JP6236794B2 - Optical system and optical equipment - Google Patents

Description

  The present invention relates to a wide-angle, large-diameter optical system that is optimal for photographing optical systems such as digital cameras, film cameras, and video cameras.

  In recent years, there has been proposed a wide-angle lens having a lens barrel that can be retracted into the camera when the camera is not used and having a small and wide angle of view (see, for example, Patent Document 1).

JP 2008-40033 A

  However, the conventional wide-angle lens cannot be said to have sufficient brightness, and a further increase in aperture is expected.

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 having a small aperture and a wide angle of view and a large aperture.

In order to achieve such an object, the first optical system according to the present invention substantially includes a front group disposed closest to the object side and a rear group disposed closest to the image side across the aperture stop. The front group includes a meniscus negative lens having a concave surface facing the image side closest to the object side, and the rear group includes a first positive lens arranged in order from the object side, and a negative lens. The lens is composed of a cemented lens including a lens and a second positive lens, and a third positive lens, and satisfies the following conditional expression.

-1.2 <(L22r1 + L21r2) / (L22r1-L21r2) <-0.7
0.8 <fGF / f <1.2
However,
L21r2: radius of curvature of the image side surface of the first positive lens in the rear group,
L22r1: the radius of curvature of the object side surface of the negative lens in the rear group ,
fGF: focal length of the front group,
f: Focal length of the entire optical system.
Further, the second optical system according to the present invention is substantially composed of a front group disposed closest to the object side and a rear group disposed closest to the image side across the aperture stop, and the front group Is composed of a negative meniscus lens having a concave surface facing the image side, and a cemented lens composed of a positive lens and a negative lens, and the rear group is arranged in order from the object side. The lens includes a first positive lens, a cemented lens including a negative lens and a second positive lens, and a third positive lens, and satisfies the following conditional expression.
-1.2 <(L22r1 + L21r2) / (L22r1-L21r2) <-0.7
However,
L21r2: radius of curvature of the image side surface of the first positive lens in the rear group,
L22r1: The radius of curvature of the object side surface of the negative lens in the rear group.
Further, the third optical system according to the present invention is substantially composed of a front group disposed closest to the object side and a rear group disposed closest to the image side across the aperture stop, and the front group Has a meniscus negative lens with a concave surface facing the image side closest to the object side, and the rear group is arranged in order from the object side, a first positive lens, a negative lens, and a second positive lens The cemented lens of the cemented lens composed of the negative lens and the second positive lens has a concave surface facing the image side, and the following conditional expression: Satisfied.
-1.2 <(L22r1 + L21r2) / (L22r1-L21r2) <-0.7
−0.08 <(nL22−nL23) <− 0.05
However,
L21r2: radius of curvature of the image side surface of the first positive lens in the rear group,
L22r1: the radius of curvature of the object side surface of the negative lens in the rear group ,
nL22: refractive index with respect to d-line of the optical material of the negative lens constituting the cemented lens disposed in the rear group,
nL23: Refractive index with respect to the d-line of the optical material of the second positive lens constituting the cemented lens disposed in the rear group.

  The optical apparatus according to the present invention includes any one of the above-described optical systems.

ADVANTAGE OF THE INVENTION According to this invention, while having a small and wide angle of view, an optical system and optical apparatus with a large aperture can be provided.

FIG. 2 is a cross-sectional view showing a lens configuration of an optical system according to Example 1, where (a) shows an infinitely focused state, and (b) shows a state with an imaging magnification β = −1 / 20. FIG. 4A is a diagram illustrating various aberrations of the optical system according to Example 1, where FIG. 9A illustrates various aberrations in the infinite focus state, and FIG. . It is sectional drawing which shows the lens structure of the optical system which concerns on 2nd Example, (a) is an infinite focus state, (b) shows the state of imaging magnification (beta) =-1/20. FIG. 5A is a diagram illustrating various aberrations of the optical system according to Example 2, wherein FIG. 9A is a diagram illustrating various aberrations in the infinite focus state, and FIG. It is sectional drawing which shows the lens structure of the optical system which concerns on 3rd Example, (a) is an infinite focus state, (b) shows the state of imaging magnification (beta) =-1/20. FIG. 6A is a diagram illustrating various aberrations of the optical system according to Example 3. FIG. 9A is a diagram illustrating various aberrations in the infinite focus state, and FIG. is there. It is sectional drawing which shows the lens structure of the optical system which concerns on 4th Example, (a) is an infinite focus state, (b) shows the state of imaging magnification (beta) =-1/20. FIG. 6A is a diagram illustrating various aberrations of the optical system according to Example 4, wherein FIG. 9A is a diagram illustrating aberrations in an infinite focus state, and FIG. is there. 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.9 (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 the present embodiment includes a front group GF disposed closest to the object side with the aperture stop S interposed therebetween, and a rear group GR disposed closest to the image side. The front group GF has a meniscus negative lens L11 having a concave surface facing the image side closest to the object side, and the rear group GR includes a first positive lens L21 and a negative lens arranged in order from the object side. The lens includes a cemented lens including L22 and the second positive lens L23, and a third positive lens L24, and satisfies the following conditional expression (1).

