JP6273797B2 - OPTICAL SYSTEM, OPTICAL DEVICE, AND OPTICAL SYSTEM MANUFACTURING METHOD - Google Patents

Description

  The present invention relates to an optical system including a diffractive optical element, an optical apparatus, and a method for manufacturing the optical system.

  Conventionally, an optical system having a first lens group having a positive refractive power and a second lens group having a negative refractive power in order from the object side as a lens type suitable for a photographing optical system having a long focal length. A so-called telephoto lens is known.

  In a telephoto lens having a long focal length, chromatic aberrations such as longitudinal chromatic aberration and lateral chromatic aberration tend to deteriorate as aberrations increase as the focal length increases. In order to satisfactorily correct these chromatic aberrations, various telephoto lenses have been proposed which are achromatic by combining a positive lens using a low dispersion glass material and a negative lens using a high dispersion glass material. On the other hand, as a method for correcting chromatic aberration of an optical system, a diffractive optical system in which a diffraction grating having a diffractive action is provided on a lens surface or a part of an optical system as compared with a method of combining two glass materials (lenses) having different dispersion A method of reducing chromatic aberration using an element is disclosed (see, for example, Patent Document 1).

  A diffractive optical element is an optical element having a slit-like or groove-like lattice structure with a few evenly spaced per minute interval (1 mm). It has the property of producing a diffracted light beam in a direction determined by (interval) and the wavelength of light. Such a diffractive optical element is used in various optical systems. For example, recently, a diffractive optical element that collects diffracted light of a specific order at one point and uses it as a lens is known.

  By using such a diffractive optical element, a telephoto optical system (telephoto lens) having high optical performance with a small tele-ratio (short lens overall length) while satisfactorily correcting various aberrations such as chromatic aberration. Can be realized.

JP 2009-271345 A

  However, in a conventional optical system using a diffractive optical element, a relatively large amount of flare occurs due to light diffusion on the diffractive surface.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an optical system, an optical apparatus, and a method for manufacturing the optical system that have high optical performance while suppressing the occurrence of flare.

In order to achieve such an object, an optical system according to the first invention includes a focusing lens for performing focusing on an object, and a plurality of lenses disposed on the object side of the focusing lens. And a diffractive optical element disposed on any lens on the image side with respect to the most object side lens among the plurality of lenses, and satisfies the following conditional expression.
0.075 <Ldoe / f <0.125
0.50 <L / f <0.75
However,
Ldoe: the distance from the most object side lens surface in the optical system to the diffractive surface in the diffractive optical element,
f: the focal length at the time of infinity focusing of the optical system,
L: Distance from the lens surface closest to the object side to the image plane in the optical system.

An optical system according to a second invention includes a focusing lens for performing focusing on an object, a plurality of lenses disposed closer to the object than the focusing lens, and the plurality of lenses A diffractive optical element disposed on any lens on the image side of the lens closest to the object side, and satisfies the following conditional expression.
0.075 <Ldoe / f <0.125
1.02 <Rdoe / Ddoe <1.35
However,
Ldoe: the distance from the most object side lens surface in the optical system to the diffractive surface in the diffractive optical element,
f: focal length of the optical system when focused at infinity,
Rdoe: radius of curvature of the diffractive surface of the diffractive optical element,
Ddoe: A distance from the position of the focal point on the rear side of the lens group from the lens closest to the object side to the lens on which the diffractive optical element is disposed, among the plurality of lenses, to the diffractive surface of the diffractive optical element.

  An optical apparatus according to the present invention is an optical apparatus including an optical system that forms an image of an object on a predetermined surface, and uses the optical system according to the present invention as the optical system.

Further, in the method of manufacturing an optical system according to the present invention, a focusing lens for performing focusing on an object is disposed, a plurality of lenses are disposed closer to the object than the focusing lens, and the plurality of lenses A diffractive optical element is arranged in any one of the lenses on the image side of the lens closest to the object side so that the following conditional expression is satisfied.
0.075 <Ldoe / f <0.125
0.50 <L / f <0.75
However,
Ldoe: the distance from the most object side lens surface in the optical system to the diffractive surface in the diffractive optical element,
f: the focal length at the time of infinity focusing of the optical system,
L: Distance from the lens surface closest to the object side to the image plane in the optical system.

  ADVANTAGE OF THE INVENTION According to this invention, generation | occurrence | production of a flare can be suppressed and the optical system which had high optical performance, and an optical apparatus provided with the same can be obtained.

