JP2014160106A - Optical system, optical device, and method for manufacturing optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical system which is compact and has excellent optical performance, an optical device and a method for manufacturing the optical system.SOLUTION: The optical system comprises, in order from the object side along the optical axis: a first lens L1 having negative refractive power; a second lens L2 having positive refractive power; a third lens L3 having positive refractive power; a fourth lens L4 having negative refractive power; a fifth lens L5 having negative refractive power; and a sixth lens L6 having positive refractive power. The optical system satisfies the following conditional expression (1): (1) 0.88<L4R2/f, where L4R2 is the curvature radius of the image side surface of the fourth lens L4, and f is the focal distance of the entire lens system.

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, zoom lenses for compact digital cameras are mostly so-called collapsible lens barrels that store a lens barrel in the camera when the camera is not used. Also, like a zoom lens, the lens barrel can be retracted into the camera when the camera is not used, and it has a wide angle of view and does not change the focal length with respect to an infinite object point. Has been proposed (see, for example, Patent Document 1).

JP 2008-40033 A

  However, the conventional single-focus wide-angle lens does not have sufficient brightness and the total length of the optical system is long.

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

  In order to achieve such an object, an optical system according to the present invention includes a first lens having a negative refractive power and a second lens having a positive refractive power, which are arranged in order from the object side along the optical axis. A third lens having a positive refractive power, a fourth lens having a negative refractive power, a fifth lens having a negative refractive power, and a sixth lens having a positive refractive power, Satisfies the conditional expression.

0.88 <L4R2 / f
However,
L4R2: radius of curvature of the image side surface of the fourth lens,
f: Focal length of the entire lens system.

  The optical system according to the present invention preferably satisfies the following conditional expression.

−1.450 <(L5R1 + L4R2) / (L5R1−L4R2) <− 0.310
However,
L5R1: The radius of curvature of the object side surface of the fifth lens.

  The optical system according to the present invention preferably satisfies the following conditional expression.

L3f / f <0.56
However,
L3f: focal length of the third lens.

  In the optical system according to the present invention, it is preferable that the first lens is a negative meniscus lens having a concave surface facing the image side.

  In the optical system according to the present invention, it is preferable that the image side surface of the lens located closest to the image side is an aspherical surface.

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

  The method of manufacturing an optical system according to the present invention includes a first lens having a negative refractive power, a second lens having a positive refractive power, and a positive refractive power arranged in order from the object side along the optical axis. And a fourth lens having a negative refractive power, a fifth lens having a negative refractive power, and a sixth lens having a positive refractive power. Each lens is incorporated in the lens barrel so that the following conditional expression is satisfied.

0.88 <L4R2 / f
However,
L4R2: radius of curvature of the image side surface of the fourth lens,
f: Focal length of the entire lens system.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the optical system which has small and high optical performance, an optical apparatus, and an optical system can be provided.

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 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.7 (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 L1 having negative refractive power and a second lens having positive refractive power, which are arranged in order from the object side along the optical axis. L2, a third lens L3 having a positive refractive power, a fourth lens L4 having a negative refractive power, a fifth lens L5 having a negative refractive power, and a sixth lens L6 having a positive refractive power And the following conditional expression (1) is satisfied.

0.88 <L4R2 / f (1)
However,
L4R2: radius of curvature of the image side surface of the fourth lens L4,
f: Focal length of the entire lens system.

  In general, in designing an imaging optical system such as a photographic lens, it is difficult to increase the angle of view and increase the aperture while maintaining the size of the optical system. As the aperture becomes larger, it becomes more difficult to correct spherical aberration and to correct coma and astigmatism. Further, if the angle is widened without enlarging the optical system, it becomes difficult to correct spherical aberration, astigmatism, and various chromatic aberrations.

  The optical system WL according to this embodiment is configured as described above, so that the total lens thickness (distance from the lens front surface to the lens final surface) is shortened, and the lens barrel is retracted in the camera when the camera is not used. The lens barrel when the camera is not in use can be made thin, and the camera can be thinned. Although it is small, it has a bright Fno of about 2.8 and a wide angle of view of about 75 °. It is possible to satisfactorily correct spherical aberration, coma aberration, and chromatic aberration with a small number of lenses while ensuring an angle.

