JP5639625B2 - Imaging optical system and imaging apparatus having the same - Google Patents

Description

  The present invention relates to an imaging optical system and an imaging apparatus having the imaging optical system, and is suitable for, for example, a video camera using a solid-state imaging device, a digital still camera, a TV camera, a surveillance camera, a film camera using a silver salt film, and the like. is there.

  As a long focal length imaging optical system, a so-called telephoto imaging optical system (telephoto lens) comprising a front lens group having a positive refractive power and a rear lens group having a negative refractive power in order from the object side to the image side. )It has been known. Here, the long focal length means, for example, a long focal length compared to the size of the effective imaging range. In general, in a telephoto imaging optical system with a long focal length, the entire optical system becomes larger and heavier as the focal length increases. In particular, the front lens group becomes heavier. Of various aberrations, particularly, chromatic aberration such as longitudinal chromatic aberration and lateral chromatic aberration occurs.

  Various imaging optical systems have been proposed in which these chromatic aberrations are corrected using a low dispersion material having anomalous partial dispersion such as fluorite (which has been achromatic). For example, an imaging optical system in which chromatic aberration is corrected by using a material having a large partial dispersion ratio (θgF) for a positive lens on the front side (object side) of the aperture stop is known (Patent Document 1). Patent Document 1 discloses a telephoto imaging optical system having a focal length of about 400 mm and an F number of about 2.8.

  On the other hand, as a method for reducing the lens weight while correcting various aberrations including chromatic aberration of the imaging optical system, a diffractive optical element in which a diffractive optical part having a diffractive action is provided on a substrate as a part of the imaging optical system A method of using is known. An imaging optical system is known that uses this method to reduce the overall lens weight by correcting the chromatic aberration while shortening the overall lens length, or by constructing the lens with a relatively light glass material specific gravity. (Patent Document 2).

  Patent Document 2 discloses a telephoto imaging optical system having a focal length of about 800 mm and an F number of about 5.8. Also, in many telephoto imaging optical systems, there is known an imaging optical system using an inner focus type in which a relatively small and lightweight lens group other than the front lens group is moved in order to perform focusing at high speed. (Patent Document 3). In Patent Document 3, in order from the object side, a first lens group having a positive refractive power and a second lens group having a negative refractive power are provided, and focusing is performed by moving the second lens group.

JP 58-82217 A JP 2008-096656 A JP 2009-271354 A

  In general, in the telephoto imaging optical system, the entire lens system is increased in size and weight as the focal length is increased. For this reason, in the telephoto imaging optical system, it is important to reduce the size and weight of the entire lens system.

  In general, as the focal length becomes longer in a telephoto imaging optical system, the front lens unit having a positive refractive power becomes larger and heavier. Further, the occurrence of chromatic aberration increases. For this reason, in the telephoto imaging optical system, setting the lens configuration of the front lens unit having a positive refractive power appropriately reduces the size and weight of the entire system, and corrects chromatic aberration well, and has high optical performance. It becomes important to obtain performance. If the lens configuration of the front lens group is inappropriate, the entire system becomes larger and heavier, various aberrations increase, and it becomes very difficult to obtain high optical performance.

  An object of the present invention is to provide an imaging optical system that can easily reduce the size of the entire system and reduce the weight of the lens, and an imaging apparatus having the imaging optical system.

The imaging optical system of the present invention includes, in order from the object side to the image side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, an aperture stop, and a third lens group . The first lens group and the third lens group are stationary, the second lens group moves, and the first lens group has an eleventh positive refractive power on the object side with the widest air gap as a boundary. The lens group has a twelfth lens group on the image side, and the eleventh lens group is composed of one positive lens G1, the refractive index of the material of the positive lens G1 is NG1, the specific gravity is dG1, the focal length is fG1, When the focal length of the entire system is f,
dG1 <−3.1 × ( NG1 ) ² + 14.7 × NG1-12.8
0.4 <fG1 / f <0.8
It is characterized by satisfying the following conditional expression.

  According to the present invention, it is possible to obtain an imaging optical system that can easily reduce the size of the entire system and reduce the weight of the lens.

(A), (B) Lens cross-sectional view and aberration diagram of the imaging optical system of Example 1 of the present invention at an object distance of infinity (A), (B) Lens cross-sectional view and aberration diagram of the imaging optical system of Example 2 of the present invention at an object distance of infinity (A), (B) Lens cross-sectional view and aberration diagram of the imaging optical system of Example 3 of the present invention at an infinite object distance (A), (B) Lens cross-sectional view and aberration diagram of the imaging optical system of Example 4 of the present invention at an infinite object distance (A), (B) Lens cross-sectional view and aberration diagram of the imaging optical system of Example 5 of the present invention at an infinite object distance Explanatory diagram showing the relationship between the focal length and weight of the lens Explanatory drawing of the diffractive optical element according to the present invention Explanatory drawing of the diffractive optical element according to the present invention Explanatory drawing of the imaging device of the present invention

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. The imaging optical system of the present invention includes, in order from the object side to the image side, a first lens group having a positive refractive power, a second lens group having a negative refractive power that moves in the optical axis direction for focusing, an aperture stop, Or a third lens unit having a negative refractive power.

  FIG. 1A to FIG. 5A are lens cross-sectional views of Examples 1 to 5 of the imaging optical system of the present invention. FIGS. 1B to 5B are longitudinal aberration diagrams of Examples 1 to 5 of the imaging optical system of the present invention. FIG. 6 is an explanatory diagram showing the relationship between the focal length and weight of the lens. 7A, 7B, 8A, 8B, and 8C are explanatory views of the diffractive optical element according to the present invention. FIG. 9 is a schematic diagram of a main part of a single-lens reflex camera system (imaging device) in which the photographing optical system of the present invention is mounted on the camera body.

In each lens cross-sectional view, L0 is an imaging optical system. SP is an aperture stop that determines the axial maximum luminous flux diameter. The imaging optical system L0 includes a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power that moves during focusing, and a positive or negative third lens unit L3. The first lens unit L1 includes an eleventh lens unit L11 having a positive refractive power on the object side and a twelfth lens unit L12 on the image side with the widest air gap as a boundary. During focusing, the first lens unit L1 and the third lens unit L3 do not move.

  The third lens unit L3 moves in order from the object side to the image side so as to have a component in the direction perpendicular to the fixed thirty-first lens unit L31, and the image (image formation position) is perpendicular to the optical axis direction. And a fixed thirty-third lens unit L33.

