JP2014056195A - Imaging optical system and imaging device having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging optical system in which color aberration is easily corrected and the size of the whole system and the lens weight can be easily reduced.SOLUTION: The imaging optical system comprises, successively from an object side to an image side: a positive first lens group L1; a negative second lens group L2 that is moved upon focusing; an aperture diaphragm SP; and a third lens group L3. The first lens group L1 comprises: an eleventh lens group L11 having a positive refractive power on an object side; and a twelfth group L12 on an image side, separated by a largest air gap, and also comprises at least one diffractive optical element DOE on the object side than a position where a pupil paraxial ray intersects the optical axis. The eleventh lens group L11 comprises a single positive lens. A refractive index NG1, a specific gravity dG1 and a focal length fG1 of the material of the positive lens, a refractive index fDOE of the diffraction optical element, and a focal length f of the whole system satisfy conditional expressions of dG1<-3.1×NG1×NG1+14.7×NG1-12.8, 0.4<fG1/f<0.8, and 5<fDOE/f<50.

Description

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

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

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

  On the other hand, as a method for reducing the lens weight while correcting various aberrations including chromatic aberration of the imaging optical system, a diffractive optical element in which a diffractive optical part having a diffractive action is provided on a substrate as a part of the imaging optical system A method of using is known. An imaging optical system is known that uses this method to reduce the overall lens weight by correcting the chromatic aberration while shortening the overall lens length, or by constructing the lens with a relatively light glass material specific gravity. (Patent Document 2). Patent Document 2 discloses a telephoto imaging optical system having a focal length of about 800 mm and an F number of about 5.8.

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

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

  In general, in the telephoto imaging optical system, the entire lens system is increased in size and weight as the focal length is increased. For this reason, in the telephoto imaging optical system, it is important to reduce the size and weight of the entire lens system. In addition, among various aberrations generated by increasing the focal length, it is important to particularly correct chromatic aberration. Furthermore, it is important to perform focusing quickly with a small and light lens group other than the front lens group and with less burden on the driving device.

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

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

The imaging optical system according to the present invention includes, in order from the object side to the image side, a first lens group having a positive refractive power, a second lens group having a negative refractive power that moves during focusing, an aperture stop, and a third lens group. The first lens group has an eleventh lens group having a positive refractive power on the object side and a twelfth lens group on the image side with the widest air space as a boundary, and a position where the pupil paraxial ray intersects the optical axis. It has at least one diffractive optical element on the object side, and the eleventh lens group is composed of one positive lens G1, the refractive index of the material of the positive lens G1 is NG1, the specific gravity is dG1, the focal length is fG1, When the focal length of the diffractive optical unit is fDOE and the focal length of the entire system is f,
dG1 <−3.1 × NG1 × NG1 + 14.7 × NG1-12.8
0.4 <fG1 / f <0.8
5 <fDOE / f <50
It is characterized by satisfying the following conditional expression.

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

(A), (B) Lens cross-sectional view and aberration diagram of the imaging optical system of Example 1 of the present invention at an object distance of infinity (A), (B) Lens cross-sectional view and aberration diagram of the imaging optical system of Example 2 of the present invention at an object distance of infinity (A), (B) Lens cross-sectional view and aberration diagram of the imaging optical system of Example 3 of the present invention at an infinite object distance (A), (B) Lens cross-sectional view and aberration diagram of the imaging optical system of Example 4 of the present invention at an infinite object distance (A), (B) Lens cross-sectional view and aberration diagram of the imaging optical system of Example 5 of the present invention at an infinite object distance (A), (B) Lens cross-sectional view and aberration diagram of the imaging optical system of Example 6 of the present invention at an infinite object distance Explanatory diagram showing the relationship between the focal length and weight of the lens Explanatory drawing of the diffractive optical element according to the present invention Explanatory drawing of the diffractive optical element according to the present invention Explanatory drawing of the imaging device of the present invention

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. The imaging optical system of the present invention includes, in order from the object side to the image side, a first lens group having a positive refractive power, a second lens group having a negative refractive power that moves in the optical axis direction for focusing, an aperture stop, Or it has the 3rd lens group of negative refractive power.

