JP2009271354A - Photographic optical system and imaging apparatus having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photographic optical system which is excellently corrected in color aberration, has high optical performance and is short in entire lens length and to provide an imaging apparatus having the photographic optical system. <P>SOLUTION: The photographic optical system comprises a first lens group having positive refractive power, a second lens group moving when focusing is performed and a third lens group in order from an object side to an image side and has a first diffractive optical part having positive refractive power in one of the lens groups and a second diffractive optical part having negative refractive power in a position nearer the image side than the first diffractive optical part in the third lens group. Refractive power ϕR based on the diffractive action of the diffractive surface of the second diffractive optical part and a distance DFR on an optical axis between the first diffractive optical part and the second diffractive optical part are properly set respectively. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

  2. Description of the Related Art Conventionally, as a long focal length photographing optical system, a so-called telephoto photographing optical system (telephoto lens) 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 lens having a long focal length, chromatic aberrations such as longitudinal chromatic aberration and lateral chromatic aberration tend to deteriorate as aberrations increase as the focal length increases.

  As a method for correcting chromatic aberration of an optical system, a method of combining two materials (lenses) of two materials having different dispersions is well known.

  Conventionally, chromatic aberration was corrected by combining a positive lens using a low dispersion material having anomalous partial dispersion such as fluorite and the trade name FK01 and a negative lens using a high dispersion material (achromatized). Various telephoto lenses have been proposed.

  Anomalous partially dispersive glass such as fluorite and trade name FK01 is effective in correcting chromatic aberration. On the other hand, it is difficult to process and the specific gravity is relatively larger than other low-dispersion glasses that do not have anomalous partial dispersion, and using them tends to make the entire lens system heavy. For example, the specific gravity of fluorite is 3.18, and the specific gravity of the trade name FK01 is 3.63. On the other hand, the specific gravity of the product name FK5 having a small anomalous partial dispersibility is 2.46, and the specific gravity of the product name BK7 is 2.52. Further, the abnormal partly dispersible glass has a problem that the surface thereof is relatively easily damaged, and that the product name FK01 and the like has a large diameter, and is easily broken by a sudden temperature change.

  As a method of correcting chromatic aberration, a method of reducing chromatic aberration by using a diffractive optical element having a diffractive optical part having a diffractive action on a substrate on a lens surface or a part of an optical system is known (Patent Document). 1-5).

  In Patent Document 1, at least one diffractive optical element having a positive refractive power, at least one refractive optical element having a positive refractive power, and at least one refractive optical element having a negative refractive power are used. An optical system is disclosed that is bright and has chromatic aberration corrected satisfactorily.

  Patent Document 2 discloses an optical system having high optical performance over the entire screen by appropriately combining a diffractive optical element and a refractive optical element.

  In Patent Document 3, a diffractive optical unit is introduced into a part of the optical system, and a combination of the diffractive optical action and the achromatic effect of the refractive system provides excellent optical performance over the entire zoom range from the wide-angle end to the telephoto end. A zoom lens having the same is disclosed.

  Patent Document 4 discloses a lightweight and compact zoom lens in which at least one diffractive optical unit is provided in an eccentric lens used for camera shake correction, and various aberrations are favorably corrected in both the normal state and the camera shake correction state. .

  Patent Document 5 discloses a large-aperture telephoto lens in which various aberrations such as chromatic aberration are favorably corrected without using an abnormal partial dispersion glass by using two diffractive optical parts.

Also, an inner focus telephoto lens using a diffractive optical element has been proposed (Patent Document 6). The telephoto lens of Patent Document 6 includes a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group in order from the object side to the image side. A telephoto lens is disclosed in which a diffractive optical element is used for the first lens group, the second lens group is composed of a single lens, and focusing is performed by the second lens group.
Japanese Patent Laid-Open No. 06-324262 JP 2001-324673 A JP 2002-107624 A JP 09-265042 A JP-A-11-109222 Japanese Patent Laid-Open No. 2000-258685

  In general, when a plurality of diffractive optical elements (diffractive optical units) are used in an optical system, it is easy to obtain high optical performance with good correction of chromatic aberration while shortening the total lens length.

  However, even if a plurality of diffractive optical units are simply provided in the optical system, if the position, power, etc. are not set appropriately, it is possible to obtain an optical system with high optical performance with good correction of chromatic aberration while shortening the overall lens length. difficult.

  For example, if a plurality of diffractive optical parts are arranged at positions where the incident height (height from the optical axis) is large when the axial paraxial ray and the pupil paraxial ray enter the optical system, axial chromatic aberration and lateral chromatic aberration It becomes easy to correct. However, when it is applied to a telephoto lens having a large aperture, the effective diameter of the diffractive optical part becomes large, making it difficult to manufacture.

  For this reason, in order to correct axial chromatic aberration and lateral chromatic aberration satisfactorily using a plurality of diffractive optical parts that are easy to manufacture and have a small effective diameter, and to obtain high optical performance, the plurality of diffractive optical parts are appropriately used in an optical system. It is important to arrange them at appropriate positions.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a photographing optical system that corrects chromatic aberration satisfactorily and has high optical performance and a short overall lens length, and an imaging apparatus having the same.

