JP2010217505A - Imaging optical system, camera, and personal digital assistant - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging optical system that is comparatively small and sufficiently decreases various aberration, thereby enabling high image quality photographing despite high performance, an angle of view that is as wide as 76° or greater, and a large aperture with an Fno of approximately 2.0 or smaller, and to provide a camera and a personal digital assistant. <P>SOLUTION: The imaging optical system includes, in order from an object side to an image surface, a first lens group G1, an aperture diaphragm FA, and a second lens group G2. The first lens group G1 includes a front lens group 1F of negative refractive power and a rear first lens group 1R of positive refractive power having a space interval therebetween which is the widest in the first lens group G1. The second lens group G2 includes: a front second lens group 2F having, in order from the object side, a cemented lens formed of a first positive lens and a first negative lens, and a cemented lens formed of a second negative lens and a second positive lens; and a rear second lens group 2R having at least one lens. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an improvement of a single-focus imaging lens used as an imaging optical system in various cameras including a so-called silver salt camera, and in particular, an imaging optical system suitable for cameras such as digital cameras and video cameras, and such The present invention relates to a camera device having an imaging optical system and a portable information terminal device.

In recent years, the market for digital cameras has become very large, and the demands of users for digital cameras are also diverse. Among them, the category of compact and high-quality compact cameras equipped with high-performance single focus lenses has gained a certain amount of support from users, and expectations are high. As a request from the user, in addition to high performance, there is a high weight for the small F number, that is, the large aperture.
Here, in terms of performance enhancement, in addition to having a resolution corresponding to at least an image sensor of 10 million to 20 million pixels, from the full aperture to a high contrast and a peripheral portion of the angle of view with little coma flare. It is necessary that there is no distortion of the point image, that there is no chromatic aberration and that no unnecessary coloring is generated even in a portion with a large luminance difference, that there is little distortion and that a straight line can be drawn as a straight line.
Furthermore, in terms of increasing the diameter, at least F2.4 or less is necessary because of the need to differentiate from a general compact camera equipped with a zoom lens, and many people desire F2.0 or less.
In addition, regarding the angle of view of the photographic lens, there are many users who desire a certain wide angle, and it is desirable that the half angle of view of the imaging optical system is 38 degrees or more. A half angle of view of 38 degrees corresponds to a focal length of 28 mm in terms of a 35 mm silver salt camera (so-called Leica version).

There are many types of imaging optical systems for digital cameras, but typical configurations of wide-angle single focus lenses include a negative refractive power lens group on the object side and a positive refractive power lens group on the image side. A so-called retrofocus type in which is provided. This is because of the characteristics of an area sensor having a color filter and a microlens for each pixel, there is a need to move the exit pupil position away from the image plane so that the peripheral luminous flux is incident on the sensor at an angle close to vertical. This is the main reason why the retro focus type is adopted. However, the retrofocus type has a large asymmetry in its refractive power arrangement, and tends to be incompletely corrected for coma, distortion, lateral chromatic aberration, and the like.
Among the conventional examples of such a retrofocus type imaging optical system, Patent Document 1 (Japanese Patent Laid-Open No. 06-308385), which has a relatively large aperture and a half field angle of about 38 degrees, There are some disclosed in Patent Document 2 (Japanese Patent Laid-Open No. 09-218350), Patent Document 3 (Japanese Patent Laid-Open No. 2006-349920), and the like.

However, although the imaging optical system disclosed in Patent Document 1 has a large aperture of F1.4, astigmatism and curvature of field are large, and it has sufficient performance up to the periphery near the aperture stop. I can't say that. The imaging optical system disclosed in Patent Document 2 is inferior in terms of F2.8 and a large aperture, and has large astigmatism, curvature of field, and lateral chromatic aberration, and this also has sufficient performance up to the peripheral part. It cannot be said that it has. In both cases, the distortion aberration exceeds 2% in absolute value.
In addition, the imaging optical system disclosed in Patent Document 3 is well corrected for astigmatism, curvature of field, and distortion, but has a large color difference of coma aberration not shown in the specification. In addition, an embodiment with a small F number is insufficient in terms of miniaturization.

The present invention has been made in view of the above circumstances, and an object of the present invention is to have a wide angle with an angle of view of about 76 degrees or more and a relatively large aperture with an F number of about 2.0 or less. The object is to provide a high-performance imaging optical system that is small in size and sufficiently reduces various aberrations.
An object of the invention described in claim 2 is to provide an imaging optical system capable of reducing both axial chromatic aberration and lateral chromatic aberration more effectively and improving the degree of freedom for aberration correction.
An object of the invention described in claim 3 is to provide an imaging optical system capable of realizing a wide angle and a large aperture.
The object of the invention described in claim 4 is to provide an imaging optical system in which manufacturing errors are substantially reduced, stable performance is easily obtained, and the number of parts of the lens barrel that actually holds the lens can be reduced. There is to do.
An object of the invention described in claim 5 is to provide an imaging optical system capable of improving axial chromatic aberration correction and the degree of freedom for aberration correction.
An object of the invention described in claim 6 is to provide an imaging optical system that makes it easy to obtain a stable state by reducing manufacturing errors while improving aberration correction and reducing the size.

The object of the invention described in claim 7 is that the weight of the moving part can be reduced as compared with a method of moving and focusing the entire imaging optical system, which is advantageous for speeding up focusing and power saving. When the imaging optical system according to the present invention is incorporated in a camera device, when the lens system has a mechanism for shortening the interval between the lens groups and the back focus portion when not in use and storing them in a compact manner, It is an object of the present invention to provide a convenient camera device that can share a mechanism with a focusing mechanism.
The object of the invention described in claim 8 is a camera that has a wide angle of view of 76 ° or more, a large aperture with an F number of about 2.0 or less, and is small and capable of shooting with high image quality. To provide an apparatus.
The object of the invention described in claim 9 is a wide angle of view of 76 ° or more, a small aperture with an F number of about 2.0 or less and a large aperture, and sufficiently reducing each aberration. Another object of the present invention is to provide a digital camera device capable of photographing with high image quality.
The object of the invention described in claim 10 is a wide angle of view of 76 ° or more, a small aperture with an F number of about 2.0 or less and a small diameter, and sufficiently reducing each aberration. An object of the present invention is to provide a high-quality portable information terminal device capable of photographing.

