JP6304962B2 - Optical system and imaging apparatus having the same - Google Patents

Description

  The present invention relates to an optical system, and is suitable for an imaging optical system used in an imaging apparatus such as a silver salt film camera, a digital still camera, a digital video camera, a surveillance camera, and a TV camera.

  In recent years, an imaging optical system used in an imaging apparatus having a solid-state imaging device has been required to have a wide angle of view because it has high resolution and good portability, is small, and can easily shoot a wide range. In addition, if the incident angle of the light beam incident on the solid-state imaging device is large, the amount of light on the periphery of the screen is reduced and shading and color misregistration occur. Therefore, good telecentricity is required. Furthermore, since various optical elements such as a low-pass filter and a color correction filter are disposed between the lens surface closest to the image side and the imaging surface, it is required to have a relatively long back focus.

  Conventionally, as a photographing optical system that satisfies these requirements, a retrofocus type photographing optical system including a first lens unit having a negative refractive power, an aperture stop, and a second lens group having a positive refractive power in order from the object side to the image side. Systems are known (Patent Documents 1 and 2). Patent Documents 1 and 2 disclose a photographing optical system having a back focus of a predetermined length and having a good overall system size and good image side telecentricity.

JP 2010-176018 A JP-A-7-63986

  A retrofocus type photographing optical system can easily achieve a wide angle of view while ensuring a long back focus. Many retrofocus imaging optical systems diverge the light beam by the first lens unit having a negative refractive power and converge the light beam by the second lens group having a positive refractive power. Becomes asymmetric. Therefore, many spherical aberrations, coma aberrations, etc. occur. Further, in order to ensure a sufficiently long back focus while keeping the entire lens length short, it is necessary to increase the negative refractive power of the first lens unit. Therefore, various aberrations such as spherical aberration and coma aberration are generated more.

  In order to obtain a long back focus, small overall system, wide angle of view, good image-side telecentricity, and high optical performance over the entire screen, the lens configuration of the lens groups before and after the aperture stop in the photographic optical system It is important to set up properly. If these settings are not appropriate, it will be difficult to obtain a photographing optical system with high optical performance.

  An object of the present invention is to provide an optical system that has a long back focus and is easy to obtain a high-quality image over the entire screen while the entire system is small and has a wide angle of view.

The optical system of the present invention is an optical system including a first lens group having a negative refractive power, an aperture stop, and a second lens group having a positive refractive power, which are arranged in order from the object side to the image side.
The second lens group includes a lens G21 having a positive refractive power arranged closest to the object among the lenses included in the second lens group , a lens G2n having a negative refractive power, and a lens G2p having a positive refractive power. A cemented lens, and
The focal length of the lens G21 is f21, the focal length of the second lens group is f2, the radius of curvature of the lens surface on the object side of the lens G21 is R21a, the radius of curvature of the lens surface of the image side of the lens G21 is R21b , When the focal length of the first lens group is f1, the focal length of the entire system is f, the Abbe number of the material of the lens G2n is ν2n, and the Abbe number of the material of the lens G2p is ν2p ,
1.54 <f21 / f2 <3.00
−7.0 <(R21b + R21a) / (R21b−R21a) <− 3.0
-150.0 <f1 / f <-8.10
3.0 <ν2p / ν2n
It satisfies the following conditional expression.

  According to the present invention, it is possible to obtain an optical system that has a long back focus and is easy to obtain a high-quality image over the entire screen while the entire system is small and has a wide angle of view.

(A), (B) Lens cross-sectional view and aberration diagram of Example 1 of the present invention (A), (B) Lens sectional view and aberration diagram of Example 2 of the present invention (A), (B) Lens sectional view and aberration diagram of Example 3 of the present invention (A), (B) Lens sectional view and aberration diagram of Example 4 of the present invention (A), (B) Lens sectional view and aberration diagram of Example 5 of the present invention (A), (B) Lens sectional view and aberration diagram of Example 6 of the present invention Schematic diagram of main parts of an imaging apparatus of the present invention

  The optical system of the present invention includes, in order from the object side to the image side, a first lens group having a negative refractive power, an aperture stop, and a second lens group having a positive refractive power.

