8 = −2.43179E-07
A10 = 4.227923E-09
In Example 1, the variable distance DA between the seventh lens L7 of the third lens group G3 and the eighth lens L8 of the fourth lens group G4, the eighth lens L8 of the fourth lens group G4, and the filter glass are used. The variable interval such as the variable interval DB between the BF and the BF varies as shown in Table 2 below when focusing on infinity and focusing on a short distance (focusing at a shooting magnification of 0.05).

In this case, the values corresponding to the conditional expressions (1) to (6) are as shown in Table 3 below, which satisfy the conditional expressions (1) to (6), respectively.

  FIG. 2 is a diagram showing aberration curves of various aberrations in d-line and g-line at the time of focusing on infinity of the imaging optical system according to Example 1, that is, spherical aberration, astigmatism, distortion aberration, and coma aberration. Show. FIG. 3 is an aberration curve diagram for the d-line and the g-line when the imaging optical system according to Example 1 is in close focus. In the aberration curve diagrams of FIGS. 2 and 3, 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. 4 is an optical arrangement diagram showing the movement trajectory of the image pickup optical system according to the second embodiment of the present invention and Example 2, and FIG. FIG. 6B is an optical layout diagram at the time of focusing on a distant object; ing.
That is, the imaging optical system according to Example 2 of the present invention sequentially includes the first lens L1, the second lens L2, the third lens L3, and the first lens from the object side to the image plane side, as shown in FIG. 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 L1 constitutes a first lens group G1 having negative refractive power. The second lens L2 to the fourth lens L4 constitute a second lens group G2 having a positive refractive power. The fifth lens L5 to the seventh lens L7 constitute a third lens group G3 having positive refractive power. The eighth lens L8 constitutes a fourth lens group G4 having a negative refractive power. That is, the imaging optical system shown in FIG. 4 moves these first lens group G1, second lens group G2, aperture stop S, third lens group G3, and fourth lens group G4 from the object side to the image plane side. Thus, the arrangement is sequentially arranged.

More specifically, the first lens group G1 is formed with an aspheric surface on both surfaces, and a first lens L1 made of a negative lens having a negative meniscus shape with the concave surface facing the image surface side is arranged to provide a negative refractive power. It is configured to show. The second lens group G2 includes a second lens L2 composed of a positive lens having a biconvex shape with a convex surface having a larger curvature than the object-side surface facing the image surface side, and a concave surface having a larger curvature than the object-side surface. A third lens L3 made of a negative lens having a biconcave shape directed toward the side, and a fourth lens L4 made of a positive lens having a positive meniscus shape having a convex surface directed toward the object side are arranged to have a positive refractive power It is configured to show. 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 bonded to form a cemented lens including three lenses.
An aperture stop S is disposed between the second lens group G2 and the third lens group G3.
The third lens group G3 includes, from the object side to the image surface side, a fifth lens L5 made of a positive lens having a convex surface having a curvature larger than that of the object side surface toward the image surface side. A sixth lens L6 made of a negative lens having a biconcave shape with a concave surface having a curvature larger than that of the image surface side facing the object side, and a positive surface formed by forming the aspheric surface on the image surface side with the concave surface facing the object side A seventh lens L7 composed of a positive meniscus lens is arranged so as to exhibit positive refractive power. The two lenses of the third lens group G3, that is, the fifth lens L5 and the sixth lens L6, are closely bonded to each other and joined together to form a cemented lens composed of two lenses.

The fourth lens group G4 includes an eighth lens L8 made of a negative meniscus negative lens having a concave surface directed toward the object side, and is configured to exhibit negative refractive power.
Further, behind the fourth lens group G4, that is, on the image plane 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 formed as equivalent parallel plates. The filter glass BF shown is arranged.
An image plane is located further on the image side of the filter glass BF. This image plane matches the light receiving surface of the image sensor.
The first lens group G1, the second lens group G2, the aperture stop S, and the third lens group G3 are supported by an appropriate support frame or the like at least when used, and the fourth lens is used for focusing to focus on the subject. The group G4 is moved along the optical axis direction to perform focusing. That is, the eighth lens L8 of the fourth lens group G4 is in focus at a short distance from the position shown in FIG. 4A when focused at infinity (when focused at a shooting magnification of 0.05). Is moved in the direction shown in FIG. 4B, that is, the image plane side.

