JP5217694B2 - Lens system and optical device - Google Patents

Description

  The present invention relates to a lens system suitable for an interchangeable lens for single-lens reflex cameras, a copying lens, and the like, and an optical apparatus having the lens system.

Conventionally, a so-called double Gauss type lens system has been used as a lens system used for interchangeable lenses for single-lens reflex cameras, copying lenses, and the like (see, for example, Patent Document 1).
JP 2007-333790 A

  Conventional lens systems have large coma and cannot be said to have sufficiently high optical performance.

In order to solve the above problems, the present invention provides:
In a lens system consisting essentially of two lens groups, in order from the object side along the optical axis, by a first lens group and a second lens group having positive refractive power,
An aperture stop is provided between the first lens group and the second lens group;
The first lens group includes a sub lens group having a positive refractive power and a sub lens group having a negative refractive power,
The positive refractive power sub-lens group includes only positive refractive power lenses,
The negative lens sub lens group includes a meniscus lens having a convex surface facing the object side,
The second lens group includes at least one lens having a negative refractive power in which a surface on the object side faces a concave surface on the object side,
A lens system characterized by satisfying the following conditions is provided.
nNh> 1.820
−0.400 <f / f1 <0.500
0.300 <| r2Na | / f <0.600
Where nNh is the refractive index of the negative refractive power lens at the d-line (wavelength 587.6 nm), f1 is the focal length of the first lens group, f is the focal length of the entire lens system, and r2Na is the negative refraction. The radius of curvature of the object side surface of the force lens .
The present invention also provides:
In a lens system consisting essentially of two lens groups, in order from the object side along the optical axis, by a first lens group and a second lens group having positive refractive power,
An aperture stop is provided between the first lens group and the second lens group;
The first lens group includes a sub lens group having a positive refractive power and a sub lens group having a negative refractive power,
The positive refractive power sub-lens group includes only positive refractive power lenses,
The negative lens sub lens group includes a meniscus lens having a convex surface facing the object side,
A lens system characterized by satisfying the following conditions is provided.
nNh> 1.820
−0.400 <f / f1 <0.500
0.800 <| r2a | / r1b <1.200
Where nNh is the refractive index of the negative refractive power lens at the d-line (wavelength 587.6 nm), f1 is the focal length of the first lens group, f is the focal length of the entire lens system, and r1b is the first refractive index. The radius of curvature of the lens surface closest to the image side of the lens group, r2a is the radius of curvature of the lens surface closest to the object side of the second lens group.

  The present invention also provides an optical device comprising the lens system.

  According to the present invention, it is possible to provide a lens system having high optical performance in which various aberrations are well corrected, and an optical device having the lens system.

  Hereinafter, a lens system according to an embodiment of the present application will be described.

  The lens system according to this embodiment includes a first lens unit and a second lens unit having a positive refractive power in order from the object side along the optical axis. It is composed of a lens group and a negative lens power sub-lens group. The negative power sub-lens group has a meniscus lens with a convex surface facing the object side, so-called symmetric double Gauss type The refractive power arrangement is realized, distortion and lateral chromatic aberration are corrected well, and spherical aberration and curvature of field are corrected.

In addition, the lens system according to the present embodiment includes at least one lens having negative refractive power that satisfies the following conditional expression (1), and the following conditional expressions (1) and (2) are satisfied. Satisfied.
(1) nNh> 1.820
(2) −0.400 <f / f1 <0.500
Here, nNh is the refractive index of the negative refractive power lens at the d-line (wavelength 587.6 nm), f1 is the focal length of the first lens group, and f is the focal length of the entire lens system.

  Conditional expression (1) is a conditional expression for satisfactorily correcting spherical aberration and sagittal coma generated in the lens system and obtaining high optical performance.

  When the lower limit value of conditional expression (1) is not reached, sagittal coma aberration is greatly generated by the negative lens, and high optical performance cannot be obtained.

  In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (1) to 1.840. In order to further secure the effect of the embodiment, it is more preferable to set the lower limit of conditional expression (1) to 1.860. In order to secure the effect of the embodiment, it is preferable to make conditional expression (1) smaller than 2.800. By making conditional expression (1) smaller than 2.800, the transmittance of visible light in the optical material of the lens having a negative refractive power can be sufficiently secured, and a lens system can be configured.

  Conditional expression (2) is a conditional expression for satisfactorily correcting distortion aberration and lateral chromatic aberration generated in the lens system and obtaining high optical performance.

  If the lower limit of conditional expression (2) is not reached, the refractive power of the first lens group becomes too negative. Then, it becomes difficult to correct negative distortion and lateral chromatic aberration, and high optical performance cannot be realized.

  If the upper limit of conditional expression (2) is exceeded, it becomes difficult to correct positive distortion occurring in the first lens group, and high optical performance cannot be realized.

  In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (2) to −0.250. In order to further secure the effect of the embodiment, it is more preferable to set the lower limit of conditional expression (2) to −0.100. In order to further secure the effect of the embodiment, it is more preferable to set the lower limit of conditional expression (2) to 0.000. In order to further secure the effect of the embodiment, it is more preferable to set the lower limit of conditional expression (2) to 0.100. In order to secure the effect of the embodiment, it is preferable to set the upper limit of conditional expression (2) to 0.400. In order to further secure the effect of the embodiment, it is more preferable to set the upper limit of conditional expression (2) to 0.360.

  Further, in the lens system according to the present embodiment, the first lens group includes a sub lens group having a positive refractive power and a sub lens group having a negative refractive power in order from the object side along the optical axis. desirable.

  With this configuration, distortion and lateral chromatic aberration can be corrected more favorably.

  The lens system according to the present embodiment preferably has an aperture stop between the first lens group and the second lens group.

  With this configuration, distortion and lateral chromatic aberration can be favorably corrected.

  In the lens system according to the present embodiment, the sub lens unit having positive refractive power has a lens component having positive refractive power closest to the object side. The lens component has an absolute value of the radius of curvature of the object side surface. It is desirable that it is smaller than the absolute value of the radius of curvature of the side surface.

  With this configuration, it is possible to gently bend the light beam toward the center of the screen with the lens component. As a result, it is possible to suppress the occurrence of aberrations generated by the lens component, particularly spherical aberration, and to realize high optical performance.

