JP2010191211A - Converter lens, optical device, method for extending focal length of master lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a converter lens having high imaging performance and an optical device provided with the same; and to provide a method for extending the focal length of a master lens. <P>SOLUTION: The converter lens CL to be detachably installed to the image side of the master lens ML for use includes a cemented lens having positive refractive power composed of at least a positive lens L3, a negative lens L4, and a positive lens L5. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a converter lens, an optical device having the converter lens, and a method for expanding the focal length of a master lens.

  Conventionally, a detachable converter lens that changes the focal length of the entire lens system has been proposed in order to increase the focal length of a telephoto lens or the like (see, for example, Patent Document 1).

JP 63-201624 A

  However, the conventional converter lens has insufficient imaging performance.

  In order to solve the above-described problems, the present invention is a detachable converter lens that is used by being attached to the image side of a master lens, and is a cemented lens having a positive refractive power, which includes at least a positive lens, a negative lens, and a positive lens The converter lens characterized by including.

  The present invention also provides an optical apparatus comprising the converter lens.

  In addition, the present invention provides a method for enlarging the focal length of a master lens by attaching a converter lens including a cemented lens having at least a positive refractive power, a negative lens, and a positive lens to the image side of the master lens. To do.

  According to the present invention, it is possible to provide a converter lens having high imaging performance, an optical device having the converter lens, and a method for enlarging the focal length of the master lens.

It is a figure which shows the structure which mounted | wore the master lens ML with the converter lens CL which concerns on 1st Example. FIG. 6 is a diagram illustrating various aberrations of the converter lens CL according to Example 1 when focused on infinity. It is a figure which shows the structure which mounted | wore the master lens ML with the converter lens CL which concerns on 2nd Example. FIG. 12 is a diagram illustrating various aberrations of the converter lens CL according to Example 2 when focusing on infinity. It is a figure which shows the structure which mounted | wore the master lens ML with the converter lens CL which concerns on 3rd Example. FIG. 12 is a diagram illustrating various aberrations of the converter lens CL according to Example 3 when focusing on infinity. It is a figure which shows the structure which mounted | wore the master lens ML with the converter lens CL which concerns on 4th Example. FIG. 11 is a diagram illustrating all aberrations when the converter lens CL according to Example 4 is in focus at infinity. It is a figure which shows the structure which mounted | wore the master lens ML with the converter lens CL which concerns on 5th Example. FIG. 12 is various aberration diagrams of the converter lens CL according to Example 5 when focusing on infinity. It is an aberration diagram of the master lens ML when focusing on infinity. It is a figure which shows the structure of the camera provided with the converter lens CL which concerns on 1st Example.

Hereinafter, a converter lens according to an embodiment of the present application will be described.
In general, the converter lens not only increases the focal length of the master lens, but also increases the aberration of the master lens at the same time, so it is difficult to correct the aberration. This becomes more prominent as the enlargement magnification is higher. Therefore, the higher the magnification, the better the optical performance.

  The converter lens according to the present embodiment is used by being attached to the image side of the master lens, and is a detachable converter lens, and includes at least a positive lens, a negative lens, and a positive lens cemented lens including a positive lens. It is. With this configuration, the power of the negative lens can be increased, and the Petzval sum can be reduced, so that a good image surface with less field curvature can be formed. Comatic aberration and spherical aberration can be corrected well.

  In addition, the converter lens according to the present embodiment desirably includes a first lens having a positive refractive power and a second lens having a negative refractive power in order from the most object side. With this configuration, spherical aberration can be corrected satisfactorily.

In addition, it is desirable that the converter lens according to this embodiment includes the first lens group and the second lens group in order from the object side, and satisfies the following conditional expression (1).
(1) 0.01 <D / TL <0.25
Where D is the distance from the most image side surface of the first lens group to the most object side surface of the second lens group, and TL is the light from the most object side lens surface of the converter lens to the most image side lens surface. The distance on the axis.

  Conditional expression (1) is the distance from the most image side surface of the first lens group to the most object side surface of the second lens group, and from the most object side lens surface to the most image side lens surface of the converter lens. Is a relational expression with a distance on the optical axis (total length of the converter lens).