It is sectional drawing of the optical system which concerns on 1st Example. FIG. 7 is a diagram illustrating various aberrations of the optical system according to the first example. It is a graph which shows the wavelength characteristic of the axial chromatic aberration of the optical system which concerns on 1st Example, Comprising: (a) shows the state of an optical system independent, (b) shows a state when a teleconverter is attached. It is sectional drawing of the optical system which concerns on 2nd Example. It is an aberration diagram of the optical system according to the second example. It is a graph which shows the wavelength characteristic of the axial chromatic aberration of the optical system which concerns on 2nd Example, Comprising: (a) shows the state of an optical system independent, (b) shows a state when a teleconverter is attached. It is sectional drawing of the optical system which concerns on 3rd Example. It is an aberration diagram of the optical system according to the third example. It is a graph which shows the wavelength characteristic of the axial chromatic aberration of the optical system which concerns on 3rd Example, (a) shows the state of an optical system independent, (b) shows the state when a teleconverter is attached. It is sectional drawing of a digital single-lens reflex camera. It is a flowchart which shows the manufacturing method of an optical system. It is sectional drawing which shows an example of a diffractive optical element. (A) is sectional drawing which shows the state in which light injects into the conventional optical system from the diagonal direction, (b) is sectional drawing which shows the state in which light injects into the optical system of this embodiment from the diagonal direction.

  Hereinafter, preferred embodiments of the present application will be described with reference to the drawings. A digital single-lens reflex camera CAM provided with the optical system TL according to the present application is shown in FIG. In the digital single-lens reflex camera CAM shown in FIG. 10, light from an object (subject) (not shown) is collected by an optical system (telephoto lens) TL as a photographic lens, and is focused on a focusing screen F via a quick return mirror M. Imaged on top. The light imaged on the focusing screen F is reflected a plurality of times in the pentaprism P and guided to the eyepiece lens E. Thus, the photographer can observe the image of the object (subject) as an erect image through the eyepiece lens E.

  When a release button (not shown) is pressed by the photographer, the quick return mirror M is retracted out of the optical path, and the light from the object (subject) collected by the optical system TL forms an image on the image sensor C. To form an image of the subject. As a result, light from the object (subject) is imaged on the image sensor C, picked up by the image sensor C, and recorded in a memory (not shown) as an image of the object (subject). In this way, the photographer can photograph an object (subject) with the digital single-lens reflex camera CAM. Even if the camera does not have the quick return mirror M, the same effect as the camera CAM can be obtained. Further, the digital single-lens reflex camera CAM shown in FIG. 10 may be configured to hold the optical system TL in a removable manner, or may be configured integrally with the optical system TL.

  For example, as shown in FIG. 1, the optical system TL includes a focusing lens LF for performing focusing on an object, a plurality of lenses disposed on the object side of the focusing lens LF, and a plurality of lenses. The lens has a diffractive optical element DOE disposed on any lens on the image side of the lens closest to the object side, and satisfies the following conditional expression (1).

0.075 <Ldoe / f <0.125 (1)
However,
Ldoe: distance from the most object-side lens surface in the optical system TL to the diffractive surface in the diffractive optical element DOE,
f: Focal length when the optical system TL is focused at infinity.

  The diffractive optical element DOE in the present embodiment is formed by stacking diffractive element elements having a surface on which sawtooth-shaped diffraction grating grooves are formed, as shown in FIG. 12, for example, and a desired wide wavelength region (for example, It has a feature that high diffraction efficiency is maintained in almost the entire visible light region, that is, the wavelength characteristic is good. In general, as a multi-layer type diffractive optical element, for example, a so-called close-contact multi-layer type diffractive optical element which is composed of two types of diffractive element elements made of different materials and is in close contact with the same diffraction grating groove is known. It has been.

  As shown in FIG. 12, an edge surface PE is formed on the diffractive optical element DOE. When strong light is incident on the diffractive optical element DOE from an oblique direction (for example, at an incident angle of 45 degrees), the edge surface PE Flares are generated by the generated higher-order diffracted light and diffused light. As shown in FIG. 13A, in the conventional optical system TLA using the diffractive optical element DOE, the diffractive optical element DOE is provided at a position close to the object side. Light from the direction arrives. The half angle of view of the optical system TLA illustrated in FIG. 13A is about 4.2 °. In principle, light incident on the optical system TLA at an incident angle of 45 degrees does not reach the image plane IA. . However, light from an oblique direction (incident angle of 45 °) enters a wide range of the diffractive optical element DOE, and higher-order diffracted light and diffused light generated on the edge surface PE reach the image plane IA as flare. , Resulting in degradation of image quality.

  On the other hand, the conditional expression (1) is a conditional expression that defines an appropriate position of the diffractive optical element DOE. By satisfying conditional expression (1), as shown in FIG. 13B, the diffractive optical element DOE is positioned on the image plane I side as compared with the conventional case, and the optical system TL has an incident angle larger than the half field angle. Since light from an oblique direction incident on the diffractive optical element does not easily reach the diffractive optical element DOE, the occurrence of flare can be suppressed. As described above, according to the present embodiment, the telephoto optical system TL having a small tele ratio and high optical performance while suppressing the occurrence of flare and correcting various aberrations such as chromatic aberration, and the like, and this The optical apparatus (digital single-lens reflex camera CAM) provided with can be obtained.

  When the condition is lower than the lower limit value of the conditional expression (1), the position of the diffractive optical element DOE is too close to the object side, so that strong direct light from the sun or the like diffuses on the diffractive surface in the diffractive optical element DOE, Causes flare. Note that the lens hood can be expected to prevent flare, but if the condition is below the lower limit of conditional expression (1), the effect of the lens hood is also limited. On the other hand, when the condition exceeds the upper limit value of the conditional expression (1), the position of the diffractive optical element DOE is too close to the image plane I side, so that the optical effect of the diffractive optical element DOE is limited, and the optical performance is reduced. Incurs a decline.

