JP2015172710A - Optical system, optical device, and method for manufacturing optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical system having a low telephoto ratio and high optical performance, while satisfactorily correcting color aberrations over the whole of a used wavelength band.SOLUTION: An optical system includes: a focus lens LF for performing focusing to an object; a diffraction optical element DOE arranged closer to an object side than the focus lens LF; and a negative lens L13 that is arranged closer to the object side than the focus lens LF and satisfies a conditional expression (1) nd2<1.89-0.00637×νd2 and a conditional expression (2) νd2>35, where a refraction index of the negative lens L13 with respect to a d-line is represented by nd2 and an Abbe number of the negative lens L13 with respect to the d-line is represented by νd2.

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, compared to a method of combining two glass materials (lenses) having different dispersions. 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), and when light is incident, the pitch of the slits and grooves. 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. In particular, in the case of axial chromatic aberration, apochromatic correction in which axial chromatic aberration is corrected at three wavelengths can be achieved by using a diffractive optical element, compared to achromatic correction in which axial chromatic aberration is corrected at two general wavelengths.

JP 2009-271345 A

  However, when such a diffractive optical element is applied to an optical system having a longer focal length, or when an attempt is made to reduce the tele ratio in an optical system using the diffractive optical element, axial chromatic aberration in the wavelength range used is reduced. The amount of axial chromatic aberration at wavelengths other than zero becomes a problem.

  The present invention has been made in view of such problems, and has an optical system, an optical apparatus, and an optical system that have a small tele ratio and high optical performance while favorably correcting chromatic aberration in the entire wavelength range used. It aims at providing the manufacturing method of.

In order to achieve such an object, the optical system according to the present invention includes a focusing lens for performing focusing on an object, a diffractive optical element disposed on the object side of the focusing lens, and the focusing lens. And at least one negative lens that is disposed closer to the object side than the focal lens and satisfies the following conditional expression.
nd2 <1.89−0.00637 × νd2
νd2> 35
However,
nd2: refractive index of the negative lens with respect to d-line,
νd2: Abbe number of the negative lens with respect to d-line

In the above-described optical system, it is preferable that the optical system includes at least one positive lens that is disposed closer to the object side than the focusing lens and satisfies the following conditional expression.
θgF1− (0.644−0.00168 × νd1)> 0.030
νd1> 70
However,
νd1: Abbe number for the d-line of the positive lens,
θgF1 is a partial dispersion ratio of the positive lens, the refractive index of the positive lens with respect to g-line is ng1, the refractive index of the positive lens with respect to F-line is nF1, and the refractive index of the positive lens with respect to C-line is nC1 Is defined by the following formula.
θgF1 = (ng1−nF1) / (nF1−nC1)

In the above-described optical system, it is preferable that the first lens group including the optical element disposed on the object side with respect to the focusing lens has a positive refractive power and satisfies the following conditional expression.
0.001 <f1 / fdoe <0.030
However,
f1: focal length of the first lens group,
fdoe: focal length of the diffractive optical element.

In the above-described optical system, it is preferable that the optical system includes an achromatic lens including a positive lens and a negative lens disposed on the image side of the focusing lens, and the achromatic lens satisfies the following conditional expression. .
−15 <νd3−νd4 <15
However,
νd3: Abbe number with respect to d-line of the positive lens in the achromatic lens,
νd4: Abbe number with respect to d-line of the negative lens in the achromatic lens.

In the above optical system, it is preferable that 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,
f: Focal length when the optical system is focused at infinity.

  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, the method of manufacturing an optical system according to the present invention includes a focusing lens for performing focusing on an object, a diffractive optical element disposed on the object side of the focusing lens, and the focusing lens. Also, at least one negative lens satisfying the following conditional expression is arranged on the object side.
nd2 <1.89−0.00637 × νd2
νd2> 35
However,
nd2: refractive index of the negative lens with respect to d-line,
νd2: Abbe number with respect to the d-line of the negative lens.

