JP2014186101A - Image capturing optical system and image capturing device having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image capturing optical system which is compact, easily corrects for various aberrations including chromatic aberration, and easily offers high optical performance by appropriately utilizing a diffractive optical element and an aspherical lens.SOLUTION: An image capturing optical system comprises, in order from the object side to the image side, a first lens group L1 having positive refractive power, a second lens group L2 which has negative refractive power and moves toward the image side along an optical axis when adjusting focus from an object at infinity to an object at a very close distance, an aperture stop S, and a third lens group L3. The first lens group includes a diffractive optical element and an aspherical lens having an aspherical surface. A focal length of the diffractive optical element on a diffraction surface, aspherical departure of the aspherical lens, a total lens length, and the likes are appropriately set.

Description

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

  In general, in an imaging optical system used in an imaging apparatus, axial chromatic aberration and lateral chromatic aberration increase as the overall lens length (distance from the first lens surface to the image plane) is shortened and the entire optical system is reduced in size. In the telephoto imaging optical system, chromatic aberration increases as the focal length increases. As a method for reducing chromatic aberration, a method using an abnormal partial dispersion material as an optical material and a method using a diffractive optical element are known. If these methods are used, chromatic aberration generated in the imaging optical system can be corrected. However, as the total lens length is shortened, various aberrations other than chromatic aberration, particularly spherical aberration and coma aberration, increase.

  The imaging optical system of Patent Document 1 includes a first lens group having a positive refractive power, a second lens group that moves during focusing, and a third lens group that includes an aperture stop. In addition to having a first diffractive surface having a positive refractive power and a second diffractive surface having a negative refractive power, one or more aspherical lens surfaces are provided. In the imaging optical system of Patent Document 2, in a lens configuration similar to that of Patent Document 1, an aspherical lens in which negative refractive power is increased in the periphery in the first lens group, and positive in any lens group. A diffractive surface of refractive power is provided.

JP 2009-271354 A JP 2010-145797

  When a diffractive optical element is used in a photographing optical system, high optical performance can be obtained due to a high chromatic aberration correction effect. However, when a diffractive optical element is used, it is important to dispose it with an appropriate refractive power at an appropriate position in the imaging optical system. For example, if the refractive power of the diffractive optical element is increased too much, the grating pitch of the diffraction grating becomes too fine, and flare due to diffracted light other than the designed diffraction order increases.

  On the other hand, when using an aspheric lens, it is important to appropriately set the amount of difference (aspheric amount) between the aspheric surface and the paraxial spherical surface in the optical axis direction at the position of the aspherical light beam effective diameter of the aspheric lens. Come. If the difference amount at this time is large, the aspherical surface processing amount increases, and the influence on the optical performance increases due to grinding marks remaining on the molded product or the mold. Grinding marks are shaving irregularities that arise from the relationship between the cutting angle of the cutting edge of the cutting tool and the rotational speed in the process of cutting and processing the glass or mold to be molded while rotating using the cutting tool.

  Also, the effect of grinding marks on the optical performance is, for example, when a light source that is an object is photographed in a slightly out-of-focus state, the light source is photographed in a blurred state. The phenomenon etc. which the nonuniformity resulting from an aspherical grinding mark generate | occur | produces are mentioned.

  The present invention provides an imaging optical system that can easily correct various aberrations including chromatic aberration and easily obtain high optical performance while appropriately reducing the size of the entire system by appropriately using a diffractive optical element and an aspheric lens. The purpose is to do.

The imaging optical system of the present invention has a negative refractive power that moves from the object side to the image side in the order of the first lens unit having a positive refractive power and the optical axis moving toward the image side during focusing from an object at infinity to a close object. In the imaging optical system including the second lens group, the aperture stop, and the third lens group, the first lens group has an aspheric lens including a diffractive optical element and an aspheric lens surface, and the aspheric surface The effective radius of the shape lens surface is _{ha max} , the point where the aspherical lens surface intersects the optical axis is the origin, and from the position at the effective radius _hamax of the aspheric lens surface to the optical axis through the origin _Xb is the distance to the plane perpendicular to the plane, and xa is the distance from the position at half the effective radius _{ha max} ( _hamax / 2) of the aspherical lens surface to the plane perpendicular to the optical axis through the origin. Half of the effective radius _hamax of the origin and the aspherical lens surface (h _amax / 2) where the radius of the virtual sphere passing through the position is R, and the radius R satisfies R = (4 * xa ² + _hamax ² ) / (8 * xa), and the effective radius h _{amax of the} virtual sphere Xb ′ = R−√ (R ² −h _amax) , where xb ′ is the distance from the position to the plane passing through the origin and perpendicular to the optical axis, and the aspheric lens surface is convex on the object side ²⁾ ((a xb '= R + √ (R 2 -h amax 2) If concave)) satisfy, Fgdoe the overall focal length of the diffractive optical element including a diffraction surface, the diffractive optical Fg is the focal length of only the refracting part excluding the diffraction surface from the element, fdoe is the focal length of the diffractive surface of the diffractive optical element, f is the focal length of the entire system when focusing on an infinite object, and the total lens length is L is an aspherical amount ΔdbA in the optical axis direction at the effective radius of the aspherical lens surface of the aspherical lens, and a focal point representing the aspherical component amount on the diffractive surface of the diffractive optical element The distance ΔdbD,
ΔdbA = xb-xb '
ΔdbD = (fgdoe-fg) -fdoe
When
1.00 × 10 ^-6 <| ΔdbA / ΔdbD | <4.30 × 10 ^-6
5.0 <| (fdoe / f) * (L / f) | <20.0
It satisfies the following conditional expression.

  According to the present invention, by appropriately using a diffractive optical element and an aspherical lens, an imaging optical system that can easily correct various aberrations including chromatic aberration and easily obtain high optical performance while reducing the size of the entire system. Is obtained.

Sectional view of the imaging optical system of Example 1 of the present invention Aberration diagram at the time of an object at infinity in the imaging optical system of Example 1 of the present invention Sectional view of the lens of the imaging optical system of Example 2 of the present invention Aberration diagram for an object at infinity in the imaging optical system of Example 2 of the present invention Schematic diagram of paraxial arrangement for explaining optical action of imaging optical system using diffractive optical element Schematic diagram of paraxial arrangement for explaining the arrangement position of the diffraction surface of the diffractive optical element in the imaging optical system using the diffractive optical element Simplified lens surface with an aspherical surface for explaining conditional expression (1) of the present invention (A), (B), (C) Explanatory drawing of the diffractive optical element according to the present invention (A), (B), (C) Graph explaining the wavelength dependence characteristics of the diffraction efficiency of the diffractive optical element according to the present invention Schematic diagram of main parts of an imaging apparatus of the present invention

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The imaging optical system of the present invention, in order from the object side to the image side, negative refraction that moves to the image side on the optical axis in accordance with the first lens unit having a positive refractive power and the focus from an object at infinity to a close object. It consists of a second lens group of force, an aperture stop, and a third lens group. The first lens group has an aspheric lens including a diffractive optical element and an aspheric lens surface.

1 and 2 are a lens cross-sectional view and aberration diagrams of Example 1 of the imaging optical system of the present invention. 3 and 4 are a lens cross-sectional view and aberration diagrams of Embodiment 2 of the imaging optical system of the present invention. In the lens cross-sectional view, L1 is a first lens unit having a positive refractive power, and L2 is a first lens unit having a negative refractive power that moves to the image side on the optical axis with the focus from an object at infinity to a close object. 2 lens groups. S is an aperture stop. L3 is a third lens unit having a negative refractive power. The first lens unit L1 includes a diffractive optical element Ldoe and an aspheric lens L _asph .

