JP6938845B2 - Optical system and optical equipment - Google Patents

Description

The present invention relates to an optical system and an optical device using the same.

Conventionally, a bright wide-angle lens suitable for wide-angle photography has been proposed as an optical system used in an optical device such as a digital single-lens reflex camera or a digital video camera (see, for example, Patent Document 1). For example, some wide-angle lenses are configured by providing an afocal converter on the object side of a Gaussian lens configuration. However, in such an optical system, the overall length and diameter of the optical system become large, and the optical system may become large as a whole.

Japanese Unexamined Patent Publication No. 2014-202952

The optical system according to the present invention is substantially composed of two lens groups consisting of a first lens group and a second lens group arranged in order from the object side, and the distance between adjacent lens groups at the time of focusing is provided. The first lens group is composed of a front group having a negative refractive force and a rear group having a positive refractive force arranged in order from the object side, and the front group is arranged in order from the object side. However, it consists of a meniscus-shaped first negative lens with a convex surface facing the object side and a meniscus-shaped first positive lens with a convex surface facing the object side, and the rear group is arranged in order from the object side. The biconcave second negative lens and the biconvex second positive lens substantially consist of two lenses, satisfying the following conditional expression.
0.716 ≤ f2 / f1 <1.40
2.00 <(-fG1a) /fG1b <3.50
However, f1: the focal length of the first lens group,
f2: Focal length of the second lens group,
fG1a: Focal length of the previous group,
FG1b: focal length of the rear group.

Further, the optical device according to the present invention is configured to include the above optical system.

It is a figure which shows the lens structure of the optical system which concerns on 1st Example of this Embodiment. FIG. 2A is a diagram of various aberrations of the optical system according to the first embodiment during infinity focusing, and FIG. 2B is a diagram of various aberrations of the optical system according to the first embodiment during short-distance focusing. It is a figure. It is a figure which shows the lens structure of the optical system which concerns on 2nd Example of this Embodiment. FIG. 4A is a diagram of various aberrations of the optical system according to the second embodiment during infinity focusing, and FIG. 4B is a diagram of various aberrations of the optical system according to the second embodiment during short-distance focusing. It is a figure. It is a figure which shows the structure of the camera provided with the optical system which concerns on this embodiment. It is a flowchart which shows the manufacturing method of the optical system which concerns on this embodiment.

Hereinafter, the optical system and the optical device of the present embodiment will be described with reference to the drawings. As an example of the optical system (wide-angle lens) WL according to the present embodiment, the optical system WL (1) shown in FIG. 1 has a first lens group G1 and a second lens group G2 arranged in order from the object side. It is composed of. The first lens group G1 includes a meniscus-shaped first negative lens having a convex surface facing the object side, a meniscus-shaped first positive lens having a convex surface facing the object side, and both concave lenses arranged in order from the object side. It is configured to have a second negative lens having a shape and a second positive lens having a biconvex shape. Such an optical system WL (1)
In the above, the distance between the first lens group G1 and the second lens group G2 changes at the time of focusing. With this configuration, it is possible to obtain an optical system having a large aperture ratio, a small size, and good optical performance.

The optical system WL according to the present embodiment may be the optical system WL (2) shown in FIG. Each lens group of the optical system WL (2) shown in FIG. 3 is configured in the same manner as the optical system WL (1) shown in FIG.

As described above, in the optical system WL according to the present embodiment, the first lens group G1 has a meniscus-shaped first negative lens having a convex surface facing the object side and a meniscus-shaped first lens having a convex surface facing the object side. It is configured to have a positive lens of 1, a second negative lens having a biconcave shape, and a second positive lens having a biconvex shape. Conventionally, it has been very difficult to increase the angle of view and reduce the thickness of the optical system at the same time while maintaining the brightness of the optical system. However, according to the present embodiment, incident light is emitted from a wide angle of view. By configuring the first lens group G1 to be received as described above, various aberrations such as coma, distortion, and spherical aberration can be satisfactorily corrected.

The optical system WL of the present embodiment preferably satisfies the following conditional expression (1).

ndm> 1.70 ... (1)
However, ndm: the average refractive index of the first positive lens and the second positive lens in the first lens group G1 with respect to the d line.

The conditional expression (1) is a conditional expression for defining an appropriate range of the average refractive index of the positive lens included in the first lens group G1. If the corresponding value of the conditional expression (1) is less than the lower limit value, the Petzval sum becomes too small, and it becomes difficult to correct astigmatism and curvature of field. In order to ensure the effect of the present embodiment, the lower limit of the conditional expression (1) may be preferably 1.71 and more preferably 1.72.

In the optical system WL of the present embodiment, the first lens group G1 includes a front group G1a composed of a first negative lens and a first positive lens arranged in order from the object side and having a negative refractive power, and a first group G1a. It is preferably composed of a rear group G1b having a negative lens of 2 and a second positive lens and having a positive refractive power, and satisfying the following conditional expression (2).

