JP2011242520A - Imaging optical system and imaging apparatus comprising the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging optical system suitable for an optical system using an electronic imaging element and advantageous in securing a wide viewing angle and reducing the size.SOLUTION: The imaging optical system includes, in order from an object side: a front-side lens group (LF) having a plurality of lenses including at least one negative lens; a brightness diaphragm (S); and a rear-side lens group (LR) of positive refractive power. The rear-side lens group (LR) includes, in order from the object side, a sub-lens group (LF1) of positive refractive power and a focus lens group (LRF) of positive refractive power. The lens closest to the object in the front-side lens group (LF) is fixed, and conditional expressions (1) and (2) are satisfied: (1) 1.15≤fb/IHω≤1.7 and (2) -4.0≤fn/IHω≤-1.3, where "f" represents the focal distance of the entire system, "fn" is the focal distance of the negative lens (n1) closest to the object in the front-side lens group (LF), "ft" represents a back focus at an infinite object point, the back focus being an air conversion length from the refraction face closest to the image to the imaging surface, and "IHω" represents the height of the principal ray at the maximum viewing angle (ω) on the imaging surface at the infinite object point.

Description

  The present invention relates to an optical system used for an imaging apparatus or the like, and more particularly to an imaging optical system used for a digital camera or the like and an imaging apparatus using the imaging optical system.

  In recent years, a camera using an electronic image sensor such as a digital camera has been reduced in size and performance. Accordingly, there is an increasing need for miniaturization and high performance of the optical system. Even with interchangeable lens cameras, portability is high and is no exception. In addition, a lens system having a wide angle range in which the maximum incident half angle of view is 32 degrees or more (an angle of view exceeding the angle of view of a focal length of 35 mm in terms of 135 format) is an angle of view that is easy to use in terms of portrait photography and landscape photography. . A fisheye optical system with a wider angle of view is also preferred because it can shoot with the deformation effect. The following are known as conventional techniques of an imaging optical system having a relatively wide angle region.

JP-A-1-319909 JP 55-67715 A JP 2001-83411 A JP 59-216114 A Japanese Patent Application Laid-Open No. 11-052229 JP-A-49-020217 JP 2005-227426 A

  Patent Document 1 discloses an optical system having a half field angle of 47 degrees and a wide field angle, the final lens group being composed of two lenses, and the focus group being downsized. Although this optical system has a wide angle of view, the incident angle of the light ray incident at the maximum image height on the image plane is close to 20 degrees.

  When an electronic image sensor is used in such an optical system, the amount of peripheral light is likely to decrease due to light vignetting. Further, the transmittance of filters such as an IR cut filter varies depending on the incident angle. Further, assuming an interchangeable lens camera, when the incident angle characteristic of the image sensor is optimized in the optical system disclosed in Patent Document 1, the exit pupil of the telephoto lens system must be close to the image plane. Disappear. Further, even in an image pickup system in which the image pickup device and the optical system are fixed, it is difficult to share the electronic image pickup device, which is disadvantageous in terms of common parts, resulting in a cost increase.

  The lens system disclosed in Patent Document 2 has a long back focus and tends to have a long total lens length.

  The lens system disclosed in Patent Document 3 has a half angle of view of 31.6 degrees or less.

  The lens system disclosed in Patent Document 4 is a rear focus type lens system, but it is necessary to focus drive a lens group that has a large number of lenses in the focus group and is relatively heavy with respect to the size of the lens system. There is. This makes it difficult to obtain stable focus stop accuracy.

  The lens system disclosed in Patent Document 5 discloses a fish eye optical system having a long back focus and a peripheral ray emission angle of 20 degrees or more.

  The lens system disclosed in Patent Document 6 discloses a fish eye optical system in which the back focus is short and the emission angle of peripheral rays is 20 degrees or more.

  The lens system disclosed in Patent Document 7 discloses a fisheye optical system having a short spherical focus and large astigmatism, although the back focus is short and the emission angle of peripheral rays is as gentle as about 14 degrees.

  The present invention has been invented in view of such circumstances, and has a constant total length during focusing that facilitates downsizing, securing of a peripheral light amount, and ensuring good imaging performance while ensuring a wide angle of view. It is an object of the present invention to provide an imaging optical system. It is another object of the present invention to provide an imaging apparatus using such an imaging optical system.

In order to solve the above problems, the imaging optical system according to the present invention is:
The aperture stop,
A front lens group (LF) disposed closer to the object side than the aperture stop,
A rear lens group (LR) having a positive refractive power disposed on the image side of the aperture stop,
The front lens group (LF) includes a first sub lens group (L1) having a negative refractive power and a second sub lens group (L2) having a positive refractive power in order from the object side to the image side.
The rear lens group (LR) includes, in order from the object side to the image side, a third sub-lens group (L3) whose surface closest to the image side is a convex surface and a fourth sub-lens group (L4) having a positive refractive power. ,
The first sub-lens group is basically configured so that its position is fixed.

  Hereinafter, the reason and effect | action which took such a structure are demonstrated.

  The imaging optical system according to the present invention has such a basic configuration, so that a so-called retrofocus type lens arrangement is obtained, and an imaging optical system that easily separates the exit pupil from the image plane while ensuring a wide angle of view. Become. In this lens arrangement, by allowing distortion in the negative direction, the back focus can be shortened appropriately, and further miniaturization and performance securing in this lens arrangement type can be achieved.

  The above-described basic configuration, that is, the first sub-lens group (L1) having negative refractive power on the object side in the front lens group (LF) and the second sub-lens group having positive refractive power disposed on the image side thereof ( L2) is advantageous for securing a wide angle of view while mainly suppressing the occurrence of spherical aberration.

  Further, the third sub-lens group (L3) on the aperture stop side of the rear lens group (LR) has a convex surface on the most image side surface, and a fourth sub-lens group (L4) having a positive refractive power is disposed behind the convex surface. By doing so, it is possible to guide the image to the imaging plane by gradually refracting the incident light ray angle toward the image plane while setting the back focus to an appropriate length. Thereby, since the incident angle on the imaging surface can be reduced, it is possible to provide an imaging optical system that is not easily affected by the decrease in the amount of peripheral light and the angular characteristics of the wavelength transmittance of the filters.

  In addition, this basic configuration makes it easy to cancel the curvature of the Petzval image plane between the front lens group and the rear lens group, and correction of field curvature and astigmatism correction, which is particularly important in wide-angle shooting. Is advantageous.

  In addition, in the basic configuration of the present invention, as described above, the position of the first sub lens group is fixed during focusing.

  When the first sub lens group is a focusing lens group, abrupt aberrations are likely to occur due to the second sub lens group (L2) and subsequent lenses. On the other hand, as in the present invention, the occurrence of aberration can be suppressed by performing focusing by moving at least one lens (single or plural) in the second sub lens group or in the lens group on the image side of the second sub lens group. It becomes possible. In addition, by adopting the inner focus method and the rear focus method in this way, an imaging optical system whose total length is unchanged is obtained. Accordingly, it is possible to reduce the weight of the lens (single or plural) that moves during focusing, which is advantageous for achieving high-speed focusing and quietness during shooting. Furthermore, it is easy to ensure continuous focusing accuracy, for example, when shooting moving images.

  In such a basic configuration, it is more preferable to arrange the focusing lens group for performing focusing in the rear lens group.

  In order to ensure performance, it is necessary to gradually converge the light beam diverged from the first sub-lens group (L1) having negative refractive power in the front lens group toward the image plane by a plurality of positive lens groups. However, by making the lens group that performs focusing at this time have a positive refractive power, it is advantageous to achieve both the focusing function and the effect of converging the light beam, and to further simplify the configuration of the optical system.

  In addition, the configuration of the rear lens group (LR) is advantageous for securing an appropriate back focus and improving the optical performance in the off-axis region as described above. In addition, it occurs in the fourth sub lens group (L4). This also has the effect of reducing aberrations. Therefore, it is more preferable to perform focusing with the fourth sub-lens group (L4), which leads to a reduction in aberration fluctuations and fluctuations in the emission angle of peripheral rays.

  In addition, it is more preferable that the lens group for focusing is moved by moving only one lens group in terms of simplifying the frame configuration, reducing the cost, and reducing the weight of the movable group.

  It is preferable that the above basic configuration further satisfies any one or more of the following.

The first sub lens group has a most object side lens surface convex to the object side,
The third sub lens group has a concave object side lens surface on the object side;
It is preferable that the following conditional expressions (1), (2), and (3) are satisfied.
-140% ≤ DT ≤ -7% (1)
−2.2 ≦ R_L3f / f ≦ −0.25 (2)
0.8 ≦ R_L1f / f ≦ 5.5 (3)
However,
DT = (IHω−f · tan ω) / (f · tan ω) × 100%,
ω is the maximum half field angle of the imaging optical system,
IHω is the distance from the optical axis at the point where the principal ray with the maximum half angle of view ω intersects the image plane,
f is the focal length of the entire imaging optical system,
R_L3f is the paraxial radius of curvature of the lens surface closest to the object side in the third sub lens group,
R_L1f is the paraxial radius of curvature of the lens surface closest to the object side of the first sub lens group,
fLF is the focal length of the front lens group.

  Each conditional expression is a condition in a state where the imaging optical system is focused on an object point at the longest distance. Similarly, the following conditional expressions are also set in a state where the imaging optical system is focused on the object point at the farthest distance.

  Conditional expression (1) is a preferable condition for sufficiently drawing out the characteristics of the above basic configuration in order to reduce the size of the imaging optical system.

  By making sure that the lower limit of conditional expression (1) is not exceeded, it becomes easier to reduce field curvature, and the increase in the number of front lens groups for correcting field curvature is suppressed, leading to miniaturization. In addition, it is easy to suppress an increase in the incident angle of the light beam incident on the maximum image height in the imaging surface.

  By intentionally generating negative distortion so as not to exceed the upper limit of conditional expression (1), it is advantageous to appropriately shorten the back focus.

  Conditional expression (2) is a preferable condition for efficiently suppressing the off-axis light beam to the imaging surface while suppressing the occurrence of ascoma.

  By making sure that the lower limit of conditional expression (2) is not exceeded, it becomes easier to obtain an as-coma aberration correction effect in the rear lens group, which is advantageous in securing optical performance. In addition, the curvature of the concave surface on the object side of the third sub-lens group is secured, and the off-axis light beam is refracted away from the optical axis on this surface, and the height of the light beam after the concave surface is increased, thereby increasing the height after the concave surface. It becomes easy to ensure the function of separating the exit pupil from the image plane by the convergence action.

  By making sure that the upper limit of conditional expression (2) is not exceeded, it is easy to suppress an excess of as-coma correction effect.

  Conditional expression (3) is a preferable condition for securing a wide angle of view and mainly reducing the generation of asses.

  By making sure that the lower limit of conditional expression (3) is not exceeded, it is easy to secure the negative refractive power of the first sub lens unit, which is advantageous for securing the back focus and widening the angle of view.

  By avoiding exceeding the upper limit of conditional expression (3), it is easy to reduce the generation of asses, which is advantageous in securing optical performance.

In the above-described basic configuration, or in the imaging optical system that satisfies any one or more of the above-described conditional expressions (2) and (3) in the basic configuration,
The rear lens group (LR) has a focusing lens group that moves during focusing;
The first sub lens group includes at least one negative lens;
When the negative lens disposed closest to the object side among the negative lenses in the first sub lens group is the first negative lens (n1),
The first negative lens is a negative meniscus lens having a concave surface facing the image side,
It is preferable that the following conditional expressions (1) and (4) are satisfied.
-140% ≤ DT ≤ -7% (1)
1.1 ≦ SFn1 ≦ 5.0 (4)
However,
DT = (IHω−f · tan ω) / (f · tan ω) × 100%,
ω is the maximum half field angle of the imaging optical system,
IHω is the distance from the optical axis at the point where the principal ray with the maximum half angle of view ω intersects the image plane,
f is the focal length of the entire imaging optical system,
SFn1 = (Rn1f + Rn1r) / (Rn1f−Rn1r), and Rn1f is a paraxial radius of curvature of the object side surface of the first negative lens,
Rn1r is the paraxial radius of curvature of the image side surface of the first negative lens.

  By making the first negative lens a negative meniscus lens having a concave surface facing the image side, various off-axis aberrations that are likely to occur when the refractive power of this lens is increased to ensure the angle of view, mainly astigmatism. It is advantageous for reduction.

  Conditional expression (4) is a more preferable condition for maintaining good coma and astigmatism while ensuring a wide angle of view.

  By making sure that the lower limit of conditional expression (4) is not exceeded, it is easy to suppress the refractive power of the first negative lens, which is advantageous in reducing coma. In addition, the tendency of the Petzval image surface to bend to the plus side can be suppressed, which is advantageous in maintaining good astigmatism while maintaining a wide angle of view.