FIG. 4 also shows the surface number of each optical surface in the optical system of the imaging lens. Note that each reference symbol shown in FIG. 4 is used independently for each embodiment in order to avoid complication of explanation due to an increase in the number of digits of the reference symbol. Therefore, FIG. 1, FIG. 7, FIG. 13 and 16 and the like are attached with the same reference numerals.
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 = 18.30, Fno = 2.88, and ω = 38.27, respectively. . Optical characteristics such as the radius of curvature of the optical surface (paraxial curvature radius for an aspheric surface) R, the distance D between adjacent optical surfaces, the refractive index Nd, the Abbe number νd, and the glass type in each optical element in Example 2 are as follows: This is shown in Table 4 below.

In Table 4, the lens surface with the surface number indicated by adding “* (asterisk)” to the surface number is an aspherical surface. 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). The same applies to the other embodiments.
That is, in Table 4, 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 the equation (7) are as follows. It is.
Aspheric parameter 1st surface K = 0.0
A4 = 5.68822E-05
A6 = 4.48553E-06
A8 = −1.21038E-07
A10 = 1.11112E-09

Second side K = 0.0
A4 = 2.78470E-04
A6 = 8.77929E-06
A8 = -1.377788E-07
A10 = 2.19198E-09
Twelfth surface K = −11.34742
A4 = −6.74645E−04
A6 = 2.04147E-05
A8 = -3.844460E-07
A10 = 4.334066E-09
In Example 2, the axially variable distance DA between the seventh lens L7 of the third lens group G3 and the eighth lens L8 of the fourth lens group G4 and the eighth lens L8 of the fourth lens group G4 are used. The variable interval such as the variable interval DB between the filter glass BF and the filter glass BF changes as shown in Table 5 below when focusing on infinity and focusing on a short distance (focusing at a shooting magnification of 0.05). To do.

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

  FIG. 5 shows various aberration curves of d-line and g-line aberrations, that is, spherical aberration, astigmatism, distortion aberration and coma aberration, when the imaging optical system according to Example 2 is focused at infinity. Show. FIG. 6 is an aberration curve diagram for the d-line and the g-line when the imaging optical system according to Example 2 is in close focus. In the aberration curve diagrams of FIGS. 5 and 6, 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. 7 is an optical arrangement diagram showing the movement trajectory of the image pickup optical system according to the third embodiment of the present invention and Example 3, and FIG. FIG. 6B is an optical layout diagram at the time of focusing on a distant object; ing.
That is, the imaging optical system according to Example 3 of the present invention sequentially includes a first lens L1, a second lens L2, a third lens L3, and an aperture from the object side to the image plane side, as shown in FIG. An aperture S, a fourth lens L4, a fifth lens L5, a sixth lens L6, and a seventh lens L7 are disposed. The second lens L2 and the third lens L3, and the fourth lens L4 and the fifth lens L5 each constitute a cemented lens, and have a so-called five-group seven-element configuration.
Focusing on the lens group configuration, the first lens L1 constitutes a first lens group G1 having negative refractive power. The second lens L2 to the third lens L3 constitute a second lens group G2 having a positive refractive power. The fourth lens L4 to the sixth lens L6 constitute a third lens group G3 having a positive refractive power. The seventh lens L7 constitutes a fourth lens group G4 having a negative refractive power. That is, the imaging optical system shown in FIG. 7 moves these first lens group G1, second lens group G2, aperture stop S, third lens group G3, and fourth lens group G4 from the object side to the image plane side. Thus, the arrangement is sequentially arranged.

