JP6236795B2 - Optical system and optical equipment - Google Patents

Description

  The present invention relates to an optical system optimal for a photographing optical system such as a digital camera, a film camera, and a video camera.

  In recent years, a compact single focus lens having a wide angle of view has been proposed (for example, see Patent Document 1).

JP 2011-076021 A

  However, the conventional wide-angle single focal length lens has a long optical system length and a large front lens diameter. For this reason, mounting a lens barrel in a compact camera that can be retracted into the camera when the camera is not used is disadvantageous for downsizing the camera.

The present invention has been made in view of such problems, and an object thereof is to provide an optical system and an optical apparatus that are small in size and have high optical performance.

In order to achieve such an object, the optical system according to the present invention is substantially constituted by a first lens group, an aperture stop, and a second lens group, which are arranged in order from the object side along the optical axis. The first lens group is composed of a negative lens and a positive lens arranged in order from the object side along the optical axis, and the second lens group has a lens surface closest to the object side with a convex surface facing the object side. A positive lens having a meniscus shape having a convex shape facing the image side, and the lens arranged closest to the image side satisfies the following conditional expression.

0 . 172 <L1r2 / L2r2 <0.700
1.00 <f1 / f2 <9.00
However,
L1r2: radius of curvature of the image side lens surface of the negative lens of the first lens group,
L2r2: radius of curvature of the image side lens surface of the positive lens of the first lens group,
f1: the focal length of the first lens group,
f2: focal length of the second lens group.

  An optical apparatus according to the present invention is equipped with any of the optical systems described above.

According to the present invention, it is possible to provide an optical system and an optical apparatus that are small and have high optical performance.

It is sectional drawing which shows the structure of the optical system which concerns on 1st Example. FIG. 5 is a diagram illustrating various aberrations of the optical system according to Example 1 during photographing at infinity. It is sectional drawing which shows the structure of the optical system which concerns on 2nd Example. FIG. 12 is a diagram illustrating various aberrations of the optical system according to Example 2 when photographing at infinity. It is sectional drawing which shows the structure of the optical system which concerns on 3rd Example. FIG. 10 is a diagram illustrating various aberrations of the optical system according to Example 3 at the time of photographing at infinity. It is sectional drawing which shows the structure of the optical system which concerns on 4th Example. FIG. 12 is a diagram illustrating various aberrations of the optical system according to Example 4 during photographing at infinity. It is sectional drawing which shows the structure of the optical system which concerns on 5th Example. FIG. 11 is various aberration diagrams of the optical system according to Example 5 at the time of photographing at infinity. It is a figure explaining the digital camera (optical apparatus) carrying the optical system which concerns on this embodiment, (a) is a front view, (b) is a rear view. It is sectional drawing along the AA 'line of Fig.11 (a). It is a flowchart for demonstrating the manufacturing method of the optical system which concerns on this embodiment.

  Hereinafter, embodiments will be described with reference to the drawings.

  As shown in FIG. 1, the optical system WL according to this embodiment includes a first lens group G1, an aperture stop S, and a second lens group G2, which are arranged in order from the object side along the optical axis. The first lens group G1 is composed of a negative lens L1 and a positive lens L2 arranged in order from the object side along the optical axis. The second lens group G2 is the lens surface closest to the object side (the lens in FIG. 1). The surface m6 corresponds to a convex surface facing the object side, and a positive lens (corresponding to the lens L8 in FIG. 1) is disposed closest to the image side, which satisfies the following conditional expression (1).

0.172 <L1r2 / L2r2 <0.700 (1)
However,
L1r2: radius of curvature of the image side lens surface of the negative lens L1 of the first lens group G1,
L2r2: radius of curvature of the image side lens surface of the positive lens L2 of the first lens group G1.

  According to this configuration, the lens barrel can be retracted into the camera when the camera is not used. The lens barrel is small, has a wide angle of view (about 76 °), is bright (about Fno 2.8), and has high optical performance. An optical system having performance can be provided.

  Conditional expression (1) defines the curvature radius ratio between the image side surface of the negative lens L1 and the image side surface of the positive lens L2 in the first lens group G1, and coma aberration, astigmatism generated in the first lens group G1, This is a conditional expression for satisfactorily correcting distortion. If the lower limit value of conditional expression (1) is not reached, the image side surface of the negative lens L1 becomes relatively smaller than the image side surface of the positive lens L2, which is advantageous for correcting the Petzval sum and reducing the lens size. It becomes difficult to correct coma and distortion in the entire system. If the conditional expression (1) is exceeded, the image side surface of the negative lens L1 becomes relatively larger than the image side surface of the positive lens L2, which is advantageous for correcting distortion aberration in the entire lens system. It becomes difficult to correct coma. Further, in order to correct the Petzval sum with the first lens group G1, the distance between the negative lens L1 and the positive lens L2 must be increased, and the size reduction cannot be achieved.