  Examples 2 to 5 have at least one diffractive optical element DOE closer to the object side than the position where the pupil paraxial ray intersects the optical axis. G is an optical block corresponding to an optical filter, a face plate, a crystal low-pass filter, an infrared cut filter, or the like. IP is an image plane, and when used as a photographing optical system of a video camera or a digital camera, an imaging surface of a CCD sensor, a CMOS sensor or the like (photoelectric conversion element) that receives an image is used for a silver salt film camera. It corresponds to a film surface when used as an imaging optical system.

  In each aberration diagram, d-line and g-line are d-line and g-line, respectively. ΔM and ΔS are a meridional image plane and a sagittal image plane. Lateral chromatic aberration is represented by the g-line. Fno is the F number, and ω is the half angle of view. In all aberration diagrams, when each numerical example described later is expressed in mm, spherical aberration is 0.2 mm, astigmatism is 0.2 mm, distortion is 2%, and lateral chromatic aberration is drawn on a scale of 0.025 mm. It is. The imaging optical system L0 of each embodiment is of a telephoto type, and the characteristic configuration is as follows.

In the image pickup optical system of each embodiment, the eleventh lens unit L11 includes one positive lens G1. The refractive index of the material of the positive lens G1 is NG1, the specific gravity is dG1, and the focal length is fG1. Let f be the focal length of the entire system. At this time,
dG1 <−3.1 × ( NG1 ) ² + 14.7 × NG1-12.8 (1)
0.4 <fG1 / f <0.8 (2)
The following conditional expression is satisfied.

  Conventionally, a so-called telephoto type imaging optical system including a front lens group having a positive refractive power and a rear lens group having a negative refractive power in order from the object side to the image side is used in many imaging apparatuses. Yes.

  When the telephoto type is adopted, the effective range (effective diameter) of the front lens is dominated by the effective range of axial rays. The telephoto type imaging optical system has a lens group having positive and negative refractive powers, and shortens the total lens length by narrowing the axial ray. That is, the effective diameter of the lens on the object side is large and decreases toward the stop surface (image side). If the F value (F number) is decreased, the effective lens diameter is increased in inverse proportion, and the weight of the lens is increased to the third power. Therefore, when reducing the lens weight, it is effective to reduce the weight of the front lens.

  When reducing the refractive power of one lens constituting a lens group and reducing the weight by reducing the thickness of the lens, if the other lens becomes larger and thicker in order to maintain the refractive power of the entire lens group As a result, weight reduction cannot be achieved. When the refractive index of the material and the target focal length (reciprocal of power) are given, the volume of the lens for constructing the necessary refractive power is almost uniquely determined. Multiply this by the specific gravity to determine the required weight of the lens. The inventor has devised a method for optimizing the lens weight from the relationship between the refractive index and specific gravity of a lens material having a desired refractive power.

  FIG. 6 is a plot of the weight of a single lens under certain conditions for each specific gravity of the glass material. Here, the lens diameter is 140 mm, the shape factor is 1.30, the edge around the lens is 2.5 mm, and the focal length of the lens is 240 mm. When the refractive index of the lens material and the focal length (refractive power) of the lens are changed, the first lens surface of the lens and the center thickness of the lens are changed so that the above condition is satisfied. .

  For example, FIG. 6 shows that when the specific gravity of the material is 2.46, the lens weight is about 500 g when the refractive index is 1.53. It can also be seen that if the specific gravity is also 2.46 and the refractive index is 1.81, the lens weight is about 340 g. In FIG. 6, the relationship between the refractive index and the specific gravity necessary to satisfy the lens weight can be read, and a lighter area than the conventional configuration can be shown as a broken line in FIG. If the glass material in the region below the broken line shown in FIG. 6 is used, the lens can be easily reduced in weight.

  Conditional expression (1) is set in view of the above conditions, and defines the range in which the eleventh lens unit L11 can be easily reduced in terms of the refractive index and specific gravity. If a material in a range exceeding the value of conditional expression (1) is used, it is difficult to reduce the weight of the lens. When the refractive power of the eleventh lens unit L11 is small, the positive lens G1 approaches a parallel plate, so that the difference in weight due to the shape is small. For this reason, when the refractive power of the eleventh lens unit L11 is weak, the effect of using a material satisfying conditional expression (1) is reduced.

  Conditional expression (2) defines the focal length of the positive lens G1 of the eleventh lens unit L11. If the focal length of the positive lens G1 is increased beyond the upper limit of the conditional expression (2), the effect of reducing the weight is reduced. When the refractive power of the positive lens G1 is weakened, the subsequent lens group has a large diameter, and it is difficult to reduce the weight of the entire optical system. Further, if the focal length of the positive lens G1 becomes shorter than the lower limit of the conditional expression (2), the weight of the eleventh lens unit L11 having a dominant contribution to the weight of the entire system increases, which is not desirable.

  Thus, the weight of the eleventh lens L11 is reduced by using a material that satisfies the conditional expression (1) for the positive lens G1 with a refractive power that satisfies the conditional expression (2). More preferably, the numerical values of conditional expressions (1) and (2) are set as follows.

dG1 <−3.1 × ( NG1 ) ² + 14.7 × NG1-12.9 (1a)
0.45 <fG1 / f <0.75 (2a)
By taking the above configuration, it is possible to easily obtain a photographing optical system that can obtain a light image with high quality as a whole. More preferably, at least one of the following conditions should be satisfied, whereby further high optical performance can be easily obtained.

D1ab the distance on the optical axis of the first lens subunit L11 and the second lens subunit L12, to the distance to the image plane (overall lens length) and L from the lens surface closest to the object side. The focal length of the jth negative lens Gnj counted from the object side of the negative lens included in the twelfth lens unit L12 is fnj, and the Abbe number of the material is νdnj. The Abbe number of the material of at least one positive lens included in the twelfth lens unit L12 is νd12p. At this time, it is preferable to satisfy one or more of the following conditional expressions.

1.5 <NG1 (3)
0.05 <D1ab / L <0.40 (4)
−0.251 ≦ Σ (f / (fnj × νdnj)) <− 0.15 (5)
80 <νd12p (6)
Here, Σ represents the sum.