The aperture stop S is disposed between the second lens group L2 and the third lens group L3. O is the optical axis, and IP is the image plane, which corresponds to the imaging plane of the imaging device. G represents a glass block such as a crystal low-pass filter or an infrared cut filter. The diffractive optical element Ldoe is composed of a cemented lens in which a negative lens G4 and a positive lens G5 are cemented, and the cemented surface of the cemented lens is a diffractive optical surface (diffractive surface) (diffractive optical unit) DOE. The second lens G2 counted from the object side is a positive lens _Lanm . asph is the aspherical surface of the aspherical lens L _asph .

  The third lens unit L3 includes a lens unit (anti-vibration lens unit) LIS that moves in a direction having a component perpendicular to the optical axis and moves the imaging position in a direction perpendicular to the optical axis. 2 and 4 are aberration diagrams of Examples 1 and 2 at an infinite object distance. 2 and 4, the solid line d is the d line, and the two-dot chain line g is the g line. In astigmatism, a solid line ΔS represents a d-line sagittal ray, and a dotted line ΔM represents a d-line meridional ray. Further, in the lateral chromatic aberration, g of the two-dot chain line represents the g line.

In each embodiment, _{ha max} is the effective radius of the aspherical lens surface. Let xb be the point where the aspherical lens surface intersects the optical axis, and be the distance from the position of the aspherical lens surface at the effective radius _hamax to the plane passing through the origin and perpendicular to the optical axis. Let xa be the distance from a position at half the effective radius _{ha max} ( _{ha max} / 2) of the aspherical lens surface to a plane passing through the origin and perpendicular to the optical axis. Let R be the radius of the phantom sphere passing through the position at half the effective radius _{ha max} of the origin and the aspherical lens surface ( _hamax / 2). The radius R satisfies R = (4 * xa ² + _{ha max} ² ) / (8 * xa).

Let xb ′ be the distance from the position at the effective radius _{ha max} on the phantom sphere to the plane perpendicular to the optical axis through the origin. Xb '= R-√ (R ² -h _amax ² ) ((xb' = R + √ (R ² -h _amax ^{2 for} concave shape) when the aspherical lens surface is convex on the object side. Is satisfied)). Let fgdoe be the focal length of the entire diffractive optical element including the diffractive surface, and fg be the focal length of only the refractive part of the diffractive optical element excluding the diffractive surface. Let fdoe be the focal length of the diffraction surface DOE of the diffractive optical element Ldoe, f be the focal length of the entire system when focusing on an object at infinity, and L be the total lens length.

  The aspherical amount ΔdbA in the optical axis direction at the effective radius of the aspherical lens surface of the aspherical lens and the focal length ΔdbD representing the aspherical component amount on the diffractive surface DOE of the diffractive optical element Ldoe are defined as follows.

ΔdbA = xb-xb '
ΔdbD = (fgdoe-fg) -fdoe
At this time,
1.00 × 10 ^-6 <| ΔdbA / ΔdbD | <4.30 × 10 ^-6 --------- (1)
5.0 <| (fdoe / f) * (L / f) | <20.0 --------- (2)
The following conditional expression is satisfied.

  Next, features of the imaging optical system of the present invention will be described. In the imaging optical system of the present invention, the first lens unit L1 having a positive refractive power in order from the object side to the image side, the first moving on the optical axis to the image plane side during focusing from an infinite object to a short-distance object. It consists of two lens units L2 and a third lens unit L3.

The imaging optical system of the present invention is a telephoto type. In the imaging optical system, the diffractive optical element Ldoe and the aspherical lens L _asph are provided in the first lens group L1 having a relatively high position on the optical axis through which the axial paraxial ray and the pupil paraxial ray pass. Here, the on-axis paraxial ray is a paraxial ray that is normalized by setting the focal length of the entire optical system to 1, and entering the optical system parallel to the optical axis and with a height of 1 from the optical axis. is there.

On the other hand, the paraxial ray of the pupil normalizes the focal length of the entire optical system to 1, and passes through the intersection of the entrance pupil of the optical system and the optical axis among the rays incident at -45 ° to the optical axis. It is a paraxial ray. The incident angle to the optical system is positive from the optical axis in the clockwise direction and negative in the counterclockwise direction. By providing the diffractive optical element Ldoe and the aspherical lens L _asph in the first lens unit L1, chromatic aberration, higher order spherical aberration and monochromatic spherical aberration are corrected in a balanced manner.

  Next, the optical action will be described. First, the diffractive optical element Ldoe plays a role of correcting axial chromatic aberration and lateral chromatic aberration due to shortening of the total lens length (distance from the first lens surface to the image plane) in the imaging optical system of the present invention. This will be described using an axial chromatic aberration coefficient and a magnification chromatic aberration coefficient.

  FIG. 5 is a schematic diagram of a paraxial arrangement for explaining the optical action of an optical system using a diffractive optical element. In FIG. 5, DOE is a diffractive optical part (diffractive surface) constituting a diffractive optical element, M is a refractive optical system part composed of a plurality of ordinary lenses (refractive indexes N1, N2, N3...), And Q is on-axis. Paraxial ray, R is the pupil paraxial ray. h is the height from the optical axis when the axial paraxial ray Q passes through each optical part, and hb is the height from the optical axis when the pupil paraxial ray R passes through each optical part. Yes. In addition, O represents an optical axis, and IP represents an imaging surface. In order to simplify the configuration, all the constituting lenses are treated as thin single lenses.

  The longitudinal chromatic aberration coefficient L (λ) and the lateral chromatic aberration coefficient T (λ) in the entire optical system of FIG. 5 are expressed by the following equations (a1) and (a2).

Here, hdoe is the height from the optical axis of the on-axis paraxial ray incident on the thin single lens constituting the diffractive optical unit, and hbdoe is the optical axis of the pupil paraxial ray incident on the thin single lens constituting the diffractive optical unit Φdoe is the refractive power of the thin single lens constituting the diffractive optical part. H _Mi is the height from the optical axis of the on-axis paraxial ray incident on each thin single lens in the refractive optical unit, and hb _Mi is the optical axis of the pupil paraxial ray incident on each thin single lens in the refractive optical unit. , Φ _Mi is the refractive power of the thin single lens constituting the refractive optical part. Λ is an arbitrary wavelength, and λ 0 is a design wavelength.

  In the above formulas (a1) and (a2), the first term on the right side represents the chromatic aberration coefficient of the diffractive optical unit DOE, and the second term on the right side represents each chromatic aberration coefficient of the refractive optical unit M. A normal optical system must correct each chromatic aberration in the absence of a diffractive optical element, so the second term is set to 0 without the first term on the right side in the above equations (a1) and (a2). It is designed to be (close to 0).

From this point, if the refractive power φ _Mi of each lens is increased in order to reduce the size of the optical system, the second term of the equations (a1) and (a2) becomes zero. Thereafter, it is necessary to appropriately select the glass material of each component lens of the refractive optical system so that the linearity of the imaging position with respect to the wavelength, which is a characteristic of the diffractive optical element, can be made to be a refractive optical system configuration. That is, in terms of the first-order differential values dL (λ) / dλ and dT (λ) / dλ with respect to the wavelengths of the equations (a1) and (a2), the term of the refractive optical unit M has no wavelength characteristics, The following formulas (b1) and (b2) are used.

This means that the values d ² L (λ) / dλ ² and d ² T (λ) / dλ ² of the second derivative with respect to the wavelength λ in the equations (a1) and (a2) become zero. Yes.

  The above equations (c1) and (c2) should approach 0 and the first-order differential values dL (λ) / dλ and dT (λ) / dλ should be constants that do not have wavelength characteristics. . By doing so, in the term of the diffractive optical part DOE, the height hdoe and the refractive power φdoe (position to be inserted into the optical system and refractive power) are optimally given so as to cancel the term of the refractive optical part M, and dL (λ ) / dλ and dT (λ) / dλ can be made zero.

