JP6387631B2 - Optical system and optical equipment - Google Patents

Description

The present invention relates to an optical system and an optical apparatus provided with a diffractive optical element.

  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). 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 2009-271354 A

  However, there is a demand to satisfactorily correct not only axial chromatic aberration but also lateral chromatic aberration.

The present invention has been made in view of such problems, and provides an optical system and an optical apparatus having high optical performance with a small tele-ratio while satisfactorily correcting axial chromatic aberration and lateral chromatic aberration. With the goal.

In order to achieve such an object, an optical system according to the present invention is disposed adjacent to the object side of a focusing lens for performing focusing on an object, and has a first lens group having a positive refractive power and And a second lens group which is disposed on the image side of the first lens group and has a negative refractive power including the focusing lens, and is substantially composed of two lens groups . A diffractive optical element that is rotationally symmetric with respect to the optical axis and has a positive refractive power is disposed on at least one lens surface of the constituting lenses, and at least one of the lenses constituting the second lens group. A diffractive optical element having a negative refracting power and a rotationally symmetric shape with respect to the optical axis is disposed on one lens surface, and the following conditional expression is satisfied.
0.001 <f1 / fdoe1 < 0.018
0.005 <f2 / fdoe2 <0.030
However,
f1: focal length of the first lens group,
fdoe1: the sum of the focal lengths of the diffractive optical elements in the first lens group,
f2: focal length of the second lens group,
fdoe2: the sum of the focal lengths of the diffractive optical elements in the second lens group.

  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.

  According to the present invention, it is possible to obtain an optical system having a high telescopic performance with a small tele ratio and an optical apparatus including the same while correcting axial chromatic aberration and lateral chromatic aberration satisfactorily.

It is sectional drawing of the optical system which concerns on 1st Example. It is a longitudinal aberration diagram of the optical system according to the first example. It is a lateral aberration diagram of the optical system according to the first example. It is sectional drawing of the optical system which concerns on 2nd Example. It is a longitudinal aberration diagram of the optical system according to the second example. It is a lateral aberration diagram of the optical system according to the second example. It is sectional drawing of a digital single-lens reflex camera. It is a flowchart which shows the manufacturing method of an optical system.

  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. 7, light from an object (subject) (not shown) is collected by an optical system (telephoto lens) TL as a photographing lens, and is connected to 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. 7 may be configured to hold the optical system TL in a detachable manner, or may be configured integrally with the optical system TL.

  For example, as shown in FIG. 1, the optical system TL is disposed on the object side of a focusing lens LF for performing focusing on an object, and has a first lens group G1 having a positive refractive power, and a first lens. The second lens group G2 is disposed on the image side of the group G1 and includes a focusing lens LF and has a negative refractive power. The first lens group G1 has at least one diffractive optical element DOE1 having a rotationally symmetric shape with respect to the optical axis and having a positive refractive power. The second lens group G2 has at least one diffractive optical element DOE2 that is rotationally symmetric with respect to the optical axis and has negative refractive power. The first lens group G1 and the second lens group G2 satisfy the following conditional expressions (1) to (2).

0.001 <f1 / fdoe1 <0.030 (1)
0.005 <f2 / fdoe2 <0.030 (2)
However,
f1: the focal length of the first lens group G1,
fdoe1: Sum of focal lengths of the diffractive optical element DOE1 in the first lens group G1,
f2: focal length of the second lens group G2,
fdoe2: sum of focal lengths of the diffractive optical element DOE2 in the second lens group G2.

  Conditional expression (1) is a conditional expression that defines the power of the diffractive optical element DOE1 disposed in the first lens group G1. By satisfying conditional expression (1), axial chromatic aberration and lateral chromatic aberration can be corrected effectively. Conditional expression (2) is a conditional expression that defines the power of the diffractive optical element DOE2 disposed in the second lens group G2. By satisfying conditional expression (2), it is possible to effectively correct lateral chromatic aberration. Thus, by satisfying the conditional expressions (1) to (2), according to the present embodiment, the axial chromatic aberration and the lateral chromatic aberration were corrected well, and the optical performance was small and the tele ratio was small. A telephoto optical system TL and an optical apparatus (digital single-lens reflex camera CAM) including the telephoto optical system TL can be obtained.

  In addition, when it is the conditions exceeding the upper limit of conditional expression (1), since the power of the diffractive optical element DOE1 is too strong and the diffraction flare increases, it is not preferable. On the other hand, if the condition is lower than the lower limit value of the conditional expression (1), the effect of disposing the diffractive optical element DOE1 in the first lens group G1 cannot be sufficiently obtained, and the correction of axial chromatic aberration and lateral chromatic aberration is insufficient. Become.