The photographing optical system of the present invention is composed of a first lens group having a positive refractive power in order from the object side to the image side, a second lens group that moves during focusing, and a third lens group.
A first diffractive optical part having a positive refractive power in any one of the lens groups, and a second refracting power having a negative refractive power in the third lens group, closer to the image side than the first diffractive optical part. Having a diffractive optical part,
The refractive power based on the diffractive action of the diffractive surface of the second diffractive optical part is φR,
When the distance on the optical axis between the first diffractive optical part and the second diffractive optical part is DFR −20 <1 / (φR · DFR) <− 5
It satisfies the following conditional expression.

  According to the present invention, it is possible to obtain a photographing optical system having a short lens total length and having a high optical performance with good chromatic aberration correction and an imaging apparatus having the same.

  The photographic optical system of the present invention includes a first lens group having a positive refractive power in order from the object side to the image side, a second lens group that moves during focusing, and a third lens group.

  The first diffractive optical part having a positive refractive power in any one of the lens groups and the second diffractive power having a negative refractive power in the third lens group closer to the image side than the first diffractive optical part. It has a diffractive optical part.

  Examples of the present invention will be described.

  FIG. 1 is a lens cross-sectional view of Embodiment 1 of the present invention. FIGS. 2A and 2B are aberration diagrams when the object distance is infinity and the closest distance (3.5 m from the image side) according to the first embodiment of the present invention.

  FIG. 3 is a lens cross-sectional view of Embodiment 2 of the present invention. FIGS. 4A and 4B are aberration diagrams when the object distance is infinity and the closest distance (3.5 m from the image side) according to the second embodiment of the present invention.

  FIG. 5 is a lens cross-sectional view of Embodiment 3 of the present invention. 6A and 6B are aberration diagrams when the object distance is infinity and the closest distance (6 m from the image side) according to the third embodiment of the present invention.

  FIG. 7 is a schematic view of the main part of the imaging apparatus of the present invention.

  The photographing optical system of each embodiment is a photographing lens system (optical system) used in an image pickup apparatus such as a video camera, a digital camera, or a silver salt film camera. In the lens cross-sectional view, the left is the object side (front) and the right is the image side (rear).

  In the lens cross-sectional view, L1 is a first lens group having a positive refractive power, L2 is a second lens group having a negative refractive power that moves during focusing, and L3 is a third lens group having a negative refractive power.

  SP is an Fno stop (aperture stop) for restricting the light flux of the open number.

  IP is an image plane, and when used as a photographing optical system for a video camera or a digital still camera, on the imaging surface of a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor, Corresponds to the film surface.

  IS is an anti-vibration lens group that moves so as to have a component substantially perpendicular to the optical axis, shifts the image in a direction perpendicular to the optical axis, and corrects image blur due to camera shake or the like.

  L3R is a rear lens group including a plurality of lenses. DF is a first diffractive optical part, and DR is a second diffractive optical part.

  The first and second diffractive optical parts DF and DR are made of a diffraction grating made of an ultraviolet curable resin formed on the lens surface.

  The * mark in the figure indicates that the lens surface is aspherical.

  In each aberration diagram, d and g represent d-line and g-line, respectively, and ΔM and ΔS represent a meridional image plane and a sagittal image plane. The lateral chromatic aberration is represented by the g-line.

  The diffractive optical element according to the present invention is manufactured by, for example, a method (so-called replica aspherical surface) in which a single or a plurality of diffraction grating layers made of an ultraviolet curable resin is attached to the optical surface (lens surface) as a diffractive optical part. .

  Here, the characteristics of the diffractive optical unit used in each example will be described.

  The diffractive optical part has optical characteristics different from those of conventional refraction by glass or plastic. That is, the diffractive optical part has characteristics of negative dispersion and anomalous dispersion.

  Specifically, the Abbe number νd = −3.45 and the partial dispersion ratio θgf = 0.296.

  In each embodiment, the chromatic aberration of the photographing optical system is favorably corrected by using two diffractive optical sections having this optical property.

  The diffractive optical part used in the photographing optical system of the present invention may have an aspherical effect by changing the pitch from the center of the optical axis to the peripheral part.

  In the imaging optical system of each embodiment, the first diffractive optical part DF having a positive refractive power in any lens group and the negative in the third lens group and closer to the image side than the first diffractive optical part DF. And a second diffractive optical part DR having a refractive power of.

  The refractive power based on the diffractive action of the diffractive surface of the second diffractive optical part is denoted by φR. The distance on the optical axis between the first diffractive optical part and the second diffractive optical part is DFR.

At this time, −20 <1 / (φR · DFR) <− 5 (1)
The following conditional expression is satisfied.

Here, the refractive power φD of the diffractive optical part is obtained as follows. The shape of the diffraction grating of the diffractive optical part is λd as the reference wavelength (d-line), h as the distance from the optical axis, and φ (h) as the phase,
φ (h) = (2π / λd) · (C ₂ · h ² + C ₄ · h ⁴ +... C ₂ · i · h ² · i +)
When expressed by the following formula, the refractive power φD is given by the coefficient C2 of the second-order term:
φD = -2 · C ₂
It becomes.

  In a so-called telephoto type photographing optical system that generally has a positive refractive power on the object side and a negative refractive power on the image side, chromatic aberration and aberration at the reference wavelength tend to deteriorate when the total lens length is shortened. There is.

