JP2017125978A - Imaging optical system and device having the imaging optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-cost imaging optical system which is small in size and has high performance and a wide angle of view of about 29° half angle of view, a large aperture with about an F-number 2 while having low distortion, and which is composed of only 7 to 8 polished spherical surfaces.SOLUTION: The imaging optical system includes, successively from an object side, a first lens group 1G having a negative refractive power, an aperture diaphragm S, and a second lens group 2G having a positive refractive power. The first lens group 1G includes, successively from the object side, a first lens L1 that is a positive lens having a convex shape on an object side surface, a second lens L2 that is a negative lens having a concave shape on an image side surface, a third lens L3 that is a negative lens having a concave shape on an image side surface, and a fourth lens L4 that is a positive lens having a convex shape on an object side surface. The second lens group 2G includes a cemented lens of a fifth lens that is a negative lens and a sixth lens L6 that is a positive lens, and a seventh lens L7 that is a positive lens.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an imaging optical system and an apparatus having the imaging optical system.

  As a type of a relatively wide-angle single-focus lens premised on a solid-state imaging device, a retrofocus type that can easily suppress the maximum incident angle on the image plane is representative. As conventional examples of a relatively wide-angle and small retrofocus type, Patent Document 1 (Japanese Patent Laid-Open No. 2012-220741), Patent Document 2 (Japanese Patent Laid-Open No. 10-31153), and Patent Document 3 (Japanese Patent Laid-Open No. 11-211977). Gazette), patent document 4 (Japanese Patent Laid-Open No. 2010-176016), patent document 5 (Japanese Patent Laid-Open No. 2010-176017), and the like.

However, the optical system disclosed in Patent Document 1 has a slightly large optical total length compared to the focal length, and a distortion aberration of about −2.5% or more remains, so it cannot be said to be a low distortion optical system.
In addition, the optical system disclosed in Patent Document 2 has a slightly large distortion aberration of about −3.5% and a dark F number of 2.8, which is difficult to say with low distortion and a large aperture. In addition, the optical system disclosed in Patent Document 3 has an aspherical surface, has a slightly large distortion of about -3%, a large total length compared to the focal length, and is said to be low distortion and compact. It's hard. Further, the optical system disclosed in Patent Document 4 has an aspheric surface, and the F number is as dark as about 3.6, which is difficult to say as a large aperture. The optical system disclosed in Patent Document 5 has a slightly larger number of aspherical surfaces as many as nine, and the F number is slightly dark at about 2.8, which is difficult to say at a low cost and a large aperture.
The present invention has been made in view of the above points, and has a low cost, a low cost, a small size, a high performance, a wide angle of view, a small F number, a large aperture, and only a polished spherical surface. An object is to provide an imaging optical system.

In order to achieve the above-described object, the imaging optical system according to claim 1
In order from the object side, the first lens group having a negative refractive power, an aperture stop, and a second lens group having a positive refractive power,
The first lens group includes, in order from the object side, a positive lens, a negative lens, a negative lens, and a positive lens.
The second lens group includes, in order from the object side, a cemented lens of a negative lens and a positive lens, and a positive lens.

  According to the present invention, it is possible to obtain a great effect on aberration correction, and while maintaining a wide field angle and a large aperture, sufficiently small size and low distortion, a very good image performance can be ensured. An obtained imaging optical system can be realized.

It is an optical arrangement | positioning figure which shows the structure of Example 1 of the imaging optical system which concerns on the 1st Embodiment of this invention. It is an optical arrangement | positioning figure which shows the structure of Example 2 of the imaging optical system which concerns on the 2nd Embodiment of this invention. It is an optical arrangement | positioning figure which shows the structure of Example 3 of the imaging optical system which concerns on the 3rd Embodiment of this invention. It is an optical arrangement | positioning figure which shows the structure of Example 4 of the imaging optical system which concerns on the 4th Embodiment of this invention. It is an optical arrangement | positioning figure which shows the structure of Example 5 of the imaging optical system which concerns on the 5th Embodiment of this invention. FIG. 6 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration in an infinite object in the imaging optical system of Example 1 shown in FIG. 1. FIG. 6 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration in an infinite object of the imaging optical system of Example 2 shown in FIG. 2. FIG. 6 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration in an infinite object of the imaging optical system of Example 3 shown in FIG. 3. FIG. 6 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma aberration in an infinite object of the imaging optical system of Example 4 shown in FIG. 4. FIG. 6 is an aberration curve diagram showing spherical aberration, astigmatism, distortion and coma in the object at infinity of the imaging optical system of Example 5 shown in FIG. 5. It is the perspective view which looked at the external appearance structure of the digital camera as a camera apparatus which concerns on the 6th 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. 11 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. 11 and FIG.

Hereinafter, based on an embodiment of the present invention, an imaging optical system and an apparatus having the imaging optical system according to the present invention will be described in detail with reference to the drawings.
Before describing specific examples, first, a fundamental embodiment of the present invention will be described.
In-vehicle camera devices mounted on automobiles have a strong need for higher image quality, smaller size, wider angle, and larger aperture, and it is necessary to develop to meet these demands. In addition, in precision measurement devices such as stereo camera devices, there is an increasing demand for low distortion in order to reduce the effect on measurement errors or to reduce the electronic image correction load. A compatible optical design is required. In addition, functional stability in harsh usage environments is also required, and fluctuations in image height or photographing magnification at the time of changes in temperature environment must be suppressed to a small level in optical design. In addition, environmental resistance, aging resistance, and low cost must be considered as necessary conditions.

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. Moreover, if the use of an aspherical surface is restricted for cost reduction, the optical system tends to become longer mainly due to spherical aberration and distortion.
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, the first lens group having a negative refractive power, an aperture stop, and a second lens group having a positive refractive power,
The first lens group includes, in order from the object side, a positive lens having a convex shape on the object side surface, a negative lens having a concave shape on the image side surface, a negative lens having a concave shape on the image side surface, and a convex shape on the object side surface. A positive lens having
The second lens group includes, in order from the object side, a cemented lens of a negative lens and a positive lens, and a positive lens (corresponding to claims 1 and 2).

