JP2018087965A - Image capturing optical system and image capturing device having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image capturing optical system which can easily obtain high optical performance while achieving a reduction in size of the entire system and in weight of lenses.SOLUTION: An image capturing optical system consists of a first lens group having positive refractive power, a second lens group having negative refractive power, an aperture diaphragm, and a third lens group arranged in the order from an object side to an image side where the second lens group is configured to move while focusing. The first lens group consists of a 1a lens element having positive refractive power, a 1b lens element having negative refractive power, and a 1c lens element having positive refractive power arranged in the order from the object side to the image side. A focal length f1b of the 1b lens element and a focal length f of the entire system are individually set appropriately.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an imaging optical system, and is suitable for an imaging apparatus such as a digital still camera, a digital video camera, a surveillance camera, a TV camera, and a silver salt film camera.

  Conventionally, as a long focal length image pickup optical system, a so-called telephoto type image pickup optical system (telephoto type) 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. Lens) is known.

  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 (becomes longer). In particular, the increase in the weight of the front lens unit disposed on the object side of the aperture stop is remarkable. Further, among various aberrations, particularly axial chromatic aberration is generated among spherical aberration and chromatic aberration. Various imaging optical systems have been proposed in which the chromatic aberration is achromatic using a low dispersion material having anomalous partial dispersion such as fluorite.

  As a method of reducing the lens weight while satisfactorily correcting various aberrations including chromatic aberration of the imaging optical system, a method using a diffractive optical part having a diffractive action as a part of the imaging optical system is known. Glass material with a higher refractive index than low-dispersion materials such as fluorite, which uses the diffraction action and reduces the number of lenses in the front lens group, which was conventionally required for aberration correction. An imaging optical system is known in which the entire system is reduced in size and weight (Patent Documents 1 and 2).

  Patent Document 1 discloses a telephoto lens having a focal length of about 600 mm in which a diffractive optical part (diffraction surface) is provided in a front lens group having a positive refractive power. In Patent Document 2, a diffractive optical unit is provided in a front lens group having a positive refractive power, and the focal length of about 400 mm is achieved by reducing the weight of the entire system by appropriately setting the specific gravity of the lens material constituting the front lens group. The telephoto lens is disclosed.

JP 2012-88427 A JP 2014-56195 A

  In general, a telephoto type imaging optical system is increased in size and weight as the entire system becomes larger as the focal length becomes longer. For this reason, in the telephoto imaging optical system, it is important to reduce the size and weight of the entire lens system. Further, in the telephoto imaging optical system, various aberrations such as chromatic aberration generally occur as the focal length increases.

  In general, in the telephoto imaging optical system, the front lens group having a positive refractive power is likely to be enlarged, so that the entire system can be reduced in size and weight while correcting chromatic aberration and obtaining high optical performance. It is important to set the lens configuration of the front lens group appropriately. If the lens configuration of the front lens group is inappropriate, the entire system becomes large and various aberrations increase, making it difficult to obtain high optical performance.

  An object of the present invention is to provide an imaging optical system that can easily obtain high optical performance while reducing the size of the entire system and reducing the weight of the lens.

The imaging optical system of the present invention includes 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, which are arranged in order from the object side to the image side. In the imaging optical system in which the second lens group moves during focusing,
The first lens group includes a first-a lens element having a positive refractive power, a first-b lens element having a negative refractive power, and a first-c lens element having a positive refractive power, which are arranged in order from the object side to the image side. When the focal length of the 1b lens element is f1b and the focal length of the entire system is f,
−0.65 <f1b / f <−0.05
It satisfies the following conditional expression.

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

Lens sectional view of Example 1 Aberration diagram of Example 1 at infinite object distance Lens sectional view of Example 2 Aberration diagram of Example 2 at infinite object distance Lens sectional view of Example 3 Aberration diagram of Example 3 at infinite object distance Schematic diagram of main parts of an imaging apparatus 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 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, which are arranged in order from the object side to the image side. . The second lens group moves during focusing.

  FIG. 1 is a lens cross-sectional view of the image pickup optical system according to the first embodiment of the present invention. FIG. 2 is a longitudinal aberration diagram of the image pickup optical system according to the first embodiment of the present invention. Example 1 is an imaging optical system having an F number of 5.80 and an imaging field angle of 3.18 degrees. FIG. 3 is a lens cross-sectional view of the image pickup optical system according to the second embodiment of the present invention. FIG. 4 is a longitudinal aberration diagram of the image pickup optical system according to the second embodiment of the present invention. Example 2 is an imaging optical system having an F number of 5.80 and an imaging field angle of 3.18 degrees.