  Each chromatic aberration of axial chromatic aberration and lateral chromatic aberration can be corrected using the above theory. In addition to the correction of chromatic aberration, the diffractive optical element must take into account flare caused by unnecessary diffraction order light other than the designed order on the diffraction surface DOE of the diffractive optical element Ldoe reaching the image plane. Specifically, this is a flare that occurs when high-intensity light source light such as sunlight directly strikes the diffractive surface DOE of the diffractive optical element Ldoe. As a countermeasure, it is necessary to consider the location of the diffractive surface DOE.

  The location of the diffractive surface DOE of the diffractive optical element Ldoe will be described with reference to FIG. Here, FIG. 6 is a paraxial diagram for explaining the optical action of the telephoto optical system including the first lens unit having a positive refractive power, the second lens unit having a negative refractive power, and the third lens unit in order from the object side. It is the schematic of arrangement | positioning. In order to simplify the configuration, all the constituting lenses are treated as thin single lenses, G1 in FIG. 6 is a thin single lens that represents the first lens group, G2 is a thin single lens that represents the second lens group, and G3 is the third lens. It is a thin single lens representing a lens group.

  The other symbols are basically the same as those in FIG. 5 except that P is the intersection of the pupil paraxial ray R and the optical axis O (the position of the aperture stop, hereinafter also referred to as the aperture stop). Here, when the diffraction surface DOE of the diffractive optical element Ldoe is disposed on the image plane side from the aperture stop (P), higher-order diffraction orders different from the above-described design orders are condensed on the image plane. Easy to increase flare. For this reason, it is assumed that the object is located closer to the object side than the aperture stop (P).

  The height hdoe of the on-axis paraxial ray Q passing through the diffractive surface DOE and the height hbdoe of the pupil paraxial ray R are set on the object side of the aperture stop (P). Based on the ratio of, let's divide from Area1 to Area3.

At this time,
Area1 is 0.50 <| hdoe / hbdoe | <0.85,
Area2 is 0.85 <| hdoe / hbdoe | <1.30,
Area3 is 1.30 <| hdoe / hbdoe | <2.00
Is within the range that satisfies the above.

  The diffraction surfaces when arranged in each Area are Gdoe1, Gdoe2, and Gdoe3, and the heights of the axial paraxial rays from the optical axis when passing through each diffraction surface are hdoe1, hdoe2, and hdoe3. Further, the heights of the pupil paraxial rays from the optical axis when passing through each diffraction plane are denoted by hbdoe1, hbdoe2, and hbdoe3.

  From the above formulas (a1) and (a2), in order to set each chromatic aberration coefficient to 0, the chromatic aberration coefficient of the refractive optical unit M is more effectively canceled out as the height hdoe is as high as possible (Area1). I can see that If the height hdoe is as high as possible (Area1), the refracting power of the diffractive surface DOE required for chromatic aberration correction is small, and conversely, the lower the height hdoe is in the position (Area3), the diffractive surface DOE. More refractive power is required.

  Chromatic aberration is possible even at a position where the height hdoe is low (Area 3), but if the refractive power of the diffractive surface DOE becomes too large, flare due to low-order diffraction orders near the design order may increase within the field of view. Concerned.

  In the same Fig. 6, this time the high-intensity light source A outside the shooting angle of view is relative to the optical axis of the light ray incident on the point where it intersects the optical axis of the diffractive surface DOE at the position represented by Gdoe1, Gdoe2, and Gdoe3. Consider the angles θ1, θ2, and θ3. The values of the angle θ1 to the angle θ3 vary depending on the focal length of the optical system and the total length of the lens (the length from the first lens surface to the image plane), but in the imaging optical system assumed in the present invention, θ1 = about 20 to 70 degrees, θ2 = about 10 to 20 degrees, and θ3 = about 5 to 10 degrees.

  At this time, it has become clear from our examination through actual devices that we can tolerate flare caused by a high-intensity light source outside the field of view if θ ≦ 20 degrees (θ2, θ3). . From these viewpoints, it is preferable that the position where the diffractive surface DOE of the diffractive optical element Ldoe is provided is provided at the position of Area2 (0.85 <| hdoe / hbdoe | <1.30) where θ2 = about 10 to 20 degrees. This relationship is defined by conditional expression (4) described later.

  As described above, the chromatic aberration correction method in the optical system having the diffractive optical element, particularly the telephoto optical system, and the arrangement position of the diffractive surface DOE of the diffractive optical element Ldoe from the viewpoint of flare reduction have been described.

  Next, it is preferable to provide an aspherical lens having at least one aspherical surface in the first lens group constituting the optical system after satisfying the above-described contents of the diffractive optical element. This is effective in correcting various aberrations other than chromatic aberration associated with the shortening of the total lens length of the optical system, particularly spherical aberration and coma aberration. In this case, the aspherical amount of the aspheric lens and the refractive power on the diffractive surface DOE can be used efficiently without overstrengthening the optical performance (for example, unevenness generated in the blurred image or flare caused by the diffractive surface). ) And aberration correction are important.

  First, the aspheric surface depends on the incident angle distribution of the light beam passing through the aspheric lens provided with the aspheric surface, and is preferably provided at a position where the width of the incident angle distribution of the light beam passing through is as small as possible. By doing so, it becomes easy to control the light beam passing through the aspheric lens in a desired direction.

  In the telephoto imaging optical system targeted by the present invention, the lens surface closer to the object side in the first lens group hits it, and an aspheric surface is provided in the vicinity thereof, which is the basic of monochromatic systems such as spherical aberration and coma aberration. This is preferable for correcting aberrations. At that time, it is preferable to provide an aspheric surface on the object side of the diffractive surface DOE of the diffractive optical element Ldoe in order to correct various aberrations and reduce flare caused by the diffractive surface DOE. Further, the arrangement of the diffractive surface closer to the aperture stop (inner arrangement) is preferable.

  Further, the aspherical surface provided in the first lens group of the optical system may be any lens surface of a positive lens and a negative lens constituting the first lens group. Regardless of which lens surface is provided, the lens surface is aspherical so that the negative refractive power becomes tighter toward the periphery of the lens surface. This is because, in order to shorten the overall length of the lens, the positive refractive power of each lens in the first lens group, especially in the vicinity of the peripheral portion, is strengthened too much, so that higher-order spherical aberration occurs on the underside. End up. By applying negative refractive power near the periphery using an aspherical surface, high-order spherical aberration is generated on the over side and canceled as a whole, so that high-order spherical aberration is corrected well. Yes.

  However, as described above, when the processing amount of the aspherical surface increases, the frequency of grinding marks remaining on the molded product or the mold increases, and there is a concern about the influence on the optical performance (unevenness generated in the blurred image). In order to reduce the influence, it is effective to reduce the processing amount of the aspherical surface, but it is difficult to simply reduce the aspherical amount in order to maintain the desired optical performance. Therefore, in order to reduce the aspherical amount of the aspherical lens while maintaining the desired optical performance, the aspherical amount necessary for aberration correction and the aspherical amount necessary for aberration correction are considered in the diffractive optical element Ldoe. It is to share the aspheric component in the diffractive surface DOE.

  Specifically, in the imaging optical system targeted by the present invention, it is desirable that the former aspheric lens is disposed closer to the object side than the first lens group effective for aberration correction as described above. . By doing so, it becomes possible to produce a larger aspherical effect with a small amount of aspherical surface.

  On the other hand, the aspheric component necessary for aberration correction is shared by the aspheric component on the diffractive surface DOE of the latter diffractive optical element Ldoe as follows. In formula (A), which will be described later, representing the phase shape of the diffractive surface DOE of the diffractive optical element Ldoe, the phase coefficient C1 on the right side is defined at the location of conditional formula (1) fdoe = -2 * C1 * (λ / λ0) Is a coefficient related to refractive power for correcting chromatic aberration of the optical system.