  In order to correct the axial chromatic aberration, it is desirable to arrange the first diffractive optical part DF where the axial light ray height is high.

  However, it is preferable to arrange the diffractive optical part with a small diameter that is easy to manufacture on the image side. As the first diffractive optical part DF is arranged on the image side, the remaining lateral chromatic aberration becomes larger, so that the refractive power of the second diffractive optical part DR needs to be increased.

  Conditional expression (1) defines an appropriate refractive power arrangement of the second diffractive optical part DR and the first diffractive optical part DF for correcting lateral chromatic aberration that cannot be corrected when the total lens length is further shortened. Yes.

  If the upper limit value of conditional expression (1) is exceeded, the secondary spectrum of lateral chromatic aberration will be undercorrected, and if the lower limit value is exceeded, it will be overcorrected.

  By satisfying conditional expression (1) as described above, axial chromatic aberration and lateral chromatic aberration are corrected well.

  For the same reason, it is more preferable to set the numerical range of the conditional expression (1) as follows.

−20 <1 / (φR · DFR) <− 7 (1a)
As described above, according to each embodiment, it is possible to obtain a high-performance photographic optical system that is easy to manufacture, has a short overall lens length, and that is well corrected for various aberrations including chromatic aberration.

  In each embodiment, it is more preferable to satisfy one or more of the following conditions.

  The refractive power based on the diffractive action of the diffractive surface of the first diffractive optical part is φF. Let the focal length of the first lens unit L1 be f1. Let f be the focal length of the entire system. Let DF be the distance on the optical axis from the first surface on the object side to the first diffractive optical part DF. However, the first surface is the object-side surface of the protective glass when the protective glass is present. The focal length of the positive lens located closest to the object side in the first lens unit L1 is defined as f11.

The first lens unit L1 includes, in order from the object side to the image side, a first lens having a positive refractive power having a convex surface on the object side and a second lens having a positive refractive power having a convex surface on the object side. ing. However, if the focal length of the entire system is f and the focal length of the lens is fa, 3 <| fa | / f (5) between the lens closest to the object side and the second lens.
Lenses (optical elements) that satisfy the following conditional expression are excluded.

  At this time, the combined focal length of the first lens and the second lens is fp. However, the combined focal length fp is the combined focal length of the first lens and the second lens when the first lens and the second lens are bonded to another lens and the bonded surface is separated and the boundary surface is air. Distance.

When the focal length of the lens is fn, −1.0 <fn / f from the most object side lens (9)
The combined focal length of the lens located on the object side of the negative lens that satisfies the conditional expression
5 <1 / (φF · DFR) <50 (2)
0.10 <f1 / f <0.51 (3)
0.1 <DF / f <0.4 (4)
0.1 <f11 / f <0.5 (6)
0.05 <fp / f <0.30 (7)
0.05 <fpp / f <0.30 (8)
It is preferable that at least one of the conditional expressions

  Conditional expression (2) defines an appropriate refractive power arrangement for correcting axial chromatic aberration and lateral chromatic aberration in the first diffractive optical section. If the upper limit value of conditional expression (2) is exceeded, the secondary spectrum of axial chromatic aberration will be overcorrected, and if the lower limit value is exceeded, it will be undercorrected.

  More preferably, the numerical range of conditional expression (2) is set as follows. It is preferable that the following conditional expression (2a) is satisfied.

7 <1 / (φF · DFR) <43 (2a)
Conditional expression (3) defines the focal length of the first lens unit L1 suitable for shortening the total lens length. If the upper limit value of conditional expression (3) is exceeded, the total lens length cannot be sufficiently shortened. On the other hand, exceeding the lower limit is not preferable because the curvature of the lens surface of the positive lens in the first lens unit L1 becomes too tight, making the processing difficult and the manufacturing sensitivity too high.

  For the same reason, it is more preferable to set the numerical range of the conditional expression (3) as follows.

0.20 <f1 / f <0.51 (3a)
Conditional expression (4) defines an appropriate arrangement in the optical path of the first diffractive optical part DF. If the upper limit value of conditional expression (4) is exceeded, the axial ray height becomes low, and axial chromatic aberration cannot be corrected sufficiently.

  If the lower limit is exceeded, the effective diameter of the first diffractive optical part DF becomes large, making it difficult to manufacture.

  In each embodiment, the first lens unit L1 is sequentially from the object side to the image side, the object side surface is a positive first lens L11 having a convex shape, and the object side surface is a positive second lens L12 having a convex shape. Is arranged. In order to shorten the total lens length, it is necessary to increase the positive refractive power of the first lens unit L1, and at the same time, the first lens unit L1 is made a telephoto type so that the principal point is located on the object side. It is necessary to push the optical system closer to the image plane.

  For this purpose, up to the second lens counted from the object side of the first lens unit L1 is composed of a positive lens whose surface on the object side is convex. However, as described above, when there is a lens (optical element) that satisfies the conditional expression (5) between the object side and the second lens, this lens is excluded.

  Here, the conditional expression (5) defines a threshold value as to whether or not it can be interpreted as protective glass among lenses that may exist on the object side. An optical element that satisfies the conditional expression (5) should be ignored from the viewpoint of shortening the total optical length.