  First, the imaging optical system according to the present invention adopts a retrofocus type in which a group having a negative refractive power is arranged in front and a group having a positive refractive power is arranged in the rear in consideration of an individual imaging device. As a result, an effect of suppressing the incident angle of off-axis light on the image plane, which tends to increase with the widening of the angle, is obtained. Then, in the first lens group in the order from the object side to positive, negative, positive power arrangement, and the first lens group as a whole to have negative power, the positive of the first lens, It is a triplet type refractive power arrangement that has a negative refractive power combined with the second and third lenses and a positive refractive power as a whole of the second lens group, and reduces the difficulty of correcting various aberrations including chromatic aberration. Yes. In addition, by configuring the first lens group positioned on the object side of the aperture stop as a whole to have a negative refractive power, it is possible to capture light rays with a wide angle of view with a relatively small size. In addition, by making the first lens a positive lens having a convex shape on the object side surface, an effect of suppressing particularly increasing spherical aberration due to an increase in diameter is obtained. By dividing the negative power in the first lens group into two lenses, a second lens and a third lens, it is not necessary to have a strong curvature on each surface, improving the productivity of the lens and manufacturing errors. In addition, it is possible to suppress performance degradation due to assembly eccentricity. Spherical aberration can be corrected well by making the image side surfaces of the second lens and the third lens concave, and making the object side of the fourth lens located closest to the image side convex in the first lens group. It becomes possible.

Further, the lens element closest to the object side in the second lens group, where the light beam is located near the aperture stop, is a cemented lens of a negative lens and a positive lens, thereby correcting mainly axial chromatic aberration. In addition, by constructing the cemented lens in order of the negative lens and the positive lens from the object side, the control of the exit pupil distance is performed by combining the positive lens of the cemented lens and the subsequent positive lens. Becomes easy. Further, configuring the cemented lens in this order from the object side in the order of the negative lens and the positive lens is a configuration in which the light incident angle and the exit angle with the cemented lens surface are suppressed to be smaller in the light beam on the image side than the aperture stop. The sensitivity of performance degradation due to manufacturing errors is easily suppressed.
According to the configuration of the imaging optical system of the present invention, as described above, it is possible to obtain a great effect on aberration correction, a wide field angle of about 29 ° half angle of view, and a large aperture of about F2 or less. However, it is possible to realize an imaging optical system that is sufficiently small and that can maintain a very good image performance while maintaining low distortion.

In order to obtain better performance, the positive lens on the most image side in the first lens group is a positive meniscus lens, and the object side surface of the negative lens on the most object side in the second lens group is concave. The shape is desirable (corresponding to claim 3).
An air lens formed by the final surface (most image side surface) of the first lens group and the leading surface (most surface of the object side) of the second lens group has a biconvex shape, thereby sandwiching the aperture stop. By forming a concave surface facing each other, it is easy to increase with widening the angle, and it is possible to reduce the degree of difficulty in correcting distortion by balancing the distortion, which tends to worsen with a retrofocus type with a biased refractive power balance. .
In order to achieve higher performance, the following conditional expression (1) should be satisfied (corresponding to claim 4).
0.20 <| f / fa | <1.00 (1)
Conditional expression (1) is formed by the most image side surface (final surface) of the first lens group and the most object side surface (leading surface) of the second lens group with respect to the focal length f of the entire system. The optimum range of the focal length fa of the air lens is defined.

If the upper limit of conditional expression (1) is exceeded, the distance before and after the aperture stop may increase and the overall length of the optical system may be increased. Further, the light beam tilt angle on the refracting surface becomes too large, and there is a risk that the sensitivity of performance degradation to manufacturing errors increases. If the lower limit of conditional expression (1) is not reached, the contribution to distortion correction becomes too small, which may lead to an increase in the size of the entire optical system.
In order to achieve better performance, it is desirable to satisfy the following conditional expression (1A).
0.40 <| f / fa | <0.80 (1A)
Furthermore, in order to achieve higher performance, the following conditional expression (2) should be satisfied (corresponding to claim 5).
0.01 <| f / f1 | <0.50 (2)
Conditional expression (2) defines the optimum range of the focal length f1 of the first lens group with respect to the focal length f of the entire system. When the upper limit value of conditional expression (2) is exceeded, the negative refractive power of the second lens in the first lens group becomes too small and the chromatic aberration correction capability decreases, or the positive and negative refraction in the first lens group. There is a concern that the sensitivity of performance degradation to manufacturing errors in the first lens group may increase because the force difference becomes too large.

If the lower limit of conditional expression (2) is not reached, the difference in refractive power between the first lens group and the second lens group becomes too large, and the sensitivity of performance degradation to manufacturing errors increases, or the entire optical system is large. There is a risk of becoming.
In order to obtain better performance, it is desirable to satisfy the following conditional expression (2A).
0.01 <| f / f1 | <0.30 (2A)
In order to achieve higher performance, the following conditional expression (3) should be satisfied (corresponding to claim 6).
0.10 <f / AL <0.45 (3)
Conditional expression (3) defines the optimum range of the optical total distance AL, that is, the distance on the optical axis from the first surface of the first lens group to the image plane when focusing on infinity with respect to the focal length f of the entire system. Yes. If it is essential to suppress the incident angle with respect to the image sensor, if the upper limit value of the conditional expression (3) is exceeded, the degree of difficulty in correcting distortion aberrations increases mainly due to approaching the front aperture system, and the desired image performance may not be obtained. is there. If the lower limit of conditional expression (3) is not reached, it will be advantageous in correcting aberrations, but the optical system will be lengthened and a compact optical system cannot be constructed.