  In addition, the lens component in this application is a general term including a single lens and a cemented lens.

  In the lens system according to the present embodiment, it is desirable that the sub-lens group having positive refractive power is composed only of lens components having positive refractive power.

  With this configuration, the number of lens components in the lens system can be reduced, flare caused by lens surface reflection can be reduced, and high optical performance can be realized.

In the lens system according to the present embodiment, it is preferable that the following conditional expression (3) is satisfied when the Abbe number of the d-line of the lens having the negative refractive power is νdN.
(3) 12.0 <νdN <24.0

  Conditional expression (3) is a conditional expression for obtaining high optical performance while suppressing chromatic aberration.

  If the lower limit of conditional expression (3) is not reached, the spherical aberration of color is overcorrected, and high optical performance cannot be obtained. If the upper limit value of conditional expression (3) is exceeded, the spherical aberration of color is insufficiently corrected, and high optical performance cannot be obtained.

  In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (3) to 16.0. In order to further secure the effect of the embodiment, it is more preferable to set the lower limit of conditional expression (3) to 18.0.

The lens system according to the present embodiment has the following conditions when the refractive index at the d-line (wavelength: 587.6 nm) of the lens having the highest refractive index of the d-line among the lenses constituting the lens system is ndh. It is desirable to satisfy Formula (4).
(4) ndh> 1.910

  Conditional expression (4) is a conditional expression for satisfactorily correcting spherical aberration and sagittal coma generated in the lens system and obtaining high optical performance.

  When the lower limit value of conditional expression (4) is not reached, the following two cases are conceivable. That is, the case where the lens having the highest refractive index for d-line is a positive lens and a negative lens.

  In the former case, the negative spherical aberration that occurs in the lens system becomes excessive, so the correction is performed by increasing the curvature of the negative lens in the lens system (decreasing the radius of curvature). A large sagittal coma aberration occurs. In the latter case, the sagittal coma aberration is greatly generated by the negative lens. Therefore, in any case, high optical performance cannot be obtained.

  In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (4) to 1.940. In order to secure the effect of the embodiment, it is preferable to make conditional expression (4) smaller than 2.800. By making conditional expression (4) smaller than 2.800, it is possible to sufficiently ensure the visible light transmittance of the optical material having the highest refractive index in the lens system, and to configure the lens system.

  In the lens system according to the present embodiment, it is preferable that the negative refractive power lens has a meniscus shape.

  With this configuration, the occurrence of coma aberration can be suppressed and high optical performance can be obtained.

  In the lens system according to the present embodiment, the lens having the negative refractive power is arranged closest to the object side in the second lens group, and the object-side surface of the lens having the negative refractive power faces a concave surface toward the object side. It is desirable that

  With this configuration, the occurrence of coma, particularly sagittal coma, can be suppressed, and high optical performance can be obtained.

  In the lens system according to the present embodiment, the lens having the negative refractive power is disposed closest to the image side in the first lens group, and the image side surface of the lens having the negative refractive power faces a concave surface toward the image side. It is desirable that

  With this configuration, the occurrence of coma, particularly sagittal coma, can be suppressed, and high optical performance can be obtained.

In the lens system according to the present embodiment, the second lens group includes at least one lens having a negative refractive power with the object side surface facing the concave surface on the object side, and the object side surface is the object side surface. When the radius of curvature of the object side surface of at least one lens having a negative refractive power with the concave surface facing is set to r2Na, it is desirable to satisfy the following conditional expression (5).
(5) 0.300 <| r2Na | / f <0.600

  Conditional expression (5) is a conditional expression for suppressing sagittal coma and realizing high optical performance.

  If the lower limit value of the conditional expression (5) is not reached, sagittal coma aberration is greatly generated on the object side surface of the negative refractive power lens in which the object side surface is concave on the object side, and high optical performance cannot be realized.

  If the upper limit of conditional expression (5) is exceeded, negative spherical aberration occurring in the second lens group cannot be corrected satisfactorily. In addition, focusing from infinity to a short distance with the lens system, or aberration variation when the magnification ratio is changed with a projection apparatus or copying machine to which the lens system of the present embodiment is applied becomes excessively large. High optical performance cannot be maintained up to or over a wide magnification range.

  In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (5) to 0.320. In order to secure the effect of the embodiment, it is preferable to set the upper limit of conditional expression (5) to 0.530.

  In the lens system according to the present embodiment, it is desirable that at least one lens having a negative refractive power whose surface on the object side is concave on the object side is disposed closest to the object side in the second lens group. .

  By disposing at least one lens having negative refractive power with the object side surface facing the concave surface on the object side, on the most object side of the second lens group, distortion aberration and lateral chromatic aberration generated by the lens having negative refractive power Can be suppressed, and high optical performance can be obtained.

In the lens system according to the present embodiment, when the radius of curvature of the lens surface closest to the image side of the first lens group is r1b and the radius of curvature of the lens surface closest to the object of the second lens group is r2a, It is desirable to satisfy conditional expression (6).
(6) 0.800 <| r2a | / r1b <1.200

  Conditional expression (6) is a conditional expression for realizing high optical performance while suppressing sagittal coma.

  If the lower limit of conditional expression (6) is not reached, that is, the curvature of the lens surface closest to the object side of the second lens group is excessively large (the radius of curvature is small) compared to the curvature of the lens surface closest to the image side of the first lens group. ), A large sagittal coma aberration occurs on the object side surface of the second lens group, and high optical performance cannot be realized.

  If the upper limit of conditional expression (6) is exceeded, that is, the curvature of the lens surface closest to the image side of the first lens group is excessively large (the radius of curvature is small) compared to the curvature of the lens surface closest to the object side of the second lens group. ), A large sagittal coma aberration occurs on the image side surface of the first lens group, and high optical performance cannot be realized.

  In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (6) to 0.900. In order to secure the effect of the embodiment, it is preferable to set the upper limit of conditional expression (6) to 1.150. In order to further secure the effect of the embodiment, it is more preferable to set the upper limit of conditional expression (6) to 1.100.

