JP6949608B2 - Optical system and imaging device with it - Google Patents

Description

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

It is known to use a diffractive optical element to correct chromatic aberration in a telephoto type optical system having a long focal length.

Patent Document 1 discloses a telephoto type optical system including a first lens group arranged in order from the object side, a second lens group that moves during focusing, and a third lens group. In the optical system of Patent Document 1, the first lens group is composed of a positive lens and a diffractive optical element arranged adjacent to the image side of the positive lens, and the distance between the positive lens and the diffractive optical element is widened. Therefore, the effective diameter of the diffractive optical element is reduced.

Japanese Unexamined Patent Publication No. 2012-002999

However, in the optical system of Patent Document 1, the power of the positive lens arranged on the object side of the diffractive optical element is relatively small, and the diameter of the diffractive optical element arranged on the image side cannot be sufficiently reduced. From the viewpoint of reducing the manufacturing cost and the weight of the optical system, it is desired to further reduce the diameter of the diffractive optical element.

An object of the present invention is to reduce the diameter of a diffractive optical element while satisfactorily correcting various aberrations such as chromatic aberration in an optical system including a diffractive optical element.

The optical system of the present invention is composed of a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive or negative refractive power arranged in order from the object side to the image side. This is an optical system in which the distance between adjacent lens groups changes during focusing.
The first lens group includes a diffraction optical element, and a configured sub lens group at all lens disposed on the object side of the diffraction optical element,
The diffractive optical element has a convex diffractive surface on the image side and has a convex diffractive surface.
When the focal length of the partial lens group is f _1a and the focal length of the optical system is f,
0.26 <f _1a / f <0.43
It is characterized in that it satisfies the conditional expression.

Further, in the other optical system of the present invention, the first lens group having a positive refractive force, the second lens group having a negative refractive force, and the first lens group having a positive or negative refractive force are arranged in order from the object side to the image side. It is an optical system consisting of three lens groups, and the distance between adjacent lens groups changes during focusing. The first lens group is adjacent to a partial lens group having a positive refractive force and an image side of the partial lens group. The diffractive optical element is provided with a diffractive optical element arranged on the image side, and the diffractive optical element has a convex diffracting surface on the image side.
When the focal length of the partial lens group is f _1a and the focal length of the optical system is f,
0.26 <f _1a / f <0.43
It is characterized in that it satisfies the conditional expression.

According to the present invention, in an optical system including a diffractive optical element, the diameter of the diffractive optical element can be reduced while satisfactorily correcting various aberrations such as chromatic aberration.

It is sectional drawing and aberration diagram at the time of infinity focusing of the optical system of Example 1. FIG. It is sectional drawing and aberration diagram at the time of infinity focusing of the optical system of Example 2. FIG. It is sectional drawing and aberration diagram at the time of infinity focusing of the optical system of Example 3. FIG. It is sectional drawing and aberration diagram at the time of infinity focusing of the optical system of Example 4. FIG. It is a figure explaining the preferable shape of a diffractive optical element. It is the schematic of the image pickup apparatus.

Hereinafter, examples of the optical system of the present invention and an imaging apparatus having the same will be described with reference to the accompanying drawings. The optical systems of each embodiment are arranged in order from the object side to the image side, the first lens group having a positive refractive power, the second lens group having a negative refractive power, and the third lens group having a positive or negative refractive power. Consists of. In addition, the distance between adjacent lens groups changes during focusing. The lens group may have one or more lenses.

1 (a), 2 (a), 3 (a), and 4 (a) are cross-sectional views of the optical systems of Examples 1 to 4 at infinity in focus, respectively. The optical system of each embodiment is an optical system used for an image pickup device such as a video camera, a digital camera, a silver salt film camera, and a television camera.

In each lens cross-sectional view, the left side is the object side (front) and the right side is the image side (rear). Further, L0 is the optical system of each embodiment, L1 is the first lens group, L2 is the second lens group, and L3 is the third lens group. The first lens group L1 in the optical system L0 of each embodiment has a partial lens group L1a having a positive refractive power and a diffractive optical element DOE arranged adjacent to the image side of the partial lens group L1a. The partial lens group L1a is a lens group composed of all the lenses arranged on the object side of the diffractive optical element DOE in the first lens group L1.

The diffractive optical element DOE is an optical element provided with a diffractive surface D and integrally configured. Strictly speaking, the diffraction grating portion D is a surface composed of a thick diffraction grating portion as shown in FIG. 5B, but the thickness is ignored when referring to the “diffraction surface” in the present specification.