  In order to secure the effect of the present application, it is desirable to set the upper limit of conditional expression (1) to 0.120. On the other hand, in order to ensure the effect of the present application, it is desirable to set the lower limit value of conditional expression (1) to 0.080.

  In addition, when a close-contact multilayer diffractive optical element is disposed, there is a configuration in which it is disposed on the joint surface of two glass lenses. However, if a diffractive optical element is disposed on the joint surface of two glass lenses, diffraction occurs due to stress. There is a problem in that the refractive index of the optical element changes and the diffraction efficiency tends to decrease. Therefore, in the case of disposing a contact multilayer diffractive optical element, a method of disposing the diffractive optical element on one surface of the lens is suitable. The diffractive optical element DOE preferably has a rotationally symmetric shape with respect to the optical axis.

  In such an optical system TL, it is preferable that the following conditional expression (2) is satisfied.

0.30 <f1a / f <0.40 (2)
However,
f1a: The focal length of the lens group from the lens closest to the object side to the lens on which the diffractive optical element DOE is disposed among the plurality of lenses.

  Conditional expression (2) defines the power of the lens group from the lens closest to the object side to the lens on which the diffractive optical element DOE is disposed. Hereinafter, this lens group may be referred to as a front group G1a for convenience. In a telephoto optical system (telephoto lens) with a tele ratio of about 0.65, the focal length of the front group G1a having positive power is appropriate to be about 35% of the focal length of the entire optical system. Conditional expression (2) indicates that the diffractive optical element DOE is disposed in the vicinity of the final surface of the front group G1a having a positive power. When the condition is less than the lower limit value of the conditional expression (2), the focal length of the front group G1a becomes too short, which causes aberration deterioration. On the other hand, when the condition exceeds the upper limit value of the conditional expression (2), the focal length of the front group G1a becomes too long, and therefore it is necessary to increase the power of the lens arranged on the image side relative to the diffractive optical element DOE. As a result, aberrations are deteriorated.

  In order to secure the effect of the present application, it is desirable to set the upper limit of conditional expression (2) to 0.39. On the other hand, in order to ensure the effect of the present application, it is desirable to set the lower limit value of conditional expression (2) to 0.31.

  In such an optical system TL, it is preferable that the following conditional expression (3) is satisfied.

1.02 <Rdoe / Ddoe <1.35 (3)
However,
Rdoe: radius of curvature of the diffractive surface in the diffractive optical element DOE,
Ddoe: A distance from the position of the focal point on the rear side of the lens group from the lens closest to the object side to the lens on which the diffractive optical element DOE is disposed among the plurality of lenses to the diffractive surface of the diffractive optical element DOE.

  Conditional expression (3) is a conditional expression for avoiding a ghost generated on the diffractive surface while keeping the light incident on the diffractive optical element DOE substantially perpendicular to the diffractive surface. In conditional expression (3), the state of Rdoe / Ddoe = 1 is a state in which the axial light beam is perpendicularly incident on the diffractive surface of the diffractive optical element DOE. By satisfying the conditional expression (3), it is out of the state of Rdoe / Ddoe = 1, so that the ghost can be easily avoided. Further, since the light beam can be incident substantially perpendicularly on the entire diffractive surface of the diffractive optical element DOE, the shape of the diffractive optical element DOE is simplified, for example, the grating height of the diffractive optical element DOE can be made constant. It becomes possible. If the condition is lower than the lower limit value of the conditional expression (3), it becomes close to the state of Rdoe / Ddoe = 1, and it is difficult to avoid ghost. On the other hand, when the condition exceeds the upper limit value of the conditional expression (3), it is necessary to change the grating height or the like according to the incident angle of light incident on the diffractive optical element DOE, and the shape of the diffractive optical element DOE is complicated. Become.

  In order to secure the effect of the present application, it is desirable to set the upper limit value of conditional expression (3) to 1.30. On the other hand, in order to ensure the effect of the present application, it is desirable to set the lower limit value of conditional expression (3) to 1.03.

  In such an optical system TL, it is preferable that the following conditional expression (4) is satisfied.

0.50 <L / f <0.80 (4)
However,
L: Distance from the lens surface closest to the object side to the image plane in the optical system TL.

  Conditional expression (4) is a conditional expression for defining a tele ratio obtained by dividing the total optical length of the entire optical system TL by the focal length. When the condition exceeds the upper limit value of the conditional expression (4), the focal length of the diffractive optical element DOE becomes too long, and the meaning of inserting the diffractive optical element DOE is lost. On the other hand, when the condition is lower than the lower limit value of the conditional expression (4), the aberration generated in the entire optical system TL becomes too large, and the performance deteriorates.

  In order to secure the effect of the present application, it is desirable to set the upper limit value of conditional expression (4) to 0.75.