Next, the technical meaning of each conditional expression described above will be described. Conditional expression (3) defines the refractive index of the material of the positive lens G1. If a material having a refractive index lower than the lower limit of the conditional expression (3) is used, the weight of the eleventh lens unit L11 increases rapidly when the refractive power is increased as shown in FIG. . The first lens unit L1 includes an eleventh lens unit L11 disposed on the most object side and a twelfth lens unit L12 disposed on the image side of the eleventh lens unit L11.
Conditional expression (4) is a ratio between the distance on the optical axis between the eleventh lens unit L11 and the twelfth lens unit L12 and the distance on the optical axis from the lens surface closest to the object side to the image plane (lens total length). Is specified. If the lower limit of conditional expression (4) is not reached, the twelfth lens unit L12 has a large diameter, which makes it difficult to reduce the weight of the first lens unit L1. If the upper limit of conditional expression (4) is exceeded, it will be difficult to correct the lateral chromatic aberration and axial chromatic aberration generated in the eleventh lens unit L11 in a balanced manner.

Conditional expression (5) defines the focal length of the negative lens and the Abbe number of the material included in the twelfth lens unit L12. By satisfying conditional expression (5), the chromatic aberration is corrected in a well-balanced manner by appropriately setting the achromatic effect of the negative lens. If the lower limit of conditional expression (5) is not reached, the weight of the negative lens increases, which is not desirable. If the upper limit of conditional expression (5) is exceeded, it will be difficult to correct the lateral chromatic aberration and axial chromatic aberration that occur in the eleventh lens unit L11 in a well-balanced manner.

  Conditional expression (6) defines the Abbe number of the material of the positive lens of the twelfth lens unit L12 for correcting chromatic aberration occurring in the eleventh lens unit L11. If the lower limit of conditional expression (6) is not reached, it will be difficult to correct chromatic aberration occurring in the eleventh lens unit L11. Desirably, two or more positive lenses satisfying conditional expression (6) are used in each embodiment.

Instead of satisfying conditional expression (6), at least one diffractive optical element may be arranged on the object side of the position where the pupil paraxial ray intersects the optical axis. Since the diffractive optical element has a high ability to correct chromatic aberration, axial chromatic aberration and lateral chromatic aberration can be effectively corrected by disposing the pupil paraxial ray closer to the object side than the position where it intersects the optical axis. In general, a glass material satisfying conditional expression (6) has a large specific gravity and is likely to increase in weight. When the diffractive optical element is used, a light glass material can be used for the first lens unit L1, and the entire optical system can be easily reduced in weight. More preferably, the numerical values of the conditional expressions (3), (4) and (6) are set as follows.

1.53 <NG1 (3a)
0.1 <D1ab / L <0.3 (4a )
90 <νd12p (6a)
Generally, when the Abbe numbers of the positive and negative lenses are close to each other, when correcting chromatic aberration, the power of each lens tends to increase. For this reason, even if the chromatic aberration is corrected, it may be difficult to correct the monochromatic aberration. In each of the embodiments, in such a case, it is easy to effectively correct monochromatic aberration by using an aspherical surface.

  As described above, according to each embodiment, it is easy to obtain a photographic optical system that can easily correct chromatic aberration and that can easily reduce the weight of the lens, and an imaging apparatus having the same. Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[Example 1]
Example 1 shown in FIG. 1 is a telephoto imaging optical system having a diagonal angle of view of about 6.32 degrees. The first exemplary embodiment includes, in order from the object side to the image side, a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power, and a third lens unit L3 having a positive refractive power. The first lens unit L1 includes an eleventh lens unit L11 and a twelfth lens unit L12 with the widest air gap as a boundary. An aperture stop SP is provided between the second lens unit L2 and the third lens unit L3. The third lens unit L3 includes a thirty-first lens unit L31 having a positive refractive power, a thirty-second lens unit L32 having a negative refractive power, and a thirty-third lens unit L33 having a positive refractive power.

  Focusing from an infinitely distant object to a close object is performed by moving the second lens unit L2 to the image side. In the case of a lens having a long focal length, it is difficult to focus by moving the entire lens because the lens is large and heavy.

  Therefore, in this embodiment, focusing is performed by moving some small and light lens groups other than the first lens group L1. When the imaging optical system LO vibrates, the correction of the blur of the captured image is performed by moving the thirty-second lens unit L32 as a movable lens unit in a direction having a component perpendicular to the optical axis.

  The positive lens G1 of the eleventh lens unit L11 is made of OHARA INC. Product name S-TIH3, and satisfies the conditional expressions (1), (2), and (3). The weight of the eleventh lens unit L11 in Example 1 is about 513 g. However, if the product name S-FSL5 is used under the same conditions, the weight is about 628 g, which is about 115 g. . The twelfth lens unit L12 includes a positive lens, a negative lens, a positive lens, and a positive lens in order from the object side to the image side.

  When the distance between the eleventh lens group L11 and the twelfth lens group L12 satisfies the conditional expression (4), the number of lenses of the eleventh lens group L11 having a large aperture on the object side is reduced, and the imaging optical system is reduced in weight. ing. The second lens unit L2 is composed of a single negative lens. In the third lens unit L3, the 31st lens unit L31 includes a pair of cemented lenses in which a negative lens and a positive lens are cemented. The thirty-second lens unit L32 includes a cemented lens obtained by cementing a positive lens and a negative lens, and a negative lens. The thirty-third lens unit L33 includes a positive lens and a cemented lens in which a positive lens and a negative lens are cemented.

[Example 2]
The second embodiment is a telephoto imaging optical system having a diagonal field angle of about 6.32 degrees. The first exemplary embodiment includes, in order from the object side to the image side, a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power, and a third lens unit L3 having a positive refractive power.

  The first lens unit L1 includes an eleventh lens unit L11 and a twelfth lens unit L12 with the widest air gap as a boundary. An aperture stop SP is provided between the second lens unit L2 and the third lens unit L3. The third lens unit L3 includes a thirty-first lens unit L31 having a positive refractive power, a thirty-second lens unit L32 having a negative refractive power, and a thirty-third lens unit L33 having a positive refractive power. Focusing from an infinitely distant object to a close object is performed by moving the second lens unit L2 to the image side. In the case of a lens having a long focal length, it is difficult to focus by moving the entire lens because the lens is large and heavy.

  Therefore, in this embodiment, focusing is performed by moving some small and light lens groups other than the first lens group L1. When the imaging optical system OL vibrates, the blur of the captured image is corrected by moving the thirty-second lens unit L32 as a movable lens unit in a direction having a component perpendicular to the optical axis. The positive lens G1 of the eleventh lens unit L11 is made of OHARA INC. Trade name S-TIH1, and satisfies the conditional expressions (1), (2), and (3). The eleventh lens unit L11 of Example 2 is about 462 g. However, if the product name S-FSL5 of OHARA INC. Is used under the same conditions, it becomes about 525 g, which is about 63 g in weight.