  FIG. 5 is a lens cross-sectional view of the image pickup optical system according to the third embodiment of the present invention. FIG. 6 is a longitudinal aberration diagram of the image pickup optical system according to the third embodiment of the present invention. Example 3 is an imaging optical system having an F number of 5.80 and an imaging field angle of 3.18 degrees. FIG. 7 is a schematic view of the main part of the imaging apparatus of the present invention.

  In the lens cross-sectional view, the left side is the object side, and the right side is the image side. L0 is an imaging optical system, L1 is a first lens group having a positive refractive power, L2 is a second lens group having a negative refractive power, and L3 is a third lens group. L1a is a 1a lens element having a positive refractive power, L1b is a 1b lens element having a negative refractive power, and L1c is a 1c lens element having a positive refractive power. Here, the lens element refers to a lens system including a single lens or a cemented lens obtained by cementing a plurality of lenses.

  DOE is a diffractive optical part (diffraction surface), and SP is an aperture stop. IP is an image plane corresponding to an image pickup surface of a solid-state image pickup device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor. G represents a parallel plate such as a low-pass filter, and is disposed in front of the imaging surface as necessary.

  In the spherical aberration diagram, Fno is an F number. The solid line d is d-line (wavelength 587.6 nm), and the alternate long and short dash line g is g-line (wavelength 435.8 nm). In the astigmatism diagram, the dotted line ΔM is the meridional image plane at the d line, and the solid line ΔS is the sagittal image plane at the d line. The distortion diagram shows the d-line. The lateral chromatic aberration diagram shows the g-line. ω is a half angle of view (degree).

  Hereinafter, the lens configuration of the imaging optical system L0 according to the present invention that can easily obtain the light weight and high image quality will be described.

  The imaging optical system L0 of the present invention includes a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power, an aperture stop SP, and a positive or negative lens disposed in order from the object side to the image side. A so-called telephoto lens arrangement including the third lens unit L3 having refractive power is employed. Thereby, good optical performance is obtained while shortening the total lens length of the entire system. The first lens unit L1 includes a 1a lens element L1a composed of one positive lens, a 1b lens element L1b composed of a cemented lens obtained by cementing a positive lens and a negative lens, and a first c lens element L1c composed of a positive lens. Has been.

  In order to reduce the weight of the entire system, it is important to reduce the effective diameter while reducing the number of lenses in the object side lens group. The 1a lens element L1a arranged on the most object side is composed of one positive lens.

  In general, the effective diameter of the front lens of a telephoto imaging optical system is determined by the F number, and becomes the lens with the largest effective diameter in the imaging optical system. In order to reduce the weight of the entire system, it is important to reduce the number of lenses having a large effective diameter, and this configuration is effective for reducing the weight of the imaging optical system.

  If the 1a lens element L1a is composed of one positive lens, chromatic aberration is likely to occur. Therefore, the 1b lens element L1b is configured with a negative refractive power. With this configuration, the chromatic aberration generated from the 1a lens element L1a is effectively corrected.

The first c lens element L1c has a positive refractive power. The 1b lens element L1b has negative refractive power (power), and it is necessary to converge the axial luminous flux in order to reduce the diameter and weight of the second lens unit L2. This configuration is effective for reducing the weight of the imaging optical system. The focal length of the first lens element L1b is f1b, and the focal length of the entire system is f. At this time,
−0.65 <f1b / f <−0.05 (1)
The following conditional expression is satisfied.

  Conditional expression (1) is for obtaining high image quality while reducing the weight of the entire system. If the negative focal length of the 1b lens element L1b becomes too short beyond the upper limit of conditional expression (1) (the absolute value of the negative focal length becomes too small), various aberrations such as spherical aberration and chromatic aberration occur. It increases and it becomes difficult to obtain high image quality. If the negative focal length of the 1b lens element L1b becomes too long beyond the lower limit value of the conditional expression (1) (the absolute value of the negative focal length becomes too large), the effective diameter of the 1b lens element L1b becomes large. It becomes large and it becomes difficult to reduce the weight of the entire system.