In order to achieve the above-described object, the imaging optical system according to the first aspect of the present invention includes a first lens group positioned on the object side with an aperture stop interposed therebetween, and a second lens group positioned on the image side. In the imaging optical system constituted by: a front first lens group having at least two negative lenses in order from the object side toward the first lens group, with the widest air interval in the first lens group as a boundary; A rear first lens group having at least one positive lens, and the second lens group in order from the object side is a first positive lens, a first negative lens, a second negative lens, and a second positive lens. As a whole, it is characterized by comprising a front second lens group in which positive cemented lenses are continuously arranged and a rear second lens group comprising at least one lens.
The imaging optical system according to the present invention described in claim 2 is the imaging optical system according to claim 1,
The combined focal length of the first positive lens and the first negative lens in the front second lens group is f21, and the second negative lens and the second positive lens in the front second lens group as a whole are positive. Let f22 be the focal length of a cemented lens having a refractive power of
Conditional expression:
| F22 / f21 | <0.5 (1)
It is characterized by satisfying.

The imaging optical system according to the present invention described in claim 3 is the imaging optical system according to claim 1 or 2,
The focal length of the entire imaging optical system is f, and the focal length f2 of the front second lens group is
Conditional expression:
0.2 <f / f2 <0.5 (2)
It is characterized by satisfying.
The imaging optical system according to a fourth aspect of the present invention is the imaging optical system according to any one of the first to third aspects, wherein the first positive lens and the first lens in the front second lens group are the same. One negative lens is cemented.
The imaging optical system according to a fifth aspect of the present invention is the imaging optical system according to any one of the first to fourth aspects, wherein the first negative lens in the front second lens group is an image. It is characterized by a meniscus lens convex to the side.
The imaging optical system according to the present invention described in claim 6 is the imaging optical system according to any one of claims 1 to 5,
The focal length of the first lens group is f1, and the focal length f of the entire imaging optical system is
Conditional expression:
| F1 | / f> 8.0 (3)
It is characterized by satisfying.

An imaging optical system according to a seventh aspect of the present invention is the imaging optical system according to any one of the first to sixth aspects, wherein the second lens group is moved in whole or in part to be infinite. It is characterized by focusing from a long distance to a short distance.
A camera apparatus according to an eighth aspect of the present invention includes the imaging optical system according to any one of the first to seventh aspects.
A camera device according to a ninth aspect of the present invention is the camera device according to the eighth aspect, wherein the camera device has a function of converting a captured image into digital information.
A portable information terminal device according to a tenth aspect of the present invention includes the imaging optical system according to any one of the first to seventh aspects.

  According to the first aspect of the present invention, in the imaging optical system including the first lens group located on the object side across the aperture stop and the second lens group located on the image side, the first lens In order from the object side, the front side first lens group having at least two negative lenses and the rear side first having at least one positive lens with the widest air interval in the first lens group as a boundary. The second lens group is composed of a first positive lens, a first negative lens, a second negative lens, and a second positive lens in order from the object side. By comprising the front second lens group provided and the rear second lens group comprising at least one lens, it has a high performance and a wide field angle of 76 ° or more, and is small and has an F number of 2. Imaging optics with a large aperture of about 0 or less It can provide, by extension, it is possible to realize a camera device and a portable information terminal device capable of shooting with high image quality, yet wide angle of view, large diameter and small.

According to the invention described in claim 2, in the imaging optical system according to claim 1,
The combined focal length of the first positive lens and the first negative lens in the front second lens group is f21, and the second negative lens and the second positive lens in the front second lens group as a whole are positive. Let f22 be the focal length of a cemented lens having a refractive power of
Conditional expression:
| F22 / f21 | <0.5 (1)
By satisfying
In particular, it is possible to provide an imaging optical system that can more effectively reduce both axial chromatic aberration and lateral chromatic aberration and improve the degree of freedom for aberration correction.
According to the invention of claim 3, in the imaging optical system of claim 1 or 2,
The focal length of the entire imaging optical system is f, and the focal length f2 of the front second lens group is
Conditional expression:
0.2 <f / f2 <0.5 (2)
By satisfying
An imaging optical system capable of realizing a wide angle and a large aperture can be provided.

According to the invention described in claim 4, in the imaging optical system according to any one of claims 1 to 3, the first positive lens and the first negative lens in the front second lens group are cemented. As a result, it is possible to provide an imaging optical system in which manufacturing errors are substantially reduced, stable performance is easily obtained, and the number of parts of the lens barrel that actually holds the lens can be reduced.
According to a fifth aspect of the present invention, in the imaging optical system according to any one of the first to fourth aspects, the first negative lens in the front second lens group is a meniscus convex to the image side. Since it is a lens, it is possible to provide an imaging optical system that can improve the correction of axial chromatic aberration and the degree of freedom for aberration correction.
According to the invention described in claim 6, in the imaging optical system according to any one of claims 1 to 5,
The focal length of the first lens group is f1, and the focal length f of the entire imaging optical system is
Conditional expression:
| F1 | / f> 8.0 (3)
By satisfying the above, it is possible to provide an imaging optical system that makes it easy to obtain a stable state by reducing manufacturing errors while improving the aberration correction and reducing the size.

According to the seventh aspect of the present invention, in the imaging optical system according to any one of the first to sixth aspects, the whole or part of the second lens group is moved from infinity to a short distance. By performing this focusing, it is possible to reduce the weight of the moving part compared to the method of moving the entire imaging optical system to perform focusing, which is advantageous for speeding up focusing and power saving. When the imaging optical system is incorporated into the camera device, when there is a mechanism for shortening the distance between the lens groups and the back focus portion when not in use and storing them in a compact manner, the mechanism for storing the second lens group is a focusing mechanism. And a convenient camera device can be provided.
According to the present invention described in claim 8, by having the imaging optical system according to any one of claims 1 to 7,
It is possible to provide a camera device having a wide angle of view of 76 ° or more, a large aperture having an F number of about 2.0 or less, and capable of shooting with high quality while being small.

According to the ninth aspect of the present invention, in the camera device according to the eighth aspect of the present invention, the camera apparatus has a function of using a captured image as digital information, thereby having a wide angle of view of 76 ° or more and an F-number. Although it has a large aperture of about 2.0 or less, it is small in size, and each aberration can be sufficiently reduced to provide a high-quality digital camera device.
According to the tenth aspect of the present invention, by having the imaging optical system according to any one of the first to seventh aspects, the wide angle of view is 76 ° or more and the F number is 2. Although it has a large aperture of about 0 or less, it is small in size, and each aberration can be sufficiently reduced to provide a high-quality portable information terminal device.