  FIGS. 1A and 1B are a lens sectional view of Example 1 of the present invention and aberration diagrams when focused on infinity. 2A and 2B are aberration diagrams when focusing on infinity with the lens cross-sectional view of Example 2 of the present invention. FIGS. 3A and 3B are lens cross-sectional views of Example 3 of the present invention and aberration diagrams when focused on infinity. FIGS. 4A and 4B are lens cross-sectional views of Example 4 of the present invention and aberration diagrams when focused on infinity.

  FIGS. 5A and 5B are lens cross-sectional views of Example 5 of the present invention and aberration diagrams when focused on infinity. FIGS. 6A and 6B are lens sectional views of Example 6 of the present invention and aberration diagrams when focused on infinity. FIG. 7 is a schematic view of a camera (imaging device) including the optical system of the present invention.

  The optical system of each embodiment is a photographing optical system used for an imaging device (optical device) such as a digital still camera, a digital video camera, or a silver salt film camera. In the lens cross-sectional view, the left side is the object side (front), and the right side is the image side (rear). In addition, you may use the optical system of each Example as projection lenses, such as a projector. At this time, the left side is the screen side and the right side is the projected image side.

  In the lens cross-sectional view, LA is an optical system. The optical system LA includes a first lens unit L1 having a negative refractive power on the object side and a second lens unit L2 having a positive refractive power on the image side with the aperture stop SP interposed therebetween.

  GB is an optical block corresponding to an optical filter, a face plate, a crystal low-pass filter, an infrared cut filter, and the like. IP is an image plane. When used as an imaging optical system for a digital video camera or a digital still camera, an imaging plane of a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor is used for a silver salt film camera. Sometimes it corresponds to the film surface.

  Each aberration diagram represents spherical aberration, astigmatism, distortion, and lateral chromatic aberration in order from the left. In the diagram showing spherical aberration, the solid line represents the d-line (587.6 nm), and the two-dot chain line represents the g-line (435.8 nm). In the diagram showing astigmatism, the solid line represents the sagittal direction ΔS of the d line, and the broken line represents the meridional direction ΔM of the d line. Moreover, the figure which shows distortion represents the distortion in d line | wire. The lateral chromatic aberration is shown for the g-line with respect to the d-line. Fno represents the F number, and ω represents the half angle of view (degrees) of the shooting angle of view.

Next, features of the optical system of the present invention will be described. In each embodiment, the first lens unit L1 includes a lens G11 having a negative refractive power, a lens G12 having a negative refractive power, and a lens G13 having a positive refractive power, which are arranged in order from the object side to the image side. The second lens unit L2 includes , in order from the object side to the image side, a positive refractive power lens G21 having a convex lens surface on the image side, and a cemented lens in which a negative refractive power lens and a positive refractive power lens are cemented. G22 is composed of a biconvex lens G2im having a positive refractive power. In particular, on the most object side of the second lens unit L2, a lens G21 having a positive refractive power with a convex surface facing the image side is disposed.

  The spherical aberration and coma generated in the first lens unit L1 are corrected by the lens G21. The second lens unit L2 includes a cemented lens G22 in which a lens G2n having a negative refractive power on the object side and a lens G2p having a positive refractive power on the image side are cemented. The second lens unit L2 includes a lens G2im having a positive refractive power on the most image side.

  Each embodiment is an optical system having a short F, F, and a wide F / number, while ensuring a long back focus. In addition, it has high optical performance with various aberrations corrected well to the peripheral field angle.

  In each embodiment, focusing is performed by moving the entire lens system or a part of the lens in the optical axis direction according to the object distance. Note that the optical system of the present invention does not have a focus adjustment mechanism by using a pan focus lens.