The diffraction surface D may be formed on the lens surface of the single lens or on the junction surface of the junction lens. When the diffractive surface D is provided on the single lens, the single lens and the diffractive surface are collectively called a diffractive optical element. Further, when the diffraction surface D is provided on the junction surface of the junction lens, the junction lens itself is called a diffraction optical element.

The light incident on the diffraction surface D is converged by the diffraction action of the light. That is, the diffraction surface D has a positive optical power due to the diffraction action.

Further, SP represents an aperture stop and IP represents an image plane. When the optical system L0 of each embodiment is used as a photographing optical system of a video camera or a digital camera, a solid-state image sensor (photoelectric conversion element) such as a CCD sensor or a CMOS sensor is arranged on the image plane IP. When the optical system L0 of each embodiment is used as an imaging optical system of a silver halide film camera, a film is arranged.

1 (b), 2 (b), 3 (b), and 4 (b) are aberration diagrams of the optical systems L0 of Examples 1 to 4 at infinity in focus, respectively. In the spherical aberration diagram, Fno is an F number and indicates the amount of spherical aberration with respect to the d-line (wavelength 587.6 nm) and the g-line (wavelength 435.8 nm). In the astigmatism diagram, ΔS indicates the amount of astigmatism on the sagittal image plane, and ΔM indicates the amount of astigmatism on the meridional image plane. In the distortion diagram, the amount of distortion with respect to the d line is shown. The chromatic aberration diagram shows the amount of chromatic aberration on the g-line. ω is the imaging half angle of view (°). Each aberration diagram is in millimeters.

The optical system L0 of each embodiment is a so-called telephoto lens whose focal length is longer than the total length of the lens. In a telephoto lens, on the object side of the point P where the optical axis and the pupil paraxial ray intersect, the height of the paraxial ray passing through the lens surface from the optical axis increases as the distance from the point P toward the object increases. Therefore, it is preferable that the diffractive optical element DOE is arranged at a position away from the point P on the object side. As a result, the height of the light rays incident on the diffractive optical element DOE can be increased, and the effect of correcting axial chromatic aberration can be increased.

On the other hand, when the diffractive optical element DOE is arranged at a position close to the object in the first lens group L1, light outside the shooting angle of view is likely to be incident on the diffractive optical element DOE. When strong light such as sunlight outside the shooting angle of view enters the diffractive optical element DOE, flare and ghost occur. Therefore, in order to reduce flare and ghost caused by the diffractive optical element DOE, it is preferable to arrange the diffractive optical element DOE at a position where light outside the shooting angle of view is unlikely to be incident.

In view of these circumstances, in the optical system L0 of each embodiment, the diffractive optical element DOE is arranged adjacent to the image side of the partial lens group L1a in the first lens group L1.

Further, the optical system L0 of each embodiment satisfies the following conditional expression (1) in such a configuration.
0.26 <f _1a / f <0.43 (1)

In the formula (1), f _1a is the focal length of the partial lens group L1a, and f is the focal length of the entire optical system L0.

Equation (1) relates to the condition of the refractive power of the partial lens group L1a for reducing the effective diameter of the diffractive optical element DOE. As the positive refractive power of the partial lens group L1a is increased, the effect of converging light by the partial lens group L1a is increased, and the effective diameter of the diffractive optical element DOE can be reduced.

If the refractive power of the partial lens group L1a becomes small enough to exceed the upper limit of the formula (1), the effect of converging light by the partial lens group L1a becomes small, and the effective diameter of the diffractive optical element DOE becomes large. In this case, the manufacturing cost increases due to the increase in the effective diameter of the diffractive optical element DOE. Further, it becomes difficult to reduce the weight of the optical system L0.

If the refractive power of the partial lens group L1a increases as the value falls below the lower limit of the equation (1), it becomes difficult to satisfactorily correct the axial chromatic aberration that occurs in the partial lens group L1a.

The numerical range of the formula (1) is more preferably set as in the following formula (1a), and further preferably set as in the formula (1b).
0.28 <f _1a / f <0.42 (1a)
0.29 <f _1a / f <0.41 (1b)

Next, a preferable configuration of the diffractive optical element DOE will be described with reference to FIG.

FIG. 5A shows a cross-sectional view of the case where the diffraction grating portion 14 is provided on the junction surface of the positive lens 12 and the negative lens 13 to form the diffraction optical element DOE as an example of the diffraction optical element DOE. The diffraction grating portion 14 is a portion of the diffraction optical element DOE that constitutes the diffraction surface D.