1 is an optical arrangement diagram illustrating a cross-sectional configuration of a first embodiment of an imaging optical system according to the present invention. It is an optical arrangement | positioning figure which shows the cross-sectional structure of Example 2 of the imaging optical system concerning this invention. It is an optical arrangement | positioning figure which shows the cross-sectional structure of Example 3 of the imaging optical system concerning this invention. It is an optical arrangement | positioning figure which shows the cross-sectional structure of Example 4 of the imaging optical system concerning this invention. It is an optical arrangement | positioning figure which shows the cross-sectional structure of Example 5 of the imaging optical system concerning this invention. FIG. 6 is an aberration curve diagram of an object at infinity of the imaging optical system according to the first example. FIG. 9 is an aberration curve diagram of an object at infinity of the imaging optical system according to the second example. FIG. 10 is an aberration curve diagram of an object at infinity of the imaging optical system according to the third example. FIG. 10 is an aberration curve diagram of an object at infinity of the imaging optical system according to the fourth example. FIG. 10 is an aberration curve diagram of an object at infinity of the imaging optical system according to the fifth example.

The broken line of spherical aberration represents the sine condition, the solid line in the figure of astigmatism represents sagittal, and the broken line represents meridional. The thin line is the d line, and the thick line is an aberration curve diagram with respect to the g line.
It is a perspective view which shows the external appearance of the camera seen from the front side which is an object, ie, a subject side, in which (a) shows a state in which the lens barrel is retracted, and (b) shows a state in which the lens barrel is extended. Indicates. It is a perspective view which shows the external appearance of the camera apparatus seen from the back side which is a photographer side. It is a block diagram which shows the function structure of a camera apparatus.

Hereinafter, based on an embodiment and an example concerning the present invention, an imaging optical system, a camera device, and a personal digital assistant device of the present invention are explained in detail with reference to drawings. Before describing specific embodiments and examples, the basic configuration of the present invention will be described first.
A retrofocus type imaging optical system like the present invention generally has a negative refracting power on the object side and a positive refracting power on the image side. Etc. are likely to occur, and the reduction of these aberrations becomes a major issue. Further, with the increase in diameter, it becomes difficult to correct coma aberration and the color difference of coma aberration, and further problems are accumulated. The present invention has been found that these aberration correction problems can be solved by adopting the following configuration.
That is, in the present invention, in the imaging optical system including the first lens group located on the object side with the aperture stop interposed therebetween and the second lens group located on the image side, the first lens group is disposed from the object side. In order, the first lens group having a negative refractive power at the widest air interval in the first lens group (positionally on the object side, but hereinafter referred to as “front side”), A first lens unit having a positive refractive power (positionally on the image side, but hereinafter referred to as “rear side”), and the second lens unit in order from the object side. A front second lens group including a positive lens, a first negative lens, a second negative lens, and a second positive lens as a whole, in which a positive cemented lens is continuously arranged, and a rear second lens composed of at least one lens. The imaging optical system is constituted by a lens group (corresponding to claim 1).

  First, in the imaging optical system of the present invention, it can be considered that the first lens group plays a role like a wide converter added to the second lens group. Here, the first lens group is configured so that negative refractive power (front first lens group) and positive refractive power (rear first lens group) are sequentially arranged from the object side, By ensuring a relatively large interval, it is possible to secure both a sufficient angle of view and correction of various aberrations including spherical aberration. Here, the rear first lens group is opposed to the front second lens group with the aperture stop interposed therebetween, and has an aspect of controlling coma aberration by the balance of positive refractive powers of both. What characterizes the present invention most is the role and configuration of the front second lens group. In the imaging optical system of the present invention, the front second lens group is responsible for the main imaging function, and can be said to be the most important lens group in terms of aberration correction. Here, the front second lens group is based on a so-called triplet type of positive, negative, and positive as its refractive power arrangement, but the central negative refractive power is divided into two, and the last positive lens is A cemented lens made up of a second negative lens and a second positive lens was used to form a four-lens configuration, and a tesser type was configured. Since the aperture stop is disposed on the object side of the front second lens group, the first positive lens and first negative lens pair and the second negative lens and second positive lens pair have high off-axis rays. This makes it possible to effectively reduce both axial chromatic aberration and lateral chromatic aberration. Further, since the aperture stop is disposed on the object side of the front second lens group, the positive power balance before and after the first negative lens is directly within the front second lens group as in the case of a normal Tesser type. Therefore, the degree of freedom for correcting coma aberration and reducing decentration sensitivity is increased.

The rear second lens group serves to balance aberrations and control the exit pupil distance. Needless to say, having positive refracting power is effective in securing the exit pupil distance, but if the exit pupil distance can be short, giving negative refracting power contributes to shortening the overall lens length. It is also possible.
According to the configuration of the imaging optical system of the present invention, as described above, it is possible to obtain a large effect on aberration correction, a half angle of view of a wide angle of about 38 degrees, and an F number of about 2.0 or less. It is possible to achieve very high image performance even under severe conditions such as a large aperture.
In order to achieve higher performance, the following conditional expression (1) should be satisfied (corresponding to claim 2).
| F22 / f21 | <0.5 (1)
However, f21 is a composite focal length of the first positive lens and the first negative lens in the front second lens group, and f22 is a whole composed of the second negative lens and the second positive lens in the front second lens group. It represents the focal length of the positive cemented lens.

  In the front second lens group, the focal length of the overall positive cemented lens composed of the second negative lens and the second positive lens is made smaller than the combined focal length of the first positive lens and the first negative lens, The off-axis light beam passes through the positive cemented lens as a whole consisting of the second negative lens and the second positive lens, and both axial chromatic aberration and lateral chromatic aberration can be reduced more effectively. The degree of freedom is improved. When the combined focal length of the first positive lens and the first negative lens in the front second lens group is positive, if the upper limit value of the conditional expression (1) is exceeded, a pair of the first positive lens and the first negative lens, The difference between the heights of off-axis rays between the second negative lens and the second positive lens becomes small, making it difficult to effectively reduce both axial chromatic aberration and chromatic aberration of magnification, and the degree of freedom in correcting aberrations. The chromatic aberration may be insufficiently corrected. When the combined focal length of the first positive lens and the first negative lens in the front second lens group is negative, if the upper limit value of the conditional expression (1) is exceeded, the whole composed of the second negative lens and the second positive lens As a result, the off-axis light beam in the positive cemented lens becomes too high, and the positive cemented lens as a whole becomes excessive. In addition, the exchange of various aberrations between the pair of the first positive lens and the first negative lens and the pair of the second positive lens and the second negative lens becomes excessive, and the required accuracy with respect to the decentration of the lens and the air gap becomes too high. End up.