  Here, fdoe is a focal length at the diffraction surface DOE of the diffractive optical element Ldoe, and its refractive power is represented by the reciprocal of the focal length, λ represents an arbitrary wavelength, and λ0 represents a design wavelength. The remaining phase coefficients (C2, C3,...) On the right side of equation (A), which will be described later, are related to ΔdbD = (fgdoe-fg)-fdoe, which is defined at the location of conditional equation (1). This is the coefficient for the aspheric effect on the surface.

  Where ΔdbD represents the refractive power related to the aspheric effect on the diffractive surface, fgdoe is the focal length of the entire diffractive optical element including the diffractive surface, and fg is only the cemented lens excluding the diffractive surface from the diffractive optical element. Represents the focal length at.

  In order to share the amount of aspheric surface necessary for aberration correction with the aspheric surface component on the diffractive surface, it is necessary to further increase the refractive power represented by ΔdbD. Further, it is preferable to provide the aspheric lens and the diffraction surface relatively close to each other in the same lens group, because the aspherical amount and refractive power of both lenses are not excessively increased, and aberration correction is facilitated.

  From the above, in a telephoto imaging optical system with a shortened overall lens length, the aspherical amount of the aspherical lens and the refractive power on the diffractive surface can be used in a balanced and efficient manner to correct for various aberrations and the optical performance of each optical element. This is the reason why the adverse effects on performance can be reduced.

Based on the above contents, each conditional expression will be described below. Conditional expressions (1) and (2) define the relationship between the refractive power at the diffractive surface DOE of the diffractive optical element Ldoe and the aspheric amount of the aspheric lens. Focal length ΔdbD representing the aspherical component amount in the diffraction plane DOE aspherical amount ΔdbA and diffractive optical element Ldoe the optical axis direction in the effective diameter position of the lens surface having an aspherical shape of the aspherical lens L _asph is, the conditional expression ( 1) is satisfied.

Here, _{ha max} is an effective radius through which light rays pass through a lens surface having an aspherical shape. The point where the lens surface having an aspheric shape intersects the optical axis is the origin. At this time, xb is a distance from the position of the aspherical lens surface at the effective radius _hamax to the plane perpendicular to the optical axis through the origin. xa is the distance from the position of the aspherical lens surface at the intermediate position (h _amax / 2) between the effective radius _{ha max} and the optical axis to the plane perpendicular to the optical axis through the origin.

R is the radius of the phantom sphere passing through points on the aspheric surface at the origin and the intermediate position (h _amax / 2), and satisfies R = (4 * xa ² + _{ha max} ² ) / (8 * xa) Value. xb 'is the distance from the point on the phantom sphere at the effective radius _hamax to the plane passing through the origin and perpendicular to the optical axis, and xb when the lens surface having an aspherical shape is convex on the object side It is assumed that '= R-√ (R ² −h _amax ² ) is satisfied. However, in the case of a concave shape, xb ′ = R + √ (R ² −ha _max ² ). Here, in order to clarify the relationship of each variable, it demonstrates using FIG.

FIG. 7 is a simplified diagram schematically showing a lens surface provided with an aspherical shape. In FIG. 7, the left and right represent the optical axis direction, the top and bottom represent the radial direction of the lens surface, and the aspherical shape (solid line in the figure) passes through the origin O where the optical axis and the radial axis intersect. From FIG. 7, it is assumed that the effective radius through which light passes through the lens surface having the aspherical shape of the optical system is _hamax . Optical axis direction of the coordinates on the non-spherical shape in this case the effective radius h _amax is xb, the optical axis direction of the coordinates on the non-spherical shape at an intermediate position h _amax / 2 in the radial direction of the effective radius h _amax is at xa is there.

The phantom spherical surface of radius R passing through the origin O and the position (xa, _{ha max} / 2) is indicated by a dotted line, and the coordinate in the optical axis direction on the virtual spherical shape at the position of the effective radius _{ha max} is xb ′. is there. Although FIG. 7 shows an aspherical shape having a convex shape on the object side (left side in the figure), it may be a concave shape. Further, fgdoe is the focal length of the entire diffractive optical element Ldoe including the diffractive surface, fg is the focal length of only the cemented lens excluding the diffractive surface DOE from the diffractive optical element, fdoe is the focal point of the diffractive optical element Ldoe on the diffractive surface DOE Distance. At this time, the above-described conditional expression (1) is satisfied.

Conditional expression (1) defines the relationship between the focal length representing the amount of aspherical component of the diffractive optical element Ldoe provided in the first lens unit L1 of the imaging optical system of the present invention and the amount of aspherical surface of the aspherical lens. Here, the aspherical amount ΔdbA is the value of the effective radius h _amax is aspherical amount is continuous changes toward the periphery from the center in the radial direction, and the negative refractive power at the peripheral portion This is because it is strengthened (aspheric amount increases).

Therefore, the aspheric amount can be determined by _{looking at} the value at the effective radius _hamax . From conditional expression (1), the aspherical amount ΔdbA in the optical axis direction at the effective diameter position of the lens surface provided with the aspherical shape is compared with the focal length ΔdbD representing the aspherical component amount on the diffractive surface DOE of the diffractive optical element Ldoe. It represents less. This means a reduction in the amount of aspherical processing, and accordingly, the amount of grinding marks remaining on the molded product or mold can also be reduced, thereby mitigating the influence on optical performance (blurred image unevenness, etc.).

The reason why the aspherical amount _ΔdbA of the aspherical lens _Lasph can be reduced is that the aspherical amount necessary to correct various aberrations including the spherical aberration that increases with the shortening of the total lens length is reduced by the diffractive optical element. This is because the aspherical component in the Ldoe diffraction surface DOE is shared. In conditional expression (1), if the upper limit is exceeded, the aspherical amount ΔdbA of the aspherical lens _Lasph becomes too large, and the aspherical processing amount increases accordingly, which affects the optical performance such as blurred images and unevenness. Since it is in the direction of increasing, it is not preferable.

On the other hand, when the lower limit is exceeded, the aspherical amount _ΔdbA of the aspherical lens _Lasph becomes too small, and it becomes difficult to satisfactorily correct various aberrations including spherical aberration that increases as the total lens length is shortened. . Conditional expression (1) is more preferably within the following range. This is preferable from the viewpoint of the balance between the aspherical amount _ΔdbA of the aspherical lens Lasph and the focal length fdoe on the diffractive surface DOE of the diffractive optical element Ldoe and the correction of various aberrations.

1.50 × 10 ^-6 <| ΔdbA / ΔdbD | <4.00 × 10 ^-6 ------------ (1-a)
More preferably, the numerical range of conditional expression (1a) is set as follows.

2.00 × 10 ^-6 <| ΔdbA / ΔdbD | <3.80 × 10 ^-6 ------------ (1-b)
If the conditional expression (2) is satisfied after satisfying the conditional expression (1), it is preferable for reducing the aspherical amount of the aspheric lens L _asph and reducing the flare caused by the diffractive surface DOE of the diffractive optical element Ldoe.

  Conditional expression (2) defines the relationship of the focal length on the diffractive surface DOE of the diffractive optical element Ldoe with respect to the tele ratio of the imaging optical system (= lens total length / total focal length of the optical system). This conditional expression (2) reduces the flare caused by the diffractive surface by reducing the refractive power (= 1 / focal length) at the diffractive surface DOE of the diffractive optical element Ldoe with respect to the tele ratio of the imaging optical system. belongs to. In conditional expression (2), if the refractive power at the diffractive surface DOE of the diffractive optical element Ldoe becomes too weak beyond the upper limit, correction of axial chromatic aberration and lateral chromatic aberration becomes difficult.

  On the other hand, if the refractive power at the diffractive surface DOE of the diffractive optical element Ldoe becomes too strong beyond the lower limit, the grating pitch of the diffraction grating becomes finer, and a lot of flare due to diffracted light other than the design order occurs, which is not preferable. .