  If the lower limit value of conditional expression (1) is not reached, correction of coma aberration is insufficient, which is not desirable. If the upper limit value of conditional expression (1) is exceeded, the diameter of the cemented lens increases, conversely large coma occurs, which is not desirable. Also, correction of spherical aberration becomes difficult.

  In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (1) to 0.03. In order to further secure the effect of the embodiment, it is more preferable to set the lower limit of conditional expression (1) to 0.05. In order to secure the effect of the embodiment, it is preferable to set the upper limit of conditional expression (1) to 0.20. In order to further secure the effect of the embodiment, it is more preferable to set the upper limit of conditional expression (1) to 0.15.

In the converter lens according to this embodiment, it is desirable that the cemented lens satisfies the following conditional expression (2).
(2) 0.02 <(− fn) / fc <2.00
Here, fc is the combined focal length of the cemented lens, and fn is the focal length of the negative lens of the cemented lens.

  Conditional expression (2) is a relational expression between the combined focal length of the cemented lens and the focal length of the negative lens of the cemented lens.

  If the lower limit of conditional expression (2) is not reached, it is difficult to correct coma aberration, which is not desirable. If the upper limit of conditional expression (2) is exceeded, the negative power of the cemented lens will be weakened, making it difficult to correct the Petzval sum, which is not desirable.

  In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (2) to 0.03. In order to secure the effect of the embodiment, it is preferable to set the upper limit of conditional expression (2) to 1.80. In order to further secure the effect of the embodiment, it is more preferable to set the upper limit of conditional expression (2) to 1.70.

In the converter lens according to this embodiment, it is preferable that the cemented lens satisfies the following conditional expression (3).
(3) 0.75 <Np1 / Nn <0.95
Here, Nn is the refractive index of the d-line of the negative lens of the cemented lens, and Np1 is the refractive index of the d-line of the positive lens on the object side that is cemented to the negative lens of the cemented lens.

  Conditional expression (3) is a relational expression of the refractive index of the glass material.

  If the lower limit value of conditional expression (3) is not reached, the cost increases because an expensive glass material is used. Further, the Petzval sum is increased, and field curvature and coma are deteriorated. If the upper limit of conditional expression (3) is exceeded, the Petzval sum will decrease, and field curvature and coma will deteriorate.

  In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (3) to 0.80. In order to further secure the effect of the embodiment, it is more preferable to set the lower limit value of conditional expression (3) to 0.84. In order to secure the effect of the embodiment, it is preferable to set the upper limit of conditional expression (3) to 0.935. In order to further secure the effect of the embodiment, it is more preferable to set the upper limit of conditional expression (3) to 0.92.

In the converter lens according to this embodiment, it is preferable that the cemented lens satisfies the following conditional expression (4).
(4) 0.70 <Np2 / Nn <0.95
Here, Nn is the refractive index of the d-line of the negative lens of the cemented lens, and Np2 is the refractive index of the d-line of the positive lens on the image side that is cemented to the negative lens of the cemented lens.

  Conditional expression (4) is a relational expression of the refractive index of the glass material.

  If the lower limit value of conditional expression (4) is not reached, the cost increases because an expensive glass material is used. Further, the Petzval sum is increased, and field curvature and coma are deteriorated. If the upper limit of conditional expression (4) is exceeded, the Petzval sum will decrease, and field curvature and coma will deteriorate, which is undesirable.

  In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (4) to 0.75. In order to further secure the effect of the embodiment, it is more preferable to set the lower limit of conditional expression (4) to 0.80. In order to secure the effect of the embodiment, it is preferable to set the upper limit of conditional expression (4) to 0.90. In order to further secure the effect of the embodiment, it is more preferable to set the upper limit of conditional expression (4) to 0.85.

Moreover, it is desirable that the converter lens according to the present embodiment satisfies the following conditional expression (5).
(5) 1.40 ≦ β
Where β is the magnification of the converter lens.

  Conditional expression (5) defines the magnification at which the converter lens enlarges the focal length of the master lens in the infinitely focused state.