-1.2 <(L22r1 + L21r2) / (L22r1-L21r2) <-0.7 (1)
However,
L21r2: radius of curvature of the image side surface of the first positive lens L21 of the rear group GR,
L22r1: The radius of curvature of the object side surface of the negative lens L22 of the rear group GR.

  According to the optical system WL having the above-described configuration, the lens barrel can be retracted into the camera when the camera is not used. The lens barrel is small in size and has a wide angle of view (about 77 degrees of view angle) and a large aperture ( An optical system of about Fno 2.8) can be provided.

  Conditional expression (1) defines the shape of the air gap (so-called air lens) formed between the positive lens L21 and the negative lens L22 of the rear group GR. By satisfying conditional expression (1), coma, curvature of field, and astigmatism can each be corrected satisfactorily. If conditional expression (1) is below the lower limit, coma increases and correction becomes difficult. If conditional expression (1) exceeds the upper limit, it is difficult to correct astigmatism and field curvature. Further, coma becomes an inner coma, and correction becomes difficult.

  In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (1) to −1.0. In order to ensure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (1) to −0.8.

  In the optical system WL according to the present embodiment, focusing from an object at infinity to a near object moves the third positive lens L24 disposed closest to the image side in the rear group GR along the optical axis. It is preferable that the following conditional expressions (2) and (3) are satisfied.

4.0 <fL24 / f <7.0 (2)
0.35 <dL23L24 / f <0.60 (3)
However,
fL24: focal length of the third positive lens L24 of the rear group GR,
f: focal length of the entire optical system WL;
dL23L24: an air space on the optical axis between the second positive lens L23 and the third positive lens L24 in the rear group GR.

  From the viewpoint of miniaturization, when the lens barrel is retracted into the camera when the camera is not used, focusing from an infinitely distant object to a finite distance object is performed by a third positive lens disposed on the most image side in the rear group GR. It is preferable to carry out at L24. In addition, by performing the third positive lens L24 alone, the weight of the lens that is driven during focusing is reduced, so that quick focusing is possible.

  Conditional expression (2) defines the focal length of the positive lens L24 located closest to the image side of the rear group GR. Conditional expression (3) defines the air space on the optical axis between the positive lens L23 and the positive lens L24 constituting the rear group GR. By satisfying these conditional expressions (2) and (3), various aberrations can be corrected satisfactorily while securing a sufficient amount of movement of the positive lens L24 during focusing.

  If the lower limit value of conditional expression (2) is not reached, the amount of focus movement decreases, but the Petzval sum increases, which is disadvantageous in terms of aberration correction. If the upper limit value of conditional expression (2) is exceeded, the Petzval sum decreases, which is advantageous in terms of aberration correction, but is not preferable because the amount of focus movement increases.

  In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (2) to 5.5. In order to ensure the effect of this embodiment, it is preferable to set the upper limit of conditional expression (2) to 6.5.

  If the lower limit value of conditional expression (3) is not reached, it is difficult to ensure the movement interval of the positive lens L24 by focusing, the Petzval sum increases, and aberration correction becomes difficult. In addition, aberration fluctuations in a finite system increase, making it difficult to obtain good performance. Exceeding the upper limit value of conditional expression (3) is advantageous for securing the movement distance of the positive lens L24 by focusing, but is not preferable because aberration fluctuations in a finite system increase and it becomes difficult to obtain good performance. .

  In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (3) to 0.35. In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (3) to 0.45.

  In the optical system WL according to the present embodiment, the front group GF includes a meniscus negative lens L11 arranged in order from the object side and a concave surface facing the image side, and a cemented lens including a positive lens L12 and a negative lens L13. It is preferable to satisfy the following conditional expression (4).