2.00 <(-fG1a) /fG1b <3.50 ... (2)
However, fG1a: the focal length of the front group G1a,
fG1b: Focal length of the rear group G1b.

The conditional expression (2) is a conditional expression for defining an appropriate range of power balance between the front group G1a and the rear group G1b in the first lens group G1. It is desirable that the first lens group G1 is composed of a substantially afocal front group G1a and a rear group G1b having a positive refractive power.

By satisfying the conditional expression (2), various aberrations such as coma, distortion, and spherical aberration can be satisfactorily corrected. In order to ensure the effect of the present embodiment, the upper limit value of the conditional expression (2) may be preferably 3.35, and more preferably 3.20.

Further, in order to ensure the effect of the present embodiment, the lower limit value of the conditional expression (2) may be preferably 2.15, and more preferably 2.30.

The optical system WL of the present embodiment preferably satisfies the following conditional expression (3).

0.10 <Y / BL <0.56 ... (3)
However, Y: the radius of the image circle of the optical system WL,
BL: The distance on the optical axis from the lens surface on the most object side to the lens surface on the image side in the optical system WL in the infinity focused state.

The conditional expression (3) is a conditional expression for defining an appropriate range between the radius (that is, the maximum image height) of the image circle of the optical system WL and the lens thickness. When the corresponding value of the conditional expression (3) exceeds the upper limit value, the lens configuration is thin with respect to the format size of the image pickup element, but it becomes difficult to correct off-axis aberrations such as coma. In order to ensure the effect of the present embodiment, the upper limit of the conditional expression (3) may be preferably 0.50, more preferably 0.40.

If the corresponding value of the conditional expression (3) is less than the lower limit value, the maximum image height of the optical system WL becomes small, so that a sufficient angle of view cannot be secured. In addition, it becomes difficult to correct spherical aberration and the like. In order to ensure the effect of the present embodiment, the lower limit of the conditional expression (3) may be preferably 0.15, more preferably 0.20.

The optical system WL of the present embodiment preferably satisfies the following conditional expression (4).

0.20 <f / TL <0.35 ... (4)
However, f: the focal length of the optical system WL in the infinity focused state,
TL: The distance on the optical axis from the lens plane on the most object side to the image plane in the optical system WL in the infinity focused state, and the air conversion distance from the lens plane on the image side to the image plane.

The conditional expression (4) is a conditional expression for defining an appropriate range between the focal length and the total length of the optical system WL. By satisfying the conditional expression (4), good optical performance can be obtained while keeping the total length of the optical system WL as small as possible.

When the corresponding value of the conditional expression (4) exceeds the upper limit value, the total length of the optical system WL becomes short, so that it is necessary to increase the power of each group, and it becomes difficult to correct spherical aberration, coma aberration, and the like. In order to ensure the effect of the present embodiment, the upper limit of the conditional expression (4) may be preferably 0.30, more preferably 0.28.

When the corresponding value of the conditional expression (4) is less than the lower limit value, the total length of the optical system WL becomes long, so that the diameter of the negative lens of the first lens group G1 increases, and it becomes difficult to correct off-axis aberration and chromatic aberration. .. In order to ensure the effect of the present embodiment, the lower limit of the conditional expression (4) may be preferably 0.21 and more preferably 0.23.

The optical system WL of the present embodiment preferably satisfies the following conditional expression (5).

1.30 <DG1 / f <2.20 ... (5)
However, DG1: the distance on the optical axis from the lens surface on the most object side to the lens surface on the image side in the first lens group G1.
f: Focal length of the optical system WL in the infinity focused state.

The conditional expression (5) is a conditional expression for defining an appropriate range of the total thickness (lens thickness) of the first lens group G1 with respect to the focal length of the optical system WL. If the corresponding value of the conditional expression (5) exceeds the upper limit value, the first lens group G1 becomes large, which is not preferable. In addition, as the size of the first lens group G1 increases, aberrations at locations away from the optical axis increase, making it difficult to correct chromatic aberrations and the like. In general, in a bright optical system (wide-angle lens), the first lens group tends to be large, and the large size of the first lens group causes the entire lens barrel to be large. In order to ensure the effect of the present embodiment, the upper limit of the conditional expression (5) may be preferably 2.10, and more preferably 2.00.

If the corresponding value of the conditional expression (5) is less than the lower limit value, the first lens group G1 becomes too small, and it becomes difficult to correct curvature of field, distortion, and the like. In order to ensure the effect of the present embodiment, the lower limit of the conditional expression (5) may be preferably 1.33, more preferably 1.36.

The optical system WL of this embodiment preferably satisfies the following conditional expression (6).

2.95 <TL / (FNO × Bf) <4.20 ... (6)
However, FNO: F number of the optical system WL in the infinity focused state,
Bf: Air conversion distance on the optical axis from the lens plane on the image side to the image plane in the optical system WL in the infinity focused state,
TL: The distance on the optical axis from the lens plane on the most object side to the image plane in the optical system WL in the infinity focused state, and the air conversion distance from the lens plane on the image side to the image plane.