  In order to secure the effect of the present application, it is desirable to set the upper limit of conditional expression (1) to 0.020. It is more desirable to set the upper limit value of conditional expression (1) to 0.018. 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 0.003.

  Note that if the condition exceeds the upper limit value of the conditional expression (2), the power of the diffractive optical element DOE2 is too strong and the diffraction flare increases, which is not preferable. On the other hand, when the condition is lower than the lower limit value of the conditional expression (2), the effect of disposing the diffractive optical element DOE2 in the second lens group G2 cannot be sufficiently obtained, and the correction of the lateral chromatic aberration becomes insufficient.

  In order to secure the effect of the present application, it is desirable to set the upper limit value of conditional expression (2) to 0.028. On the other hand, in order to ensure the effect of the present application, it is desirable to set the lower limit of conditional expression (2) to 0.010.

  The diffractive optical elements DOE1 and DOE2 in the present embodiment are formed by stacking diffractive element elements having surfaces on which sawtooth-shaped diffraction grating grooves are formed, and a desired wide wavelength region (for example, a visible light region). High diffraction efficiency is maintained in almost the entire 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.

  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.

  In such an optical system TL, it is preferable that the first lens group G1 has one diffractive optical element DOE1 having a positive refractive power and satisfies the following conditional expression (1A).

  0.005 <f1 / fdoe1 <0.015 (1A)

  Conditional expression (1A) indicates that the diffractive optical element DOE1 having a relatively short focal length is arranged in the first lens group G1 having a positive refractive power. By satisfying conditional expression (1A), it is possible to reduce high-order axial chromatic aberration that occurs in the refractive optical system, and thus it is possible to reduce the variation of axial chromatic aberration over the entire wavelength range used. .

  In order to secure the effect of the present application, it is desirable to set the upper limit value of conditional expression (1A) to 0.012. 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 (1A) to 0.007.

  In such an optical system TL, the second lens group G2 includes an achromatic lens including a positive lens and a negative lens disposed on the image side of the focusing lens LF. The following conditional expression ( It is preferable to satisfy 3).

−15 <νd3−νd4 <15 (3)
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 (3) 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. By satisfying conditional expression (3), higher-order axial chromatic aberration can be further reduced. In the case where the upper limit value and the lower limit value of conditional expression (3) are exceeded, it is difficult to reduce the variation of 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 (3) 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 the conditional expression (3) to −10.

  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,
f: Focal length when the optical system TL is focused at infinity.

  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 lengths of the diffractive optical elements DOE1 and DOE2 become too long, and the meaning of inserting the diffractive optical elements DOE1 and DOE2 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 manufacturing method of the optical system TL having the above-described configuration will be described with reference to FIG. First, the first lens group G1 having a positive refractive power is disposed on the object side of the focusing lens LF in the cylindrical lens barrel, and the focusing lens LF is included on the image side of the first lens group G1 and is negative. A second lens group G2 having a refractive power of 2 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).

  In step ST10 for incorporating the lens, at least one diffractive optical element DOE1 having a positive refractive power is disposed in the first lens group G1 so as to satisfy the conditional expressions (1) to (2) described above, At least one diffractive optical element DOE2 having negative refractive power is disposed in the second lens group G2. According to such a manufacturing method, it is possible to obtain a telephoto optical system TL having a small tele ratio (short lens total length) and high optical performance while satisfactorily correcting axial chromatic aberration and lateral chromatic aberration. .

(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. It is comprised from the 3rd positive lens L14 by which DOE1 is arrange | positioned. A diffractive optical element DOE1 having a positive refractive power is disposed on the lens surface on the image plane I side of the third positive lens L14. The diffractive optical element DOE1 of the first lens group G1 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. A primary diffraction grating (a diffraction grating having a rotationally symmetric shape with respect to the optical axis) having a length of about 20 μm 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 the second achromatic lens LC2 and a ninth positive lens L30 on which the diffractive optical element DOE2 is disposed. 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. A diffractive optical element DOE2 having negative refractive power is disposed on the object-side lens surface of the ninth positive lens L30. The diffractive optical element DOE2 of the second lens group G2 is the same as the diffractive optical element DOE1 of the first lens group G1, and detailed description thereof is omitted. 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 and 2 are shown below, which are values that list the specifications of the optical systems (telephoto lenses) according to the first and second 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 f2 is the second lens group G2. The focal length, fdoe1 represents the sum of the focal lengths of the diffractive optical elements DOE1 in the first lens group G1, and fdoe2 represents the sum of the focal lengths of the diffractive optical elements DOE2 in the second lens group G2. 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 represents the refractive index for the d-line (wavelength λ = 587.6 nm), and νd represents the Abbe number for the d-line (wavelength λ = 587.6 nm). Note that the radius of curvature “∞” indicates a plane, and the refractive index of air nd = 1.0000 is omitted.

