JP2010014895A - Lens system and optical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lens system having high optical performance wherein various aberrations are sufficiently corrected, and to provide an optical device including the lens system. <P>SOLUTION: The lens system includes, in order from an object side along an optical axis, a first lens group G1 and a second lens group G2 of positive refractive power. The first lens group G1 includes an eleventh sub-lens group GS11 of positive refractive power and a twelfth sub-lens group GS12 of negative refractive power. The twelfth sub-lens group GS12 includes a meniscus-shaped lens with a convex surface directed to the object side, and the lens system satisfies predetermined conditions. <P>COPYRIGHT: (C)2010,JPO&INPIT

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-described problems, the present invention provides a lens system including a first lens group and a second lens group having a positive refractive power in order from the object side along the optical axis. The lens unit includes a refractive power sub lens group and a negative refractive power sub lens group, and the negative refractive power sub lens group includes a meniscus lens having a convex surface directed toward the object side, and constitutes the lens system. Among the lenses, the refractive index at the d-line (wavelength 587.6 nm) of the lens having the highest refractive index of the d-line is ndh, the focal length of the first lens group is f1, and the focal length of the entire lens system is f. In this case, a lens system is provided that satisfies the following conditions.
ndh> 1.910
−0.400 <f / f1 <0.500

  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 favorably corrected, and an optical apparatus 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 the lens system according to the present embodiment, 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, and the focal point of the first lens group. When the distance is f1 and the focal length of the entire lens system is f, the following conditional expressions (1) and (2) are satisfied.
(1) ndh> 1.910
(2) −0.400 <f / f1 <0.500

  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, the following two cases are conceivable. That is, the case where the lens having the highest refractive index for the 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 (1) to 1.940. 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, 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.

  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 highest refractive index of the d-line is νdh.
(3) νdh> 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, if the lens with the highest d-line refractive index is a positive lens, the spherical aberration of color will be undercorrected, and the lens with the highest d-line refractive index will be negative. In the case of a lens, the chromatic spherical aberration is overcorrected, 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 25.0. In order to secure the effect of the embodiment, it is preferable to make conditional expression (3) smaller than 30.0. By making conditional expression (3) smaller than 30.0, the spherical aberration of color can be corrected well, and higher optical performance can be obtained.

In the lens system according to the present embodiment, it is desirable that the lens system has at least one lens having negative refractive power that satisfies the following conditional expression (4).
(4) nNh> 1.820
Here, nNh is the refractive index at the d-line (wavelength 587.6 nm) of the lens having the negative refractive power.

  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 of conditional expression (4) 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 (4) 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 (4) to 1.860. 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 of the lens having a negative refractive power, and to constitute a lens system.

  In the lens system according to the present embodiment, it is desirable that the most image-side lens in the negative-power sub-lens group is a negative-power lens having a concave surface facing the image side.

  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. Spherical aberration can be corrected satisfactorily by constructing the lens closest to the image side in the negative lens power sub-lens group with a negative power lens having a concave surface facing the image side, and the entire first lens group is spherical. Occurrence of aberration can be suppressed low. Further, coma aberration can be corrected in the same manner, and high optical performance can be obtained as a whole lens system.

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 having the highest refractive index for the d-line is the 121st lens L121. The twenty-first lens L21 is also a negative-refractive-power lens LN that satisfies the conditional expression (4), and is also a negative-refractive-power second N lens L2N with the object-side surface facing the concave surface toward the object side. Here, the radius of curvature of the object side surface of the 21st lens L21 is r2Na and r2a, and the radius of curvature of the image side surface of the 12th R lens L12R is r1b.

(Values for conditional expressions)
(1) ndh = 2.003300
(2) f / f1 = 0.3461
(3) νdh = 28.27
(4) nNh = 1.846660
(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 lens having the highest refractive index for the d-line is the 121st lens L121. The twelfth R lens L12R is a lens LN having a negative refractive power that satisfies the conditional expression (4), and the twenty-first lens L21 is a second N lens L2N having a negative refractive power in which the object side surface faces the concave surface toward the object side. is there. Here, the radius of curvature of the object side surface of the 21st lens L21 is r2Na and r2a, and the radius of curvature of the image side surface of the 12th R lens L12R is r1b.