  By making sure that the upper limit of conditional expression (4) is not exceeded, it is possible to ensure the effect of correcting aberrations and to suppress the enlargement of the lens on the object side compared to the aperture stop.

In the above-described basic configuration, or in an imaging optical system that further satisfies any one or more of the above-described conditions (1), (2), (3), and (4) in the basic configuration,
The rear lens group (LR) has a positive refractive power focusing lens group that moves during focusing;
The first sub lens group includes at least a negative lens;
When the negative lens arranged closest to the object side among the negative lenses in the first sub lens group is the first negative lens (n1),
The first negative lens is a negative meniscus lens having a concave surface facing the image side,
It is preferable that the following conditional expressions (5), (6), and (7) are satisfied.
−3 ≦ fn1 / fLR ≦ −0.5 (5)
-2 ≦ fn11 / fLR ≦ −0.1 (6)
Tmax / IHω30 ≦ 1.2 (7)
However,
fn1 is a focal length of the first negative lens;
fn11 is a combined focal length of the first negative lens and a lens disposed immediately after the image side of the negative lens,
fLR is the focal length of the rear lens group,
Tmax is the maximum value of the distances of the spaces between the plurality of lenses in the imaging optical system excluding the image-side space in contact with the first negative lens,
IHω30 is the distance from the optical axis at the point where the principal ray having a half angle of view of 30 degrees intersects the image plane.

  Conditional expression (5) satisfies the requirements of the front lens group (LF) and the fourth sub-lens group (L4) having a positive refractive power while ensuring appropriate back focus, ensuring optical performance, miniaturization, and shortening the optical total length. This is a preferable condition for simplifying the configuration.

  By ensuring the refractive power of the first negative lens so that it does not fall below the lower limit of conditional expression (5), it becomes easier to secure the back focus when the angle of view is widened, and the Petzval image surface tends to become negative. This is advantageous for correcting curvature of field. In addition, since the first negative lens bears the function of ensuring the back focus, it is possible to reduce the number of lenses in the front lens group (LF), thereby reducing the overall length of the optical system and the front lens group. It leads to size reduction.

  By preventing the upper limit of conditional expression (5) from being exceeded, the tendency of the Petzval image surface to become positive can be reduced, which is advantageous for correcting curvature of field. In addition, it is easy to suppress an increase in back focus while reducing the number of constituent lenses of the fourth lens group, particularly the fourth sub lens group. When focusing with a positive refractive power lens group in the rear lens group, the configuration of the focusing lens group can be simplified, the weight of the focusing lens group can be reduced, and the focusing operation is speeded up and quiet. This is advantageous for ensuring continuous focusing accuracy, such as when shooting and moving images.

  Conditional expression (6) satisfies the constitution of the front lens group (LF) and the fourth sub lens group (L4) while ensuring the back focus and reducing the size and shortening the total length of the optical system while widening the angle of view. This is a preferable condition for making it easier and easier.

  By making sure that the lower limit of conditional expression (6) is not exceeded, it becomes easier to secure the back focus at the time of widening the angle of view, and the function of securing the back focus is borne by the two lenses, so that the front lens group ( LF), the number of lenses can be reduced, leading to a reduction in the overall length of the optical system and a reduction in the size of the front lens group. In addition, the tendency of the Petzval image surface to become negative is suppressed, which leads to correction of the astigmatism difference.

  By not exceeding the upper limit of conditional expression (6), the tendency of the Petzval image surface to become positive can be reduced, which is advantageous for correction of field curvature. In addition, it is easy to suppress an increase in back focus while reducing the number of constituent lenses of the rear lens group, particularly the fourth sub lens group. When focusing with a positive refractive power lens group in the rear lens group, the configuration of the focusing lens group can be simplified, the weight of the focusing lens group can be reduced, and the focusing operation is speeded up and quiet. This is advantageous for ensuring continuous focusing accuracy, such as when shooting and moving images.

  Conditional expression (7) is a preferable condition for advantageously shortening the length (Σd) from the most object side lens surface to the most image side lens surface of the imaging optical system and reducing the outer diameter of the optical system. It is.

  The first negative lens (n1) is a negative meniscus lens having a concave surface facing the image side in order to secure a wide angle of view and ensure performance, and satisfies the above-mentioned conditions to sufficiently secure negative refractive power. It is preferable. Therefore, in order to suppress aberration, it is effective to make the image side surface a concave meniscus shape. Therefore, by securing an air space immediately after the image side of the first negative lens (n1), this negative lens is secured. It is advantageous to secure the function of On the other hand, when looking at each air space on the image side from this air space, the air space between each lens is shortened to reduce the outer diameter of the lens, and from the most object side lens surface of the imaging optical system to the most image side lens The length to the surface (Σd) can be reduced.

  The above-described configuration of the present invention is advantageous in securing performance without using a large air gap. Therefore, it is preferable to satisfy the conditional expression (7) and to shorten the length (Σd) from the most object side lens surface to the most image side lens surface of the imaging optical system and to reduce the lens outer diameter.

  Of course, a configuration satisfying the conditional expression (1) “−140% ≦ DT ≦ −7%” is more preferable in terms of miniaturization and securing performance.

Further, in the above-described basic configuration, or in the basic configuration, imaging that satisfies any one or more of the above-described conditional expressions (2), (4), (5), (6), and (7) In the optical system,
The rear lens group (LR) has a focusing lens group that moves during focusing;
It is preferable that the following conditional expressions (1) and (3) are satisfied.
-140% ≤ DT ≤ -7% (1)
0.8 ≦ R_L1f / f ≦ 5.5 (3)
However,
DT = (IHω−f · tan ω) / (f · tan ω) × 100%,
ω is the maximum half field angle of the imaging optical system,
IHω is the distance from the optical axis at the point where the principal ray with the maximum half angle of view ω intersects the image plane,
f is the focal length of the entire imaging optical system,
R_L1f is the paraxial radius of curvature of the lens surface closest to the object side of the first sub lens group,
It is.

  It is preferable to obtain the functions described above for each component.

In the above basic configuration, or in the basic configuration, any one or more of the above conditional expressions (2), (3), (4), (5), (6), (7) In a satisfactory imaging optical system,
It is preferable that the rear lens group (LR) has a positive refractive power focusing lens group that moves during focusing, and satisfies the following conditional expression (8).
−140% <DT <−40% (8)
However,
DT = (IHω−f · tan ω) / (f · tan ω) × 100%,
ω is the maximum half field angle of the imaging optical system,
IHω is the distance from the optical axis at the point where the principal ray with the maximum half angle of view ω intersects the image plane,
f is the focal length of the entire imaging optical system,
R_L1f is the paraxial radius of curvature of the lens surface closest to the object side of the first sub lens group,
It is.

  Conditional expression (8) is a preferable condition for miniaturization of an imaging optical system having a wide angle of view in which the maximum incident angle (= maximum half angle of view) exceeds 40 degrees. It is advantageous to pull out.

  By making sure that the lower limit of conditional expression (8) is not exceeded, it becomes easier to reduce the field curvature, and the increase in the number of constituent lenses of the front lens group for correcting the field curvature is suppressed, leading to a reduction in size. In addition, it is easy to suppress an increase in the incident angle of the light beam incident on the maximum image height in the imaging surface.

  By intentionally generating negative distortion so as not to exceed the upper limit of conditional expression (8), it is advantageous for achieving both a wide angle of view and miniaturization.

  In any of the above-described inventions, it is more preferable that any one of the following configurations is satisfied.

It is preferable that the following conditional expression (9) is satisfied.
0.8 ≦ fb / f ≦ 2.7 (9)
However,
fb is an air equivalent distance from the lens surface closest to the image side of the imaging optical system to the image plane;
f is the focal length of the entire imaging optical system,
It is.

  Conditional expression (9) is a condition for ensuring the functions of the above-described inventions, and is particularly advantageous for shortening the overall length and reducing the diameter of the optical system.

  Preventing the final lens from getting too close to the image plane so as not to fall below the lower limit of conditional expression (9) is advantageous in reducing the size of the final lens.

  Arranging the rear lens group without excessively exceeding the upper limit of conditional expression (9) is advantageous for both shortening the overall length of the optical system and relaxing the incident angle on the imaging surface.

It is preferable that the following conditional expression (10) is satisfied.
0.8 ≦ fb / IHω ≦ 2.4 (10)
However,
fb is an air equivalent distance IHω from the lens surface closest to the image side of the imaging optical system to the image plane, and is a distance from the optical axis at the point where the principal ray having the maximum half angle of view ω intersects the image plane,
It is.

  Conditional expression (10), like conditional expression (9), is a condition for ensuring the functions of the present invention, and is particularly advantageous for shortening the overall length and reducing the diameter of the optical system.

  Preventing the final lens from getting too close to the image plane so as not to fall below the lower limit of conditional expression (10) is advantageous in reducing the size of the final lens.

  Arranging the rear lens group without excessively exceeding the upper limit of conditional expression (10) is advantageous for both shortening the overall length of the optical system and relaxing the incident angle on the imaging surface.

  Preferably, the imaging optical system is a single focus lens, and the movable lens group in the imaging optical system is only one focusing lens group.

  As a result, the frame configuration can be further simplified, and downsizing and cost reduction can be achieved. In addition, by adopting a single focus lens specialized for the wide-angle region effective in the present configuration, not as a zoom lens, the present configuration can be a high-performance and compact optical system.

  As a more preferable configuration, the total number of lenses in the focusing lens group is 2 or less, which is advantageous for reducing the weight of the drive unit, and is more preferable.

  Preferably, the fourth sub lens group (L4) is the only lens group that moves during focusing, and the total number of lenses included in the fourth sub lens group is two or less.

  By using only one lens group that moves during focusing, the frame configuration can be further simplified, which is advantageous for weight reduction, size reduction, and cost reduction.

  In addition, the present invention is easy to achieve both high-performance enhancement by ensuring moderate back focus and gradually relaxing the incident ray angle of the imaging surface toward the image plane, and the fourth sub lens group ( It is easy to reduce the aberration generated in L4).

  Therefore, by using the fourth sub lens group (L4) as a focusing lens group, it is possible to reduce aberration fluctuations and fluctuations in the emission angle of peripheral rays, and to reduce fluctuations during incident angle focusing.

  The fourth sub-lens group that is easy to suppress aberration fluctuations has a lens configuration of two or less lenses, so that the weight can be further reduced, which is advantageous in increasing the speed of focusing and noise reduction. Furthermore, it is advantageous for ensuring continuous focusing accuracy when shooting moving images.

It is preferable that the following conditional expression (11) is satisfied.
−1 ≦ R_L3f / fLR ≦ −0.2 (11)
However,
R_L3f is the paraxial radius of curvature of the lens surface closest to the object side in the third sub lens group,
fLR is the focal length of the rear lens group,
It is.

  Conditional expression (11) is a condition for effectively reducing the off-axis light beam toward the image plane while suppressing the occurrence of astigmatism and coma.

  The curvature of the object side lens surface of the third sub lens group is secured so as not to fall below the lower limit of the conditional expression (11), and the function of canceling astigmatism and coma aberration of the rear lens group is sufficiently secured on this surface. It is preferable.

  By avoiding exceeding the upper limit of conditional expression (11), it becomes easy to suppress overcorrection of astigmatism and coma aberration.

  It is preferable that the fourth sub lens group is a lens group disposed closest to the image side.

  The present invention is advantageous for miniaturization and securing of performance, and the fourth sub lens unit is arranged on the most image side to obtain the function of the present invention, while obtaining the function of the present invention from the most object side lens surface of the imaging optical system to the most image side lens surface. It is further advantageous to shorten the length (Σd) up to.

Furthermore, it is preferable that the following conditional expression (12) is satisfied.
-1.1 ≦ SF_L4 ≦ 4.0 (12)
However,
SF_L4 = (RL4f + RL4r) / (RL4f−RL4r), and RL4f is the paraxial radius of curvature of the object side surface of the fourth sub lens group,
RL4r is a paraxial radius of curvature of the image side surface of the fourth sub lens group.

  Conditional expression (12) is a conditional expression that exhibits effectiveness when a wide angle of view is secured. In particular, it is more preferable that the conditional expression (12) is satisfied when the maximum half angle of view (ω) of the imaging optical system exceeds 40 degrees.

  By making sure that the lower limit of conditional expression (12) is not exceeded, it is easier to suppress the negative curvature of the Petzval image surface in the fourth sub-lens group (L4), and the field curvature and astigmatism are kept good. Especially advantageous. By making it easier to suppress aberrations, it is possible to reduce the number of lenses in other lens groups and the large number of aspheric surfaces, thereby reducing costs or the length from the most object side lens surface to the most image side lens surface of the imaging optical system (Σd ).