Specifically, in the first lens group G1, a negative lens is formed by sequentially arranging a first lens L1 formed of a negative lens having an aspheric surface on both surfaces and a negative meniscus shape with a concave surface facing the image surface side. It is configured to show refractive power. The second lens group G2 includes, in order from the object side, a second lens L2 composed of a negative lens having a biconcave shape in which a concave surface having a larger curvature than the object side surface is directed toward the image surface side, and a curvature from the image surface side surface. And a third lens L3 made of a positive lens having a biconvex shape with its large convex surface facing the object side, and is configured to exhibit positive refractive power. Note that the two lenses, the second lens L2 and the third lens L3, are closely bonded to each other and are integrally joined to form a cemented lens composed of two lenses.
An aperture stop S is disposed between the second lens group G2 and the third lens group G3.
The third lens group G3 includes, from the object side to the image surface side, a fourth lens L4 made of a positive lens having a biconvex shape with a convex surface having a larger curvature than the object side surface directed toward the image surface side. A fifth lens L5 composed of a negative lens having a biconcave shape with a concave surface having a larger curvature than the image surface side facing the object side, and a positive surface formed by directing the concave surface to the object side and forming an aspheric surface on the image surface side A sixth lens L6 made of a positive lens having a meniscus shape is arranged so as to exhibit positive refractive power. The two lenses of the fourth lens L4 and the fifth lens L5 of the third lens group G3 are closely bonded to each other and are integrally joined to form a cemented lens composed of two lenses. The fourth lens group G4 includes a seventh lens L7 made of a negative meniscus negative lens having a concave surface facing the object side, and is configured to exhibit negative refractive power.

Further, behind the fourth lens group G4, that is, on the image plane 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 formed as equivalent parallel plates. The filter glass BF shown is arranged.
An image plane is located further on the image side of the filter glass BF. This image plane matches the light receiving surface of the image sensor.
The first lens group G1, the second lens group G2, the aperture stop S, and the third lens group G3 are supported by an appropriate support frame or the like at least during use. In focusing to focus on the subject, the fourth lens group G4 is moved along the optical axis direction to perform focusing. That is, the seventh lens L7 of the fourth lens group G4 is in focus at a short distance from the position shown in FIG. 7A when focused at infinity (when focused at a shooting magnification of 0.05). Is moved in the direction shown in FIG. 7B, that is, the image plane side.
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 = 38.28, respectively. . Optical characteristics such as the radius of curvature of the optical surface (paraxial curvature radius for an aspheric surface) R, the surface interval D of adjacent optical surfaces, the refractive index Nd, the Abbe number νd, and the glass type in each optical element in Example 3 are as follows: It is as following Table 7.

In Table 7, the lens surface with the surface number indicated by adding “* (asterisk)” to the surface number is an aspherical surface. 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). The same applies to the other embodiments.
That is, in Table 7, the optical surfaces of the first surface, the second surface, and the eleventh surface marked with “*” are aspheric surfaces, and the parameters of each aspheric surface in Equation (7) are as follows. It is.
Aspheric parameter 1st surface K = 0.0
A4 = 1.94210E-04
A6 = 1.38851E-06
A8 = -1.38163E-07
A10 = 11.70008E-09
Second side K = 0.0
A4 = 5.333269E-04
A6 = 7.71136E-06
A8 = −9.667786E−08
A10 = 3.660169E-09

11th surface K = 0.70784
A4 = 1.79300E-04
A6 = 2.56458E-06
A8 = −2.332266E−08
A10 = 1.58423E-09
In Example 3, the variable distance DA between the sixth lens L6 of the third lens group G3 and the seventh lens L7 of the fourth lens group G4, the seventh lens L7 of the fourth lens group G4, and the filter glass are used. The variable interval such as the variable interval DB with the BF changes as shown in Table 8 below when focusing on infinity and focusing on a short distance (focusing at a shooting magnification of 0.05).

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

  FIG. 8 is a diagram showing aberration curves of various aberrations in d-line and g-line at the time of focusing on infinity of the imaging optical system according to Example 3, that is, spherical aberration, astigmatism, distortion aberration, and coma aberration. Show. FIG. 9 is an aberration curve diagram for the d-line and the g-line when the imaging optical system according to the third embodiment is in focus at a short distance. In the aberration curve diagrams of FIGS. 8 and 9, 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. 10 is an optical arrangement diagram showing the movement trajectory of the imaging optical system according to the fourth embodiment of the present invention and Example 4, and FIG. FIG. 6B is an optical layout diagram at the time of focusing on a distant object; ing.
That is, as shown in FIG. 10, the imaging optical system according to Example 4 of the present invention sequentially has a first lens L1, a second lens L2, a third lens L3, a first lens, from the object side to the image plane side. Four lenses 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 L1 constitutes a first lens group 1G having negative refractive power. The second lens L2 to the fourth lens L4 constitute a second lens group G2 having a positive refractive power. The fifth lens L5 to the seventh lens L7 constitute a third lens group G3 having positive refractive power. The eighth lens L8 constitutes a fourth lens group G4 having a negative refractive power.