The conditional expression (6) is a conditional expression that defines an appropriate balance between the total length of the optical system WL, the back focus, and the F number as a bright single focus lens (wide-angle lens). If the corresponding value of the conditional expression (6) exceeds the upper limit value, the total length of the optical system WL is too long, which is not preferable. Further, since the F number of the optical system WL is too small, it becomes difficult to correct the spherical aberration. In order to ensure the effect of the present embodiment, the upper limit of the conditional expression (6) may be preferably 4.10, and more preferably 4.00.

If the corresponding value of the conditional expression (6) is less than the lower limit value, the total length of the optical system WL is too short, and it becomes difficult to correct coma aberration and the like. In order to ensure the effect of the present embodiment, the lower limit of the conditional expression (6) may be preferably 3.10, and more preferably 3.30.

The optical system WL of the present embodiment preferably satisfies the following conditional expression (7).

0.35 <f2 / f1 <1.60 ... (7)
However, f1: the focal length of the first lens group G1
f2: Focal length of the second lens group G2.

The conditional expression (7) is a conditional expression for defining an appropriate power distribution (distribution of refractive power) between the first lens group G1 and the second lens group G2. If the corresponding value of the conditional expression (7) exceeds the upper limit value, the power (refractive power) of the second lens group G2 is too weak, so that the magnification cannot be obtained in the second lens group G2 and the second lens group G2. This is not preferable because it makes focusing difficult and narrows the options for the focus method. Further, since the power of the first lens group G1 is too strong, it is difficult to correct off-axis aberrations such as curvature of field, and the entire optical system becomes large, which is not preferable. In order to ensure the effect of the present embodiment, the upper limit of the conditional expression (7) may be preferably 1.40, and more preferably 1.20.

If the corresponding value of the conditional expression (7) is less than the lower limit value, the power of the second lens group G2 is too strong, and it becomes difficult to correct spherical aberration, coma aberration, and the like. In order to ensure the effect of the present embodiment, the lower limit of the conditional expression (7) may be preferably 0.38, more preferably 0.40.

In the optical system WL of the present embodiment, the lens arranged on the image side of the first lens group G1 is the second positive lens, and it is preferable that the following conditional expression (8) is satisfied.

0 <(Rp2 + Rp1) / (Rp2-Rp1) <2.00 ... (8)
However, Rp1: the radius of curvature of the lens surface on the object side in the second positive lens,
Rp2: Radius of curvature of the lens surface on the image side of the second positive lens.

The conditional expression (8) is a conditional expression for defining an appropriate range of the shape factor of the second positive lens arranged on the image side of the first lens group G1. If the corresponding value of the conditional expression (8) exceeds the upper limit value, it becomes difficult to correct the distortion. In order to ensure the effect of the present embodiment, the upper limit of the conditional expression (8) may be preferably 1.85, and more preferably 1.70.

When the corresponding value of the conditional expression (8) is less than the lower limit value, the degree of meniscus of the shape of the second positive lens of the first lens group G1 is too strong, so that field curvature on the meridional image plane occurs and astigmatism occurs. It becomes difficult to correct point aberration. Further, it becomes difficult to shorten the total length of the optical system WL. In order to ensure the effect of the present embodiment, the lower limit of the conditional expression (8) may be preferably 0.20, more preferably 0.30.

In the optical system WL of the present embodiment, it is preferable that the lens surface on the image side of the first lens group G1 is an aspherical surface. This makes it possible to satisfactorily correct coma while reducing the size of the optical system.

In the optical system WL of the present embodiment, the aperture aperture S is arranged between the first lens group G1 and the second lens group G2, and is arranged on the most object side of the second lens group G2 located on the image side of the aperture aperture S. The lens is a negative lens, and the lens surface on the object side of the negative lens arranged on the object side of the second lens group G2 is concave, and it is preferable that the following conditional expression (9) is satisfied.

0.70 <(-R21) /φSt <3.30 ... (9)
However, R21: the radius of curvature of the lens surface on the object side of the negative lens arranged on the most object side of the second lens group G2,
φSt: Aperture diameter of the aperture stop S.

Conditional expression (9) is a condition for defining an appropriate range between the radius of curvature of the lens surface on the object side of the negative lens arranged on the most object side of the second lens group G2 and the aperture diameter of the aperture diaphragm S. It is an expression. The opening diameter of the opening diaphragm S is the diameter of the opening when the opening diaphragm S is in the most open state (open diaphragm). If the corresponding value of the conditional expression (9) exceeds the upper limit value, the curvature of the negative lens arranged on the most object side of the second lens group G2 is too small, and it becomes difficult to correct coma aberration and the like. In order to ensure the effect of the present embodiment, the upper limit of the conditional expression (9) may be preferably 3.20, and more preferably 3.10.