The lens system according to the present embodiment desirably satisfies the following conditional expression (7), where Bf is the distance from the lens surface closest to the image side of the lens system on the optical axis to the image surface.
(7) 0.600 <Bf / f <1.00

  Conditional expression (7) is a conditional expression for realizing high optical performance.

  If the lower limit value of conditional expression (7) is not reached, the back focus becomes too short with respect to the focal length of the lens system, so the refractive power arrangement of the lens system is far from the symmetrical type, and distortion is corrected. High optical performance cannot be realized.

  If the upper limit value of conditional expression (7) is exceeded, the back focus becomes too long with respect to the focal length of the lens system, so the refractive power arrangement of the lens system is far from the symmetrical type, and distortion is corrected. High optical performance cannot be realized.

  In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (7) to 0.650. In order to further secure the effect of the embodiment, it is more preferable to set the lower limit of conditional expression (7) to 0.700. In order to secure the effect of the embodiment, it is preferable to set the upper limit of conditional expression (7) to 0.850. In order to further secure the effect of the embodiment, it is more preferable to set the upper limit value of conditional expression (7) to 0.800.

  When a plane parallel plate is inserted between the lens surface closest to the image side and the image surface, Bf is an air conversion length.

  In the lens system according to this embodiment, it is desirable that the distance between the first lens group and the second lens group on the optical axis is always fixed.

  With such a configuration, the first lens group and the first lens group can be used when focusing from infinity to a short distance with the lens system, or when changing the magnification ratio with a projection apparatus or a copying machine to which the lens system of the present embodiment is applied. The two lens groups can be moved mechanically and integrally, and compared to when they are moved separately, the occurrence of decentration coma due to the mutual decentration of the first lens group and the second lens group is suppressed, and a short distance from infinity. High optical performance can be realized over the entire range or over a variable magnification range.

  The lens surface may be formed as a spherical surface, a flat surface, or an aspheric surface.

  When the lens surface is a spherical surface or a flat surface, lens processing and assembly adjustment are facilitated, and optical performance deterioration due to errors in processing and assembly adjustment can be prevented. Further, even when the image plane is deviated, it is preferable because there is little deterioration in drawing performance.

  When the lens surface is an aspheric surface, the aspheric surface is an aspheric surface by grinding, a glass mold aspheric surface made of glass with an aspheric shape, or a composite aspheric surface made of resin with an aspheric shape on the glass surface. Any aspherical surface may be used. The lens surface may be a diffractive surface, and the lens may be a gradient index lens (GRIN lens) or a plastic lens.

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

(First embodiment)
FIG. 1 is a cross-sectional view showing a configuration of a lens system according to the first example.

  The lens system according to the first example includes a first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power in order from the object side along the optical axis. An aperture stop S is disposed between the first lens group G1 and the second lens group G2.

  The first lens group G1 includes, in order from the object side along the optical axis, a positive meniscus 111th lens L111 having a refractive power stronger than that of the image side with the object side surface facing the convex surface toward the object side. An eleventh sub-lens group GS11 having a positive refractive power composed of a single lens, and a positive meniscus 121st lens L121 having a refractive power stronger than that of the image side with the object side surface facing the convex surface toward the object side. And a negative refracting power twelfth sub-lens group GS12 including a negative meniscus twelfth lens L12R having a concave surface facing the image side.

  The second lens group G2 includes, in order from the object side along the optical axis, a negative meniscus 21st lens L21 with the object side surface facing the concave surface on the object side, and an object side surface joined to the 21st lens L21. Is a positive meniscus twenty-second lens L22 having a concave surface facing the object side and weaker refractive power than the image-side surface, and a positive meniscus twenty-third lens with the image-side surface facing the convex surface with respect to the image surface. L23, and the object side surface disposed closest to the image surface side is composed of a biconvex 24th lens L24 having a stronger refractive power than the image side surface, and the light emitted from the 24th lens is image surface I To form an image.

  Focusing on a short-distance object is performed by moving the first lens group G1 and the second lens group G2 together to the object side.

  Table 1 below lists specifications of the lens system according to the first example.

  In (surface data) in the table, the object surface is the object surface, the surface number is the lens surface number from the object side, r is the radius of curvature, d is the surface spacing, and nd is the refractive index at the d-line (wavelength 587.6 nm). , Νd represents the Abbe number in the d-line (wavelength 587.6 nm), (aperture) represents the aperture stop S, and the image plane represents the image plane I. Note that the refractive index of air nd = 1.000 000 is omitted. In addition, “∞” in the curvature radius r column represents a plane.

  In (various data), f is the focal length of the entire lens system, FNo is the F number, ω is the half field angle (unit: degree), Y is the image height, and TL is the object side of the 111th lens in the infinite focus state. The total lens length from the surface to the image plane I is shown.

  In (variable data), R is the shooting distance, the distance from the object to the image plane I (unit: m), β is the shooting magnification, and Bf is the back focus.

  (Conditional expression corresponding value) indicates the corresponding value of each conditional expression.

  In all the following specification values, “mm” is generally used as the focal length f, radius of curvature r, surface interval d and other lengths, etc. unless otherwise specified, but the optical system is proportional. Even if it is enlarged or proportionally reduced, the same optical performance can be obtained. Further, the unit is not limited to “mm”, and other appropriate units may be used. Further, the explanation of these symbols is the same in the other embodiments, and the explanation is omitted.

(Table 1)

(Surface data)
Surface number rd nd νd
Object ∞ ∞
1 61.1028 5.2000 1.834807 42.71
2 421.6037 0.1000
3 26.6848 4.5000 2.003300 28.27
4 42.4965 1.8000
5 55.6668 2.0000 1.808090 22.79
6 18.6474 9.3000
7 (Aperture) ∞ 7.7000
8 -18.7111 1.8000 1.846660 23.78
9 -64.8673 6.0000 1.788001 47.37
10 -29.0381 0.2000
11 -90.5334 5.5000 1.834807 42.71
12 -33.0755 0.1000
13 114.2530 3.0000 1.772499 49.60
14 -161.9377 (Bf)
Image plane ∞

(Various data)
f = 51.61
FNo = 1.45
ω = 23.10
Y = 21.60
TL = 85.66

(Variable data)
Infinite focus state Short range focus state
R ∞ 1.64
β 0.0 -1/30
Bf 38.4641 40.1846

  In the lens system according to the first example, the lens LN having a negative refractive power that satisfies the conditional expression (1) is the 21st lens L21, has a negative meniscus shape, and is disposed on the most object side in the second lens group. And has a concave surface facing the object side. The lens with the highest refractive index for the d-line is the 121st lens L121. The twenty-first lens L21 is also a second N lens L2N, and is disposed closest to the object side in the second lens group. The curvature radii of the object side surface of the twenty-first lens L21 are r2Na and r2a, and the curvature radii of the image side surface of the twelfth R lens L12R are r1b.