  FIGS. 1A to 6A are lens sectional views of Examples 1 to 6 of the imaging optical system of the present invention. FIGS. 1B to 6B are longitudinal aberration diagrams of Examples 1 to 6 of the imaging optical system of the present invention. FIG. 7 is an explanatory diagram showing the relationship between the focal length of the lens and the weight. 8A, 8B, 9A, 9B, and 9C are explanatory views of the diffractive optical element according to the present invention.

  FIG. 10 is a schematic view of the main part of a single-lens reflex camera system (imaging device) in which the photographing optical system of the present invention is mounted on the camera body. In each lens cross-sectional view, L0 is an imaging optical system. SP is an aperture stop that determines the axial maximum luminous flux diameter. The imaging optical system L0 includes a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power that moves during focusing, and a positive or negative third lens unit L3.

  The first lens unit L1 includes an eleventh lens unit L11 having a positive refractive power on the object side and a twelfth lens unit L12 on the image side with the widest air gap as a boundary. The third lens unit L3 moves in order from the object side to the image side so as to have a component in the direction perpendicular to the fixed thirty-first lens unit L31, and the image (image formation position) is perpendicular to the optical axis direction. And a fixed thirty-third lens unit L33. At least one diffractive optical element DOE is provided on the object side of the position where the pupil paraxial ray intersects the optical axis. G is an optical block corresponding to an optical filter, a face plate, a crystal low-pass filter, an infrared cut filter, or the like.

  IP is an image plane, and when used as a photographing optical system of a video camera or a digital camera, an imaging surface of a CCD sensor, a CMOS sensor or the like (photoelectric conversion element) that receives an image is used for a silver salt film camera. It corresponds to a film surface when used as an imaging optical system.

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

In the image pickup optical system of each embodiment, the eleventh lens unit L11 includes one positive lens G1. The refractive index of the material of the positive lens G1 is NG1, the specific gravity is dG1, and the focal length is fG1. The focal length of the diffractive optical part D is fDOE, and the focal length of the entire system is f. At this time,
dG1 <-3.1 × NG1 × NG1 + 14.7 × NG1-12.8 (1)
0.4 <fG1 / f <0.8 (2)
5 <fDOE / f <50 (3)
The following conditional expression is satisfied.

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

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

  When reducing the refractive power of one lens constituting a lens group and reducing the weight by reducing the thickness of the lens, if the other lens becomes larger and thicker in order to maintain the refractive power of the entire lens group As a result, weight reduction cannot be achieved.

  Therefore, in the present invention, in order to reduce the weight of the lens unit while maintaining the refractive power of the lens unit, a material having a high refractive index and a low specific gravity is used.

  FIG. 7 shows the relationship between the focal length and the weight for each of the three types of glass materials A, B, and C having the characteristics shown in Table 1. In FIG. 7, the vertical axis represents the lens weight, and the horizontal axis represents the focal length of the lens. In FIG. 7, the lens diameter is 140 mm, the radius of curvature of the second lens surface is −4000 mm, and the edge of the lens periphery is 3.5 mm. When the refractive index of the lens material and the focal length (refractive power) of the lens are changed, the first lens surface of the lens and the center thickness of the lens are changed so that the above condition is satisfied. .

  The glass material A is a glass material that has been conventionally used for lenses having a positive refractive power in the front lens group of a telephoto lens. Since the glass material A has a low refractive index, the lens is thick and heavy. On the other hand, the specific gravity of the glass material B and the glass material C is larger than that of the glass material A, but since the refractive index is sufficiently high, the effect of thinning the lens is greater and lighter. Thus, if there is a certain relationship between the refractive index and the specific gravity, it is easy to reduce the weight of the lens.

  Conditional expression (1) is set in view of the above conditions, and defines the range in which the eleventh lens unit L11 can be easily reduced in terms of the refractive index and specific gravity. If a material in a range exceeding the value of conditional expression (1) is used, it is difficult to reduce the weight of the lens.