In order to achieve better performance, it is desirable to satisfy the following conditional expression (3A).
0.15 <f / AL <0.40 (3A)
In order to achieve higher performance, the positive lens closest to the object in the first lens group may be a positive meniscus lens (corresponding to claim 7).
By making the first lens a positive meniscus lens that is convex on the object side, it becomes possible to further reduce the correction difficulty of spherical aberration that particularly increases with an increase in diameter.
In order to achieve higher performance, the second lens group includes a positive second F lens group as a whole and a positive second R lens group as a whole, and the second F lens group includes at least one negative lens. And one positive lens, and the second R lens group may include one positive lens (corresponding to claim 8).

By having at least one negative lens and one positive lens in the second F lens group, the negative second lens and the negative third lens in the first lens group are paired with each other, and an effect on chromatic aberration correction is achieved. Enlargement is possible. Further, by providing one or more positive lenses in the second R lens group and providing the function of adjusting the exit pupil position, it is effective in suppressing the incident angle of the light beam on the image plane.
In order to exhibit the effect of the above configuration more appropriately, the following conditional expression (4) should be satisfied (corresponding to claim 9).
0.05 <| f / f2F | <0.50 (4)
Conditional expression (4) defines the optimum range of the combined focal length f2F of the cemented lens of the negative lens closest to the object side of the second lens group and the positive lens with respect to the focal length f of the entire system. When the upper limit value of conditional expression (4) is exceeded, it is necessary to increase the refractive power of the second R lens group, the function of adjusting the exit pupil of the second R lens group is reduced, and the function of the first lens group is reduced. There is a risk that the spherical aberration correction ability and the chromatic aberration correction ability exhibited in a pair with the negative lens are reduced, and the image performance is deteriorated. If the lower limit of conditional expression (4) is not reached, the exchange of aberrations with the first lens group becomes excessive, and the sensitivity of performance degradation to manufacturing errors may increase, or the entire optical system may be enlarged.

In order to obtain better performance, it is desirable to satisfy the following conditional expression (4A).
0.10 <| f / f2F | <0.40 (4A)
In order to improve resistance to environmental fluctuations and changes over time, all the lenses may be made of glass spherical lenses.
By adopting glass lenses for all lenses that have a smaller coefficient of thermal expansion than optical resin materials and small fluctuations in optical properties due to environmental fluctuations, it is possible to construct an optical system with excellent resistance to environmental fluctuations and changes over time. It becomes. In addition, by using a spherical lens that can be selected at low cost for polishing with relatively small residual internal stress, it is possible to obtain an effect of further suppressing changes in optical characteristics due to environmental fluctuations.

In the imaging optical system of the present invention, it is desirable that the second lens and the third lens in the first lens group are negative meniscus lenses having a convex object side surface. By adopting a meniscus shape that is convex toward the object side, it is possible to more favorably correct spherical aberration that increases as the diameter increases.
The second R lens group mainly has a function of securing an exit pupil distance. In order to reduce the size of the lens system, it is necessary to have a simple configuration as much as possible, and it is desirable that the number of positive lenses is about two or less.
It is preferable that the negative lens and the positive lens constituting the cemented lens located closest to the object side in the second lens group satisfy the following conditional expression.
1.75 <N21 <2.20, 15 <ν21 <35
1.65 <N22 <2.20, 35 <ν22 <55
Here, N21 is the refractive index of the negative lens constituting the cemented lens, ν21 is the Abbe number of the negative lens,
N22 represents the refractive index of the positive lens constituting the cemented lens, and ν22 represents the Abbe number of the positive lens. By selecting such a glass type, it is possible to satisfactorily correct chromatic aberration while balancing the Petzval sum.

The fourth lens in the first lens group preferably satisfies the following conditional expression.
1.75 <N14 <2.20
Here, N14 represents the refractive index of the fourth lens. By selecting such a glass type, it is easy to configure the fourth lens as a positive meniscus lens, and it is possible to mainly correct spherical aberration and distortion.

[First Embodiment]
Next, specific examples based on the above-described embodiment of the present invention will be described in detail. Examples 1 to 5 are examples of specific configurations based on numerical examples of the imaging optical system according to the first to fifth embodiments of the present invention. FIG. 1 is a diagram for explaining an imaging optical system in Example 1 according to the first embodiment of the present invention. FIG. 2 is a view for explaining an imaging optical system in Example 2 according to the second embodiment of the present invention. FIG. 3 is a view for explaining the imaging optical system in Example 3 according to the third embodiment of the present invention.
FIG. 4 is a view for explaining the imaging optical system in Example 4 according to the fourth embodiment of the present invention. FIG. 5 illustrates an imaging optical system in Example 5 according to the fifth embodiment of the present invention.
The aberrations in Examples 1 to 5 are sufficiently corrected. That is, by configuring the imaging optical system as in the first to fifth embodiments according to the present invention, it is small in size and high in performance while having low distortion, for example, a half angle of view 29. It is clear from these first to fifth embodiments that a low-cost imaging optical system composed only of a polished spherical surface with a wide field angle of about ° and a large aperture of about F2 can be realized. It can be seen that it has good performance.

The meanings of symbols common to the first to fifth embodiments are as follows.
f: Focal length of the entire system Fno: F value (F number)
ω: Half angle of view R: Radius of curvature y ': Maximum image height D: Plane spacing nd: Refractive index at d-line νd: Abbe number of d-line is there.

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 fourth lens from the object side toward the image plane side. L4, aperture stop S, fifth lens L5, sixth lens L6, and seventh lens L7 are disposed. The fifth lens L5 and the sixth lens L6 each constitute a cemented lens, and so-called six groups. It has 7 sheets.
Focusing on the lens group configuration, the first lens group 1G is configured by the first lens L1 to the fourth lens L4. The fifth lens L5 to the seventh lens L7 constitute a second lens group 2G. The fifth lens L5 and the sixth lens L6 constitute a second F lens group 2FG having a positive refractive power. The seventh lens L7 constitutes a second R lens group 2RG having a positive refractive power. That is, the imaging optical system shown in FIG. 1 has a configuration in which the first lens group 1G, the aperture stop S, the second F lens group 2FG, and the second R lens group 2RG are sequentially arranged from the object side to the image plane side. It is said.