  In Example 3, the image side surface of the lens G11 of the first lens unit L1 has an aspherical shape. Thereby, spherical aberration and curvature of field are corrected more satisfactorily. In Example 6, the object side surface of the lens G2im of the second lens unit L2 has an aspherical shape. As a result, an optical system having a bright F number of Fno 2.0 and having satisfactorily corrected spherical aberration, curvature of field, astigmatism and the like is achieved.

The optical system LA of the present invention includes, in order from the object side to the image side, a first lens unit L1 having a negative refractive power, an aperture stop SP, and a second lens unit L2 having a positive refractive power. The second lens unit L2 has a lens G21 having a positive refractive power closest to the object side, the focal length of the lens G21 is f21, the focal length of the second lens unit L2 is f2, and the curvature of the lens surface on the object side of the lens G21. The radius is R21a, and the radius of curvature of the lens-side lens surface of the lens G21 is R21b. At this time,
1.54 <f21 / f2 <3.00 (1)
−7.0 <(R21b + R21a) / (R21b−R21a) <− 3.0 (2)
The following conditional expression is satisfied.

  Next, the technical meaning of conditional expressions (1) and (2) will be described. Conditional expression (1) and conditional expression (2) are mainly for satisfactorily correcting spherical aberration and coma in a retrofocus optical system.

  Conditional expression (1) defines the refractive power of the lens G21 closest to the object side in the second lens unit L2 in order to correct various aberrations. When the lower limit of conditional expression (1) is exceeded and the focal length f21 of the lens G21 becomes shorter than the focal length f2 of the second lens unit L2 (when the refractive power increases), the curvature of each lens surface of the lens G21 becomes tight (small). ), Too much spherical aberration, coma, and the like occur.

  Furthermore, many higher-order aberrations are likely to occur. When the upper limit of conditional expression (1) is exceeded and the focal length f21 of the lens G21 is increased (when the refractive power is decreased), the refractive power of the lens G21 is decreased. As a result, it becomes difficult to sufficiently correct the aberration, and the luminous flux cannot be sufficiently converged, and the effective diameter of the lens close to the image side of the second lens unit L2 is increased. If the focal length f2 of the second lens unit L2 becomes shorter than the upper limit of the conditional expression (1), the refractive power of the second lens unit L2 becomes too large (strong), and a sufficiently long back focus is secured. It becomes difficult to do.

  Conditional expression (2) defines the lens shape of the lens G21 in order to satisfactorily correct the spherical aberration and coma generated in the first lens unit L1 from on-axis to off-axis. Conditional expression (2) indicates that the lens G21 has a convex meniscus shape on the image side when the expression value is less than -1. If the lower limit of conditional expression (2) is exceeded and the meniscus shape of the lens G21 becomes tight, spherical aberration and coma will occur excessively, making it difficult to correct various aberrations.

  In addition, since the curvature of each lens surface of the lens G21 becomes tight, many higher-order aberrations occur, which is not preferable. When the upper limit of conditional expression (2) is exceeded and the meniscus shape of the lens G21 becomes loose, sufficient aberration correction becomes difficult. More preferably, the numerical ranges of conditional expression (1) and conditional expression (2) should be set as follows.

1.54 <f21 / f2 <2.85 (1a)
−6.5 <(R21b + R21a) / (R21b−R21a) <− 3.2 (2a)
More preferably, the numerical ranges of conditional expression (1a) and conditional expression (2a) are set as follows.
1.54 <f21 / f2 <2.82 (1b)
−6.0 <(R21b + R21a) / (R21b−R21a) <− 3.4 (2b)
As described above, a long back focus can be obtained, and an optical system having good optical performance can be obtained.