  In particular, the higher the refractive index, the smaller the increase in weight when the refractive power is increased, and the higher the effect of reducing the lens weight. Further, increasing the positive refractive power of the eleventh lens unit L11 is effective in reducing the diameter and weight of the subsequent lens unit. That is, if a material having a high refractive index is used, the subsequent lens group can be reduced in weight while suppressing an increase in the weight of the eleventh lens group L11 when the refractive power of the eleventh lens group L11 is increased, and the entire optical system can be reduced. Weight reduction becomes easy.

  On the other hand, in the region where the refractive power of the lens in FIG. 7 is weak (the focal length is long), the difference in shape due to the refractive index is small, so the difference in weight is small. That is, when the refractive power is weak, the effect of using a material satisfying conditional expression (1) is reduced.

  Conditional expression (2) defines the focal length of the positive lens G1 of the eleventh lens unit L11. If the focal length of the positive lens G1 is increased beyond the upper limit of the conditional expression (2), the effect of reducing the weight is reduced. When the refractive power of the positive lens G1 is weakened, the subsequent lens group has a large diameter, and it is difficult to reduce the weight of the entire optical system. Further, when the focal length of the positive lens G1 becomes shorter than the lower limit of the conditional expression (2), it becomes difficult to correct chromatic aberration generated in the eleventh lens unit L11. As described above, the eleventh lens unit L11 is reduced in weight by using a material satisfying the conditional expression (1) for the positive lens G1 with a refractive power satisfying the conditional expression (2).

  In general, a material having a high refractive index and a low specific gravity has a large dispersion. When a material with large dispersion is used as a positive lens for the lens group on the object side of the telephoto imaging optical system, chromatic aberration increases and it becomes difficult to correct chromatic aberration.

  Therefore, in the present invention, the correction of chromatic aberration is facilitated by using a diffractive optical element having a high effect of correcting chromatic aberration in the optical system with an appropriate refractive power. In particular, axial chromatic aberration and lateral chromatic aberration are effectively corrected by disposing the diffractive optical element on the object side of the aperture stop.

  Conditional expression (3) defines the focal length of the diffractive optical part D. When the upper limit of conditional expression (3) is exceeded and the refractive power of the diffractive optical part D becomes weak, correction of chromatic aberration is insufficient. If the refractive power of the diffractive optical part D is increased below the lower limit of conditional expression (3), it is difficult to correct axial chromatic aberration and lateral chromatic aberration in a balanced manner. In each embodiment, the numerical ranges of conditional expressions (1) to (3) are more preferably set as follows.

dG1 <−3.1 × NG1 × NG1 + 14.7 × NG1-12.87 (1a)
0.4 <fG1 / f <0.8 (2a)
5 <fDOE / f <50 (3a)
By adopting the above configuration, an imaging optical system that can obtain a high-quality image that is lightweight as a whole can be easily obtained. More preferably, at least one of the following conditions should be satisfied, whereby further high optical performance can be easily obtained.

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

1.5 <NG1 (4)
0.05 <D1ab / L <0.40 (5)
−0.60 <Σ (f / fnj × νdnj) <− 0.15 (6)
Here, Σ represents the sum.

Next, the technical meaning of each conditional expression described above will be described. Conditional expression (4) defines the refractive index of the material of the positive lens G1. If a material having a refractive index lower than the lower limit of the conditional expression (4) is used, the weight of the eleventh lens unit L11 increases rapidly when the refractive power is increased as shown in FIG. . The first lens unit L1 includes an eleventh lens unit L11 disposed on the most object side and a twelfth lens unit L12 disposed on the image side of the eleventh lens unit L11.
Conditional expression (5) is the ratio between the distance on the optical axis between the eleventh lens unit L11 and the twelfth lens unit L12 and the distance on the optical axis from the lens surface closest to the object side to the image plane (lens total length). Is specified. If the lower limit of conditional expression (5) is not reached, the diameter of the twelfth lens unit L12 becomes large, making it difficult to reduce the weight of the first lens unit L1. If the upper limit of conditional expression (5) is exceeded, it will be difficult to correct the lateral chromatic aberration and axial chromatic aberration generated in the eleventh lens unit L11 in a balanced manner.