  By making sure that the upper limit of conditional expression (12) is not exceeded, it is advantageous to ensure the aberration correction effect in the fourth sub lens group (L4) and the function of efficiently relaxing the peripheral ray angle toward the image plane. . As a result, the number of lenses and the extensive use of aspheric surfaces can be reduced, which is advantageous for cost reduction or shortening of the length (Σd) from the most object side lens surface to the most image side lens surface of the imaging optical system.

It is preferable that the following conditional expression (13) is satisfied.
0.895 ≦ IHω30 / (f · tan30 °) ≦ 0.99 (13)
However,
IHω30 is the distance from the optical axis at the point where the principal ray with a half angle of view of 30 degrees intersects the image plane,
f is the focal length of the entire imaging optical system,
It is.

  In the configuration of the present invention, by generating negative distortion, the configuration is advantageous for downsizing and high performance. A wide angle of view can be obtained by utilizing the optically generated distortion.

  On the other hand, an image signal including optically generated distortion formed on the image pickup surface of the image pickup device can be corrected by electrical image processing to be recorded, displayed, and the like.

  This enables the optical system to positively generate negative distortion, achieve miniaturization and high performance, and reduce the distortion of the captured image, thereby further utilizing the advantages of both miniaturization and high performance. It becomes.

  By making sure that the lower limit of conditional expression (13) is not exceeded, it is possible to suppress an excessive amount of distortion correction when electrical correction is performed, and to easily prevent reduction of resolution in the off-axis region.

  By making sure that the upper limit of conditional expression (13) is not exceeded, it is advantageous for securing the angle of view by positive use of distortion.

It is preferable that the following conditional expression (14) is satisfied.
1.5 ≦ Σd / IHω ≦ 6.0 (14)
However,
Σd is the length from the most object side lens surface to the most image side lens surface of the imaging optical system,
IHω is the distance from the optical axis at the point where the principal ray with the maximum half angle of view ω intersects the image plane,
It is.

  Conditional expression (14) specifies a preferable thickness on the optical axis of the imaging optical system.

  It is preferable not to fall below the lower limit of conditional expression (14) so that it is easy to secure the number of lenses and it is advantageous for securing optical performance.

  It is preferable to reduce the size of the imaging optical system so as not to exceed the upper limit of conditional expression (14).

  The lens group that moves during focusing is preferably a single positive lens.

  By configuring the focusing lens group with a single positive lens, it is possible to achieve both the focusing operation and the light beam convergence effect, and to further simplify the imaging optical system. In addition, by configuring the focusing lens group with only one lens, it is possible to achieve a significant weight reduction of the focusing lens group, which is advantageous for speeding up focusing and quieting during shooting. Furthermore, it is possible to achieve a structure in which it is easy to ensure continuous focusing accuracy when shooting moving images.

Furthermore, it is preferable that the specific gravity of the single positive lens that moves during focusing satisfies the following conditional expression (15).
0.8 ≦ Dfo ≦ 1.5 (15)
However,
Dfo is the specific gravity of the single positive lens that moves during focusing, and its unit is g / cm ^3.
It is.

  By making sure that the upper limit of conditional expression (15) is not exceeded, it is advantageous for further reducing the weight of the focusing lens group.

  By making sure that the lower limit of conditional expression (15) is not exceeded, the lens can be configured with a material having a sufficient refractive index, which is advantageous in securing performance.

In addition, at least one positive lens moves during focusing,
It is preferable that the following conditional expression (16) is satisfied.
νd_fo> 50 (16)
However,
νd_fo is the maximum value among the Abbe numbers of the positive lens that moves during focusing.

  By satisfying conditional expression (16), it is possible to suppress fluctuations in chromatic aberration due to focusing and to obtain good performance even in the immediate vicinity. In particular, it is possible to suppress the occurrence of chromatic aberration that becomes conspicuous when only one positive lens is used as the lens that moves during focusing.

The first sub lens group (L1) is composed of only two lenses, a first negative lens having a negative refractive power and a second lens arranged on the image side in order from the object side.
The first negative lens is a negative meniscus lens having a concave surface facing the image side;
The second lens has a concave image side surface whose absolute value of curvature is larger than that of the object side surface;
It is preferable that the following conditional expression (17) is satisfied.
0.4 ≦ SF2 ≦ 6.0 (17)
However,
SF2 = (R2f + R2r) / (R2f−R2r), and R2f is a paraxial radius of curvature of the object side surface of the second lens,
R2r is a paraxial radius of curvature of the image side surface of the second lens.

  Arranging the second lens immediately on the image side of the first negative lens and satisfying the conditional expression (17) is advantageous in widening the angle of view and ensuring the optical performance.

  By making sure that the lower limit of conditional expression (17) is not exceeded, it is possible to prevent the second lens from becoming a lens having a strong negative refractive power, and to suppress coma aberration and curvature on the plus side of the Petzval image surface.

  By making sure that the upper limit of conditional expression (17) is not exceeded, it is possible to secure the aberration correction effect of the second lens, to easily suppress the refractive power of the first negative lens, to reduce asphalt and to reduce the size of the front lens group. It is advantageous for the conversion.

The first sub lens group includes at least a negative lens;
When the negative lens arranged closest to the object side among the negative lenses in the first sub lens group is the first negative lens (n1),
The first negative lens is a negative lens having a concave surface facing the image side,
It is preferable that the following condition (18) is satisfied.
Tmax / Σd ≦ 0.27 (18)
However,
Tmax is the maximum value of the distances of the spaces between the plurality of lenses in the imaging optical system excluding the image-side space in contact with the first negative lens,
Σd is the length from the most object side lens surface of the imaging optical system to the most image side lens surface,
It is.

  Conditional expression (18) is a preferable condition that is advantageous for securing performance and shortening the overall length and reducing the outer diameter of the imaging optical system.

The first negative lens (n1) is preferably a negative lens having a concave surface facing the image side in order to ensure a wide angle of view and performance, and sufficiently ensure negative refractive power. At this time, it is advantageous for securing the function of the negative lens by securing the air gap immediately after the image side of the first negative lens (n1). On the other hand, when looking at each air space on the image side from this air space, the air space between each lens is shortened to reduce the outer diameter of the lens and to reduce the outermost lens surface of the imaging optical system from the lens surface closest to the object side. The length (Σd) to the lens surface can be reduced.
The above-described configuration of the present invention is advantageous in securing performance without using a large air gap.
Therefore, it is preferable to satisfy Conditional Expression (18) and to shorten the length (Σd) from the most object side lens surface to the most image side lens surface of the imaging optical system and to reduce the lens outer diameter.

The first sub lens group includes at least a negative lens;
When the negative lens arranged closest to the object side among the negative lenses in the first sub lens group is the first negative lens (n1),
The first negative lens is a negative meniscus lens having a concave surface facing the image side,
The first negative lens is preferably a lens disposed closest to the object side in the first sub lens group.

  By making the most object side lens in the first sub lens group (L1) a negative meniscus lens (n1) having a concave surface facing the image side, the negative refractive power of the first sub lens group (L1) can be sufficiently increased. This makes it easy to ensure a wide angle of view, which is advantageous for correcting various off-axis aberrations, particularly astigmatism, that are likely to occur when the diameter is reduced or the angle of view is increased.

Moreover, it is preferable that the following conditional expression (19) is satisfied.
−1 ≦ f / fLF ≦ 1.5 (19)
However,
f is the focal length of the entire imaging optical system,
fLF is the focal length of the front lens group.

  By preventing the refractive power of the front lens unit from becoming a strong negative refractive power so as not to fall below the lower limit of conditional expression (19), the rear lens can be reduced even if the back focus is shortened appropriately for miniaturization and the like. The positive refracting power of the group (LR) can be weakened, the curvature of the Petzval image surface to the minus side can be suppressed, and the field curvature and astigmatism can be easily corrected.

  By making the refractive power of the front lens unit not to be a strong positive refractive power so as not to exceed the upper limit of conditional expression (19), it becomes easier to secure the positive refractive power of the rear lens unit (LR), and the back focus. Is easily secured. Thereby, it becomes easy to ensure the function of reducing the emission angle of the peripheral rays.

The first sub lens group is composed of two negative lens components having a concave surface facing the image side,
The absolute value of the paraxial curvature of the image side surface of the two negative lens components is smaller than the absolute value of the paraxial curvature of the object side surface,
The second sub lens group is composed of two to four lenses including a positive lens,
The third sub lens group includes one negative lens and two or less positive lenses disposed on the image side of the one negative lens;
More preferably, the fourth sub lens group comprises one positive lens component.
Here, the lens component means a lens body in which only two refracting surfaces of the incident side and the image side are in contact with air on the optical axis.

  Such a configuration is preferable because it is advantageous for shortening the overall length while ensuring the angle of view of the imaging optical system, adjusting the exit angle, and ensuring the optical performance.

  Each of the above constituent requirements and conditional expressions may be arbitrarily satisfied.

For example, in each of the above-described inventions, the following conditional expression (5) may be satisfied.
−3 ≦ fn1 / fLR ≦ −0.5 (5)

For example, in each of the above-described inventions, the following conditional expression (6) may be satisfied.
-2 ≦ fn11 / fLR ≦ −0.1 (6)

For example, in each of the above-described inventions, the following conditional expression (7) may be satisfied.
Tmax / IHω30 ≦ 1.2 (7)

  These imaging optical systems are effective when used in an imaging apparatus such as a digital camera because the exit pupil is easily separated from the image plane and the performance is easily improved.

  An imaging apparatus having an imaging optical system and an imaging element having an imaging surface that is disposed on the image side of the imaging optical system and converts an optical image into an electrical signal. An imaging optical system is preferable.

  Moreover, it is more preferable that each of the above-described inventions satisfies a plurality at the same time.

  Moreover, about each conditional expression, the upper limit value or the lower limit value is preferably limited as follows, whereby the effect can be more reliably ensured.

In conditional expression (1), it is more preferable to set the lower limit value to −120%, and more preferably to −100%. On the assumption that the distortion is electrically corrected, the lower limit value may be further set to −15%. It is easy to suppress the flow of images during image correction.
More preferably, the upper limit value is -13%, more preferably -12%. If it is desired to take a picture taking advantage of distortion, the upper limit value should be further set to -40%.

In conditional expression (2), it is more preferable to set the lower limit to −1.6, and further to −1.4.
More preferably, the upper limit value is -0.4, more preferably -0.55.

In conditional expression (3), it is more preferable to set the lower limit value to 1.1, and further to 1.5.
More preferably, the upper limit value is 4.5, more preferably 4.0.

For conditional expression (4), it is more preferable to set the lower limit value to 1.4, more preferably 1.6.
More preferably, the upper limit value is 3.5, more preferably 3.0.

For conditional expression (5), it is more preferable to set the lower limit value to −2.3, more preferably −1.8.
The upper limit value is more preferably −0.6, and further preferably −0.7.

In conditional expression (6), it is more preferable to set the lower limit value to -1, and further to -0.85.
More preferably, the upper limit value is -0.15, more preferably -0.19.

For conditional expression (7), it is more preferable to set the upper limit value to 1.0, more preferably 0.6.
It is preferable to set a lower limit value so that it does not fall below 0.1 or 0.2. This is advantageous for securing a space for arranging a variable aperture.

For conditional expression (8), it is more preferable to set the lower limit value to −120%, more preferably −110%.
The upper limit value is more preferably −60%, and further preferably −80%.

In conditional expression (9), it is more preferable to let the lower limit value to be 1.0, further 1.2.
More preferably, the upper limit value is 2.5, more preferably 2.3.

In conditional expression (10), the lower limit value is more preferably 1.0, and still more preferably 1.2.
More preferably, the upper limit value is 1.75, more preferably 1.6.

For conditional expression (11), it is more preferable to let the lower limit value to be −0.85, more preferably −0.7.
More preferably, the upper limit value is -0.3, more preferably -0.35.

For conditional expression (12), it is more preferable to let the lower limit value to be −0.9, −0.7, and further −0.3.
More preferably, the upper limit value is 3.5, more preferably 3.3.

Conditional expression (13) Assuming that distortion is electrically corrected,
More preferably, the lower limit value is 0.9, more preferably 0.93.
To be advantageous for shooting taking advantage of distortion,
More preferably, the upper limit value is 0.95, more preferably 0.93.

In conditional expression (14), it is more preferable to set the lower limit value to 2.0, more preferably 2.3.
More preferably, the upper limit value is 5.0, more preferably 4.5.

For conditional expression (16), it is more preferable to set the upper limit value to 55, more preferably 60.

For conditional expression (17), it is more preferable to let the lower limit value to be 0.55, further 0.7.
More preferably, the upper limit value is 4.5, more preferably 2.5.

For conditional expression (18), the upper limit value is more preferably 0.18, and even more preferably 0.15.
By providing a lower limit value of 0.04, further 0.06, and not exceeding this value, it is advantageous for securing a space for arranging a variable diaphragm or the like.