In order to achieve better performance, it is desirable to satisfy the following conditional expression (1) ′.
| F22 / f21 | <0.25 (1) ′
In order to achieve higher performance, it is desirable that the following conditional expression (2) is satisfied (corresponding to claim 3).
0.2 <f / f2 <0.5 (2)
Here, f is the focal length of the entire imaging optical system, and f2 is the focal length of the front second lens group. If the lower limit value of the conditional expression (2) is exceeded, the influence of the image forming action of the front second lens group in the entire system becomes too small, and in the configuration of the imaging optical system including the front second lens group described above. The effect may be reduced, and it may be difficult to maintain high performance under severe conditions such as a wide angle and a large aperture. If the upper limit value of the conditional expression (2) is exceeded, the influence of the image forming action of the front second lens group in the entire imaging optical system becomes so great that a spherical surface is formed in the front second lens group. Excessive exchange of aberrations and other aberrations becomes excessive, and the required accuracy for lens decentration and air spacing becomes too high.

In order to achieve higher performance, the first positive lens and the first negative lens in the front second lens group may be cemented (corresponding to claim 4).
In each lens surface in the front second lens group, in order to reduce the final aberration amount, each aberration is greatly exchanged, and the manufacturing error sensitivity tends to be high. By joining the first positive lens and the first negative lens, and the second negative lens and the second positive lens, the substantial manufacturing error sensitivity is reduced, and stable performance is easily obtained. It also leads to a reduction in the parts of the lens barrel that actually holds the lens.
In order to achieve higher performance, the first negative lens in the front second lens group may be a meniscus lens convex to the image side (corresponding to claim 5).
The first positive lens and the first lens in the front second lens group described above are suppressed by reducing the incident angle and the outgoing angle of the off-axis principal ray on the object side surface and the image side surface of the first negative lens in the front second lens group. The role of correcting the longitudinal chromatic aberration by the pair of negative lenses can be further enhanced. On the other hand, chromatic aberration of magnification can be performed by sharing the roles of axial chromatic aberration correction and magnification chromatic aberration correction by performing correction mainly with a pair of the second negative lens and the second positive lens. The degree of freedom is improved.

In order to achieve higher performance, the following conditional expression should be satisfied (corresponding to claim 6).
| F1 | / f> 8.0 (3)
Here, f1 is the focal length of the first lens group, and f is the focal length of the entire imaging optical system. If the lower limit of conditional expression (3) is exceeded when the first lens group is positive, the image forming action of the front second lens group becomes relatively weak, and the role of aberration correction that is played in the entire optical system There is a risk that it becomes difficult to effectively reduce both axial chromatic aberration and lateral chromatic aberration. If the lower limit of conditional expression (3) is exceeded when the first lens group is negative, the axial marginal light passing through the front second lens group becomes too high, and the effective diameter of the front second lens group becomes excessive. It is difficult to construct a compact and compact imaging optical system. In addition, the aperture diameter is excessive. Further, the refractive power of the second lens group must be made relatively strong, which is not preferable because the curvature of the image surface becomes large and negative distortion tends to occur greatly. In addition, if the lower limit value of the conditional expression (3) is exceeded regardless of whether the power of the first lens group is positive or negative, the exchange of various aberrations including spherical aberration in the first lens group becomes excessive, and between the lenses. The required accuracy for eccentricity and air spacing becomes too high.

In order to perform better aberration correction, it is desirable to satisfy the following conditional expression (3) ′.
f1 / f> 8.0 (3) ′
If the power of the first lens group is negative, the refractive power of the second lens group must be made relatively strong, and the curvature of the image surface becomes large or negative distortion tends to occur greatly. Because.
Further, in order to keep the performance at the time of focusing high, it is sufficient to adopt a configuration in which the whole or a part of the second lens group is moved to perform focusing from infinity to a short distance (corresponding to claim 7).
According to such a focusing method, the weight of the moving part can be reduced compared to a method of moving and focusing the entire imaging optical system, which is advantageous for speeding up focusing and power saving. In addition, when the imaging optical system of the present invention is incorporated in a camera, when it has a mechanism for shortening the distance between the lens groups and the back focus portion when not in use and storing them in a compact manner, The mechanism can be shared with the focusing mechanism, which is convenient. Since the focal length of the first lens group is relatively long, even if the air spacing between the first lens group and the second lens group changes, the height of the on-axis marginal light passing through the surface closest to the object side of the second lens group is high. There is little change in length, and performance degradation is unlikely to occur.

Next, specific examples based on the above-described embodiment of the present invention will be described in detail.
Examples 1 to 5 described below are also embodiments of the imaging optical system according to the present invention, and also show examples of specific configurations based on specific numerical examples.
Embodiments of the camera device and the portable information terminal device according to the present invention using the imaging optical system as shown in the first to fifth embodiments will be described later with reference to FIGS.
Specific numerical examples of the imaging optical system of the present invention will be shown below. In all the examples, the maximum image height is 4.80 mm.
In each embodiment, the parallel plate MF disposed on the image plane side of the rear second lens group 2R is made of various filters such as an optical low-pass filter and an infrared cut filter, and a cover glass of a light receiving element such as a CCD sensor ( Seal glass).
The aberration in each example is corrected at a high level, and the spherical aberration and the axial chromatic aberration are so small that they do not cause a problem. Astigmatism, curvature of field, and lateral chromatic aberration are sufficiently small, coma and disturbance of the color difference are well suppressed to the outermost periphery, and distortion aberration is 2.0% or less in absolute value. By configuring the image pickup optical system as in the present invention, it is possible to ensure a very good image performance while having a wide angle of view of about 76 ° and a large aperture of F number of about 2.0 or less. It is clear from the examples that it is obtained.

The meanings of the symbols in this embodiment are as follows.
f: Focal length of the entire imaging lens Fno: F number ω: Half angle of view Y ′: Maximum image height R: Curvature radius D: Surface interval N _d : Refractive index ν _d : Abbe number K: Conical constant of aspheric surface A ₂ : Second-order aspheric coefficient A ₄ : Fourth-order aspheric coefficient A ₆ : Sixth-order aspheric coefficient A ₈ : Eighth-order aspheric coefficient A ₁₀ : Tenth-order aspheric coefficient However, paraxial radius of curvature Where the reciprocal (paraxial curvature) is C and the height from the optical axis is H, the amount of displacement in the optical axis direction from the surface apex is X, and the aspheric coefficient is A _2i. Defined in 4).