  Here, a method for manufacturing the optical system TL having the above-described configuration will be described with reference to FIG. First, a focusing lens LF is arranged in a cylindrical barrel, a plurality of lenses are arranged on the object side of the focusing lens LF, and the image side of the lens closest to the object side among the plurality of lenses is arranged. The diffractive optical element DOE is disposed on any of the lenses (step ST10). Then, by moving the focusing lens LF along the optical axis, the focusing lens LF is configured to be drivable so that focusing from an infinite object to a finite distance object is performed (step ST20).

  In step ST10 in which the lens is incorporated, the diffractive optical element DOE and the like are arranged so as to satisfy the conditional expression (1) and the like. According to such a manufacturing method, a telephoto optical system having a small tele ratio (short lens overall length) and high optical performance while suppressing the occurrence of flare and correcting various aberrations such as chromatic aberration. TL can be obtained.

(First embodiment)
Embodiments of the present application will be described below with reference to the accompanying drawings. First, a first embodiment of the present application will be described with reference to FIGS. FIG. 1 is a cross-sectional view of an optical system TL (TL1) according to the first example. The optical system TL1 according to the first example includes a first lens group G1 having a positive refractive power and a second lens group G2 having a negative refractive power, which are arranged in order from the object side along the optical axis. Configured.

  The first lens group G1 includes a front group G1a that is arranged in order from the object side along the optical axis, and a rear group G1b that is separated from the front group G1a by the longest air interval in the first lens group G1. Composed. The front group G1a of the first lens group G1 includes, in order from the object side, a cemented lens in which a first positive lens L11 that is a single lens, a second positive lens L12, and a first negative lens L13 are bonded together, and a diffractive optical element. And a third positive lens L14 on which the DOE is disposed. A diffractive optical element DOE is disposed on the lens surface on the image plane I side of the third positive lens L14. The diffractive optical element DOE is a close-contact multi-layer diffractive optical element in which two types of diffractive element elements made of different materials are in contact with each other through the same diffraction grating groove. The next diffraction grating (diffraction grating having a rotationally symmetric shape with respect to the optical axis) is formed. The rear group G1b of the first lens group G1 includes a cemented lens in which a second negative lens L15 and a fourth positive lens L16 are bonded in order from the object side.

  In the second lens group G2, a focusing lens LF in which a fifth positive lens L21 and a third negative lens L22 are bonded together, a fourth negative lens L23, and a sixth positive lens L24 are bonded in order from the object side. The first achromatic lens LC1, the cemented lens in which the seventh positive lens L25 and the fifth negative lens L26 are bonded together, the sixth negative lens L27 that is a single lens, the eighth positive lens L28, and the seventh negative lens L29 Are affixed to a second achromatic lens LC2 and a ninth positive lens L30 that is a single lens. When focusing from an object at infinity to an object at a short distance (finite distance), the focusing lens LF moves toward the image plane I along the optical axis. In addition, a stop S is disposed between the focusing lens LF and the first achromatic lens LC1 in the second lens group G2.

  Tables 1 to 3 are shown below, and these are tables showing values of specifications of the optical systems (telephoto lenses) according to the first to third examples. In [Overall specifications] in each table, f is the focal length, FNO is the F number, ω is the half angle of view (maximum incident angle: unit is “°”), Y is the image height, and Bf is the back focus. (Air equivalent length) is shown respectively. In [Overall specifications], L is the total length of the optical system (distance from the first lens surface to the image plane I), Ldoe is the distance from the first lens surface to the diffraction surface, and f1a is the front group. Ddoe indicates the distance from the rear focal point position of the front group to the diffraction surface. In [Lens Data], the surface number is the lens surface number counted from the object side, Ri is the radius of curvature of the i-th lens surface from the object side, Di is the i-th lens surface and i + 1-th lens surface from the object side. Nd is the refractive index for the d-line (wavelength λ = 587.6 nm), νd is the Abbe number for the d-line (wavelength λ = 587.6 nm), and θgF is Each partial dispersion ratio is shown.

  Note that the radius of curvature “∞” indicates a plane, and the refractive index of air nd = 1.0000 is omitted. Further, the refractive index of each lens with respect to g-line (wavelength λ = 435.8 nm) is ng, the refractive index of each lens with respect to d-line (wavelength λ = 587.6 nm) is nd, and the F-line (wavelength λ) of each lens. = 486.1 nm) is nF, and the refractive index of each lens for the C-line (wavelength λ = 656.3 nm) is nC. At this time, the partial dispersion ratio θgF of each lens is defined by the following equation (A).

  θgF = (ng−nF) / (nF−nC) (A)

  Further, the phase shape ψ of the diffractive surface shown in [Diffraction surface data] is expressed by the following equation (B).

ψ (h, m) = {2π / (m × λ0)} × (C 2 × h ² + C 4 × h ⁴ + C 6 × h ⁶ ...) (B)
However,
h: height in a direction perpendicular to the optical axis,
m: diffraction order of diffracted light,
λ0: Design wavelength,
Ci: Phase coefficient (i = 1, 2, 3,...).