In conditional expression (19), it is more preferable to let the lower limit value to be −0.45, more preferably −0.30.
More preferably, the upper limit value is 1.0, more preferably 0.8.

As described above, according to the present invention, there is provided an imaging optical system having a constant total length at the time of focusing, which facilitates miniaturization, securing a peripheral light amount, and ensuring good imaging performance while ensuring a wide angle of view. It becomes possible to do. Furthermore, it is possible to provide an imaging apparatus using such an imaging optical system.

2 is a cross-sectional view of the optical system of Example 1. FIG. 6 is a cross-sectional view of an optical system according to Example 2. FIG. 6 is a sectional view of an optical system according to Example 3. FIG. 6 is a sectional view of an optical system according to Example 4. FIG. 10 is a cross-sectional view of an optical system according to Example 5. FIG. 10 is a cross-sectional view of an optical system according to Example 6. FIG. 10 is a cross-sectional view of an optical system according to Example 7. FIG. 10 is a sectional view of the optical system according to Example 8. FIG. 10 is a sectional view of an optical system according to Example 9. FIG. 10 is a sectional view of the optical system according to Example 10. FIG. 10 is a cross-sectional view of the optical system according to Example 11. FIG. FIG. 6 is a diagram illustrating various aberrations of the optical system of Example 1 in an infinitely focused state. FIG. 6 is a diagram illustrating various aberrations of the optical system of Example 2 in an infinitely focused state. FIG. 6 is a diagram illustrating various aberrations of the optical system according to Example 3 in an infinitely focused state. FIG. 10 is a diagram illustrating various aberrations of the optical system according to Example 4 in an infinitely focused state. FIG. 10 is a diagram illustrating various aberrations of the optical system according to Example 5 in a focused state at infinity. FIG. 12 is a diagram illustrating various aberrations of the optical system according to Example 6 in a focused state at infinity. FIG. 10 is a diagram illustrating various aberrations of the optical system according to Example 7 in a focused state at infinity. FIG. 10 is a diagram illustrating various aberrations of the optical system according to Example 8 in a focused state at infinity. FIG. 10 is a diagram illustrating various aberrations of the optical system according to Example 9 in a focused state at infinity. FIG. 11 is a diagram illustrating various aberrations of the optical system according to Example 10 in an infinitely focused state. FIG. 10 is a diagram illustrating all aberrations of the optical system according to Example 11 at an infinite focus state. It is sectional drawing of the lens interchangeable camera which used the wide angle lens of this invention as an interchangeable lens. It is a front perspective view which shows the external appearance of the digital camera by this invention. It is a rear view of the digital camera of FIG. It is a cross-sectional view of the digital camera of FIG. FIG. 25 is a configuration block diagram of an internal circuit of a main part of the digital camera of FIG. 24.

  Examples 1 to 11 of the present invention will be described.

  FIG. 1 is a sectional view of the optical system according to the first embodiment. The optical system of Example 1 constitutes a fish eye lens. The focusing lens is a positive lens closest to the image side. The moving direction of the focusing lens at a short distance is the object side.

  As shown in FIG. 1, the optical system according to the first exemplary embodiment includes a front lens unit LF, an aperture stop S, and a rear lens unit LR in order from the object side to the image side. The front lens unit LF includes, in order from the object side to the image side, a first sub lens unit L1 having a negative refractive power and a second sub lens unit L2 having a positive refractive power. The LR includes a third sub lens unit L3 whose surface closest to the image surface is convex from the object side to the image side, and a fourth sub lens unit L4 as a focus lens unit having positive refracting power. Has been.

  The front lens unit LF includes, in order from the object side, a first sub lens unit L1 including a negative meniscus lens n1 as a first negative lens having a convex surface directed toward the object side and a biconcave negative lens n2 as a second negative lens; And a second sub lens unit L2 composed of a biconvex positive lens and a positive meniscus lens having a convex surface facing the image surface side.

  The rear lens unit LR includes, in order from the object side, a biconcave negative lens, a third sub lens unit L3 including a positive meniscus lens having a convex surface facing the image surface side, and a biconvex positive lens, and a convex surface facing the image surface side. The fourth sub lens unit L4 is composed of a positive meniscus lens. The focus lens group includes a fourth sub lens group L4. I is the image plane.

  FIG. 2 is a sectional view of the optical system according to the second embodiment. The optical system of Example 2 constitutes a fish eye lens. The focusing lens is a positive lens closest to the image side. The moving direction of the focusing lens at a short distance is the object side.

  As shown in FIG. 2, the optical system of Example 2 includes a front lens group LF, an aperture stop S, and a rear lens group LR in order from the object side to the image side. The front lens unit LF includes, in order from the object side to the image side, a first sub lens unit L1 having a negative refractive power and a second sub lens unit L2 having a positive refractive power. LR is an order from the object side to the image side, from the third sub lens unit L3 whose surface closest to the image side is convex to the image side, and from the fourth sub lens unit L4 as the focus lens unit LF having positive refractive power. It is configured.

  The front lens unit LF includes, in order from the object side, a first sub lens unit L1 including a negative meniscus lens n1 as a first negative lens having a convex surface directed toward the object side and a biconcave negative lens n2 as a second negative lens; It comprises a biconvex positive lens, a negative meniscus lens having a convex surface facing the object side, and a second sub-lens group L2 composed of a cemented lens of the biconvex positive lens.

  The rear lens unit LR includes, in order from the object side, a biconcave negative lens, a third sub lens unit L3 including a positive meniscus lens having a convex surface facing the image surface side, and a biconvex positive lens, and a convex surface facing the image surface side. The fourth sub lens unit L4 is composed of a positive meniscus lens. The focus lens group includes a fourth sub lens group L4. I is the image plane.

  FIG. 3 is a sectional view of the optical system according to the third embodiment. The optical system of Example 3 constitutes a fish eye lens. The focusing lens is a positive lens closest to the image side. The moving direction of the focusing lens at a short distance is the object side.

  As shown in FIG. 3, the optical system of Example 3 includes a front lens group LF, an aperture stop S, and a rear lens group LR in order from the object side to the image side. The front lens unit LF includes, in order from the object side to the image side, a first sub lens unit L1 having a negative refractive power and a second sub lens unit L2 having a positive refractive power. The LR includes a third sub lens unit L3 whose surface closest to the image surface is convex from the object side to the image side, and a fourth sub lens unit L4 as a focus lens unit having positive refracting power. Has been.

  The front lens unit LF includes, in order from the object side, a first sub lens unit L1 including a first negative meniscus lens n1 and a biconcave negative lens n2 having a convex surface facing the object side, a biconvex positive lens, and a biconvex positive lens. And a second sub lens unit L2.

  The rear lens unit LR includes, in order from the object side, a biconcave negative lens, a third sub lens unit L3 including a positive meniscus lens having a convex surface facing the image surface side, and a biconvex positive lens, and a convex surface facing the image surface side. The fourth sub lens unit L4 is composed of a positive meniscus lens. The focus lens group includes a fourth sub lens group L4. I is the image plane.

  FIG. 4 is a sectional view of the optical system of Example 4. The optical system of Example 4 constitutes a fish eye lens. The focusing lens is a positive lens closest to the image side. The moving direction of the focusing lens at a short distance is the object side.

  As shown in FIG. 4, the optical system of Example 4 includes a front lens unit LF, an aperture stop S, and a rear lens unit LR in order from the object side to the image side. The front lens unit LF includes, in order from the object side to the image side, a first sub lens unit L1 having a negative refractive power and a second sub lens unit L2 having a positive refractive power. The LR includes a third sub lens unit L3 whose surface closest to the image surface is convex from the object side to the image side, and a fourth sub lens unit L4 as a focus lens unit having positive refracting power. Has been.

  The front lens unit LF includes, in order from the object side, a first sub lens unit L1 including a negative meniscus lens n1 as a first negative lens having a convex surface directed toward the object side and a biconcave negative lens n2 as a second negative lens; It comprises a biconvex positive lens, a negative meniscus lens having a convex surface facing the object side, and a second sub-lens group L2 composed of a cemented lens of the biconvex positive lens.

  The rear lens unit LR includes, in order from the object side, a biconcave negative lens, a third sub lens unit L3 including a positive meniscus lens having a convex surface facing the image surface side, and a biconvex positive lens, and a convex surface facing the image surface side. The fourth sub lens unit L4 is composed of a positive meniscus lens. The focus lens group includes a fourth sub lens group L4. I is the image plane.

  FIG. 5 is a sectional view of the optical system of Example 5. The optical system of Example 5 constitutes a fish eye lens. The focusing lens is a positive lens closest to the image side. The moving direction of the focusing lens at a short distance is the object side.

  As shown in FIG. 5, the optical system of Example 5 includes a front lens unit LF, an aperture stop S, and a rear lens unit LR in order from the object side to the image side. The front lens unit LF includes, in order from the object side to the image side, a first sub lens unit L1 having a negative refractive power and a second sub lens unit L2 having a positive refractive power. The LR includes a third sub lens unit L3 whose surface closest to the image surface is convex from the object side to the image side, and a fourth sub lens unit L4 as a focus lens unit having positive refracting power. Has been.

  The front lens unit LF includes, in order from the object side, a first negative meniscus lens n1 as a first negative lens having a convex surface directed toward the object side and a second negative meniscus lens n2 as a second negative lens having a convex surface directed toward the object side. And a second sub lens unit L2 including a cemented lens of a negative meniscus lens having a convex surface facing the object side and a biconvex positive lens.

  The rear lens unit LR includes, in order from the object side, a third sub lens unit L3 including a cemented lens of a biconcave negative lens and a biconvex positive lens and a biconvex positive lens, and a positive meniscus lens having a convex surface facing the image surface side. And a fourth sub lens unit L4. The focus lens group includes a fourth sub lens group L4. I is the image plane.

  The aspheric surfaces are used for the two surfaces of the biconvex positive lens on the most image side of the third sub lens unit L3 of the rear lens unit LR.

  FIG. 6 is a sectional view of the optical system according to the sixth embodiment. The optical system of Example 6 constitutes a wide-angle lens. The focusing lens is a positive lens closest to the image side. The moving direction of the focusing lens at a short distance is the object side.

  As shown in FIG. 6, the optical system of Example 6 includes a front lens unit LF, an aperture stop S, and a rear lens unit LR in order from the object side to the image side. The front lens unit LF includes, in order from the object side to the image side, a first sub lens unit L1 having a negative refractive power and a second sub lens unit L2 having a positive refractive power. The LR includes a third sub lens unit L3 whose surface closest to the image surface is convex from the object side to the image side, and a fourth sub lens unit L4 as a focus lens unit having positive refracting power. Has been.

  The front lens unit LF includes, in order from the object side, a first negative meniscus lens n1 as a first negative lens having a convex surface directed toward the object side and a second negative meniscus lens n2 as a second negative lens having a convex surface directed toward the object side. And a second sub lens unit L2 including a biconvex positive lens, a biconcave negative lens, and a biconvex positive lens.

  The rear lens unit LR includes, in order from the object side, a negative meniscus lens having a convex surface facing the image surface side, a positive meniscus lens having a convex surface facing the image surface side, and a positive meniscus lens having a convex surface facing the image surface side. The third sub lens unit L3 and the fourth sub lens unit L4 including a positive meniscus lens having a convex surface facing the object side. The focus lens group includes a fourth sub lens group L4. I is the image plane.

  The aspheric surfaces are 4 on both surfaces of the second negative meniscus lens n2 of the first sub lens unit L1 of the front lens unit LF and on both surfaces of the most positive meniscus lens on the third sub lens unit L3 of the rear lens unit LR. Used on the surface.

  FIG. 7 is a sectional view of the optical system according to the seventh embodiment. The optical system of Example 7 constitutes a wide angle lens. The focusing lens is a positive lens closest to the image side. The moving direction of the focusing lens at a short distance is the object side.

  As shown in FIG. 7, the optical system according to the seventh embodiment includes a front lens unit LF, an aperture stop S, and a rear lens unit LR in order from the object side to the image side. The front lens unit LF includes, in order from the object side to the image side, a first sub lens unit L1 having a negative refractive power and a second sub lens unit L2 having a positive refractive power. The LR includes a third sub lens unit L3 whose surface closest to the image surface is convex from the object side to the image side, and a fourth sub lens unit L4 as a focus lens unit having positive refracting power. Has been.

  The front lens unit LF includes, in order from the object side, a first negative meniscus lens n1 as a first negative lens having a convex surface directed toward the object side and a second negative meniscus lens n2 as a second negative lens having a convex surface directed toward the object side. And a second sub-lens group L2 including a biconvex positive lens, a negative meniscus lens having a convex surface facing the image surface side, and a positive meniscus lens having a convex surface facing the image surface side. .