  Conditional expression (6) defines the refractive power of the first lens L11 necessary to make the first lens unit L1 in the telephoto type. If the upper limit of conditional expression (6) is exceeded, the total lens length cannot be sufficiently shortened. On the other hand, if the lower limit is exceeded, the curvature of the lens surface of the positive lens becomes too tight, making it difficult to process, and the manufacturing sensitivity becomes too high.

  Conditional expression (7) defines the combined refractive power of the first lens L11 having a positive refractive power and the second lens L12 having a positive refractive power necessary for making the first lens unit L1 into a telephoto type. is there. If the upper limit value of conditional expression (7) is exceeded, the total lens length cannot be shortened sufficiently. On the other hand, if the lower limit is exceeded, the curvature of the lens surface of the positive lens becomes too tight, making it difficult to process, and the manufacturing sensitivity becomes too high.

  Conditional expression (8) defines the combined refractive power of the positive lens unit on the object side in the first lens unit L1 necessary for making the first lens unit L1 into a telephoto type. By increasing the positive refractive power on the object side of the negative lens that satisfies the conditional expression (9), the inside of the first lens unit L1 is made a stronger telephoto type.

  If the upper limit of conditional expression (8) is exceeded, the total lens length cannot be shortened sufficiently. On the other hand, if the lower limit is exceeded, the curvature of the lens surface of the positive lens becomes too tight, making it difficult to process, and the manufacturing sensitivity becomes too high.

  More preferably, the numerical ranges of the conditional expressions (4), (6), (7) and (8) described above are set as follows.

0.12 <DF / f <0.39 (4a)
0.20 <f11 / f <0.49 (6a)
0.100 <fp / f <0.295 (7a)
0.100 <fpp / f <0.295 (8a)
In each embodiment, the first lens unit L1 has an aspheric surface. As the overall lens length is shortened, the deterioration of chromatic aberration becomes more prominent. However, if the chromatic aberration is corrected by a diffractive optical unit, etc., and the overall lens length is further shortened, it will be difficult to correct the reference wavelength aberration this time. It becomes.

  In the telephoto photographic lens, particularly, spherical aberration and coma aberration often occur. Therefore, by providing an aspheric surface in the first lens unit L1, spherical aberration, coma aberration and the like are favorably corrected. Of course, a plurality of aspherical surfaces may be used in order to further correct aberrations.

  In each embodiment, one of the first and second diffractive optical parts DF and DR is present in the cemented lens surface. By having the diffractive optical part in the cemented lens surface, changes in the shape and refractive index of the material constituting the diffractive optical part with respect to environmental changes are reduced.

  In each embodiment, the second lens group has a negative refractive power, and the third lens group has a negative refractive power. When shortening the total lens length, it is necessary to make the entire optical system stronger telephoto type, and in particular, the negative refractive power is arranged in the third lens unit L3 to facilitate the shortening of the total lens length.

  In each embodiment, the third lens unit L3 includes an anti-vibration lens unit IS that can move so as to have a component perpendicular to the optical axis in order to prevent camera shake. By introducing the anti-vibration lens group IS into the third lens group L3, it is easy to reduce the diameter and weight of the anti-vibration lens group IS.

  Hereinafter, the lens configuration of the imaging optical system of each embodiment will be described.

  Hereinafter, unless otherwise noted, it is assumed that each lens group and each lens are arranged in order from the object side to the image side.

  The first embodiment shown in FIG. 1 includes a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power that moves to the image side during focusing from an object at infinity to a close object, and an aperture stop SP. And a third lens unit L3 having negative refractive power and having an anti-vibration lens unit IS.

  The first lens unit L1 includes a positive lens having a surface with a strong refractive power on the object side compared to the image side, a cemented lens in which a positive lens having a surface with a strong refractive power on the object side compared to the image side and a negative lens are cemented, and a negative lens. It is composed of a cemented lens in which a positive lens is cemented.

  The object side surface of each lens in the first lens unit L1 has an aspherical shape, thereby correcting spherical aberration, coma aberration, curvature of field, etc. that occur when the total length is shortened.

  In addition, the first diffractive optical part DF having a positive refractive power is introduced into the cemented surface of the cemented lens closest to the image side in the first lens unit L1 to correct axial chromatic aberration and lateral chromatic aberration that occur when the total length is shortened. ing.

  The second lens unit L2 includes one negative lens. The second focus group L2 uses a low-dispersion material in order to reduce fluctuations in chromatic aberration during focusing.

  The third lens unit L3 includes an aperture stop SP, a cemented lens in which a negative lens and a positive lens are cemented, and an anti-vibration lens group IS. The anti-vibration lens group IS is composed of a cemented lens obtained by cementing a positive lens and a negative lens, and a negative lens.

  The anti-vibration lens group IS moves so as to have a component perpendicular to the optical axis. As a result, the imaging position is shifted in the direction perpendicular to the optical axis.

  A third R lens group (rear lens group) L3R is provided on the image side following the image stabilizing lens group IS. The third R lens unit L3R has one aspherical surface and a second diffractive optical part DR having a negative refractive power.