In each embodiment, with the above configuration, an imaging optical system is obtained in which the entire system is lightweight and easy to obtain high image quality. In each embodiment, the numerical range of conditional expression (1) is preferably set as follows.
−0.45 <f1b / f <−0.13 (1a)
More preferably, the numerical range of the conditional expression (1a) is set as follows.
−0.34 <f1b / f <−0.17 (1b)

  In each embodiment, it is more preferable that one or more of the following conditions be satisfied. The distance between the 1a lens element L1a and the 1b lens element L1b is d1a. Let the focal length of the 1a lens element L1a be f1a. The distance between the first b lens element L1b and the first c lens element L1c is d1b. The distance between the first c lens element L1c and the second lens unit L2 at the time of focusing on infinity is d1c. Let the focal length of the first c lens element L1c be f1c. The effective diameter of the lens surface closest to the object side of the 1b lens element L1b is assumed to be ea1b. The effective diameter of the lens surface closest to the object side of the second lens unit L2 is set to ea2.

At this time, it is preferable to satisfy one or more of the following conditional expressions.
0.43 <d1a / f1a <0.80 (2)
0.07 <d1b / | f1b | <0.35 (3)
0.12 <d1c / f1c <0.45 (4)
10.4 <f / ea1b <16.0 (5)
17.0 <f / ea2 <24.0 (6)

  Next, the technical meaning of each conditional expression described above will be described. Conditional expression (2) is for obtaining high image quality while reducing the weight of the entire system. If the distance d1a is too wide beyond the upper limit value of conditional expression (2), the incident height from the optical axis of the axial light beam incident on the 1b lens element L1b becomes too low to correct various aberrations such as spherical aberration. Difficult to do. If the distance d1a is too narrow beyond the lower limit value of the conditional expression (2), it is difficult to reduce the diameter of the lens located on the object side, and it is difficult to reduce the weight of the entire system.

  Conditional expression (3) is for obtaining high image quality. If the distance d1a becomes too large beyond the upper limit value of conditional expression (3), the total lens length (the length from the first lens surface to the image plane) becomes too long, which is not good. If the lower limit of conditional expression (3) is exceeded and the distance d1a becomes too narrow, it becomes difficult to fully utilize the reduction effect of the off-axis light beam by the first b lens element L1b, and the one-stop is remarkable. Here, the single stop means that the principal ray of the off-axis meridian beam does not coincide with the center position of the upper ray and the lower ray. When a single aperture is used, when the F-number is increased, the amount of light outside the screen is significantly reduced, resulting in poor image quality.

  Conditional expression (4) is for obtaining weight reduction of the entire system. If the distance d1c is too wide beyond the upper limit of conditional expression (4), the total lens length becomes too long, which is not good. If the distance d1c is too narrow beyond the lower limit of conditional expression (4), it is difficult to reduce the diameter of the second lens unit L2, and it is difficult to reduce the weight of the entire system.

  Conditional expression (5) is for obtaining high image quality while reducing the weight of the entire system. If the effective diameter of the lens surface closest to the object side of the 1b lens element L1b becomes too small beyond the upper limit value of the conditional expression (5), an aberration correcting action such as chromatic aberration, spherical aberration, and coma aberration by the 1b lens element L1b. Becomes weak and it becomes difficult to obtain high image quality. If the effective diameter of the lens surface closest to the object side of the 1b lens element L1b becomes too large beyond the lower limit value of the conditional expression (5), it is difficult to reduce the weight of the entire system.

  Conditional expression (6) is for obtaining high image quality while reducing the weight of the entire system. If the upper limit of conditional expression (6) is exceeded and the effective diameter of the lens surface closest to the object in the second lens unit L2 becomes too small, the aberration correction function of the second lens unit L2, such as chromatic aberration and spherical aberration, becomes weak. It is difficult to obtain high image quality. If the lower limit of conditional expression (6) is exceeded and the effective diameter of the lens surface closest to the object side of the second lens unit L2 becomes too large, it is difficult to reduce the weight of the entire system.

Preferably, the numerical ranges of conditional expressions (2) to (6) are set as follows.
0.45 <d1a / f1a <0.65 (2a)
0.09 <d1b / | f1b | <0.28 (3a)
0.17 <d1c / f1c <0.37 (4a)
11.3 <f / ea1b <15.0 (5a)
17.5 <f / ea2 <22.5 (6a)

More preferably, the numerical ranges of the conditional expressions (2a) to (6a) are set as follows.
0.46 <d1a / f1a <0.55 (2b)
0.11 <d1b / | f1b | <0.20 (3b)
0.19 <d1c / f1c <0.30 (4b)
12.0 <f / ea1b <14.0 (5b)
18.5 <f / ea2 <21.0 (6b)

  In each embodiment, it is preferable to have a diffractive optical part (diffractive surface) DOE on the cemented surface of the 1b lens element L1b. By setting the diffractive optical part to the first-b lens element L1b, it becomes easy to correct chromatic aberration satisfactorily and to improve the image quality. In each embodiment, it is preferable that the image-side lens surface of the 1a lens element L1a has an aspherical shape. By setting an aspherical surface to the first-a lens element L1a, spherical aberration and coma can be corrected well, and high image quality can be easily obtained.