0.8 <fGF / f <1.2 (4)
However,
fGF: focal length of front group GF,
f: The focal length of the entire optical system WL.

  With the above configuration, various aberrations (particularly coma aberration) with respect to the angle of view can be favorably corrected in the front group GF.

  Conditional expression (4) defines the focal length of the front group GF in order to satisfactorily correct various aberrations while achieving downsizing. If the lower limit value of conditional expression (4) is not reached, the back focus is shortened, which is advantageous for downsizing, but it is difficult to sufficiently correct various aberrations (particularly coma aberration). If the upper limit of conditional expression (4) is exceeded, the focal length of the rear group GR will be shortened, which is disadvantageous for correcting spherical aberration. Moreover, since the back focus becomes long, it is not preferable because it is disadvantageous for downsizing.

  In order to ensure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (4) to 0.9. In order to ensure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (4) to 1.1.

  In the optical system WL according to the present embodiment, the rear group GR preferably has a positive refractive power. With this configuration, spherical aberration can be corrected satisfactorily.

  In the optical system WL according to this embodiment, the cemented surface of the cemented lens including the negative lens L22 and the second positive lens L23 disposed in the rear group GR has a concave surface facing the image side. It is preferable to satisfy conditional expression (5).

−0.08 <(nL22−nL23) <− 0.05 (5)
However,
nL22: the refractive index of the optical material of the negative lens L22 constituting the cemented lens disposed in the rear group GR with respect to the d-line,
nL23: Refractive index with respect to d line of the optical material of the second positive lens L23 constituting the cemented lens arranged in the rear group GR.

  Conditional expression (5) defines the difference in refractive index between the negative lens L22 and the positive lens L23 constituting the rear group GR in order to achieve an appropriate value for the Petzval sum while achieving miniaturization. When the cemented surface of the negative lens L22 and the positive lens L23 is concave toward the image side and satisfies the conditional expression (5), it is advantageous for correcting the Petzval sum, and corrects field curvature and astigmatism. can do. When the conditional expression (5) is not satisfied, in order to reduce the Petzval sum, the refractive power of L24 of the positive lens located closest to the image side in the rear group GR is weakened, or the second positive lens L23 and the third lens The distance between the positive lens L24 and the positive lens L24 must be widened, and the total length of the optical system becomes longer, which 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 (5) to −0.07. In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (5) to −0.06.

  In the optical system WL according to this embodiment, the cemented surface of the cemented lens including the positive lens L12 and the negative lens L13 disposed in the front group GF has a concave surface directed toward the object side, and the following conditional expression ( It is preferable to satisfy 6).

0.06 <(nL12−nL13) <0.09 (6)
However,
nL12: refractive index with respect to d-line of the optical material of the positive lens L12 constituting the cemented lens arranged in the front group GF,
nL13: Refractive index with respect to the d-line of the optical material of the negative lens L13 constituting the cemented lens arranged in the front group GF.

  Conditional expression (6) defines an appropriate difference in refractive index between the positive lens L12 and the negative lens L13 in the front group GF in order to achieve an appropriate value for the Petzval sum while achieving miniaturization. When the cemented surface of the positive lens L12 and the negative lens L13 is concave on the object side and satisfies the conditional expression (6), it is advantageous for correcting the Petzval sum, and corrects field curvature and astigmatism. can do. When the conditional expression (6) is not satisfied, in order to reduce the Petzval sum, the refractive power of the positive lens L12 must be increased, or the interval between the negative lens L11 and the positive lens L12 must be increased. The total length of the optical system becomes long, which is disadvantageous for miniaturization.

  In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (6) to 0.07. In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (6) to 0.08.

  In the optical system WL according to this embodiment, it is preferable that at least one of the optical surfaces constituting the rear group GR is an aspherical surface. With this configuration, correction of spherical aberration, coma aberration, and field curvature is improved.

  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 the lens barrel is small, has a wide angle of view, and has a large aperture. An optical system 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.

  9 and 10 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, and is small and has a wide angle of view. At the same time, a large-diameter camera can be realized.