(Values for conditional expressions)
(1) nNh = 1.846660
(2) f / f1 = 0.3461
(3) νdN = 23.78
(4) ndh = 2.003300
(5) | r2Na | /f=0.36253
(6) | r2a | /r1b=1.040342
(7) Bf / f = 0.74525

  2A and 2B are graphs showing various aberrations of the lens system according to the first example, where FIG. 2A is in focus at infinity (β = 0.0), and FIG. 2B is in focus at short distance (β = −1 / 30 ) Shows various aberration diagrams.

  In each aberration diagram, FNO is an F number, A is a half angle of view (unit: degree), NA is a numerical aperture, and H0 is an object height (unit: “mm”). Further, d represents d-line (wavelength 587.6 nm), g represents various aberrations with respect to g-line (wavelength 435.8 nm), and those not described represent various aberrations with respect to d-line. In the astigmatism diagram, the solid line indicates the sagittal image plane, and the broken line indicates the meridional image plane. The coma diagram shows the meridional coma aberration for the d-line and the g-line at each half field angle or the object height, the sagittal coma aberration generated in the meridional direction with respect to the d-line, and the right side from the origin The broken line represents the sagittal coma aberration generated in the sagittal direction with respect to the d line.

  In the following examples, the same symbols are used, and the following description is omitted.

  From each aberration diagram, it can be seen that the lens system according to Example 1 has various optical aberrations corrected and high optical performance.

(Second embodiment)
FIG. 3 is a cross-sectional view showing a configuration of a lens system according to the second example.

  The lens system according to the second example includes, in order from the object side along the optical axis, a first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power. An aperture stop S is disposed between the first lens group G1 and the second lens group G2.

  The first lens group G1 includes, in order from the object side along the optical axis, a positive meniscus 111th lens L111 having a refractive power stronger than that of the image side with the object side surface facing the convex surface toward the object side. An eleventh sub-lens group GS11 having a positive refractive power composed of a single lens, and a positive meniscus 121st lens L121 having a refractive power stronger than that of the image side with the object side surface facing the convex surface toward the object side. And a negative refracting power twelfth sub-lens group GS12 including a negative meniscus twelfth lens L12R having a concave surface facing the image side.

  The second lens group G2 includes, in order from the object side along the optical axis, a negative meniscus 21st lens L21 with the object side surface facing the concave surface on the object side, and an object side surface joined to the 21st lens L21. Is a positive meniscus twenty-second lens L22 having a concave surface facing the object side and weaker refractive power than the image-side surface, and a positive meniscus twenty-third lens with the image-side surface facing the convex surface with respect to the image surface. L23, and the object side surface disposed closest to the image surface side is composed of a biconvex 24th lens L24 having a stronger refractive power than the image side surface, and the light emitted from the 24th lens is image surface I To form an image.

  Focusing on a short-distance object is performed by moving the first lens group G1 and the second lens group G2 together to the object side.

  Table 2 below lists specifications of the lens system according to the second example.

(Table 2)

(Surface data)
Surface number rd nd νd
Object ∞ ∞
1 52.2387 6.0000 1.834807 42.71
2 565.2751 0.1000
3 28.1185 4.4000 2.000690 25.46
4 45.6886 1.5000
5 78.8809 2.0000 1.860740 23.06
6 19.8082 9.3000
7 (Aperture) ∞ 7.7000
8 -19.2024 1.8000 1.805181 25.42
9 -125.5269 6.0000 1.788001 47.37
10 -29.9331 0.2000
11 -92.9638 5.5000 1.834807 42.71
12 -33.8967 0.1000
13 112.4183 3.3000 1.772499 49.60
14 -161.9377 (Bf)
Image plane ∞

(Various data)
f = 51.61
FNo = 1.45
ω = 23.07
Y = 21.60
TL = 86.39

(Variable data)
Infinite focus state Short range focus state
R ∞ 1.64
β 0.0 -1/30
Bf 38.4874 40.2076

  In the lens system according to the second example, the negative refractive power lens LN that satisfies the conditional expression (1) is the twelfth R lens L12R, has a negative meniscus shape, and is disposed on the most image side in the first lens group. The concave surface is directed to the image side. The lens with the highest refractive index for the d-line is the 121st lens L121. The twenty-first lens L21 is a second N lens L2N, and is disposed closest to the object side in the second lens group. The curvature radii of the object side surface of the twenty-first lens L21 are r2Na and r2a, and the curvature radii of the image side surface of the twelfth R lens L12R are r1b.

(Values for conditional expressions)
(1) nNh = 1.860740
(2) f / f1 = 0.29794
(3) νdN = 23.06
(4) ndh = 2.000690
(5) | r2Na | /f=0.37209
(6) | r2a | /r1b=0.96941
(7) Bf / f = 0.745579

  4A and 4B show various aberration diagrams of the lens system according to Example 2. FIG. 4A is a diagram when focusing on infinity (β = 0.0), and FIG. 4B is a graph when focusing on short distance (β = −1 / 30). ) Shows various aberration diagrams.

  From each aberration diagram, it can be seen that the lens system according to Example 2 has various optical aberrations corrected and high optical performance.

(Third embodiment)
FIG. 5 is a sectional view showing the configuration of a lens system according to the third example.

  The lens system according to the third example includes, in order from the object side along the optical axis, a first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power. An aperture stop S is disposed between the first lens group G1 and the second lens group G2.

  The first lens group G1 includes, in order from the object side along the optical axis, a positive meniscus 111th lens L111 having a refractive power stronger than that of the image side with the object side surface facing the convex surface toward the object side. An eleventh sub-lens group GS11 having a positive refractive power composed of a single lens, and a positive meniscus 121st lens L121 having a refractive power stronger than that of the image side with the object side surface facing the convex surface toward the object side. And a negative refracting power twelfth sub-lens group GS12 including a negative meniscus twelfth lens L12R having a concave surface facing the image side.