When the corresponding value of the conditional equation (9) is less than the lower limit value, the curvature of the negative lens arranged on the most object side of the second lens group G2 is too large, and it becomes difficult to correct spherical aberration and coma. In order to ensure the effect of the present embodiment, the lower limit of the conditional expression (9) may be preferably 0.75, and more preferably 0.80.

In the optical system WL of the present embodiment, it is preferable that the first lens group G1 is fixed and the second lens group G2 moves along the optical axis at the time of focusing. This makes it possible to simplify the mechanical configuration that drives the lens and reduce the weight of the focus group (focus group).

In the optical system WL of the present embodiment, it is preferable that the lens surface on the image side of the lens arranged on the image side of the second lens group G2 is a convex surface. As a result, the Petzval sum can be appropriately corrected, and the position of the exit pupil sufficiently distant from the image plane I can be secured.

The optical device of the present embodiment is configured to include the optical system WL having the above-described configuration. As a specific example thereof, a camera (optical device) provided with the above optical system WL will be described with reference to FIG. As shown in FIG. 5, the camera 1 is a digital camera provided with the optical system WL according to the above embodiment as the photographing lens 2. In the camera 1, the light from an object (subject) (not shown) is collected by the photographing lens 2 and reaches the image sensor 3. As a result, the light from the subject is captured by the image sensor 3 and recorded as a subject image in a memory (not shown). In this way, the photographer can shoot the subject with the camera 1. The camera 1 may be a mirrorless camera or a single-lens reflex type camera having a quick return mirror. Further, the camera 1 is not limited to a single-lens reflex type camera in which the lens barrel and the camera body body can be attached and detached, and the camera 1 may be a compact type camera in which the lens barrel and the camera body body are integrated. good. According to such a configuration, by mounting the optical system WL as a photographing lens, it is possible to obtain an optical device having a large aperture ratio, a small size, and good optical performance.

Subsequently, the method for manufacturing the above-mentioned optical system WL will be outlined with reference to FIG. First, the first lens group G1 and the second lens group G2 are arranged in the lens barrel in order from the object side (step ST1). At this time, the first lens group G1 is arranged in order from the object side, a meniscus-shaped first negative lens having a convex surface facing the object side, and a meniscus-shaped first positive lens having a convex surface facing the object side. Each lens is arranged in the lens barrel so as to have a biconcave second negative lens and a biconvex second positive lens. Then, at the time of focusing, the distance between the first lens group G1 and the second lens group G2 is changed (step ST2). According to such a manufacturing method, it is possible to manufacture an optical system having a large diameter ratio, a small size, and good optical performance. In addition, each lens may be arranged in the lens barrel so as to satisfy the above conditional expression (1) and the like.

Hereinafter, the optical system (wide-angle lens) WL according to the embodiment of the present embodiment will be described with reference to the drawings. 1 and 3 are cross-sectional views showing the configuration and refractive power distribution of the optical systems WL {WL (1) to WL (2)} according to the first to second embodiments. Each cross-section describes the position of each group (denoted as "infinity" and "short distance") when focusing from infinity to a short-range object.

In FIGS. 1 and 3, each lens group is represented by a combination of reference numerals G and numbers, and each lens is represented by a combination of reference numerals L and numbers. In this case, in order to prevent the types and numbers of the symbols and numbers from becoming large and complicated, the lens group and the like are represented by independently using combinations of the symbols and numbers for each embodiment. Therefore, even if the same combination of reference numerals and numbers is used between the examples, it does not mean that they have the same configuration.

Tables 1 and 2 are shown below. Among them, Table 1 is a table showing each specification data in the first embodiment, and Table 2 is a table showing each specification data in the second embodiment. In each embodiment, the d-line (wavelength λ = 587.6 nm) and the g-line (wavelength λ = 435.8 nm) are selected as the calculation targets of the aberration characteristics.

In the [Overall Specifications] table, f indicates the focal length of the entire system in the optical system WL in the infinity focused state, and FNO indicates the F number. 2ω indicates the angle of view (the unit is ° (degrees), and ω is the half angle of view), and Y indicates the image height (maximum image height). Bf indicates the air conversion distance (back focus) on the optical axis from the lens surface on the image side to the image plane I in the optical system WL in the infinity in-focus state, and TL is the air-equivalent distance (back focus) in the optical system WL in the infinity-focused state. The distance (total length) on the optical axis from the lens surface on the most object side to the image plane I is shown. In TL, the air conversion distance from the lens surface on the image side of the optical system WL to the image surface I is shown. Further, the values of TL and Bf are shown in the [variable interval data] described later for each of the infinity focused state and the short range (close range) focused state.

Further, fG1a indicates the focal length of the front group G1a, and fG1b indicates the focal length of the rear group G1b. φSt indicates the aperture diameter of the aperture diaphragm S.