  Conditional expression (6) defines the focal length of the negative lens and the Abbe number of the material included in the eleventh lens unit L11 and the twelfth lens unit L12. By satisfying conditional expression (6), the achromatic effect of the negative lens is obtained, and chromatic aberration is corrected in a well-balanced manner together with the effect of the diffractive optical element. If the lower limit of conditional expression (6) is not reached, the weight of the negative lens increases, which is not desirable. If the upper limit of conditional expression (6) is exceeded, it will be difficult to correct the lateral chromatic aberration and axial chromatic aberration that occur in the eleventh lens unit L11 in a well-balanced manner. More preferably, the numerical ranges of the conditional expressions (4) to (6) are set as follows.

1.53 <NG1 (4a)
0.1 <D1ab / L <0.3 (5a)
−0.55 <Σ (f / fnj × νdnj) <− 0.20 (6a)
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

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

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

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

  The positive lens G1 of the eleventh lens unit L11 is made of OHARA INC. Trade name S-TIH1, and satisfies the conditional expressions (1), (2), and (4). The twelfth lens unit L12 includes, in order from the object side to the image side, a meniscus lens having a convex surface directed toward the object side, a cemented lens in which a negative lens and a positive lens are cemented, and a positive lens. The cemented lens constitutes a diffractive optical element DOE, and has a diffractive optical part D on the cemented surface of the cemented lens. Chromatic aberration generated in the eleventh lens unit L11 is corrected by the diffractive optical part D that satisfies the conditional expression (3).

  When the distance between the eleventh lens group L11 and the twelfth lens group L12 satisfies the conditional expression (5), the number of lenses of the eleventh lens group L11 having a large aperture on the object side is reduced, and the imaging optical system is reduced in weight. ing. The second lens unit L2 is composed of a single negative lens. In the third lens unit L3, the thirty-first lens unit L31 includes a cemented lens in which a negative lens and a positive lens are cemented. The thirty-second lens unit L32 includes a cemented lens obtained by cementing a positive lens and a negative lens, and a negative lens. The thirty-third lens unit L33 includes a positive lens and a cemented lens in which a negative lens and a positive lens are cemented.

[Example 2]
The second embodiment is a telephoto imaging optical system having a diagonal field angle of about 6.32 degrees. The positive lens G1 of the eleventh lens unit L11 is made of OHARA INC. Trade name S-TIH53 and satisfies the conditional expressions (1), (2), and (4). The twelfth lens unit L12 includes a positive lens, a cemented lens obtained by cementing a negative lens and a positive lens, and a positive lens. Other configurations are the same as those of the first embodiment.

[Example 3]
The third embodiment is a telephoto imaging optical system having a diagonal field angle of about 6.32 degrees. The positive lens G1 of the eleventh lens unit L11 is made of OHARA INC. Product name S-TIM22 and satisfies conditional expressions (1), (2), and (4). Other configurations are the same as those of the first embodiment.

[Example 4]
The fourth embodiment is a telephoto imaging optical system having a diagonal field angle of about 6.32 degrees. The positive lens G1 of the eleventh lens unit L11 is made of OHARA CORPORATION trade name S-TIM25, and satisfies the conditional expressions (1), (2), and (4). The twelfth lens unit L12 includes a cemented lens obtained by cementing a negative lens and a positive lens, and a positive lens. Other configurations are the same as those of the first embodiment.

[Example 5]
The fifth embodiment is a telephoto imaging optical system having a diagonal field angle of about 6.32 degrees. The positive lens G1 of the eleventh lens unit L11 is made of OHARA INC. And trade name S-TIL27, and satisfies conditional expressions (1), (2), and (4). Other configurations are the same as those of the first embodiment.

[Example 6]
The sixth embodiment is a telephoto imaging optical system having a diagonal field angle of about 3.2 degrees. In Example 6, in order from the object side to the image side, a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power, and a third lens unit L3 having a negative refractive power are provided. The first lens unit L1 includes an eleventh lens unit L11 and a twelfth lens unit L12 with the widest air gap as a boundary. An aperture stop SP is provided between the second lens unit L2 and the third lens unit L3.