  Further, by arranging a lens group having a positive refractive power on the image side of the first lens L1 having a negative refractive power, and making it a retrofocus type, the coma aberration and the curvature of field can be reduced while being small. It is possible to suppress various aberrations and achieve a wide angle of view.

  Conditional expression (1) defines the ratio between the radius of curvature of the image side surface of the fourth lens L4 and the focal length of the fourth lens L4. The optical system WL of the present embodiment can reduce spherical aberration and coma aberration by satisfying conditional expression (1). When the lower limit value of conditional expression (1) is not reached and L4R2 takes a positive value, the radius of curvature of the object side surface of the fourth lens L4 becomes too small. As a result, introverted coma and distortion can be corrected effectively, but spherical aberration becomes overcorrected, making it difficult to correct it. Further, when the lower limit value of conditional expression (1) is not reached and L4R2 takes a negative value, the object side surface of the fourth lens L4 has a positive refractive power, and therefore upper coma and distortion are generated. It becomes large and it becomes difficult to correct this.

  In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (1) to 0.90. In order to maximize the effects of the present embodiment, it is more preferable to set the lower limit of conditional expression (1) to 0.99.

  In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (1) to 8.60.

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

-1.450 <(L5R1 + L4R2) / (L5R1-L4R2) <-0.310 (2)
However,
L5R1: The radius of curvature of the object side surface of the fifth lens L5.

  Conditional expression (2) defines the shape factor of the air lens formed between the image side surface of the fourth lens L4 and the object side surface of the fifth lens L5. By satisfying conditional expression (2), the optical system WL according to the present embodiment can correct coma and distortion satisfactorily and obtain a flat image surface while being small. If the lower limit value of conditional expression (2) is not reached and L4R2 takes a negative value, L4R2 has a positive refractive power, so the occurrence of upper coma and distortion will increase, and this should be corrected. Becomes difficult. When the lower limit value of conditional expression (2) is not reached and L5R1 takes a positive value, L5R1 has a positive refractive power, so that the occurrence of distortion increases and it is difficult to correct this. . Further, since the Petzval sum becomes too large, it becomes difficult to obtain a flat image surface. Further, when the conditional expression (2) exceeds the upper limit value, the radius of curvature of the object side surface of the fourth lens L4 becomes too small. As a result, introverted coma and distortion can be corrected effectively, but spherical aberration becomes overcorrected, making it difficult to correct it.

  In order to secure the effect of the present embodiment, it is preferable to set the lower limit value of conditional expression (2) to −1.200. In order to maximize the effects of the present embodiment, it is more preferable to set the lower limit value of conditional expression (2) to -1.000.

  In order to secure the effect of the present embodiment, it is preferable to set the upper limit value of conditional expression (2) to −0.510.

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

L3f / f <0.56 (3)
However,
L3f: focal length of the third lens L3.

  Conditional expression (3) defines the focal length of the third lens L3. By satisfying conditional expression (3), the optical system WL according to the present embodiment can correct coma and astigmatism well and obtain a flat image surface while being compact. When the corresponding value of conditional expression (3) exceeds the upper limit value, the positive refractive power of the third lens L3 becomes too small. This increases the size of the entire lens system. At this time, it is possible to achieve downsizing by increasing the positive refractive power of the second lens L2, but coma and astigmatism generated in the first lens L1 and the second lens L2 become too large. Therefore, it becomes difficult to correct aberrations in the entire lens system.

  In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (3) to 0.53. In order to maximize the effects of the present embodiment, it is more preferable to set the upper limit of conditional expression (3) to 0.49.

  In the optical system WL according to the present embodiment, the first lens L1 is preferably a negative meniscus lens having a concave surface facing the image side. With this configuration, it is possible to satisfactorily correct distortion and coma.