  In each embodiment, the 1b lens element L1b may be composed of a positive lens and a negative lens. By configuring the first b lens element L1b from two lenses, it is easy to reduce the weight of the entire system. In each embodiment, it is preferable to move the second lens unit L2 from the object side to the image side during focusing from infinity to close. According to this, the effective diameter of the aperture stop SP is reduced, and the optical system can be easily reduced in weight.

Further, in each embodiment, when the diffractive optical element DOE is provided on the cemented surface of the 1b lens element L1b, and the focal length at the reference wavelength (d line) of the first-order diffracted light by the optical path difference function of the diffractive optical unit DOE is fC2. The following conditional expression should be satisfied.
5.00 <fC2 / f <16.50 (7)
Here, the focal length fC2 is the focal length of the condensing action by diffraction in the diffractive optical unit DOE. fC2 is expressed by the following equation using the phase coefficient C2 of the optical path difference function.
fC2 = −1 / (2 × C2)
Conditional expression (7) is for improving the image quality. If fC2 becomes too long beyond the upper limit of conditional expression (7), it will be difficult to easily correct chromatic aberration. If the lower limit of conditional expression (7) is exceeded and fC2 becomes too short, a lot of diffraction flare is likely to occur, which is not good.

Preferably, the numerical range of conditional expression (7) is set as follows.
7.00 <fC2 / f <14.00 (7a)
More preferably, the range of conditional expression (7a) is set as follows.
9.00 <fC2 / f <12.00 (7b)

Furthermore, it is preferable that the optical system of each embodiment satisfies at least one of the following conditional expressions (8) and (9).
0.20 <f1a / f <0.60 (8)
0.10 <f1c / f <0.30 (9)

  Conditional expression (8) relates to the focal length of the 1a lens element L1a. If the focal length f1a becomes too small beyond the lower limit value of the conditional expression (8), it is difficult to sufficiently correct the aberration generated in the 1a lens element L1a with the lens disposed on the image side from the 1a lens element L1a. It becomes. If the focal length f1a becomes too large beyond the upper limit value of the conditional expression (8), it is difficult to sufficiently reduce the diameter of the first b lens element L1b.

  Conditional expression (9) relates to the focal length of the first c lens element L1c. When the focal length f1c is reduced beyond the lower limit value of conditional expression (9), various aberrations such as spherical aberration and chromatic aberration increase. When the focal length f1c increases beyond the upper limit value of conditional expression (9), it is difficult to sufficiently reduce the diameter of the second lens unit L2.

Preferably, the numerical ranges of conditional expressions (8) and (9) are set as follows.
0.27 <f1a / f <0.50 (8a)
0.13 <f1c / f <0.30 (9b)
More preferably, the numerical ranges of conditional expressions (8) and (9) should be set as follows.
0.32 <f1a / f <0.45 (8a)
0.15 <f1c / f <0.25 (9b)

Furthermore, it is preferable that the 1b lens element L1b is formed including a negative lens having a biconcave shape. As a result, the first b lens element L1b can be made compact while the focal length of the first b lens element L1b is appropriately set. In this case, it is preferable that the biconcave negative lens included in the 1b lens element L1b satisfies the following conditional expression (10).
−0.20 <(ra + rb) / (ra−rb) <0.20 (10)

  In conditional expression (10), ra is the radius of curvature of the object-side lens surface of the biconcave negative lens included in the first-b lens element L1b. rb is the radius of curvature of the image-side lens surface of the biconcave negative lens included in the 1b lens element L1b. Conditional expression (10) relates to the shape factor of the biconcave negative lens included in the 1b lens element L1b. When the upper limit value or lower limit value of Expression (10) is exceeded, it is difficult to make the first b lens element L1b compact while setting the focal length of the first b lens element L1b to an appropriate length.

Preferably, the numerical range of conditional expression (10) is set as follows.
−0.15 <(ra + rb) / (ra−rb) <0.15 (10a)

More preferably, the numerical range of conditional expression (10) should be set as follows.
−0.12 <(ra + rb) / (ra−rb) <0.12 (10b)

  In each embodiment, any lens or lens element or sensor may be moved so as to have a component perpendicular to the optical axis to correct image blur. Further, the distortion aberration may be corrected electronically by applying various known methods.