(Values for conditional expressions)
(1) ndh = 2.000690
(2) f / f1 = 0.29794
(3) νdh = 25.46
(4) nNh = 1.860740
(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 with the highest refractive index for the d-line is the 121st lens L121. The twelfth R lens L12R is a lens LN having a negative refractive power that satisfies the conditional expression (4), and the twenty-first lens L21 is a second N lens L2N having a negative refractive power in which the object side surface faces the concave surface toward the object side. is there. Here, the radius of curvature of the object side surface of the 21st lens L21 is r2Na and r2a, and the radius of curvature of the image side surface of the 12th R lens L12R is r1b.

(Values for conditional expressions)
(1) ndh = 2.000690
(2) f / f1 = 0.30465
(3) νdh = 25.46
(4) nNh = 1.922860
(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 with the highest refractive index for the d-line is the 121st lens L121. The twelfth R lens L12R is a lens LN having a negative refractive power that satisfies the conditional expression (4), and the twenty-first lens L21 is a second N lens L2N having a negative refractive power in which the object side surface faces the concave surface toward the object side. is there. Here, the radius of curvature of the object side surface of the 21st lens L21 is r2Na and r2a, and the radius of curvature of the image side surface of the 12th R lens L12R is r1b.

(Values for conditional expressions)
(1) ndh = 2.003300
(2) f / f1 = 0.25576
(3) νdh = 28.27
(4) nNh = 1.922860
(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 lens with the highest refractive index for the d-line is the 24th lens L24. The twenty-first lens L21 and the twenty-fifth lens L25 are negative-refractive-power lenses LN that satisfy the conditional expression (4), and the negative-refractive-power second N lens L2N having a concave surface facing the object side. But there is. Here, the radius of curvature of the object side surface of the 21st lens L21 is r2Na and r2a, and the radius of curvature of the image side surface of the 12th R lens L12R is r1b.

(Values for conditional expressions)
(1) ndh = 2.003300
(2) f / f1 = 0.28536
(3) νdh = 28.27
(4) nNh = 1.846660 (21st lens L21)
(4) nNh = 1.922860 (25th lens L25)
(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 lens with the highest refractive index for d-line is the twelfth R lens L12R. The 121st lens L121 and the 21st lens L21 are lenses LN having a negative refractive power that satisfies the conditional expression (4). The 21st lens L21 has a negative refractive power having a concave surface facing the object side. It is also the second N lens L2N. Here, the radius of curvature of the object side surface of the 21st lens L21 is r2Na and r2a, and the radius of curvature of the image side surface of the 12th R lens L12R is r1b.

(Values for conditional expressions)
(1) ndh = 2.019600
(2) f / f1 = −0.02715
(4) nNh = 1.834807 (121st lens L121)
(4) nNh = 1.860740 (21st lens L21)
(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 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 6 has various optical aberrations corrected and high optical performance.

(Seventh embodiment)
FIG. 13 is a cross-sectional view showing a configuration of a lens system according to the seventh example.

  The lens system according to Example 7 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. Has a positive meniscus 22nd lens L22 having a refractive power weaker than that of the image side with the concave surface facing the object side, and a negative meniscus 23rd lens L23 having a concave surface facing the object side of the object side. A positive meniscus twenty-fourth lens L24 that is cemented to the twenty-third lens L23 and has a concave surface facing the object side and a weak refractive power compared to the image-side surface, and a convex surface directed toward the image surface The 25th lens L25 having a positive meniscus shape and the 26th lens L26 having a refracting power stronger than that of the image side surface and disposed on the most image side are composed of a 26th lens L26. The emitted light beam 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 7 below provides specifications of the lens system according to the seventh example.