FIG. 1 shows the configuration of an imaging optical system according to an embodiment (numerical embodiment) 1 of the present invention, and schematically shows a longitudinal section along the optical axis.
The optical system shown in FIG. 1 has, in order from the object side to the image surface, a first lens E1 composed of a negative meniscus negative lens having a convex surface facing the object side, and a strong concave surface formed with an aspheric surface on the image surface side. The second lens E2 made of a negative meniscus negative lens, the third lens E3 that is a biconvex positive lens, the aperture stop FA, the fourth lens E4 that is a biconvex positive lens, and the negative meniscus negative. A cemented lens obtained by closely bonding a fifth lens E5 that is a lens, a sixth lens E6 that is a negative meniscus negative lens, and a seventh lens E7 that is a biconvex positive lens are closely bonded. A cemented lens and an eighth lens E8, which is a positive meniscus type positive lens having an aspheric surface on the object side, are arranged.
The first lens E1 to the third lens E3 constitute the first lens group G1, and the fourth lens E4 to the eighth lens E8 constitute the second lens group G2.
In the first lens group G1, the front first lens group 1F is constituted by the first lens E1 and the second lens E2 which are located on the object side having negative refractive power with the widest air interval as a boundary, The third lens E3 located on the image side having positive refractive power constitutes the rear first lens group 1R.

The second lens group G2 includes, in order from the object side, a fourth lens E4 as a first positive lens, a fifth lens E5 as a first negative lens, a sixth lens E6 as a second negative lens, and a second positive lens. The seventh lens E7 as a lens constitutes the front second lens group 2F, and the eighth lens E8 constitutes the rear second lens group 2R. In the imaging optical system L1, the whole or part of the second lens group G2 is moved to perform focusing on a finite distance object (an object from infinity to a short distance).
For example, in an imaging optical system of a camera using a solid-state imaging device such as a CCD imaging device, such as a digital still camera, a low-pass filter or an infrared cut is provided between the final surface of the eighth lens E8 and the image plane FS. It constitutes at least one of cover glasses (hereinafter collectively referred to as “optical filter MF”) for protecting the light receiving surface of the filter and the CCD image pickup device.
FIG. 6 is an aberration curve diagram showing the respective aberration characteristics of spherical aberration, astigmatism, distortion aberration and coma aberration of the imaging optical system according to Numerical Example 1 according to the present invention shown in FIG.
In Example 1, the focal length f = 5.88 mm and Fno = 1.95. The characteristics of each optical surface are as shown in Table 1.

  In Table 1, the optical surfaces of the fourth surface and the fourteenth surface with an asterisk “*” in the surface number are aspherical surfaces, and the parameters in the respective aspherical expressions are as shown in Table 2.

  Further, the numerical values related to the conditional expressions (1), (2), and (3) described in the first embodiment are as shown in Table 3 below.

  Therefore, the numerical values related to the conditional expressions (1), (2), and (3) of the present invention described in the first embodiment are all within the range of the conditional expressions.

  FIG. 6 is an aberration curve diagram showing aberration characteristics of the respective aberration spherical aberration, astigmatism, distortion aberration and coma aberration of the imaging optical system L1 of the present invention shown in FIG. 1 according to Example 1 described above.

  In each aberration curve, a broken line in spherical aberration represents a sine condition, a solid line in astigmatism represents sagittal, and a broken line represents meridional.

  In FIG. 6, the thick line is an aberration curve diagram with respect to the g line, and the thin line is an aberration curve diagram with respect to the d line.

  According to the imaging optical system L1 having the configuration shown in FIG. 1 according to the first embodiment of the present invention described above, the aberration is corrected at a high level as shown in FIG. 6, and spherical aberration and axial chromatic aberration are problematic. Small enough not to become. Astigmatism, curvature of field, and lateral chromatic aberration are sufficiently small, coma and disturbance of the color difference are well suppressed to the outermost periphery, and distortion aberration is 2.0% or less in absolute value. By configuring the imaging optical system L1 as in Example 1 according to the present invention, the half angle of view is as wide as 39 degrees, and the F number is as large as about 1.95 or less. It is clear that good image performance can be ensured.

  FIG. 2 shows a configuration of an imaging optical system according to Example 2 (numerical example) of the present invention, and schematically shows a longitudinal section along the optical axis.

  The optical system shown in FIG. 2 has, in order from the object side to the image surface, a first lens E1 composed of a negative meniscus negative lens having a convex surface facing the object side, and a strong concave surface formed with an aspheric surface on the image surface side. A second lens E2 composed of a negative meniscus negative lens, a third lens E3 that is a biconvex positive lens, an aperture stop FA, a fourth lens E4 that is a biconvex positive lens, and a negative meniscus negative. A cemented lens obtained by closely bonding a fifth lens E5, which is a lens, and a sixth lens E6, which is a negative meniscus type negative lens, and a seventh lens E7, which is a biconvex type positive lens, are closely bonded. A cemented lens and an eighth lens E8, which is a biconvex positive lens having an aspheric surface on the object side, are arranged.

  The first lens E1 to the third lens E3 constitute the first lens group G1, and the fourth lens E4 to the eighth lens E8 constitute the second lens group G2.

  In the first lens group G1, the front first lens group 1F is constituted by the first lens E1 and the second lens E2 which are located on the object side having negative refractive power with the widest air interval as a boundary, The third lens E3 located on the image side having positive refractive power constitutes the rear first lens group 1R.

  The second lens group G2 includes, in order from the object side, a fourth lens E4 as a first positive lens, a fifth lens E5 as a first negative lens, a sixth lens E6 as a second negative lens, and a second positive lens. The seventh lens E7 as a lens constitutes the front second lens group 2F, and the eighth lens E8 constitutes the rear second lens group 2R. In the imaging optical system L2, the whole or part of the second lens group G2 is moved to perform focusing on a finite distance object (an object from infinity to a short distance).

  For example, in an imaging optical system of a camera using a solid-state imaging device such as a CCD imaging device, such as a digital still camera, a low-pass filter or an infrared cut is provided between the final surface of the eighth lens E8 and the image plane FS. It constitutes at least one of cover glasses (hereinafter collectively referred to as “optical filter MF”) for protecting the light receiving surface of the filter and the CCD image pickup device.

  FIG. 7 is an aberration curve diagram showing the respective aberration characteristics of spherical aberration, astigmatism, distortion and coma aberration of the imaging optical system according to Numerical Example 2 according to the present invention shown in FIG.

  In the first embodiment, the focal length f = 5.95 mm and Fno = 1.95. Table 4 shows the characteristics of each optical surface.

  In Table 4, each optical surface of the fourth surface and the fourteenth surface with an asterisk “*” attached to the surface number is an aspheric surface, and the parameters in the equations for each aspheric surface are as shown in Table 5.

  Further, the numerical values related to the conditional expressions (1), (2), and (3) described in the second embodiment are as shown in Table 6 below.

  Therefore, the numerical values related to the conditional expressions (1), (2), and (3) of the present invention described in the second embodiment are all within the range of the conditional expressions.

  FIG. 7 is an aberration curve diagram showing each aberration characteristic of each aberration spherical aberration, astigmatism, distortion aberration and coma aberration of the imaging optical system L2 of the present invention shown in FIG. 2 according to Example 2 described above.