  In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (1) to 0.175. In order to maximize the effects of the present embodiment, it is preferable to set the lower limit of conditional expression (1) to 0.180.

  In order to secure the effect of the present embodiment, it is preferable to set the upper limit value of conditional expression (1) to 0.600. In order to maximize the effects of the present embodiment, it is preferable to set the upper limit of conditional expression (1) to 0.500.

  In the optical system WL according to this embodiment, the first lens group G1 has a positive refractive power, and the negative lens L1 disposed closest to the object side of the first lens group G1 has a concave surface directed toward the image side. It preferably has a shape. With this configuration, it is possible to satisfactorily correct various aberrations in the entire lens system while reducing distortion generated in the first lens group G1.

  The optical system WL according to this embodiment preferably satisfies the following conditional expression (2).

1.00 <f1 / f2 <9.00 ... (2)
However,
f1: Focal length of the first lens group G1
f2: focal length of the second lens group G2.

  Conditional expression (2) defines the ratio of the focal lengths of the first lens group G1 and the second lens group G2. When the conditional expression (2) is below the lower limit, the symmetry with respect to the aperture stop S is good, and it is advantageous for correcting coma aberration, distortion aberration, and lateral chromatic aberration, but the Petzval sum increases and correction of field curvature is improved. It becomes difficult. If the upper limit value of conditional expression (2) is exceeded, the focal length of the first lens group G1 becomes too large relative to the focal length of the second lens group G2, so that the symmetry with respect to the aperture stop S deteriorates, and the coma. This is disadvantageous for correction of aberration, distortion, and lateral chromatic aberration.

  In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (2) to 1.05. In order to maximize the effects of the present embodiment, it is preferable to set the lower limit of conditional expression (2) to 1.10.

  In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (2) to 8.00.

  In the optical system WL according to the present embodiment, it is preferable that the positive lens arranged closest to the image side of the second lens group G2 has a meniscus shape with a convex surface facing the image side. With this configuration, the incident angle to the image plane can be suppressed without increasing the back focus or the total length, and thus downsizing can be achieved. Further, it is possible to satisfactorily correct field curvature, coma aberration, and the like.

  In the optical system WL according to the present embodiment, the second lens group G2 preferably has at least two cemented lenses. With this configuration, it is possible to satisfactorily correct axial chromatic aberration, astigmatism, lateral chromatic aberration, and coma.

  The optical system WL according to this embodiment preferably satisfies the following conditional expression (3).

1.9 <TL / f <2.5 (3)
However,
TL: distance from the lens surface closest to the object side of the optical system WL to the paraxial image plane,
f: The focal length of the entire optical system WL.

  Conditional expression (3) defines an appropriate total length of the optical system WL for balancing the downsizing of the entire system and aberration correction. If the lower limit of conditional expression (3) is not reached, the total length of the optical system WL is reduced, which is advantageous for downsizing, but it is difficult to correct various aberrations such as astigmatism, field curvature, and coma, and is high. Since optical performance cannot be obtained, it is not preferable. Exceeding the upper limit value of conditional expression (3) is advantageous in correcting various aberrations such as astigmatism, field curvature, and coma, and provides high optical performance, but the total length of the optical system WL becomes too large. Therefore, it is not preferable for downsizing.

  In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (3) to 2.0. In order to maximize the effects of the present embodiment, it is preferable to set the lower limit of conditional expression (3) to 2.1.

  In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (3) to 2.4. In order to maximize the effects of the present embodiment, it is preferable to set the upper limit of conditional expression (3) to 2.3.

  In the optical system WL according to this embodiment, the second lens group G2 includes a positive lens having a convex surface on the object side and a negative lens having a concave surface on the image side, which are arranged in order from the object side along the optical axis. It is preferable to include a cemented lens, a cemented lens of a negative lens having a concave surface facing the object side, and a positive lens having a convex surface facing the image side, and a positive meniscus lens having a convex surface facing the image side. With this configuration, it is possible to satisfactorily correct various aberrations such as spherical aberration and coma, and high optical performance can be obtained as a whole lens.

  In the optical system WL according to this embodiment and the second lens group G2, it is preferable that at least one surface is an aspherical surface. With this configuration, spherical aberration, astigmatism, and coma can be favorably corrected.