  If the lower limit of conditional expression (5) is not reached, the magnification will be insufficient and the lens will not function as a converter lens.

  In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (5) to 1.50. In order to further secure the effect of the embodiment, it is more preferable to set the lower limit of conditional expression (5) to 1.70.

  In addition, the converter lens according to the present embodiment desirably has an aspherical surface. By using an aspherical surface, the effect of correcting spherical aberration and field curvature is particularly improved.

  In addition, it is desirable that the converter lens according to the present embodiment has an aspheric surface on the image side from the cemented lens. With this configuration, it is possible to particularly favorably correct curvature of field.

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

(First embodiment)
FIG. 1 is a diagram showing a configuration in which a converter lens CL according to the first example is mounted on a master lens ML. In FIG. 1, the left side is the object side, and the right side is the image plane I side (the same applies to FIGS. 3, 5, 7, and 9).

  The converter lens CL according to the first example includes, in order from the object side, a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power.

  The first lens group G1 includes, in order from the object side, a biconvex positive lens L1 and a biconcave negative lens L2.

  The second lens group G2 includes, in order from the object side, a cemented positive lens of a biconvex positive lens L3, a biconcave negative lens L4, and a biconvex positive lens L5, and a positive surface with a concave surface facing the object side. It comprises a meniscus lens L6 and a biconcave negative lens L7.

  Table 1 below lists specifications of the master lens ML and the converter lens CL according to the first example attached to the image side of the master lens ML.

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

In (Aspherical data) (described in Tables 2, 3, and 4), the aspherical surface is expressed by the following equation.
X (y) = (y ² / r) / [1+ [1-κ (y ² / r ² )] ^1/2 ]
+ A4 × y ⁴ + A6 × y ⁶ + A8 × y ⁸ + A10 × y ¹⁰
Here, the height in the direction perpendicular to the optical axis is y, the amount of displacement in the optical axis direction at height y is X (y), the radius of curvature of the reference sphere (paraxial radius of curvature) is r, the cone coefficient is κ, Let the n-th order aspheric coefficient be An. “En” represents “× 10 ⁻ⁿ ”, for example “1.234E-05” represents “1.234 × 10 ⁻⁵ ”. Each aspherical surface is indicated with “*” on the right side of the surface number in (surface data).

  In (various data), f (ML) is the focal length of the master lens ML, FNO (ML) is the F number of the master lens ML, R is the shooting distance, S is the aperture diameter, and f1 is the composite focal point of the first lens group G1. The distance, f2 is the combined focal length of the second lens group G2, f (ML + CL) is the combined focal length when the converter lens CL is attached to the master lens ML, FNO is the F number of the converter lens CL, and 2ω is the converter lens CL. Angle of view (unit: “°”), Y is the image height of the converter lens CL, Bf is the back focus, D is the most image side surface of the first lens group G1 to the most object side surface of the second lens group G2. TL is the distance on the optical axis from the lens surface closest to the object side to the lens surface closest to the image side of the converter lens CL (the total length of the converter lens CL), and fc is the composition of the cemented lens. The focal length, fn is the focal length of the negative lens of the cemented lens, Np1 is the refractive index of the d-line of the positive lens on the object side that is cemented to the negative lens of the cemented lens, and Nn is the refractive index of the d-line of the negative lens of the cemented lens. , Np2 represents the refractive index of the d-line of the positive lens on the image side that is cemented to the negative lens of the cemented lens.