  Next, a method for manufacturing the above-described optical system WL will be described with reference to FIG. First, the lenses are assembled in the lens barrel so that the front group GF is positioned closest to the object side and the rear group GR is positioned closest to the image side with the aperture stop S therebetween (step ST10). At this time, as the front group GF, a lens is incorporated so that the meniscus negative lens L11 having a concave surface facing the image side is located closest to the object side (step ST20). Further, as the rear group GR, in order from the object side, each lens is arranged such that the first positive lens L21, the cemented lens including the negative lens L22 and the second positive lens L23, and the third positive lens L24 are arranged. Is incorporated (step ST30). Then, each lens is incorporated in the lens barrel so as to satisfy the conditional expression (1) (step ST40).

-1.2 <(L22r1 + L21r2) / (L22r1-L21r2) <-0.7 (1)
However,
L21r2: radius of curvature of the image side surface of the first positive lens L21 of the rear group GR,
L22r1: The radius of curvature of the object side surface of the negative lens L22 of the rear group GR.

  Here, as an example of the lens arrangement in the present embodiment, in the optical system WL shown in FIG. 1, as the front group GF, a meniscus negative lens 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 a cemented lens including L11, a biconvex positive lens L12, and a biconcave negative lens L13 is arranged in this order. As the rear group GR, a cemented lens including a meniscus positive lens L21 having a convex surface facing the object side from the object side along the optical axis, a biconcave negative lens L22, and a biconvex positive lens L23; Each lens is incorporated in the lens barrel so as to be arranged in the order of the biconvex positive lens L24. At this time, the conditional expression (1) is satisfied (corresponding value -0.972).

  According to the manufacturing method of the optical system WL as described above, the lens barrel can be retracted into the camera when the camera is not used, and a small-sized optical system having a wide angle of view and a large aperture is obtained. be able to.

  Each example according to the present embodiment will be described with reference to the drawings. Tables 1 to 4 are shown below, but these are tables of specifications in the first to fourth 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 (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 the air equivalent distance), TL is the total lens length (the distance from the foremost lens surface to the last lens surface on the optical axis plus BF) Indicates.

  In [Variable Interval Data] in the table, each variable interval Di in the state of focusing at infinity (shooting magnification β = 0.00) and shooting magnification β = −1 / 20 is shown. Di represents a variable interval between the i-th surface and the (i + 1) -th surface.

  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 (6).

  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. As shown in FIG. 1, the optical system WL (WL1) according to the first example includes a front group GF having a positive refractive power, an aperture stop S, and a positive aperture, which are arranged in order from the object side along the optical axis. And a filter group FL.

  The front group GF is a cemented lens composed of a meniscus negative lens L11 having a concave surface facing the image side, a biconvex positive lens L12, and a biconcave negative lens L13 arranged in order from the object side along the optical axis. It consists of a lens.

  The rear group GR is a cemented lens array composed of a meniscus positive lens L21 having a convex surface facing the object side, a biconcave negative lens L22, and a biconvex positive lens L23 arranged in order from the object side along the optical axis. The lens includes a biconvex positive lens L24. An aspheric surface is formed on the image side lens surface of the positive lens L23.

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

  In the optical system WL1 according to the present embodiment, focusing from an object at infinity to an object at a finite distance is performed by moving the positive lens L24 disposed closest to the image side in the rear group GR along the optical axis. .

  Table 1 below shows the values of each item in the first example. Surface numbers 1 to 17 in Table 1 correspond to the optical surfaces having the curvature radii R1 to R17 shown in FIG. In the first embodiment, the eleventh surface is formed in an aspherical shape.

(Table 1)
[Lens specifications]
Surface number R D nd νd
Object ∞
1 3.0935 0.0653 1.62280 57.10
2 0.5713 0.5438
3 0.6509 0.2284 1.81600 46.59
4 -1.3074 0.1088 1.74077 27.74
5 25.1245 0.1196
6 (Aperture S) ∞ 0.0778
7 2.7190 0.0979 1.79504 28.69
8 34.1231 0.0696
9 -0.4895 0.0435 1.69895 30.13
10 0.8594 0.1903 1.76802 49.23
* 11 (Aspherical surface) -0.8257 D11 (variable)
12 4.2417 0.1088 1.69680 55.52
13 -114.5150 D13 (variable)
14 ∞ 0.0865 1.51680 64.20
15 ∞ 0.0544
16 ∞ 0.0381 1.51680 64.20
17 ∞ 0.033
Image plane ∞

[Aspherical data]
11th surface κ = -2.1683, A4 = 2.51801E-01, A6 = 4.63597E + 00, A8 = -2.43802E + 00