Next, the lens configuration of each lens group in each embodiment will be described.
[Example 1]
Example 1 is an imaging optical system having a focal length of 780.00 mm and an F number of about 5.80. The first lens unit L1 includes a first-a lens element L1a having a positive refractive power, a first-b lens element L1b having a negative refractive power, and a first-c lens element L1c having a positive refractive power, which are arranged in order from the object side to the image side. Has been.

  The 1a lens element L1a is a biconvex positive lens, and the image-side lens surface is aspheric. Various aberrations such as spherical aberration are satisfactorily corrected by this aspherical surface. The 1b lens element L1b is composed of a cemented lens in which a biconvex positive lens and a biconcave negative lens are cemented. The cemented surface of the cemented lens is a diffractive optical part (diffraction surface). This corrects chromatic aberration well.

  The first c lens element L1c is composed of a biconvex positive lens. Accordingly, the diameters of the second lens unit L2 and the third lens unit L3 described later are reduced. The second lens unit L2 having a negative refractive power is composed of a cemented lens in which a biconvex positive lens and a biconcave negative lens are cemented. During focusing from infinity to the closest distance, the second lens unit L2 moves from the object side to the image side.

  The third lens unit L3 includes a cemented lens in which a meniscus negative lens having a convex surface directed toward the object side and a biconvex positive lens are cemented, and a cemented lens in which a biconvex positive lens and a biconcave negative lens are cemented. It is composed of a biconcave negative lens.

  Furthermore, a cemented lens in which a biconvex positive lens and a biconcave negative lens are cemented, a cemented lens in which a biconvex positive lens and a meniscus negative lens having a convex surface facing the image side are cemented, and a biconcave lens It consists of a negative lens. Further, it is composed of a cemented lens in which a biconvex positive lens and a meniscus negative lens having a convex surface facing the image side are cemented. Thereby, curvature of field, lateral chromatic aberration and the like are corrected satisfactorily.

[Example 2]
Example 2 is an imaging optical system having a focal length of 780.00 mm and an F number of about 5.80. The first lens unit L1 includes a first-a lens element L1a having a positive refractive power, a first-b lens element L1b having a negative refractive power, and a first-c lens element L1c having a positive refractive power, which are arranged in order from the object side to the image side. Has been.

  The 1a lens element L1a is a biconvex positive lens, and the image-side lens surface is aspheric. Various aberrations such as spherical aberration are satisfactorily corrected by this aspherical surface. The 1b lens element L1b is composed of a cemented lens in which a biconcave negative lens and a biconvex positive lens are cemented. The cemented surface of the cemented lens is a diffractive optical part (diffraction surface). This corrects chromatic aberration well.

  The first c lens element L1c is composed of a biconvex positive lens. Accordingly, the diameters of the second lens unit L2 and the third lens unit L3 described later are reduced. The lens configuration of the second lens unit L2 is the same as that of the first embodiment. The third lens unit L3 includes a cemented lens in which a meniscus negative lens having a convex surface directed toward the object side and a biconvex positive lens are cemented, and a cemented lens in which a biconvex positive lens and a biconcave negative lens are cemented. It is composed of a biconcave negative lens.

  Furthermore, a cemented lens in which a biconvex positive lens and a meniscus negative lens with a convex surface facing the image side are cemented, a meniscus positive lens with a convex surface facing the image side, and a meniscus negative with a convex surface facing the image side It is composed of a cemented lens in which lenses are cemented and a biconcave negative lens. Further, it is composed of a cemented lens in which a biconvex positive lens and a biconcave negative lens are cemented. Thereby, curvature of field, lateral chromatic aberration and the like are corrected satisfactorily.

[Example 3]
Example 3 is an imaging optical system having a focal length of 780.00 mm and an F number of about 5.80. The lens configuration of the first lens unit L1 is the same as that of the first embodiment. The second lens unit L2 having a negative refractive power is composed of a biconcave negative lens. During focusing from infinity to the closest distance, the second lens unit L2 moves from the object side to the image side. The lens configuration of the third lens unit L3 is the same as that of Example 1.

Next, an embodiment in which the imaging optical system of the present invention is applied to an imaging apparatus (camera system) will be described.
FIG. 7 is a schematic diagram of a main part of a single-lens reflex camera. In FIG. 7, reference numeral 10 denotes an imaging lens having the imaging optical system 1 of any one of the first to third 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 shooting, the quick return mirror 3 is retracted from the optical path, and an image is formed on the photosensitive surface 7 by the imaging lens 10. The image sensor 7 receives an image formed by the imaging optical system 1.

  The imaging apparatus of the present invention can be similarly applied to a mirrorless single-lens reflex camera without the quick return mirror 3.