  In each aberration curve, a broken line in spherical aberration represents a sine condition, a solid line in astigmatism represents sagittal, and a broken line represents meridional.

  In FIG. 7, a thick line is an aberration curve diagram with respect to the g line, and a thin line is an aberration curve diagram with respect to the d line.

  According to the imaging optical system L2 having the configuration shown in FIG. 2 according to the second embodiment of the present invention described above, the aberration is corrected at a high level as shown in FIG. 7, and spherical aberration and longitudinal chromatic aberration are problematic. Small enough not to become. Astigmatism, curvature of field, and lateral chromatic aberration are sufficiently small, coma and disturbance of the color difference are well suppressed to the outermost periphery, and distortion aberration is 2.0% or less in absolute value. By configuring the imaging optical system L2 as in Example 2 according to the present invention, a very good image with a focal length of 5.95 and a large aperture with an F number of about 1.95 or less. It is clear that performance can be ensured.

FIG. 3 shows the configuration of an imaging optical system according to Example 3 (numerical example) of the present invention, and schematically shows a longitudinal section along the optical axis.
The optical system shown in FIG. 3 has, in order from the object side to the image surface, a first lens E1 composed of a negative meniscus negative lens having a convex surface facing the object side, and a strong concave surface formed with an aspheric surface on the image surface side. A second lens E2 composed of a negative meniscus type negative lens directed to, a third lens E3 that is a biconvex type positive lens, an aperture stop FA, a fourth lens E4 that is a positive meniscus type positive lens, and a negative meniscus type negative lens. A cemented lens obtained by closely bonding a fifth lens E5 that is a lens, a sixth lens E6 that is a negative meniscus type negative lens, and a seventh lens E7 that is a positive meniscus type positive lens are closely bonded. A cemented lens and an eighth lens E8, which is a biconvex positive lens having an aspheric surface on the object side, are arranged.
The first lens E1 to the third lens E3 constitute the first lens group G1, and the fourth lens E4 to the eighth lens E8 constitute the second lens group G2.
In the first lens group G1, the front first lens group 1F is constituted by the first lens E1 and the second lens E2 which are located on the object side having negative refractive power with the widest air interval as a boundary, The third lens E3 located on the image side having positive refractive power constitutes the rear first lens group 1R.

The second lens group G2 includes, in order from the object side, a fourth lens E4 as a first positive lens, a fifth lens E5 as a first negative lens, a sixth lens E6 as a second negative lens, and a second positive lens. The seventh lens E7 as a lens constitutes the front second lens group 2F, and the eighth lens E8 constitutes the rear second lens group 2R. In the imaging optical system L3, the whole or part of the second lens group G2 is moved to perform focusing on a finite distance object (an object from infinity to a short distance).
For example, in an imaging optical system of a camera using a solid-state imaging device such as a CCD imaging device, such as a digital still camera, a low-pass filter or an infrared cut is provided between the final surface of the eighth lens E8 and the image plane FS. It constitutes at least one of cover glasses (hereinafter collectively referred to as “optical filter MF”) for protecting the light receiving surface of the filter and the CCD image pickup device.
FIG. 8 is an aberration curve diagram showing the respective aberration characteristics of spherical aberration, astigmatism, distortion and coma aberration of the imaging optical system according to Numerical Example 3 according to the present invention shown in FIG.
In the third embodiment, the focal length f = 5.95 mm and Fno = 1.95. The characteristics of each optical surface are as shown in Table 7 below.

  In Table 7, the optical surfaces of the fourth surface and the fourteenth surface with an asterisk “*” attached to the surface number are aspheric surfaces, and the parameters in the equations for each aspheric surface are as shown in Table 8.

  Further, the numerical values relating to the conditional expressions (1), (2), and (3) described in the third embodiment are as shown in Table 9 below.

Therefore, the numerical values related to the conditional expressions (1), (2), and (3) of the present invention described in the third embodiment are all within the range of the conditional expressions.
FIG. 8 is an aberration curve diagram showing the respective aberration characteristics of spherical aberration, astigmatism, distortion and coma aberration of the imaging optical system L3 of the present invention shown in FIG. 3 according to Example 3 described above.

In each aberration curve, a broken line in spherical aberration represents a sine condition, a solid line in astigmatism represents sagittal, and a broken line represents meridional.
In FIG. 8, the thick line is an aberration curve diagram with respect to the g line, and the thin line is an aberration curve diagram with respect to the d line.
According to the imaging optical system L3 having the configuration shown in FIG. 3 according to the third embodiment of the present invention described above, the aberration is corrected at a high level as shown in FIG. 8, and spherical aberration and longitudinal chromatic aberration are problematic. Small enough not to become. Astigmatism, curvature of field, and lateral chromatic aberration are sufficiently small, coma and disturbance of the color difference are well suppressed to the outermost periphery, and distortion aberration is 2.0% or less in absolute value. By configuring the imaging optical system L3 as in the third embodiment according to the present invention, the half angle of view is as wide as 39 degrees and the F number is as large as about 1.95 or less. It is clear that good image performance can be ensured.

FIG. 4 shows the configuration of an imaging optical system according to Example 4 (numerical example) of the present invention, and schematically shows a longitudinal section along the optical axis.
The optical system shown in FIG. 4 has, in order from the object side to the image surface, a first lens E1 composed of a negative meniscus negative lens having a convex surface facing the object side, and a strong concave surface formed with an aspheric surface on the image surface side. A second lens E2 composed of a negative meniscus type negative lens directed to, a third lens E3 that is a biconvex type positive lens, an aperture stop FA, a fourth lens E4 that is a positive meniscus type positive lens, and a negative meniscus type negative lens. A cemented lens obtained by closely bonding a fifth lens E5 that is a lens, a sixth lens E6 that is a negative meniscus negative lens, and a seventh lens E7 that is a biconvex positive lens are closely bonded. A cemented lens to be combined, and an eighth lens E8, which is a positive meniscus type positive lens in which aspheric surfaces are formed on the object side and the image side, are arranged.
The first lens E1 to the third lens E3 constitute the first lens group G1, and the fourth lens E4 to the eighth lens E8 constitute the second lens group G2.

In the first lens group G1, the front first lens group 1F is constituted by the first lens E1 and the second lens E2 which are located on the object side having negative refractive power with the widest air interval as a boundary, The third lens E3 located on the image side having positive refractive power constitutes the rear first lens group 1R.
The second lens group G2 includes, in order from the object side, a fourth lens E4 as a first positive lens, a fifth lens E5 as a first negative lens, a sixth lens E6 as a second negative lens, and a second positive lens. The seventh lens E7 as a lens constitutes the front second lens group 2F, and the eighth lens E8 constitutes the rear second lens group 2R. In the imaging optical system L4, the whole or a part of the second lens group G2 is moved to perform focusing on a finite distance object (an object from infinity to a short distance).