  The third lens unit L3 includes a thirty-first lens unit L31 having a positive refractive power, a thirty-second lens unit L32 having a negative refractive power, and a thirty-third lens unit L33 having a positive refractive power. Focusing from an infinitely distant object to a close object is performed by moving the second lens unit L2 to the image side. When the imaging optical system is vibrated, the blur of the captured image is corrected by moving the thirty-second lens unit L32 as a movable lens unit in a direction having a component perpendicular to the optical axis.

  The positive lens G1 of the eleventh lens unit L11 is made of OHARA CORPORATION trade name S-TIM25, and satisfies the conditional expressions (1), (2), and (4). The twelfth lens unit L12 includes, in order from the object side to the image side, a meniscus positive lens having a convex surface facing the object side, and a cemented lens in which a negative lens and a positive lens are cemented. The cemented lens constitutes a diffractive optical element DOE. A diffractive optical part D is provided on the cemented surface of the cemented lens. Chromatic aberration generated in the eleventh lens unit L11 is corrected by the diffractive optical part D that satisfies the conditional expression (3).

  When the distance between the eleventh lens group L11 and the twelfth lens group L12 satisfies the conditional expression (5), the number of lenses of the eleventh lens group L11 having a large aperture on the object side is reduced, and the imaging optical system is reduced in weight. ing. The second lens unit L2 includes a cemented lens in which a positive lens and a negative lens are cemented. In the third lens unit L3, the thirty-first lens unit L31 includes a cemented lens in which a negative lens and a positive lens are cemented. The thirty-second lens unit L32 includes a cemented lens obtained by cementing a positive lens and a negative lens, and a positive lens.

  The thirty-third lens unit L33 includes a positive lens, a cemented lens in which the positive lens and the negative lens are cemented, a negative lens, and a cemented lens in which the positive lens and the negative lens are cemented.

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

  FIG. 8A is an enlarged cross-sectional view of a part of the diffractive optical part of the diffractive optical element 31. In FIG. 8A, a diffraction grating (diffractive optical part) 33 composed of one layer is provided on a substrate (transparent substrate) 32. FIG. 8B is an explanatory diagram showing the characteristics of the diffraction efficiency of the diffractive optical element 31. In FIG. 8B, the horizontal axis represents wavelength and the vertical axis represents diffraction efficiency. Note that the diffraction efficiency is the ratio of the amount of diffracted light to the total transmitted light beam, and the reflected light at the boundary surface of the grating portion 3a is not considered here because the explanation is complicated.

The optical material of the diffraction grating 33 is an ultraviolet curable resin (refractive index n _d = 1.513, Abbe number ν _d = 51.0). The grating thickness d ₁ of the grating part 3a is set to 1.03 μm so that the diffraction efficiency of + 1st order diffracted light is the highest at a wavelength of 530 nm. That is, the design order is + 1st order and the design wavelength is 530 nm. In FIG. 8B, the diffraction efficiency of the + 1st order diffracted light is indicated by a solid line.

  Further, in FIG. 8B, the diffraction efficiencies of the diffraction orders in the vicinity of the design order (the 0th order and the + 2nd order which are + 1st order ± 1st order) are also shown. As can be seen from the figure, the diffraction efficiency at the design order is highest near the design wavelength, and gradually decreases at other wavelengths. The decrease in diffraction efficiency at this design order becomes diffracted light of other orders (unnecessary light), which causes flare. When the diffractive optical element 31 is used at a plurality of locations in the optical system, a decrease in diffraction efficiency at a wavelength other than the design wavelength leads to a decrease in transmittance.

  Next, a laminated diffractive optical element in which a plurality of diffraction gratings made of different materials are laminated will be described. 9A is a partially enlarged cross-sectional view of the laminated diffractive optical element 31, and FIG. 9B is the wavelength of the diffraction efficiency of the + 1st order diffracted light of the diffractive optical element 31 shown in FIG. 9A. It is a figure showing dependence.