  Conditional expression (2) is more preferably within the following range. This is preferable for reducing flare caused by the diffractive surface DOE of the diffractive optical element Ldoe.

8.0 <| (f doe / f) * (L / f) | <18.0 -------------- (2-a)
Furthermore, it is preferable to set the numerical range of conditional expression (2a) as follows.

10.0 <| (f doe / f) * (L / f) | <17.0 -------------- (2-a)
As described above, each embodiment uses a diffractive optical element and an aspheric lens, and appropriately sets the refractive power on the diffractive surface and the aspheric amount of the aspheric lens, thereby obtaining an imaging optical system having high optical performance. ing. In each embodiment, it is preferable that at least one of the following conditional expressions is satisfied. The aspherical lens surface in the first lens unit L1 is preferably disposed closer to the object side than the diffractive surface of the diffractive optical element Ldoe.

Where h _asph is the height from the optical axis of the on-axis paraxial ray incident on the aspherical lens surface, and hb _asph is the height from the optical axis of the pupil paraxial ray incident on the aspherical lens surface. Say it. Also, h _doe is the height from the optical axis of the on-axis paraxial ray incident on the diffractive surface DOE of the diffractive optical element Ldoe, and h b _doe is the height from the optical axis of the pupil paraxial ray incident on the diffractive surface DOE. Further, Lad is a distance on the optical axis between the aspherical lens surface and the diffractive surface DOE of the diffractive optical element Ldoe. At this time,
0.70 <| h _asph / hb _asph | <1.00 -------------- (3)
0.85 <| h _doe / hb _doe | <1.30 -------------- (4)
0.01 <| Lad / f | <0.30 -------------- (5)
It is good to satisfy the following conditional expression.

  The aspherical shape of the aspherical lens surface provided in the first lens unit L1 is continuously changing in the radial direction from the central part to the peripheral part, and the negative refractive power is strengthened in the peripheral part. ing. If the lens surface having an aspheric shape in the first lens unit L1 and the diffractive surface DOE of the diffractive optical element Ldoe satisfy the conditional expressions (3) to (5), adverse effects on the optical performance of each optical element It is possible to reduce the various aberrations. Conditional expression (3) defines the location of the lens surface having an aspheric shape in the first lens unit L1. On the other hand, the conditional expression (4) defines the location of the diffractive surface DOE of the diffractive optical element Ldoe in the same first lens group L1.

Conditional expression (5) defines the relationship between the lens surface having an aspherical shape and the location of the diffractive surface DOE of the diffractive optical element Ldoe. In addition, it is preferable that the lens surface that satisfies the conditional expressions (3) to (5) and has an aspherical shape is disposed closer to the object side than the diffractive surface DOE of the diffractive optical element Ldoe. This is preferable for reducing the amount of aspheric surface of the aspheric lens L _asph and reducing flare caused by the diffractive surface DOE of the diffractive optical element Ldoe.

  In conditional expression (3), when the aspherical surface is located beyond the aperture stop S beyond the upper limit, it is difficult to achieve various performances such as spherical aberration. Exceeding the lower limit is not preferable because the aspherical surface is arranged closer to the object side, the entire lens length becomes longer, and the weight including the lens barrel increases.

  In the conditional expression (4), when the diffractive surface DOE of the diffractive optical element Ldoe exceeds the upper limit value and is arranged from the aperture stop S, the refractive power at the diffractive surface DOE is changed to correct axial chromatic aberration and lateral chromatic aberration. We must strengthen it. Then, flare due to low-order diffraction order light in the vicinity of the design order within the photographing field angle increases.

  On the other hand, if the location of the diffractive surface DOE is too close to the object side beyond the lower limit, a high-intensity light source outside the shooting angle of view is likely to directly hit the diffractive surface DOE. Accordingly, the generation of flare of high-order diffracted light increases, which is not preferable.

  In conditional expression (5), if the upper limit value is exceeded, the distance between the aspherical surface and the diffractive surface of the diffractive optical element will be too far, and the aspherical amount of the aspherical lens necessary to correct various aberrations will be calculated. Since it becomes difficult to share the aspherical component on the diffractive surface, it is not preferable.

  On the other hand, if the distance between the lens surface provided with the aspherical shape and the diffractive surface DOE of the diffractive optical element Ldoe is too close beyond the lower limit value, high-order spherical aberration increases, which is not preferable. Conditional expressions (3) to (5) are more preferably within the following ranges.

0.72 <| hasph / hbasph | <0.90 -------------- (3-a)
0.88 <| hdoe / hbdoe | <1.10 -------------- (4-a)
0.02 <| Lad / f | <0.25 -------------- (5-a)
More preferably, the numerical ranges of conditional expressions (3a) to (5) are set as follows.

0.74 <| hasph / hbasph | <0.88 -------------- (3-a)
0.90 <| hdoe / hbdoe | <1.00 -------------- (4-a)
0.03 <| Lad / f | <0.22 -------------- (5-a)
In each embodiment, it is more preferable to satisfy one or more of the following conditional expressions.

The second lens G2 counted from the object side of the first lens unit L1 is a positive lens _Lanm , and νd _anm is the Abbe number of the material of the positive lens _Lanm . _{Let hanm be} the height from the optical axis when the axial paraxial ray passes through the object-side lens surface of the positive lens _Lanm . Let hb _{anm be} the height from the optical axis when the pupil paraxial ray passes through the object-side lens surface of the positive lens _Lanm . Let f _{anm be} the focal length of the positive lens L _anm . At this time,
70 <νd _anm <100 -------------- (6)
0.70 <| h _anm / hb _anm | <0.90 -------------- (7)
0.10 <f _anm /f<0.50 -------------- (8)
It is good to satisfy the following conditional expression.

Conditional expressions (6) to (8) are for reducing the size and performance of the imaging optical system. Conditional expression (6) defines the range of the Abbe number of the material used for the second positive lens _Lanm among the lenses counted from the object side of the first lens unit L1. Conditional expression (7) _defines an arrangement location of the second positive lens _Lanm among the lenses counted from the object side of the first lens unit L1. Conditional expression (8) defines the range of the refractive power of the positive lens _Lanm .

  If the upper limit of conditional expression (6) is exceeded and the material becomes too low-dispersed, the diffractive optical element Ldoe causes a balance with the general high-dispersion material used for the negative lens in the first lens unit L1. It becomes difficult to correct the wavelength-dependent characteristics of the generated chromatic aberration. On the other hand, if the material exceeds the lower limit and the material becomes too highly dispersed, the diffractive surface is used to correct the property from the balance with the general high dispersion material used for the negative lens in the first lens unit L1. It will be necessary to strengthen the refractive power of. Then, since many flares occur, it is not preferable.

If the upper limit value of conditional expression (7) is exceeded and the arrangement position of the positive lens _Lanm is too close to the aperture stop S side, it is difficult to obtain a desired effect for correcting chromatic aberration. On the other hand, _if the location where the positive lens _Lanm is placed too close to the object side beyond the lower limit value, correction of chromatic aberration becomes easy, but this is not preferable because the effective lens diameter becomes large and the entire system becomes large.

If the upper limit of conditional expression (8) is exceeded and the refractive power of the positive lens _Lanm becomes too weak, the location for correcting chromatic aberration must be closer to the object side. As a result, the lens diameter becomes large and the entire system becomes large, which is not preferable. On the other hand, _if the refractive power of the positive lens _Lanm becomes too strong beyond the lower limit value, the chromatic aberration is excessively corrected due to the balance with correction of chromatic aberration by other optical elements, which is not preferable. Conditional expressions (6) to (8) are more preferably within the following range.