In the [Lens Specifications] table, the surface numbers indicate the order of the optical surfaces from the object side along the direction in which the light beam travels, and R is the radius of curvature of each optical surface (the surface whose center of curvature is located on the image side). (Positive value), D is the distance on the optical axis from each optical surface to the next optical surface (or image surface), nd is the refractive index of the material of the optical member with respect to the d line, and νd is optical. The Abbe number based on the d-line of the material of the member is shown. The radius of curvature "∞" indicates a plane or an aperture, and (aperture S) indicates an aperture stop S. The description of the refractive index nd of air = 1.00000 is omitted. When the lens surface is aspherical, the surface number is marked with * and the radius of curvature R indicates the paraxial radius of curvature.

In the table of [Aspherical surface data], the shape of the aspherical surface shown in [Lens specifications] is shown by the following equation (a). X (y) is the distance (zag amount) along the optical axis direction from the tangent plane at the aspherical apex to the position on the aspherical surface at the height y, and R is the radius of curvature of the reference sphere (near axis curvature radius). , Kappa is the conical constant, and Ai is the i-th order aspherical coefficient. "E-n" indicates " ^{x10 -n".} For example, 1.234E-05 = 1.234 × 10 ^-5 . The second-order aspherical coefficient A2 is 0, and the description thereof is omitted.

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 the table of [lens group data], the start surface (the surface closest to the object side) and the focal length of each of the first lens group G1 and the second lens group G2 are shown.

The table of [variable spacing data] shows the plane spacing Di to the next plane at the plane number i in which the plane spacing is "variable" in the table showing [lens specifications]. For example, in the first embodiment, the surface spacings D9 and D21 at the surface numbers 9 and 21 are shown. These values are shown for each of the infinity focused state and the short range (close range) focused state.

The table of [Conditional expression corresponding values] shows the values corresponding to the above conditional expressions (1) to (9).

Hereinafter, in all the specification values, "mm" is generally used for the focal length f, the radius of curvature R, the plane spacing D, other lengths, etc., unless otherwise specified, but the optical system is expanded proportionally. Alternatively, it is not limited to this because the same optical performance can be obtained even if the proportional reduction is performed.

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

(First Example)
The first embodiment will be described with reference to FIGS. 1 to 2 and Table 1. FIG. 1 is a diagram showing a lens configuration of an optical system according to a first embodiment of the present embodiment. The optical system WL (1) according to the first embodiment is composed of a first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power arranged in order from the object side. .. Further, an aperture diaphragm S is arranged between the first lens group G1 and the second lens group G2. The symbol (+) or (-) attached to the symbol of each lens group indicates the refractive power of each lens group, and this also applies to all the following examples.

The first lens group G1 includes a meniscus-shaped first negative lens L11 having a convex surface facing the object side, and a meniscus-shaped first positive lens L12 having a convex surface facing the object side, arranged in order from the object side. It is composed of a biconcave second negative lens L13 and a biconvex second positive lens L14. That is, the first lens group G1 is composed of four lenses. The second positive lens L14 has an aspherical lens surface on the image side. In the first embodiment, the first negative lens L11 and the first positive lens L12 constitute a front group G1a having a negative refractive power. Further, the second negative lens L13 and the second positive lens L14 form a rear group G1b having a positive refractive power of the present embodiment.

The second lens group G2 includes a meniscus-shaped first negative lens L21 arranged in order from the object side and having a convex surface facing the image side, a biconvex first positive lens L22, and a biconcave second lens. A junction lens composed of a negative lens L23, a biconvex second positive lens L24, a biconcave third negative lens L25, a biconcave fourth negative lens L26, and a biconvex third. It is composed of a bonded lens made of the positive lens L27 of the above. That is, the second lens group G2 is composed of seven lenses. The second positive lens L24 has an aspherical lens surface on the image side. The third positive lens L27 has an aspherical lens surface on the image side.

The image plane I is arranged on the image side of the second lens group G2. In order to cut a spatial frequency equal to or higher than the limit resolution of an image sensor (for example, CCD, CMOS, etc.) arranged on the image plane I in the vicinity of the image plane I between the second lens group G2 and the image plane I. Low-pass filter FL is arranged. In the optical system WL (1) according to the first embodiment, when focusing on a short-range object from infinity, the first lens group G1 is fixed and the second lens group G2 is on the object side along the optical axis. It is configured so that the distance between the first lens group G1 and the second lens group G2 changes (becomes smaller) by moving to. Further, at the time of focusing, the aperture diaphragm S is configured to be fixed together with the first lens group G1.

Table 1 below lists the values of the specifications of the optical system according to the first embodiment.