For example, in an imaging optical system of a camera using a solid-state imaging device such as a CCD imaging device, such as a digital still camera, a low-pass filter or an infrared cut is provided between the final surface of the eighth lens E8 and the image plane FS. It constitutes at least one of cover glasses (hereinafter collectively referred to as “optical filter MF”) for protecting the light receiving surface of the filter and the CCD image pickup device.
FIG. 9 is an aberration curve diagram showing the respective aberration characteristics of spherical aberration, astigmatism, distortion and coma aberration of the imaging optical system according to Numerical Example 4 according to the present invention shown in FIG.
In the fourth embodiment, the focal length f = 5.95 mm and Fno = 1.96. Table 10 shows the characteristics of each optical surface.

  In Table 10, the optical surfaces of the fourth surface, the fourteenth surface, and the fifteenth surface with an asterisk “*” attached to the surface number are aspheric surfaces, and the parameters in the equations for each aspheric surface are as shown in Table 11 below. is there.

  Further, the numerical values related to the conditional expressions (1), (2), and (3) described in the fourth embodiment are as shown in Table 12 below.

Therefore, the numerical values related to the conditional expressions (1), (2), and (3) of the present invention described in the fourth embodiment are all within the range of the conditional expressions.
FIG. 9 is an aberration curve diagram showing the respective aberration characteristics of spherical aberration, astigmatism, distortion and coma aberration of the imaging optical system L4 of the present invention shown in FIG. 4 according to Example 4 described above.
In each aberration curve, a broken line in spherical aberration represents a sine condition, a solid line in astigmatism represents sagittal, and a broken line represents meridional.
In FIG. 9, a thick line is an aberration curve diagram with respect to the g line, and a thin line is an aberration curve diagram with respect to the d line.
According to the imaging optical system L4 having the configuration shown in FIG. 4 according to the fourth embodiment of the present invention described above, the aberration is corrected at a high level as shown in FIG. 9, and spherical aberration and axial chromatic aberration are problematic. Small enough not to become. Astigmatism, curvature of field, and lateral chromatic aberration are sufficiently small, coma and disturbance of the color difference are well suppressed to the outermost periphery, and distortion aberration is 2.0% or less in absolute value. By configuring the imaging optical system L4 as in the fourth embodiment according to the present invention, the half angle of view is as wide as 39 degrees and the F number is as large as about 1.95 or less. It is clear that good image performance can be ensured.

FIG. 5 shows a configuration of an imaging optical system according to Example (numerical example) 5 of the present invention, and schematically shows a longitudinal section along the optical axis.
The optical system shown in FIG. 5 has, in order from the object side to the image surface, a first lens E1 composed of a negative meniscus negative lens having a convex surface facing the object side, and a strong concave surface formed with an aspheric surface on the image surface side. A second lens E2 composed of a negative meniscus type negative lens directed to, a third lens E3 that is a biconvex type positive lens, an aperture stop FA, a fourth lens E4 that is a positive meniscus type positive lens, and a negative meniscus type negative lens. A cemented lens obtained by closely bonding a fifth lens E5 that is a lens, a sixth lens E6 that is a negative meniscus negative lens, and a seventh lens E7 that is a biconvex positive lens are closely bonded. A cemented lens to be combined, and an eighth lens E8, which is a positive meniscus type positive lens in which aspheric surfaces are formed on the object side and the image side, are arranged.
The first lens E1 to the third lens E3 constitute the first lens group G1, and the fourth lens E4 to the eighth lens E8 constitute the second lens group G2.

In the first lens group G1, the front first lens group 1F is constituted by the first lens E1 and the second lens E2 which are located on the object side having negative refractive power with the widest air interval as a boundary, The third lens E3 located on the image side having positive refractive power constitutes the rear first lens group 1R.
The second lens group G2 includes, in order from the object side, a fourth lens E4 as a first positive lens, a fifth lens E5 as a first negative lens, a sixth lens E6 as a second negative lens, and a second positive lens. The seventh lens E7 as a lens constitutes the front second lens group 2F, and the eighth lens E8 constitutes the rear second lens group 2R. In the imaging optical system L5, the whole or a part of the second lens group G2 is moved to perform focusing on a finite distance object (an object from infinity to a short distance).
For example, in an imaging optical system of a camera using a solid-state imaging device such as a CCD imaging device, such as a digital still camera, a low-pass filter or an infrared cut is provided between the final surface of the eighth lens E8 and the image plane FS. It constitutes at least one of cover glasses (hereinafter collectively referred to as “optical filter MF”) for protecting the light receiving surface of the filter and the CCD image pickup device.
FIG. 10 is an aberration curve diagram showing the respective aberration characteristics of spherical aberration, astigmatism, distortion and coma aberration of the image pickup optical system according to Numerical Example 5 according to the present invention shown in FIG.
In Example 5, the focal length f = 5.95 mm and Fno = 2.00. Table 13 shows the characteristics of each optical surface.

  In Table 13, the optical surfaces of the fourth surface, the fourteenth surface, and the fifteenth surface with an asterisk “*” attached to the surface number are aspheric surfaces. The parameters in the respective aspheric surface equations are as shown in Table 14.

  Further, the numerical values related to the conditional expressions (1), (2), and (3) described in the fifth embodiment are as shown in Table 15 below.

Therefore, the numerical values related to the conditional expressions (1), (2), and (3) of the present invention described in the fifth embodiment are all within the range of the conditional expressions.
FIG. 10 is an aberration curve diagram showing spherical aberration, astigmatism, distortion aberration and coma aberration characteristics of the imaging optical system L5 of the present invention shown in FIG. 5 according to Example 5 described above.
In each aberration curve, a broken line in spherical aberration represents a sine condition, a solid line in astigmatism represents sagittal, and a broken line represents meridional.
In FIG. 10, a thick line is an aberration curve diagram with respect to the g line, and a thin line is an aberration curve diagram with respect to the d line.
According to the imaging optical system L5 having the configuration shown in FIG. 5 according to the fifth embodiment of the present invention described above, the aberration is corrected at a high level as shown in FIG. 10, and spherical aberration and longitudinal chromatic aberration are problematic. Small enough not to become. Astigmatism, curvature of field, and lateral chromatic aberration are sufficiently small, coma and disturbance of the color difference are well suppressed to the outermost periphery, and distortion aberration is 2.0% or less in absolute value. By configuring the imaging optical system L5 as in the fifth embodiment according to the present invention, the half angle of view is as wide as 39 degrees, and the F number is as large as about 2.00 or less. It is clear that good image performance can be ensured.