  The rear lens unit LR includes, in order from the object side, a third sub lens unit L3 including a negative meniscus lens having a convex surface facing the image surface, a biconvex positive lens, and a positive meniscus lens having a convex surface facing the image surface. The lens unit includes a fourth sub lens unit L4 including a biconvex positive lens. The focus lens group includes a fourth sub lens group L4. I is the image plane.

  The aspheric surfaces are 4 on both surfaces of the second negative meniscus lens n2 of the first sub lens unit L1 of the front lens unit LF and on both surfaces of the most positive meniscus lens on the third sub lens unit L3 of the rear lens unit LR. Used on the surface.

  The second negative meniscus lens n2, the most image side lens of the third sub lens unit L3, and the biconvex positive lens of the fourth sub lens unit L4 are made of a plastic lens using a cycloolefin polymer having a specific gravity of 1.01. . By using a lightweight material such as plastic, it is possible to improve the focusing speed and reduce the driving power.

  FIG. 8 is a sectional view of the optical system according to the eighth embodiment. The optical system of Example 8 constitutes a wide angle lens. The focusing lens is a positive lens closest to the image side. The moving direction of the focusing lens at a short distance is the object side.

  As shown in FIG. 8, the optical system of Example 8 includes a front lens group LF, an aperture stop S, and a rear lens group LR in order from the object side to the image side. The front lens unit LF includes, in order from the object side to the image side, a first sub lens unit L1 having a negative refractive power and a second sub lens unit L2 having a positive refractive power. The LR includes a third sub lens unit L3 whose surface closest to the image surface is convex from the object side to the image side, and a fourth sub lens unit L4 as a focus lens unit having positive refracting power. Has been.

  The front lens unit LF includes, in order from the object side, a first negative meniscus lens n1 as a first negative lens having a convex surface directed toward the object side and a second negative meniscus lens n2 as a second negative lens having a convex surface directed toward the object side. And a second sub-lens group L2 including a positive meniscus lens having a convex surface facing the object side and a positive meniscus lens having a convex surface facing the image surface side.

  The rear lens unit LR includes, in order from the object side, a third sub lens unit L3 including a negative meniscus lens having a convex surface facing the image surface, a biconvex positive lens, and a positive meniscus lens having a convex surface facing the image surface. The lens unit includes a fourth sub lens unit L4 including a biconvex positive lens. The focus lens group includes a fourth sub lens group L4. I is the image plane.

  The aspherical surfaces of the image side surface of the second negative meniscus lens n2 of the first sub lens unit L1 of the front lens unit LF and the most meniscus positive meniscus lens of the third sub lens unit L3 of the rear lens unit LR. Used on 3 sides.

  The most image-side lens of the third sub-lens group L3 and the biconvex positive lens of the fourth sub-lens group L4 are made of a plastic lens using a cycloolefin polymer having a specific gravity of 1.01. By using a lightweight material such as plastic, it is possible to improve the focusing speed and reduce the driving power.

  FIG. 9 is a sectional view of the optical system according to Example 9. The optical system of Example 9 constitutes a wide angle lens. The focusing lens is a positive lens closest to the image side. The moving direction of the focusing lens at a short distance is the object side.

  As shown in FIG. 9, the optical system according to the ninth embodiment includes a front lens unit LF, an aperture stop S, and a rear lens unit LR in order from the object side to the image side. The front lens unit LF includes, in order from the object side to the image side, a first sub lens unit L1 having a negative refractive power and a second sub lens unit L2 having a positive refractive power. The LR includes a third sub lens unit L3 whose surface closest to the image surface is convex from the object side to the image side, and a fourth sub lens unit L4 as a focus lens unit having positive refracting power. Has been.

  The front lens unit LF includes, in order from the object side, a first negative meniscus lens n1 as a first negative lens having a convex surface directed toward the object side and a second negative meniscus lens n2 as a second negative lens having a convex surface directed toward the object side. And a second sub-lens group L2 composed of a positive meniscus lens having a convex surface facing the object side and a cemented lens of a biconcave negative lens and a biconvex positive lens.

  The rear lens unit LR includes, in order from the object side, a third sub lens unit L3 including a negative meniscus lens having a convex surface facing the image surface, a biconvex positive lens, and a positive meniscus lens having a convex surface facing the image surface. The lens unit includes a fourth sub lens unit L4 including a biconvex positive lens. The focus lens group includes a fourth sub lens group L4. I is the image plane.

  The aspherical surfaces of the image side surface of the second negative meniscus lens n2 of the first sub lens unit L1 of the front lens unit LF and the most meniscus positive meniscus lens of the third sub lens unit L3 of the rear lens unit LR. Used on 3 sides.

  FIG. 10 is a sectional view of the optical system according to Example 10. The optical system of Example 10 constitutes a fish eye lens. The focusing lens is the second positive lens from the image side. The moving direction of the focusing lens at a short distance is the object side.

  As shown in FIG. 10, the optical system of Example 10 includes a front lens unit LF, an aperture stop S, and a rear lens unit LR in order from the object side to the image side. The front lens unit LF includes, in order from the object side to the image side, a first sub lens unit L1 having a negative refractive power and a second sub lens unit L2 having a positive refractive power. LR, in order from the object side to the image side, a third sub lens unit L3 whose surface closest to the image side is convex on the image side, a fourth sub lens unit L4 as a focus lens unit having positive refractive power, And a fifth lens unit L5 having a positive refractive power.

  The front lens unit LF includes, in order from the object side, a first sub lens unit L1 including a first negative meniscus lens n1 as a first negative lens having a convex surface directed toward the object side and a biconcave negative lens n2 as a second negative lens. And a second sub-lens group L2 composed of a biconvex positive lens and a positive meniscus lens having a convex surface facing the image surface side.

  The rear lens unit LR includes, in order from the object side, a biconcave negative lens, a third sub lens unit L3 including a positive meniscus lens having a convex surface facing the image surface side, and a fourth sub lens unit L4 including a biconvex positive lens. And a fifth sub lens unit L5 composed of a positive meniscus lens having a convex surface facing the image surface side. The focus lens group includes a fourth sub lens group L4. I is the image plane.

  FIG. 11 is a sectional view of the optical system according to Example 11. The optical system of Example 11 constitutes a wide angle lens. The focusing lens is a positive lens just before the stop. The moving direction of the focusing lens at a short distance is the image side.

  As shown in FIG. 11, the optical system of Example 11 includes a front lens unit LF, an aperture stop S, and a rear lens unit LR in order from the object side to the image side. The front lens unit LF includes, in order from the object side to the image side, a first sub lens unit L1 having a negative refractive power and a second sub lens unit L2 having a positive refractive power. The LR includes a third sub-lens group L3 as a focus lens group whose surface closest to the image side is convex on the image side, and a fourth sub-lens group L4 having positive refractive power in order from the object side to the image side. Has been.

  The front lens unit LF includes, in order from the object side, a first negative meniscus lens n1 as a first negative lens having a convex surface directed toward the object side and a second negative meniscus lens n2 as a first negative lens having a convex surface directed toward the object side. A second sub lens unit L1 composed of a positive meniscus lens having a convex surface facing the object side, a biconcave negative lens, and a cemented lens of a biconvex positive lens and a negative meniscus lens having a convex surface facing the image side. A lens unit L2.

  The rear lens unit LR includes, in order from the object side, a third sub lens unit L3 including a negative meniscus lens having a convex surface facing the image surface, a biconvex positive lens, and a positive meniscus lens having a convex surface facing the image surface. The lens unit includes a fourth sub lens unit L4 including a biconvex positive lens. The focus lens group includes a third sub lens group L3. I is the image plane.

  The aspheric surfaces are 4 on both surfaces of the second negative meniscus lens n2 of the first sub lens unit L1 of the front lens unit LF and on both surfaces of the most positive meniscus lens on the third sub lens unit L3 of the rear lens unit LR. Used on the surface.

  The numerical data of Examples 1 to 11 are shown below. In the numerical data of Examples 1 to 11, r is the radius of curvature of the lens surface, d is the lens thickness and air spacing, Nd and νd are the refractive index and Abbe number at the d-line (λ = 587.6 nm), and f is Focal length, Fno is an F number, and ω is a half angle of view (°). IO indicates a close distance.

In the specification table for explaining the embodiments, the surface with (aspherical surface) is an aspherical surface. The expression representing the aspherical shape is as follows: the height perpendicular to the optical axis is H, the amount of displacement in the optical axis direction at the height H when the top is the origin is X (H), the paraxial radius of curvature is r, the cone When the coefficients are K, 2nd order, 4th order, 6th order, 8th order, 10th order, and 12th order, the aspherical coefficients are A2, A4, A6, A8, A10, and A12, respectively. The
X (H) = (H ² / r) / {1+ [1− (1 + K) · (H ² / r ² )] ^1/2 }
+ A4H ⁴ + A6H ⁶ + A8H ⁸ + A10H ¹⁰ + A12H ¹²

Numerical example 1
Unit mm

Surface data surface number r d nd νd
1 25.537 1.312 1.77250 49.60
2 12.203 7.677
3 -298.932 1.312 1.72916 54.68
4 8.389 3.891
5 21.543 5.818 1.84666 23.78
6 -38.486 1.477
7 -200.001 7.266 1.72916 54.68
8 -13.098 1.009
9 (Aperture) ∞ 0.850
10 -10.293 0.706 1.84666 23.78
11 29.636 0.416
12 -49.806 2.162 1.72916 54.68
13 -10.736 0.953
14 35.833 4.469 1.49700 81.54
15 -20.922 d1
16 -177.472 4.233 1.51633 64.14
17 -17.646 d2
Image plane ∞

Infinite IO = 20cm
d1 2.87153 2.21183
d2 15.05353 15.71323

Various data
f (mm) 7.973
Fno 3.578
2ω (angle of view (°)) 180.0
FB (mm) 15.054

Numerical example 2
Unit mm

Surface data surface number r d nd νd
1 26.659 1.300 1.88300 40.76
2 11.072 6.949
3 -55.898 1.300 1.74100 52.64
4 8.386 2.400
5 18.914 5.197 1.84666 23.78
6 -42.757 0.540
7 33.063 3.182 1.80400 46.57
8 6.463 6.288 1.67790 55.34
9 -11.187 1.000
10 (Aperture) ∞ 2.266
11 -11.274 0.700 1.84666 23.78
12 31.002 0.469
13 -55.449 3.184 1.72916 54.68
14 -11.265 0.100
15 26.327 3.784 1.49700 81.54
16 -28.876 d1
17 -36.149 3.602 1.72916 54.68
18 -18.915 d2
Image plane ∞

Infinite IO = 20cm
d1 1.74050 0.84631
d2 15.85997 16.75417

Various data
f (mm) 8.097
Fno 3.571
2ω (angle of view (°)) 180.0
FB (mm) 15.860

Numerical example 3
Unit mm

Surface data surface number r d nd νd
1 23.076 1.300 1.88300 40.76
2 10.604 6.766
3 -242.498 1.300 1.72916 54.68
4 7.415 2.888
5 18.801 5.393 1.84666 23.78
6 -33.860 0.307
7 555.916 7.000 1.53996 59.46
8 -10.452 1.603
9 (Aperture) ∞ 1.000
10 -9.704 0.700 1.84666 23.78
11 30.764 0.362
12 -65.567 2.140 1.72916 54.68
13 -10.008 0.985
14 34.634 3.021 1.49700 81.54
15 -21.817 d1
16 -202.933 3.714 1.51633 64.14
17 -17.890 d2
Image plane ∞

Infinite IO = 20cm
d1 4.52093 3.85135
d2 14.53338 15.2029

Various data
f (mm) 7.992
Fno 3.541
2ω (angle of view (°)) 178.9
FB (mm) 14.533

Numerical example 4
Unit mm

Surface data surface number r d nd νd
1 26.028 1.300 1.88300 40.76
2 10.500 6.116
3 -60.301 1.300 1.72916 54.68
4 7.473 2.199
5 15.552 5.105 1.84666 23.78
6 -44.411 0.646
7 25.252 2.135 1.88300 40.76
8 6.404 5.391 1.67790 55.34
9 -10.164 1.000
10 (Aperture) ∞ 2.137
11 -11.003 0.700 1.84666 23.78
12 31.451 0.598
13 -28.269 2.181 1.72916 54.68
14 -10.686 0.343
15 34.427 3.640 1.49700 81.54
16 -23.275 d1
17 -53.532 3.184 1.72916 54.68
18 -17.928 d2
Image plane ∞