As for the shape of the diffraction grating of the diffractive optical part DOE in each embodiment, 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 represented 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, if the diffractive optical unit is disposed on a surface passing through a position where the height from the optical axis is high, It is also effective for correcting axial chromatic aberration.

Numerical data 1 to 3 corresponding to the first to third embodiments of the present invention are shown below. In each numerical data, 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 interval 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, F-number, half angle of view (degrees), image height, total lens length, and back focus of the entire system when focused at infinity are shown.

  The back focus BF is an air equivalent distance from the final lens surface to the image plane. The total lens length is a value obtained by adding back focus to the distance from the first lens surface to the final lens surface. The diffractive optical part (diffractive surface) is represented 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 conditional expressions and various numerical values in the numerical data.

[Numeric data 1]
Unit mm

Surface data surface number rd nd νd Effective diameter
1 155.316 19.75 1.48749 70.2 134.48
2 * -11936.522 149.66 133.10
3 141.692 11.62 1.43875 94.7 63.51
4 (Diffraction) -129.418 2.95 1.85478 24.8 61.55
5 138.580 25.24 59.24
6 148.568 6.77 1.80810 22.8 57.68
7 -430.938 36.30 57.05
8 376.152 3.64 1.80810 22.8 38.04
9 -341.903 2.41 1.91082 35.3 37.19
10 81.473 37.49 35.74
11 (Aperture) ∞ 5.00 30.10
12 59.113 1.51 1.95375 32.3 29.02
13 32.603 5.41 1.48749 70.2 28.08
14 -132.255 7.19 27.87
15 144.910 2.87 1.85478 24.8 25.20
16 -73.159 1.31 1.76385 48.5 24.89
17 60.985 1.97 23.89
18 -103.864 1.26 1.76385 48.5 23.87
19 101.074 3.51 23.85
20 44.068 6.16 1.65412 39.7 24.93
21 -221.182 1.26 1.59522 67.7 25.11
22 43.719 5.06 25.26
23 111.425 7.42 1.65412 39.7 27.09
24 -32.515 1.36 1.43875 94.9 27.68
25 -71.229 0.32 27.85
26 -65.657 1.36 1.49700 81.5 27.83
27 91.771 0.10 28.15
28 70.818 6.82 1.65412 39.7 28.27
29 -36.701 1.38 1.80810 22.8 28.28
30 -1117.363 66.61 28.59
31 ∞ 2.20 1.51633 64.1 50.00
32 ∞ 60.71 50.00
Image plane ∞

Aspheric data 2nd surface
K = 0.00000e + 000 A 4 = 1.33317e-008 A 6 = -2.16396e-013 A 8 = 1.24478e-017 A10 = -7.29012e-022

4th surface (diffractive surface)
C2 = -6.17761e-005 C4 = 2.95632e-009 C6 = 1.29493e-012 C8 = -1.75952e-015
C10 = 5.04522e-019

Various data

Focal length 780.00
F number 5.80
Half angle of view (degrees) 1.59
Statue height 21.64
Total lens length 485.85
BF 128.77

Entrance pupil position 1529.20
Exit pupil position -51.23
Front principal point position -1070.79
Rear principal point position -651.23

Lens group data group Start surface Focal length Lens configuration length Front principal point position Rear principal point position
1 1 272.27 215.99 154.27 -159.51
2 8 -108.04 6.05 4.02 0.72
3 12 1845.10 56.25 68.75 25.59
1a 1 314.68 19.75 0.17 -13.11
1b 3 -168.62 14.56 14.30 4.24
1c 6 137.43 6.77 0.97 -2.80

Single lens Data lens Start surface Focal length
1 1 314.68
2 3 156.20
3 4 -78.66
4 6 137.43
5 8 222.14
6 9 -72.04
7 12 -78.41
8 13 54.24
9 15 57.22
10 16 -43.36
11 18 -66.88
12 20 56.70
13 21 -61.22
14 23 39.28
15 24 -137.82
16 26 -76.79
17 28 37.91
18 29 -46.99