In the present invention, it is more preferable to satisfy one or more of the following conditions. The first lens unit L1 includes a negative refractive power lens G11, a negative refractive power lens G12, and a positive refractive power lens G13, which are arranged in order from the object side to the image side. The focal length of the first lens unit L1 is f1, the focal length of the entire system is f, the focal length of the lens G11 is f11, and the focal length of the lens G12 is f12.

The second lens unit L2 includes a cemented lens G22 formed by joining a lens G2n having a negative refractive power (negative lens G2n) and a positive power lens G2p (positive lens G2p), the Abbe number of the negative lens G2n material The Abbe number of the material of ν2n and the positive lens G2p is ν2p. The radius of curvature of the object-side lens surface of the positive lens G2p is R2pa, and the radius of curvature of the image-side lens surface is R2pb. The thickness on the optical axis of the second lens unit L2 (the distance on the optical axis from the most object side lens surface to the most image side lens surface in the second lens unit L2) is denoted by DL2, and the first lens unit L1. The interval on the optical axis of the second lens unit L2 is DL12.

The second lens unit L2 includes a lens G2im having a positive refractive power disposed on the most image side among the lenses included in the second lens unit L2, and the focal length of the lens G2im is set to f2im. The air conversion length from the lens surface or al image surface on the most image side of the second lens group and BF. At this time, it is preferable to satisfy one or more of the following conditional expressions.

-150.00 <f1 / f < -8.10 (3)
0.70 <f11 / f12 <1.60 (4)
3.00 <ν2p / ν2n (5)
−1.0 <(R2pb + R2pa) / (R2pb−R2pa) <1.0 (6)
3.0 <DL2 / DL12 <20.0 (7)
1.40 <f2im / f2 <2.00 (8)
1.00 <BF / f <2.00 (9)
Next, the technical meaning of each conditional expression described above will be described.

  Conditional expressions (3) and (4) are for satisfactorily correcting distortion while ensuring a long back focus with a wide angle of view in a retrofocus type optical system. Conditional expression (3) defines the refractive power of the first lens unit L1, and conditional expression (4) defines the refractive power of the lens G11 and the lens G12.

  When the lower limit of conditional expression (3) is exceeded and the absolute value of the focal length f1 of the first lens unit L1 increases, the negative refractive power of the first lens unit L1 decreases (weakens), and a sufficiently long back focus is achieved. It becomes difficult to secure. When the upper limit of conditional expression (3) is exceeded and the absolute value of the focal length f1 is reduced, the negative refractive power of the first lens unit L1 is excessively increased (intensified), and various aberrations, particularly distortion, increase.

  If the lower limit of conditional expression (4) is exceeded and the absolute value of the focal length f11 of the lens G11 becomes small, the refractive power of the lens G11 becomes too large and distortion increases. In addition, since the curvature of the lens surface of the lens G11 is strong (small), the effective diameter of the front lens is increased in order to ensure a sufficient lens edge thickness. When the upper limit of conditional expression (4) is exceeded and the absolute value of the focal length of the lens G11 increases, the refractive power of the lens G11 becomes too small. For this reason, it is necessary to relatively increase the refractive power of the lens G12. As a result, more distortion is generated than in the lens G12.

It is more preferable to set the numerical ranges of conditional expression (3) and conditional expression (4) as follows.
-140.00 <f1 / f < -8.10 (3a)
0.80 <f11 / f12 <1.50 (4a)
More preferably, the numerical ranges of conditional expression (3a) and conditional expression (4a) are set as follows.
-135.00 <f1 / f <-8.10 (3b)
0.90 <f11 / f12 <1.45 (4b)

  Conditional expression (5) is for satisfactorily correcting axial chromatic aberration and off-axis chromatic aberration in the second lens unit L2 in the retrofocus optical system. By arranging a cemented lens in the second lens unit L2, axial chromatic aberration and off-axis chromatic aberration are effectively corrected.