Infinite IO = 20cm
d1 1.52528 0.87829
d2 15.91143 16.55842

Various data
f (mm) 8.196
Fno 3.580
2ω (angle of view (°)) 180.0
FB (mm) 15.911

Numerical example 5
Unit mm

Surface data surface number r d nd νd
1 31.981 1.300 1.88300 40.76
2 7.900 3.336
3 27.433 1.300 1.72916 54.68
4 9.394 1.322
5 17.826 2.800 1.72916 54.68
6 5.801 4.363 1.78470 26.29
7 -31.469 1.000
8 (Aperture) ∞ 1.974
9 -8.708 0.700 1.84666 23.78
10 18.135 2.623 1.72916 54.68
11 -10.770 0.100
12 38.301 3.586 1.49700 81.54
13 -10.110 d1
14 -91.516 2.176 1.72916 54.68
15 -26.333 d2
Image plane ∞

Aspheric data 12th surface
K = 0.0000, A4 = -1.8322E-004, A6 = 4.1784E-007, A8 = 3.2461E-009
Side 13
K = 0.0000, A4 = 2.8568E-005, A6 = -5.1944E-007, A8 = 5.8954E-009, A10 = -5.9788E-010

Infinite IO = 20cm
d1 1.52001 0.81803
d2 17.8276 18.52964

Various data
f (mm) 8.091
Fno 3.580
2ω (angle of view (°)) 179.7
FB (mm) 17.828

Numerical example 6
Unit mm

Surface data surface number r d nd νd
1 22.606 1.300 1.72916 54.68
2 11.000 4.774
3 (Aspherical) 34.070 1.300 1.49700 81.54
4 (Aspherical surface) 9.635 1.708
5 16.792 3.784 1.84666 23.78
6 -144.046 1.033
7 -27.287 2.627 1.80518 25.42
8 18.198 0.100
9 12.817 4.328 1.88300 40.76
10 -35.320 4.052
11 (Aperture) ∞ 1.687
12 -7.629 0.700 1.84666 23.78
13 -43.264 0.100
14 -412.872 2.312 1.72916 54.68
15 -18.418 0.050
16 (Aspherical surface) -52.097 5.700 1.72916 54.68
17 (Aspherical surface) -11.919 d1
18 30.926 2.844 1.72916 54.68
19 -494.396 d2
Image plane ∞

Aspheric data 3rd surface
K = 0.0000, A4 = 3.7228E-005, A6 = -6.5360E-007, A8 = 4.4385E-009
4th page
K = 0.0000, A4 = -8.9286E-005, A6 = -1.4980E-006, A8 = -5.1285E-009, A10 = 2.4033E-011
16th page
K = 0.0000, A4 = -8.9177E-005, A6 = 5.6335E-007, A8 = -1.0779E-008
17th page
K = 0.0000, A4 = 3.3603E-005, A6 = 1.5726E-007, A8 = 2.7065E-009, A10 = -2.3966E-011, A12 = 2.6347E-014

Infinite IO = 20cm
d1 2.10128 0.74329
d2 16.43147 17.7894

Various data
f (mm) 12.282
Fno 1.851
2ω (angle of view (°)) 91.5
FB (mm) 16.431

Numerical example 7
Unit mm

Surface data surface number r d nd νd
1 33.391 1.300 1.58913 61.14
2 8.700 2.563
3 (Aspherical) 14.957 1.500 1.53113 55.80
4 (Aspherical surface) 7.763 2.402
5 11.415 3.370 1.90366 31.32
6 -12810.386 1.128
7 -18.543 0.700 1.84666 23.78
8 -30.437 1.869 1.48749 70.23
9 -13.512 2.056
10 (Aperture) ∞ 2.201
11 -6.924 0.700 1.84666 23.78
12 -41.871 0.100
13 115.593 4.268 1.72916 54.68
14 -10.030 0.100
15 (Aspherical surface) -26.464 2.250 1.53113 55.80
16 (Aspherical surface) -13.646 d1
17 25.463 3.821 1.53113 55.80
18 -121.573 d2
Image plane ∞

Aspheric data 3rd surface
K = 0.0000, A4 = 1.6516E-004, A6 = -1.8552E-006, A8 = 9.3914E-009
4th page
K = 0.0000, A4 = -3.9730E-005, A6 = -5.5610E-006, A8 = -1.4707E-008, A10 = -6.1975E-010
15th page
K = 0.0000, A4 = -8.4240E-005, A6 = 1.1973E-006, A8 = -3.8484E-010
16th page
K = 0.0000, A4 = 5.5262E-005, A6 = 1.9772E-006, A8 = -9.1438E-009, A10 = 4.4737E-010, A12 = -3.7042E-012

Infinite IO = 20cm
d1 2.17158 0.81998
d2 15.09187 16.44346

Various data
f (mm) 12.284
Fno 2.838
2ω (angle of view (°)) 90.4
FB (mm) 15.092

Numerical example 8
Unit mm

Surface data surface number r d nd νd
1 18.991 1.300 1.74100 52.64
2 8.700 2.813
3 15.201 1.500 1.49700 81.54
4 (Aspherical surface) 7.248 2.820
5 12.268 2.842 1.90366 31.32
6 105.059 2.275
7 -18.650 1.640 1.48749 70.23
8 -11.455 1.263
9 (Aperture) ∞ 2.207
10 -6.945 0.700 1.84666 23.78
11 -59.552 0.100
12 109.913 4.256 1.72916 54.68
13 -9.978 0.100
14 (Aspherical surface) -22.042 2.250 1.53113 55.80
15 (Aspherical surface) -12.471 d1
16 24.893 3.806 1.53113 55.80
17 -137.292 d2
Image plane ∞

Aspheric data 4th surface
K = 0.0000, A4 = -2.3503E-004, A6 = -5.0402E-006, A8 = 4.6076E-008, A10 = -1.8927E-009
14th page
K = 0.0000, A4 = -7.6376E-005, A6 = 2.4694E-006, A8 = -7.1225E-009
15th page
K = 0.0000, A4 = 5.5064E-005, A6 = 2.7701E-006, A8 = -1.3255E-008, A10 = 6.3187E-010, A12 = -5.5319E-012

Infinite IO = 20cm
d1 2.12831 0.81692
d2 15.90411 17.21550

Various data
f (mm) 12.287
Fno 2.835
2ω (angle of view (°)) 90.4
FB (mm) 15.904

Numerical example 9
Unit mm

Surface data surface number r d nd νd
1 24.929 1.300 1.58913 61.14
2 9.904 4.536
3 (Aspherical) 35.300 1.500 1.49700 81.54
4 (Aspherical surface) 8.309 3.804
5 10.730 3.703 1.90366 31.32
6 113.647 1.241
7 -33.764 0.700 1.80810 22.76
8 91.774 2.189 1.48749 70.23
9 -15.848 1.763
10 (Aperture) ∞ 2.242
11 -6.274 0.700 1.84666 23.78
12 -24.483 0.100
13 334.732 2.896 1.72916 54.68
14 -15.781 0.100
15 (Aspherical surface) -34.786 3.851 1.58913 61.14
16 (Aspherical surface) -9.163 d1
17 33.907 3.312 1.72916 54.68
18 -200.000 d2
Image plane ∞

Aspheric data 3rd surface
K = 0.0000, A4 = 2.0831E-004, A6 = -2.8865E-006, A8 = 1.4553E-008
4th page
K = 0.0000, A4 = 5.3524E-006, A6 = -1.0573E-006, A8 = -1.0958E-007, A10 = 9.0487E-010
15th page
K = 0.0000, A4 = -1.5448E-004, A6 = 2.4159E-006, A8 = -8.1475E-009
16th page
K = 0.0000, A4 = 1.0917E-004, A6 = 4.1350E-009, A8 = 5.6916E-008, A10 = -3.5194E-010, A12 = 3.6760E-012

Infinite IO = 20cm
d1 1.56416 0.48612
d2 14.53567 15.61372

Various data
f (mm) 10.711
Fno 2.857
2ω (angle of view (°)) 98.3
FB (mm) 14.536

Numerical example 10
Unit mm

Surface data surface number r d nd νd
1 25.537 1.312 1.77250 49.60
2 12.203 7.677
3 -298.932 1.312 1.72916 54.68
4 8.389 3.891
5 21.543 5.818 1.84666 23.78
6 -38.486 1.477
7 -200.001 7.266 1.72916 54.68
8 -13.098 1.009
9 (Aperture) ∞ 0.850
10 -10.293 0.706 1.84666 23.78
11 29.636 0.416
12 -49.806 2.162 1.72916 54.68
13 -10.736 d1
14 35.833 4.469 1.49700 81.54
15 -20.922 d2
16 -177.472 4.233 1.51633 64.14
17 -17.646 d2
Image plane ∞

Infinite IO = 40cm
d1 0.95255 0.44108
d2 2.87153 3.38299

Various data
f (mm) 7.973
Fno 3.578
2ω (angle of view (°)) 180.0
FB (mm) 15.054

Numerical example 11
Unit mm

Surface data surface number r d nd νd
1 25.406 1.300 1.51633 64.14
2 9.921 2.500
3 (Aspherical) 19.577 1.300 1.49700 81.54
4 (Aspherical) 9.911 3.796
5 18.558 2.381 1.90366 31.32
6 39.785 1.893
7 -25.885 1.031 1.49700 81.54
8 19.566 d1
9 11.900 3.300 1.58913 61.14
10 -19.340 0.860 1.59551 39.24
11 -25.112 d2
12 (Aperture) ∞ 3.321
13 -8.611 0.700 1.84666 23.78
14 -70.087 0.100
15 54.102 3.013 1.72916 54.68
16 -22.699 0.100
17 (Aspherical surface) -39.887 2.958 1.67790 55.34
18 (Aspherical surface) -12.288 2.100
19 39.423 2.888 1.72916 54.68
20 -108.634
Image plane ∞

Aspheric data 3rd surface
K = 0.0000, A4 = 4.0081E-004, A6 = -3.4017E-006, A8 = 3.0491E-008
4th page
K = 0.0000, A4 = 3.7954E-004, A6 = -2.4199E-006, A8 = -1.4760E-009, A10 = 5.5307E-010
17th page
K = 0.0000, A4 = -1.0226E-004, A6 = 4.3804E-007, A8 = 8.9066E-009
18th page
K = 0.0000, A4 = 4.7263E-005, A6 = 4.3180E-007, A8 = 4.4250E-009, A10 = 2.3859E-010, A12 = -1.6112E-012

Infinite IO = 20cm
d1 2.28937 3.30296
d2 2.47490 1.46131

Various data
f (mm) 12.131
Fno 2.099
2ω (angle of view (°)) 92.3
FB (mm) 17.415

  12 to 22 are graphs showing various aberrations of the optical systems of Examples 1 to 11 in an infinitely focused state. Spherical aberration and lateral chromatic aberration are 404.7 nm (H line: dotted line), 435.8 nm (g line: long broken line), 486.1 nm (F line: one-dot chain line), 546.1 nm (E line: two-dot chain line) , 587.6 nm (d line: solid line) and 656.3 nm (C line: short wave line). Astigmatism, the solid line indicates the sagittal image plane, and the dotted line indicates the meridional image plane. FNO represents the F number, and FIY represents the image height.

  Next, the element values of the conditional expressions and the values of the conditional expressions (1) to (15) in the above embodiments will be shown.