O in FIG. 5A indicates an optical axis. As described above, since the diffractive optical element DOE is arranged adjacent to the image side of the partial lens group L1a, the convergent light 18 is incident on the diffractive optical element DOE.

FIG. 5B is an enlarged view of the area shown by the dotted line in FIG. 5A. As shown in FIG. 5B, the diffraction grating portion 14 has a first diffraction grating 15 and a second diffraction grating 16 having a refractive index larger than that of the first diffraction grating 15. The interface between the first diffraction grating 15 and the second diffraction grating 16 is saw-toothed, and the lattice surface 14a and the lattice wall surface 14b are alternately formed. That is, the diffraction grating portion 14 is composed of a first diffraction grating 15 and a second diffraction grating 16 which are blaze type diffraction gratings. By forming the diffraction grating portion 14 with a blaze type diffraction grating, it is possible to improve the diffraction efficiency of the diffracted light having a specific diffraction order.

The lattice surface is a surface that diffracts incident light to generate diffracted light of a specific order. The lattice wall surface is a surface connecting the ends of adjacent diffraction surfaces. Both the first diffraction grating 15 and the second diffraction grating 16 have a concentric lattice shape centered on the optical axis O.

As shown in FIG. 5B, the lattice wall surface 14b of the diffraction grating portion 14 is tilted by θ with respect to the straight line 17 parallel to the optical axis. That is, the inner diameter of the lattice wall surface 14b decreases from the object side toward the image side.

By tilting the lattice wall surface 14b in this way, when the incident light 18 is incident on the diffraction grating portion 14 as convergent light, the angle formed by the incident light 18 and the lattice wall surface 14b can be reduced. As a result, the amount of incident light incident on the lattice wall surface 14b can be reduced, and the occurrence of flare caused by the lattice wall surface 14b can be reduced.

Generally, a diffraction grating is manufactured by molding a resin or the like using a mold, but as shown in FIG. 5B, a diffraction grating portion 14 is provided on a lens surface having a convex shape on the image side to form a mold. The shape can be made so that the mold and the diffraction grating do not easily interfere with each other when the mold is released in the direction parallel to the optical axis. Further, since the angle formed by the lattice surface 14a and the lattice wall surface 14b can be increased, the tip of the diffraction grating can be easily formed. Therefore, the mold release step when manufacturing DOE10 can be easily performed. Therefore, it is preferable that the diffraction surface D of the diffraction optical element DOE is provided on the lens surface having a convex shape on the image side.

Further, in order to improve the dustproof property, the assembly workability, and the mechanical strength of the diffraction surface D, as shown in FIG. 5B, the diffraction grating portion 14 is formed on the bonding surface of the bonding lens in which the positive lens and the negative lens are bonded. It is preferable to provide.

Further, it is preferable that the optical system L0 of each embodiment satisfies the following equation (2).
−5.24 <ν _d2N × f ₂ / f <-2.26 (2)

In the formula (2), f ₂ is the focal length of the second lens group L2. Further, ν _d2N is the Abbe number of the negative lens having the smallest refractive power among the negative lenses included in the second lens group L2. It can be said that ν _d2N is the Abbe number of the negative lens having the strongest negative refractive power among the negative lenses included in the second lens group L2.

Note that the Abbe number [nu _d is, F line (486.1 nm), C line (656.3 nm), the refractive index, respectively _N F at the d-line _(587.6nm), N _C, when the _{N d,} the following It is a value defined by the equation (3).
_{ν d = (N d -1)} / (N F -N C) (3)

Equation (2) relates to the configuration of the second lens group L2. When the positive refractive power of the partial lens group L1a is increased so as to satisfy the above equation (1), the axial chromatic aberration in the partial lens group L1a increases. If an attempt is made to increase the number of lenses constituting the first lens group L1 in order to correct these aberrations, the weight of the optical system L0 cannot be sufficiently reduced. Therefore, when the second lens group L2 satisfies the equation (2), the axial chromatic aberration generated in the partial lens group L1a can be corrected.

If the upper limit of the equation (2) is exceeded, the chromatic aberration generated in the second lens group L2 becomes too large. Therefore, the axial chromatic aberration generated in the partial lens group L1a is excessively corrected.

When it is less than the lower limit of the formula (2), the chromatic aberration generated in the second lens group L2 becomes small. Therefore, it becomes difficult to correct the axial chromatic aberration generated in the partial lens group L1a.