  Further, the refractive power φD of the diffractive surface at an arbitrary wavelength λ and an arbitrary diffraction order m can be expressed by the following equation (C) using the lowest-order phase coefficient C1.

  φD (h, m) = − 2 × C1 × m × λ / λ0 (C)

The phase coefficient is shown in [Diffraction plane data], and “En” represents “× 10 ⁻ⁿ ”. [Conditional Expression Corresponding Value] indicates the corresponding value of each conditional expression. The focal length f, the radius of curvature Ri, the surface interval Di, and other length units listed in all the following specification values are generally “mm”, but the optical system is proportionally expanded or contracted. However, the same optical performance can be obtained, and the present invention is not limited to this. In addition, the same reference numerals as those in the present embodiment are used in the specification values of the second to third embodiments described later.

  Table 1 below shows specifications in the first embodiment. In addition, the curvature radius Ri of the 1st surface-the 29th surface in Table 1 respond | corresponds to code | symbol R1-R29 attached | subjected to the 1st surface-the 29th surface in FIG. In the first embodiment, the eighth surface is a diffractive surface.

(Table 1)
[Overall specifications]
f = 294
FNO = 4.08
2ω = 8.4
Y = 21.63
Bf = 54.00
L = 190.5
Ldoe = 28.73
f1a = 106.69
Ddoe = 87.77
[Lens specifications]
Surface number Ri Di nd νd θgF
1 112.614 7.31 1.4875 70.3 0.5291
2 1198.911 0.27
3 80.591 11.45 1.4978 82.6 0.5386
4 -504.430 2.50 1.5750 41.5 0.5764
5 215.439 2.00
6 77.236 5.00 1.5168 63.9 0.5359
7 106.549 0.20 1.5278 33.4 ―
8 106.549 0.30 1.5572 50.0 ― (Diffraction surface)
9 106.549 26.05
10 40.477 1.50 1.9108 35.2 0.5822
11 26.124 7.51 1.4875 70.3 0.5291
12 71.781 6.54
13 124.603 2.59 1.6200 36.4 0.5877
14 -321.404 1.20 1.6968 55.5 0.5430
15 42.442 23.41
16 ∞ 2.99 (Aperture)
17 53.509 1.78 1.9108 35.2 0.5822
18 23.591 2.77 1.5750 41.5 0.5764
19 222.119 2.69
20 64.088 2.37 1.7283 28.4 0.6069
21 -67.244 0.85 1.7292 54.6 0.5442
22 29.850 2.27
23 -66.093 0.80 1.7292 54.6 0.5442
24 107.388 2.17
25 69.491 3.09 1.5481 45.5 0.5684
26 -55.525 1.00 1.7880 47.4 0.5559
27 -315.000 10.29
28 68.665 5.55 1.4875 70.3 0.5291
29 -68.665 54.00
[Diffraction surface data]
m = 1
C1 = -4.058E-05
C2 = -3.974E-09
[Conditional expression values]
Conditional expression (1) Ldoe / f = 0.10
Conditional expression (2) f1a / f = 0.36
Conditional expression (3) Rdoe / Ddoe = 1.21
Conditional expression (4) L / f = 0.65

  Thus, in this embodiment, it can be seen that all the conditional expressions (1) to (4) are satisfied.

  FIG. 2 is a diagram illustrating various aberrations of the optical system TL1 according to the first example. In the various aberration diagrams, FNO represents the F number, and Y represents the image height. Also, in the various aberration diagrams, d indicates the aberration at the d-line (λ = 587.6 nm), and g indicates the aberration at the g-line (λ = 435.8 nm). In the aberration diagrams showing astigmatism, the solid line shows the sagittal image plane, and the broken line shows the meridional image plane. The description of the various aberration diagrams is the same in the other examples. As can be seen from FIG. 2, in the first example, various aberrations are corrected favorably and the optical performance is excellent. As a result, by mounting the optical system TL1 of the first embodiment, excellent optical performance can be secured even in the digital single-lens reflex camera CAM.

  FIG. 3A is a graph showing the wavelength characteristic of longitudinal chromatic aberration of the optical system TL1 according to the first example. FIG. 3A shows that in the first example, the axial chromatic aberration is corrected well in the entire used wavelength range. FIG. 3B is a graph showing the wavelength characteristics of longitudinal chromatic aberration when a teleconverter is attached to the optical system TL1 according to the first example. FIG. 3B shows that the axial chromatic aberration is corrected well in the first embodiment even when the teleconverter is attached.

(Second embodiment)
Hereinafter, the second embodiment of the present application will be described with reference to FIGS. 4 to 6 and Table 2. FIG. FIG. 4 is a cross-sectional view of the optical system TL (TL2) according to the second embodiment. The optical system TL2 according to the second example includes a first lens group G1 having a positive refractive power and a second lens group G2 having a negative refractive power, which are arranged in order from the object side along the optical axis. Configured.