  Specifically, the third R lens unit L3R includes a cemented lens obtained by cementing a positive lens and a negative lens having an aspheric surface on the image side, a positive lens, and a second diffractive optical unit DR having a negative refractive power on the object side surface. A negative lens and a positive lens.

  The second diffractive optical part DR corrects aberrations at the reference wavelength, lateral chromatic aberration, etc. that cannot be corrected by the first lens unit L1.

  Both the first diffractive optical part DF and the second diffractive optical part DR are introduced into a lens surface having a small incident angle of light in order to improve the diffraction efficiency. Further, since the chromatic aberration can be easily corrected by the first diffractive optical part DF and the second diffractive optical part DR, an abnormal partial dispersion material is not used for the positive lens in the first lens unit L1.

  Example 2 shown in FIG. 3 includes a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power that moves to the image side during focusing from an object at infinity to a close object, and an aperture stop SP. And a third lens unit L3 having negative refractive power and having an anti-vibration lens unit IS.

  The first lens unit L1 includes a positive lens having a surface with a strong refractive power on the object side compared to the image side, a cemented lens in which a positive lens having a surface with a strong refractive power on the object side compared to the image side and a negative lens are cemented, and a negative lens. It is composed of a cemented lens in which a positive lens is cemented.

  The object side surface of each lens in the first lens unit L1 has an aspherical shape, thereby correcting spherical aberration, coma aberration, curvature of field, etc. that occur when the total length is shortened.

  The second lens unit L2 includes one negative lens. The second focus group L2 uses a low-dispersion material in order to reduce fluctuations in chromatic aberration during focusing.

  The third lens unit L3 includes an aperture stop SP, a cemented lens having a first diffractive optical part DF having a positive refractive power on the cemented surface, and an anti-vibration lens group IS. The anti-vibration lens group IS is composed of a cemented lens obtained by cementing a positive lens and a negative lens, and a negative lens.

  The anti-vibration lens group IS moves so as to have a component perpendicular to the optical axis. As a result, the imaging position is shifted in the direction perpendicular to the optical axis.

  A third R lens group (rear lens group) L3R is provided on the image side following the image stabilizing lens group IS. The third R lens unit L3R has one aspherical surface and a second diffractive optical part DR having a negative refractive power.

  Specifically, the third R lens unit L3R is a cemented lens in which a positive lens and a negative lens having an aspheric surface on the image side are cemented, and a second diffractive optical part DR having a negative refractive power is formed on the cemented surface; It consists of a positive lens, a negative lens, and a positive lens.

  The second diffractive optical part DR corrects aberrations of the reference wavelength, lateral chromatic aberration, etc. that cannot be corrected by the first lens unit L1 and the first diffractive optical part DF, respectively.

  Both the first diffractive optical part DF and the second diffractive optical part DR are introduced into a lens surface having a small incident angle of light in order to improve the diffraction efficiency. Further, since the chromatic aberration can be easily corrected by the first diffractive optical part DF and the second diffractive optical part DR, an abnormal partial dispersion material is not used for the positive lens in the first lens unit L1. G is a protective glass.

  Example 3 shown in FIG. 5 includes a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power that moves to the image side during focusing from an object at infinity to a close object, and an aperture stop SP. And a third lens unit L3 having negative refractive power and having an anti-vibration lens unit IS.

  The first lens unit L1 includes a positive lens having a surface having a strong refractive power on the object side compared to the image side, a positive lens having a surface having a strong refractive power on the object side compared to the image side, a biconcave negative lens, a positive lens, and a negative lens. It is composed of

  The object-side surface of the third positive lens in the first lens unit L1 has an aspherical shape, thereby correcting spherical aberration, coma aberration, curvature of field, etc. that occur when the total length is shortened.

  The second lens unit L2 includes a cemented lens in which a positive lens and a negative lens are cemented. As a result, the second focus group L2 reduces variations in chromatic aberration during focusing.

  The third lens unit L3 joins a positive lens and a negative lens, a cemented lens in which the first diffractive optical part DF having a positive refractive power is formed on the cemented surface, an aperture stop SP, and an object side surface is aspherical. A negative lens and a positive lens are cemented and an anti-vibration lens group IS is provided. The anti-vibration lens group IS is composed of a cemented lens obtained by cementing a positive lens and a negative lens, and a negative lens.

  The anti-vibration lens group IS moves so as to have a component perpendicular to the optical axis. As a result, the imaging position is shifted in the direction perpendicular to the optical axis.

  A third R lens group (rear lens group) L3R is provided on the image side following the image stabilizing lens group IS. The third R lens unit L3R includes a cemented lens and a positive lens in which a positive lens and a negative lens are cemented and a second diffractive optical part DR having a negative refractive power is formed on the cemented surface.

  The second diffractive optical part DR corrects aberrations of the reference wavelength, lateral chromatic aberration, etc. that cannot be corrected by the first lens unit L1 and the first diffractive optical part DF, respectively.

  Both the first diffractive optical part DF and the second diffractive optical part DR are introduced into a lens surface having a small incident angle of light in order to improve the diffraction efficiency. Further, since the chromatic aberration can be easily corrected by the first diffractive optical part DF and the second diffractive optical part DR, an abnormal partial dispersion material is not used for the positive lens in the first lens unit L1. Ga and Gb are protective glasses.