  In the optical system WL according to the present embodiment, it is preferable that the image side surface of the lens located closest to the image side (corresponding to the image side surface m13 of the seventh lens L7 in FIG. 1) is an aspherical surface. With this configuration, a surface through which off-axis rays pass through a position far from the optical axis becomes an aspheric surface, and effective aberration correction can be performed. Further, by using an aspherical surface whose refractive power decreases as it goes from the optical axis to the periphery, it is possible to satisfactorily correct curvature of field and astigmatism and to correct aberrations of the entire lens system.

  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, it is possible to reduce the thickness of the lens barrel portion in the retracted storage state as much as possible to achieve a thinner camera.

  7 and 8 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 can be attached and detached is 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. In addition, the thickness of the lens barrel portion in the retracted state can be reduced as much as possible to achieve a thin camera.

  Next, a method for manufacturing the above-described optical system WL will be described with reference to FIG. First, in the lens barrel, in order from the object side, a first lens L1 having a negative refractive power, a second lens L2 having a positive refractive power, a third lens L3 having a positive refractive power, and a negative Each lens is incorporated so that the fourth lens L4 having a negative refractive power, the fifth lens L5 having a negative refractive power, and the sixth lens L6 having a positive refractive power are aligned (step ST10). At this time, each lens is incorporated so as to satisfy the following conditional expression (1) (step ST20).

0.88 <L4R2 / f (1)
However,
L4R2: radius of curvature of the image side surface of the fourth lens L4,
f: Focal length of the entire lens system.

  Here, as an example of the lens arrangement in the present embodiment, the optical system WL shown in FIG. 1 has a convex surface facing the object side from the object side as the first lens L1 having negative refractive power along the optical axis. A negative meniscus lens, a positive meniscus lens having a convex surface facing the object as the second lens L2 having positive refractive power, a biconvex positive lens as the third lens L3 having positive refractive power, A biconcave negative lens as the fourth lens L4 having refractive power, a biconcave negative lens as the fifth lens L5 having negative refractive power, and a biconvex shape as the sixth lens L6 having positive refractive power Each member is incorporated in the lens barrel so that the positive lens and the biconvex positive lens as the seventh lens L7 are arranged in this order. The biconvex positive lens L3 and the biconcave negative lens L4 are bonded together to form a cemented lens. The biconcave negative lens L5 and the biconvex positive lens L6 constitute a cemented lens. Further, the optical system WL satisfies the conditional expression (1) (corresponding value 0.993).

  According to the manufacturing method of the optical system WL according to the present embodiment as described above, the lens barrel can be retracted into the camera when the camera is not used, and it is small, wide angle of view, bright, and high optical. An optical system having performance can be obtained. 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.

  Hereinafter, each example according to the present embodiment will be described with reference to the drawings.

  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.

  Tables 1 to 3 are shown below, but these are tables of specifications in the first to third examples.

  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 an object plane, (variable) is a variable plane spacing, the radius of curvature R = ∞ is a plane or an aperture, (aperture S) is an aperture stop S, and the image plane is an 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 lens system, 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 (optical axis). The distance from the last lens surface to the paraxial image surface in terms of the air equivalent length), TL is the total lens length (the back focus is added to the distance from the foremost lens surface to the last lens surface on the optical axis) Stuff).

  [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 is arranged in order from the object side along the optical axis, as shown in FIG. 1, and a negative meniscus lens having a convex surface directed toward the object side. A second lens L2 that is a positive meniscus lens having a convex surface facing the object side, a third lens L3 that is a biconvex positive lens, and a fourth lens that is a biconcave negative lens. A cemented lens with L4, an aperture stop S, a fifth lens L5 which is a biconcave negative lens, a sixth lens L6 which is a positive meniscus lens having a convex surface facing the image side, and a convex surface facing the image side In addition, the lens unit includes a seventh lens L7 that is a positive meniscus lens and a filter group FL. An aspheric surface is formed on the image side surface of the seventh 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, CCD or CMOS) disposed on the image plane I. ing.

  Table 1 below shows the values of each item in the first example. Surface numbers 1 to 18 in Table 1 correspond to the optical surfaces m1 to m18 shown in FIG. In the first embodiment, the fourteenth surface is an aspherical surface.