  The twelfth lens unit L12 includes, in order from the object side to the image side, a meniscus positive lens having a convex surface facing the object side, a cemented lens in which a negative lens and a positive lens are cemented, and a positive lens. The cemented lens constitutes a diffractive optical element DOE, and has a diffractive optical part D on the cemented surface of the cemented lens. By using the diffractive optical element DOE for the first lens unit L1, chromatic aberration can be easily corrected. As a result, a glass material having a lower specific gravity can be used for the lens located on the image side than the eleventh lens unit L11, thereby facilitating weight reduction of the entire system.

  When the distance between the eleventh lens group L11 and the twelfth lens group L12 satisfies the conditional expression (4), the number of lenses of the eleventh lens group L11 having a large aperture on the object side is reduced, and the imaging optical system is reduced in weight. ing. The second lens unit L2 is composed of one negative lens. In the third lens unit L3, the thirty-first lens unit L31 includes a cemented lens in which a negative lens and a positive lens are cemented. The thirty-second lens unit L32 includes a cemented lens obtained by cementing a positive lens and a negative lens, and a negative lens. The thirty-third lens unit L33 includes a positive lens and a cemented lens in which a negative lens and a positive lens are cemented.

[Example 3]
The third embodiment is a telephoto imaging optical system having a diagonal field angle of about 6.32 degrees. The positive lens G1 of the eleventh lens unit L11 is made of OHARA INC. Product name S-TIH53, and satisfies the conditional expressions (1), (2), and (3). The eleventh lens unit L11 is about 441 g. However, if the product name S-FSL5 of OHARA INC. Is used under the same conditions, the weight is about 493 g, which is about 52 g. The twelfth lens unit L12 includes a positive lens, a cemented lens obtained by cementing a negative lens and a positive lens, and a positive lens. Other configurations are the same as those of the second embodiment.

[Example 4]
The fourth embodiment is a telephoto imaging optical system having a diagonal field angle of about 6.32 degrees. The positive lens G1 of the eleventh lens unit L11 includes a product name S-TIM22 of OHARA INC. And satisfies conditional expressions (1), (2), and (3). The eleventh lens unit L11 is about 404 g. However, if the product name S-FSL5 of OHARA INC. Is used under the same conditions, it becomes about 451 g, which is about 47 g in weight. Other configurations are the same as those in the second embodiment.

[Example 5]
The fifth embodiment is a telephoto imaging optical system having a diagonal field angle of about 3.18 degrees. The fifth exemplary embodiment includes, in order from the object side to the image side, a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power, and a third lens unit L3 having a negative refractive power. The first lens unit L1 includes an eleventh lens unit L11 and a twelfth lens unit L12 with the widest air gap as a boundary. An aperture stop SP is provided between the second lens unit L2 and the third lens unit L3. The third lens unit L3 includes a thirty-first lens unit L31 having a positive refractive power, a thirty-second lens unit L32 having a negative refractive power, and a thirty-third lens unit L33 having a positive refractive power.

  Focusing from an infinitely distant object to a close object is performed by moving the second lens unit L2 to the image side. The correction of the shake of the captured image when the imaging optical system vibrates is performed by moving the thirty-second lens unit L32 as a movable lens unit in a direction perpendicular to the optical axis. The positive lens G1 of the eleventh lens unit L11 is made of OHARA Co., Ltd. trade name S-TIM27 and satisfies conditional expressions (1), (2), and (3). The eleventh lens unit L11 is about 332 g. However, if the product name S-FSL5 of OHARA INC. Is used under the same conditions, the weight is about 360 g, which is about 28 g.

  The twelfth lens unit L12 includes, in order from the object side to the image side, a meniscus positive lens having a convex surface facing the object side, and a cemented lens in which a negative lens and a positive lens are cemented. The cemented lens constitutes a diffractive optical element fDOE. A diffractive optical part DOE is provided on the object side surface of the cemented lens. When the distance between the eleventh lens group L11 and the twelfth lens group L12 satisfies the conditional expression (4), the number of lenses of the eleventh lens group L11 having a large aperture on the object side is reduced, and the imaging optical system is reduced in weight. ing.

  The second lens unit L2 includes a cemented lens of a positive lens and a negative lens. In the third lens unit L3, the thirty-first lens unit L31 includes a cemented lens in which a negative lens and a positive lens are cemented. The thirty-second lens unit L32 includes a cemented lens obtained by cementing a positive lens and a negative lens, and a positive lens. The thirty-third lens unit L33 includes a positive lens, a cemented lens in which the positive lens and the negative lens are cemented, a negative lens, and a cemented lens in which the positive lens and the negative lens are cemented.

  Here, the configuration of the diffractive optical element DOE used in the imaging optical system of each embodiment will be described. The diffractive optical part D constituting the diffractive optical element DOE disposed in the imaging optical system is composed of a diffraction grating that is rotationally symmetric with respect to the optical axis.

  FIG. 7A is an enlarged cross-sectional view of a part of the diffractive optical part of the diffractive optical element 31. In FIG. 7A, a diffraction grating (diffractive optical part) 33 composed of one layer is provided on a substrate (transparent substrate) 32. FIG. 7B is an explanatory diagram showing the characteristics of the diffraction efficiency of the diffractive optical element 31. In FIG. 7B, the horizontal axis represents wavelength and the vertical axis represents diffraction efficiency. Note that the diffraction efficiency is the ratio of the amount of diffracted light to the total transmitted light beam, and the reflected light at the boundary surface of the grating portion 3a is not considered here because the explanation is complicated.

The optical material of the diffraction grating 33 is an ultraviolet curable resin (refractive index n _d = 1.513, Abbe number ν _d = 51.0). The grating thickness d ₁ of the grating part 3a is set to 1.03 μm so that the diffraction efficiency of + 1st order diffracted light is the highest at a wavelength of 530 nm. That is, the design order is + 1st order and the design wavelength is 530 nm. In FIG. 7B, the diffraction efficiency of the + 1st order diffracted light is indicated by a solid line. Further, in FIG. 7B, the diffraction efficiencies of diffraction orders in the vicinity of the design order (0th order and + 2nd order of + 1st order ± 1st order) are also shown. As can be seen from the figure, the diffraction efficiency at the design order is highest near the design wavelength, and gradually decreases at other wavelengths.