75 <νd _anm <97 ------------------ (6-a)
0.75 <| h _anm / hb _anm | <0.87 ------------------ (7-a)
0.20 <f _anm / f <0.40 ------------------ (8-a)
Next, each example will be described.

  The imaging optical system of Example 1 is a telephoto lens (focal length 392.19 mm, Fno 4.12), and FIG. 1 is a lens cross-sectional view at an infinite object distance. In FIG. 1, L1 is a first lens group having a positive refractive power, L2 is a second lens group having a negative refractive power, and L3 is a third lens group having a negative refractive power.

Ldoe is a diffractive optical element. The diffractive optical element Ldoe includes a cemented lens in which a fourth lens G4 and a fifth lens G5 counted from the object side are cemented and a diffractive surface DOE is provided on the cemented surface. L _anm is a positive lens. The positive lens _Lanm is a second lens G2 counted from the object side of the first lens unit L1, and is made of a material having an abnormal partial dispersion characteristic.

L _asph is an aspheric lens. The aspheric lens L _asph is _composed of a third lens G3 counted from the object side. The image side of the lens G3 is an aspheric surface asph. The aspheric surface asph is provided closer to the object side than the diffractive surface DOE. Further, focusing from an infinite object point to a close object point is performed by moving the second lens unit L2 including the cemented lens Lfo to the image plane side. The third lens unit L3 moves in a direction having a component perpendicular to the optical axis O, thereby moving the imaging position in a direction perpendicular to the optical axis and correcting image blur due to camera shake or the like. I have a LIS.

In Example 1, in order from the object side to the image side, the first lens unit L1 includes a positive lens, a positive lens, a negative lens having an aspherical lens surface, a negative lens and a positive lens cemented, and a diffractive optical unit on the cemented surface. It consists of a cemented lens with The second lens unit L2 includes a cemented lens in which a positive lens and a negative lens are cemented. The imaging optical system of Example 1 satisfies the above-described conditional expressions, and appropriately sets the refractive power at the diffractive surface DOE of the diffractive optical element Ldoe and the aspheric amount of the aspheric lens L _asph . This realizes an imaging optical system in which the entire system is small and light and various aberrations are corrected.

  The imaging optical system of Example 2 of the present invention is a telephoto lens (focal length 392.19, Fno 4.12) substantially the same as that of Example 1, and FIG. 3 is a lens cross-sectional view at an infinite object distance. Each symbol in FIG. 3 is the same as that shown in FIG. The difference from the first embodiment is that the lens surface provided with the aspheric surface asph is the optical surface closest to the object side.

In Example 2, in order from the object side to the image side, the first lens unit L1 includes a positive lens having an aspherical lens surface, a positive lens, a negative lens, a negative lens and a positive lens, and a diffractive optical unit on the cemented surface. It consists of a cemented lens with In Example 2, the configuration of the second lens unit L2 is the same as that of Example 1. The imaging optical system of Example 2 also satisfies the above-described conditional expressions as in Example 1. The refractive power at the diffractive surface DOE and the aspheric amount of the aspheric lens _Lasph are set appropriately. This realizes an imaging optical system in which the entire system is small and light and various aberrations are corrected.

  Although the diffractive optical element is provided on the optical surface, the radius of curvature of the optical surface may be spherical, flat, or aspheric. In each embodiment, the diffractive optical element is provided on the cemented surface of the cemented lens. However, the present invention is not limited to this.

  As a manufacturing method of the diffractive optical element in each embodiment, a method in which a binary optics shape is directly formed on the lens surface with a photoresist can be applied. In addition, a method of performing replica molding or molding using a mold created by this method can be applied. In addition, if a saw-shaped kinoform is used, the diffraction efficiency increases, and a diffraction efficiency close to the ideal value can be expected.

  Next, the configuration of the diffractive optical element used in the imaging optical system of the present invention will be described. As the structure of the diffractive optical element, a two-layer structure having an air layer as shown in FIG. 8 (A), or a three-layer structure having an air layer as shown in FIG. 8 (B), As shown in FIG. 8C, a two-layer structure in which two layers are in close contact with the same lattice thickness can be applied.

  In FIG. 8A, a first diffraction grating portion 2 is formed by forming a first diffraction grating 6 made of an ultraviolet curable resin on a base material 4. A second diffractive optical unit 3 is configured by forming a second diffraction grating 7 made of an ultraviolet curable resin different from the first diffraction grating 6 on another base material 5. Then, the first diffractive optical part 2 and the second diffractive optical part 3 are arranged close to each other via an air layer 8 with a distance D. Together, these two diffraction gratings 6 and 7 function as one diffractive optical element 1.

  At this time, the grating thickness of the first diffraction grating 6 is d1, and the grating thickness of the second diffraction grating 6 is d2. The grating direction monotonically decreases as the first diffraction grating 6 moves from top to bottom, while the second diffraction grating 7 tends to monotonically increase the grating thickness from top to bottom. is there. Further, as shown in FIG. 8A, when incident light is entered from the left side, the first-order light travels obliquely downward to the right and the zero-order light travels straight.

Fig. 9 (A) shows the wavelength dependence of the diffraction efficiency of the first order diffracted light that is the designed order and the 0th order diffracted light that is the designed order ± 1st order and the second order diffracted light in the two-layer diffractive optical element shown in Fig. 8 (A). Show the characteristics. As an element configuration, the material of the first diffraction grating 6 is (nd1, νd1) = (1.636, 22.8) and the grating thickness d1 = 7.88 μm. The material of the second diffraction grating 7 is (nd2, νd2) = (1.524, 51.6), the grating thickness d2 = 10.71 μm, and the air gap D1 = 1.5 μm.

  Further, from FIG. 8A, the lattice pitch P = 200 μm. As can be seen from FIG. 9A, the diffraction efficiency of the designed order light (primary light) is about 90% or higher over the entire wavelength range, and diffraction of unwanted diffraction order light (0, second order light) is achieved. Efficiency is also suppressed to about 5% or less over the entire operating wavelength range.

  In FIG. 8 (B), a first diffraction grating 6 made of an ultraviolet curable resin is formed on a base material 4, and a second made of the same ultraviolet curable resin as the first diffraction grating 6 is formed on another base material 5. The diffraction grating 7 is formed, and the second diffraction grating 7 is filled with a different ultraviolet curable resin 9. Then, the first diffraction grating 6 and the second diffraction grating 7 are arranged close to each other via an air layer 8 having a distance D. These two diffraction gratings 6 and 7 are combined to function as one diffractive optical element.

  At this time, the grating thickness of the first diffraction grating 6 is d1, and the grating thickness of the second diffraction grating 7 is d2. The direction of the grating is such that the grating thickness monotonously increases from the top to the bottom of both the first diffraction grating 6 and the second diffraction grating 7. Further, as shown in FIG. 8B, when incident light is entered from the left side, the first-order light travels obliquely downward to the right, and the zero-order light travels straight.

  FIG. 9B shows the wavelength of the diffraction efficiency of the first-order diffracted light that is the designed order and the zero-order diffracted light that is the designed order ± 1st order and the second-order diffracted light in the three-layer diffractive optical element 1 shown in FIG. 8B. Shows dependency characteristics. As an element configuration, the material of the first diffraction grating 6 is (nd1, νd1) = (1.636, 22.8) and the grating thickness d1 = 2.83 μm. The material of the second diffraction grating 7 is (nd2-1, νd2-1) = (1.524,51.6) and (nd2-2, νd2-2) = (1.636,22.8), the grating thickness d2 = 7.88 μm, and air The interval D = 1.5 μm.

  From FIG. 8B, the grating pitch P = 200 μm. As can be seen from FIG. 9 (B), the diffraction efficiency of the designed order light (first order light) is as high as 90% or more over the entire wavelength range, as in FIG. 9 (A), and the unnecessary diffraction order light (0 The diffraction efficiency of secondary light) is suppressed to about 5% or less over the entire wavelength range.