  The second lens group G2 includes, in order from the object side along the optical axis, a negative meniscus 21st lens L21 with the object side surface facing the concave surface on the object side, and an object side surface joined to the 21st lens L21. Is a positive meniscus twenty-second lens L22 having a concave surface facing the object side and weaker refractive power than the image-side surface, and a positive meniscus twenty-third lens with the image-side surface facing the convex surface with respect to the image surface. L23, and the object side surface disposed closest to the image surface side is composed of a biconvex 24th lens L24 having a stronger refractive power than the image side surface, and the light emitted from the 24th lens is image surface I To form an image.

  Focusing on a short-distance object is performed by moving the first lens group G1 and the second lens group G2 together to the object side.

  Table 3 below lists specifications of the lens system according to the third example.

(Table 3)

(Surface data)
Surface number rd nd νd
Object ∞ ∞
1 61.1431 4.8000 1.882997 40.76
2 389.5756 0.3000
3 26.8932 4.5000 2.000690 25.46
4 44.9000 2.2000
5 57.4287 2.0000 1.922860 20.50
6 19.2263 8.0000
7 (Aperture) ∞ 7.8000
8 -18.6558 1.8000 1.805181 25.42
9 -114.6796 6.0000 1.788001 47.37
10 -30.1134 0.3000
11 -114.9741 6.0000 1.834807 42.71
12 -34.5098 0.1000
13 126.4714 3.2000 1.804000 46.57
14 -161.9377 (Bf)
Image plane ∞

(Various data)
f = 51.61
FNo = 1.45
ω = 23.14
Y = 21.60
TL = 85.48

(Variable data)
Infinite focus state Short range focus state
R ∞ 1.64
β 0.0 -1/30
Bf 38.4783 40.1986

  In the lens system according to the third example, the lens LN having a negative refractive power that satisfies the conditional expression (1) is the twelfth lens L12R, has a negative meniscus shape, and is disposed on the most image side in the first lens group. The concave surface is directed to the image side. The lens with the highest refractive index for the d-line is the 121st lens L121. The twenty-first lens L21 is a second N lens L2N, and is disposed closest to the object side in the second lens group. The curvature radii of the object side surface of the twenty-first lens L21 are r2Na and r2a, and the curvature radii of the image side surface of the twelfth R lens L12R are r1b.

(Values for conditional expressions)
(1) nNh = 1.922860
(2) f / f1 = 0.30465
(3) νdN = 20.50
(4) ndh = 2.000690
(5) | r2Na | /f=0.36149
(6) | r2a | /r1b=0.70333
(7) Bf / f = 0.745558

  FIGS. 6A and 6B are graphs showing various aberrations of the lens system according to the third example. FIG. 6A is a diagram when focusing on infinity (β = 0.0), and FIG. ) Shows various aberration diagrams.

  From each aberration diagram, it can be seen that the lens system according to Example 3 has various optical aberrations corrected and high optical performance.

(Fourth embodiment)
FIG. 7 is a cross-sectional view showing a configuration of a lens system according to the fourth example.

  The lens system according to the fourth example includes a first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power in order from the object side along the optical axis. An aperture stop S is disposed between the first lens group G1 and the second lens group G2.

  The first lens group G1 includes, in order from the object side along the optical axis, a positive meniscus 111th lens L111 having a refractive power stronger than that of the image side with the object side surface facing the convex surface toward the object side. An eleventh sub-lens group GS11 having a positive refractive power composed of a single lens, and a positive meniscus 121st lens L121 having a refractive power stronger than that of the image side with the object side surface facing the convex surface toward the object side. And a negative refracting power twelfth sub-lens group GS12 including a negative meniscus twelfth lens L12R having a concave surface facing the image side.

  The second lens group G2 is joined to the 21st lens L21 and a biconcave 21st lens L21 whose surface on the object side has a stronger refractive power than the surface on the image side in order from the object side along the optical axis. The biconvex 22nd lens L22 having a refractive power weaker than the image side surface and the positive meniscus 23rd lens L23 having the image side surface facing the image surface. And a positive meniscus twenty-fourth lens L24 with the image-side surface facing the convex surface with respect to the image surface, and the object-side surface disposed closest to the image surface has a stronger refractive power than the image-side surface. The bi-convex 25th lens L25 is formed, and the light beam emitted from the 25th lens forms an image on the image plane I.

  Focusing on a short-distance object is performed by moving the first lens group G1 and the second lens group G2 together to the object side.

  Table 4 below lists specifications of the lens system according to the fourth example.

(Table 4)

(Surface data)
Surface number rd nd νd
Object ∞ ∞
1 57.5740 5.5000 1.903660 31.31
2 206.0906 0.2000
3 29.5832 6.0000 2.003300 28.27
4 38.8499 2.0000
5 41.1771 2.0000 1.922860 18.90
6 19.7787 9.5000
7 (Aperture) ∞ 9.2000
8 -19.4166 2.0000 1.805181 25.42
9 3374.4434 7.0000 1.804000 46.57
10 -36.6779 0.2000
11 -56.5118 4.0000 1.882997 40.76
12 -42.4595 0.1000
13 -143.9382 5.0000 1.834807 42.71
14 -44.3487 0.3000
15 103.1998 4.0000 1.754999 52.32
16 -161.9377 (Bf)
Image plane ∞

(Various data)
f = 51.63
FNo = 1.25
ω = 23.33
Y = 21.60
TL = 94.94

(Variable data)
Infinite focus state Short range focus state
R ∞ 1.64
β 0.0 -1/30
Bf 37.9374 39.6583

  In the lens system according to the fourth example, the lens LN having a negative refractive power that satisfies the conditional expression (1) is the twelfth lens L12R, has a negative meniscus shape, and is disposed on the most image side in the first lens group. The concave surface is directed to the image side. The lens with the highest refractive index for the d-line is the 121st lens L121. The twenty-first lens L21 is a second N lens L2N, and is disposed closest to the object side in the second lens group. The curvature radii of the object side surface of the twenty-first lens L21 are r2Na and r2a, and the curvature radii of the image side surface of the twelfth R lens L12R are r1b.