[Various data]
f 1.00
Fno 2.88
ω 39.03
Y 0.79
BF 0.49
TL 2.55

[Variable interval data]
Infinity β = -1 / 20
D11 0.40785 0.17389
D13 0.31544 0.54940

[Lens group data]
Group number Group first surface Group focal length GF 1 1.00
GR 7 5.36

[Conditional expression]
Conditional expression (1) (L22r1 + L21r2) / (L22r1-L21r2) =-0.972
Conditional expression (2) fL24 / f = 5.872
Conditional expression (3) dL23L24 / f = 0.408
Conditional expression (4) fGF / f = 0.997
Conditional expression (5) (nL22−nL23) = − 0.069
Conditional expression (6) (nL12-nL13) = 0.075

  From Table 1, it can be seen that the optical system WL1 according to the present example satisfies the conditional expressions (1) to (6).

  FIG. 2 is a diagram showing various aberrations (spherical aberration diagram, astigmatism diagram, distortion diagram, coma aberration diagram and chromatic aberration diagram of magnification) of the optical system WL1 according to the first example, and (a) is infinite focus. The various aberration diagrams in the state (imaging magnification β = 0.00), and (b) show the various aberration diagrams in the state of the imaging magnification β = −1 / 20.

  In each aberration diagram, FNO is an F number, NA is a numerical aperture, A is a half angle of view (unit: °) with respect to each image height, and H0 is an object 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.

  The description regarding these aberration diagrams is the same in other examples, and the description thereof is omitted.

  As is apparent from the respective aberration diagrams shown in FIG. 2, it can be seen that in the first example, various aberrations are satisfactorily corrected and the optical performance is excellent.

(Second embodiment)
A second embodiment will be described with reference to FIGS. 3 and 4 and Table 2. FIG. As shown in FIG. 3, the optical system WL (WL2) according to the second example includes a front group GF having a positive refractive power, an aperture stop S, and a positive aperture arranged in order from the object side along the optical axis. And a filter group FL.

  The front group GF is a cemented lens composed of a meniscus negative lens L11 having a concave surface facing the image side, a biconvex positive lens L12, and a biconcave negative lens L13 arranged in order from the object side along the optical axis. It consists of a lens.

  The rear group GR is a cemented lens array composed of a meniscus positive lens L21 having a convex surface facing the object side, a biconcave negative lens L22, and a biconvex positive lens L23 arranged in order from the object side along the optical axis. The lens includes a biconvex positive lens L24. An aspheric surface is formed on the image side lens surface of the positive lens L23.

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

  In the optical system WL2 according to the present embodiment, focusing from an object at infinity to an object at a finite distance is performed by moving the positive lens L24 arranged closest to the image side in the rear group GR along the optical axis. .

  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 having the curvature radii R1 to R17 shown in FIG. In the second embodiment, the eleventh surface is formed in an aspherical shape.

(Table 2)
[Lens specifications]
Surface number R D nd νd
Object ∞
1 2.81876 0.06533 1.65100 56.24
2 0.57178 0.53895
3 0.62198 0.22320 1.81600 46.59
4 -1.46662 0.10888 1.74077 27.74
5 5.74708 0.11977
6 (Aperture S) ∞ 0.06533
7 1.63318 0.13610 1.77250 49.62
8 8.16592 0.07077
9 -0.43794 0.03811 1.69895 30.13
10 1.49543 0.18509 1.76802 49.23
* 11 (Aspherical) -0.73787 D11 (variable)
12 4.35516 0.10888 1.69680 55.52
13 -114.64001 D13 (variable)
14 ∞ 0.08656 1.51680 64.20
15 ∞ 0.05444
16 ∞ 0.03811 1.51680 64.20
17 ∞ 0.037
Image plane ∞

[Aspherical data]
11th surface κ = -0.9570, A4 = 3.34667E-01, A6 = 4.42540E + 00, A8 = -2.28401E + 00

[Various data]
f 1.00
Fno 2.88
ω 38.98
Y 0.79
BF 0.43
TL 2.53

[Variable interval data]
Infinity β = -1 / 20
D11 0.43552 0.18100
D13 0.26000 0.51452

[Lens group data]
Group number Group first surface Group focal length GF 1 1.06
GR 7 4.48

[Conditional expression]
Conditional expression (1) (L22r1 + L21r2) / (L22r1-L21r2) =-0.898
Conditional expression (2) fL24 / f = 6.024
Conditional expression (3) dL23L24 / f = 0.436
Conditional expression (4) fGF / f = 1.062
Conditional expression (5) (nL22−nL23) = − 0.069
Conditional expression (6) (nL12-nL13) = 0.075

  From Table 2, it can be seen that the optical system WL2 according to the present example satisfies the conditional expressions (1) to (6).