  In FIG. 8 (C), a first diffraction grating 6 made of an ultraviolet curable resin is formed on a base material 4, and a second made of an ultraviolet curable resin different from the first diffraction grating 6 is formed on another base material 5. The diffraction grating 7 is formed, and these are closely adhered with the same grating thickness d1. Together, these two diffraction gratings 6 and 7 function as one diffractive optical element 1.

  The direction of the grating is such that the grating thickness monotonously increases as the first diffraction grating 6 goes from top to bottom, while the grating thickness monotonously decreases as the second diffraction grating 7 goes from top to bottom. It is. Also, as shown in FIG. 8 (C), when incident light is entered from the left side, the first-order light travels diagonally downward to the right, and the zero-order light travels straight.

  FIG. 9C shows the diffraction efficiencies of the first order diffracted light that is the designed order and the zeroth order diffracted light that is the designed order ± 1st order and the second order diffracted light in the diffractive optical element 1 having the two-layer structure shown in FIG. 8C. The wavelength dependence characteristic is shown. As the element configuration, the material of the first diffraction grating 6 is (nd1, νd1) = (1.567, 46.6), and the material of the second diffraction grating 7 is the same as (nd2, νd2) = (1.504, 16.3). The grating thickness is d = 9.29 μm. Further, the lattice pitch P in FIG. 8C is 200 μm.

  As can be seen from Fig. 9 (C), the diffraction efficiency of the designed order light (first-order light) is much higher than 99.5% over the entire wavelength range, as shown in Figs. 9 (A) and 9 (B). The diffraction efficiency of diffraction order light (0, 2nd order light) is also considerably suppressed to about 0.05% or less over the entire operating wavelength range. As described above, the diffractive optical element used in each example has been described. However, the present invention is not limited to this as long as the basic performance such as diffraction efficiency is equal to or higher than that of the diffractive optical element described above.

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

  In FIG. 10, reference numeral 20 denotes an imaging lens having the imaging optical system 11 of any one of the first and second embodiments. The imaging optical system 11 is held by a lens barrel 12 that is a holding member. Reference numeral 30 denotes a camera body. The camera body includes a quick return mirror 13 that reflects the light beam from the imaging lens 20 upward, a focusing screen 14 that is disposed at an image forming position of the imaging lens 20, and a pentagon that converts an inverted image formed on the focusing screen 14 into an erect image. It has a Dach prism 15. Further, it is constituted by an eyepiece 16 for observing the erect image.

  Reference numeral 17 denotes a photosensitive surface, on which an image sensor (photoelectric conversion element) (image sensor) such as a CCD sensor or a CMOS sensor that receives an image, or a silver salt film is arranged. At the time of photographing, the quick return mirror 13 is retracted from the optical path, and an image is formed on the photosensitive surface 17 by the photographing lens 20. In this way, by applying the imaging optical system of Embodiments 1 and 2 to an imaging apparatus such as a photographic camera, a video camera, or a digital still camera, a lightweight imaging apparatus having high optical performance is realized.

  In this embodiment, the present invention can be similarly applied to a mirrorless camera having no quick return mirror.

  Numerical Examples 1 and 2 corresponding to Embodiments 1 and 2 of the present invention are shown below. In each numerical example, i indicates the order of the surfaces from the object side, ri is the radius of curvature of the i-th surface from the object side, di is the i-th and i + 1-th interval from the object side, ndi and νdi Are the refractive index and Abbe number of the i-th optical member. It also shows the effective diameter of each surface.

  Indicates focal length, F-number, half angle of view (degrees), image height, and total lens length. The back focus (BF) is a distance from the final surface (the surface of the glass block) to the image surface. In each numerical example, the two surfaces closest to the image side are glass blocks such as filters. The variable of the distances d9 and d12 means that the distances change during focusing. The numerical value indicates when focusing on an object at infinity. Further, the aspherical shape is such that X is the amount of displacement from the surface vertex in the optical axis direction, h is the height from the optical axis in the direction perpendicular to the optical axis, R is the paraxial radius of curvature, k is the conic constant, B, When C, D, E... Are the aspheric coefficients of the respective orders, they are expressed by the following equation (B).

  In addition, the phase function ψ of the diffractive optical surface of each example is expressed as follows: the diffraction order of the diffracted light is m, the design wavelength is λ0, the height perpendicular to the optical axis is h, and the phase coefficient is Ci (i = 1, 2 , 3 ...), it is expressed by the following equation.

ψ (h, m) = (2π / mλ0) * (C1 · h ² + C2 · h ⁴ + C3 · h ⁶ + ...)
Table 1 shows the conditional expressions in each example.

[Numerical Example 1]
Unit mm

Surface data surface number rd nd νd Effective diameter
1 101.267 17.97 1.48749 70.2 95.20
2 -1421.586 22.11 93.39
3 86.833 14.57 1.49700 81.5 76.00
4 -293.957 0.20 73.61
5 -271.960 3.90 1.77250 49.6 73.59
6 * 192.089 14.97 68.73
7 91.543 2.85 1.78590 44.2 58.60
8 (Diffraction) 43.425 12.04 1.48749 70.2 54.03
9 321.773 (variable) 52.38
10 289.030 3.07 1.80809 22.8 35.18
11 -202.911 1.80 1.83400 37.2 34.44
12 65.357 (variable) 32.61
13 (Aperture) ∞ 11.29 26.38
14 76.835 1.30 1.84666 23.9 25.59
15 25.815 5.39 1.67300 38.1 25.28
16 -280.474 0.50 25.31
17 61.261 3.83 1.84666 23.9 25.30
18 -110.422 1.30 1.77250 49.6 24.99
19 30.826 3.63 24.13
20 -76.495 1.30 1.88300 40.8 24.19
21 83.961 1.15 25.23
22 ∞ 0.00 25.12
23 54.285 8.79 1.61340 44.3 26.48
24 -19.696 1.80 1.59282 68.6 27.00
25 156.426 1.28 29.13
26 -4817.483 1.80 1.80809 22.8 29.46
27 50.905 5.15 1.65412 39.7 30.75
28 -127.436 0.15 31.48
29 70.581 3.55 1.74077 27.8 33.04
30 646.175 2.38 33.17
31 ∞ 2.00 1.51633 64.1 33.52
32 ∞ 63.27 33.73
Image plane ∞

Aspheric data 6th surface
K = 1.38187e + 000 B = 1.48156e-008 C = -6.46138e-012 D = 1.87902e-015
E = -1.34902e-018

8th surface (diffractive surface)
C1 = -5.59649e-005 C2 = -1.39074e-008 C3 = 8.27359e-012 C4 = -2.27361e-014
C5 = 1.55673e-017

Various data

Focal length 392.19
F number 4.12
Half angle of view (degrees) 3.16
Statue height 21.64
Total lens length 262.18
BF 63.27

d 9 26.13
d12 22.72

Entrance pupil position 519.88
Exit pupil position -73.10
Front principal point position -456.73
Rear principal point position -352.93

Zoom lens group data group Start surface Focal length Lens configuration length Front principal point position Rear principal point position
1 1 151.03 88.61 -3.87 -69.64
2 10 -100.02 4.87 3.44 0.74
3 13 -557.05 80.59 -26.25 -100.65

Single lens Data lens Start surface Focal length
1 1 194.67
2 3 136.61
3 5 -145.20
4 7 -107.93
5 8 101.54
6 10 147.94
7 11 -59.09
8 14 -46.46
9 15 35.38
10 17 47.02
11 18 -31.07
12 20 -45.16
13 23 24.68
14 24 -29.40
15 26 -62.32
16 27 56.25
17 29 106.68
18 31 0.00