(Table 1)
[Overall specifications]
f = 24.89
FNO = 1.85
2ω = 84.2
Y = 21.60
Bf = 16.080 (air equivalent length)
TL = 98.489 (air equivalent length)
fG1a = -215.401
fG1b = 83.533
φSt = 21.52
[Lens specifications]
Surface number RD nd νd
1 259.93798 1.800 1.61800 63.3
2 23.21609 17.645
3 57.64328 3.617 1.85026 32.4
4 825.22838 10.110
5 -34.47703 1.000 1.80518 25.4
6 537.21533 0.500
7 87.30361 5.646 1.85108 40.1
8 * -33.94300 2.539
9 ∞ D9 (variable) (aperture S)
10 -51.86043 2.000 1.63980 34.5
11 -625.30255 0.100
12 25.00000 11.041 1.61800 63.3
13 -27.39159 1.000 1.62588 35.7
14 27.16911 0.782
15 24.68610 5.040 1.88202 37.2
16 * -127.35739 3.526
17 -866.88526 1.000 1.64769 33.7
18 37.60165 3.974
19 -29.83312 1.000 1.69895 30.1
20 108.02024 3.000 1.82098 42.5
21 * -34.70573 D21 (variable)
22 ∞ 1.500 1.51680 63.9
23 ∞ 0.100
[Aspherical data]
Side 8 κ = 4.89200E-01
A4 = 8.32980E-07, A6 = 1.36681E-09, A8 = 2.95579E-12, A10 = -9.22667E-15
16th surface κ = -1.97822E + 01
A4 = 1.34043E-05, A6 = -1.68712E-08, A8 = -6.06266E-11, A10 = 1.67715E-13
Surface 21 κ = 1.03830E + 00
A4 = 2.78128E-05, A6 = 1.14967E-08, A8 = 6.40144E-10, A10 = -8.79238E-13
[Lens group data]
Focal length
G1 1 73.76
G2 10 52.78
[Variable interval data]
Infinity in-focus state Short-range in-focus state
f = 24.89 β = -0.1527
D0 ∞ 150.00
D9 7.089
2.926
D21 14.991 19.153
Bf (air) 16.080 20.242
TL (air) 98.489 98.489
[Conditional expression correspondence value]
Conditional expression (1) ndm = 1.85
Conditional expression (2) (-fG1a) / fG1b = 2.58
Conditional expression (3) Y / BL = 0.26
Conditional expression (4) f / TL = 0.25
Conditional expression (5) DG1 / f = 1.62
Conditional expression (6) TL / (FNO × Bf) = 3.31
Conditional expression (7) f2 / f1 = 0.716
Conditional expression (8) (Rp2 + Rp1) / (Rp2-Rp1) = -0.44
Conditional expression (9) (-R21) /φSt=2.41

FIG. 2A is an aberration diagram at infinity focusing of the optical system according to the first embodiment. In each aberration diagram of FIG. 2A, FNO indicates an F number and A indicates a half angle of view. The spherical aberration diagram shows the value of the F number corresponding to the maximum aperture, the astigmatism diagram and the distortion diagram show the maximum value of the half angle of view, and the transverse aberration diagram shows the value of each half angle of view. FIG. 2B is a diagram of various aberrations at the time of short-range (close-range) focusing of the optical system according to the first embodiment. In each aberration diagram of FIG. 2B, NA indicates the numerical aperture and H0 indicates the object height. The spherical aberration diagram shows the numerical aperture value corresponding to the maximum aperture, the astigmatism diagram and the distortion diagram show the maximum value of the object height, and the transverse aberration diagram shows the value of each object height. Further, in each aberration diagram of FIGS. 2 (a) and 2 (b), d indicates a d line (wavelength λ = 587.6 nm) and g indicates a g line (wavelength λ = 435.8 nm). In the astigmatism diagram, the solid line shows the sagittal image plane and the broken line shows the meridional image plane. In the aberration diagrams of each of the following examples, the same reference numerals as those of the present embodiment will be used, and duplicate description will be omitted.

From each aberration diagram, it can be seen that the optical system according to the first embodiment satisfactorily corrects various aberrations and has excellent imaging performance.

(Second Example)
The second embodiment will be described with reference to FIGS. 3 to 4 and Table 2. FIG. 3 is a diagram showing a lens configuration of an optical system according to a second embodiment of the present embodiment. The optical system WL (2) according to the second embodiment is composed of a first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power arranged in order from the object side. .. Further, an aperture diaphragm S is arranged between the first lens group G1 and the second lens group G2.

The first lens group G1 includes a meniscus-shaped first negative lens L11 having a convex surface facing the object side, and a meniscus-shaped first positive lens L12 having a convex surface facing the object side, arranged in order from the object side. It is composed of a biconcave second negative lens L13 and a biconvex second positive lens L14. That is, the first lens group G1 is composed of four lenses. The second positive lens L14 has an aspherical lens surface on the image side. In the first embodiment, the first negative lens L11 and the first positive lens L12 constitute a front group G1a having a negative refractive power. Further, the second negative lens L13 and the second positive lens L14 form a rear group G1b having a positive refractive power of the present embodiment.

The second lens group G2 includes a meniscus-shaped first negative lens L21 arranged in order from the object side and having a convex surface facing the image side, a biconvex first positive lens L22, and a biconcave second lens. A junction lens composed of a negative lens L23, a biconvex second positive lens L24, a biconcave third negative lens L25, a biconcave fourth negative lens L26, and a biconvex third. It is composed of a bonded lens made of the positive lens L27 of the above. That is, the second lens group G2 is composed of seven lenses. The second positive lens L24 has an aspherical lens surface on the image side. The third positive lens L27 has an aspherical lens surface on the image side.