The numerical range of the formula (2) is more preferably set as in the following formula (2a), and further preferably set as in the formula (2b).
-5.13 <ν _d2N x f ₂ / f <-2.57 (2a)
−5.05 <ν _d2N × f ₂ / f <-2.70 (2b)

Further, it is preferable that the optical system L0 of each embodiment satisfies the following formula (4).
-2.61 <f ₁ / f ₂ <-1.87 (4)

In the formula (4), f ₁ is the focal length of the first lens group L1.

Equation (4) relates to the refractive power of the first lens group L1 and the second lens group L2. When the upper limit of the formula (4) is exceeded, the refractive power of the first lens group L1 becomes too large with respect to the refractive power of the second lens group L2. Therefore, it becomes difficult for the second lens group L2 to sufficiently correct the spherical aberration and the coma aberration generated in the first lens group L1.

When it is less than the lower limit of the formula (4), the refractive power of the first lens group L1 becomes too small with respect to the refractive power of the second lens group L2. In this case, the effect of converging light by the first lens group L1 is reduced, and the lens diameter of the second lens group L2 is increased, so that it is difficult to sufficiently reduce the weight of the optical system L0.

It is more preferable to set the numerical range of the formula (4) as in the following formula (4a), and it is further preferable to set it as in the formula (4b).
-2.54 <f ₁ / f ₂ <-1.90 (4a)
-2.50 <f ₁ / f ₂ <-1.94 (4b)

In the optical system L0 of each embodiment, the second lens group L2 may include at least one positive lens. In this case, it is preferable to satisfy the following formula (5).
-12.0 <ν _d2P −ν _d2N <−2.0 (5)

In the formula (5), ν _d2P is the Abbe number of the positive lens having the largest refractive power among the positive lenses included in the second lens group L2.

Equation (5) relates to the Abbe number difference between the positive lens and the negative lens in the second lens group L2. When the upper limit of the equation (5) is exceeded, the Abbe number of the negative lens included in the second lens group L2 becomes too small with respect to the Abbe number of the positive lens. In this case, the amount of chromatic aberration generated in the second lens group L2 becomes too large, and the correction of the chromatic aberration generated in the first lens group L1 becomes excessive.

If it is less than the lower limit of the equation (5), the Abbe number of the negative lens included in the second lens group L2 becomes too large with respect to the Abbe number of the positive lens. In this case, the amount of chromatic aberration generated in the second lens group L2 becomes too small, and it becomes difficult to sufficiently correct the chromatic aberration generated in the first lens group L1.

The numerical range of the formula (5) is more preferably set as in the following formula (5a), and further preferably set as in the formula (5b).
-11.0 <ν _d2P −ν _d2N <−2.5 (5)
-10.0 <ν _d2P −ν _d2N <-3.0 (5)

Next, a preferable configuration of the partial lens group L1a will be described.

In the optical system L0 of each embodiment, in order to reduce the spherical aberration generated in the partial lens group L1a, it is preferable to share the positive refractive power of the partial lens group L1a among a plurality of positive lenses. Therefore, it is preferable to provide a plurality of positive lenses in the partial lens group L1a. Specifically, the partial lens group L1a preferably has a first positive lens arranged closest to the object side and a second positive lens arranged adjacent to the first positive lens. In this case, it is preferable to satisfy the following formula (6).
0.11 <D _{1a /} LD <0.25 (6)

In the formula (6), D _1a is the distance between the first positive lens and the second positive lens on the optical axis, and LD is the total length of the optical system L0. The total length of the optical system L0 is the distance from the lens surface to the image surface on the most object side of the optical system L0.

When the distance between the first positive lens and the second positive lens increases so as to exceed the upper limit of the equation (6), spherical aberration and chromatic aberration generated in the partial lens group L1a are sufficiently corrected by the lenses of the partial lens group L1a and later. It becomes difficult to do.

If the distance between the first positive lens and the second positive lens becomes smaller than the lower limit of the equation (6), the effective diameter of the second positive lens becomes large, and the optical system L0 is sufficiently reduced in weight. It becomes difficult to do.

The numerical range of the formula (6) is more preferably set as in the following formula (6a), and further preferably set as in the formula (6b).
0.12 <D _{1a /} LD <0.23 (6a)
0.13 <D _{1a /} LD <0.20 (6b)

It is preferable that the first positive lens is a positive meniscus lens with a convex surface facing the object side, and the second positive lens is a biconvex lens. Thereby, the spherical aberration can be satisfactorily corrected. Further, in order to correct the spherical aberration more satisfactorily, it is preferable that the surface on the image side of the meniscus lens arranged on the object side of the partial lens group L1a is an aspherical surface.