  According to the optical system WL according to the present embodiment configured as described above, the lens barrel can be retracted into the camera when the camera is not used, and is small, wide-angle, bright, and has high optical performance. An optical system having the following can be realized. In addition, this makes it possible to reduce the thickness of the lens barrel portion in the retracted retracted state as much as possible, thereby achieving a thinner camera.

  11 and 12 show a configuration of a digital still camera CAM (optical device) as an optical device including the above-described optical system WL. In this digital still camera CAM, when a power button (not shown) is pressed, a shutter (not shown) of a photographing lens (optical system WL) is opened, and light from a subject (object) is condensed by the optical system WL, and an image is displayed. An image is formed on an image sensor C (for example, a CCD or a CMOS) disposed on the surface I (see FIG. 1). The subject image formed on the image sensor C is displayed on the liquid crystal monitor M disposed behind the digital still camera CAM. The photographer determines the composition of the subject image while looking at the liquid crystal monitor M, and then depresses the release button B1 to photograph the subject image with the image sensor C, and records and saves it in a memory (not shown).

  The camera CAM is provided with an auxiliary light emitting unit EF for emitting auxiliary light when the subject is dark, a function button B2 used for setting various conditions of the digital still camera CAM, and the like. Here, a compact type camera in which the camera CAM and the optical system WL are integrally formed is illustrated. However, as an optical device, a single-lens reflex camera in which a lens barrel having the optical system WL and a camera body main body are detachable can be used. good.

  According to the camera CAM having the above configuration, by mounting the above-described optical system WL as a photographing lens, the lens barrel can be retracted into the camera when the camera is not used. A bright camera with high optical performance can be realized.

  Next, a method for manufacturing the above-described optical system WL will be described with reference to FIG. First, each lens is incorporated in the lens barrel so that the first lens group G1, the aperture stop S, and the second lens group G2 are arranged in order from the object side along the optical axis (step ST10). At this time, as the first lens group G1, the lenses are incorporated so that the negative lens L1 and the positive lens L2 are arranged in order from the object side along the optical axis (step ST20). As the second lens group G2, each lens is incorporated such that the lens surface closest to the object side faces the convex surface toward the object side and the positive lens is disposed closest to the image side (step ST30). Then, each lens is incorporated so as to satisfy the following conditional expression (1) (step ST40).

0.172 <L1r2 / L2r2 <0.700 (1)
However,
L1r2: radius of curvature of the image side lens surface of the negative lens L1 of the first lens group G1,
L2r2: radius of curvature of the image side lens surface of the positive lens L2 of the first lens group G1.

  Here, as an example of the lens arrangement in the present embodiment, in the optical system WL shown in FIG. 1, as the first lens group G1, a meniscus shape having a concave surface directed from the object side to the image side along the optical axis. Each lens is incorporated in the lens barrel so that the negative lens L1 and the meniscus positive lens L2 having a convex surface facing the object are arranged in this order. Further, as the second lens group G2, a cemented lens of a meniscus negative lens L3 having a convex surface facing the object side and a biconvex positive lens L4 arranged in order from the object side along the optical axis, and the object side A negative meniscus lens L5 with a convex surface facing the lens, a cemented lens of a biconcave negative lens L6 and a biconvex positive lens L7, and a meniscus positive lens L8 with a convex surface facing the image side. Each lens is incorporated in the lens barrel so that they are lined up. At this time, the conditional expression (1) is satisfied (corresponding value 0.437).

  According to the manufacturing method of the optical system WL according to the present embodiment as described above, the lens barrel can be retracted in the camera when the camera is not used, and a small optical system having high optical performance is obtained. be able to. In addition, it is possible to obtain an optical system that can contribute to thinning of the camera by reducing the thickness dimension of the lens barrel portion in the retracted state as much as possible.

  Each example according to the present embodiment will be described with reference to the drawings. Tables 1 to 5 are shown below, but these are tables of specifications in the first to fifth examples.

  In addition, each reference code with respect to FIG. 1 according to the first embodiment is used independently for each embodiment in order to avoid complication of explanation due to an increase in the number of digits of the reference code. Therefore, even if the same reference numerals as those in the drawings according to the other embodiments are given, they are not necessarily in the same configuration as the other embodiments.

  In each embodiment, C-line (wavelength 656.2730 nm), d-line (wavelength 587.5620 nm), F-line (wavelength 486.1330 nm), and g-line (wavelength 435.8350 nm) are selected as the aberration characteristic calculation targets.