That is, the imaging optical system shown in FIG. 10 moves these first lens group G1, second lens group G2, aperture stop S, third lens group G3, and fourth lens group G4 from the object side to the image plane side. Thus, the arrangement is sequentially arranged.
Specifically, the first lens group G1 is formed of a negative lens having a negative meniscus shape in which an aspheric surface is formed on both surfaces sequentially from the object side to the image surface side, and a concave surface is directed to the image surface side. The first lens L1 is arranged so as to exhibit negative refractive power. The second lens group G2, in order from the object side to the image plane side, in turn, a second lens L2 made of a positive lens having a biconvex shape with a convex surface having a larger curvature than the object side surface facing the image plane side; A third lens L3 composed of a negative lens having a biconcave shape with a concave surface having a larger curvature than the object side surface facing the image surface side, and a positive meniscus shape having a convex surface having a curvature larger than the image surface side directed to the object side A fourth lens L4 made of a positive lens is 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 bonded to form a cemented lens including three lenses.
An aperture stop S is disposed between the second lens group G2 and the third lens group G3.

The third lens group G3 includes, from the object side to the image surface side, a fifth lens L5 made of a positive lens having a convex surface having a curvature larger than that of the object side surface toward the image surface side. A sixth lens L6 made of a negative lens having a biconcave shape with a concave surface having a curvature larger than that of the image surface side facing the object side, and a positive surface formed by forming the aspheric surface on the image surface side with the concave surface facing the object side A seventh lens L7 composed of a positive meniscus lens is arranged so as to exhibit positive refractive power. The two lenses of the third lens group G3, that is, the fifth lens L5 and the sixth lens L6, are closely bonded to each other and joined together to form a cemented lens composed of two lenses. The fourth lens group G4 includes a seventh lens L7 made of a negative meniscus negative lens having a concave surface facing the object side, and is configured to exhibit negative refractive power.
Further, behind the fourth lens group G4, that is, on the image plane 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 formed as equivalent parallel plates. The filter glass BF shown is arranged.
An image plane is located further on the image side of the filter glass BF. This image plane matches the light receiving surface of the image sensor.

The first lens group G1, the second lens group G2, the aperture stop S, and the third lens group G3 are substantially integrally supported by an appropriate support frame or the like at least during use, and during focusing to focus on the subject. The fourth lens group G4 is moved along the optical axis direction for focusing. That is, the eighth lens L8 of the fourth lens group G4 is in focus at a short distance from the position shown in FIG. 10A when focused at infinity (when focused at a shooting magnification of 0.05). Is moved in the direction shown in FIG. 10B, that is, the image plane side.
FIG. 10 also shows the surface number of each optical surface in the optical system of the imaging lens. Note that each reference symbol shown in FIG. 10 is used independently for each embodiment in order to avoid complication of explanation due to an increase in the number of digits of the reference symbol. Therefore, FIG. 1, FIG. 4, FIG. 13 and 16 and the like are attached with the same reference numerals.
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 = 38.29, 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. 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). The same applies to the other embodiments.
That is, in Table 10, 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 the equation (7) are as follows. It is.
Aspheric parameter 1st surface K = 0.0
A4 = 1.94265E-04
A6 = 1.80289E-06
A8 = −6.80746E−08
A10 = 6.183552E-10

Second side K = 0.0
A4 = 4.59814E-04
A6 = 4.88953E-06
A8 = 1.82822E-08
A10 = 7.07672E-10
12th surface K = -12.89251
A4 = -6.47822E-04
A6 = 2.006198E-05
A8 = -3.96639E-07
A10 = 4.889925E-09
In Example 4, the variable distance DA between the seventh lens L7 of the third lens group G3 and the eighth lens L8 of the fourth lens group G4, the eighth lens L8 of the fourth lens group G4, and the filter glass are used. The variable interval such as the variable interval DB with the BF changes as shown in Table 11 below when focusing on infinity and focusing on a short distance (focusing at a shooting magnification of 0.05).