Further, in order to reduce the weight of the optical system L0, it is preferable that the number of lenses constituting the first lens group L1 is small. Therefore, the partial lens group L1a is preferably composed of a first positive lens and a second positive lens.

Further, it is preferable to perform focusing by moving the second lens group L2. By moving the small and lightweight second lens group L2 for focusing, the drive device for driving the lens can be made compact. In addition, focusing can be performed quickly.

Next, numerical examples 1 to 4 corresponding to Examples 1 to 4 are shown. Diffraction surface of each embodiment, the first diffraction grating (refractive index n _{d =} 1.499, Abbe number ν _{d =} 54) and a second stacked in close contact with the image side of the first diffraction grating diffraction grating (refractive index _n d = 1.598, Abbe number _{ν d} = 28) is formed by.

In the surface data of each numerical example, r represents the radius of curvature of each optical surface, and d (mm) represents the axial distance (distance on the optical axis) between the mth plane and the (m + 1) th plane. .. However, m is the number of the surface counted from the light incident side. Further, nd represents the refractive index of each optical member with respect to the d line, and ν _d represents the Abbe number of the optical member.

Further, in the surface data of each numerical example, (aspherical surface) is added after the surface number for the optical surface having an aspherical shape. In addition, the aspherical surface data shows the aspherical coefficient of each aspherical surface. For the aspherical shape of the optical surface, the amount of displacement from the surface apex in the optical axis direction is X, the height from the optical axis in the direction perpendicular to the optical axis is H, the paraxial radius of curvature is R, and the conical constant is K. When the aspherical coefficient is A ₄ , A ₆ , A ₈ , A ₁₀ , it is expressed by the following equation (7).

In each numerical example, d, focal length (mm), F number, and half angle of view (°) are all values when the optical system of each example focuses on an infinity object. The back focus BF is the distance from the final lens surface to the image surface. The total lens length (total length LD of the optical system L0) is a value obtained by adding the back focus to the distance from the first lens surface to the final lens surface.

Further, in the surface data of each numerical example, (diffraction) is added after the surface number for the optical surface to be the diffraction surface. The phase Φ (H) of the diffraction surface at the position of height H from the optical axis is as follows when the diffraction order is m, the reference wavelength is λ ₀ , and the phase coefficient is C _2n (n is an integer of 1 or more). It is given by the equation (8).
Φ (H) = (2π × m / λ ₀ ) × (C ₂ × H ² + C ₄ × H ⁴ + ・ ・ ・ + C _2n × H ²ⁿ ) (8)

_{Further, the optical power φ D} of the near-axis primary diffracted light (m = 1) at the reference wavelength λ ₀ of the diffractive surface is expressed as φ _D = -2C _{2. From this, the focal length f DOE} due only to the diffraction component of the diffractive optical portion of the diffractive optical element DOE is given by the following equation (9).
f _DOE = 1 / φ _D = -1 / (2 × C ₂ ) (9)

In addition, "e ± B" in the aspherical coefficient and the phase coefficient means "× 10 ^{± B} ".

[Numerical Example 1]
Unit mm

Surface data Surface number rd nd νd Effective diameter
1 141.462 20.36 1.48749 70.2 141.19
2 (Aspherical surface) 1260.312 57.02 139.59
3 505.639 11.12 1.43387 95.1 114.68
4-351.744 47.64 113.47
5 115.120 13.25 1.43875 94.7 71.79
6 (diffraction) -156.499 3.43 1.67300 38.1 69.25
7 400.099 24.57 64.79
8 308.518 3.76 1.84666 23.9 46.00
9 -152.837 2.18 1.95375 32.3 45.43
10 70.295 33.66 42.36
11 (Aperture) ∞ 2.50 34.96
12 -478.306 1.71 1.78470 26.3 34.43
13 107.627 4.47 1.58313 59.4 34.08
14 -88.521 0.10 33.97
15 113.890 1.64 1.65412 39.7 32.91
16 47.615 3.90 1.48749 70.2 31.85
17 511.504 3.20 31.44
18 118.840 4.76 1.80810 22.8 29.85
19 -51.258 1.48 1.78470 26.3 29.28
20 66.235 2.08 27.50
21 -214.255 1.39 1.88300 40.8 27.45
22 85.799 3.20 27.17
23 76.536 1.40 1.90366 31.3 27.53
24 39.305 4.29 1.69895 30.1 27.22
25 -368.213 43.63 27.42
26 154.638 10.53 1.61340 44.3 39.65
27 -37.670 2.09 1.49700 81.5 39.88
28 43.165 0.13 39.57
29 43.496 18.10 1.58144 40.8 39.63
30 -49.022 1.75 1.52417 51.5 38.93
31 -36.175 0.10 1.60401 20.8 38.92
32 -48.827 2.04 1.59522 67.7 38.85
33 155.614 62.79 38.53
34 (image plane) ∞