  The first lens group G1 includes a front group G1a that is arranged in order from the object side along the optical axis, and a rear group G1b that is separated from the front group G1a by the longest air interval in the first lens group G1. Composed. The front group G1a of the first lens group G1 includes, in order from the object side, a cemented lens in which a first positive lens L11 that is a single lens, a second positive lens L12, and a first negative lens L13 are bonded together, and a diffractive optical element. And a third positive lens L14 on which the DOE is disposed. A diffractive optical element DOE is disposed on the lens surface on the image plane I side of the third positive lens L14. The diffractive optical element DOE is the same as the diffractive optical element of the first embodiment, and a detailed description thereof will be omitted. The rear group G1b of the first lens group G1 includes a cemented lens in which a second negative lens L15 and a fourth positive lens L16 are bonded in order from the object side.

  In the second lens group G2, a focusing lens LF in which a fifth positive lens L21 and a third negative lens L22 are bonded together, a fourth negative lens L23, and a sixth positive lens L24 are bonded in order from the object side. The first achromatic lens LC1, the cemented lens in which the seventh positive lens L25 and the fifth negative lens L26 are bonded together, the sixth negative lens L27 that is a single lens, the eighth positive lens L28, and the seventh negative lens L29 Are affixed to a second achromatic lens LC2 and a ninth positive lens L30 that is a single lens. When focusing from an object at infinity to an object at a short distance (finite distance), the focusing lens LF moves toward the image plane I along the optical axis. In addition, a diaphragm S is provided between the focusing lens LF and the first achromatic lens LC1 in the second lens group G2.

  Table 2 below shows specifications in the second embodiment. In addition, the curvature radius Ri of the 1st surface-29th surface in Table 2 respond | corresponds to code | symbol R1-R29 attached | subjected to the 1st surface-29th surface in FIG. In the second embodiment, the eighth surface is a diffractive surface.

(Table 2)
[Overall specifications]
f = 294
FNO = 4.08
2ω = 8.4
Y = 21.63
Bf = 54.00
L = 191.2
Ldoe = 28.51
f1a = 104.65
Ddoe = 85.88
[Lens specifications]
Surface number Ri Di nd νd θgF
1 115.035 7.27 1.4875 70.3 0.5291
2 1569.495 0.25
3 81.363 11.29 1.4978 82.6 0.5386
4 -504.430 2.50 1.5750 41.5 0.5764
5 237.414 2.00
6 69.392 5.00 1.5168 63.9 0.5359
7 91.430 0.20 1.5278 33.4 ―
8 91.430 0.30 1.5572 50.0 ― (Diffraction surface)
9 91.430 25.64
10 41.929 1.50 1.9108 35.2 0.5822
11 26.360 7.48 1.4875 70.3 0.5291
12 75.456 6.47
13 132.140 2.50 1.6200 36.4 0.5877
14 -380.902 1.20 1.6968 55.5 0.5430
15 43.133 23.98
16 ∞ 2.81 (Aperture)
17 53.404 2.10 1.9108 35.2 0.5822
18 23.876 2.91 1.5750 41.5 0.5764
19 211.100 2.48
20 65.496 2.33 1.7283 28.4 0.6069
21 -64.938 0.85 1.7292 54.6 0.5442
22 29.867 2.33
23 -65.880 0.80 1.7292 54.6 0.5442
24 112.996 2.13
25 70.766 3.08 1.5481 45.5 0.5684
26 -54.825 1.00 1.7880 47.4 0.5559
27 -274.728 10.60
28 69.243 5.50 1.4875 70.3 0.5291
29 -69.243 54.00
[Diffraction surface data]
m = 1
C1 = -4.106E-05
C2 = -4.838E-09
[Conditional expression values]
Conditional expression (1) Ldoe / f = 0.10
Conditional expression (2) f1a / f = 0.36
Conditional expression (3) Rdoe / Ddoe = 1.06
Conditional expression (4) L / f = 0.65

  Thus, in this embodiment, it can be seen that all the conditional expressions (1) to (4) are satisfied.

  FIG. 5 is a diagram illustrating various aberrations of the optical system TL2 according to the second example. From FIG. 5, it can be seen that in the second example, various aberrations are satisfactorily corrected and the optical performance is excellent. As a result, by mounting the optical system TL2 of the second embodiment, excellent optical performance can be secured even in the digital single-lens reflex camera CAM.

  FIG. 6A is a graph showing the wavelength characteristic of axial chromatic aberration of the optical system TL2 according to the second example. From FIG. 6A, it can be seen that in the second example, the longitudinal chromatic aberration is well corrected in the entire used wavelength range. FIG. 6B is a graph showing the wavelength characteristics of longitudinal chromatic aberration when a teleconverter is attached to the optical system TL2 according to the second example. FIG. 6B shows that in the second example, the longitudinal chromatic aberration is corrected well even when the teleconverter is attached.

(Third embodiment)
Hereinafter, a third embodiment of the present application will be described with reference to FIGS. FIG. 7 is a cross-sectional view of the optical system TL (TL3) according to the third embodiment. The optical system TL3 according to the third example includes a first lens group G1 having a positive refractive power and a second lens group G2 having a negative refractive power, which are arranged in order from the object side along the optical axis. Configured.