  In this case, the values corresponding to the conditional expressions (1) to (6) are as shown in the following table 12, which respectively satisfy the conditional expressions (1) to (6).

  FIG. 11 is a diagram showing aberration curves of various aberrations in d-line and g-line at the time of focusing on infinity of the imaging optical system according to Example 4, that is, spherical aberration, astigmatism, distortion aberration, and coma aberration. Show. FIG. 12 is an aberration curve diagram for the d-line and the g-line when the imaging optical system according to Example 4 is in close focus. In the aberration curve diagrams of FIGS. 11 and 12, 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. 13 is an optical arrangement diagram showing the movement trajectory of the image pickup optical system according to the fifth embodiment of the present invention and Example 5, and FIG. FIG. 6B is an optical layout diagram at the time of focusing on a distant object; ing.
That is, in the imaging optical system according to Example 5 of the present invention, as shown in FIG. 13, the first lens L1, the second lens L2, the third lens L3, Four lenses 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 L1 constitutes a first lens group 1G having negative refractive power. The second lens L2 to the fourth lens L4 constitute a second lens group G2 having a positive refractive power. The fifth lens L5 to the seventh lens L7 constitute a third lens group G3 having positive refractive power. The eighth lens L8 constitutes a fourth lens group G4 having a negative refractive power. That is, the imaging optical system shown in FIG. 13 moves these first lens group G1, second lens group G2, aperture stop S, third lens group G3, and fourth lens group G4 from the object side to the image plane side. Thus, the arrangement is sequentially arranged.

Specifically, the first lens group G1 is formed by sequentially forming aspheric surfaces on both sides from the object side to the image plane side, and both concave surfaces having a curvature larger than the object side surface are directed to the image plane side. A first lens L1 made of a negative lens having a concave shape is arranged so as to exhibit negative refractive power. The second lens group G2 includes a second lens L2 composed of a positive lens having a biconvex shape with a convex surface having a larger curvature than the object-side surface facing the image surface side, and a concave surface having a larger curvature than the object-side surface. A third lens L3 made of a negative lens having a biconcave shape directed toward the side, and a fourth lens L4 made of a positive lens having a positive meniscus shape having a convex surface directed toward the object side are arranged to have a positive refractive power It is configured to show. 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 bonded to form a cemented lens including three lenses.
An aperture stop S is disposed between the second lens group G2 and the third lens group G3.
The third lens group G3 includes, from the object side to the image surface side, a fifth lens L5 made of a positive lens having a convex surface having a curvature larger than that of the object side surface toward the image surface side. A sixth lens L6 formed of a negative lens having a biconcave shape with a concave surface having a curvature larger than that of the image side surface directed toward the object side, and a positive meniscus formed with a concave surface directed toward the object side and aspheric surfaces formed on both sides A seventh lens L7 made of a positive lens having a shape is arranged so as to exhibit positive refractive power.

The two lenses of the third lens group G3, that is, the fifth lens L5 and the sixth lens L6, are closely bonded to each other and joined together to form a cemented lens composed of two lenses. The fourth lens group G4 is configured so as to exhibit a negative refractive power by disposing an eighth lens L8 made of a biconcave negative lens in which a concave surface having a curvature larger than that of the image side surface is directed toward the object side. doing.
Further, behind the fourth lens group G4, that is, on the image plane 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 formed as equivalent parallel plates. The filter glass BF shown is arranged.
An image plane is located further on the image side of the filter glass BF. This image plane matches the light receiving surface of the image sensor.
The first lens group G1, the second lens group G2, the aperture stop S, and the third lens group G3 are supported by an appropriate support frame or the like at least when used, and the fourth lens is used for focusing to focus on the subject. The group G4 is moved along the optical axis direction to perform focusing. That is, the eighth lens L8 of the fourth lens group G4 is in focus at a short distance from the position shown in FIG. 13A when focused at infinity (when focused at a shooting magnification of 0.05). Is moved in the direction shown in FIG. 13B, that is, the image plane side.