  The decrease in diffraction efficiency at this design order becomes diffracted light of other orders (unnecessary light), which causes flare. When the diffractive optical element 31 is used at a plurality of locations in the optical system, a decrease in diffraction efficiency at a wavelength other than the design wavelength leads to a decrease in transmittance.

  Next, a laminated diffractive optical element in which a plurality of diffraction gratings made of different materials are laminated will be described. 8A is a partially enlarged cross-sectional view of the laminated diffractive optical element 31, and FIG. 8B is the wavelength of the diffraction efficiency of the + 1st order diffracted light of the diffractive optical element 31 shown in FIG. 8A. It is a figure showing dependence.

In the diffractive optical element 31 shown in FIG. 8A, a first diffraction grating 104 made of an ultraviolet curable resin (refractive index n _d = 1.499, Abbe number ν _d = 54) is formed on a substrate 102. Further, a second diffraction grating 105 (refractive index n _d = 1.598, Abbe number ν _d = 28) is formed thereon. In this combination of materials, the grating thickness d ₁ of the grating portion 104 a of the first diffraction grating 104 is d ₁ = 13.8 μm, and the grating thickness d ₂ of the grating portion 105 a of the second diffraction grating 105 is d ₂ = 10. 5 μm.

  As can be seen from FIG. 8B, by using the diffractive optical element 31 including the diffraction gratings 104 and 105 having a laminated structure, 95% or more in the entire wavelength range (in this case, the visible region) in the diffracted light of the designed order. High diffraction efficiency is obtained. Note that, as the diffractive optical element 31 having a laminated structure, the grating thicknesses of the two layers 104 and 105 may be equal depending on the combination of materials as shown in FIG. In this case, two diffraction grating layers may be arranged with an air layer therebetween.

The diffractive optical part is provided on the optical surface, but its base may be spherical, flat or aspheric. Further, the diffractive optical part may be made of a so-called replica aspherical surface, which is a method of attaching a film such as a plastic as a diffractive optical part (diffractive surface) to these optical surfaces. As for the shape of the diffraction grating, the phase φ (H) at the distance H from the optical axis is expressed by the following equation when the phase coefficient of the 2i-order term is C _2i . Where m is the diffraction order and λ ₀ is the reference wavelength.

In general, the Abbe number (dispersion value) ν _d of a refractive optical material such as a lens or a prism is expressed by the following equation when the refractive power at each wavelength of d, C, and F lines is N _d , N _C , and N _F. Is done.

ν _d = (N _d −1) / (N _F −N _C )> 0 (b)
On the other hand, the Abbe number ν _d of the diffractive optical unit is ν _d = λ _d / (λ _F −λ _C ) (c) when the wavelengths of the d, C, and F lines are λ _d , λ _C , and λ _F. )
And ν _d = −3.45. Thereby, the dispersibility at an arbitrary wavelength has an adverse effect on the refractive optical element.

Further, the refractive power φ of the paraxial temporary diffracted light (m = 1) at the reference wavelength of the diffractive optical part is obtained when the coefficient of the second order term is C ₂ from the previous formula (a) representing the phase of the diffractive optical part. , Φ _D = −2 · C ₂ . Further, when the arbitrary wavelength is λ and the reference wavelength is λ ₀ , the refractive power change with respect to the reference wavelength of the arbitrary wavelength is expressed by the following equation.

_{φ D '= (λ / λ} 0) × (-2 · C 2) ··· (d)
Thus, as a feature of the diffractive optical part, by varying the phase coefficients C ₂ of Equation (a), large dispersion can be obtained by a weak paraxial refractive power change. This means that chromatic aberration is corrected without greatly affecting various aberrations other than chromatic aberration.

With respect to the higher order coefficients of the phase coefficient C ₄ and later, the refractive power changes to the light incident height variation of the diffractive optical part can be obtained an effect similar to aspheric. At the same time, it is possible to change the refractive power at an arbitrary wavelength with respect to the reference wavelength according to the change in the incident light height. Therefore, it is effective for correcting lateral chromatic aberration. Further, as in the first lens unit L1 of the imaging optical system of the present invention, when the axial light beam passes through the lens surface, the diffractive optical element DOE is disposed on a surface that passes through a position where the height from the optical axis is high. It is also effective in correcting axial chromatic aberration.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

Numerical examples 1 to 5 corresponding to the first to fifth embodiments of the present invention are shown below. In each numerical example, i indicates the order of the surfaces from the object side, r _i is the radius of curvature of the i-th surface from the object side, d _i is the i-th and i + 1-th distance from the object side, nd _i and νd _i are the refractive index and Abbe number of the i-th optical member. The focal length, the F number, and the angle of view (degree) each represent a time when the object is focused on an infinite object. The back focus BF is represented by the distance from the final surface (glass block surface) to the image surface.

  The diffractive optical element (diffractive surface) is expressed by giving a phase coefficient of the phase function of the above-described equation (a). Aspherical shape is X axis in the optical axis direction, H axis in the direction perpendicular to the optical axis, positive light traveling direction, R is paraxial radius of curvature, k is eccentricity, A4, A6, A8, A10, A12 When the aspheric coefficient is used,

It is expressed by the following formula. For example, the display of “ ^ez ” means “10 ^−Z ”. Table 1 shows the relationship between the above-described conditional expressions and various numerical values in the numerical examples.