  In [Lens Specifications] in the table, the surface number is the order of the optical surfaces from the object side along the light traveling direction, R is the radius of curvature of each optical surface, D is the next optical surface from each optical surface ( Or nd is the refractive index of the material of the optical member with respect to the d-line, and νd is the Abbe number based on the d-line of the material of the optical member. The object plane is the object plane, (variable) is the variable plane spacing, the curvature radius “∞” is the plane or aperture, (aperture S) is the aperture stop S, and the image plane is the image plane I. The refractive index of air “1.00000” is omitted. When the optical surface is an aspherical surface, the surface number is marked with *, and the column of curvature radius R indicates the paraxial curvature radius.

In [Aspherical data] in the table, the shape of the aspherical surface shown in [Lens specifications] is shown by the following equation (a). X (y) is the distance along the optical axis direction from the tangential plane at the apex of the aspheric surface to the position on the aspheric surface at height y, r is the radius of curvature of the reference sphere (paraxial radius of curvature), and κ is Ai represents the i-th aspherical coefficient. “E-n” indicates “× 10 ⁻ⁿ ”. For example, 1.234E-05 = 1.234 × 10 ⁻⁵ .

X (y) = (y ² / r) / {1+ (1−κ × y ² / r ² ) ^1/2 }
^{+ A4 × y 4 + A6 ×} y 6 + A8 × y 8 + A10 × y 10 ... (a)

  In [various data] in the table, f is the focal length of the entire optical system WL, Fno is the F number, ω is the half field angle (maximum incident angle, unit: °), Y is the image height, and BF is the back focus ( The distance from the last lens surface to the paraxial image surface on the optical axis is expressed in terms of air length. TL 'is the total lens length (back focus to the distance from the foremost lens surface to the last lens surface on the optical axis) Is added).

  In [Lens Group Data] in the table, G represents the group number, the first group surface represents the surface number closest to the object in each group, and the group focal length represents the focal length of each group.

  [Conditional expression] in the table indicates values corresponding to the conditional expressions (1) to (3).

  Hereinafter, in all the specification values, “mm” is generally used for the focal length f, curvature radius R, surface interval D, and other lengths, etc. unless otherwise specified, but the optical system is proportionally enlarged. Alternatively, the same optical performance can be obtained even by proportional reduction, and the present invention is not limited to this. Further, the unit is not limited to “mm”, and other appropriate units can be used.

  The description of the table so far is common to all the embodiments, and the description below is omitted.

(First embodiment)
A first embodiment will be described with reference to FIGS. 1 and 2 and Table 1. FIG. The optical system WL (WL1) according to the first example is a wide-angle single-focus lens, and as illustrated in FIG. 1, a first lens group having positive refractive power arranged in order from the object side along the optical axis. G1 includes an aperture stop S, a second lens group G2 having a positive refractive power, and a filter group FL.

  The first lens group G1 includes a meniscus negative lens L1 having a concave surface facing the image side and a meniscus positive lens L2 having a convex surface facing the object side, which are arranged in order from the object side along the optical axis. .

  The second lens group G2 includes a cemented lens of a meniscus negative lens L3 having a convex surface directed toward the object side and a biconvex positive lens L4 arranged in order from the object side along the optical axis, and a convex surface toward the object side. A negative meniscus lens L5 facing the lens, a cemented lens of a biconcave negative lens L6 and a biconvex positive lens L7, and a meniscus positive lens L8 having a convex surface facing the image side. An aspheric surface is formed on the image side lens surface of the positive lens L8.

  The filter group FL is composed of a low-pass filter, an infrared cut filter, and the like for cutting a spatial frequency higher than the limit resolution of a solid-state imaging device (for example, a CCD or a CMOS) disposed on the image plane I. .

  Table 1 below shows the values of each item in the first example. Surface numbers 1 to 19 in Table 1 correspond to the optical surfaces m1 to m19 shown in FIG. In the first embodiment, the fifteenth surface is an aspherical surface.