[Numeric data 2]
Unit mm

Surface data surface number rd nd νd Effective diameter
1 155.647 21.59 1.48749 70.2 134.48
2 * -1114.571 139.48 133.04
3 -161.207 2.84 1.85478 24.8 63.51
4 (Diffraction) 127.094 11.14 1.43875 94.7 62.79
5 -156.440 29.50 62.99
6 228.731 6.40 1.80810 22.8 59.19
7 -289.712 34.69 58.66
8 228.801 4.36 1.80810 22.8 40.00
9 -379.033 2.40 1.91082 35.3 38.94
10 73.684 37.82 37.21
11 (Aperture) ∞ 5.00 31.66
12 55.564 1.58 1.95375 32.3 30.54
13 32.399 6.06 1.48749 70.2 29.48
14 -207.155 3.88 29.16
15 154.516 4.01 1.85478 24.8 27.61
16 -66.541 1.36 1.76385 48.5 27.12
17 69.812 3.00 25.98
18 -106.915 1.29 1.76385 48.5 25.77
19 100.460 7.56 25.73
20 66.635 6.22 1.65412 39.7 27.37
21 -54.067 1.30 1.59522 67.7 27.67
22 -615.289 10.52 27.92
23 -256.386 4.46 1.65412 39.7 29.04
24 -38.652 1.38 1.43875 94.9 29.26
25 -74.872 2.52 29.27
26 -94.269 1.39 1.49700 81.5 28.79
27 44.161 0.42 28.75
28 50.666 7.24 1.65412 39.7 28.78
29 -34.245 1.40 1.80810 22.8 28.71
30 784.994 62.87 28.93
31 ∞ 2.20 1.51633 64.1 50.00
32 ∞ 60.71 50.00
Image plane ∞

Aspheric data 2nd surface
K = 0.00000e + 000 A 4 = 2.09277e-008 A 6 = -4.70861e-013 A 8 = 1.93144e-017 A10 = -8.69953e-022

4th surface (diffractive surface)
C2 = -5.93393e-005 C4 = 3.90393e-010 C6 = 1.88978e-012 C8 = -6.92242e-016
C10 = -5.02508e-021

Various data

Focal length 780.00
F number 5.80
Half angle of view (degrees) 1.59
Statue height 21.64
Total lens length 485.85
BF 125.03

Entrance pupil position 1446.52
Exit pupil position -54.97
Front principal point position-1153.47
Rear principal point position -654.97

Lens group data group Start surface Focal length Lens configuration length Front principal point position Rear principal point position
1 1 272.72 210.96 173.29 -157.32
2 8 -111.83 6.75 5.14 1.41
3 12 3012.50 65.60 -45.25 -94.69
1a 1 281.73 21.59 1.79 -12.80
1b 3 -182.79 13.99 -3.89 -13.49
1c 6 159.05 6.40 1.57 -1.99

Single lens Data lens Start surface Focal length
1 1 281.73
2 3 -82.76
3 4 158.78
4 6 159.05
5 8 177.13
6 9 -67.56
7 12 -84.28
8 13 57.95
9 15 54.87
10 16 -44.41
11 18 -67.62
12 20 46.58
13 21 -99.67
14 23 69.02
15 24 -184.26
16 26 -60.31
17 28 32.33
18 29 -40.58

[Numeric data 3]
Unit mm

Surface data surface number rd nd νd Effective diameter
1 156.273 19.10 1.48749 70.2 134.48
2 * -24883.763 151.56 133.26
3 135.673 11.87 1.43875 94.7 63.34
4 (Diffraction) -125.010 2.95 1.85478 24.8 61.36
5 132.968 20.35 59.01
6 140.658 5.93 1.80810 22.8 58.10
7 -461.544 37.23 57.68
8 -688.978 2.41 1.88300 40.8 38.71
9 125.930 40.18 37.75
10 (Aperture) ∞ 5.00 31.12
11 61.430 1.51 1.95375 32.3 29.95
12 32.808 5.81 1.48749 70.2 28.95
13 -110.302 1.15 28.74
14 187.739 3.10 1.85478 24.8 27.86
15 -71.920 1.31 1.76385 48.5 27.55
16 68.565 3.05 26.43
17 -113.322 1.26 1.76385 48.5 26.23
18 113.731 3.59 26.19
19 45.862 6.63 1.65412 39.7 26.94
20 -142.991 1.26 1.59522 67.7 26.35
21 45.848 6.33 25.75
22 117.974 7.03 1.65412 39.7 27.16
23 -36.165 1.36 1.43875 94.9 27.63
24 -88.833 4.25 27.73
25 -71.971 1.36 1.49700 81.5 27.36
26 61.745 0.11 27.65
27 62.183 7.70 1.65412 39.7 27.68
28 -37.559 1.38 1.80810 22.8 27.74
29 -638.763 68.94 28.07
30 ∞ 2.20 1.51633 64.1 50.00
31 ∞ 60.71 50.00
Image plane ∞

Aspheric data 2nd surface
K = 0.00000e + 000 A 4 = 1.06987e-008 A 6 = -1.34605e-013 A 8 = 5.73865e-018 A10 = -3.16749e-022