  If the ratio of the Abbe number of the material of the negative lens G2n and the positive lens G2p is reduced beyond the lower limit of the conditional expression (5), the axial chromatic aberration is insufficiently corrected. Further, when the axial chromatic aberration is corrected beyond the lower limit of the conditional expression (5), the refractive power of the negative lens G2n and the positive lens G2p of the cemented lens G22 becomes too strong, various aberrations increase, and high optical performance is achieved. It becomes difficult to obtain. More preferably, conditional expression (5) and numerical range should be set as follows.

3.30 <ν2p / ν2n (5a)
More preferably, the numerical range of conditional expression (5a) is set as follows.
3.35 <ν2p / ν2n (5b)

  Conditional expression (6) is for effectively correcting axial chromatic aberration and off-axis chromatic aberration and correcting off-axis coma and curvature of field in the cemented lens G22 of the second lens unit L2. The lens shape of the positive lens G2p of the cemented lens G22 is defined. Being within the range of conditional expression (6) indicates that the positive lens G2p of the cemented lens G22 has a biconvex shape.

  When the lower limit of conditional expression (6) is exceeded, the curvature of the lens surface on the image side of the positive lens G2p becomes too tight, and the curvature of field increases. Further, in order to secure the negative refractive power of the negative lens G2n of the cemented lens G22, the curvature of the object side lens surface of the negative lens G2n of the cemented lens G22 becomes too tight, and the coma aberration increases. When the upper limit of conditional expression (6) is exceeded, the curvature of the lens surface on the object side of the positive lens G2p becomes tight, and more coma occurs than in the lens G21. Also, the field curvature increases. More preferably, the numerical range of conditional expression (6) should be set as follows.

−0.5 <(R2pb + R2pa) / (R2pb−R2pa) <0.5 (6a)
More preferably, the numerical range of conditional expression (6a) is set as follows.
0.0 <(R2pb + R2pa) / (R2pb−R2pa) <0.4 (6b)

Conditional expression (7) is for defining the position of the lens G21 in the optical axis direction in order to satisfactorily correct spherical aberration and coma by the lens G21. When the upper limit of conditional expression (7) is exceeded and the lens G21 approaches the first lens group L1, the height of the off-axis light incident on the lens G21 becomes too low, making it difficult to correct coma. become. When the lower limit of conditional expression (7) is exceeded, the lens G21 moves away from the first lens unit L1 side, making it difficult to correct spherical aberration and coma. Further, the effective diameter of the lens G21 is increased, and the entire system is increased in size.

More preferably, the numerical range of conditional expression (7) should be set as follows.
4.0 <DL2 / DL12 <10.0 (7a)
More preferably, the numerical range of conditional expression (7a) is set as follows.
4.5 <DL2 / DL12 <9.8 (7b)

  Conditional expression (8) is for satisfactorily correcting curvature of field generated in the entire lens system and ensuring image-side telecentricity. A lens G2im having a positive refractive power is disposed closest to the image side of the second lens unit L2, and the refractive power of the lens G2im is defined. If the lower limit of conditional expression (8) is exceeded and the focal length f2im of the lens G2im becomes shorter, the refractive power of the lens G2im becomes too strong and a lot of field curvature occurs. When the focal length f2im of the lens G2im is increased beyond the upper limit of the conditional expression (8), the effect of correcting the field curvature is weakened and the total lens thickness is increased. Further, the image side telecentricity is also lowered.

More preferably, the numerical range of conditional expression (8) should be set as follows.
1.40 <f2im / f2 <1.80 (8a)
More preferably, the numerical range of conditional expression (8a) is set as follows.
1.45 <f2im / f2 <1.75 (8b)

  Conditional expression (9) is for ensuring a desired length of back focus while maintaining high optical performance in a retrofocus type optical system. If the lower limit of conditional expression (9) is exceeded, the back focus becomes too short with respect to the focal length of the entire system, and it becomes difficult to obtain a desired back focus.