[Numerical Example 2]
Unit mm

Surface data surface number rd nd νd Effective diameter
1 * 94.907 17.00 1.48749 70.2 95.20
2 -2762.889 21.51 93.79
3 95.584 14.93 1.49700 81.5 76.59
4 -187.814 0.13 74.44
5 -181.884 3.90 1.77250 49.6 74.43
6 294.362 15.37 69.77
7 77.931 2.85 1.78590 44.2 57.32
8 (Diffraction) 39.096 10.62 1.48749 70.2 52.21
9 116.147 (variable) 50.48
10 188.678 2.87 1.80809 22.8 35.18
11 -596.641 1.80 1.83400 37.2 34.44
12 65.402 (variable) 32.78
13 (Aperture) ∞ 10.55 26.47
14 59.928 1.30 1.84666 23.9 25.68
15 24.737 5.21 1.67300 38.1 25.22
16 1725.376 0.50 25.17
17 57.688 3.79 1.84666 23.9 25.30
18 -133.427 1.30 1.81600 46.6 24.95
19 29.867 3.81 24.07
20 -68.339 1.30 1.81600 46.6 24.14
21 100.805 1.36 25.30
22 ∞ 0.00 25.27
23 53.488 9.28 1.61340 44.3 26.72
24 -21.712 1.80 1.59282 68.6 27.46
25 93.003 1.38 29.47
26 320.402 1.80 1.80809 22.8 29.82
27 46.456 4.87 1.65412 39.7 31.04
28 -312.497 0.15 31.76
29 65.840 4.45 1.63980 34.5 33.39
30 -283.057 2.38 33.64
31 ∞ 2.00 1.51633 64.1 34.06
32 ∞ 34.25
Image plane ∞

Aspheric data 1st surface
K = -1.05229e-002 B = -7.55660e-009 C = 5.97002e-013 D = 9.89658e-017
E = 1.12786e-019

8th surface (diffractive surface)
C1 = -6.13697e-005 C2 = -8.78881e-009 C3 = -1.00912e-011
C4 = 2.05921e-015
C5 = 9.82979e-020

Various data

Focal length 392.19
F number 4.12
Half angle of view (degrees) 3.16
Statue height 21.64
Total lens length 261.26
BF 63.27

d 9 27.06
d12 22.72

Entrance pupil position 521.30
Exit pupil position -74.49
Front principal point position -438.60
Rear principal point position -352.93

Zoom lens group data group Start surface Focal length Lens configuration length Front principal point position Rear principal point position
1 1 164.78 86.32 -22.30 -77.32
2 10 -119.44 4.67 3.92 1.31
3 13 -577.30 81.23 -31.35 -107.65

Single lens Data lens Start surface Focal length
1 1 188.59
2 3 129.72
3 5 -145.01
4 7 -103.16
5 8 115.66
6 10 177.68
7 11 -70.59
8 14 -50.61
9 15 37.25
10 17 48.01
11 18 -29.80
12 20 -49.74
13 23 26.42
14 24 -29.52
15 26 -67.44
16 27 62.16
17 29 83.91
18 31 0.00

L1: First lens group L2: Second lens group L3: Third lens group
Ldoe: Diffractive optical element L _anm : Second positive lens from the object side using anomalous partial dispersion glass
Lfo: Focus lens group LIS: Anti-vibration lens group asph: Aspheric surface S: Aperture stop

Claims (9)

First lens group with positive refractive power in order from the object side to the image side, second lens group with negative refractive power that moves to the image side on the optical axis when focusing from an object at infinity to a close object, aperture stop In the imaging optical system composed of the third lens group,
The first lens group includes a diffractive optical element and an aspheric lens including an aspheric lens surface,
The effective radius of the aspheric lens surface is _hamax ,
The point where the aspherical lens surface intersects the optical axis is the origin, and the distance from the position at the effective radius _hamax of the aspherical lens surface to the plane passing through the origin and perpendicular to the optical axis is xb,
The distance from the position at half the effective radius _{ha max} ( _hamax / 2) of the aspherical lens surface to the plane passing through the origin and perpendicular to the optical axis is xa,
Let R be the radius of the phantom spherical surface passing through the origin and the half of the effective radius _{ha max} (h _amax / 2) of the aspheric lens surface, and the radius R is R = (4 * xa ² + _{ha max} ² ) / (8 * xa)
The distance from the position at the effective radius _{ha max} of the virtual spherical surface to the plane passing through the origin and perpendicular to the optical axis is xb ′, and xb ′ = R when the aspherical lens surface is convex on the object side -√ (R ² -h _amax ² ) ((xb '= R + √ (R ² -h _amax ² ) for concave shape))
Fgdoe the overall focal length of the diffractive optical element including the diffractive surface,
The focal length of only the refractive part excluding the diffraction surface from the diffractive optical element is fg,
Focal length fdoe at the diffractive surface of the diffractive optical element,
The focal length of the entire system when focusing on an object at infinity is f,
Let the total lens length be L,
An aspherical amount ΔdbA in the optical axis direction at an effective radius of the aspherical lens surface of the aspherical lens,
Focal length ΔdbD representing the amount of aspheric component on the diffractive surface of the diffractive optical element
ΔdbA = xb-xb '
ΔdbD = (fgdoe-fg) -fdoe
When
1.00 × 10 ^-6 <| ΔdbA / ΔdbD | <4.30 × 10 ^-6
5.0 <| (fdoe / f) * (L / f) | <20.0
An imaging optical system that satisfies the following conditional expression: The aspherical lens surface is disposed closer to the object side than the diffractive surface of the diffractive optical element,
The height from the optical axis of the on-axis paraxial ray incident on the aspherical lens surface is _asph ,
Hb _{asph is} the height from the optical axis of the paraxial ray of the pupil incident on the aspherical lens surface,
The height from the optical axis of the on-axis paraxial ray incident on the diffraction surface of the diffractive optical element is h _doe ,
Hb _{doe is} the height from the optical axis of the paraxial ray of the pupil incident on the diffractive surface of the diffractive optical element,
When the distance on the optical axis between the aspheric lens surface and the diffractive surface of the diffractive optical element is Lad,
0.70 <| h _asph / hb _asph | <1.00
0.85 <| h _doe / hb _doe | <1.30
0.01 <| Lad / f | <0.30
2. The imaging optical system according to claim 1, wherein the following conditional expression is satisfied.   The aspherical shape of the aspherical lens surface is continuously changing in the radial direction from the center to the periphery, and the negative refractive power is increased at the periphery. The imaging optical system according to 2. The second lens counting from the object side of the first lens group is a positive lens,
The Abbe number of the material of the positive lens is νd _anm ,
The height from the optical axis when the axial paraxial ray passes through the object-side lens surface of the positive lens is h _anm ,
Hb _anm , the height from the optical axis when the pupil paraxial ray passes through the object-side lens surface of the positive lens,
When the focal length of the positive lens is _fanm ,
70 <νd _anm <100
0.70 <| h _anm / hb _anm | <0.90
0.10 <f _anm /f<0.50
4. The imaging optical system according to claim 1, wherein the following conditional expression is satisfied.   In order from the object side to the image side, the first lens group includes a positive lens, a positive lens, a negative lens having an aspherical lens surface, a negative lens and a positive lens cemented, and a cemented optical unit formed on the cemented surface. 5. The imaging optical system according to claim 1, comprising a lens.   In order from the object side to the image side, the first lens unit includes a positive lens having an aspheric lens surface, a positive lens, a negative lens, a negative lens and a positive lens, and a cemented surface in which a diffractive optical part is formed. 5. The imaging optical system according to claim 1, comprising a lens.   7. The imaging optical system according to claim 1, wherein the second lens group includes a cemented lens in which a positive lens and a negative lens are cemented.   The third lens group includes a lens unit that moves in a direction having a component perpendicular to the optical axis to move an imaging position in a direction perpendicular to the optical axis. 7. The imaging optical system according to any one of 7 above.   9. 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.