(Table 1)
[Lens specifications]
Surface number R D nd νd
Object ∞
1 8.9738 0.0649 1.51823 58.82
2 0.4819 0.2865
3 0.7445 0.1189 1.72916 54.61
4 1.6219 0.0676
5 1.0084 0.1568 1.81600 46.59
6 -0.7623 0.0757 1.60342 38.03
7 8.5872 0.0703
8 (Aperture S) ∞ 0.1270
9 -0.6482 0.0432 1.80809 22.74
10 -11.2813 0.0108
11 -3.7444 0.1135 1.81600 46.59
12 -0.7338 0.0054
13 -1.6423 0.0757 1.80139 45.46
* 14 (Aspherical surface) -1.0658 0.9636
15 ∞ 0.0508 1.51680 64.20
16 ∞ 0.0703
17 ∞ 0.0378 1.51680 64.20
18 ∞ 0.1080
Image plane ∞

[Aspherical data]
14th surface κ = 1.0000, A4 = 7.2951E-01, A6 = 3.2482E + 00, A8 = 0.000E + 00, A10 = 3.124E + 01

[Various data]
f 1.00
Fno 2.87
ω 39.01
Y 0.790
BF 0.980
TL 2.196

[Conditional expression]
Conditional expression (1) L4R2 / f = 8.587
Conditional expression (2) (L5R1 + L4R2) / (L5R1-L4R2) = − 0.860
Conditional expression (3) L3f / f = 0.554

  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 is arranged in order from the object side along the optical axis, as shown in FIG. 3, and a negative meniscus lens having a convex surface facing the object side. A first lens L1, a second lens L2 that is a positive meniscus lens having a convex surface facing the object side, an aperture stop S, a third lens L3 that is a biconvex positive lens, and a biconcave negative lens A cemented lens with a fourth lens L4, a cemented lens with a fifth lens L5, which is a biconcave negative lens, and a sixth lens L6, which is a biconvex positive lens, and a biconvex positive lens. A seventh lens L7 and a filter group FL are included. An aspheric surface is formed on the image side surface of the seventh 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, CCD or CMOS) disposed on the image plane I. ing.

  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 1.9223 0.0632 1.57957 53.74
2 0.5749 0.3992
3 0.5513 0.1062 1.77250 49.62
4 1.0806 0.1583
5 (Aperture S) ∞ 0.0928
6 0.7481 0.1367 1.88300 40.66
7 -0.7562 0.0316 1.69895 30.13
8 0.9931 0.0974
9 -0.5135 0.0368 1.69895 30.13
10 3.0398 0.0635 1.75500 52.33
11 -7.5617 0.0105
12 3.3409 0.1196 1.79050 45.01
* 13 (Aspherical surface) -0.8993 0.6750
14 ∞ 0.0963 1.51680 64.20
15 ∞ 0.0774
16 ∞ 0.0368 1.51680 64.20
17 ∞ 0.0380
Image plane ∞

[Aspherical data]
13th surface κ = 1.0000, A4 = 1.016E + 00, A6 = 3.4411E + 00, A8 = 2.7592E + 00, A10 = -4.1017E + 01

[Various data]
f 1.00
Fno 2.88
ω 38.87
Y 0.790
BF 0.853
TL 2.169

[Conditional expression]
Conditional expression (1) L4R2 / f = 0.993
Conditional expression (2) (L5R1 + L4R2) / (L5R1-L4R2) = − 0.318
Conditional expression (3) L3f / f = 0.445

  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 of various aberrations (spherical aberration diagram, astigmatism diagram, distortion diagram, coma diagram, and chromatic aberration diagram of magnification) of the optical system WL2 according to the second example at the time of photographing 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 is arranged in order from the object side along the optical axis, as shown in FIG. 5, and a negative meniscus lens having a convex surface facing the object side. A second lens L2 that is a positive meniscus lens having a convex surface facing the object side, a third lens L3 that is a biconvex positive lens, and a fourth lens that is a biconcave negative lens. The lens unit includes a cemented lens with L4, an aperture stop S, a cemented lens with a fifth lens L5 that is a biconcave negative lens and a sixth lens L6 that is a biconvex positive lens, and a filter group FL. ing. An aspherical surface is formed on the image side surface of the sixth lens L6, which is a positive lens. 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, CCD or CMOS) disposed on the image plane I. ing.