(Table 1)
[Lens specifications]
Surface number R D nd νd
Object ∞
1 2.2578 0.0654 1.57957 53.74
2 0.5236 0.4054
3 0.6149 0.1396 1.77250 49.62
4 1.1992 0.1253
5 (Aperture S) ∞ 0.0832
6 0.8390 0.0327 1.75520 27.57
7 0.5307 0.1382 1.83481 42.73
8 -3.2042 0.0163
9 2.3764 0.0327 1.69895 30.13
10 0.9620 0.0954
11 -0.6331 0.0381 1.74077 27.74
12 1.4300 0.0969 1.88300 40.66
13 -3.4365 0.0109
14 -5.3852 0.0817 1.79050 45.01
* 15 (Aspherical surface) -0.9963 0.7377
16 ∞ 0.0997 1.51680 64.20
17 ∞ 0.0801
18 ∞ 0.0381 1.51680 64.20
19 ∞ 0.0272
Image plane ∞

[Aspherical data]
15th surface κ = 1.0000, A4 = 1.21955E + 00, A6 = 3.81700E + 00, A8 = 5.993920E + 00, A10 = -3.00852E + 01

[Various data]
f 1.00
Fno 2.88
ω 38.86
Y 0.79
BF 0.932
TL '2.21

[Lens group data]
Group number Group first surface Group focal length G1 1 66.96
G2 6 1.22

[Conditional expression]
Conditional expression (1) L1r2 / L2r2 = 0.437
Conditional expression (2) f1 / f2 = 54.707
Conditional expression (3) TL / f = 2.209

  From Table 1, it can be seen that the optical system WL1 according to the first example satisfies the conditional expressions (1) to (3).

  FIG. 2 is a diagram of various aberrations (spherical aberration diagram, astigmatism diagram, distortion diagram, coma diagram, and chromatic aberration diagram of magnification) of the optical system WL1 according to the first example when photographing at infinity.

  In each aberration diagram, FNO is an F number, and A is a half field angle (unit: °) with respect to each image height. d is the d-line, g is the g-line, C is the C-line, and F is the F-line aberration. Those not described indicate aberrations at the d-line. In the astigmatism diagram, the solid line indicates the sagittal image plane, and the broken line indicates the meridional image plane. Note that the same reference numerals as in this embodiment are used in the aberration diagrams of each embodiment described later.

  As is apparent from the respective aberration diagrams shown in FIG. 2, it can be seen that the optical system WL1 according to the first example has various aberrations corrected well and has excellent imaging performance.

(Second embodiment)
The second embodiment will be described with reference to FIGS. 3 and 4 and Table 2. FIG. The optical system WL (WL2) according to the second example is a wide-angle single-focus lens, and as shown in FIG. 3, a first lens group having positive refractive power arranged in order from the object side along the optical axis. G1 includes an aperture stop S, a second lens group G2 having a positive refractive power, and a filter group FL.

  The first lens group G1 includes a biconcave negative lens L1 arranged in order from the object side along the optical axis, and a meniscus positive lens L2 having a convex surface facing the object side.

  The second lens group G2 includes a cemented lens of a biconvex positive lens L3 and a biconcave negative lens L4, a biconcave negative lens L5, and a biconvex that are arranged in order from the object side along the optical axis. A cemented lens with a positive lens L6 having a shape and a positive meniscus lens L7 having a convex surface facing the image side. An aspherical surface is formed on the image side lens surface of the positive lens L7.

  The filter group FL is composed of a low-pass filter, an infrared cut filter, and the like for cutting a spatial frequency higher than the limit resolution of a solid-state imaging device (for example, a CCD or a CMOS) disposed on the image plane I. .

  Table 2 below shows the values of each item in the second embodiment. Surface numbers 1 to 17 in Table 2 correspond to the optical surfaces m1 to m17 shown in FIG. In the second embodiment, the thirteenth surface is an aspherical surface.

(Table 2)
[Lens specifications]
Surface number R D nd νd
Object ∞
1 -629.2740 0.0545 1.57957 53.74
2 0.6862 0.4030
3 0.6216 0.1498 1.71300 53.96
4 3.8122 0.1225
5 (Aperture S) ∞ 0.0654
6 0.8972 0.1253 1.88300 40.66
7 -1.2949 0.0408 1.69895 30.13
8 1.2951 0.1062
9 -0.5587 0.0381 1.69895 30.13
10 1.4075 0.1470 1.75500 52.34
11 -1.5477 0.0109
12 -2.1784 0.0926 1.79050 44.98
* 13 (Aspherical surface) -0.9062 0.6873
14 ∞ 0.0997 1.51680 64.20
15 ∞ 0.0801
16 ∞ 0.0381 1.51680 64.20
17 ∞ 0.0272
Image plane ∞

[Aspherical data]
13th surface κ = 1.0000, A4 = 1.04405E + 00, A6 = 4.01005E + 00, A8 = 1.69331E + 00, A10 = 0.00000E + 00

[Various data]
f 1.00
Fno 2.88
ω 38.91
Y 0.79
BF 0.885
TL '2.24

[Lens group data]
Group number Group first surface Group focal length G1 1 2.21
G2 6 1.99

[Conditional expression]
Conditional expression (1) L1r2 / L2r2 = 0.180
Conditional expression (2) f1 / f2 = 1.109
Conditional expression (3) TL / f = 2.242

  From Table 2, it can be seen that the optical system WL2 according to the second example satisfies the conditional expressions (1) to (3).