Specifically, the first lens group 1G is formed from a positive lens having a positive meniscus shape with a convex surface facing the object side sequentially from the object side to the image surface side, that is, a positive lens having a convex shape on the object side surface. The first lens L1, the negative lens having a negative meniscus shape with the concave surface facing the image surface side, that is, the second lens L2 made of a negative meniscus negative lens having the concave shape on the image side surface, and the concave surface on the image surface side A negative lens having a negative meniscus shape facing the lens, that is, a third lens L3 composed of a negative meniscus negative lens having a concave shape on the image side surface, and a positive lens comprising a positive meniscus shape having a convex shape on the object side surface. Four lenses L4 are arranged to show negative refractive power.
An aperture stop S is disposed between the first lens group 1G and the second lens group 2G.
The second F lens group 2FG includes, from the object side to the image surface side, a fifth lens L5 made of a negative lens having a concave shape with a concave surface having a larger curvature than the object side surface. A sixth lens L6 made of a positive lens having a biconvex shape with a convex surface having a larger curvature than the surface on the image side facing the object side is arranged so as to exhibit positive refractive power. The two lenses of the fifth lens L5 and the sixth lens L6 of the second F lens group 2FG are closely bonded to each other and bonded together to form a cemented lens composed of two lenses. Yes.

The second R lens group 2RG is configured to have a positive refractive power by disposing a seventh lens L7 formed of a biconvex positive lens having the same curvature on the image side and the object side.
Further, behind the second lens group 2G, 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 F 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 filter glass F described above as representative of these is equivalently shown as two parallel flat plates. In Examples 2 to 5, the filter glass F is equivalently shown as two parallel flat plates. Similarly to the filter glass F in this example, a back insertion glass, a low-pass filter, an infrared cut It represents at least one of glass and cover glass.

When performing focusing, the first lens group 1G, the aperture stop S, and the second lens group 2G are integrated, and are moved in the optical axis direction to perform focusing.
In the above embodiment, the second R lens group 2RG is composed of one positive lens, but may be composed of a plurality of lenses. However, by configuring the second R lens group 2RG with a minimum number of one, there is an effect of minimizing the thickness in the optical axis direction and suppressing the increase in the radial direction of the second R lens group 2RG.
FIG. 1 also shows the surface numbers of the optical surfaces in the imaging optical system. In addition, in order to avoid complication of explanation due to an increase in the number of digits of the reference code, each reference code shown in FIG. 1 is used independently for each embodiment, and therefore, the same reference code as in FIGS. Is attached.
In Example 1, the focal length f, the open F value Fno, and the half angle of view ω [degrees] of the entire optical system are f = 5.40, Fno = 1.91, and ω = 29.43, respectively. The optical characteristics of the optical elements in Example 1, such as the radius of curvature R of the optical surface, the distance D between adjacent optical surfaces, the refractive index Nd, the Abbe number νd, and the glass type, are as shown in Table 1 below.

The name of the manufacturer is abbreviated as OHARA (Ohara Corporation) after the glass type name of the glass material of the optical glass lens.
The same applies to the other embodiments.
In the case of Example 1, the values corresponding to the conditional expressions (1) to (4) are as follows, and satisfy the conditional expressions (1) to (4), respectively.
Conditional formula calculation result (1) 0.520
(2) 0.058
(3) 0.275
(4) 0.213

FIG. 6 shows aberration curves of various aberrations in the d-line and g-line of the imaging optical system according to Example 1, that is, spherical aberration, astigmatism, distortion aberration, and coma aberration.
In the aberration curve diagram of FIG. 6, the broken line in spherical aberration represents the sine condition, the solid line in astigmatism represents sagittal, and the broken line represents meridional. Further, in each aberration diagram of spherical aberration, astigmatism, and coma aberration, the thin line represents the d line and the thick line represents the g line. The same applies to the aberration curve diagrams according to other examples.
The aberration of the imaging optical system in Example 1 is sufficiently corrected.
By configuring the imaging optical system as in Example 1 according to the first embodiment, it is sufficiently small and has low distortion with a wide field angle of about 29 ° and a large aperture of about F2 or less. Obviously, it is possible to realize an imaging optical system that can ensure a very good image performance at a low cost, which is composed of only seven polished spherical surfaces.

[Second Embodiment]
FIG. 2 shows an optical arrangement of the imaging optical system of Example 2 according to the second embodiment of the present invention.

As shown in FIG. 2, the imaging optical system according to Example 2 of the present invention sequentially includes a first lens L1, a second lens L2, a third lens L3, and a fourth lens from the object side toward the image plane side. L4, aperture stop S, fifth lens L5, sixth lens L6, and seventh lens L7 are disposed. The fifth lens L5 and the sixth lens L6 each constitute a cemented lens, and so-called six groups. It has 7 sheets.
Focusing on the lens group configuration, the first lens group 1G is configured by the first lens L1 to the fourth lens L4. The fifth lens L5 to the seventh lens L7 constitute a second lens group 2G. The fifth lens L5 and the sixth lens L6 constitute a second F lens group 2FG having a positive refractive power. The seventh lens L7 constitutes a second R lens group 2RG having a positive refractive power. That is, the imaging optical system shown in FIG. 2 has a configuration in which the first lens group 1G, the aperture stop S, the second F lens group 2FG, and the second R lens group 2RG are sequentially arranged from the object side to the image plane side. It is said.