(Values for conditional expressions)
(1) nNh = 1.922860
(2) f / f1 = 0.25576
(3) νdN = 18.90
(4) ndh = 2.003300
(5) | r2Na | /f=0.37608
(6) | r2a | /r1b=0.998169
(7) Bf / f = 0.34881

  FIGS. 8A and 8B are graphs showing various aberrations of the lens system according to Example 4. FIG. 8A is a diagram when focusing on infinity (β = 0.0), and FIG. ) Shows various aberration diagrams.

  From each aberration diagram, it can be seen that the lens system according to Example 4 has various optical aberrations corrected and high optical performance.

(5th Example)
FIG. 9 is a cross-sectional view showing a configuration of a lens system according to the fifth example.

  The lens system according to Example 5 includes, in order from the object side along the optical axis, a first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power. An aperture stop S is disposed between the first lens group G1 and the second lens group G2.

  The first lens group G1 includes, in order from the object side along the optical axis, a positive meniscus 111th lens L111 having a refractive power stronger than that of the image side with the object side surface facing the convex surface toward the object side. An eleventh sub-lens group GS11 having a positive refractive power composed of a single lens, and a positive meniscus 121st lens L121 having a refractive power stronger than that of the image side with the object side surface facing the convex surface toward the object side. And a negative refracting power twelfth sub-lens group GS12 including a negative meniscus twelfth lens L12R having a concave surface facing the image side.

  The second lens group G2 includes, in order from the object side along the optical axis, a negative meniscus 21st lens L21 with the object side surface facing the concave surface on the object side, and an object side surface joined to the 21st lens L21. Is a positive meniscus twenty-second lens L22 having a concave surface facing the object side and weaker refractive power than the image-side surface, and a positive meniscus twenty-third lens with the image-side surface facing the convex surface with respect to the image surface. L23, a 24th lens L24 having a positive refractive power whose curvature radius of the image side surface is smaller than that of the object side surface, and a negative meniscus 25th lens which is cemented to the 24th lens L24 and has a concave surface facing the object side The light beam which is composed of L25 and exits from the 25th lens forms an image on the image plane I.

  Focusing on a short-distance object is performed by moving the first lens group G1 and the second lens group G2 together to the object side.

  Table 5 below lists specifications of the lens system according to Example 5.

(Table 5)

(Surface data)
Surface number rd nd νd
Object ∞ ∞
1 62.5707 4.6000 1.834807 42.71
2 1079.5273 0.1000
3 27.8402 4.5000 1.903660 31.31
4 48.9187 2.0000
5 83.6288 1.6000 1.805181 25.42
6 20.6020 9.5000
7 (Aperture) ∞ 7.7000
8 -19.6349 1.8000 1.846660 23.78
9 -36.0084 6.0000 1.754999 52.32
10 -28.9194 0.2000
11 -100.0147 4.5000 1.834807 42.71
12 -35.2169 0.1000
13 140.8843 5.0000 2.003300 28.27
14 -49.8565 1.5000 1.922860 18.90
15 -391.9566 (Bf)
Image plane ∞

(Various data)
f = 51.61
FNo = 1.45
ω = 23.13
Y = 21.60
TL = 87.36

(Variable data)
Infinite focus state Short range focus state
R ∞ 1.65
β 0.0 -1/30
Bf 38.2645 39.9850

  In the lens system according to Example 5, the negative refracting power lenses LN satisfying the conditional expression (1) are the 21st lens L21 and the 25th lens L25, have a negative meniscus shape, and the 21st lens L21 has the 21st lens L21. It is a shape that is disposed closest to the object side in the two lens groups and has a concave surface directed toward the object side. The lens with the highest refractive index for the d-line is the 24th lens L24. The twenty-first lens L21 is also a second N lens L2N, and is disposed closest to the object side in the second lens group. The curvature radii of the object side surface of the twenty-first lens L21 are r2Na and r2a, and the curvature radii of the image side surface of the twelfth R lens L12R are r1b.

(Values for conditional expressions)
(1) nNh = 1.846660 (21st lens L21)
(1) nNh = 1.922860 (25th lens L25)
(2) f / f1 = 0.28536
(3) νdN = 23.78 (21st lens L21)
(3) νdN = 18.90 (25th lens L25)
(4) ndh = 2.003300
(5) | r2Na | /f=0.38041 (21st lens L21)
(6) | r2a | /r1b=0.95306
(7) Bf / f = 0.74135

  FIG. 10 shows various aberration diagrams of the lens system according to Example 5, wherein (a) is in focus at infinity (β = 0.0), and (b) is in focus at short distance (β = −1 / 30). ) Shows various aberration diagrams.

  From each aberration diagram, it can be seen that the lens system according to Example 5 has various optical aberrations corrected and high optical performance.

(Sixth embodiment)
FIG. 11 is a cross-sectional view showing a configuration of a lens system according to the sixth example.

  The lens system according to Example 6 includes, in order from the object side along the optical axis, a first lens group G1 having negative refractive power and a second lens group G2 having positive refractive power. An aperture stop S is disposed between the first lens group G1 and the second lens group G2.

  The first lens group G1 includes, in order from the object side along the optical axis, a positive meniscus 111th lens L111 having a refractive power stronger than that of the image side with the object side surface facing the convex surface toward the object side. An eleventh sub-lens group GS11 having a positive refractive power composed of a single lens, a negative meniscus 121st lens L121 with the object-side surface facing the convex surface toward the object side, and the image-side surface concave toward the image side And a negative refracting power twelfth sub-lens group GS12 including a positive meniscus twelfth lens L12R.

  The second lens group G2 includes, in order from the object side along the optical axis, a negative meniscus 21st lens L21 with the object side surface facing the concave surface on the object side, and an object side surface joined to the 21st lens L21. Is a positive meniscus twenty-second lens L22 having a concave surface facing the object side and weaker refractive power than the image-side surface, and a positive meniscus twenty-third lens with the image-side surface facing the convex surface with respect to the image surface. L23 and the image-side surface disposed on the most image plane side have a strong refractive power compared to the object-side surface, and are formed of a biconvex twenty-fourth lens L24. To form an image.