  FIG. 4 is a diagram illustrating various aberrations (spherical aberration diagram, astigmatism diagram, distortion diagram, coma diagram, and chromatic aberration diagram of magnification) when the optical system WL2 according to the second example is photographed at infinity. As is apparent from the respective aberration diagrams shown in FIG. 4, it is understood that the optical system WL2 according to the second example has excellent aberrations and excellent imaging performance.

(Third embodiment)
A third embodiment will be described with reference to FIGS. 5 and 6 and Table 3. FIG. The optical system WL (WL3) according to the third example is a wide-angle single-focus lens, and as shown in FIG. 5, a first lens group having positive refractive power arranged in order from the object side along the optical axis. G1 includes an aperture stop S, a second lens group G2 having a positive refractive power, and a filter group FL.

  The first lens group G1 includes a meniscus negative lens L1 having a concave surface facing the image side and a meniscus positive lens L2 having a convex surface facing the object side, which are arranged in order from the object side along the optical axis. .

  The second lens group G2 includes a cemented lens of a biconvex positive lens L3 and a biconcave negative lens L4, a biconcave negative lens L5, and a biconvex that are arranged in order from the object side along the optical axis. A cemented lens with a positive lens L6 having a shape and a positive meniscus lens L7 having a convex surface facing the image side. An aspherical surface is formed on the image side lens surface of the positive lens L7.

  The filter group FL is composed of a low-pass filter, an infrared cut filter, and the like for cutting a spatial frequency higher than the limit resolution of a solid-state imaging device (for example, a CCD or a CMOS) disposed on the image plane I. .

  Table 3 below shows values of various specifications in the third example. Surface numbers 1 to 17 in Table 3 correspond to the optical surfaces m1 to m17 shown in FIG. In the third embodiment, the thirteenth surface is an aspherical surface.

(Table 3)
[Lens specifications]
Surface number R D nd νd
Object ∞
1 2.3006 0.0654 1.57957 53.74
2 0.5242 0.3268
3 0.6120 0.1198 1.79500 45.31
4 1.2254 0.1389
5 (Aperture S) ∞ 0.0545
6 0.8972 0.1471 1.88300 40.66
7 -0.6104 0.0381 1.69895 30.13
8 1.9132 0.1144
9 -0.5568 0.0381 1.69895 30.13
10 2.3580 0.1416 1.75500 52.34
11 -1.0186 0.0109
12 -1.7973 0.0817 1.79050 44.98
* 13 (Aspherical surface) -1.0056 0.7339
14 ∞ 0.0997 1.51680 64.20
15 ∞ 0.0801
16 ∞ 0.0381 1.51680 64.20
17 ∞ 0.0272
Image plane ∞

[Aspherical data]
13th surface κ = 1.0000, A4 = 9.92351E-01, A6 = 2.72773E + 00, A8 = 8.26531E + 00, A10 = -3.36149E + 01

[Various data]
f 1.00
Fno 2.88
ω 38.86
Y 0.79
BF 0.932
TL '2.21

[Lens group data]
Group number Group first surface Group focal length G1 1 66.96
G2 6 1.22

[Conditional expression]
Conditional expression (1) L1r2 / L2r2 = 0.428
Conditional expression (2) f1 / f2 = 54.707
Conditional expression (3) TL / f = 2.209

  From Table 3, it can be seen that the optical system WL3 according to the third example satisfies the conditional expressions (1) to (3).

  FIG. 6 is a diagram illustrating various aberrations (spherical aberration diagram, astigmatism diagram, distortion diagram, coma aberration diagram, and chromatic aberration diagram of magnification) of the optical system WL3 according to the third example during photographing at infinity. As is apparent from the respective aberration diagrams shown in FIG. 6, it can be seen that the optical system WL3 according to the third example has excellent imaging performance with various aberrations corrected well.

(Fourth embodiment)
A fourth embodiment will be described with reference to FIGS. 7 and 8 and Table 4. FIG. The optical system WL (WL4) according to the fourth example is a wide-angle single focus lens, and as illustrated in FIG. 7, a first lens group having positive refractive power, which is arranged in order from the object side along the optical axis. G1 includes an aperture stop S, a second lens group G2 having a positive refractive power, and a filter group FL.