In the diffractive optical element 31 in FIG. 9A, a first diffraction grating 104 made of an ultraviolet curable resin (refractive index n _d = 1.499, Abbe number ν _d = 54) is formed on a substrate 102. Further, a second diffraction grating 105 (refractive index n _d = 1.598, Abbe number ν _d = 28) is formed thereon. In this combination of materials, the grating thickness d ₁ of the grating portion 104 a of the first diffraction grating 104 is d ₁ = 13.8 μm, and the grating thickness d ₂ of the grating portion 105 a of the second diffraction grating 105 is d ₂ = 10. 5 μm.

  As can be seen from FIG. 9B, by using the diffractive optical element 31 including the diffraction gratings 104 and 105 having a laminated structure, 95% or more in the entire wavelength range (in this case, the visible range) in the diffracted light of the designed order. High diffraction efficiency is obtained. Note that, as the diffractive optical element 31 having a laminated structure, the grating thicknesses of the two layers 104 and 105 may be equal depending on the combination of materials as shown in FIG. 9C. In this case, two diffraction grating layers may be arranged with an air layer therebetween.

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

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

ν _d = (N _d −1) / (N _F −N _C )> 0 (b)
Meanwhile, the Abbe number [nu _d of the diffractive optical portion d, C, each wavelength of F-line λ _d, λ _C, λ when the _{F ν d = λ d / (} λ F -λ C) ··· (c )
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 . Accordingly, the focal length f _D due to only the diffraction component of the diffractive optical part _D is

It becomes. Further, when the arbitrary wavelength is λ and the reference wavelength is λ ₀ , the refractive power change with respect to the reference wavelength of the arbitrary wavelength is expressed by the following equation.

_{φ D '= (λ / λ} 0) × (-2 · C 2) ··· (d)
Thus, as a feature of the diffractive optical part, by varying the phase coefficients C ₂ of Equation (a), large dispersion can be obtained by a weak paraxial refractive power change. This means that chromatic aberration is corrected without greatly affecting various aberrations other than chromatic aberration. With respect to the higher order coefficients of the phase coefficient C ₄ and later, the refractive power changes to the light incident height variation of the diffractive optical part can be obtained an effect similar to aspheric.

  At the same time, it is possible to change the refractive power at an arbitrary wavelength with respect to the reference wavelength according to the change in the incident light height. Therefore, it is effective for correcting lateral chromatic aberration. Further, as in the first lens unit L1 of the imaging optical system of the present invention, when the axial light beam passes through the lens surface, the diffractive optical element DOE is disposed on the surface passing through a position where the height from the optical axis is high. It is also effective in correcting axial chromatic aberration.

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

Numerical examples 1 to 6 corresponding to the first to sixth embodiments of the present invention are shown below. In each numerical example, i indicates the order of the surfaces from the object side, r _i is the radius of curvature of the i-th surface from the object side, d _i is the i-th and i + 1-th distance from the object side, nd _i and νd _i are the refractive index and Abbe number of the i-th optical member. f, fno, and 2ω represent the focal length, F-number, and angle of view (degree) of the entire system when focusing on an object at infinity, respectively. The back focus BF is represented by the distance from the final surface (glass block surface) to the image surface.

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

It is expressed by the following formula. For example, the display of “ ^ez ” means “10 ^−Z ”. Table 2 shows the relationship between the above-described conditional expressions and numerical values in the numerical examples.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

(Numerical example 4)
f = 392.00mm Fno = 2.89 2ω = 6.32 °
Surface data surface number rd nd νd Effective diameter
1 * 151.416 19.52 1.67270 32.1 135.64
2 -11006.533 61.25 134.27
3 * 422.577 4.48 1.84666 23.8 92.92
4 (Diffraction) 87.567 15.37 1.48749 70.2 87.13
5 1260.297 41.54 85.98
6 164.946 9.79 1.60311 60.6 70.35
7 -239.424 1.00 69.01
8 288.494 2.50 1.73800 32.3 64.43
9 68.390 71.09 60.03
10 (Aperture) ∞ 4.00 40.73
11 95.792 2.60 1.84666 23.8 38.93
12 38.185 6.00 1.74320 49.3 37.03
13 402.651 1.88 36.59
14 120.177 4.43 1.84666 23.8 36.42
15 -91.968 1.80 1.76200 40.1 36.20
16 51.757 4.75 34.86
17 -135.820 3.54 1.74400 44.8 34.97
18 107.413 2.50 36.33
19 85.639 10.30 1.73800 32.3 38.48
20 -91.339 0.10 39.47
21 -96.777 2.60 1.49700 81.5 39.46
22 71.428 7.35 1.72047 34.7 40.31
23 -72665.163 4.50 40.40
24 ∞ 2.20 1.51633 64.1 50.00
25 ∞ 50.00