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

ψ (h, m) = {2π / (m × λ 0)} × (C 2 × h ² + C 4 × h ⁴ + C 6 × h ⁶ ...) (A)
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 (B) using the lowest-order phase coefficient C1.

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

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. 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 in this embodiment are also used in the specification values of the second embodiment described later.

  Table 1 below shows specifications in the first embodiment. In addition, the curvature radius Ri of the 1st surface-the 31st surface in Table 1 respond | corresponds to code | symbol R1-R31 attached | subjected to the 1st surface-the 31st surface in FIG. In the first embodiment, the eighth and 29th surfaces are diffraction surfaces.

(Table 1)
[Overall specifications]
f = 294
FNO = 4.1
2ω = 8.4
Y = 21.63
Bf = 54.00
L = 190.4
f1 = 99.86
f2 = -71.18
fdoe1 = 11135.50
fdoe2 = -5343.01
[Lens specifications]
Surface number Ri Di nd νd
1 119.301 6.91 1.4875 70.3
2 1138.274 1.01
3 80.232 11.49 1.4978 82.6
4 -504.651 2.50 1.5750 41.5
5 246.455 2.02
6 73.087 5.00 1.5168 63.9
7 98.376 0.20 1.5278 33.4
8 98.376 0.30 1.5572 50.0 (Diffraction surface)
9 98.376 26.00
10 41.419 1.50 1.9108 35.2
11 26.417 7.50 1.4875 70.3
12 76.338 6.33
13 125.596 2.38 1.6200 36.4
14 -356.488 1.20 1.6968 55.5
15 42.511 23.65
16 ∞ 2.77 (Aperture)
17 52.557 2.08 1.9108 35.2
18 23.312 2.76 1.5750 41.5
19 226.400 2.58
20 60.916 2.13 1.7283 28.4
21 -102.282 0.85 1.7292 54.6
22 30.417 2.18
23 -71.955 0.80 1.7292 54.6
24 83.995 2.33
25 78.862 3.04 1.5481 45.5
26 -52.965 1.00 1.7880 47.4
27 -240.018 10.32
28 68.731 0.20 1.5572 50.0
29 68.731 0.20 1.5278 33.4 (Diffraction surface)
30 68.731 5.15 1.4875 70.3
31 -68.731 54.00
[Diffraction surface data]
8th surface 29th surface m 1 1
C1 -4.490E-05 9.358E-05
C2 -2.488E-09 -2.112E-07
[Conditional expression values]
Conditional expressions (1), (1A) f1 / fdoe1 = 0.0090
Conditional expression (2) f2 / fdoe2 = 0.0133
Conditional expression (3) νd3−νd4 = 6.3 (first achromatic lens LC1)
νd3−νd4 = -1.9 (second achromatic lens LC2)
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 longitudinal aberration diagram of the optical system TL1 according to the first example, and FIG. 3 is a lateral aberration diagram of the optical system TL1 according to the first example. In each aberration diagram, d indicates an aberration at the d-line (λ = 587.6 nm), and g indicates an 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 each aberration diagram is the same in the other examples. 2 and 3, it can be seen that in the first example, various aberrations such as longitudinal chromatic aberration and lateral chromatic aberration are corrected well, 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.

(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. It is comprised from the 3rd positive lens L14 by which DOE1 is arrange | positioned. A diffractive optical element DOE1 having a positive refractive power is disposed on the lens surface on the image plane I side of the third positive lens L14. The diffractive optical element DOE1 of the first lens group G1 is the same as the diffractive optical element of the first example, and a detailed description thereof is 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 the second achromatic lens LC2 and a ninth positive lens L30 on which the diffractive optical element DOE2 is disposed. 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. A diffractive optical element DOE2 having negative refractive power is disposed on the object-side lens surface of the ninth positive lens L30. The diffractive optical element DOE2 of the second lens group G2 is the same as the diffractive optical element of the first example, and a detailed description thereof is omitted. 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-the 31st surface in Table 2 respond | corresponds to code | symbol R1-R31 attached | subjected to the 1st surface-the 31st surface in FIG. In the second embodiment, the eighth and 29th surfaces are diffractive surfaces.