  According to the present invention, it is possible to obtain an optical system having a small tele-ratio and high optical performance, and an optical apparatus including the same, while correcting chromatic aberration in the entire use wavelength range.

It is sectional drawing of the optical system which concerns on 1st Example. FIG. 6 is a diagram illustrating all aberrations of the optical system according to Example 1. 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 a graph which shows the wavelength characteristic of the axial chromatic aberration of the conventional optical system, Comprising: (a) shows the state of an optical system independent, (b) shows a state when a teleconverter is attached. It is a graph which shows the wavelength characteristic of the axial chromatic aberration of the conventional optical system using a diffractive optical element, (a) shows the state of an optical system independent, (b) shows the state when a teleconverter is attached. .

  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 diffractive optical element DOE disposed on the object side of the focusing lens LF, and a focusing lens. And at least one negative lens that satisfies the following conditional expressions (1) to (2), which is disposed on the object side of the LF.

nd2 <1.89−0.00637 × νd2 (1)
νd2> 35 (2)
However,
nd2: refractive index with respect to d-line of the negative lens,
νd2: Abbe number with respect to d-line of the negative lens.

  Conditional expressions (1) to (2) indicate that at least one negative lens using a glass material having a relatively large dispersion and a low refractive index is disposed on the object side of the focusing lens LF. . By satisfying conditional expressions (1) and (2), higher-order axial chromatic aberration generated in the refractive optical system can be reduced. Therefore, by using a negative lens that satisfies the conditional expressions (1) to (2) and the diffractive optical element DOE, the longitudinal chromatic aberration is changed over the entire wavelength range while avoiding an increase in the tele ratio. It can be made smaller. As described above, according to the present embodiment, the telescopic optical system TL having a small tele ratio and high optical performance while satisfactorily correcting the chromatic aberration in the entire used wavelength range, and an optical apparatus ( A digital single lens reflex camera CAM) can be obtained. Further, a glass material having a relatively large dispersion and a low refractive index having an Abbe number of about 35 is called old glass, and has the smallest specific gravity among the glass materials and is inexpensive. By using such an optical material having a small specific gravity for the front lens having a large lens diameter, it is possible to reduce the weight of the optical system.

  When a teleconverter (converter for extending the focal length of the optical system) is attached to a conventional optical system using a diffractive optical element, the amount of aberration is increased by this teleconverter, and the teleconverter is used for achromatic correction. Since the lens is specialized, chromatic aberration is further increased.

  FIG. 12A shows the wavelength characteristics of axial chromatic aberration of a conventional optical system that does not use a diffractive optical element and has a focal length of 300 mm. This optical system corrects axial chromatic aberration at two wavelengths. It is achromatic correction. When a double teleconverter is attached to this conventional optical system, the wavelength characteristic of the longitudinal chromatic aberration is as shown in FIG. By making the axial chromatic aberration of the teleconverter opposite to the axial chromatic aberration of the conventional optical system, as shown in FIG. 12B, even if the teleconverter is attached, the overall axial chromatic aberration is extremely deteriorated. It is configured so that there is nothing.

  On the other hand, FIG. 13A shows the wavelength characteristics of axial chromatic aberration of an optical system using a diffractive optical element and having a focal length of 300 mm. As shown in FIG. 13A, this optical system has apochromatic correction in which axial chromatic aberration is corrected at three wavelengths. Achromatic correction by the conventional optical system shown in FIG. 13A is characterized in that the sign of longitudinal chromatic aberration on the long wavelength side is reversed. When the teleconverter described above is attached to an optical system using this diffractive optical element, the wavelength characteristic of the longitudinal chromatic aberration is as shown in FIG. As shown in FIG. 13B, since the wavelength characteristics are different from those of the conventional achromatic correction optical system, it can be understood that the axial chromatic aberration is extremely deteriorated by attaching a teleconverter.

  On the other hand, according to the present embodiment, as described above, it is possible to reduce the variation of the longitudinal chromatic aberration over the entire use wavelength range, and even when the teleconverter is attached, the chromatic aberration in the entire use wavelength range. Can be corrected satisfactorily.