Aspherical data second surface
K = 0.00000e + 000 A ₄ = 4.06937e-008 A ₆ = 2.72351e-015 A ₈ = 1.90048e-017
A ₁₀ = 8.44440e-022

6th plane (diffraction plane)
C ₂ = -5.65522e-005 C ₄ = 3.25134e-009 C ₆ = 6.64756e-013 C ₈ = 3.83272e-016
C ₁₀ =-4.27150e-019

Various data focal length 582.00
F number 4.12
Half angle of view (°) 2.13
Image height 21.64
Lens overall length 394.25
BF 62.79

Entrance pupil position 931.14
Exit pupil position -123.00
Front principal point position -491.13
Rear principal point position -536.00

Lens group data group Start surface Focal length Front principal point position Rear principal point position
L1 1 189.79 43.20 -103.98
L2 8 -87.61 3.87 0.69
L3 11 1208.78 199.85 133.22

[Numerical Example 2]
Unit mm

Surface data Surface number rd nd νd Effective diameter
1 130.319 11.62 1.50848 63.8 98.25
2 (Aspherical surface) 2026.851 58.66 97.45
3 261.301 7.24 1.45969 89.8 76.31
4-283.638 41.36 75.67
5 102.757 7.12 1.44754 92.6 45.90
6 (diffraction) -125.758 2.29 1.65822 30.2 44.41
7 452.380 6.51 42.25
8 471.766 4.88 1.88441 24.6 37.68
9 -58.607 1.80 1.87997 28.4 37.08
10 54.742 36.20 34.03
11 (Aperture) ∞ 2.50 27.50
12 -945.187 1.37 1.82774 36.8 27.03
13 59.212 6.72 1.71760 55.2 26.75
14 -120.130 3.20 26.44
15 127.617 2.07 1.80809 22.8 25.15
16 -221.115 1.28 1.50217 55.9 24.88
17 58.830 1.80 23.96
18 -193.516 1.23 1.96261 31.5 23.91
19 105.857 5.21 23.73
20 82.903 5.26 1.64355 31.2 25.53
21 -323.397 43.63 26.29
22 -1286.186 8.97 1.83209 36.3 37.59
23 -74.773 2.05 1.43974 94.4 38.60
24 34.039 0.23 39.15
25 34.447 12.55 1.50642 54.4 39.33
26 -88.263 1.75 1.52417 51.5 39.30
27 -51.876 0.10 1.60401 20.8 39.29
28 -72.161 2.08 1.67669 58.8 39.34
29 -879.833 50.46 39.62
30 (image plane) ∞

Aspherical data second surface
K = 0.00000e + 000 A ₄ = 7.16138e-008 A ₆ = -1.19504e-013 A ₈ = 2.08188e-017
A ₁₀ = 1.92779e-020

6th plane (diffraction plane)
C ₂ =-7.95330e-005 C ₄ = 6.23724e-009 C ₆ = -2.30293e-011 C ₈ = 7.17216e-014
C ₁₀ = -6.70511e-017

Various data focal length 405.00
F number 4.12
Half angle of view (°) 3.06
Image height 21.64
Lens overall length 330.16
BF 50.46

Entrance pupil position 685.39
Exit pupil position -123.00
Front principal point position 119.88
Rear principal point position -358.99

Lens group data group Start surface Focal length Front principal point position Rear principal point position
L1 1 143.57 52.60 -82.65
L2 8 -71.34 4.06 0.48
L3 11 250.83 84.02 7.78