FIG. 13 also shows the surface number of each optical surface in the optical system of the imaging lens. Note that each reference symbol shown in FIG. 13 is used independently for each embodiment in order to avoid complicated explanation due to an increase in the number of digits of the reference symbol. Therefore, FIG. 1, FIG. 4, FIG. 10 and 16 and the like are attached with the same reference numerals.
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 = 38.29, 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. 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). The same applies to the other embodiments.
That is, in Table 13, the optical surfaces of the first surface, the second surface, the eleventh surface, and the twelfth surface marked with “*” are aspheric surfaces, and the parameters of each aspheric surface in Equation (7) are as follows: It is as follows.
Aspheric parameter 1st surface K = 0.0
A4 = 1.09773E-04
A6 = -2.20638E-06
A8 = −3.665387E-09
A10 = 2.98426E-10
Second side K = 0.0
A4 = 2.36168E-04
A6 = 4.83996E-06
A8 = −2.666383E-07
A10 = 4.335424E-09

11th surface K = 0.0
A4 = −1.02763E−04
A6 = −4.006356E-07
A8 = 1.62922E-07
12th surface K = -7.97367
A4 = −6.668393E−04
A6 = 1.48881E-05
A8 = −1.80359E−07
A10 = 4.0767E-09
In Example 5, the variable distance DA between the seventh lens L7 of the third lens group G3 and the eighth lens L8 of the fourth lens group G4, the eighth lens L8 of the fourth lens group G4, and the filter glass are used. The variable interval such as the variable interval DB with the BF changes as shown in Table 14 below when focusing on infinity and focusing on a short distance (when focusing at a shooting magnification of 0.05).

  In this case, the values corresponding to the conditional expressions (1) to (6) are as shown in Table 15 below, which satisfy the conditional expressions (1) to (6), respectively.

  In addition, FIG. 14 shows various aberration curves of d-line and g-line at the time of focusing on infinity of the imaging optical system according to Example 5, that is, spherical aberration, astigmatism, distortion aberration, and coma aberration. Show. FIG. 15 shows aberration curves for the d-line and the g-line when the imaging optical system according to Example 5 is in close focus. In the aberration curve diagrams of FIGS. 14 and 15, 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. 16 is an optical arrangement diagram showing the movement trajectory of the imaging optical system according to the sixth embodiment of the present invention and Example 6, and (a) is an infinite focusing (infinity) of the imaging optical system. FIG. 6B is an optical layout diagram at the time of focusing on a distant object; ing.
That is, in the imaging optical system according to Example 6 of the present invention, as shown in FIG. 16, the first lens L1, the second lens L2, the third lens L3, and the aperture are sequentially formed from the object side to the image plane side. An aperture S, a fourth lens L4, a fifth lens L5, a sixth lens L6, and a seventh lens L7 are arranged. The second lens L2 and the third lens L3, and the fourth lens L4 and the fifth lens L5 These lenses constitute a cemented lens, which is a so-called five-group seven-element configuration.
Focusing on the lens group configuration, the first lens L1 constitutes a first lens group 1G having negative refractive power. The second lens L2 to the third lens L3 constitute a second lens group G2 having a positive refractive power. The fourth lens L4 to the sixth lens L6 constitute a third lens group G3 having a positive refractive power. The seventh lens L7 constitutes a fourth lens group G4 having a negative refractive power. That is, the imaging optical system shown in FIG. 16 moves these first lens group G1, second lens group G2, aperture stop S, third lens group G3, and fourth lens group G4 from the object side to the image plane side. Thus, the arrangement is sequentially arranged.

Specifically, in the first lens group G1, a negative lens is formed by forming a first lens L1 formed of a negative lens having an aspheric surface on both sides and a negative meniscus shape with a concave surface facing the image surface side. It is configured to show refractive power. The second lens group G2 includes a second lens L2 composed of a negative lens having a biconcave shape with a concave surface having a curvature larger than the object side surface facing the image surface side, and a convex surface having a curvature larger than the image surface side surface. A third lens L3 made of a positive lens having a biconvex shape directed toward the side is disposed so as to exhibit a positive refractive power. Note that the two lenses, the second lens L2 and the third lens L3, are closely bonded to each other and are integrally joined to form a cemented lens composed of two lenses.
An aperture stop S is disposed between the second lens group G2 and the third lens group G3.
The third lens group G3 includes, from the object side to the image surface side, a fourth lens L4 made of a positive lens having a biconvex shape with a convex surface having a larger curvature than the object side surface directed toward the image surface side. A fifth lens L5 composed of a negative lens having a biconcave shape with a concave surface having a larger curvature than the image surface side facing the object side, and a positive surface formed by directing the concave surface to the object side and forming an aspheric surface on the image surface side A sixth lens L6 made of a positive lens having a meniscus shape is arranged so as to exhibit positive refractive power. The two lenses of the fourth lens L4 and the fifth lens L5 of the third lens group G3 are closely bonded to each other and are integrally joined to form a cemented lens composed of two lenses. The fourth lens group G4 includes a seventh lens L7 made of a negative meniscus negative lens having a concave surface facing the object side, and is configured to exhibit negative refractive power.