  The first lens group G1 includes a biconcave negative lens L1 arranged in order from the object side along the optical axis, and a meniscus positive lens L2 having a convex surface facing the object side.

  The second lens group G2 includes a cemented lens of a biconvex positive lens L3 and a biconcave negative lens L4, a biconcave negative lens L5, and a biconvex that are arranged in order from the object side along the optical axis. A cemented lens with a positive lens L6 having a shape and a positive meniscus lens L7 having a convex surface facing the image side. An aspherical surface is formed on the image side lens surface of the positive lens L7.

  The filter group FL is composed of a low-pass filter, an infrared cut filter, and the like for cutting a spatial frequency higher than the limit resolution of a solid-state imaging device (for example, a CCD or a CMOS) disposed on the image plane I. .

  Table 4 below shows values of various specifications in the fourth embodiment. Surface numbers 1 to 17 in Table 4 correspond to the optical surfaces m1 to m17 shown in FIG. In the fourth embodiment, the thirteenth surface is an aspherical surface.

(Table 4)
[Lens specifications]
Surface number R D nd νd
Object ∞
1 -13.2676 0.0654 1.53172 48.78
2 0.6131 0.2945
3 0.6163 0.1371 1.79500 45.31
4 1.5253 0.1253
5 (Aperture S) ∞ 0.0708
6 0.7852 0.1743 1.88300 40.66
7 -1.0156 0.0408 1.75211 25.05
8 2.3728 0.1171
9 -0.5930 0.0381 1.69895 30.13
10 1.1609 0.1634 1.79952 42.09
11 -1.7522 0.0109
12 -2.7233 0.0817 1.79050 45.01
* 13 (Aspherical surface) -1.1464 0.6216
14 ∞ 0.0997 1.51680 64.20
15 ∞ 0.0801
16 ∞ 0.0381 1.51680 64.20
17 ∞ 0.0272
Image plane ∞

[Aspherical data]
13th surface κ = 1.0000, A4 = 1.22717E + 00, A6 = 3.46350E + 00, A8 = 4.993210E + 00, A10 = -3.04555E + 01

[Various data]
f 1.00
Fno 2.88
ω 38.86
Y 0.79
BF 0.820
TL '2.14

[Lens group data]
Group number Group first surface Group focal length G1 1 10.42
G2 6 1.31

[Conditional expression]
Conditional expression (1) L1r2 / L2r2 = 0.402
Conditional expression (2) f1 / f2 = 7.957
Conditional expression (3) TL / f = 2.139

  From Table 4, it can be seen that the optical system WL4 according to the fourth example satisfies the conditional expressions (1) to (3).

  FIG. 8 is a diagram illustrating various aberrations (spherical aberration diagram, astigmatism diagram, distortion diagram, coma diagram, and lateral chromatic aberration diagram) at the time of shooting at infinity of the optical system WL4 according to the fourth example. As is apparent from the respective aberration diagrams shown in FIG. 8, it is understood that the optical system WL4 according to the fourth example has excellent imaging performance with various aberrations corrected well.

(5th Example)
The fifth embodiment will be described with reference to FIGS. 9 and 10 and Table 5. FIG. The optical system WL (WL5) according to the fifth example is a wide-angle single focus lens, and as shown in FIG. 9, a first lens group having a positive refractive power, arranged in order from the object side along the optical axis. G1 includes an aperture stop S, a second lens group G2 having a positive refractive power, and a filter group FL.

  The first lens group G1 includes a meniscus negative lens L1 having a concave surface facing the image side and a meniscus positive lens L2 having a convex surface facing the object side, which are arranged in order from the object side along the optical axis. .

  The second lens group G2 includes a cemented lens of a biconvex positive lens L3 and a biconcave negative lens L4, a biconcave negative lens L5, and a biconvex that are arranged in order from the object side along the optical axis. A cemented lens with a positive lens L6 having a shape and a positive meniscus lens L7 having a convex surface facing the image side. An aspherical surface is formed on the image side lens surface of the positive lens L6.

  The filter group FL is composed of a low-pass filter, an infrared cut filter, and the like for cutting a spatial frequency higher than the limit resolution of a solid-state imaging device (for example, a CCD or a CMOS) disposed on the image plane I. .

  Table 5 below shows values of various specifications in the fifth example. Surface numbers 1 to 17 in Table 5 correspond to the optical surfaces m1 to m17 shown in FIG. In the fifth embodiment, the eleventh surface is an aspherical surface.