The image plane I is arranged on the image side of the second lens group G2. In order to cut a spatial frequency equal to or higher than the limit resolution of an image sensor (for example, CCD, CMOS, etc.) arranged on the image plane I in the vicinity of the image plane I between the second lens group G2 and the image plane I. Low-pass filter FL is arranged. In the optical system WL (2) according to the second embodiment, the first lens group G1 is fixed and the second lens group G2 is on the object side along the optical axis when focusing on a short-range object from infinity. It is configured so that the distance between the first lens group G1 and the second lens group G2 changes (becomes smaller) by moving to. Further, at the time of focusing, the aperture diaphragm S is configured to be fixed together with the first lens group G1.

Table 2 below lists the values of the specifications of the optical system according to the second embodiment.

(Table 2)
f = 24.88
FNO = 1.85
2ω = 85.0
Y = 21.60
Bf = 16.084 (air equivalent length)
TL = 98.489 (air equivalent length)
fG1a = -260.663
fG1b = 84.025
φSt = 21.65
[Lens specifications]
Surface number RD nd νd
1 311.04316 1.800 1.61800 63.3
2 23.23403 17.966
3 53.06674 3.753 1.85026 32.4
4 524.38118 9.489
5 -36.35863 1.200 1.80518 25.4
6 321.12595 0.500
7 86.27627 5.718 1.85108 40.1
8 * -34.48263 2.220
9 ∞ D9 (variable) (aperture S)
10 -48.48648 2.000 1.63980 34.5
11 -383.13109 0.100
12 25.00000 10.035 1.60300 65.4
13 -28.47157 1.000 1.62588 35.7
14 27.69283 1.053
15 25.37798 5.249 1.88202 37.2
16 * -99.38873 3.512
17 -3108.75430 1.000 1.64769 33.7
18 38.11144 4.048
19 -29.70213 1.000 1.69895 30.1
20 80.32765 3.642 1.82098 42.5
21 * -37.16425 D21 (variable)
22 ∞ 1.500 1.51680 64.2
23 ∞ 0.100
[Aspherical data]
Side 8 κ = 4.87100E-01
A4 = 9.57616E-07, A6 = 1.30032E-09, A8 = 1.39336E-12, A10 = -6.18169E-15
16th surface κ = -6.72550E + 00
A4 = 1.26488E-05, A6 = -1.58130E-08, A8 = -4.86762E-11, A10 = 1.46674E-13
Surface 21 κ = 1.28460E + 00
A4 = 2.74071E-05, A6 = 1.81033E-08, A8 = 5.13415E-10, A10 = -6.63454E-13
[Lens group data]
Focal length
G1 1 70.44
G2 10 53.52
[Variable interval data]
Infinity in-focus state Short-range in-focus state
f = 24.88 β = -0.1525
D0 ∞ 150.00
D9 7.119
2.916
D21 14.995 19.198
Bf (air) 16.084 20.287
TL (air) 98.489 98.489
[Conditional expression correspondence value]
Conditional expression (1) ndm = 1.85
Conditional expression (2) (-fG1a) /fG1b=3.10
Conditional expression (3) Y / BL = 0.26
Conditional expression (4) f / TL = 0.25
Conditional expression (5) DG1 / f = 1.62
Conditional expression (6) TL / (FNO × Bf) = 3.31
Conditional expression (7) f2 / f1 = 0.760
Conditional expression (8) (Rp2 + Rp1) / (Rp2-Rp1) = -0.43
Conditional expression (9) (-R21) /φSt=2.24

FIG. 4A is a diagram of various aberrations of the optical system according to the second embodiment at infinity in focus. FIG. 4B is a diagram of various aberrations of the optical system according to the second embodiment when focusing at a short distance (close distance). From each aberration diagram, it can be seen that the optical system according to the second embodiment satisfactorily corrects various aberrations and has excellent imaging performance.

According to each of the above embodiments, it is possible to realize an optical system having a large aperture ratio, a small size, and good optical performance.

Here, each of the above examples shows a specific example of the present invention, and the present invention is not limited thereto.

The following contents can be appropriately adopted as long as the optical performance of the optical system of the present embodiment is not impaired.

As a numerical example of the optical system of the present embodiment, a two-group configuration is shown, but the present application is not limited to this, and an optical system having another group configuration (for example, three groups or the like) can also be configured. Specifically, a lens or a lens group may be added to the most object side or the most image plane side of the optical system of the present embodiment.

In the optical system of the present embodiment, not only the second lens group G2 but also a single lens group, a plurality of lens groups, or a partial lens group is moved in the optical axis direction to focus from an infinity object to a short-range object. It may be a focusing lens group. This focusing lens group can also be applied to autofocus, and is also suitable for driving a motor for autofocus (using an ultrasonic motor or the like).