Further, the exit pupil becomes shorter with respect to the image plane, and the image side telecentricity is lowered. When the exit pupil is made longer with respect to the image plane, coma increases. When the upper limit of conditional expression (9) is exceeded, the back focus becomes longer, but the refractive power of the first lens unit L1 becomes too strong, so that field curvature, astigmatism, coma, and the like increase. More preferably, the numerical range of conditional expression (9) should be set as follows.
1.10 <BF / f <2.00 (9a)
More preferably, the numerical range of conditional expression (9a) is set as follows.
1.12 <BF / f <1.50 (9b)

  Next, numerical examples 1 to 6 corresponding to the first to sixth embodiments of the present invention will be described. In these numerical examples, the surface number i indicates the order from the object side, ri is the radius of curvature of the i-th surface in order from the object side, and di is between the i-th and i + 1-th in order from the object side. Lens thickness or air spacing. ndi and νdi are respectively the refractive index and Abbe number at the d-line of the material of the i-th optical member in order from the object side. In the numerical example, two surfaces closest to the image side are surfaces of an optical block such as a filter and a face plate.

  The aspherical shape is the X axis in the optical axis direction, the H axis in the direction perpendicular to the optical axis, the light traveling direction is positive, R is the paraxial radius of curvature, and K, A4, and A6 are aspherical coefficients, respectively.

It is expressed by the following formula. The display of “e-0X” means “10 ^−X ”. In each numerical example, the back focus (BF) represents the distance from the lens final surface to the paraxial image surface by an air-converted length. The total lens length is the distance from the most object-side surface to the final lens surface plus back focus. Table 1 shows the correspondence with the above-described conditional expressions in each numerical example.

[Numerical Example 1]
Unit mm

Surface data surface number rd nd νd
1 7.174 0.90 1.91082 35.3
2 3.290 1.54
3 9.597 0.90 1.83481 42.7
4 3.515 0.79
5 31.506 2.60 2.00 100 29.1
6 -6.834 0.71
7 (Aperture) ∞ 0.59
8 -6.615 1.05 1.80 400 46.6
9 -4.499 2.57
10 620.492 0.45 1.95906 17.5
11 5.487 2.70 1.51823 58.9
12 -6.644 0.10
13 23.714 1.10 2.00 100 29.1
14 -23.714 2.69
15 ∞ 4.87 1.51633 64.1
16 ∞ 0.13
Image plane ∞

Various data focal length 4.10
F number 2.56
Half angle of view (degrees) 36.24
Statue height 3.01
Total lens length 23.70
BF 6.03

Lens group data group Start surface Focal length
1 1 -120.30
2 7 7.16

[Numerical Example 2]
Unit mm

Surface data surface number rd nd νd
1 6.921 1.14 1.95375 32.3
2 3.349 1.63
3 10.760 0.52 1.83481 42.7
4 3.481 0.80
5 52.408 2.72 2.00 100 29.1
6 -7.068 1.17
7 (Aperture) ∞ 0.32
8 -8.747 1.10 1.80 400 46.6
9 -4.852 3.00
10 -74.050 0.63 1.95906 17.5
11 5.650 2.55 1.51823 58.9
12 -6.367 0.10
13 16.448 1.17 2.00 100 29.1
14 -24.004 1.80
15 ∞ 4.76 1.51633 64.1
16 ∞ 0.52
Image plane ∞

Various data focal length 3.80
F number 2.50
Half angle of view (degrees) 38.37
Statue height 3.01
Total lens length 23.93
BF 5.47

Lens group data group Start surface Focal length
1 1 -30.56
2 7 6.74

[Numerical Example 3]
Unit mm

Surface data surface number rd nd νd
1 6.998 0.90 1.91082 35.3
2 * 3.209 1.63
3 23.927 0.90 1.83481 42.7
4 3.576 0.79
5 10.588 2.60 1.95375 32.3
6 -7.281 0.90
7 (Aperture) ∞ 0.51
8 -6.695 1.05 1.80 400 46.6
9 -4.765 2.57
10 37.102 0.45 1.95906 17.5
11 5.170 2.70 1.48749 70.2
12 -6.573 0.10
13 12.685 1.10 2.00 100 29.1
14 -227.275 1.80
15 ∞ 4.87 1.51633 64.1
16 ∞ 0.75
Image plane ∞