Element Value Example 1 Example 2 Example 3 Example 4
f 7.973 8.097 7.992 8.196
Σd 46.421 44.000 43.000 39.500
fb 15.054 15.860 14.533 15.911
Total length 61.475 59.860 57.533 55.411
ω 90.000 90.000 90.000 90.000
IHω 11.300 11.300 11.900 11.700
fn1 -31.611 -22.320 -23.360 -20.747
fn11 -6.994 -5.561 -5.738 -5.201
fLF 11.304 11.341 12.864 10.595
fLR 24.105 26.070 23.257 26.346
T max 3.891 3.266 2.888 3.137
IHω30 4.168 4.230 4.188 4.291

Element Value Example 5 Example 6 Example 7 Example 8
f 8.091 12.282 12.284 12.287
Σd 28.100 40.500 32.500 32.000
fb 17.828 16.431 15.092 15.904
Total length 45.928 56.931 47.592 47.904
ω 90.000 45.743 45.221 45.210
IHω 11.900 11.150 11.150 11.150
fn1 -12.190 -30.841 -20.369 -22.897
fn11 -6.715 -13.340 -11.586 -11.983
fLF -36.552 36.617 42.450 37.599
fLR 13.686 18.009 17.634 18.472
T max 2.974 5.739 4.257 3.470
IHω30 4.218 6.801 6.817 6.826

Element Value Example 9 Example 10 Example 11
f 10.711 7.973 12.131
Σd 35.500 46.421 38.307
fb 14.536 15.054 17.415
Total length 50.036 61.475 55.721
ω 49.129 90.000 46.128
IHω 11.150 11.300 11.150
fn1 -28.819 -31.611 -32.453
fn11 -11.380 -6.994 -17.476
fLF 31.605 11.304 33.923
fLR 16.461 24.105 21.410
T max 4.005 3.891 5.796
IHω30 6.038 4.168 6.757

Conditional Example Example 1 Example 2 Example 3 Example 4
(1) -100.000 -100.000 -100.000 -100.000
(2) -1.291 -1.392 -1.214 -1.342
(3) 3.203 3.293 2.888 3.176
(4) 2.830 2.421 2.700 2.352
(5) -1.311 -0.856 -1.004 -0.787
(6) -0.290 -0.213 -0.247 -0.197
(7) 0.934 0.772 0.690 0.731
(8) -100.000 -100.000 -100.000 -100.000
(9) 1.888 1.959 1.819 1.941
(10) 1.332 1.404 1.221 1.360
(11) -0.427 -0.432 -0.417 -0.418
(12) 1.221 3.195 1.193 2.007
(13) 0.905 0.905 0.908 0.907
(14) 4.108 3.894 3.613 3.376
(15) 2.52 4.18 2.52 4.18
(16) 64.140 54.680 64.140 54.680
(17) 0.945 0.739 0.941 0.779
(18) 0.084 0.074 0.067 0.079
(19) 0.705 0.714 0.621 0.774

Conditional Example Example 5 Example 6 Example 7 Example 8
(1) -100.000 -11.540 -9.929 -9.915
(2) -1.076 -0.621 -0.564 -0.565
(3) 3.953 1.841 2.718 1.546
(4) 1.656 2.896 1.705 2.691
(5) -0.891 -1.713 -1.155 -1.240
(6) -0.491 -0.741 -0.657 -0.649
(7) 0.705 0.844 0.624 0.508
(8) -100.000 -11.540 -9.929 -9.915
(9) 2.203 1.338 1.229 1.294
(10) 1.498 1.474 1.354 1.426
(11) -0.636 -0.424 -0.393 -0.376
(12) 1.808 -0.882 -0.654 -0.693
(13) 0.903 0.959 0.961 0.962
(14) 2.361 3.632 2.915 2.870
(15) 4.18 4.18 1.01 1.01
(16) 54.680 54.680 55.800 55.800
(17) 2.041 1.789 3.158 2.823
(18) 0.106 0.142 0.131 0.108
(19) -0.221 0.335 0.289 0.327

Conditional Example Example 9 Example 10 Example 11
(1) -9.917 -100.000 -11.638
(2) -0.586 -1.291 -0.710
(3) 2.327 3.203 2.094
(4) 2.318 2.830 2.281
(5) -1.751 -1.311 -1.516
(6) -0.691 -0.290 -0.816
(7) 0.663 0.934 0.858
(8) -9.917 -100.000 -11.638
(9) 1.357 1.888 1.436
(10) 1.304 1.332 1.562
(11) -0.381 -0.427 -0.402
(12) -0.710 1.221 -0.467
(13) 0.976 0.905 0.965
(14) 3.184 4.108 3.436
(15) 4.18 3.62 cemented lens
(16) 54.680 81.540 61.140
(17) 1.616 0.945 3.051
(18) 0.113 0.084 0.151
(19) 0.339 0.705 0.358

  The effective imaging area of the imaging surface in each embodiment has IHω * 2 as an image circle. It is also possible to determine the effective imaging area so as to capture a circular image having a diameter of IHω * 2. In such a case, the imaging optical systems of Examples 1 to 5 and Example 10 can be used as a circumferential fish eye lens. Further, assuming that the rectangular effective imaging region having a diagonal length of IHω * 2, the imaging optical systems of Examples 1 to 5 and Example 10 can be used as diagonal fisheye lenses, and Examples 6 to 9 and Example 11 can be used as a general wide-angle lens. Note that the effective imaging region may be a barrel type, and the barrel type image may be converted into a rectangular image by signal processing. In addition, the shape of the effective imaging region may be arbitrarily determined in consideration of peripheral distortion and image flow due to image correction.

  The imaging optical system shown in each embodiment that satisfies the structural requirements of the present invention is suitable mainly for an optical system using an electronic image sensor, and has a wide-angle region with a half angle of view of 32 degrees or more, which is optimal for ensuring performance. The total thickness of the optical system is shortened while ensuring a good back focus, thereby achieving miniaturization. In addition, it is possible to obtain a structure capable of obtaining good performance and achieving high speed focusing and low noise. For example, it is an imaging optical system that can easily ensure continuous focusing accuracy, such as when shooting moving images.

  FIG. 23 is a cross-sectional view of a single-lens mirrorless camera as an electronic image pickup apparatus using a lens of the present invention and using a small CCD or CMOS as an image pickup device. In FIG. 23, 1 is a single-lens mirrorless camera, 2 is a photographic lens system disposed in the lens barrel, 3 is a lens barrel mount that allows the photographic lens system 2 to be attached to and detached from the single-lens mirrorless camera 1, and a screw Type mounts and bayonet type mounts are used. In this example, a bayonet type mount is used. Reference numeral 4 denotes an image sensor surface, and 5 denotes a back monitor.

  As the photographing lens system 2 of the single-lens mirrorless camera 1 having such a configuration, for example, the lens of the present invention shown in the above Examples 1 to 11 is used.

  According to the present invention described above, as an interchangeable lens suitable for a single-lens mirrorless type digital camera, while performing distortion correction to some extent, various aberrations such as chromatic aberration and curvature of field are particularly well corrected, and telecentricity is ensured. Therefore, it is possible to provide a compact wide-angle optical system with a small number of components.

  24 to 27 are conceptual diagrams of the configuration of another imaging apparatus according to the present invention in which a lens is incorporated in the photographing optical system 41. FIG. 24 is a front perspective view showing the appearance of the digital camera 40, FIG. 25 is a rear view thereof, and FIG. 26 is a schematic cross-sectional view showing the configuration of the digital camera 40.

  In this example, the digital camera 40 includes a photographic optical system 41 positioned on the photographic optical path 42, a finder optical system 43 positioned on the finder optical path 44, a shutter button 45, a pop-up flash 46, a liquid crystal display monitor 47, and the like. In addition, when a shutter button 45 disposed on the upper portion of the camera 40 is pressed, photographing is performed through the photographing optical system 41, for example, the lens of the first embodiment, in conjunction therewith. The object image formed by the photographing optical system 41 is formed on the image pickup surface (photoelectric conversion surface) of the CCD 49 as an image pickup element provided in the vicinity of the image forming surface. The object image received by the CCD 49 is displayed as an electronic image on the liquid crystal display monitor 47 provided on the back of the camera or the finder image display element 54 via the processing means 51. Further, the processing means 51 is connected to a recording means 52 so that a photographed electronic image can be recorded.

  The recording unit 52 may be provided separately from the processing unit 51, or may be configured to perform recording and writing electronically using a flexible disk, a memory card, an MO, or the like. Further, it may be configured as a silver salt camera in which a silver salt film is arranged in place of the CCD 49.

  Further, a finder eyepiece lens 59 is disposed on the finder optical path 44. The object image displayed on the finder image display element 54 is magnified by the finder eyepiece lens 59 and adjusted to a diopter that is easy for the observer to see, and is guided to the observer eyeball E. A cover member 50 is disposed on the exit side of the finder eyepiece lens 59.

  FIG. 27 is a block diagram showing the internal circuitry of the main part of the digital camera 40. In the following description, the processing unit 51 includes, for example, the CDS / ADC unit 24, the temporary storage memory 17, the image processing unit 18, and the like, and the storage unit 52 includes, for example, the storage medium unit 19 and the like.

  As shown in FIG. 27, the digital camera 40 is connected to the operation unit 12, the control unit 13 connected to the operation unit 12, and the control signal output port of the control unit 13 via buses 14 and 15. An imaging drive circuit 16, a temporary storage memory 17, an image processing unit 18, a storage medium unit 19, a display unit 20, and a setting information storage memory unit 21 are provided.

  The temporary storage memory 17, the image processing unit 18, the storage medium unit 19, the display unit 20, and the setting information storage memory unit 21 are configured to be able to input or output data with each other via the bus 22. The imaging drive circuit 16 is connected with a CCD 49 and a CDS / ADC unit 24.

  The operation unit 12 includes various input buttons and switches, and is a circuit that notifies the control unit of event information input from the outside (camera user) via these input buttons and switches. The control unit 13 is a central processing unit composed of, for example, a CPU, and has a built-in program memory (not shown). The control unit 13 is input by a camera user via the operation unit 12 according to a program stored in the program memory. This circuit controls the entire digital camera 40 in response to the instruction command.

  The CCD 49 receives an object image formed via the photographing optical system 41 according to the present invention. The CCD 49 is an image pickup element that is driven and controlled by the photographing drive circuit 16 and converts the light amount of each pixel of the object image into an electrical signal and outputs it to the CDS / ADC unit 24.

  The CDS / ADC unit 24 amplifies the electric signal input from the CCD 49 and performs analog / digital conversion, and temporarily generates the raw video data (Bayer data, hereinafter referred to as RAW data) that has just been subjected to the amplification and digital conversion. It is a circuit that outputs to the memory 17.

  The temporary storage memory 17 is a buffer made of, for example, SDRAM or the like, and is a memory device that temporarily stores the RAW data output from the CDS / ADC unit 24. The image processing unit 18 reads out the RAW data stored in the temporary storage memory 17 or the RAW data stored in the storage medium unit 19, and performs various corrections including distortion correction based on the image quality parameter designated by the control unit 13. It is a circuit that performs image processing electrically.

  The storage medium unit 19 detachably mounts a card-type or stick-type recording medium made of, for example, a flash memory, and RAW data transferred from the temporary storage memory 17 to the card-type or stick-type flash memory. It is a control circuit of an apparatus that records and holds image data processed by the image processing unit 18.

  The display unit 20 includes a liquid crystal display monitor 47 and a finder image display element 54, and is a circuit that displays an image, an operation menu, and the like on the liquid crystal display monitor 47 and the finder image display element 54. The setting information storage memory unit 21 stores a ROM unit in which various image quality parameters are stored in advance, and an image quality parameter selected by an input operation of the operation unit 12 among the image quality parameters read from the ROM unit. RAM section is provided. The setting information storage memory unit 21 is a circuit for controlling input / output to / from these memories.

  According to the present invention, the digital camera 40 configured in this manner is compact with a small number of components, in which various aberrations such as chromatic aberration and curvature of field are corrected well, and telecentricity is ensured while performing distortion correction to some extent. An imaging apparatus using a wide-angle optical system can be provided.

  The present invention may be applied not only to a so-called compact digital camera that photographs a general subject as described above, but also to a surveillance camera or the like that requires a wide angle of view.

LF ... front lens group LR ... rear lens group L1 ... first sub lens group L2 ... second sub lens group L3 ... third sub lens group L4 ... fourth sub lens group L5 ... fifth sub lens group n1 ... first Negative lens n2 ... second negative lens S ... aperture stop I ... image plane 1 ... interchangeable lens camera 2 ... taking lens system 3 ... mount unit 4 ... imaging element surface 5 ... back monitor 12 ... operation unit 13 ... control Sections 14, 15 ... Bus 16 ... Imaging drive circuit 17 ... Temporary storage memory 18 ... Image processing section 19 ... Storage medium section 20 ... Display section 21 ... Setting information storage memory section 22 ... Bus 24 ... CDS / ADC section 40 ... Digital camera 41 ... Optical optical system 42 ... Optical optical path 43 ... Finder optical system 44 ... Optical path for finder 45 ... Shutter button 46 ... Pop-up strobe 47 ... Liquid crystal display monitor 49 ... CCD
DESCRIPTION OF SYMBOLS 50 ... Cover member 51 ... Processing means 52 ... Recording means 54 ... Image display element 59 for finder ... Eyepiece for finder

Claims (32)