In addition, the lens group or partial lens group is moved so as to have a component in the direction perpendicular to the optical axis, or is rotationally moved (swinged) in the in-plane direction including the optical axis to cause image blur caused by camera shake. It may be a group of anti-vibration lenses to be corrected.

The lens surface may be formed on a spherical surface or a flat surface, or may be formed on an aspherical surface. When the lens surface is spherical or flat, lens processing and assembly adjustment are facilitated, and deterioration of optical performance due to processing and assembly adjustment errors can be prevented, which is preferable. Further, even if the image plane is deviated, the depiction performance is less deteriorated, which is preferable.

When the lens surface is aspherical, the aspherical surface is an aspherical surface formed by grinding, a glass mold aspherical surface formed by forming glass into an aspherical shape, or a composite aspherical surface formed by forming resin on the glass surface into an aspherical shape. It doesn't matter which one. Further, the lens surface may be a diffraction surface, and the lens may be a refractive index distribution type lens (GRIN lens) or a plastic lens.

The aperture diaphragm is preferably arranged between the first lens group and the second lens group, but the role may be substituted by the frame of the lens without providing the member as the aperture diaphragm.

An antireflection film having a high transmittance in a wide wavelength range may be applied to each lens surface in order to reduce flare and ghost and achieve high contrast optical performance. As a result, flare and ghost can be reduced, and high optical performance with high contrast can be achieved.

G1 1st lens group G2 2nd lens group I image plane S aperture stop

Claims (11)

The first lens group and the second lens group, which are arranged in order from the object side, are substantially composed of two lens groups.
When focusing, the distance between adjacent lens groups changes,
The first lens group consists of a front group having a negative refractive power and a rear group having a positive refractive power arranged in order from the object side.
The front group consists of a meniscus-shaped first negative lens having a convex surface facing the object side and a meniscus-shaped first positive lens having a convex surface facing the object side, which are arranged in order from the object side.
The rear group is substantially composed of two lenses, that is, a second negative lens having a biconcave shape and a second positive lens having a biconvex shape, which are arranged in order from the object side.
An optical system characterized by satisfying the following conditional expression.
0.716 ≤ f2 / f1 <1.40
2.00 <(-fG1a) /fG1b <3.50
However, f1: the focal length of the first lens group,
f2: Focal length of the second lens group,
fG1a: Focal length of the previous group,
fG1b: Focal length of the rear group. The optical system according to claim 1 , wherein the optical system satisfies the following conditional expression.
0.20 <f / TL <0.35
However, f: the focal length of the optical system in the infinity focused state,
TL: The distance on the optical axis from the lens surface on the most object side to the image plane in the optical system in the infinity focused state, and the air conversion distance from the lens surface on the image side to the image plane. The optical system according to claim 1 or 2 , wherein the optical system satisfies the following conditional expression.
1.30 <DG1 / f <2.20
However, DG1: the distance on the optical axis from the lens surface on the most object side to the lens surface on the image side in the first lens group,
f: Focal length of the optical system in the infinity focused state. The optical system according to any one of claims 1 to 3 , wherein the optical system satisfies the following conditional expression.
2.95 <TL / (FNO x Bf) <4.20
However, FNO: F number of the optical system in the infinity focused state,
Bf: Air conversion distance on the optical axis from the lens surface on the image side to the image surface in the optical system in the infinity focused state,
TL: The distance on the optical axis from the lens surface on the most object side to the image plane in the optical system in the infinity focused state, and the air conversion distance from the lens surface on the image side to the image plane. An aperture diaphragm is arranged between the first lens group and the second lens group.
The lens arranged on the object side of the second lens group located on the image side of the aperture diaphragm is a negative lens.
The lens surface on the object side of the negative lens arranged on the most object side of the second lens group is a concave surface.
The optical system according to any one of claims 1 to 4 , wherein the optical system satisfies the following conditional expression.
0.70 <(-R21) /φSt <3.30
However, R21: the radius of curvature of the lens surface on the object side of the negative lens arranged on the most object side of the second lens group,
φSt: The aperture diameter of the aperture diaphragm. The optical system according to any one of claims 1 to 5 , wherein the first lens group is fixed at the time of focusing, and the second lens group moves along an optical axis. The optical system according to any one of claims 1 to 6 , wherein the optical system satisfies the following conditional expression.
ndm> 1.70
However, ndm: the average refractive index of the first positive lens and the second positive lens in the first lens group with respect to the d line. The optical system according to any one of claims 1 to 7 , wherein the optical system satisfies the following conditional expression.
0.10 <Y / BL <0.56
However, Y: the radius of the image circle of the optical system,
BL: The distance on the optical axis from the lens surface on the most object side to the lens surface on the image side in the optical system in the infinity focused state. The optical system according to any one of claims 1 to 8 , wherein the lens surface on the most image side in the first lens group is an aspherical surface. The optical system according to any one of claims 1 to 9 , wherein the lens surface on the image side of the lens arranged on the most image side of the second lens group is a convex surface. An optical device including the optical system according to any one of claims 1 to 10.

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