Next, the camera apparatus is constructed by adopting the imaging optical system L1 to imaging optical system L5 according to the present invention as shown in the numerical example 1 to numerical example 5 described above as the imaging optical system. A sixth embodiment (embodiment) will be described with reference to FIGS. FIG. 11 is a perspective view showing the appearance of an object, that is, the camera viewed from the front side that is the subject side, in which (a) shows a state in which the lens barrel is retracted, and (b) shows that the lens barrel is in the retracted state. Indicates the extended state. FIG. 12 is a perspective view showing an appearance of the camera device viewed from the back side that is the photographer side, and FIG. 13 is a block diagram showing a functional configuration of the camera device. Although a camera device is described here, a device that incorporates a camera function in a portable information terminal device such as a so-called PDA (personal data assistant) or a cellular phone has recently appeared. Such a portable information terminal device also includes substantially the same functions and configuration as a camera device, although the appearance is slightly different. The imaging optical system according to the present invention is adopted in such a portable information terminal device. May be.
As shown in FIGS. 11 and 12, the camera apparatus includes a photographing lens 101, a shutter button 102, a viewfinder 104, a strobe 105, a liquid crystal monitor 106, an operation button 107, a power switch 108, a memory card slot 109, a communication card slot 110, and the like. It has. Further, as shown in FIG. 13, the camera device also includes a light receiving element 201, a signal processing device 202, an image processing device 203, a central processing unit (CPU) 204, a semiconductor memory 205, a communication card 206 and the like.

The camera includes a photographing lens 101 and a light receiving element 201 as an area sensor such as a CCD (charge coupled device) imaging element, and is an object to be photographed, that is, a subject formed by the photographing lens 101 that is an imaging optical system. The image is read by the light receiving element 201. As the photographing lens 101, an imaging optical system according to the present invention (that is, defined in claims 1 to 7) as described in the first to fifth embodiments is used (claims 8 and 9). Corresponding to).
The output of the light receiving element 201 is processed by the signal processing device 202 controlled by the central processing unit 204 and converted into digital image information. The image information digitized by the signal processing device 202 is subjected to predetermined image processing in the image processing device 203 which is also controlled by the central processing unit 204 and then recorded in the semiconductor memory 205 such as a nonvolatile memory. In this case, the semiconductor memory 205 may be a memory card loaded in the memory card slot 109 or a semiconductor memory built in the camera body. The liquid crystal monitor 106 can display an image being shot, and can also display an image recorded in the semiconductor memory 205. The image recorded in the semiconductor memory 205 can also be transmitted to the outside via a communication card 206 or the like loaded in the communication card slot 110.
When the camera is carried, the photographic lens 101 is in the retracted state and buried in the body of the camera as shown in FIG. 11A. When the user operates the power switch 108 to turn on the power, FIG. (B), the lens barrel is extended and protrudes from the camera body.

In many cases, focusing is performed by half-pressing the shutter button 102. Focusing in the imaging optical systems L1 to L5 as described in the first to fifth embodiments is performed by moving all or a part of the second group lens group G2, but is performed by moving the light receiving element 201. You can also. When the shutter button 102 is further pushed down to the fully depressed state, photographing is performed, and then the processing as described above is performed.
When the image recorded in the semiconductor memory 205 is displayed on the liquid crystal monitor 106 or transmitted to the outside via the communication card 206 or the like, the operation button 107 is operated in a predetermined manner. The semiconductor memory 205 and the communication card 206 are used by being loaded into dedicated or general-purpose slots such as the memory card slot 109 and the communication card slot 110, respectively.
According to the present invention described above, the half angle of view is a wide angle of about 38 degrees, and the F number is about 2.0 or less, but it is relatively small in size, astigmatism, field curvature, and magnification. To provide a small and high-quality camera device and portable information terminal device that sufficiently reduce chromatic aberration, coma color difference, distortion, etc., and use a high-performance imaging optical system as the imaging optical system of the camera function unit Therefore, the user can take a high-quality image with a camera device and a portable information terminal device excellent in portability and transmit the image to the outside.

1-17 Surface number E1-E8 1st lens-8th lens 1F Front 1st lens group 1R Rear 1st lens group 2F Front 2nd lens group 2R Rear 2nd lens group G1 1st lens group G2 2nd lens Group FA Aperture stop MF Optical filter FS Image plane 101 Shooting lens 102 Shutter button 104 Viewfinder 105 Strobe 106 Liquid crystal monitor 107 Operation button 108 Power switch 109 Memory card slot 110 Communication card slot 201 Light receiving element 202 Signal processing device 203 Image processing device 204 Central Arithmetic unit 205 Semiconductor memory 206 Communication card, etc.

Japanese Patent Laid-Open No. 06-308385 JP 09-218350 A JP 2006-349920 A

Claims (10)

In an imaging optical system including a first lens group located on the object side with an aperture stop interposed therebetween and a second lens group located on the image side, the first lens group is arranged in order from the object side. The second lens comprises a front first lens group having at least two negative lenses and a rear first lens group having at least one positive lens, with the widest air interval in the group as a boundary. A front-side second lens group in which a positive cemented lens is continuously arranged as a whole consisting of a first positive lens, a first negative lens, a second negative lens, and a second positive lens in order from the object side; An imaging optical system comprising a rear second lens group comprising a plurality of lenses. 2. The imaging optical system according to claim 1, wherein the following conditional expression is satisfied.
| F22 / f21 | <0.5 (1)
Where f21 is a combined focal length of the first positive lens and the first negative lens in the front second lens group, and f22 is the second negative lens and the second positive lens in the front second lens group. The focal length of a cemented lens having a positive refractive power as a whole. The imaging optical system according to claim 1, wherein the following conditional expression is satisfied.
0.2 <f / f2 <0.5 (2)
Where f is the focal length of the entire imaging optical system. f2 represents the focal length of the front second lens group. 4. The imaging optical system according to claim 1, wherein the first positive lens and the first negative lens in the front second lens group are cemented together. 5. . 5. The imaging optical system according to claim 1, wherein the first negative lens in the front second lens group is a meniscus lens convex to the image side. . 6. The imaging optical system according to claim 1, wherein the following conditional expression is satisfied.
| F1 | / f> 8.0 (3)
However, f1 represents the focal length of the first lens group, and f represents the focal length of the entire imaging optical system. The imaging optical system according to claim 1, wherein focusing is performed from infinity to a short distance by moving all or part of the second lens group. . A camera apparatus comprising the imaging optical system according to claim 1. 9. The camera device according to claim 8, wherein the camera device has a function of using a captured image as digital information. The portable information terminal device which has the imaging optical system of any one of Claims 1-7.

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