Aspheric data 1st surface
K = 0.00000e + 000 A 4 = -1.62600e-008 A 6 = -5.12442e-013 A 8 = -9.94408e-017 A10 = 1.08433e-020 A12 = -8.41894e-025

Third side
K = 0.00000e + 000 A 4 = -8.73064e-008 A 6 = -2.09650e-013 A 8 = 9.45587e-016 A10 = -2.16526e-019 A12 = 3.20049e-023

4th surface (diffractive surface)
C 2 = -4.65491e-005 C 4 = -3.15803e-009 C 6 = 3.99094e-013 C 8 = 2.09674e-016
C10 = -3.72269e-019 C12 = 2.28099e-022 C14 = -3.98153e-026

Focal length 392.00
F number 2.89
Half angle of view (degrees) 3.16
Statue height 21.64
Total lens length 361.23
BF 76.14

Entrance pupil position 836.13
Exit pupil position -45.58
Front principal point position -34.29
Rear principal point position -315.86

Lens group data group Start surface Focal length Lens configuration length Front principal point position Rear principal point position
1 1 166.87 151.96 110.86 -88.02
2 8 -122.05 2.50 1.89 0.45
3 10 740.81 58.55 36.30 -7.41

Single lens Data lens Start surface Focal length
1 1 222.19
2 3 -132.88
3 4 188.82
4 6 163.42
5 8 -122.05
6 11 -76.58
7 12 56.37
8 14 62.13
9 15 -43.23
10 17 -80.12
11 19 61.41
12 21 -82.27
13 22 99.05

(Numerical example 5)
f = 391.97mm Fno = 2.89 2ω = 6.32 °
Surface data surface number rd nd νd Effective diameter
1 * 152.612 18.79 1.57501 41.5 135.63
2 3022.122 47.44 134.35
3 241.396 6.87 1.48749 70.2 105.80
4 * 806.618 33.49 103.75
5 -1343.478 4.48 1.74000 28.3 85.99
6 (Diffraction) 144.938 15.21 1.43875 94.9 82.60
7 -178.832 8.65 81.48
8 87.099 11.58 1.48749 70.2 69.15
9 -641.527 1.01 66.71
10 1697.943 2.50 1.76200 40.1 64.11
11 * 53.428 86.26 57.60
12 (Aperture) ∞ 4.96 40.11
13 124.600 2.60 1.84666 23.8 38.66
14 44.525 6.09 1.74320 49.3 37.29
15 -363.098 1.88 37.02
16 172.711 4.43 1.84666 23.8 36.78
17 -86.282 1.80 1.63930 44.9 36.57
18 58.797 5.69 35.20
19 -112.795 3.54 1.72000 46.0 35.28
20 74.821 2.50 36.44
21 92.167 3.48 1.74950 35.3 38.01
22 -362.880 3.49 38.20
23 -3543.403 2.60 1.49700 81.5 39.19
24 52.697 5.76 1.65412 39.7 40.32
25 -311.964 4.50 40.40
26 ∞ 2.20 1.51633 64.1 50.00
27 ∞ 50.00

Aspheric data 1st surface
K = 0.00000e + 000 A 4 = -7.29902e-010 A 6 = 4.76022e-013 A 8 = 5.99471e-017 A10 = -1.27113e-020 A12 = 6.45302e-025

4th page
K = 0.00000e + 000 A 4 = 1.65161e-007 A 6 = 5.99123e-012 A 8 = 3.77970e-016 A10 = -8.06309e-020 A12 = 2.52635e-023