  Next, numerical examples of the present invention will be shown.

  In the numerical examples, f is a focal length, Fno is an F number, and 2ω is a comprehensive angle of view. BF is a back focus.

In the numerical examples, i indicates the order from the object side, ri is the radius of curvature of the i-th lens surface in order from the object side, di is the i-th lens thickness or air gap, and ndi and νdi are the i-th lens The refractive index and Abbe number of the lens material. The aspherical shape has a radius of curvature at the center of the lens surface as R, the optical axis direction as the X-axis, the direction perpendicular to the optical axis as the Y-axis, and the aspheric coefficient as Ai (i = 1, 2, 3... )
X = (1 / R) Y ²
1+ {1- (K + 1) (Y / R) ² } ^1/2
+ A4Y ⁴ + A6Y ⁶ + A8Y ⁸ + A10Y ¹⁰ +...
It shall be represented by

The phase shape φ of the diffractive surface is such that the height in the direction perpendicular to the optical axis is h, the diffraction order of the diffracted light is m, the design wavelength is λ 0, and the phase coefficient is Ai (i = 1, 2, 3...) When
φ (h, m) = {2π / (mλ0)} (A2Y ² + A4Y ⁴ + A6Y ⁶ +...)
It shall be represented by In each embodiment, the diffraction order m of the diffracted light is 1, and the design wavelength λ0 is the wavelength of the d-line (587.56 nm).

  However, the diffraction order m is not limited to 1. Of course, the diffraction order may be set to 2 in order to increase the diffraction grating pitch to be advantageous in manufacturing.

  The two surfaces on the object side and / or the image side without refractive power in each numerical example are surfaces (dummy surfaces) of the glass block used in the design.

  Table 1 shows the relationship between the conditional expressions described above and numerical examples.

Numerical example 1

Unit mm

Surface data surface number rd nd νd
1 * 73.112 21.00 1.58913 61.2
2 -1322.126 4.60
3 * 83.168 14.00 1.48749 70.2
4 -533.207 3.30 1.72047 34.7
5 180.994 11.00
6 * 106.927 2.90 1.81600 46.6
7 (Diffraction) 33.000 12.00 1.48749 70.2
8 739.292 14.16
9 381.494 1.80 1.43387 95.1
10 43.029 15.0
11 (Aperture) ∞ 4.00
12 -3988.324 1.30 1.80518 25.4
13 36.825 4.70 1.51633 64.1
14 -52.605 2.30
15 158.812 3.30 1.75520 27.5
16 -46.914 1.30 1.80 400 46.6
17 45.824 2.34
18 -500.040 1.30 1.80400 46.6
19 44.609 3.60
20 58.353 7.20 1.69895 30.1
21 -18.450 1.40 1.80 400 46.6
22 * 533.051 0.44
23 70.721 6.70 1.48749 70.2
24 -22.556 0.51
25 (Diffraction) -23.676 2.00 1.75 500 52.3
26 274.950 0.50
27 150.614 4.46 1.51742 52.4
28 -44.409 0.50
29 ∞ 2.20 1.51633 64.1
30 ∞

Aspheric data 1st surface
K = -3.80170e-001 A 4 = 3.64106e-008 A 6 = -5.55794e-012
A8 = -1.88086e-015 A10 = -5.88570e-019

Third side
K = -1.96674e-001 A 4 = -1.79459e-007 A 6 = -1.31934e-011
A8 = -2.41010e-015 A10 = 7.40210e-018

6th page
K = -8.22364e-001 A 4 = 1.37371e-007 A 6 = -1.49825e-011
A8 = 5.39419e-014 A10 = -2.72334e-017

7th surface (diffractive surface)
A 2 = -1.64314e-004 A 4 = -3.22250e-008 A 6 = -5.48933e-011
A 8 = 3.44011e-014

22nd page
K = 1.20870e + 003 A 4 = -1.46184e-006 A 6 = 8.71861e-010
A8 = -2.13699e-011 A10 = -1.15137e-014

25th surface (diffractive surface)
A 2 = 4.19026e-004 A 4 = -3.40226e-007 A 6 = 1.02290e-009
A 8 = 3.19058e-012

Various data focal lengths 391.33
F number 4.12
Angle of View 3.16
Statue height 21.64
Total lens length 203.90
BF 54.09

Lens group data group Start surface Focal length
1 1 110.19
2 9 -111.56
3 11 -67.00

Numerical example 2

Unit mm

Surface data surface number rd nd νd
1 * 67.947 21.00 1.58913 61.2
2 -1067.199 4.60
3 * 71.393 14.00 1.48749 70.2
4 -466.131 3.30 1.72047 34.7
5 146.322 11.00
6 * 101.383 2.90 1.81600 46.6
7 28.613 12.00 1.48749 70.2
8 380.496 9.70
9 528.470 1.80 1.43387 95.1
10 39.257 15.00
11 (Aperture) ∞ 4.00
12 -686.669 1.30 1.80518 25.4
13 (Diffraction) 38.028 4.70 1.51633 64.1
14 -55.023 2.30
15 152.739 3.30 1.75520 27.5
16 -49.340 1.30 1.80 400 46.6
17 57.702 2.34
18 -549.003 1.30 1.80 400 46.6
19 41.800 2.30