  Focusing on a short-distance object is performed by moving the first lens group G1 and the second lens group G2 together to the object side.

  In the present embodiment, the 111th lens component is composed of a single lens, but may be composed of a cemented lens. In that case, it is preferable because spherical aberration and axial chromatic aberration can be corrected satisfactorily.

  Table 6 below provides specifications of the lens system according to the sixth example.

(Table 6)

(Surface data)
Surface number rd nd νd
Object ∞ ∞
1 51.0799 4.0000 1.799516 42.22
2 153.5021 1.0000
3 25.0934 2.0000 1.834807 42.71
4 16.6855 7.0000
5 17.7942 2.5000 2.019600 21.45
6 17.4360 8.0000
7 (Aperture) ∞ 9.0000
8 -20.1623 1.5000 1.860740 23.06
9 -141.0470 8.0000 1.754999 52.32
10 -24.1458 1.0000
11 -82.3047 4.5000 1.834807 42.71
12 -39.2143 0.5000
13 187.0181 3.5000 1.804000 46.57
14 -161.9377 (Bf)
Image plane ∞

(Various data)
f = 51.60
FNo = 2.10
ω = 25.28
Y = 24.00
TL = 108.47

(Variable data)
Infinite focus state Short range focus state
R ∞ 1.66
β 0.0 -1/30
Bf 55.9690 57.6889

  In the lens system according to Example 6, the negative refractive power lenses LN satisfying the conditional expression (1) are the 121st lens L121 and the 21st lens L21, which are negative meniscus shapes, and the 21st lens L21 is the 21st lens L21. The shape is arranged closest to the object side in the two lens group G2 and has a concave surface directed toward the object side. The lens with the highest refractive index for the d-line is the 12th R lens L12R. The twenty-first lens L21 is also a second N lens L2N having a negative refractive power in which the object side surface faces the concave surface toward the object side. The curvature radii of the object side surface of the twenty-first lens L21 are r2Na and r2a, and the curvature radii of the image side surface of the twelfth R lens L12R are r1b.

(Values for conditional expressions)
(1) nNh = 1.834807 (121st lens L121)
(1) nNh = 1.860740 (21st lens L21)
(2) f / f1 = −0.02715
(3) νdN = 23.06 (21st lens L21)
(4) ndh = 2.019600
(5) | r2Na | /f=0.39073
(6) | r2a | /r1b=1.15636

  FIGS. 12A and 12B are graphs showing various aberrations of the lens system according to Example 6. FIG. 12A is a graph when focusing on infinity (β = 0.0), and FIG. 12B is a graph when focusing on short distance (β = −1 / 30). ) Shows various aberration diagrams.

  From each aberration diagram, it can be seen that the lens system according to Example 6 has various optical aberrations corrected and high optical performance.

  As described above, according to the present embodiment, it is possible to provide a lens system having a large aperture ratio and high optical performance in which various aberrations are favorably corrected.

  Next, a camera that is an optical device equipped with the lens system according to the present embodiment will be described. Although the case where the lens system according to the first example is mounted will be described, the same applies to other examples.

  FIG. 13 is a diagram illustrating a configuration of a camera including the lens system according to the first example.

  In FIG. 13, the camera 1 is a digital single-lens reflex camera provided with the lens system according to the first embodiment as the photographing lens 2. In the camera 1, light from an object (subject) (not shown) is collected by the taking lens 2 and is focused on the focusing screen 4 via the quick return mirror 3. The light imaged on the focusing screen 4 is reflected in the pentaprism 5 a plurality of times and guided to the eyepiece lens 6. Thus, the photographer can observe the subject image as an erect image through the eyepiece 6.

  When the release button (not shown) is pressed by the photographer, the quick return mirror 3 is retracted to the outside of the optical path, and the focal plane shutter 8 is also retracted to the outside of the optical path, so that light from the object (not shown) is directed to the image sensor 7. To reach. As a result, light from the subject is picked up by the image sensor 7 and recorded as a subject image in a memory (not shown). In this way, the photographer can shoot the subject with the camera 1.

  By mounting the lens system according to the first embodiment as the photographing lens 2 on the camera 1, a camera having high performance can be realized.

  The contents described below can be appropriately adopted as long as the optical performance is not impaired.

  In the embodiment, the two-group configuration is shown, but the present invention can be applied to other group configurations such as the third group, the fourth group, and the like. Specifically, a configuration in which a positive or negative lens group is added on the most object side, a configuration in which a positive or negative lens group is added on the most image side, or between the first lens group and the second lens group. Examples include a configuration in which a positive or negative lens group is added.

  A single lens group, a plurality of lens groups, or a partial lens group may be moved in the optical axis direction to be a focusing lens group that performs focusing from an object at infinity to a near object. The focusing lens group can be applied to autofocus, and is also suitable for driving a motor for autofocus (using an ultrasonic motor or the like). In particular, at least a part of the first lens group or the second lens group is preferably a focusing lens group.

  Alternatively, the lens group or the partial lens group may be moved in a direction perpendicular to the optical axis to be an anti-vibration lens group that corrects image blur caused by camera shake. In particular, at least a part of the first lens group or the second lens group is preferably an anti-vibration lens group.

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

  Each lens surface may be provided with an antireflection film having a high transmittance in a wide wavelength range in order to reduce flare and ghost and achieve high optical performance with high contrast.

  In addition, in order to explain the present invention in an easy-to-understand manner, the configuration requirements of the embodiment have been described, but it goes without saying that the present invention is not limited to this.