(Numerical example 1)
Unit mm

Surface data surface number rd nd νd Effective diameter
1 * 128.642 18.06 1.74000 28.3 135.15
2 426.327 59.42 133.08
3 105.039 20.08 1.43387 95.1 91.30
4 -209.070 0.12 87.60
5 -234.431 5.00 1.75520 27.5 86.44
6 53.610 0.78 73.93
8 734.607 39.61 73.18
9 * 86.436 7.46 1.75520 27.5 58.96
10 551.632 5.00 57.47
11 2774.965 3.50 1.73800 32.3 53.84
12 59.115 63.70 49.76
13 (Aperture) ∞ 3.00 41.96
14 238.294 3.00 1.84666 23.8 41.43
15 97.968 6.54 1.72000 43.7 40.79
16 -115.489 6.38 40.44
17 169.643 5.50 1.80000 29.8 37.97
18 -129.634 3.00 1.49700 81.5 37.47
19 44.653 5.41 35.42
20 -98.393 2.50 1.62041 60.3 35.43
21 63.955 3.00 36.54
22 102.356 4.00 1.72047 34.7 38.03
23 -1201.392 0.10 38.49
24 56.158 8.00 1.51633 64.1 39.89
25 -107.572 3.00 1.74400 44.8 39.80
26 3138.611 5.00 39.90
27 ∞ 2.20 1.51633 64.1 40.12
28 ∞ 71.21 40.18
Image plane ∞

Aspheric data 1st surface
K = 0.00000e + 000 A 4 = 2.03636e-010 A 6 = 1.90616e-013 A 8 = -9.77158e-017 A10 = 2.18671e-020 A12 = -2.50375e-024

9th page
K = 0.00000e + 000 A 4 = 1.39478e-008 A 6 = 1.54589e-012 A 8 = 5.64272e-014 A10 = -4.60026e-017 A12 = 1.09187e-020

Various data Zoom ratio 1.00

Focal length 392.00
F number 2.90
Half angle of view (degrees) 3.16
Statue height 21.64
Total lens length 372.96
BF 71.21

Entrance pupil position 980.93
Exit pupil position -46.60
Front principal point position 68.68
Rear principal point position -320.79

Zoom lens group data group Start surface Focal length Lens configuration length Front principal point position Rear principal point position
1 1 172.10 168.91 133.97 -100.16
2 11 -81.89 3.50 2.06 0.04
3 13 118.88 12.54 6.78 -1.71
4 17 -50.45 16.41 11.97 -0.38
5 22 68.66 22.30 0.37 -15.41

Single lens Data lens Start surface Focal length
1 1 242.70
2 3 164.32
3 5 -57.35
4 7 133.43
5 9 134.79
6 11 -81.89
7 14 -198.44
8 15 74.57
9 17 92.61
10 18 -66.45
11 20 -62.11
12 22 131.08
13 24 72.67
14 25 -139.74
15 27 0.00

(Numerical example 2)
f = 391.99mm Fno = 2.89 2ω = 6.32 °
Surface data surface number rd nd νd Effective diameter
1 * 163.873 17.25 1.71736 29.5 135.64
2 3022.122 50.00 134.36
3 228.252 8.00 1.48749 70.2 101.74
4 * 726.256 29.80 99.40
5 -883.297 4.48 1.84666 23.8 79.41
6 (Diffraction) 75.756 15.70 1.48749 70.2 74.29
7 -350.562 23.43 73.62
8 101.045 9.71 1.73800 32.3 62.80
9 -546.387 1.00 60.95
10 481.627 2.50 1.84666 23.8 58.19
11 * 56.655 70.00 53.52
12 (Aperture) ∞ 4.00 41.01
13 76.089 2.60 1.84666 23.8 39.71
14 38.026 10.00 1.74320 49.3 37.93
15 397.906 1.88 37.48
16 877.047 4.43 1.84666 23.8 37.36
17 -77.836 1.80 1.65844 50.9 37.24
18 66.096 4.06 36.42
19 -185.276 3.54 1.72000 46.0 36.53
20 90.701 1.50 37.71
21 123.242 3.48 1.73800 32.3 38.40
22 -191.063 0.10 38.63
23 -367.117 2.60 1.49700 81.5 38.77
24 51.731 7.35 1.69895 30.1 40.21
25 -314.722 4.50 40.40
26 ∞ 2.20 1.51633 64.1 50.00
27 ∞ 50.00

Aspheric data 1st surface
K = 0.00000e + 000 A 4 = -1.15560e-008 A 6 = -4.53533e-013 A 8 = 8.83305e-019 A10 = -6.93761e-021 A12 = 5.45233e-025

4th page
K = 0.00000e + 000 A 4 = 6.12718e-008 A 6 = -4.88171e-012 A 8 = 3.47625e-016 A10 = -2.35354e-019 A12 = 4.96639e-023

6th surface (diffractive surface)
C 2 = -6.60024e-005 C 4 = -3.66616e-009 C 6 = -1.78616e-012 C 8 = 1.13567e-014
C10 = -1.06293e-017 C12 = 4.64679e-021 C14 = -8.74708e-025

11th page
K = 0.00000e + 000 A 4 = -1.43713e-007 A 6 = -5.90038e-011 A 8 = -4.01550e-015 A10 = 1.91590e-018 A12 = -4.74095e-021

Focal length 391.99
F number 2.89
Half angle of view (degrees) 3.16
Statue height 21.64
Total lens length 367.00
BF 81.09

Entrance pupil position 926.99
Exit pupil position -41.65
Front principal point position 67.10
Rear principal point position -310.90

Lens group data group Start surface Focal length Lens configuration length Front principal point position Rear principal point position
1 1 146.19 158.37 135.22 -84.47
2 10 -76.04 2.50 1.54 0.18
3 12 271.01 54.03 12.25 -28.82

Single lens Data lens Start surface Focal length
1 1 240.93
2 3 679.24
3 5 -83.14
4 6 127.21
5 8 116.29
6 10 -76.04
7 13 -92.68
8 14 55.91
9 16 84.62
10 17 -54.02
11 19 -84.12
12 21 101.99
13 23 -91.04
14 24 64.09

(Numerical Example 3)
f = 392.00mm Fno = 2.89 2ω = 6.32 °
Surface data surface number rd nd νd Effective diameter
1 * 216.521 13.58 1.84666 23.8 135.64
2 3022.122 76.40 134.59
3 105.338 17.00 1.48749 70.2 91.92
4 * -252.532 3.80 89.98
5 -432.434 4.48 1.84666 23.8 83.40
6 (Diffraction) 66.885 14.50 1.48749 70.2 74.61
7 296.892 21.77 72.95
8 111.993 9.50 1.72825 28.5 64.73
9 -277.201 1.00 63.43
10 513.083 2.50 1.84666 23.8 59.50
11 * 57.414 70.60 54.53
12 (Aperture) ∞ 4.00 39.55
13 76.948 2.60 1.84666 23.8 38.05
14 39.114 6.00 1.74320 49.3 36.37
15 312.248 1.88 36.20
16 309.797 4.43 1.84666 23.8 36.08
17 -100.056 1.80 1.65844 50.9 35.88
18 57.544 4.37 35.03
19 -149.184 3.54 1.72000 46.0 35.15
20 99.237 2.50 36.47
21 94.711 4.65 1.73800 32.3 38.37
22 -110.876 0.56 38.55
23 -85.310 2.60 1.49700 81.5 38.56
24 82.043 7.35 1.69895 30.1 39.98
25 -182.892 4.50 40.40
26 ∞ 2.20 1.51633 64.1 50.00
27 ∞ 50.00