  FIG. 4 is a diagram showing various aberrations (spherical aberration diagram, astigmatism diagram, distortion diagram, coma aberration diagram and chromatic aberration diagram of magnification) of the optical system WL2 according to the second example, and (a) is infinite focus. The various aberration diagrams in the state (imaging magnification β = 0.00), and (b) show the various aberration diagrams in the state of the imaging magnification β = −1 / 20.

  As is apparent from the respective aberration diagrams shown in FIG. 4, it can be seen that in the second example, various aberrations are satisfactorily corrected and the optical performance is excellent.

(Third embodiment)
A third embodiment will be described with reference to FIGS. As shown in FIG. 5, the optical system WL (WL3) according to the third example includes a front group GF having a positive refractive power, an aperture stop S, and a positive aperture arranged in order from the object side along the optical axis. And a filter group FL.

  The front group GF is a cemented lens composed of a meniscus negative lens L11 having a concave surface facing the image side, a biconvex positive lens L12, and a biconcave negative lens L13 arranged in order from the object side along the optical axis. It consists of a lens.

  The rear group GR is a cemented lens array composed of a meniscus positive lens L21 having a convex surface facing the object side, a biconcave negative lens L22, and a biconvex positive lens L23 arranged in order from the object side along the optical axis. The lens includes a biconvex positive lens L24. An aspheric surface is formed on the image side lens surface of the positive lens L23.

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

  In the optical system WL3 according to the present embodiment, focusing from an object at infinity to an object at a finite distance is performed by moving the positive lens L24 disposed closest to the image side in the rear group GR along the optical axis. .

  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 having the curvature radii R1 to R17 shown in FIG. In the third embodiment, the eleventh surface is formed in an aspherical shape.

(Table 3)
[Lens specifications]
Surface number R D nd νd
Object ∞
1 3.67143 0.06515 1.58913 61.22
2 0.57061 0.54292
3 0.64353 0.22803 1.81600 46.59
4 -1.26794 0.10858 1.74077 27.74
5 9.64318 0.11944
6 (Aperture S) ∞ 0.06515
7 1.90022 0.12759 1.78800 47.35
8 7.20062 0.07058
9 -0.46932 0.03800 1.69895 30.13
10 1.65587 0.18459 1.76802 49.23
* 11 (Aspherical) -0.76832 D11 (variable)
12 4.34336 0.10858 1.69680 55.52
13 -114.32956 D13 (variable)
14 ∞ 0.08632 1.51680 64.20
15 ∞ 0.05429
16 ∞ 0.03800 1.51680 64.20
17 ∞ 0.010
Image plane ∞

[Aspherical data]
11th surface κ = -0.8431, A4 = 4.39025E-01, A6 = 4.29306E + 00, A8 = -1.16486E + 00

[Various data]
f 1.00
Fno 2.88
ω 38.65
Y 0.78
BF 0.46
TL 2.53

[Variable interval data]
Infinity β = -1 / 20
D11 0.40719 0.16188
D13 0.31493 0.56024

[Lens group data]
Group number Group first surface Group focal length GF 1 1.03
GR 7 5.02

[Conditional expression]
Conditional expression (1) (L22r1 + L21r2) / (L22r1-L21r2) =-0.878
Conditional expression (2) fL24 / f = 6.007
Conditional expression (3) dL23L24 / f = 0.407
Conditional expression (4) fGF / f = 1.029
Conditional expression (5) (nL22−nL23) = − 0.069
Conditional expression (6) (nL12-nL13) = 0.075

  From Table 3, it can be seen that the optical system WL3 according to the present example satisfies the conditional expressions (1) to (6).

  FIG. 6 is a diagram showing various aberrations (spherical aberration diagram, astigmatism diagram, distortion diagram, coma diagram, and chromatic aberration diagram of magnification) of the optical system WL3 according to the third example, and (a) is infinite focus. The various aberration diagrams in the state (imaging magnification β = 0.00), and (b) show the various aberration diagrams in the state of the imaging magnification β = −1 / 20.