  The first lens group G1 includes a front group G1a that is arranged in order from the object side along the optical axis, and a rear group G1b that is separated from the front group G1a by the longest air interval in the first lens group G1. Composed. The front group G1a of the first lens group G1 includes, in order from the object side, a cemented lens in which a first positive lens L11 that is a single lens, a second positive lens L12, and a first negative lens L13 are bonded together, and a diffractive optical element. And a third positive lens L14 on which the DOE is disposed. A diffractive optical element DOE is disposed on the lens surface on the image plane I side of the third positive lens L14. The diffractive optical element DOE is the same as the diffractive optical element of the first embodiment, and a detailed description thereof will be omitted. The rear group G1b of the first lens group G1 includes a cemented lens in which a second negative lens L15 and a fourth positive lens L16 are bonded in order from the object side.

  In the second lens group G2, a focusing lens LF in which a fifth positive lens L21 and a third negative lens L22 are bonded together, a fourth negative lens L23, and a sixth positive lens L24 are bonded in order from the object side. The first achromatic lens LC1, the cemented lens in which the seventh positive lens L25 and the fifth negative lens L26 are bonded together, the sixth negative lens L27 that is a single lens, the eighth positive lens L28, and the seventh negative lens L29 Are affixed to a second achromatic lens LC2 and a ninth positive lens L30 that is a single lens. When focusing from an object at infinity to an object at a short distance (finite distance), the focusing lens LF moves toward the image plane I along the optical axis. In addition, a diaphragm S is provided between the focusing lens LF and the first achromatic lens LC1 in the second lens group G2.

  Table 3 below shows specifications in the third embodiment. In addition, the curvature radius Ri of the 1st surface-29th surface in Table 3 respond | corresponds to code | symbol R1-R29 attached | subjected to the 1st surface-29th surface in FIG. In the third embodiment, the eighth surface is a diffractive surface.

(Table 3)
[Overall specifications]
f = 294
FNO = 4.08
2ω = 8.4
Y = 21.63
Bf = 54.00
L = 190.5
Ldoe = 30.26
f1a = 106.81
Ddoe = 85.88
[Lens specifications]
Surface number Ri Di nd νd θgF
1 112.614 7.47 1.4875 70.3 0.5291
2 1198.911 0.25
3 80.591 12.82 1.4978 82.6 0.5386
4 -504.430 2.50 1.5317 48.8 0.5621
5 215.439 2.02
6 77.236 5.00 1.5168 63.9 0.5359
7 106.549 0.20 1.5278 33.4 ―
8 106.549 0.20 1.5572 50.0 ― (Diffraction surface)
9 106.549 24.12
10 40.477 1.50 1.9027 35.7 0.5804
11 26.124 7.68 1.4875 70.3 0.5291
12 71.781 7.27
13 124.603 2.88 1.6034 38.0 0.5829
14 -321.404 1.20 1.7130 54.0 0.5451
15 42.442 23.52
16 ∞ 2.69 (Aperture)
17 53.509 2.90 1.9027 35.7 0.5804
18 23.591 2.31 1.5186 69.9 0.5318
19 222.119 2.85
20 64.088 2.49 1.7283 28.4 0.6069
21 -67.244 0.85 1.7130 54.0 0.5451
22 29.850 2.04
23 -66.093 0.80 1.7410 52.8 0.5471
24 107.388 1.87
25 69.491 3.77 1.5814 41.0 0.5763
26 -55.525 1.00 1.7292 54.6 0.5442
27 -315.000 10.00
28 68.665 4.31 1.4875 70.3 0.5291
29 -68.665 54.00
[Diffraction surface data]
m = 1
C1 = -3.635E-05
C2 = -4.806E-09
[Conditional expression values]
Conditional expression (1) Ldoe / f = 0.10
Conditional expression (2) f1a / f = 0.36
Conditional expression (3) Rdoe / Ddoe = 1.13
Conditional expression (4) L / f = 0.65

  Thus, in this embodiment, it can be seen that all the conditional expressions (1) to (4) are satisfied.

  FIG. 8 is a diagram illustrating various aberrations of the optical system TL3 according to the third example. From FIG. 8, it can be seen that in the third example, various aberrations are satisfactorily corrected and the optical performance is excellent. As a result, by mounting the optical system TL3 of the third embodiment, excellent optical performance can be secured even in the digital single-lens reflex camera CAM.

  FIG. 9A is a graph showing the wavelength characteristics of longitudinal chromatic aberration of the optical system TL3 according to the third example. From FIG. 9A, it can be seen that in the third example, the axial chromatic aberration is corrected well over the entire wavelength range used. FIG. 9B is a graph showing the wavelength characteristics of longitudinal chromatic aberration when a teleconverter is attached to the optical system TL3 according to the third example. From FIG. 9B, it can be seen that in the third example, the axial chromatic aberration is well corrected even when the teleconverter is attached.

  In the above-described embodiment, the following description can be appropriately adopted as long as the optical performance is not impaired.