[Numerical Example 3]
Unit mm

Surface data Surface number rd nd νd Effective diameter
1 130.775 22.57 1.48749 70.2 141.19
2 (Aspherical surface) 1058.133 65.09 139.18
3 3145.907 9.68 1.43875 94.9 108.57
4 -306.479 36.16 107.01
5 114.468 15.01 1.43875 94.7 74.16
6 (Diffraction) -125.762 3.43 1.70154 41.2 71.63
7 445.594 29.43 67.01
8 167.671 4.17 1.80810 22.8 46.00
9 -185.455 2.18 2.00100 29.1 45.39
10 71.424 36.06 42.47
11 (Aperture) ∞ 2.50 34.55
12 -446.825 1.71 1.68893 31.1 34.02
13 77.631 4.81 1.61340 44.3 33.59
14 -93.662 0.10 33.45
15 75.253 1.64 1.69895 30.1 32.15
16 33.219 6.14 1.51823 58.9 30.66
17 138.889 3.20 29.58
18 94.962 4.62 1.80810 22.8 28.18
19 -162.744 1.48 1.74400 44.8 27.11
20 55.828 2.13 25.77
21 -195.292 1.39 2.00330 28.3 25.71
22 92.934 3.20 25.48
23 92.067 2.42 1.80518 25.5 26.31
24 -1079.272 43.63 26.53
25 124.799 10.56 1.57501 41.5 38.92
26 -37.603 2.09 1.49700 81.5 39.12
27 41.244 0.94 39.06
28 42.136 19.24 1.53172 48.8 39.64
29 -47.348 1.75 1.52417 51.5 39.38
30 -35.609 0.10 1.60401 20.8 39.38
31 -47.490 2.04 1.49700 81.5 39.44
32 174.637 54.79 39.26
33 (image plane) ∞
Aspherical data second surface
K = 0.00000e + 000 A ₄ = 3.52000e-008 A ₆ = -3.20922e-014 A ₈ = 2.14605e-017
A ₁₀ = 3.12673e-022

6th plane (diffraction plane)
C ₂ = -5.82267e-005 C ₄ = 5.81674e-009 C ₆ = 6.87292e-013 C ₈ = -1.28177e-015
C ₁₀ = 2.16558e-019

Various data focal length 582.00
F number 4.12
Half angle of view (°) 2.13
Image height 21.64
Lens overall length 394.25
BF 54.79

Entrance pupil position 986.67
Exit pupil position -123.00
Front principal point position -435.60
Rear principal point position -536.00

Lens group data group Start surface Focal length Front principal point position Rear principal point position
L1 1 207.45 30.27 -110.38
L2 8 -99.90 5.00 1.52
L3 11 1028.47 178.89 102.35

[Numerical Example 4]
Unit mm

Surface data Surface number rd nd νd Effective diameter
1 164.561 17.34 1.48749 70.2 141.97
2 (Aspherical surface) 1157.643 82.55 140.70
3 432.215 11.14 1.43875 94.7 111.27
4-351.967 67.08 110.23
5 98.650 10.54 1.43875 94.7 61.40
6 (Diffraction) -177.331 2.99 1.66565 35.6 59.37
7 415.537 13.14 56.17
8 186.189 5.53 1.80810 22.8 45.79
9 -319.436 2.12 2.00100 29.1 44.03
10 59.987 66.60 41.08
11 (Aperture) ∞ 2.50 29.06
12 -162.608 1.45 1.80400 46.5 28.70
13 160.254 3.38 1.59282 68.6 28.63
14 -73.698 0.10 28.63
15 92.433 1.42 1.71736 29.5 27.99
16 46.831 3.58 1.49700 81.6 27.34
17 -693.850 3.20 27.02
18 107.870 3.39 1.80810 22.8 25.55
19 -66.350 1.29 1.80100 35.0 25.12
20 53.325 1.88 23.93
21 -222.111 1.23 2.00100 29.1 23.90
22 99.780 3.95 23.81
23 90.894 1.26 2.00100 29.1 24.47
24 43.262 3.51 1.76182 26.5 24.35
25 -285.739 43.63 24.38
26 153.761 9.47 1.62299 58.2 37.49
27 -38.193 1.99 1.49700 81.6 37.77
28 40.427 0.45 37.73
29 41.719 14.57 1.61340 44.3 37.93
30 -58.755 1.75 1.52417 51.5 37.48
31 -39.552 0.10 1.60401 20.8 37.47
32 -51.990 1.98 1.59522 67.7 37.41
33 154.496 105.13 37.06
34 (image plane) ∞
Aspherical data second surface
K = 0.00000e + 000 A ₄ = 2.99769e-008 A ₆ = 1.33833e-013 A ₈ = 6.67068e-018
A ₁₀ = 5.88577e-022

6th plane (diffraction plane)
C2 = -5.58903e-005 C ₄ = 2.94306e-009 C ₆ = -2.30162e-012 C ₈ = 2.53813e-015
C ₁₀ = -1.33064e-018

Various data focal length 795.00
F number 5.60
Half angle of view (°) 1.56
Image height 21.64
Lens overall length 490.24
BF 105.13

Entrance pupil position 1665.91
Exit pupil position -123.00
Front principal point position -378.80
Rear principal point position -695.44

Lens group data group Start surface Focal length Front principal point position Rear principal point position
L1 1 195.34 92.53 -119.31
L2 8 -79.02 5.58 1.36
L3 11 823.34 230.40 202.49

The various values in each numerical example are summarized in Table 1 below.