Specifically, the first lens group 1G is formed from a positive lens having a positive meniscus shape with a convex surface facing the object side sequentially from the object side to the image surface side, that is, a positive lens having a convex shape on the object side surface. The first lens L1, the negative lens having a negative meniscus shape with the concave surface facing the image surface side, that is, the second lens L2 made of a negative meniscus negative lens having the concave shape on the image side surface, and the concave surface on the image surface side A negative meniscus lens having a negative meniscus shape, i.e., a third lens L3 having a negative meniscus negative lens having a concave shape on the image surface side, and a positive lens having a positive meniscus shape having a convex shape on the object side surface. The fourth lens L4 is arranged so as to exhibit negative refractive power.
An aperture stop S is disposed between the first lens group 1G and the second lens group 2G.
The second F lens group 2FG includes, from the object side to the image surface side, a fifth lens L5 made of a negative lens having a concave shape with a concave surface having a larger curvature than the object side surface. A sixth lens L6, which is a positive lens having a biconvex shape with the same curvature on the object side surface and the image surface side surface, is arranged so as to exhibit positive refractive power. The two lenses of the fifth lens L5 and the sixth lens L6 of the second F lens group 2FG are closely bonded to each other and bonded together to form a cemented lens composed of two lenses. Yes.

The second R lens group 2RG is configured to have a positive refractive power by disposing a seventh lens L7 formed of a biconvex positive lens having the same curvature on the image side and the object side.
Further, behind the second lens group 2G, 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 F shown is arranged.
When performing focusing, the first lens group 1G, the aperture stop S, and the second lens group 2G are integrated, and are moved in the optical axis direction to perform focusing.
In the above embodiment, the second R lens group 2RG is composed of one positive lens, but may be composed of a plurality of lenses. However, by configuring the second R lens group 2RG with a minimum number of one, there is an effect of minimizing the thickness in the optical axis direction and suppressing the increase in the radial direction of the second R lens group 2RG.

FIG. 2 also shows the surface numbers of the optical surfaces in the imaging optical system. 2 are used independently for each embodiment in order to avoid complication of explanation due to an increase in the number of digits of the reference code. Therefore, the same reference numerals as those in FIG. ing.
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 = 5.41, Fno = 1.91, and ω = 29.37, respectively. The optical characteristics of each optical element in Example 2, such as the radius of curvature R of the optical surface, the distance D between adjacent optical surfaces, the refractive index Nd, the Abbe number νd, and the glass type, are as shown in Table 2 below.

The name of the manufacturer is abbreviated as OHARA (Ohara Corporation) after the glass type name of the glass material of the optical glass lens.
The same applies to the other embodiments.
In the case of Example 2, the values corresponding to the conditional expressions (1) to (4) are as follows and satisfy the conditional expressions (1) to (4), respectively.
Conditional expression calculation result (1) 0.529
(2) 0.063
(3) 0.276
(4) 0.221
In addition, FIG. 7 shows aberration curves of various aberrations in the d-line and g-line of the imaging optical system according to Example 2, that is, spherical aberration, astigmatism, distortion aberration, and coma aberration.

In the aberration curve diagram of FIG. 7, the broken line in spherical aberration represents the sine condition, the solid line in astigmatism represents sagittal, and the broken line represents meridional. Further, in each aberration diagram of spherical aberration, astigmatism, and coma aberration, the thin line represents the d line and the thick line represents the g line. The same applies to the aberration curve diagrams according to other examples.
The aberration of the imaging optical system in Example 2 is sufficiently corrected.
By configuring the imaging optical system as in Example 2 according to the second embodiment, it is sufficiently small and has low distortion with a wide field angle of about 29 ° and a large aperture of about F2 or less. Obviously, it is possible to realize an imaging optical system that is configured by only seven polished spherical surfaces and can ensure a very good image performance at a low cost.

[Third Embodiment]
FIG. 3 shows an optical arrangement of the imaging optical system of Example 3 according to the third embodiment of the present invention.

As shown in FIG. 3, 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 a fourth lens from the object side to the image plane side. L4, aperture stop S, fifth lens L5, sixth lens L6, seventh lens L7, and eighth lens L8 are disposed. The fifth lens L5 and the sixth lens L6 each constitute a cemented lens. , So-called 7 groups, 8 sheets.
Focusing on the lens group configuration, the first lens group 1G is configured by the first lens L1 to the fourth lens L4. The fifth lens L5 to the eighth lens L8 constitute a second lens group 2G. The fifth lens L5 and the sixth lens L6 constitute a second F lens group 2FG having a positive refractive power. The seventh lens L7 and the eighth lens L8 constitute a second R lens group 2RG having a positive refractive power. That is, the imaging optical system shown in FIG. 3 has a configuration in which the first lens group 1G, the aperture stop S, the second F lens group 2FG, and the second R lens group 2RG are sequentially arranged from the object side to the image plane side. It is said.

Specifically, the first lens group 1G is formed from a positive lens having a positive meniscus shape with a convex surface facing the object side sequentially from the object side to the image surface side, that is, a positive lens having a convex shape on the object side surface. The first lens L1, the negative lens having a negative meniscus shape with the concave surface facing the image surface side, that is, the second lens L2 made of a negative meniscus negative lens having the concave shape on the image side surface, and the concave surface on the image surface side A negative lens having a negative meniscus shape facing the lens, that is, a third lens L3 composed of a negative meniscus negative lens having a concave shape on the image side surface, and a positive lens comprising a positive meniscus shape having a convex shape on the object side surface. Four lenses L4 are arranged to show negative refractive power.
An aperture stop S is disposed between the first lens group 1G and the second lens group 2G.
The second F lens group 2FG includes, from the object side to the image surface side, a fifth lens L5 made of a negative lens having a concave shape with a concave surface having a larger curvature than the object side surface. A sixth lens L6 made of a positive lens having a biconvex shape with a convex surface having a larger curvature than the surface on the image side facing the object side is arranged so as to exhibit positive refractive power.