(Table 2)
[Overall specifications]
f = 294
FNO = 4.1
2ω = 8.4
Y = 21.63
Bf = 54.00
L = 190.5
f1 = 101.56
f2 = -70.80
fdoe1 = 10664.24
fdoe2 = -2695.54
[Lens specifications]
Surface number Ri Di nd νd
1 108.100 7.82 1.4875 70.3
2 1929.565 0.25
3 78.299 11.62 1.4978 82.6
4 -504.651 2.50 1.5827 46.5
5 175.188 2.06
6 77.145 5.00 1.5168 63.9
7 107.014 0.20 1.5278 33.4
8 107.014 0.30 1.5572 50.0 (Diffraction surface)
9 107.014 25.82
10 41.850 1.50 1.9108 35.2
11 26.436 7.60 1.4875 70.3
12 78.638 6.19
13 121.142 2.41 1.6200 36.4
14 -406.824 1.20 1.6968 55.5
15 41.951 23.56
16 ∞ 2.73 (Aperture)
17 48.168 2.46 1.9108 35.2
18 22.821 2.82 1.5750 41.5
19 175.142 2.59
20 56.934 2.25 1.7283 28.4
21 -105.781 0.85 1.7292 54.6
22 29.506 2.27
23 -69.059 0.80 1.7292 54.6
24 87.427 2.22
25 66.543 2.95 1.5443 52.1
26 -64.557 1.00 1.7675 40.3
27 -744.439 10.41
28 74.687 0.20 1.5572 50.0
29 74.687 0.20 1.5278 33.4 (Diffraction surface)
30 74.687 4.71 1.5218 66.5
31 -73.143 54.00
[Diffraction surface data]
8th surface 29th surface m 1 1
C1 -4.689E-05 1.855E-04
C2 -1.487E-09 -2.405E-07
[Conditional expression values]
Conditional expressions (1), (1A) f1 / fdoe1 = 0.0095
Conditional expression (2) f2 / fdoe2 = 0.0263
Conditional expression (3) νd3−νd4 = 6.3 (first achromatic lens LC1)
νd3−νd4 = 11.8 (second achromatic lens LC2)
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 longitudinal aberration diagram of the optical system TL2 according to the second example, and FIG. 6 is a lateral aberration diagram of the optical system TL2 according to the second example. From FIG. 5 and FIG. 6, it can be seen that in the second example, various aberrations such as longitudinal chromatic aberration and lateral chromatic aberration are well corrected and have excellent optical performance. 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.

  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 (3). 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 the present embodiment, one diffractive optical element DOE1 having a positive refractive power is disposed in the first lens group G1, but the present invention is not limited to this, and the diffractive optical element having a positive refractive power is not limited thereto. A plurality of DOEs 1 may be arranged. In addition, one diffractive optical element DOE2 having negative refractive power is arranged in the second lens group G2, but the present invention is not limited to this, and a plurality of diffractive optical elements DOE2 having negative refractive power are arranged. May be.

  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 DOE1 diffractive optical element DOE2 diffractive optical element S aperture I image surface

Claims (4)

A first lens group disposed adjacent to the object side of the focusing lens for performing focusing on the object and having a positive refractive power;
The second lens group is disposed on the image side of the first lens group and has a negative refractive power including the focusing lens, and substantially consists of two lens groups,
A diffractive optical element having a positive refractive power and a rotationally symmetric shape with respect to the optical axis is disposed on at least one lens surface of the lenses constituting the first lens group ,
A diffractive optical element having a negative refractive power and a rotationally symmetric shape with respect to the optical axis is disposed on at least one lens surface of the lenses constituting the second lens group ,
An optical system satisfying the following conditional expression:
0.001 <f1 / fdoe1 < 0.018
0.005 <f2 / fdoe2 <0.030
However,
f1: focal length of the first lens group,
fdoe1: the sum of the focal lengths of the diffractive optical elements in the first lens group,
f2: focal length of the second lens group,
fdoe2: the sum of the focal lengths of the diffractive optical elements in the second lens group. The second lens group has 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 claim 1, wherein the following conditional expression is satisfied.
−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,
The optical apparatus according to claim 1, wherein the optical system is an optical system according to claim 1.

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