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

  In all the following specification values, “mm” is generally used as the synthetic focal length f, curvature radius r, surface interval d and other lengths, etc. unless otherwise specified. Even if proportional expansion or proportional reduction is performed, the same optical performance can be obtained, and the present invention is not limited to this. 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 ∞ 4.00 1.51680 64.10
2 ∞ 0.60
3 173.866 12.00 1.49782 82.52
4 -978.065 0.20
5 133.636 15.00 1.49782 82.52
6 -464.694 5.00 1.80411 46.54
7 332.918 46.30
8 99.554 3.50 1.74400 45.00
9 55.631 15.90 1.49782 82.52
10 -1371.060 29.55
11 -169.969 2.70 1.51680 64.10
12 67.285 4.51
13 -192.927 7.00 1.80384 33.89
14 -43.081 2.80 1.58913 61.09
15 83.887 19.21
16 (Aperture) ∞ 1.70
17 194.039 5.80 1.51860 69.98
18 -90.958 3.10
19 -43.595 3.50 1.79504 28.56
20 -64.790 7.60
21 -175.804 6.70 1.48749 70.41
22 -53.035 14.50
23 ∞ 3.63
24 ∞ 2.00 1.51680 64.10
25 ∞ 38.62
26 56.424 5.00 1.62004 36.30
27 -92.429 1.20
28 -125.333 1.50 1.80400 46.58
29 26.565 6.00
30 37.489 9.60 1.62004 36.30
31 -20.065 2.00 1.88300 40.77
32 32.015 8.80 1.57501 41.49
33 -32.015 6.60
34 -48.625 6.50 1.58913 61.18
35 -25.283 0.10
36 -52.195 2.50 1.88300 40.77
37 158.210 (Bf)
Image plane ∞

(Various data)
f (ML) = 294.001
FNO (ML) = 2.89
f (ML + CL) = 585.3
R = ∞
S = 38.7
f1 = -59.1
f2 = 309.1
FNO = 5.7
2ω = -4.2
Y = 21.6
Bf = 45.6
D = 6.00
TL = 49.80
fc = 79.41
fn = -43.74
Np1 = 1.62004
Nn = 1.88300
Np2 = 1.57501

(Values for conditional expressions)
(1) D / TL = 0.120
(2) (−fn) /fc=0.551
(3) Np1 / Nn = 0.860
(4) Np2 / Nn = 0.836
(5) β = 1.99

FIG. 2 is a diagram illustrating various aberrations of the converter lens CL according to the first example when focusing on infinity.
In each aberration diagram, FNO represents an F number, Y represents an image height, and A represents a half angle of view (unit: “°”). D represents an aberration curve of d-line (λ = 587.6 nm), and g represents an aberration curve of g-line (λ = 435.8 nm). In the spherical aberration diagram and the astigmatism diagram, the solid line indicates the sagittal image plane, and the broken line indicates the meridional image plane.

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

  From the respective aberration diagrams, it can be seen that the converter lens CL according to the first example has excellent imaging performance with various aberrations corrected well.

(Second embodiment)
FIG. 3 is a diagram illustrating a configuration in which the converter lens CL according to the second example is mounted on the master lens ML.

  The converter lens CL according to the second example includes, in order from the object side, a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power.

  The first lens group G1 includes, in order from the object side, a biconvex positive lens L1 and a biconcave negative lens L2.

  The second lens group G2 includes, in order from the object side, a cemented positive lens of a biconvex positive lens L3, a biconcave negative lens L4, and a biconvex positive lens L5, and a positive surface with a concave surface facing the object side. It comprises a meniscus lens L6 and a negative meniscus lens L7 having a concave surface facing the object side. The lens surface on the object side of the positive meniscus lens L6 is an aspherical surface.

  Table 2 below lists specifications of the master lens ML and the converter lens CL according to the second example attached to the image side of the master lens ML.

(Table 2)

(Surface data)
Surface number rd nd νd
Object ∞ ∞
1 ∞ 4.00 1.51680 64.10
2 ∞ 0.60
3 173.866 12.00 1.49782 82.52
4 -978.065 0.20
5 133.636 15.00 1.49782 82.52
6 -464.694 5.00 1.80411 46.54
7 332.918 46.30
8 99.554 3.50 1.74400 45.00
9 55.631 15.90 1.49782 82.52
10 -1371.060 29.55
11 -169.969 2.70 1.51680 64.10
12 67.285 4.51
13 -192.927 7.00 1.80384 33.89
14 -43.081 2.80 1.58913 61.09
15 83.887 19.21
16 (Aperture) ∞ 1.70
17 194.039 5.80 1.51860 69.98
18 -90.958 3.10
19 -43.595 3.50 1.79504 28.56
20 -64.790 7.60
21 -175.804 6.70 1.48749 70.41
22 -53.035 14.50
23 ∞ 3.63
24 ∞ 2.00 1.51680 64.10
25 ∞ 38.62
26 41.365 5.00 1.62004 36.26
27 -169.892 0.80
28 -618.114 1.50 1.80400 46.58
29 22.751 5.40
30 43.584 9.00 1.62004 36.30
31 -19.386 2.00 1.88300 40.76
32 35.157 8.20 1.57501 41.49
33 -35.157 2.90
34 * -58.619 6.40 1.58913 61.16
35 -28.567 0.50
36 -34.421 2.50 1.88300 40.76
37 -121.391 (Bf)
Image plane ∞