The two lenses of the fifth lens L5 and the sixth lens L6 of the second F lens group 2FG are closely bonded to each other and bonded together to form a cemented lens composed of two lenses. Yes. The second R lens group 2RG includes a seventh lens L7 formed of a positive lens having a biconvex shape with a convex surface having a larger curvature than the object-side surface toward the image surface side, and a curvature of the object-side surface from the image-side surface. A positive lens L8 having a biconvex shape with a large convex surface facing is arranged to show positive refractive power.
Further, behind the second lens group 2G, 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 F shown is arranged.
When performing focusing, the first lens group 1G, the aperture stop S, and the second lens group 2G are integrated, and are moved in the optical axis direction to perform focusing.
In the above embodiment, the second R lens group 2RG is constituted by two positive lenses.

FIG. 3 also shows the surface numbers of the optical surfaces in the imaging optical system. Note that each reference symbol shown in FIG. 3 is used independently for each embodiment in order to avoid complication of explanation due to an increase in the number of digits of the reference symbol. Therefore, a reference symbol common to FIGS. 1 and 2 is used. Is attached.
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 = 5.40, Fno = 1.90, and ω = 29.35, respectively. In Table 3, the optical characteristics of each optical element, such as the radius of curvature R of the optical surface, the distance D between adjacent optical surfaces, the refractive index Nd, the Abbe number νd, and the glass type, are as shown in Table 3 below.

The name of the manufacturer is abbreviated as OHARA (Ohara Corporation) after the glass type name of the glass material of the optical glass lens.
The same applies to the other embodiments.
In the case of Example 3, the values corresponding to the conditional expressions (1) to (4) are as follows and satisfy the conditional expressions (1) to (4), respectively.
Conditional expression calculation result (1) 0.494
(2) 0.093
(3) 0.275
(4) 0.225
FIG. 8 shows aberration curves of various aberrations in the d-line and g-line of the imaging optical system according to Example 3, that is, spherical aberration, astigmatism, distortion aberration, and coma aberration.

In the aberration curve diagram of FIG. 8, the broken line in spherical aberration represents the sine condition, the solid line in astigmatism represents sagittal, and the broken line represents meridional. Further, in each aberration diagram of spherical aberration, astigmatism, and coma aberration, the thin line represents the d line and the thick line represents the g line. The same applies to the aberration curve diagrams according to other examples.
The aberration of the imaging optical system in Example 3 is sufficiently corrected.
By configuring the imaging optical system as in Example 3 according to the third embodiment, it is sufficiently small and has low distortion with a wide field angle of about 29 ° and a large aperture of about F2 or less. Obviously, it is possible to realize an image pickup optical system that is configured by only eight polished spherical surfaces and can ensure a very good image performance.

[Fourth Embodiment]
FIG. 4 shows an optical arrangement of the imaging optical system of Example 4 according to the fourth embodiment of the present invention.

As shown in FIG. 4, the imaging optical system according to Example 4 of the present invention sequentially includes a first lens L1, a second lens L2, a third lens L3, and a fourth lens from the object side toward the image plane side. L4, aperture stop S, fifth lens L5, sixth lens L6, and seventh lens L7 are disposed. The fifth lens L5 and the sixth lens L6 each constitute a cemented lens, and so-called six groups. It has 7 sheets.
Focusing on the lens group configuration, the first lens group 1G is configured by the first lens L1 to the fourth lens L4. The fifth lens L5 to the seventh lens L7 constitute a second lens group 2G. The fifth lens L5 and the sixth lens L6 constitute a second F lens group 2FG having a positive refractive power. The seventh lens L7 constitutes a second R lens group 2RG having a positive refractive power. That is, the imaging optical system shown in FIG. 4 has a configuration in which the first lens group 1G, the aperture stop S, the second F lens group 2FG, and the second R lens group 2RG are sequentially arranged from the object side to the image plane side. It is said.

Specifically, the first lens group 1G is formed from a positive lens having a positive meniscus shape with a convex surface facing the object side sequentially from the object side to the image surface side, that is, a positive lens having a convex shape on the object side surface. The first lens L1, the negative lens having a negative meniscus shape with the concave surface facing the image surface side, that is, the second lens L2 made of a negative meniscus negative lens having the concave shape on the image side surface, and the concave surface on the image surface side A negative lens having a negative meniscus shape facing the lens, that is, a third lens L3 composed of a negative meniscus negative lens having a concave shape on the image side surface, and a positive lens comprising a positive meniscus shape having a convex shape on the object side surface. Four lenses L4 are arranged to show negative refractive power.
An aperture stop S is disposed between the first lens group 1G and the second lens group 2G.
The second F lens group 2FG includes, from the object side to the image surface side, a fifth lens L5 made of a negative lens having a concave shape with a concave surface having a larger curvature than the object side surface. A sixth lens L6, which is a positive lens having a biconvex shape with a convex surface having a larger curvature than the object-side surface, is disposed on the image surface side so as to exhibit positive refractive power. The two lenses of the fifth lens L5 and the sixth lens L6 of the second F lens group 2FG are closely bonded to each other and bonded together to form a cemented lens composed of two lenses. Yes. The second R lens group 2RG includes a seventh lens L7, which is a biconvex positive lens made of a convex surface having a larger curvature than the surface on the image side, on the object side, and is configured to exhibit positive refractive power. Yes.

Further, behind the second lens group 2G, 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 F shown is arranged.
When performing focusing, the first lens group 1G, the aperture stop S, and the second lens group 2G are integrated, and are moved in the optical axis direction to perform focusing.
In the above embodiment, the second R lens group 2RG is composed of one positive lens, but may be composed of a plurality of lenses. However, by configuring the second R lens group 2RG with a minimum number of one, there is an effect of minimizing the thickness in the optical axis direction and suppressing the increase in the radial direction of the second R lens group 2RG.
FIG. 4 also shows the surface numbers of the optical surfaces in the imaging optical system. In addition, in order to avoid complication of explanation due to an increase in the number of digits of the reference code, each reference code shown in FIG. 4 is used independently for each embodiment, and therefore, the same reference code as in FIGS. Is attached.
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 = 5.40, Fno = 1.91, and ω = 29.40, respectively. The optical characteristics of each optical element in Example 4, such as the radius of curvature R of the optical surface, the distance D between adjacent optical surfaces, the refractive index Nd, the Abbe number νd, and the glass type, are as shown in Table 4 below.