Aspheric data 1st surface
K = 0.00000e + 000 A 4 = -1.08292e-008 A 6 = -2.39684e-013 A 8 = -2.11946e-017 A10 = 3.31560e-022 A12 = -7.12321e-026

4th page
K = 0.00000e + 000 A 4 = 1.85199e-007 A 6 = -2.05648e-011 A 8 = -1.10002e-015 A10 = 9.23235e-019 A12 = -9.69362e-023

6th surface (diffractive surface)
C 2 = -4.01382e-005 C 4 = -2.11690e-009 C 6 = -1.22963e-012 C 8 = -1.45881e-015
C10 = 3.40204e-018 C12 = -9.44823e-022 C14 = -1.04292e-025

11th page
K = 0.00000e + 000 C 4 = -1.54313e-007 C 6 = -6.50718e-011 C 8 = 6.03529e-014 C10 = -9.95895e-017 C12 = 4.40174e-020

Focal length 392.00
F number 2.89
Half angle of view (degrees) 3.16
Statue height 21.64
Total lens length 367.00
BF 78.90

Entrance pupil position 920.27
Exit pupil position -43.41
Front principal point position 55.94
Rear principal point position-313.10

Lens group data group Start surface Focal length Lens configuration length Front principal point position Rear principal point position
1 1 139.52 161.04 129.95 -79.38
2 10 -76.55 2.50 1.53 0.17
3 12 315.14 52.97 24.16 -17.24

Single lens Data lens Start surface Focal length
1 1 274.86
2 3 154.89
3 5 -68.51
4 6 171.09
5 8 110.67
6 10 -76.55
7 13 -97.01
8 14 59.61
9 16 89.77
10 17 -55.23
11 19 -82.28
12 21 69.88
13 23 -83.72
14 24 81.97

(Numerical example 4)
f = 392.10mm Fno = 2.89 2ω = 6.32 °
Surface data surface number rd nd νd Effective diameter
1 * 172.993 16.50 1.64769 33.8 135.64
2 4015.582 50.00 134.54
3 130.324 8.00 1.48749 70.2 104.01
4 * 219.200 29.80 101.83
5 298.174 4.48 1.84666 23.8 84.15
6 (Diffraction) 83.891 15.30 1.43875 94.9 78.65
7 -1108.678 9.72 76.99
8 95.119 7.50 1.72000 46.0 68.10
9 1029.661 2.00 67.00
10 6816.800 2.50 1.72047 34.7 65.27
11 * 54.342 94.24 58.79
12 (Aperture) ∞ 0.10 41.13
13 107.083 2.40 1.84666 23.8 40.70
14 43.824 6.21 1.74320 49.3 39.24
15 -502.587 1.88 38.94
16 129.128 3.91 1.84666 23.8 37.13
17 -107.119 2.40 1.69350 50.8 36.73
18 54.092 5.03 35.09
19 -138.717 2.40 1.76200 40.1 35.17
20 85.451 1.50 36.04
21 88.511 3.48 1.73800 32.3 37.05
22 -330.863 5.57 37.22
23 1514.471 2.50 1.49700 81.5 38.52
24 55.271 6.46 1.65412 39.7 39.30
25 -917.816 15.01 39.42
26 ∞ 2.20 1.51633 64.1 50.00
27 ∞ 50.00

Aspheric data 1st surface
K = 0.00000e + 000 A 4 = -1.06948e-008 A 6 = -5.32361e-013 A 8 = 5.75618e-017 A10 = -1.12738e-020 A12 = 6.05156e-025

4th page
K = 0.00000e + 000 A 4 = 4.99233e-008 A 6 = -1.53987e-012 A 8 = 1.21213e-015 A10 = -3.88266e-019 A12 = 4.06199e-023

6th surface (diffractive surface)
C 2 = -5.21738e-005 C 4 = 4.53753e-009 C 6 = -1.00852e-011 C 8 = 1.44659e-014
C10 = -1.08013e-017 C12 = 4.09807e-021 C14 = -6.24270e-025

11th page
K = 0.00000e + 000 A 4 = -2.58654e-007 A 6 = -3.79517e-011 A 8 = -1.39593e-013 A10 = 1.03639e-016 A12 = -3.94251e-020

Focal length 392.01
F number 2.89
Half angle of view (degrees) 3.16
Statue height 21.64
Total lens length 369.01
BF 67.92

Entrance pupil position 969.91
Exit pupil position -50.28
Front principal point 61.85
Rear principal point position -324.08

Lens group data group Start surface Focal length Lens configuration length Front principal point position Rear principal point position
1 1 133.21 141.30 97.25 -70.02
2 10 -76.04 2.50 1.46 0.01
3 12 306.79 61.05 5.08 -45.11

Single lens Data lens Start surface Focal length
1 1 278.65
2 3 640.45
3 5 -141.25
4 6 175.20
5 8 145.07
6 10 -76.04
7 13 -89.17
8 14 54.50
9 16 69.68
10 17 -51.51
11 19 -69.07
12 21 94.96
13 23 -115.49
14 24 79.91

(Numerical example 5)
f = 778.931mm Fno = 5.80 2ω = 3.18 °
Surface data surface number rd nd νd Effective diameter
1 * 176.164 13.00 1.63980 34.5 134.61
2 574.915 85.00 133.39
3 154.275 7.00 1.48749 70.2 100.46
4 * 523.687 44.10 99.93
5 (Diffraction) -830.164 5.00 1.74000 28.3 76.49
6 89.334 11.47 1.49700 81.5 72.69
7 -313.391 71.79 72.39
8 90.298 2.77 1.48749 70.2 38.00
9 -1241.073 1.80 1.73800 32.3 37.74
10 * 68.557 46.77 36.15
11 (Aperture) ∞ 0.10 25.83
12 158.106 1.60 1.84666 23.8 25.71
13 22.120 10.00 1.62588 35.7 24.73
14 -82.695 2.00 24.46
15 -162.739 4.00 1.80809 22.8 23.78
16 -62.491 1.60 1.83481 42.7 23.59
17 45.627 1.00 23.87
18 38.510 4.00 1.48749 70.2 24.91
19 59.950 2.10 25.57
20 70.095 4.00 1.66680 33.0 26.65
21 513.845 8.59 27.08
22 -133.189 6.00 1.69895 30.1 29.29
23 -26.016 3.00 1.43875 94.9 29.84
24 181.038 13.51 30.38
25 -163.464 1.60 1.43875 94.9 32.43
26 46.849 1.00 33.41
27 50.137 10.00 1.71736 29.5 34.00
28 -28.613 3.00 1.80809 22.8 34.06
29 -210.355 24.93 34.95
30 ∞ 2.20 1.51633 64.1 50.00
31 ∞ 50.00