  Table 3 below shows values of various specifications in the third example. Surface numbers 1 to 15 in Table 3 correspond to the optical surfaces m1 to m15 shown in FIG. In the third embodiment, the eleventh surface is an aspherical surface.

(Table 3)
[Lens specifications]
Surface number R D nd νd
Object ∞
1 6.8460 0.0630 1.60311 60.69
2 0.4999 0.2280
3 0.6265 0.1025 1.64000 60.19
4 0.9751 0.1318
5 0.6503 0.2300 1.81600 46.59
6 -0.8635 0.1207 1.69895 30.13
7 107.1331 0.0786
8 (Aperture S) ∞ 0.0788
9 -0.5702 0.0309 1.72825 28.38
10 0.9539 0.1952 1.85 135 40.10
* 11 (Aspherical surface) -0.8707 0.8336
12 ∞ 0.0493 1.51680 64.20
13 ∞ 0.0682
14 ∞ 0.0367 1.51680 64.20
15 ∞ 0.0262
Image plane ∞

[Aspherical data]
11th surface κ = 1.0000, A4 = 1.3316E + 00, A6 = 4.5790E + 00, A8 = 1.8336E + 01, A10 = -7.1378E + 01

[Various data]
f 1.00
Fno 2.90
ω 38.66
Y 0.790
BF 0.896
TL 2.155

[Conditional expression]
Conditional expression (1) L4R2 / f = 107.133
Conditional expression (2) (L5R1 + L4R2) / (L5R1-L4R2) =-0.989
Conditional expression (3) L3f / f = 0.488

  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.

  According to each of the above embodiments, the lens barrel can be retracted into the camera when the camera is not used, and although it is small, Fno is as bright as about 2.8 and the angle of view is as wide as about 75 °. In addition, an optical system that satisfactorily corrects various aberrations including spherical aberration can be realized with a small number of lenses.

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

WL (WL1 to WL3) Optical system L1 1st lens L2 2nd lens L3 3rd lens L4 4th lens L5 5th lens L6 6th lens S Aperture stop FL filter group I Image plane CAM Digital still camera (optical equipment)

Claims (7)

A first lens having negative refracting power, a second lens having positive refracting power, a third lens having positive refracting power, and a negative refracting power arranged in order from the object side along the optical axis. A fourth lens having, a fifth lens having a negative refractive power, and a sixth lens having a positive refractive power,
An optical system satisfying the following conditional expression:
0.88 <L4R2 / f
However,
L4R2: radius of curvature of the image side surface of the fourth lens,
f: Focal length of the entire lens system. The optical system according to claim 1, wherein the following conditional expression is satisfied.
−1.450 <(L5R1 + L4R2) / (L5R1−L4R2) <− 0.310
However,
L5R1: The radius of curvature of the object side surface of the fifth lens. The optical system according to claim 1, wherein the following conditional expression is satisfied.
L3f / f <0.56
However,
L3f: focal length of the third lens.   The optical system according to claim 1, wherein the first lens is a negative meniscus lens having a concave surface facing the image side.   The optical system according to any one of claims 1 to 4, wherein an image side surface of the lens located closest to the image side is an aspherical surface.   An optical apparatus comprising the optical system according to any one of claims 1 to 5. A first lens having negative refracting power, a second lens having positive refracting power, a third lens having positive refracting power, and a negative refracting power arranged in order from the object side along the optical axis. And a fourth lens having a negative refracting power and a sixth lens having a positive refracting power, and a lens mirror so as to satisfy the following conditional expression: A method of manufacturing an optical system, wherein each lens is incorporated in a cylinder.
0.88 <L4R2 / f
However,
L4R2: radius of curvature of the image side surface of the fourth lens,
f: Focal length of the entire lens system.

Images