The name of the manufacturer is abbreviated as OHARA (Ohara Corporation) after the glass type name of the glass material of the optical glass lens.
The same applies to the other embodiments.
In the case of Example 1, the values corresponding to the conditional expressions (1) to (4) are as follows, and satisfy the conditional expressions (1) to (4), respectively.
Conditional formula calculation result (1) 0.515
(2) 0.162
(3) 0.257
(4) 0.270
FIG. 9 shows aberration curves of various aberrations in the d-line and g-line of the imaging optical system according to Example 4, that is, spherical aberration, astigmatism, distortion aberration, and coma aberration.

In the aberration curve diagram of FIG. 9, the broken line in spherical aberration represents a sine condition, the solid line in astigmatism represents sagittal, and the broken line represents meridional. Further, in each aberration diagram of spherical aberration, astigmatism, and coma aberration, the thin line represents the d line and the thick line represents the g line. The same applies to the aberration curve diagrams according to other examples.
The aberration of the imaging optical system in Example 4 is sufficiently corrected.
By configuring the imaging optical system as in Example 4 according to the fourth embodiment, it is sufficiently small and has low distortion with a wide field angle of about 29 ° and a large aperture of about F2 or less. Obviously, it is possible to realize an imaging optical system that can ensure a very good image performance at a low cost, which is composed of only seven polished spherical surfaces.

[Fifth Embodiment]
FIG. 5 shows an optical arrangement of the imaging optical system of Example 5 according to the fifth embodiment of the present invention.

As shown in FIG. 5, the imaging optical system according to Example 5 of the present invention sequentially includes a first lens L1, a second lens L2, a third lens L3, and a fourth lens from the object side toward the image plane side. L4, aperture stop S, fifth lens L5, sixth lens L6, seventh lens L7 and eighth lens L8 are arranged, and the fifth lens L5 and the sixth lens L6 each constitute a cemented lens. , So-called 7 groups, 8 sheets.
Focusing on the lens group configuration, the first lens group 1G is configured by the first lens L1 to the fourth lens L4. The fifth lens L5 to the eighth lens L8 constitute a second lens group 2G. The fifth lens L5 and the sixth lens L6 constitute a second F lens group 2FG having a positive refractive power. The seventh lens L7 and the eighth lens L8 constitute a second R lens group 2RG having a positive refractive power. That is, the imaging optical system shown in FIG. 5 has a configuration in which the first lens group 1G, the aperture stop S, the second F lens group 2FG, and the second R lens group 2RG are sequentially arranged from the object side to the image plane side. It is said.

Specifically, the first lens group 1G is formed from a positive lens having a positive meniscus shape with a convex surface facing the object side sequentially from the object side to the image surface side, that is, a positive lens having a convex shape on the object side surface. The first lens L1, the negative lens having a negative meniscus shape with the concave surface facing the image surface side, that is, the second lens L2 made of a negative meniscus negative lens having the concave shape on the image side surface, and the concave surface on the image surface side A negative lens having a negative meniscus shape facing the lens, that is, a third lens L3 composed of a negative meniscus negative lens having a concave shape on the image side surface, and a positive lens comprising a positive meniscus shape having a convex shape on the object side surface. Four lenses L4 are arranged to show negative refractive power.
An aperture stop S is disposed between the first lens group 1G and the second lens group 2G.
The second F lens group 2FG includes, from the object side to the image surface side, a fifth lens L5 made of a negative lens having a concave shape with a concave surface having a larger curvature than the object side surface. A sixth lens L6, which is a positive lens having a biconvex shape with a convex surface having a larger curvature than the object-side surface, is disposed on the image surface side so as to exhibit positive refractive power.

The two lenses of the fifth lens L5 and the sixth lens L6 of the second F lens group 2FG are closely bonded to each other and bonded together to form a cemented lens composed of two lenses. Yes. The second R lens group 2RG includes a seventh lens L7 composed of a biconvex positive lens having a convex surface having a larger curvature on the image surface side than the object side surface, and a positive meniscus positive lens having a convex shape on the image side surface. An eighth lens L8 made of is arranged so as to exhibit positive refractive power.
Further, behind the second lens group 2G, 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 F shown is arranged.
When performing focusing, the first lens group 1G, the aperture stop S, and the second lens group 2G are integrated, and are moved in the optical axis direction to perform focusing.

In the fifth embodiment, the second R lens group 2RG is composed of two positive lenses.
FIG. 5 also shows the surface numbers of the optical surfaces in the imaging optical system. Note that each reference symbol shown in FIG. 5 is used independently for each embodiment in order to avoid complication of explanation due to an increase in the number of digits of the reference symbol. Therefore, the reference symbol common to FIGS. Is attached.
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 = 5.40, Fno = 1.91, and ω = 29.33, respectively. In Table 5, the optical characteristics of each optical element, such as the radius of curvature R of the optical surface, the distance D between adjacent optical surfaces, the refractive index Nd, the Abbe number νd, and the glass type, are as shown in Table 5 below.

The name of the manufacturer is abbreviated as OHARA (Ohara Corporation) after the glass type name of the glass material of the optical glass lens.
In the case of the fifth embodiment, values corresponding to the conditional expressions (1) to (4) are as follows, and satisfy the conditional expressions (1) to (4), respectively.
Conditional expression calculation result (1) 0.725
(2) 0.101
(3) 0.303
(4) 0.196

FIG. 10 shows aberration curves of various aberrations in the d-line and g-line of the imaging optical system according to Example 5, that is, spherical aberration, astigmatism, distortion aberration, and coma aberration.
In the aberration curve diagram of FIG. 10, the broken line in spherical aberration represents the sine condition, the solid line in astigmatism represents sagittal, and the broken line represents meridional. Further, in each aberration diagram of spherical aberration, astigmatism, and coma aberration, the thin line represents the d line and the thick line represents the g line. The same applies to the aberration curve diagrams according to other examples.
The aberration of the imaging optical system in Example 5 is sufficiently corrected.
By configuring the imaging optical system as in Example 5 according to the fifth embodiment, it is sufficiently small and has low distortion with a wide field angle of about 29 ° and a large aperture of about F2 or less. Obviously, it is possible to realize an image pickup optical system that is configured by only eight polished spherical surfaces and can ensure a very good image performance.