The aperture stop,
A front lens group disposed on the object side of the aperture stop;
A rear lens unit having a positive refractive power disposed on the image side of the aperture stop,
The front lens group includes a first sub lens group having a negative refractive power and a second sub lens group having a positive refractive power in order from the object side to the image side.
The rear lens group includes, in order from the object side to the image side, a third sub lens group having a convex surface on the most image side and a fourth sub lens group having a positive refractive power,
The first sub lens group has a fixed position, and the first sub lens group has a most object side lens surface convex to the object side,
The third sub lens group has a concave object side lens surface on the object side;
An imaging optical system characterized by satisfying the following conditional expressions (1), (2), and (3):
-140% ≤ DT ≤ -7% (1)
−2.2 ≦ R_L3f / f ≦ −0.25 (2)
0.8 ≦ R_L1f / f ≦ 5.5 (3)
However,
DT = (IHω−f · tan ω) / (f · tan ω) × 100%,
ω is the maximum half field angle of the imaging optical system,
IHω is the distance from the optical axis at the point where the principal ray with the maximum half angle of view ω intersects the image plane,
f is the focal length of the entire imaging optical system,
R_L3f is the paraxial radius of curvature of the lens surface closest to the object side in the third sub lens group,
R_L1f is the paraxial radius of curvature of the lens surface closest to the object side of the first sub lens group,
fLF is the focal length of the front lens group. The aperture stop,
A front lens group disposed on the object side of the aperture stop;
A rear lens unit having a positive refractive power disposed on the image side of the aperture stop,
The front lens group includes a first sub lens group having a negative refractive power and a second sub lens group having a positive refractive power in order from the object side to the image side.
The rear lens group includes, in order from the object side to the image side, a third sub lens group having a convex surface on the most image side and a fourth sub lens group having a positive refractive power,
The first sub lens group has a fixed position, and the rear lens group has a focusing lens group that moves during focusing,
The first sub lens group includes at least one negative lens;
When the negative lens disposed closest to the object side among the negative lenses in the first sub lens group is the first negative lens (n1),
The first negative lens is a negative meniscus lens having a concave surface facing the image side,
An imaging optical system characterized by satisfying the following conditional expressions (1) and (4):
-140% ≤ DT ≤ -7% (1)
1.1 ≦ SFn1 ≦ 5.0 (4)
However,
DT = (IHω−f · tan ω) / (f · tan ω) × 100%,
ω is the maximum half field angle of the imaging optical system,
IHω is the distance from the optical axis at the point where the principal ray with the maximum half angle of view ω intersects the image plane,
f is the focal length of the entire imaging optical system,
SFn1 = (Rn1f + Rn1r) / (Rn1f−Rn1r), and Rn1f is a paraxial radius of curvature of the object side surface of the first negative lens,
Rn1r is the paraxial radius of curvature of the image side surface of the first negative lens. The aperture stop,
A front lens group disposed on the object side of the aperture stop;
A rear lens unit having a positive refractive power disposed on the image side of the aperture stop,
The front lens group includes a first sub lens group having a negative refractive power and a second sub lens group having a positive refractive power in order from the object side to the image side.
The rear lens group includes, in order from the object side to the image side, a third sub lens group having a convex surface on the most image side and a fourth sub lens group having a positive refractive power,
The first sub lens group has a fixed position, and the rear lens group has a focusing lens group with positive refractive power that moves during focusing,
The first sub lens group includes at least a negative lens;
When a negative lens arranged closest to the object side among the negative lenses in the first sub lens group is a first negative lens,
The first negative lens is a negative meniscus lens having a concave surface facing the image side,
An imaging optical system characterized by satisfying the following conditional expressions (5), (6), and (7):
−3 ≦ fn1 / fLR ≦ −0.5 (5)
-2 ≦ fn11 / fLR ≦ −0.1 (6)
Tmax / IHω30 ≦ 1.2 (7)
However,
fn1 is a focal length of the first negative lens;
fn11 is a combined focal length of the first negative lens and a lens disposed immediately after the image side of the negative lens,
fLR is the focal length of the rear lens group,
Tmax is the maximum value of the distances of the spaces between the plurality of lenses in the imaging optical system excluding the image-side space in contact with the first negative lens,
IHω30 is the distance from the optical axis at the point where the principal ray having a half angle of view of 30 degrees intersects the image plane. The imaging optical system according to claim 3, wherein the following conditional expression (1) is satisfied.
-140% ≤ DT ≤ -7% (1)
However,
DT = (IHω−f · tan ω) / (f · tan ω) × 100%,
ω is the maximum half field angle of the imaging optical system,
IHω is the distance from the optical axis at the point where the principal ray with the maximum half angle of view ω intersects the image plane,
f is the focal length of the entire imaging optical system,
It is. The aperture stop,
A front lens group disposed on the object side of the aperture stop;
A rear lens unit having a positive refractive power disposed on the image side of the aperture stop,
The front lens group includes a first sub lens group having a negative refractive power and a second sub lens group having a positive refractive power in order from the object side to the image side.
The rear lens group includes, in order from the object side to the image side, a third sub lens group having a convex surface on the most image side and a fourth sub lens group having a positive refractive power,
The first sub lens group has a fixed position, and the rear lens group (LB) has a focusing lens group that moves during focusing,
An imaging optical system characterized by satisfying the following conditional expressions (1) and (3):
-140% ≤ DT ≤ -7% (1)
0.8 ≦ R_L1f / f ≦ 5.5 (3)
However,
DT = (IHω−f · tan ω) / (f · tan ω) × 100%,
ω is the maximum half field angle of the imaging optical system,
IHω is the distance from the optical axis at the point where the principal ray with the maximum half angle of view ω intersects the image plane,
f is the focal length of the entire imaging optical system,
R_L1f is the paraxial radius of curvature of the lens surface closest to the object side of the first sub lens group,
It is. The aperture stop,
A front lens group disposed on the object side of the aperture stop;
A rear lens unit having a positive refractive power disposed on the image side of the aperture stop,
The front lens group includes a first sub lens group having a negative refractive power and a second sub lens group having a positive refractive power in order from the object side to the image side.
The rear lens group includes, in order from the object side to the image side, a third sub lens group having a convex surface on the most image side and a fourth sub lens group having a positive refractive power,
The first sub lens group has a fixed position, and the rear lens group has a focusing lens group with positive refractive power that moves during focusing,
An imaging optical system characterized by satisfying the following conditional expression (8):
−140% <DT <−40% (8)
However,
DT = (IHω−f · tan ω) / (f · tan ω) × 100%,
ω is the maximum half field angle of the imaging optical system,
IHω is the distance from the optical axis at the point where the principal ray with the maximum half angle of view ω intersects the image plane,
f is the focal length of the entire imaging optical system,
R_L1f is the paraxial radius of curvature of the lens surface closest to the object side of the first sub lens group,
It is.   7. The imaging optical system according to claim 1, wherein a focusing lens group for performing focusing is disposed in the rear lens group.   The imaging optical system according to claim 7, wherein the focusing lens group that performs focusing has a positive refractive power.   9. The imaging optical system according to claim 8, wherein the fourth sub lens group is the focusing lens group.   10. An imaging optical system according to claim 7, wherein only one lens unit moves together during focusing. The imaging optical system according to claim 1, wherein the following conditional expression (9) is satisfied.
0.8 ≦ fb / f ≦ 2.7 (9)
However,
fb is an air equivalent distance from the lens surface closest to the image side of the imaging optical system to the image plane;
f is the focal length of the entire imaging optical system,
It is. The imaging optical system according to claim 1, wherein the following conditional expression (10) is satisfied.
0.8 ≦ fb / IHω ≦ 2.4 (10)
However,
fb is an air equivalent distance IHω from the lens surface closest to the image side of the imaging optical system to the image plane, and is a distance from the optical axis at the point where the principal ray having the maximum half angle of view ω intersects the image plane,
It is.   The imaging optical system is a single focus lens, and the movable lens group in the imaging optical system is only one focusing lens group. Imaging optical system.   14. The imaging optical system according to claim 13, wherein the total number of lenses in the focusing lens group is 2 or less.   15. The imaging optical system according to claim 14, wherein the fourth sub lens group is the only lens group that moves during focusing, and the total number of lenses included in the fourth sub lens group is 2 or less. . The imaging optical system according to claim 1, wherein the following conditional expression (11) is satisfied.
−1 ≦ R_L3f / fLR ≦ −0.2 (11)
However,
R_L3f is the paraxial radius of curvature of the lens surface closest to the object side in the third sub lens group,
fLR is the focal length of the rear lens group,
It is.   The imaging optical system according to claim 1, wherein the fourth sub lens group is a lens group disposed closest to the image side. The imaging optical system according to claim 17, wherein the following conditional expression (12) is satisfied.
-1.1 ≦ SF_L4 ≦ 4.0 (12)
However,
SF_L4 = (RL4f + RL4r) / (RL4f−RL4r), and RL4f is the paraxial radius of curvature of the object side surface of the fourth sub lens group,
RL4r is a paraxial radius of curvature of the image side surface of the fourth sub lens group. The imaging optical system according to claim 1, wherein the following conditional expression (13) is satisfied.
0.895 ≦ IHω30 / (f · tan30 °) ≦ 0.99 (13)
IHω30 is the distance from the optical axis at the point where the principal ray with a half angle of view of 30 degrees intersects the image plane,
f is the focal length of the entire imaging optical system,
It is. The imaging optical system according to claim 1, wherein the following conditional expression (14) is satisfied.
1.5 ≦ Σd / IHω ≦ 6.0 (14)
However,
Σd is the length from the most object side lens surface to the most image side lens surface of the imaging optical system,
IHω is the distance from the optical axis at the point where the principal ray with the maximum half angle of view ω intersects the image plane,
It is.   21. The imaging optical system according to claim 1, wherein the focusing lens group that moves during focusing is one positive lens. The imaging optical system according to claim 21, wherein the specific gravity of the one positive lens that moves during focusing satisfies the following conditional expression (15):
0.8 ≦ Dfo ≦ 1.5 (15)
However,
Dfo is the specific gravity of the single positive lens that moves during focusing, and its unit is g / cm ^3.
It is. During focusing, at least one positive lens moves,
The imaging optical system according to claim 1, wherein the following conditional expression (16) is satisfied.
νd_fo> 50 (16)
However,
νd_fo is the maximum value among the Abbe numbers of the positive lens that moves during focusing. The first sub lens group includes, in order from the object side, only two lenses, a first negative lens having a negative refractive power and a second lens arranged on the image side thereof,
The first negative lens is a negative meniscus lens having a concave surface facing the image side;
The second lens has a concave image side surface whose absolute value of curvature is larger than that of the object side surface;
24. The imaging optical system according to claim 1, wherein the following conditional expression (17) is satisfied.
0.4 ≦ SF2 ≦ 6.0 (17)
However,
SF2 = (R2f + R2r) / (R2f−R2r), and R2f is a paraxial radius of curvature of the object side surface of the second lens,
R2r is a paraxial radius of curvature of the image side surface of the second lens. The first sub lens group includes at least a negative lens;
When a negative lens arranged closest to the object side among the negative lenses in the first sub lens group is a first negative lens,
The first negative lens is a negative lens having a concave surface facing the image side,
The imaging optical system according to any one of claims 1 to 24, wherein the following condition (18) is satisfied.
Tmax / Σd ≦ 0.27 (18)
However,
Tmax is the maximum value of the distances of the spaces between the plurality of lenses in the imaging optical system excluding the image-side space in contact with the first negative lens,
Σd is the length on the optical axis from the lens surface closest to the object side to the lens surface closest to the image side of the imaging optical system,
It is. The first sub lens group includes at least a negative lens;
When a negative lens arranged closest to the object side among the negative lenses in the first sub lens group is a first negative lens,
The first negative lens is a negative meniscus lens having a concave surface facing the image side,
26. The imaging optical system according to claim 1, wherein the first negative lens is a lens arranged closest to the object side in the first sub lens group. 27. The imaging optical system according to claim 1, wherein the following conditional expression (19) is satisfied.
−1 ≦ f / fLF ≦ 1.5 (19)
f is the focal length of the entire imaging optical system,
fLF is the focal length of the front lens group. When the lens component is a lens body in which only two refracting surfaces of the incident side and the image side are in contact with air on the optical axis,
The first sub lens group is composed of two negative lens components having a concave surface facing the image side,
The absolute value of the paraxial curvature of the image side surface of the two negative lens components is smaller than the absolute value of the paraxial curvature of the object side surface,
The second sub lens group is composed of two to four lenses including a positive lens,
The third sub lens group includes one negative lens and two or less positive lenses disposed on the image side of the one negative lens;
The imaging optical system according to any one of claims 1 to 27, wherein the fourth sub lens group includes one positive lens component. The imaging optical system according to claim 1, wherein the following conditional expression (5) is satisfied.
−3 ≦ fn1 / fLR ≦ −0.5 (5)
However,
fn1 is a focal length of the first negative lens;
fLR is the focal length of the rear lens group,
It is. 30. The imaging optical system according to claim 1, wherein the following conditional expression (6) is satisfied.
-2 ≦ fn11 / fLR ≦ −0.1 (6)
However,
fn11 is a combined focal length of the first negative lens and a lens disposed immediately after the image side of the negative lens,
fLR is the focal length of the rear lens group,
It is. The imaging optical system according to claim 1, wherein the following conditional expression (7) is satisfied.
Tmax / IHω30 ≦ 1.2 (7)
However,
Tmax is the maximum value of the distances of the spaces between the plurality of lenses in the imaging optical system excluding the image-side space in contact with the first negative lens,
IHω30 is the distance from the optical axis at the point where the principal ray having a half angle of view of 30 degrees intersects the image plane. The imaging optical system according to any one of claims 1 to 31,
And an imaging device having an imaging surface disposed on the image side of the imaging optical system and converting an optical image into an electrical signal.

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