20 57.991 7.20 1.69895 30.1
21 (Diffraction) -18.905 1.40 1.80 400 46.6
22 * 240.571 0.44
23 70.446 6.70 1.48749 70.2
24 -22.980 0.51
25 -26.601 2.00 1.75500 52.3
26 191.959 0.50
27 123.635 4.46 1.51742 52.4
28 -46.077 0.50
29 ∞ 2.20 1.51633 64.1
30 ∞

Aspheric data 1st surface
K = -4.31708e-001 A 4 = 8.93092e-008 A 6 = -2.67420e-012
A8 = -1.95411e-015 A10 = -5.81349e-019

Third side
K = -8.27850e-003 A 4 = -2.97583e-007 A 6 = -2.45283e-011
A8 = -1.68847e-014 A10 = 6.99477e-018

6th page
K = -6.97213e-001 A 4 = 1.93364e-007 A 6 = -9.66874e-011
A8 = 2.35983e-013 A10 = -8.78071e-017

13th surface (diffractive surface)
A 2 = -1.55696e-003 A 4 = -7.32191e-007 A 6 = 2.29613e-009
A 8 = -3.95691e-012

21st surface (diffractive surface)
A 2 = 1.84875e-003 A 4 = 9.82265e-007 A 6 = 5.29582e-009
A 8 = -2.58681e-011

22nd page
K = 1.47785e + 002 A 4 = -7.35246e-007 A 6 = 2.56212e-009
A8 = -9.02985e-012 A10 = 5.00606e-014


Various data focal length 391.05
F number 4.12
Angle of View 3.17
Statue height 21.64
Total lens length 202.24
BF 56.89

Lens group data group Start surface Focal length
1 1 110.19
2 9 -97.50
3 11 -79.46

Numerical example 3

Unit mm

Surface data surface number rd nd νd
1 ∞ 4.50 1.51633 64.1
2 ∞ 0.90
3 82.026 24.00 1.48749 70.2
4 -413.894 6.00
5 82.265 14.00 1.48749 70.2
6 903.282 3.66
7 -248.995 3.60 1.80440 39.6
8 79.040 0.14
9 * 64.844 12.00 1.48749 70.2
10 -434.201 0.15
11 63.210 5.31 1.48749 70.2
12 45.003 14.00
13 216.033 4.60 1.80518 25.4
14 -380.150 2.20 1.83481 42.7
15 69.841 13.00
16 102.144 4.00 1.48749 70.2
17 (Diffraction) -203.882 2.00 1.48749 70.2
18 106.131 5.00
19 (Aperture) ∞ 5.00
20 * 101.535 1.80 1.84666 23.9
21 49.835 7.20 1.71999 50.2
22 610.231 0.95
23 177.537 4.25 1.84666 23.9
24 -63.837 1.65 1.60311 60.6
25 139.970 5.52
26 -101.115 1.60 1.77250 49.6
27 51.973 2.82
28 132.984 9.30 1.71999 50.2
29 (Diffraction) -23.853 1.80 1.83400 37.2
30 -135.449 0.50
31 140.666 4.50 1.69680 55.5
32 570.782 2.00
33 ∞ 2.00 1.51633 64.1
34 ∞

Aspheric data 9th surface
K = 3.04820e-001 A 4 = -5.22383e-007 A 6 = -2.26290e-011
A8 = -8.15349e-014 A10 = 2.65413e-017

17th surface (diffractive surface)
A 2 = -3.57714e-004

20th page
K = -1.19549e + 000 A 4 = 1.17473e-006 A 6 = -1.53315e-009
A8 = 6.12386e-012 A10 = -7.90439e-015

29th surface (diffractive surface)
A 2 = 5.61458e-004

Various data focal length 293.27
F number 2.91
Angle of View 4.22
Statue height 21.64
Total lens length 230.16
BF 60.21

Lens group data group Start surface Focal length
1 1 145.46
2 13 -122.40
3 16 -1076.00

  Next, an embodiment of a single-lens reflex camera system using the photographing optical system of the present invention will be described with reference to FIG.

  In FIG. 7, reference numeral 10 denotes a single-lens reflex camera body, and 11 denotes an interchangeable lens equipped with a photographing optical system according to the present invention.

  Reference numeral 12 denotes a recording unit such as a film or an image sensor for recording a subject image obtained through the interchangeable lens 11, and reference numeral 13 denotes a finder optical system for observing the subject image from the interchangeable lens 11. Reference numeral 14 denotes a rotating quick return mirror for switching and transmitting to the recording means 12 for receiving the subject image from the interchangeable lens 11 and the finder optical system 13.

  When observing the subject image with the finder, the subject image formed on the focusing plate 15 via the quick return mirror 14 is made into an erect image with the pentaprism 16 and then magnified and observed with the eyepiece optical system 17.

  At the time of shooting, the quick return mirror 14 rotates in the direction of the arrow, and the subject image is formed and recorded on the recording means 12. Reference numeral 18 denotes a submirror, and 19 denotes a focus detection device.

  Thus, by applying the imaging optical system of the present invention to an imaging apparatus such as a single-lens reflex camera interchangeable lens, an imaging apparatus having high optical performance can be realized.