[Sixth Embodiment]
Next, a digital camera as an apparatus according to the sixth embodiment of the present invention configured by adopting the imaging optical system according to the first to fifth embodiments of the present invention described above will be described. This will be described with reference to FIGS. Note that the apparatus according to the sixth embodiment of the present invention includes portable information such as a digital camera, a video camera, a silver halide film camera, an in-vehicle camera, a stereo camera and the like, a PDA (personal data assistant), a mobile phone and the like. It includes devices such as terminal devices, inspection devices such as optical sensors, and projection devices such as projectors. FIG. 11 is a perspective view schematically showing the external appearance of the digital camera viewed from the front side that is the object side, that is, the subject side, and FIG. 12 is a schematic external view of the digital camera viewed from the back side that is the photographer side. FIG. 13 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, various devices such as a so-called PDA (personal data assistant) and a portable information terminal device such as a cellular phone, which incorporate a camera function, are 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. 11 to 13, 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. 13, the digital camera includes a central processing unit (CPU) 11, an image processing device 12, a light receiving element 13, a signal processing device 14, a semiconductor memory 15 and a communication card 16.
The digital camera includes 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. The light receiving element 13 reads an optical image of a subject (object) formed by the photographing lens 1. As the photographing lens 1, the imaging optical system according to the present invention as described in the first to fifth embodiments is used.
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 a function of converting a captured image (photographed image) into digital information. This function substantially controls the light receiving element 13, the signal processing device 14, and these. A central processing unit (CPU) 11 is configured.

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 8 or shown in the first to fifth embodiments described above) includes the first lens group, the aperture stop, The lens group may be moved as a single unit by moving some lens groups of a plurality of optical systems or moving a light receiving element.

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.
The above-described digital camera (camera device), particularly an in-vehicle camera device, a stereo camera device, or a portable information terminal device that is mounted on a vehicle and controls imaging at the time of a collision accident or driving of a vehicle, has already been described. As described above, the photographic lens 1 configured using the imaging optical system as shown in the first to fifth embodiments can be used as the imaging optical system. Therefore, it is a low-cost imaging optical system that is small, has high performance, has a wide field angle of about 58 °, has a large F number of about 2 or less, and is composed only of a polished surface. A high-quality and small camera device, stereo camera device, or portable information terminal device using the system can be realized (corresponding to claim 10).
Note that the imaging optical system described above includes a shooting optical system used for a digital camera, a shooting optical system used for a video camera, a shooting optical system used for a silver salt camera, an optical system used for an optical sensor, a projection optical system used for a projection optical system, and the like. It can be applied in the field of

1G 1st lens group 2G 2nd lens group 2FG 2F lens group 2RG 2R lens group L1 to L8 1st lens to 8th lens S Aperture stop F filter

JP 2012-220741 A (Patent No. 5736924) JP 10-31153 A (Patent No. 4004587) JP 11-211977 A (Patent No. 4052493) JP 2010-176016 A (Patent No. 5458586) JP 2010-176017 A (Patent No. 5316035)

Claims (10)

In order from the object side, the first lens group having a negative refractive power, an aperture stop, and a second lens group having a positive refractive power,
The first lens group includes, in order from the object side, a positive lens, a negative lens, a negative lens, and a positive lens.
The imaging optical system, wherein the second lens group includes, in order from the object side, a cemented lens of a negative lens and a positive lens, and a positive lens.   The imaging optical system according to claim 1, wherein the first lens group includes, in order from the object side, the positive lens having a convex shape on the object side, the negative lens having a concave shape on the image side surface, and an image side surface. An imaging optical system comprising the negative lens having a concave shape and the positive lens having a convex shape on an object side surface.   3. The imaging optical system according to claim 1, wherein the positive lens on the most image side in the first lens group is a positive meniscus lens, and the negative lens on the most object side in the second lens group. An imaging optical system characterized in that the object side surface of the lens has a concave shape. The imaging optical system according to any one of claims 1 to 3, wherein the following conditional expression (1) is satisfied.
0.20 <| f / fa | <1.00 (1)
Here, f represents the focal length fa of the entire system, and the focal length of the air lens formed by the most image side surface of the first lens group and the most object side surface of the second lens group. 5. The imaging optical system according to claim 1, wherein the imaging optical system satisfies the following conditional expression (2): 6.
0.01 <| f / f1 | <0.50 (2)
However, f represents the focal length of the entire system, and f1 represents the focal length of the first lens group. 6. The imaging optical system according to claim 1, wherein the following conditional expression (3) is satisfied.
0.10 <f / AL <0.45 (3)
Here, AL represents the distance on the optical axis from the first surface of the first lens group to the image plane when focusing on infinity.   The imaging optical system according to any one of claims 1 to 6, wherein the positive lens closest to the object side of the first lens group is a positive meniscus lens.   The imaging optical system according to any one of claims 1 to 7, wherein the second lens group includes a positive second F lens group as a whole and a positive second R lens group as a whole. An imaging optical system, wherein the second F lens group includes at least one negative lens and one positive lens, and the second R lens group includes one positive lens. The imaging optical system according to any one of claims 1 to 8, wherein the following conditional expression (4) is satisfied.
0.05 <| f / f2F | <0.50 (4)
Here, f2F represents the combined focal length of the cemented lens of the negative lens closest to the object side of the second lens group and the positive lens.   The apparatus which has an imaging optical system of any one of Claim 1 thru | or 9.

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