Further, behind the fourth lens group G4, that is, on the image plane 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 formed as equivalent parallel plates. The filter glass BF shown is arranged.
An image plane is located further on the image side of the filter glass BF. This image plane matches the light receiving surface of the image sensor.
The first lens group G1, the second lens group G2, the aperture stop S, and the third lens group G3 are substantially integrally supported by an appropriate support frame or the like at least during use, and during focusing to focus on the subject. The fourth lens group G4 is moved along the optical axis direction for focusing. That is, the seventh lens L7 of the fourth lens group G4 is in focus at a short distance from the position shown in FIG. 16A when focused at infinity (when focused at a shooting magnification of 0.05). First, it moves in the direction shown in FIG.
FIG. 16 also shows the surface numbers of the optical surfaces in the optical system of the imaging lens. Note that each reference symbol shown in FIG. 16 is used independently for each embodiment in order to avoid complication of explanation due to an increase in the number of digits of the reference symbol. Therefore, FIG. 1, FIG. 4, FIG. 10 and FIG. 13 and the like are assigned the same reference numerals.

  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 = 38.28, 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 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. 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). The same applies to the other embodiments.
That is, in Table 7, the optical surfaces of the first surface, the second surface, and the eleventh surface marked with “*” are aspheric surfaces, and the parameters of each aspheric surface in Equation (7) are as follows. It is.
Aspheric parameter 1st surface K = 0.0
A4 = 2.30076E-04
A6 = 2.695951E-06
A8 = −1.48004E-07
A10 = 1.52752E-09

Second side K = 0.0
A4 = 5.67733E-04
A6 = 1.01229E-05
A8 = -1.91231E-07
A10 = 4.774193E-09
11th surface K = 0.65011
A4 = 1.68773E-04
A6 = 2.48080E-06
A8 = −2.43825E−08
A10 = 1.39894E-09
In Example 6, the variable distance DA between the sixth lens L6 of the third lens group G3 and the seventh lens L7 of the fourth lens group G4, the seventh lens L7 of the fourth lens group G4, and the filter glass are used. The variable interval such as the variable interval DB with the BF changes as shown in Table 17 below when focusing on infinity and focusing on a short distance (focusing at a shooting magnification of 0.05).

  In this case, the values corresponding to the conditional expressions (1) to (6) are as shown in Table 18 below, which satisfy the conditional expressions (1) to (6), respectively.

  FIG. 17 shows various aberration curves of d-line and g-line at the time of focusing on infinity of the imaging optical system according to Example 6, that is, spherical aberration, astigmatism, distortion aberration, and coma aberration. Show. FIG. 18 is an aberration curve diagram for the d-line and the g-line when the imaging optical system according to Example 6 is in close focus. In the aberration curve diagrams of FIGS. 17 and 18, 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.

[Seventh Embodiment]
Next, a digital camera as a camera apparatus according to the seventh embodiment of the present invention configured by adopting the imaging optical system according to the first to sixth embodiments of the present invention described above. This will be described with reference to FIGS. FIG. 19 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. 20 is a schematic external view of the digital camera viewed from the back side which is the photographer side. FIG. 21 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. 19 to 21, the digital camera includes a photographing lens 1, an optical viewfinder 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. A card slot 9 and the like are provided. Further, as shown in FIG. 21, 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 has a photographing 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. An optical image of a subject (object) formed by the photographing lens 1 is read by the light receiving element 13. As the photographing 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 photographic 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 performed by moving the fourth lens group G4. Can do. 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 photographing lens 1 configured using the imaging optical system as shown in the first to sixth embodiments. It can be used as an imaging optical system. Therefore, it has a sufficiently wide field angle of 76 degrees or more, a large aperture with an F number of about 2.8 or less, and ensures a very good image performance even with a small inner focus type. A small camera device or portable information terminal device with high image quality using the obtained imaging optical system can be realized.