  In each of the above-described embodiments, the lens group or the partial lens group is moved so as to have a component in a direction perpendicular to the optical axis, or is rotated (oscillated) in the in-plane direction including the optical axis, thereby causing camera shake. An image stabilizing lens group that corrects image blur caused by the image blur may be used. For example, at least a part of the lenses arranged on the image side of the stop S can be an anti-vibration lens group, and in particular, the seventh positive lens L25, the fifth negative lens L26, and the sixth negative lens L27 are prevented. A vibrating lens group is preferable. Further, it is more preferable to dispose achromatic lenses LC1 and LC2 including a positive lens and a negative lens on the object side and the image side of the seventh positive lens L25, the fifth negative lens L26, and the sixth negative lens L27.

  Further, the lens surface may be formed as a spherical surface, a flat surface, or an aspheric surface. When the lens surface is a spherical surface or a flat surface, lens processing and assembly adjustment are facilitated, and optical performance deterioration due to errors in processing and assembly adjustment can be prevented. Further, even when the image plane is deviated, it is preferable because there is little deterioration in drawing performance. When the lens surface is an aspheric surface, the aspheric surface is an aspheric surface by grinding, a glass mold aspheric surface made of glass with an aspheric shape, or a composite aspheric surface made of resin with an aspheric shape on the glass surface. Any aspherical surface may be used. The lens surface may be a diffractive surface, and the lens may be a gradient index lens (GRIN lens) or a plastic lens.

  The aperture stop is preferably disposed on the image side of the focusing lens LF. However, the role of the aperture stop may be substituted by a lens frame without providing a member as the aperture stop.

  Each lens surface may be provided with an antireflection film having a high transmittance in a wide wavelength range in order to reduce flare and ghost and achieve high optical performance with high contrast.

  In the present embodiment, the telephoto lens is described as an example of the optical system. However, the present invention is not limited to this. For example, an optical system such as a zoom lens may be used.

  In addition, the optical system of the present embodiment is used in a digital single-lens reflex camera, but the present invention is not limited to this. For example, the optical system can be used in an optical device such as a digital still camera or a digital video camera.

CAM digital SLR camera (optical equipment)
TL optical system G1 first lens group G2 second lens group G1a front group G1b rear group LF focusing lens DOE diffractive optical element S aperture I image plane

Claims (7)

A focusing lens for focusing on an object;
A plurality of lenses disposed on the object side of the focusing lens;
A diffractive optical element disposed on any lens on the image side of the lens on the most object side among the plurality of lenses,
An optical system satisfying the following conditional expression:
0.075 <Ldoe / f <0.125
0.50 <L / f <0.75
However,
Ldoe: the distance from the most object side lens surface in the optical system to the diffractive surface in the diffractive optical element,
f: the focal length at the time of infinity focusing of the optical system,
L: Distance from the lens surface closest to the object side to the image plane in the optical system. A focusing lens for focusing on an object;
A plurality of lenses disposed on the object side of the focusing lens;
A diffractive optical element disposed on any lens on the image side of the lens on the most object side among the plurality of lenses,
An optical system satisfying the following conditional expression:
0.075 <Ldoe / f <0.125
1.02 <Rdoe / Ddoe <1.35
However,
Ldoe: the distance from the most object side lens surface in the optical system to the diffractive surface in the diffractive optical element,
f: focal length of the optical system when focused at infinity,
Rdoe: radius of curvature of the diffractive surface of the diffractive optical element,
Ddoe: A distance from the position of the focal point on the rear side of the lens group from the lens closest to the object side to the lens on which the diffractive optical element is disposed, among the plurality of lenses, to the diffractive surface of the diffractive optical element. The optical system according to claim 1 , wherein the following conditional expression is satisfied.
1.02 <Rdoe / Ddoe <1.35
However,
Rdoe: radius of curvature of the diffractive surface of the diffractive optical element,
Ddoe: A distance from the position of the focal point on the rear side of the lens group from the lens closest to the object side to the lens on which the diffractive optical element is disposed, among the plurality of lenses, to the diffractive surface of the diffractive optical element. The optical system according to claim 2 , wherein the following conditional expression is satisfied.
0.50 <L / f <0.80
However,
L: Distance from the lens surface closest to the object side to the image plane in the optical system. The optical system according to claim 1, wherein the following conditional expression is satisfied.
0.30 <f1a / f <0.40
However,
f1a: The focal length of the lens group from the lens closest to the object side to the lens provided with the diffractive optical element among the plurality of lenses. An optical apparatus including an optical system that forms an image of an object on a predetermined surface,
An optical apparatus, wherein the optical system is the optical system according to any one of claims 1 to 5 . Place a focusing lens to focus on the object,
Arranging a plurality of lenses closer to the object side than the focusing lens,
A diffractive optical element is disposed on any lens on the image side of the lens on the most object side among the plurality of lenses,
An optical system manufacturing method characterized by satisfying the following conditional expression:
0.075 <Ldoe / f <0.125
0.50 <L / f <0.75
However,
Ldoe: the distance from the most object side lens surface in the optical system to the diffractive surface in the diffractive optical element,
f: the focal length at the time of infinity focusing of the optical system,
L: Distance from the lens surface closest to the object side to the image plane in the optical system.

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