  In addition, the optical system TL includes at least one positive lens that is disposed on the object side of the focusing lens LF and satisfies the following conditional expressions (3) to (4). Is preferred.

θgF1− (0.644−0.00168 × νd1)> 0.030 (3)
νd1> 70 (4)
However,
νd1: Abbe number with respect to d-line of the positive lens,
θgF1: Partial dispersion ratio of positive lens.

  The refractive index of the positive lens with respect to g-line (wavelength λ = 435.8 nm) is ng1, the refractive index of the positive lens with respect to d-line (wavelength λ = 587.6 nm) is nd1, and the positive lens F-line (wavelength λ = F6.1 is the refractive index for nF1, and the refractive index for the positive lens C line (wavelength λ = 656.3 nm) is nC1. At this time, the Abbe number νd1 of the positive lens with respect to the d-line is defined by the following equation (A), and the partial dispersion ratio θgF1 of the positive lens is defined by the following equation (B).

νd1 = (nd1-1) / (nF1−nC1) (A)
θgF1 = (ng1−nF1) / (nF1−nC1) (B)

  Further, the anomalous dispersion ΔPgF1 of the positive lens is obtained by the following equation (C).

  ΔPgF1 = θgF1− (0.644−0.00168 × νd1) (C)

  Conditional expressions (3) to (4) indicate that at least one positive lens using a glass material having anomalous dispersion is disposed closer to the object side than the focusing lens LF. By satisfying the conditional expressions (3) to (4), higher-order axial chromatic aberration generated in the refractive optical system can be reduced. Therefore, by combining with the diffractive optical element DOE, the entire use wavelength range can be obtained. It is possible to reduce the fluctuation of the axial chromatic aberration.

  In such an optical system TL, the first lens group G1 including optical elements disposed on the object side of the focusing lens LF has a positive refractive power and satisfies the following conditional expression (5). It is preferable to satisfy.

0.001 <f1 / fdoe <0.030 (5)
However,
f1: the focal length of the first lens group G1,
fdoe: focal length of the diffractive optical element DOE.

  Conditional expression (5) indicates that the diffractive optical element DOE having a relatively short focal length is arranged in the first lens group G1 having a positive refractive power. By satisfying conditional expression (5), higher-order axial chromatic aberration that occurs in the refractive optical system can be reduced. Therefore, in combination with the diffractive optical element DOE, axial chromatic aberration can be reduced over the entire operating wavelength range. The fluctuation can be reduced. When the condition exceeds the upper limit value of the conditional expression (5), the grating pitch around the diffractive optical element DOE becomes too fine, and the diffraction efficiency decreases. In addition, high-order axial chromatic aberration remains in the entire optical system, and the variation of axial chromatic aberration in the operating wavelength range increases. On the other hand, when the condition is lower than the lower limit value of the conditional expression (5), the effect of inserting the diffractive optical element DOE (shortening of the total length) cannot be obtained.

  In order to secure the effect of the present application, it is desirable to set the upper limit value of conditional expression (5) to 0.020. In order to further secure the effect of the present application, it is desirable to set the upper limit value of conditional expression (5) to 0.010.

  Further, the diffractive optical element DOE in the present embodiment is formed by stacking diffractive element elements having surfaces on which sawtooth-shaped diffraction grating grooves are formed, and is almost in a desired wide wavelength region (for example, a visible light region). High diffraction efficiency is maintained throughout the entire area, 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.

  In addition, when a close-contact multilayer diffractive optical element is disposed, there is a configuration in which the diffractive optical element is disposed on the joint surface of two glass lenses. 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 addition, the optical system TL includes an achromatic lens including a positive lens and a negative lens disposed on the image side of the focusing lens LF. The achromatic lens has the following conditional expression (6 ) Is preferably satisfied.