[Imaging device]
Next, an example of a digital still camera (imaging apparatus) using the optical system of the present invention as an imaging optical system will be described with reference to FIG. In FIG. 6, 10 is a camera body, and 11 is a photographing optical system configured by any of the optical systems described in Examples 1 to 4. Reference numeral 12 denotes a solid-state image sensor (photoelectric conversion element) such as a CCD sensor or a CMOS sensor, which is built in the camera body and receives an optical image formed by the photographing optical system 11 and performs photoelectric conversion. The camera body 10 may be a so-called single-lens reflex camera having a quick turn mirror, or a so-called mirrorless camera having no quick turn mirror.

By applying the optical system of the present invention to an imaging device such as a digital still camera in this way, it is possible to obtain an imaging device that is lightweight and has chromatic aberration and other aberrations satisfactorily corrected.

Although the preferred embodiments and examples of the present invention have been described above, the present invention is not limited to these embodiments and examples, and various combinations, modifications and modifications can be made within the scope of the gist thereof.

For example, the diffractive optical element DOE is not limited to the shapes shown in FIGS. 5A and 5B, and the diffractive surface D may be provided on the lens surface which is convex toward the object, for example.

L0 Optical system L1 1st lens group L2 2nd lens group L3 3rd lens group L1a Partial lens group DOE diffractive optical element

Claims (12)

It consists of a first lens group with a positive refractive power, a second lens group with a negative refractive power, and a third lens group with a positive or negative refractive power arranged in order from the object side to the image side, and adjacent lenses for focusing. An optical system in which the spacing between groups changes
The first lens group includes a diffraction optical element, and a configured sub lens group at all lens disposed on the object side of the diffraction optical element,
The diffractive optical element has a convex diffractive surface on the image side and has a convex diffractive surface.
When the focal length of the partial lens group is f _1a and the focal length of the optical system is f,
0.26 <f _1a / f <0.43
An optical system characterized by satisfying the conditional expression. The second lens group has at least one negative lens.
The focal length of the second lens group is f ₂ , The Abbe number of the negative lens with the smallest refractive power among the negative lenses included in the second lens group is ν. _d2N , When the focal length of the optical system is f,
-5.24 <ν _d2N × f ₂ / F <-2.26
The optical system according to claim 1, wherein the optical system satisfies the conditional expression. The diffraction surface is composed of a blaze type diffraction grating.
The optical system according to claim 1 or 2 , wherein the inner diameter of the lattice wall surface of the diffraction grating decreases from the object side toward the image side. When the focal length of the first lens group is f ₁ and the focal length of the second lens group is f ₂ .
-2.61 <f ₁ / f ₂ <-1.87
The optical system according to any one of claims 1 to 3 , wherein the optical system satisfies the conditional expression. The second lens group has at least one negative lens and at least one positive lens.
The Abbe number of the negative lens having the smallest refractive power among the negative lenses included in the second lens group is ν _d2N , and the Abbe number of the positive lens having the largest refractive power among the positive lenses included in the second lens group. When is ν _d2P
-12.0 <ν _d2P −ν _d2N <-2.0
The optical system according to any one of claims 1 to 4 , wherein the optical system satisfies the conditional expression. The partial lens group closest to the first of which is disposed on the object side positive lens and of claims 1 to 5, characterized in that it has the first of the second positive lens disposed adjacent to the positive lens The optical system according to any one item. The optical system according to claim 6 , wherein the first positive lens is a meniscus lens having a convex surface directed toward an object. The optical system according to claim 7 , wherein the lens surface on the image side of the first positive lens is an aspherical surface. The optical system according to any one of claims 6 to 8 , wherein the second positive lens is a biconvex lens. When the distance between the first positive lens and the second positive lens on the optical axis is D _1a and the total length of the optical system is LD,
0.11 <D _{1a /} LD <0.25
The optical system according to any one of claims 6 to 9 , wherein the optical system satisfies the conditional expression. The optical system according to any one of claims 1 to 1 0, characterized in that focusing is performed by moving the second lens group. An image pickup apparatus comprising the optical system according to any one of claims 1 to 11 and an image pickup element that photoelectrically converts an optical image formed by the optical system.

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