(Table 7)

(Surface data)
Surface number rd nd νd
Object ∞ ∞
1 81.4768 5.0000 1.804000 46.57
2 -2838.8241 0.3000
3 33.1597 7.0000 1.950 300 29.42
4 60.4403 1.4000
5 95.3280 2.0000 1.761821 26.52
6 23.0471 11.3000
7 (Aperture) ∞ 7.0000
8 -26.4313 1.6000 1.805181 25.42
9 -125.7273 4.6000 1.804000 46.57
10 -32.7268 2.7000
11 -23.4449 1.7000 1.805181 25.42
12 -64.8415 5.0000 1.882997 40.76
13 -31.7094 0.1000
14 -187.5490 4.2000 1.882997 40.76
15 -47.3960 0.1000
16 79.1117 3.8000 1.804000 46.57
17 -1019.1299 (Bf)
Image plane ∞

(Various data)
f = 51.60
FNo = 1.25
ω = 23.29
Y = 21.60
TL = 95.78

(Variable data)
Infinite focus state Short range focus state
R ∞ 1.64
β 0.0 -1/30
Bf 37.9796 39.6996

  In the lens system according to Example 7, the lens with the highest refractive index for d-line is the 121st lens L121. Further, the 21st lens L21 and the 23rd lens L23 are second N lenses L2N having negative refractive power in which the object side surface faces the concave surface toward the object side. Here, the radius of curvature of the object side surface of the 21st lens L21 is r2Na and r2a, and the radius of curvature of the image side surface of the 12th R lens L12R is r1b. The radius of curvature of the object side surface of the 23rd lens L23 is r2Na.

(Values for conditional expressions)
(1) ndh = 1.950300
(2) f / f1 = 0.30850
(3) νdh = 29.42
(5) | r2Na | /f=0.52123 (21st lens L21)
(5) | r2Na | /f=0.45435 (23rd lens L23)
(6) | r2a | /r1b=1.14684
(7) Bf / f = 0.73603

  FIGS. 14A and 14B show various aberration diagrams of the lens system according to Example 7. FIG. 14A is a diagram when focusing on infinity (β = 0.0), and FIG. 14B 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 7 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. 15 is a diagram illustrating a configuration of a camera including the lens system according to the first example.

  In FIG. 15, a camera 1 is a digital single-lens reflex camera provided with the lens system according to the first embodiment as a 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 sectional drawing which shows the structure of the lens system which concerns on 7th Example. FIG. 6 shows various aberration diagrams of the lens system according to Example 7, 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 (14)

In a lens system having a first lens group and a second lens group having a positive refractive power in order from the object side along the optical axis,
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 negative lens sub lens group includes a meniscus lens having a convex surface facing the object side,
Of the lenses constituting the lens system, the refractive index at the d-line (wavelength 587.6 nm) of the lens having the highest refractive index of the d-line is ndh, the focal length of the first lens group is f1, and the entire lens system A lens system satisfying the following condition, where f is the focal length:
ndh> 1.910
−0.400 <f / f1 <0.500   2. 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 an object side along an optical axis. Lens system.   The lens system according to claim 1, further comprising an aperture stop between the first lens group and the second lens group.   The positive refractive power sub-lens group has a positive refractive power lens component closest to the object side, and the lens component has an absolute value of the curvature radius of the object side surface that is greater than the absolute value of the curvature radius of the image side surface. 4. The lens system according to claim 1, wherein the lens system is also small.   5. The lens system according to claim 1, wherein the sub lens group having a positive refractive power includes only a lens component having a positive refractive power. 6. 6. The lens system according to claim 1, wherein the following condition is satisfied, where νdh is an Abbe number of the d-line of the lens having the highest refractive index of the d-line.
νdh> 24.0 The lens system according to claim 1, wherein the lens system includes at least one lens having negative refractive power that satisfies the following conditions.
nNh> 1.820
Here, nNh is the refractive index at the d-line (wavelength 587.6 nm) of the lens having the negative refractive power.   8. The lens system according to claim 1, wherein the lens closest to the image side in the sub lens group having negative refractive power is a lens having negative refractive power with a concave surface facing the image side. . 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. 9. The lens system according to claim 1, wherein the following condition is satisfied when a radius of curvature of the object side surface of the lens having a refractive power is r2Na.
0.300 <| r2Na | / f <0.600   10. The lens system according to claim 9, wherein 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. . 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 any one of claims 1 to 10.
0.800 <| r2a | / r1b <1.200 The following condition is satisfied, where Bf is a distance from the lens surface closest to the image side of the lens system on the optical axis to the image surface. Lens system.
0.600 <Bf / f <1.00   The lens system according to any one of claims 1 to 12, wherein a distance on the optical axis between the first lens group and the second lens group is always fixed.   An optical apparatus comprising the lens system according to claim 1.

Images