  The present invention can be similarly applied to an SLR (Single Lens Reflex) camera having no quick return mirror.

  As described above, according to each embodiment, by setting the diffractive optical unit to an appropriate position in the optical system, it is easy to form the diffractive optical unit, and has a good optical performance with small chromatic aberration. And the imaging device using the same is obtained.

Lens sectional view of Numerical Example 1 of the present invention Aberration diagrams of an object at infinity and a near object according to Numerical Example 1 of the present invention Lens sectional view of Numerical Example 2 of the present invention Aberration diagrams of an object at infinity and a near object according to Numerical Example 2 of the present invention Lens sectional view of Numerical Example 3 of the present invention Aberration diagrams for an object at infinity and a near object according to Numerical Example 3 of the present invention Schematic diagram of main parts of an imaging apparatus of the present invention

Explanation of symbols

L1 First lens group L2 Second lens group L3 Third lens group L3R Third R lens group (rear lens group)
SP Aperture stop IS Anti-vibration lens group IP Image surface * Aspherical surface DF First diffractive optical part DR described in the present invention Second diffractive optical part described in the present invention d d line g g line ΔS Sagittal image surface ΔM Meridional Image plane

Claims (13)

A first lens group having a positive refractive power in order from the object side to the image side, a second lens group that moves during focusing, and a third lens group;
A first diffractive optical part having a positive refractive power in any one of the lens groups, and a second refracting power having a negative refractive power in the third lens group, closer to the image side than the first diffractive optical part. Having a diffractive optical part,
The refractive power based on the diffractive action of the diffractive surface of the second diffractive optical part is φR,
When the distance on the optical axis between the first diffractive optical part and the second diffractive optical part is DFR −20 <1 / (φR · DFR) <− 5
An imaging optical system characterized by satisfying the following conditional expression: When the refractive power based on the diffraction action of the diffractive surface of the first diffractive optical part is φF, 5 <1 / (φF · DFR) <50
The imaging optical system according to claim 1, wherein the following conditional expression is satisfied. When the focal length of the first lens unit is f1 and the focal length of the entire system is f, 0.10 <f1 / f <0.51
The imaging optical system according to claim 1, wherein the following conditional expression is satisfied.   The photographic optical system according to claim 1, wherein the second lens group has a negative refractive power, and the third lens group has a negative refractive power. When the distance on the optical axis from the first surface on the object side to the first diffractive optical part is DF and the focal length of the entire system is f, 0.1 <DF / f <0.4
The imaging optical system according to claim 1, wherein the following conditional expression is satisfied. The first lens group includes, in order from the object side to the image side, a first lens having a positive refractive power having a convex surface on the object side and a second lens having a positive refractive power having a convex surface on the object side. (However, when the focal length of the entire system is f and the focal length of the lens is fa, 3 <| fa | / f between the lens closest to the object side and the second lens)
Excluding optical elements that satisfy the following conditional expression)
The photographic optical system according to claim 1, wherein: When the focal length of the positive lens located closest to the object side in the first lens group is f11 and the focal length of the entire system is f, 0.1 <f11 / f <0.5
The imaging optical system according to claim 1, wherein the following conditional expression is satisfied. The combined focal length of the first lens and the second lens is fp (however, when the first lens and the second lens are cemented with other lenses, the cemented surface is separated and the boundary surface is air) 0.05 <fp / f <0.30, where f is the focal length of the entire system)
The imaging optical system according to claim 6, wherein the following conditional expression is satisfied. When the focal length of the entire system is f and the focal length of the lens is fn, −1.0 <fn / f from the lens closest to the object side
0.05 <fpp / f <0.30 where the combined focal length of the lens located on the object side of the negative lens satisfying the following conditional expression is fpp
The imaging optical system according to claim 1, wherein the following conditional expression is satisfied.   The third lens group includes a lens group that moves so as to have a component in a direction perpendicular to the optical axis and changes an image position in a direction perpendicular to the optical axis. The photographing optical system according to any one of Items 9 to 9.   In order from the object side to the image side, the first lens group includes a positive lens, a cemented lens in which a positive lens and a negative lens are cemented, and a cemented lens in which a negative lens and a positive lens are cemented. Consists of a single negative lens, the third lens group is a cemented lens in which a negative lens and a positive lens are cemented, and moves so as to have a component in the direction perpendicular to the optical axis to change the image position in the direction perpendicular to the optical axis. The photographing optical system according to any one of claims 1 to 10, wherein the photographing optical system includes an anti-vibration lens group and a rear lens group including a plurality of lenses.   In order from the object side to the image side, the first lens group includes a positive lens, a positive lens, a negative lens, a positive lens, and a negative lens, and the second lens group includes a cemented lens of a positive lens and a negative lens, The third lens group is a cemented lens in which a positive lens and a negative lens are cemented, a cemented lens in which a negative lens and a positive lens are cemented, and moves so as to have a component perpendicular to the optical axis and is perpendicular to the optical axis. The imaging optical system according to any one of claims 1 to 10, further comprising an anti-vibration lens group that changes the image position and a rear lens group that includes a plurality of lenses.   An imaging apparatus comprising: the imaging optical system according to claim 1; and a solid-state imaging element that receives an image formed by the imaging optical system.