  As is apparent from the aberration diagram shown in FIG. 6, it can be seen that in the third example, various aberrations are satisfactorily corrected and the optical performance is excellent.

(Fourth embodiment)
A fourth embodiment will be described with reference to FIGS. As shown in FIG. 7, the optical system WL (WL4) according to the fourth example includes a front group GF having a positive refractive power, an aperture stop S, and a positive aperture, which are arranged in order from the object side along the optical axis. And a filter group FL.

  The front group GF is a cemented lens composed of a meniscus negative lens L11 having a concave surface facing the image side, a biconvex positive lens L12, and a biconcave negative lens L13 arranged in order from the object side along the optical axis. It consists of a lens.

  The rear group GR is a cemented lens array composed of a meniscus positive lens L21 having a convex surface facing the object side, a biconcave negative lens L22, and a biconvex positive lens L23 arranged in order from the object side along the optical axis. The lens includes a biconvex positive lens L24. An aspheric surface is formed on the image side lens surface of the positive lens L23.

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

  In the optical system WL4 according to the present embodiment, focusing from an object at infinity to an object at a finite distance is performed by moving the positive lens L24 disposed closest to the image side in the rear group GR along the optical axis. .

  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 having the curvature radii R1 to R17 shown in FIG. In the fourth embodiment, the eleventh surface is formed in an aspherical shape.

(Table 4)
[Lens specifications]
Surface number R D nd νd
Object ∞
1 3.81559 0.06487 1.58913 61.22
2 0.57102 0.54057
3 0.65152 0.22704 1.81600 46.59
4 -1.24961 0.10811 1.74077 27.74
5 13.99216 0.11892
6 (Aperture S) ∞ 0.06487
7 1.89198 0.12703 1.78800 47.35
8 5.40565 0.07027
9 -0.48370 0.03784 1.69895 30.13
10 1.43940 0.18379 1.76802 49.23
* 11 (Aspherical) -0.78223 D11 (variable)
12 4.32452 0.10811 1.69680 55.52
13 -113.83359 D13 (variable)
14 ∞ 0.08595 1.51680 64.20
15 ∞ 0.05406
16 ∞ 0.03784 1.51680 64.20
17 ∞ 0.023
Image plane ∞

[Aspherical data]
11th surface κ = -0.6683, A4 = 5.30186E-01, A6 = 4.42920E + 00, A8 = -1.47383E + 00

[Various data]
f 1.00
Fno 2.88
ω 38.66
Y 0.78
BF 0.47
TL 2.53

[Variable interval data]
Infinity β = -1 / 20
D11 0.40542 0.16424
D13 0.31356 0.55475

[Lens group data]
Group number Group first surface Group focal length GF 1 1.02
GR 7 5.17

[Conditional expression]
Conditional expression (1) (L22r1 + L21r2) / (L22r1-L21r2) =-0.836
Conditional expression (2) fL24 / f = 5.982
Conditional expression (3) dL23L24 / f = 0.405
Conditional expression (4) fGF / f = 1.024
Conditional expression (5) (nL22−nL23) = − 0.069
Conditional expression (6) (nL12-nL13) = 0.075

  From Table 4, it can be seen that the optical system WL4 according to the present example satisfies the conditional expressions (1) to (6).

  FIG. 8 is a diagram showing various aberrations (spherical aberration diagram, astigmatism diagram, distortion aberration diagram, coma aberration diagram, and chromatic aberration diagram of magnification) of the optical system WL4 according to the fourth example, and (a) is infinite focus. The various aberration diagrams in the state (imaging magnification β = 0.00), and (b) show the various aberration diagrams in the state of the imaging magnification β = −1 / 20.

  As is apparent from the respective aberration diagrams shown in FIG. 8, it can be seen that in the fourth example, various aberrations are satisfactorily corrected and the optical performance is excellent.

  According to each of the above-described embodiments, the lens barrel can be retracted into the camera when the camera is not used, and it is compact, has a wide field angle of about 77 degrees, and a bright optical system with a Fno of about 2.8. Can be realized.