−15 <νd3−νd4 <15 (6)
However,
νd3: Abbe number with respect to d-line of the positive lens in the achromatic lens,
νd4: Abbe number for the d-line of the negative lens in the achromatic lens.

  Conditional expression (6) indicates that an achromatic lens including a positive lens and a negative lens having a dispersion difference equal to or less than a desired value is disposed on the image side of the focusing lens LF. The positive lens and the negative lens in this achromatic lens may be bonded together or arranged adjacent to each other. Note that the Abbe numbers of the positive lens and the negative lens in the achromatic lens are defined by the same formula as the formula (A) described above. By satisfying conditional expression (6), higher-order axial chromatic aberration can be further reduced. In the case where the upper limit value and lower limit value of conditional expression (6) are exceeded, it is difficult to reduce the variation in longitudinal chromatic aberration in the used wavelength range in the entire optical system TL.

  In order to secure the effect of the present application, it is desirable to set the upper limit of conditional expression (6) to 10. 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 (6) to −10.

  In such an optical system TL, it is preferable that the following conditional expression (7) is satisfied.

0.50 <L / f <0.80 (7)
However,
L: distance from the lens surface closest to the object side to the image plane in the optical system TL,
f: Focal length when the optical system TL is focused at infinity.

  Conditional expression (7) 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 (7), the focal length of the diffractive optical element DOE becomes too long, and there is no point in putting the diffractive optical element DOE. On the other hand, when the condition is less than the lower limit value of the conditional expression (7), 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 (7) 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 lens barrel, the diffractive optical element DOE is arranged on the object side of the focusing lens LF, and the above conditional expression (1 ) To (2), at least one negative lens is disposed (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). According to such a manufacturing method, it is possible to obtain a telephoto optical system TL having a small tele ratio (short lens overall length) and high optical performance while satisfactorily correcting chromatic aberration in the entire use wavelength range. .

(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), f1 is the focal length of the first lens group, and fdoe is the focal length of the diffractive optical element. Respectively. 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 partial dispersion ratio θgF of each lens is defined by the same formula as the formula (B) described above.

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

ψ (h, m) = {2π / (m × λ0)} × (C 2 × h ² + C 4 × h ⁴ + C 6 × h ⁶ ...) (D)
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 (E) using the lowest-order phase coefficient C1.

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

In [Diffraction plane data], the phase coefficient is indicated, and “En” indicates “× 10 ⁻ⁿ ”. [Conditional Expression Corresponding Value] indicates the corresponding value of each conditional expression. In addition, 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 enlarged or reduced. 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
f1 = 100.53
fdoe = 12320
[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) 1.89−0.00637 × νd2 = 1.63 (> nd2 = 1.5750)
Conditional expression (2) νd2 = 41.5
Conditional expression (3) θgF1− (0.644−0.00168 × νd1) = 0.0333
Conditional expression (4) νd1 = 82.6
Conditional expression (5) f1 / fdoe = 0.0082
Conditional expression (6) νd3−νd4 = 6.3 (first achromatic lens LC1)
νd3−νd4 = -1.9 (second achromatic lens LC2)
Conditional expression (7) L / f = 0.65

  Thus, in the present embodiment, it can be seen that all the conditional expressions (1) to (7) 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
f1 = 100.89
fdoe = 12176
[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) 1.89−0.00637 × νd2 = 1.63 (> nd2 = 1.5750)
Conditional expression (2) νd2 = 41.5
Conditional expression (3) θgF1− (0.644−0.00168 × νd1) = 0.0333
Conditional expression (4) νd1 = 82.6
Conditional expression (5) f1 / fdoe = 0.0083
Conditional expression (6) νd3−νd4 = 6.3 (first achromatic lens LC1)
νd3−νd4 = -1.9 (second achromatic lens LC2)
Conditional expression (7) L / f = 0.65