Aspheric data 2nd surface
K = -1.71543e-001 A 4 = 1.44140e-004 A 6 = -1.43198e-005

Various data focal length 3.86
F number 2.56
Half angle of view (degrees) 37.94
Statue height 3.01
Total lens length 23.62
BF 5.76

Lens group data group Start surface Focal length
1 1 -446.26
2 7 7.05

[Numerical Example 4]
Unit mm

Surface data surface number rd nd νd
1 6.056 1.13 2.00 100 29.1
2 3.264 1.71
3 10.302 0.73 1.83481 42.7
4 3.568 0.83
5 -46.835 2.79 2.00100 29.1
6 -6.109 1.50
7 (Aperture) ∞ 0.43
8 -7.019 1.23 1.80 400 46.6
9 -4.972 3.02
10 18.242 0.66 1.95906 17.5
11 5.204 2.62 1.49700 81.5
12 -6.658 0.50
13 13.270 1.07 2.00 100 29.1
14 -43.957 1.00
15 ∞ 4.81 1.51633 64.1
16 ∞ 0.42
Image plane ∞

Various data
Focal length 3.37
F number 2.56
Half angle of view (degrees) 41.70
Statue height 3.01
Total lens length 24.44
BF 4.59

Lens group data group Start surface Focal length
1 1 -48.58
2 7 6.10

[Numerical Example 5]
Unit mm

Surface data surface number rd nd νd
1 4.832 0.71 1.91082 35.3
2 2.470 0.99
3 6.520 0.45 1.83481 42.7
4 2.768 0.87
5 20.631 1.62 2.00 100 29.1
6 -5.863 0.50
7 (Aperture) ∞ 0.42
8 -5.507 1.24 1.80 400 46.6
9 -3.630 1.91
10 24.685 0.45 1.95906 17.5
11 3.891 3.98 1.51823 58.9
12 -8.188 0.13
13 12.198 1.23 2.00 100 29.1
14 -182.990 3.50
15 ∞ 1.00 1.51633 64.1
16 ∞ 0.47
Image plane ∞

Various data focal length 4.10
F number 2.56
Half angle of view (degrees) 36.25
Statue height 3.01
Total lens length 19.45
BF 4.63

Lens group data group Start surface Focal length
1 1 -547.10
2 7 6.59

[Numerical Example 6]
Unit mm

Surface data surface number rd nd νd
1 7.174 0.90 1.91082 35.3
2 3.290 1.54
3 8.250 0.90 1.83481 42.7
4 3.515 0.79
5 75.000 2.60 2.00 100 29.1
6 -6.834 0.71
7 (Aperture) ∞ 0.59
8 -6.615 1.05 1.80 400 46.6
9 -4.499 2.57
10 150.000 0.45 1.95906 17.5
11 5.900 2.70 1.49700 81.5
12 -6.000 0.95
13 * 17.361 1.10 2.00 100 29.1
14 -23.714 1.50
15 ∞ 4.87 1.51633 64.1
16 ∞ 0.39
Image plane ∞

Aspherical data 13th surface
K = -6.82681e + 000 A 4 = -5.00000e-006 A 6 = 2.00000e-006

Various data focal length 3.71
F number 2.00
Half angle of view (degrees) 39.04
Statue height 3.01
Total lens length 23.62
BF 5.10

Lens group data group Start surface Focal length
1 1 -55.18
2 7 6.49

  Next, an embodiment of a digital still camera using an optical system as shown in each example as a photographing optical system will be described with reference to FIG.