  In order to make the present invention easy 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 WL4) Optical system GF Front group S Aperture stop GR Rear group FL Filter group I Image plane CAM Digital still camera (optical equipment)

Claims (11)

It is substantially composed of a front group disposed on the most object side and a rear group disposed on the most image side across the aperture stop,
The front group has a meniscus negative lens with a concave surface facing the image side closest to the object side,
The rear group is composed of a first positive lens, a cemented lens composed of a negative lens and a second positive lens, and a third positive lens, arranged in order from the object side,
An optical system satisfying the following conditional expression:
-1.2 <(L22r1 + L21r2) / (L22r1-L21r2) <-0.7
0.8 <fGF / f <1.2
However,
L21r2: radius of curvature of the image side surface of the first positive lens in the rear group,
L22r1: the radius of curvature of the object side surface of the negative lens in the rear group ,
fGF: focal length of the front group,
f: Focal length of the entire optical system. It is substantially composed of a front group disposed on the most object side and a rear group disposed on the most image side across the aperture stop,
The front group is composed of a meniscus negative lens arranged in order from the object side and having a concave surface facing the image side, and a cemented lens composed of a positive lens and a negative lens,
The rear group is composed of a first positive lens, a cemented lens composed of a negative lens and a second positive lens, and a third positive lens, arranged in order from the object side,
An optical system satisfying the following conditional expression:
-1.2 <(L22r1 + L21r2) / (L22r1-L21r2) <-0.7
However,
L21r2: radius of curvature of the image side surface of the first positive lens in the rear group,
L22r1: The radius of curvature of the object side surface of the negative lens in the rear group. It is substantially composed of a front group disposed on the most object side and a rear group disposed on the most image side across the aperture stop,
The front group has a meniscus negative lens with a concave surface facing the image side closest to the object side,
The rear group includes a first positive lens, a cemented lens including a negative lens and a second positive lens, and a third positive lens arranged in order from the object side, and the negative lens and the second lens. The cemented surface of the cemented lens composed of a positive lens is directed concave toward the image side,
An optical system satisfying the following conditional expression:
-1.2 <(L22r1 + L21r2) / (L22r1-L21r2) <-0.7
−0.08 <(nL22−nL23) <− 0.05
However,
L21r2: radius of curvature of the image side surface of the first positive lens in the rear group,
L22r1: the radius of curvature of the object side surface of the negative lens in the rear group ,
nL22: refractive index with respect to d-line of the optical material of the negative lens constituting the cemented lens disposed in the rear group,
nL23: Refractive index with respect to the d-line of the optical material of the second positive lens constituting the cemented lens disposed in the rear group. The cemented surface of the cemented lens composed of the negative lens and the second positive lens disposed in the rear group has a concave surface facing the image side,
The optical system according to claim 1, wherein the following conditional expression is satisfied.
−0.08 <(nL22−nL23) <− 0.05
However,
nL22: refractive index with respect to d-line of the optical material of the negative lens constituting the cemented lens disposed in the rear group,
nL23: Refractive index with respect to the d-line of the optical material of the second positive lens constituting the cemented lens disposed in the rear group.   The front group includes a meniscus negative lens arranged in order from the object side and having a concave surface facing the image side, and a cemented lens including a positive lens and a negative lens. The optical system described. The optical system according to claim 3, wherein the following conditional expression is satisfied.
0.8 <fGF / f <1.2
However,
fGF: focal length of the front group,
f: Focal length of the entire optical system. Focusing is performed by moving the third positive lens disposed closest to the image side in the rear group along the optical axis,
The optical system according to any one of claims 1 to 6, wherein the following conditional expression is satisfied.
4.0 <fL24 / f <7.0
0.35 <dL23L24 / f <0.60
However,
fL24: focal length of the third positive lens in the rear group,
f: focal length of the entire optical system,
dL23L24: an air space on the optical axis between the second positive lens and the third positive lens in the rear group. The rear group includes an optical system according to any one of claims 1 to 7, characterized by having a positive refractive power. The cemented surface of the cemented lens composed of the positive lens and the negative lens disposed in the front group has a concave surface facing the object side,
The optical system according to claim 1 , wherein the following conditional expression is satisfied.
0.06 <(nL12-nL13) <0.09
However,
nL12: Refractive index with respect to d-line of the optical material of the positive lens constituting the cemented lens arranged in the front group,
nL13: Refractive index with respect to d-line of the optical material of the negative lens constituting the cemented lens arranged in the front group. Among optical surfaces constituting the rear group optical system according to any one of claims 1 to 9, characterized in that at least one surface is aspherical. An optical apparatus comprising the optical system according to any one of claims 1 to 10 .

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