Aspheric data 1st surface
K = 0.00000e + 000 A 4 = -3.45280e-011 A 6 = 4.75067e-014 A 8 = 1.45809e-018 A10 = -2.66402e-021 A12 = 2.61793e-025

4th page
K = 0.00000e + 000 A 4 = 3.04821e-008 A 6 = 6.61574e-013 A 8 = -1.16903e-016 A10 = -1.25055e-019 A12 = 3.19811e-023

5th surface (diffractive surface)
C 2 = -4.41908e-005 C 4 = 3.38675e-009 C 6 = -2.45408e-012 C 8 = 2.12494e-015
C 10 = -4.99016e-019 C 12 = -5.84869e-023

10th page
K = 0.00000e + 000 A 4 = 6.89746e-009 A 6 = -2.35869e-010 A 8 = 6.62241e-013 A10 = -5.49000e-016 A12 = -2.07792e-018 A14 = 3.51982e-021

Focal length 778.93
F number 5.80
Half angle of view (degrees) 1.59
Statue height 21.60
Total lens length 485.99
BF 93.05

Entrance pupil position 1708.47
Exit pupil position -102.61
Front principal point position-613.55
Rear principal point position -685.88

Lens group data group Start surface Focal length Lens configuration length Front principal point position Rear principal point position
1 1 313.99 165.57 -14.81 -152.47
2 8 -185.19 4.57 5.85 2.86
3 11 -4942.82 104.24 -1190.94 -1671.58

Single lens Data lens Start surface Focal length
1 1 392.00
2 3 445.86
3 5 -109.82
4 6 141.21
5 8 172.79
6 9 -87.98
7 12 -30.54
8 13 28.95
9 15 123.34
10 16 -31.38
11 18 208.15
12 20 121.29
13 22 45.22
14 23 -51.62
15 25 -82.80
16 27 26.82
17 28 -41.29

  Next, an embodiment in which the imaging optical system of the present invention is applied to an imaging apparatus (camera system) will be described with reference to FIG. FIG. 9 is a schematic view of the main part of a single-lens reflex camera.

  In FIG. 9, reference numeral 10 denotes an imaging lens having the imaging optical system 1 of any one of the first to fifth embodiments. The photographing optical system 1 is held by a lens barrel 2 that is a holding member. Reference numeral 20 denotes a camera body. The camera body includes a quick return mirror 3 that reflects the light beam from the imaging lens 10 upward, a focusing plate 4 that is disposed at an image forming position of the imaging lens 10, and a pentagon that converts an inverted image formed on the focusing plate 4 into an erect image. A roof prism 5 is provided. Further, it is constituted by an eyepiece 6 for observing the erect image.

  Reference numeral 7 denotes a photosensitive surface, on which an image pickup device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor, or a silver salt film is arranged. At the time of photographing, the quick return mirror 3 is retracted from the optical path, and an image is formed on the photosensitive surface 7 by the photographing lens 10. In this manner, by applying the imaging optical system of Embodiments 1 to 5 to an imaging apparatus such as a photographic camera, a video camera, or a digital still camera, a lightweight imaging apparatus having high optical performance is realized.

  Note that the photographing optical system of the present invention can also be applied to an image pickup apparatus without a quick return mirror.

L0 photographing optical system L1 first lens group L2 second lens group L3 third lens group L11 eleventh lens group L12 twelfth lens group L31 thirty-first lens group L32 is thirty-second lens group L33 thirty-third lens group DOE diffractive optical element D Diffraction optics

Claims (9)

In order from the object side to the image side, the first lens group having a positive refractive power, the second lens group having a negative refractive power, an aperture stop, and a third lens group are configured. During focusing, the first lens group and the first lens group The three lens groups are stationary, the second lens group moves, and the first lens group has an eleventh lens group having a positive refractive power on the object side and a twelfth lens on the image side with the widest air interval as a boundary. The eleventh lens group is composed of one positive lens G1, and the refractive index of the material of the positive lens G1 is NG1, the specific gravity is dG1, the focal length is fG1, and the focal length of the entire system is f. and when,
dG1 <−3.1 × (NG1) ² + 14.7 × NG1-12.8
0.4 <fG1 / f <0.8
An imaging optical system characterized by satisfying the following conditional expression: 1.5 <NG1
The imaging optical system according to claim 1, wherein the following conditional expression is satisfied. When the distance on the optical axis between the eleventh lens group and the twelfth lens group is D1ab, and the distance from the lens surface closest to the object side to the image plane is L,
0.05 <D1ab / L <0.40
The imaging optical system according to claim 1, wherein the following conditional expression is satisfied. The twelfth lens group includes at least one negative lens. When the negative lenses included in the twelfth lens group are counted from the object side, the focal length of the jth negative lens Gnj is fnj, and the Abbe number of the material is When νdnj,
−0.251 ≦ Σ (f / (fnj × νdnj)) <− 0.15
The imaging optical system according to claim 1, wherein the conditional expression is satisfied. The twelfth lens group includes at least one positive lens, and when the Abbe number of the material of the positive lens is νd12p,
80 <νd12p
The imaging optical system according to claim 1, wherein the conditional expression is satisfied. 6. The imaging optical system according to claim 1, further comprising at least one diffractive optical element closer to the object side than a position where the pupil paraxial ray intersects the optical axis. In order from the object side to the image side, the third lens group is a thirty-first lens group having a positive refracting power, and a thirty-second lens having a negative refracting power that moves so as to have a component perpendicular to the optical axis in correcting image blur. The imaging optical system according to claim 1, comprising a lens group and a 33rd lens group having a positive refractive power. The imaging optical system according to any one of claims 1 to 7, wherein the second lens group includes a single negative lens or a cemented lens in which a positive lens and a negative lens are cemented. . An imaging apparatus comprising: the imaging optical system according to claim 1; and an imaging element that receives an image formed by the imaging optical system.