  In FIG. 7, reference numeral 20 denotes a camera body, and reference numeral 21 denotes a photographing optical system constituted by any one of the optical systems described in the first to sixth embodiments. Reference numeral 22 denotes a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor that receives a subject image formed by the photographing optical system 21 and is built in the camera body. A memory 23 records information corresponding to a subject image photoelectrically converted by the solid-state imaging device 22. Reference numeral 24 denotes a finder for observing a subject image formed on the solid-state image sensor 22, which includes a liquid crystal display panel or the like.

  Thus, by applying the optical system of the present invention to an imaging apparatus such as a digital still camera, it is possible to realize an imaging apparatus having a small size and high optical performance.

The optical system of each embodiment can be similarly applied to a single-lens reflex camera with a quick return mirror and a mirrorless single-lens reflex camera without a quick return mirror.

  As described above, according to each embodiment, it is possible to obtain an optical system in which an adequate length of back focus is ensured, the entire lens length is short, and aberrations are favorably corrected to the peripheral angle of view, and an imaging apparatus having the optical system. .

L1 First lens group L2 Second lens group

Claims (8)

An optical system including a first lens unit having a negative refractive power, an aperture stop, and a second lens group having a positive refractive power, which are arranged in order from the object side to the image side,
The second lens group includes a lens G21 having a positive refractive power arranged closest to the object among the lenses included in the second lens group , a lens G2n having a negative refractive power, and a lens G2p having a positive refractive power. A cemented lens, and
The focal length of the lens G21 is f21, the focal length of the second lens group is f2, the radius of curvature of the lens surface on the object side of the lens G21 is R21a, the radius of curvature of the lens surface of the image side of the lens G21 is R21b , When the focal length of the first lens group is f1, the focal length of the entire system is f, the Abbe number of the material of the lens G2n is ν2n, and the Abbe number of the material of the lens G2p is ν2p ,
1.54 <f21 / f2 <3.00
−7.0 <(R21b + R21a) / (R21b−R21a) <− 3.0
-150.0 <f1 / f <-8.10
3.0 <ν2p / ν2n
An optical system that satisfies the following conditional expression: The first lens group includes a negative refractive power lens G11, a negative refractive power lens G12, and a positive refractive power lens G13, which are arranged in order from the object side to the image side.
When the focal length of the lens G11 is f11 and the focal length of the lens G12 is f12,
0.7 <f11 / f12 <1.6
The optical system according to claim 1, wherein the following conditional expression is satisfied. When the radius of curvature of the lens surface on the object side of the front Symbol lens G2p R2pa, and R2pb the radius of curvature of the lens surface on the image side,
−1.0 <(R2pb + R2pa) / (R2pb−R2pa) <1.0
Optical system according to claim 1 or 2, characterized by satisfying the conditional expression. When the thickness on the optical axis of the second lens group is DL2, and the distance on the optical axis between the first lens group and the second lens group is DL12,
3.0 <DL2 / DL12 <20.0
Optical system according to any one of claims 1 to 3, characterized by satisfying the conditional expression. The second lens group includes a lens G2im having a positive refractive power arranged closest to the image side among the lenses included in the second lens group , and the focal length of the lens G2im is f2im.
1.4 <f2im / f2 <2.0
Optical system according to any one of claims 1 to 4, characterized by satisfying the conditional expression. The air conversion length BF to the lens surface or al image surface on the most image side of the second lens group, when the focal length f of the entire system,
1.0 <BF / f <2.0
Optical system according to any one of claims 1 to 5, characterized by satisfying the conditional expression. The second lens group includes, in order from the object side to the image side, the lens G21, a cemented lens in which a negative refractive power lens and a positive refractive power lens are cemented, and a biconvex positive refractive power lens. Composed of lenses,
The optical system according to any one of claims 1 to 6 , wherein a lens surface on the image side of the lens G21 has a convex shape. An optical system according to any one of claims 1 to 7, an imaging apparatus characterized by having a solid-state image pickup element for receiving an image formed by the optical system.