It is sectional drawing which shows the structure of the lens system which concerns on 1st Example. FIG. 6 shows various aberration diagrams of the lens system according to Example 1, wherein (a) shows various aberrations when focusing on infinity (β = 0.0), and (b) shows various aberrations when focusing on short distance (β = −1 / 30). Each figure is shown. It is sectional drawing which shows the structure of the lens system which concerns on 2nd Example. FIG. 6 shows various aberration diagrams of the lens system according to Example 2, wherein (a) shows various aberrations when focusing on infinity (β = 0.0), and (b) shows various aberrations when focusing on short distance (β = −1 / 30). Each figure is shown. It is sectional drawing which shows the structure of the lens system which concerns on 3rd Example. FIG. 6 shows various aberration diagrams of the lens system according to Example 3, wherein (a) shows various aberrations when focusing on infinity (β = 0.0), and (b) shows various aberrations when focusing on short distance (β = −1 / 30). Each figure is shown. It is sectional drawing which shows the structure of the lens system which concerns on 4th Example. 4A and 4B show various aberration diagrams of the lens system according to Example 4, wherein (a) shows various aberrations when focusing on infinity (β = 0.0), and (b) shows various aberrations when focusing on short distance (β = −1 / 30). Each figure is shown. It is sectional drawing which shows the structure of the lens system which concerns on 5th Example. FIG. 6 shows various aberration diagrams of the lens system according to Example 5, wherein (a) shows various aberrations when focusing on infinity (β = 0.0), and (b) shows various aberrations when focusing on short distance (β = −1 / 30). Each figure is shown. It is sectional drawing which shows the structure of the lens system which concerns on 6th Example. FIG. 6 shows various aberration diagrams of the lens system according to Example 6, wherein (a) shows various aberrations when focusing on infinity (β = 0.0), and (b) shows various aberrations when focusing on short distance (β = −1 / 30). Each figure is shown. It is a figure which shows the structure of the camera provided with the lens system which concerns on 1st Example.

Explanation of symbols

G1 1st lens group G2 2nd lens group GS11 11th sub lens group GS12 12th sub lens group L111 111st lens L121 121st lens L12R 12R lens L21 21st lens L22 22nd lens L23 23rd lens L24 24th lens L25 25th lens L26 26th lens S Aperture stop I Image surface 1 Camera

Claims (15)

In a lens system consisting essentially of two lens groups, in order from the object side along the optical axis, by a first lens group and a second lens group having positive refractive power,
An aperture stop is provided between the first lens group and the second lens group;
The first lens group includes a sub lens group having a positive refractive power and a sub lens group having a negative refractive power,
The positive refractive power sub-lens group includes only positive refractive power lenses,
The negative lens sub lens group includes a meniscus lens having a convex surface facing the object side,
The second lens group includes at least one lens having a negative refractive power in which a surface on the object side faces a concave surface on the object side,
A lens system that satisfies the following conditions.
nNh> 1.820
−0.400 <f / f1 <0.500
0.300 <| r2Na | / f <0.600
Where nNh is the refractive index of the negative refractive power lens at the d-line (wavelength 587.6 nm), f1 is the focal length of the first lens group, f is the focal length of the entire lens system, and r2Na is the negative refraction. This is the radius of curvature of the object side surface of the force lens . When the radius of curvature of the lens surface closest to the image side of the first lens group is r1b and the radius of curvature of the lens surface closest to the object side of the second lens group is r2a, the following condition is satisfied. The lens system according to claim 1 .
0.800 <| r2a | / r1b <1.200   In a lens system consisting essentially of two lens groups, in order from the object side along the optical axis, by a first lens group and a second lens group having positive refractive power,
  An aperture stop is provided between the first lens group and the second lens group;
  The first lens group includes a sub lens group having a positive refractive power and a sub lens group having a negative refractive power,
  The positive refractive power sub-lens group includes only positive refractive power lenses,
  The negative lens sub lens group includes a meniscus lens having a convex surface facing the object side,
  A lens system that satisfies the following conditions.
  nNh> 1.820
  −0.400 <f / f1 <0.500
  0.800 <| r2a | / r1b <1.200
Where nNh is the refractive index of the negative refractive power lens at the d-line (wavelength 587.6 nm), f1 is the focal length of the first lens group, f is the focal length of the entire lens system, and r1b is the first refractive index. The radius of curvature of the lens surface closest to the image side of the lens group, r2a is the radius of curvature of the lens surface closest to the object side of the second lens group. The first lens group includes, in order from the object side along the optical axis, from claim 1, characterized in that it is composed of the sub lens group having a positive refractive power and the negative refractive power group sub lens 3 The lens system according to any one of the above. The sub-lens group of positive refractive power has a lens having a positive refractive power on the most object side, the lens, the absolute value of the curvature radius of the surface on the object side than the absolute value of the radius of curvature of the image side surface lens system according to any one of claims 1, characterized in that also small 4. 6. The lens system according to claim 1, wherein the following condition is satisfied when the Abbe number of the d-line of the lens having the negative refractive power is νdN.
12.0 <νdN <24.0 The following conditions are satisfied when the refractive index at the d-line (wavelength: 587.6 nm) of the lens having the highest refractive index of the d-line among the lenses constituting the lens system is ndh: The lens system according to any one of 1 to 6.
ndh> 1.910   The lens system according to claim 1, wherein the lens having negative refractive power has a meniscus shape.   2. The lens having a negative refractive power is disposed closest to the object side in the second lens group, and an object side surface of the lens having a negative refractive power has a shape with a concave surface facing the object side. The lens system according to any one of 1 to 8.   2. The negative refractive power lens is disposed on the most image side in the first lens group, and the image side surface of the negative refractive power lens has a shape with a concave surface facing the image side. The lens system according to any one of 1 to 9. The second lens group includes at least one lens having a negative refractive power with the object side surface facing a concave surface toward the object side, and the object side surface facing at least one negative surface with a concave surface facing the object side. 11. The lens system according to claim 3 , wherein the following condition is satisfied when the radius of curvature of the object side surface of the lens having a refractive power is r2Na.
0.320 <| r2Na | / f <0.600 The second lens group includes at least one lens having a negative refractive power in which a surface on the object side faces a concave surface on the object side,
At least one negative refractive power of the lens surface of the object side is a concave surface facing the object side, any one of claims 1 to 10, characterized in that disposed on the most object side in the second lens group The lens system according to Item 1 . When the Bf the distance from the lens surface on the most image side of the lens system on the optical axis to the image plane, according to claims 1 to any one of 12, characterized in that the following condition is satisfied Lens system.
0.600 <Bf / f <1.00 The lens system according to any one of claims 1 to 13 , wherein a distance on the optical axis between the first lens group and the second lens group is always fixed. Optical apparatus characterized by having a lens system as claimed in any one of claims 1 14.

Images