4th surface (diffractive surface)
C2 = -6.27977e-005 C4 = 2.74753e-009 C6 = -1.32756e-012 C8 = 5.75052e-016
C10 = -2.69884e-019

Various data

Focal length 780.00
F number 5.80
Half angle of view (degrees) 1.59
Statue height 21.64
Total lens length 485.85
BF 131.10

Entrance pupil position 1464.99
Exit pupil position -48.92
Front principal point position -1134.88
Rear principal point position -648.91

Lens group data group Start surface Focal length Lens configuration length Front principal point position Rear principal point position
1 1 273.02 211.77 136.38 -157.92
2 8 -120.41 2.41 1.08 -0.20
3 11 -8404.54 58.16 -119.87 -165.38
1a 1 318.65 19.10 0.08 -12.77
1b 3 -162.90 14.82 14.65 4.38
1c 6 133.40 5.93 0.77 -2.53

Single lens Data lens Start surface Focal length
1 1 318.65
2 3 150.38
3 4 -75.71
4 6 134.00
5 8 -120.41
6 11 -75.78
7 12 52.57
8 14 61.17
9 15 -45.77
10 17 -74.13
11 19 53.83
12 20 -58.18
13 22 43.09
14 23 -140.12
15 25 -66.64
16 27 36.92
17 28 -49.43

L0 imaging optical system L1 first lens group L2 second lens group L3 third lens group L1a 1a lens element L1b 1b lens element L1c 1c lens element SP aperture stop

Claims (16)

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 that are arranged in order from the object side to the image side. In moving imaging optics,
The first lens group includes a first-a lens element having a positive refractive power, a first-b lens element having a negative refractive power, and a first-c lens element having a positive refractive power, which are arranged in order from the object side to the image side. When the focal length of the 1b lens element is f1b and the focal length of the entire system is f,
−0.65 <f1b / f <−0.05
An imaging optical system that satisfies the following conditional expression: When the distance between the 1a lens element and the 1b lens element is d1a and the focal length of the 1a lens element is f1a,
0.43 <d1a / f1a <0.80
The imaging optical system according to claim 1, wherein the following conditional expression is satisfied. When the distance between the first b lens element and the first c lens element is d1b and the focal length of the first b lens element is f1b,
0.07 <d1b / | f1b | <0.35
The imaging optical system according to claim 1, wherein the following conditional expression is satisfied.   The imaging optical system according to claim 1, wherein the first b lens element includes a diffractive optical unit.   5. The imaging optical system according to claim 1, wherein an image-side surface of the first lens element has an aspherical shape.   6. The imaging optical system according to claim 1, wherein the first b lens element includes a cemented lens in which a positive lens and a negative lens are cemented.   The imaging optical system according to claim 6, wherein the negative lens has a biconcave shape. When the radius of curvature of the object side surface of the negative lens is ra and the radius of curvature of the image side surface of the negative lens is rb,
−0.20 <(ra + rb) / (ra−rb) <0.20
The imaging optical system according to claim 7, wherein the following conditional expression is satisfied.   The imaging optical system according to any one of claims 1 to 8, wherein the second lens group moves toward the image side during focusing from infinity to close. When the optical system is focused at infinity, the distance between the first c lens element and the second lens group is d1c, and the focal length of the first c lens element is f1c.
0.12 <d1c / f1c <0.45
The imaging optical system according to claim 1, wherein the following conditional expression is satisfied. When the effective diameter of the lens surface closest to the object side of the 1b lens element is ea1b,
10.4 <f / ea1b <16.0
The imaging optical system according to claim 1, wherein the following conditional expression is satisfied. When the effective diameter of the lens surface closest to the object side of the second lens group is ea2,
17.0 <f / ea2 <24.0
The imaging optical system according to claim 1, wherein the following conditional expression is satisfied. The 1b lens element has a diffractive optical part, and when the focal length of the first-order diffracted light in the diffractive optical part is fC2,
5.0 <fC2 / f <16.5
The imaging optical system according to claim 1, wherein the following conditional expression is satisfied. When the focal length of the 1a lens element is f1a,
0.20 <f1a / f <0.60
The imaging optical system according to claim 1, wherein the following conditional expression is satisfied. When the focal length of the first c lens element is f1c,
0.10 <f1c / f <0.30
The imaging optical system according to claim 1, wherein the following conditional expression is satisfied.   An image pickup apparatus comprising: the image pickup optical system according to any one of claims 1 to 15; and an image pickup element that receives an image formed by the image pickup optical system.