G1 first lens group (negative)
G2 Second lens group (positive)
G3 Third lens group (positive)
G4 4th lens group (negative)
L1 1st lens L2 2nd lens L3 3rd lens L4 4th lens L5 5th lens L6 6th lens L7 7th lens L8 8th lens S Aperture stop BF Filter glass 1 Shooting lens 2 Optical viewfinder 3 Strobe (flash light)
4 Shutter button 5 Camera body 6 Power switch 7 LCD monitor 8 Operation button 11 Central processing unit (CPU)
DESCRIPTION OF SYMBOLS 12 Image processing apparatus 13 Light receiving element 14 Signal processing apparatus 15 Semiconductor memory 16 Communication card etc.

JP-A-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

Claims (12)

In order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, an aperture stop, a third lens group having a positive refractive power, and a negative refractive power. The first lens group is composed of a negative lens having a concave surface facing the image side, and the second lens group is composed of one cemented lens including a positive lens and a negative lens, The third lens group includes a cemented lens in which a positive lens having a convex surface facing the image side in order from the object side and a negative lens are cemented on the most object side, and the fourth lens group is disposed on the object side. Consists of a negative lens with a concave surface, and during focusing, the fourth lens group moves in the optical axis direction ,
When the distance on the optical axis from the image plane to the exit pupil at the time of focusing on infinity is AP, and the radius of curvature of the leading surface of the fourth lens group is Rg41, the following conditional expression (6):
0.50 <| AP / Rg41 | <1.30 (6)
An imaging optical system characterized by satisfying   2. The imaging optical system according to claim 1, wherein an air lens formed by a final surface of the second lens group and a leading surface of the third lens group has a shape with a concave surface facing the image side, and is positive An imaging optical system having a refractive power. The imaging optical system according to claim 1 or 2, wherein f is a focal length of the entire system and f4 is a focal length of the fourth lens group, and the following conditional expression (1):
0.30 <| f / f4 | <1.20 (1)
An imaging optical system characterized by satisfying The imaging optical system according to claim 1 or 2, wherein f is a focal length of the entire system and f3 is a focal length of the third lens group, and the following conditional expression (2):
0.90 <f / f3 <1.80 (2)
An imaging optical system characterized by satisfying 5. The imaging optical system according to claim 1, wherein f is a focal length of the entire system, and f <b> 12 is a combined focal length of the first lens group and the second lens group. Conditional expression (3):
0.01 <f / | f12 | <0.50 (3)
An imaging optical system characterized by satisfying 6. The imaging optical system according to claim 1, wherein the distance on the optical axis from the front surface of the first lens group to the aperture stop is Ls, and the first optical system at the time of focusing on infinity is used. Conditional expression (4) below, where TL is the distance on the optical axis from the first surface of one lens unit to the final surface of the fourth lens unit:
0.35 <Ls / TL <0.65 (4)
An imaging optical system characterized by satisfying The imaging optical system according to any one of claims 1 to 6, wherein an on-axis distance from a leading surface of the first lens group to a final surface of the fourth lens group at the time of focusing on infinity is set. Assuming that TL is the focal length of the entire system and f is the following conditional expression (5):
0.50 <TL / f <1.30 (5)
An imaging optical system characterized by satisfying The imaging optical system according to any one of claims 1 to 7 , wherein the second lens group includes a cemented lens of a biconcave negative lens and a positive lens, and the third lens group is An imaging optical system comprising a cemented lens of a biconvex positive lens and a biconcave negative lens. In the imaging optical system according to any one of claims 1 to 8, wherein the third lens group includes a cemented lens of a positive lens and a double concave negative lens of biconvex shape, a convex surface on the image side An imaging optical system characterized by comprising a positive meniscus lens facing the lens. Camera apparatus having an imaging optical system according to any one of claims 1 to 9. 11. The camera device according to claim 10, wherein the camera device 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 .

Images