6th surface (diffractive surface)
C 2 = -5.54959e-005 C 4 = 7.78013e-009 C 6 = -1.17144e-011 C 8 = 1.32062e-014
C10 = -7.80476e-018 C12 = 2.32508e-021 C14 = -2.86735e-025

11th page
K = 0.00000e + 000 A 4 = -2.34410e-007 A 6 = -3.81880e-011 A 8 = -1.48009e-013 A10 = 1.22816e-016 A12 = -5.08277e-020

Focal length 391.97
F number 2.89
Half angle of view (degrees) 3.16
Statue height 21.64
Total length of lens 366.99
BF 75.18

Entrance pupil position 945.80
Exit pupil position -46.83
Front principal point position 78.46
Rear principal point position-316.80

Lens group data group Start surface Focal length Lens configuration length Front principal point position Rear principal point position
1 1 127.65 146.51 108.43 -68.92
2 10 -72.44 2.50 1.47 0.05
3 12 314.37 55.52 21.77 -23.44

Single lens Data lens Start surface Focal length
1 1 278.86
2 3 703.86
3 5 -180.10
4 6 181.48
5 8 158.13
6 10 -72.44
7 13 -83.07
8 14 53.71
9 16 68.50
10 17 -54.43
11 19 -61.99
12 21 98.39
13 23 -104.45
14 24 69.35

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

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

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

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

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

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

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

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

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

  Next, an embodiment in which the optical system of the present invention is applied to an imaging apparatus (camera system) will be described with reference to FIG. FIG. 10 is a schematic view of the main part of a single-lens reflex camera.

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

  Reference numeral 7 denotes a photosensitive surface, on which an image pickup device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor, or a silver salt film is arranged. At the time of photographing, the quick return mirror 3 is retracted from the optical path, and an image is formed on the photosensitive surface 7 by the photographing lens 10. As described above, the imaging optical system according to the first to sixth embodiments is applied to an imaging apparatus such as a photographic camera, a video camera, or a digital still camera, thereby realizing an imaging apparatus that is lightweight and has high optical performance.

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

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

Claims (7)

In order from the object side to the image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power that moves during focusing, an aperture stop, and a third lens unit, the first lens unit being the most An eleventh lens group having a positive refractive power on the object side and a twelfth lens group on the image side with a wide air gap as a boundary, and at least one diffractive optical element on the object side from the position where the pupil paraxial ray intersects the optical axis Having elements,
The eleventh lens group includes one positive lens G1, and the refractive index of the material of the positive lens G1 is NG1, the specific gravity is dG1, the focal length is fG1, the focal length of the diffractive optical unit is fDOE, and the focal point of the entire system. When the distance is f,
dG1 <−3.1 × NG1 × NG1 + 14.7 × NG1-12.8
0.4 <fG1 / f <0.8
5 <fDOE / f <50
An imaging optical system characterized by satisfying the following conditional expression: 1.5 <NG1
The imaging optical system according to claim 1, wherein the following conditional expression is satisfied. When the distance on the optical axis between the eleventh lens group and the twelfth lens group is D1ab, and the distance from the lens surface closest to the object side to the image plane is L,
0.05 <D1ab / L <0.40
The imaging optical system according to claim 1, wherein the following conditional expression is satisfied. When the focal length of the jth negative lens Gnj counted from the object side of the negative lens included in the eleventh lens group and the twelfth lens group is fnj and the Abbe number of the material is νdnj,
−0.60 <Σ (f / fnj × νdnj) <− 0.15
The imaging optical system according to claim 1, wherein the conditional expression is satisfied.   In order from the object side to the image side, the third lens group moves in such a way as to have a component in the direction perpendicular to the optical axis by moving the third lens group to a position perpendicular to the optical axis. 5. The imaging optical system according to claim 1, wherein the imaging optical system includes a 32nd lens group having a negative refractive power and a 33rd lens group having a positive refractive power moving in a direction.   The imaging optical system according to claim 1, wherein the second lens group includes a single negative lens or a cemented lens in which a positive lens and a negative lens are cemented.   An imaging apparatus comprising: the imaging optical system according to claim 1; and an imaging element that receives an image formed by the imaging optical system.