  Thus, in the present embodiment, it can be seen that all the conditional expressions (1) to (7) 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
f1 = 102.52
fdoe = 13756
[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) 1.89−0.00637 × νd2 = 1.58 (> nd2 = 1.5317)
Conditional expression (2) νd2 = 48.8
Conditional expression (3) θgF1− (0.644−0.00168 × νd1) = 0.0333
Conditional expression (4) νd1 = 82.6
Conditional expression (5) f1 / fdoe = 0.0075
Conditional expression (6) νd3−νd4 = −13.6 (second achromatic lens LC2)
Conditional expression (7) L / f = 0.65

  Thus, in the present embodiment, it can be seen that all the conditional expressions (1) to (7) 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. In addition, achromatic lenses LC1 and LC2 each including a positive lens and a negative lens are disposed on at least one of the object side and the image side of the seventh positive lens L25, the fifth negative lens L26, and the sixth negative lens L27. The achromatic lenses LC1 and LC2 preferably satisfy the above-described conditional expression (6). The achromatic lenses LC1 and LC2 may be cemented lenses.

  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 region in order to reduce flare and ghost and achieve high optical performance with high contrast.

  In this embodiment, the diffractive optical element DOE is disposed on the third positive lens L14. However, the diffractive optical element is not limited to this as long as it is disposed on the object side of the focusing lens. The diffractive optical element is preferably arranged in the front group when the first lens group is divided into a front group and a rear group with an air space having the largest distance between the lens surfaces. The front group of the first lens group includes a diffractive optical element, a negative lens that satisfies the conditional expressions (1) to (2), and a positive lens that satisfies the conditional expressions (3) to (4). Is preferred.

  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 this embodiment, the focal length is about 300 mm. However, the present invention is not limited to this, and a telephoto lens having a focal length of about 200 to 800 mm (35 mm equivalent) 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 LF focusing lens LC1 first achromatic lens LC2 second achromatic lens L12 second positive lens L13 first negative lens DOE diffractive optical element S aperture I image surface

Claims (7)

A focusing lens for focusing on an object;
A diffractive optical element disposed on the object side of the focusing lens;
An optical system comprising: at least one negative lens that is disposed closer to the object side than the focusing lens and satisfies the following conditional expression:
nd2 <1.89−0.00637 × νd2
νd2> 35
However,
nd2: refractive index of the negative lens with respect to d-line,
νd2: Abbe number with respect to the d-line of the negative lens. The optical system according to claim 1, further comprising at least one positive lens that is disposed closer to the object side than the focusing lens and satisfies the following conditional expression.
θgF1− (0.644−0.00168 × νd1)> 0.030
νd1> 70
However,
νd1: Abbe number for the d-line of the positive lens,
θgF1 is a partial dispersion ratio of the positive lens, the refractive index of the positive lens with respect to g-line is ng1, the refractive index of the positive lens with respect to F-line is nF1, and the refractive index of the positive lens with respect to C-line is nC1 Is defined by the following formula.
θgF1 = (ng1−nF1) / (nF1−nC1) 3. The first lens group comprising optical elements disposed on the object side of the focusing lens has a positive refractive power and satisfies the following conditional expression: 3. Optical system.
0.001 <f1 / fdoe <0.030
However,
f1: focal length of the first lens group,
fdoe: focal length of the diffractive optical element. An achromatic lens composed of a positive lens and a negative lens disposed on the image side of the focusing lens;
The optical system according to any one of claims 1 to 3, wherein the achromatic lens satisfies the following conditional expression.
−15 <νd3−νd4 <15
However,
νd3: Abbe number with respect to d-line of the positive lens in the achromatic lens,
νd4: Abbe number with respect to d-line of the negative lens in the achromatic lens. The optical system according to claim 1, 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,
f: Focal length when the optical system is focused at infinity. 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,
A diffractive optical element is disposed on the object side of the focusing lens,
An optical system manufacturing method comprising: disposing at least one negative lens satisfying the following conditional expression on the object side of the focusing lens.
nd2 <1.89−0.00637 × νd2
νd2> 35
However,
nd2: refractive index of the negative lens with respect to d-line,
νd2: Abbe number with respect to the d-line of the negative lens.

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