(Table 5)
[Lens specifications]
Surface number R D nd νd
Object ∞
1 1.7851 0.0545 1.56883 56.00
2 0.5120 0.3595
3 0.5721 0.1307 1.71300 53.96
4 1.2689 0.1280
5 (Aperture S) ∞ 0.0681
6 0.8681 0.1362 1.88300 40.66
7 -0.6973 0.0381 1.67270 32.19
8 1.3555 0.1198
9 -0.5636 0.0381 1.69895 30.13
10 1.1330 0.1634 1.77377 47.25
* 11 (Aspherical surface) -0.9531 0.0109
12 -5.4466 0.0763 1.76684 46.78
13 -2.0345 0.6752
14 ∞ 0.0997 1.51680 64.20
15 ∞ 0.0801
16 ∞ 0.0381 1.51680 64.20
17 ∞ 0.0272
Image plane ∞

[Aspherical data]
11th surface κ = 1.0000, A4 = 1.15623E + 00, A6 = 6.18674E + 00, A8 = -9.96092E + 00, A10 = 0.000000 +

[Various data]
f 1.00
Fno 2.88
ω 38.88
Y 0.79
BF 0.871
TL '2.19

[Lens group data]
Group number Group first surface Group focal length G1 1 8.13
G2 6 1.33

[Conditional expression]
Conditional expression (1) L1r2 / L2r2 = 0.403
Conditional expression (2) f1 / f2 = 6.123
Conditional expression (3) TL / f = 2.195

  From Table 5, it can be seen that the optical system WL5 according to Example 5 satisfies the conditional expressions (1) to (3).

  FIG. 10 is a diagram illustrating various aberrations (spherical aberration diagram, astigmatism diagram, distortion diagram, coma diagram, and chromatic aberration diagram of magnification) of the optical system WL5 according to Example 5 at the time of shooting at infinity. As is apparent from the respective aberration diagrams shown in FIG. 10, it can be seen that the optical system WL5 according to Example 5 has various aberrations corrected well and has excellent imaging performance.

  According to each of the above-described embodiments, the lens barrel can be retracted into the camera when the camera is not used. The lens barrel is small, has a wide angle of view of about 76 °, and has a bright Fno of about 2.8. An optical system having high optical performance could be realized.

  In order to make the present invention easier to understand, the configuration requirements of the embodiment have been described, but it goes without saying that the present invention is not limited to this.

WL (WL1 to WL5) Optical system G1 First lens group S Aperture stop G2 Second lens group FL Filter group I Image plane CAM Digital still camera (optical equipment)

Claims (9)

A first lens group, an aperture stop, and a second lens group, which are arranged in order from the object side along the optical axis, are substantially configured.
The first lens group includes a negative lens and a positive lens arranged in order from the object side along the optical axis,
The second lens group is a positive lens having a shape in which a lens surface closest to the object side has a convex surface facing the object side, and a lens disposed closest to the image side has a meniscus shape having a convex surface facing the image side. ,
An optical system satisfying the following conditional expression:
0.172 <L1r2 / L2r2 <0.700
1.00 <f1 / f2 <9.00
However,
L1r2: radius of curvature of the image side lens surface of the negative lens of the first lens group,
L2r2: radius of curvature of the image side lens surface of the positive lens of the first lens group,
f1: the focal length of the first lens group,
f2: focal length of the second lens group. The optical system according to claim 1 , wherein the first lens group has a positive refractive power. Wherein said positive lens most arranged on the image side of the second lens group, an optical system according to claim 1 or 2 characterized in that it is a single lens. Wherein the negative lens of the first lens group, an optical system according to any one of claims 1 to 3, characterized in that it has a shape with a concave surface facing the image side. The optical system according to any one of claims 1 to 4 , wherein the second lens group includes at least two cemented lenses. Optical system according to any one of claims 1 to 5, characterized by satisfying the following conditional expression.
1.9 <TL / f <2.5
However,
TL: distance from the lens surface closest to the object side to the paraxial image plane of the optical system,
f: Focal length of the optical system. The second lens group includes, in order from the object side along the optical axis, a cemented lens of a positive lens having a convex surface facing the object side and a negative lens having a concave surface facing the image side, and a concave surface facing the object side. negative lens and a cemented lens of a positive lens having a convex surface directed toward the image side, according to any one of claims 1 to 6, characterized in that it has a positive meniscus lens having a convex surface directed toward the image side Optical system. The second lens group, an optical system according to any one of claims 1 to 7, characterized in that at least one surface is aspherical. An optical apparatus comprising the optical system according to any one of claims 1 to 8 .

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