(Aspheric data)
34th surface κ = 1.0000
A4 = 1.05550E-05
A6 = 7.82650E-09
A8 = 0.00000E + 00
A10 = 0.00000E + 00

(Various data)
f (ML) = 294.001
FNO (ML) = 2.89
f (ML + CL) = 581.9
R = ∞
S = 38.7
f1 = -64.8
f2 = 444.6
FNO = 5.7
2ω = -4.3
Y = 21.6
Bf = 52.5
D = 5.40
TL = 44.20
fc = 108.07
fn = -44.54
Np1 = 1.62004
Nn = 1.88300
Np2 = 1.57501

(Values for conditional expressions)
(1) D / TL = 0.122
(2) (-fn) /fc=0.512
(3) Np1 / Nn = 0.860
(4) Np2 / Nn = 0.836
(5) β = 1.97

FIG. 4 is a diagram illustrating various aberrations when the converter lens CL according to Example 2 is focused at infinity.
From each aberration diagram, it can be seen that the converter lens CL according to Example 2 has various aberrations corrected well and has excellent imaging performance.

(Third embodiment)
FIG. 5 is a diagram illustrating a configuration in which the converter lens CL according to the third example is mounted on the master lens ML.

  The converter lens CL according to the third example includes, in order from the object side, a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power.

  The first lens group G1 includes, in order from the object side, a biconvex positive lens L1 and a biconcave negative lens L2.

  The second lens group G2 includes, in order from the object side, a cemented positive lens of a biconvex positive lens L3, a biconcave negative lens L4, and a biconvex positive lens L5, and a positive surface with a concave surface facing the object side. It comprises a meniscus lens L6 and a negative meniscus lens L7 having a concave surface facing the object side. The lens surface on the object side of the positive meniscus lens L6 is an aspherical surface.

  Table 3 below lists specifications of the master lens ML and the converter lens CL according to the third example attached to the image side of the master lens ML.

(Table 3)

(Surface data)
Surface number rd nd νd
Object ∞ ∞
1 ∞ 4.00 1.51680 64.10
2 ∞ 0.60
3 173.866 12.00 1.49782 82.52
4 -978.065 0.20
5 133.636 15.00 1.49782 82.52
6 -464.694 5.00 1.80411 46.54
7 332.918 46.30
8 99.554 3.50 1.74400 45.00
9 55.631 15.90 1.49782 82.52
10 -1371.060 29.55
11 -169.969 2.70 1.51680 64.10
12 67.285 4.51
13 -192.927 7.00 1.80384 33.89
14 -43.081 2.80 1.58913 61.09
15 83.887 19.21
16 (Aperture) ∞ 1.70
17 194.039 5.80 1.51860 69.98
18 -90.958 3.10
19 -43.595 3.50 1.79504 28.56
20 -64.790 7.60
21 -175.804 6.70 1.48749 70.41
22 -53.035 14.50
23 ∞ 3.63
24 ∞ 2.00 1.51680 64.10
25 ∞ 38.62
26 43.495 5.00 1.62004 36.26
27 -176.601 1.63
28 -901.179 1.50 1.81600 46.62
29 23.156 2.49
30 40.689 8.24 1.62588 35.65
31 -20.747 2.00 1.88300 40.76
32 24.572 8.11 1.56732 42.70
33 -50.264 4.61
34 * -77.902 7.00 1.58913 61.16
35 -31.925 0.10
36 -38.235 2.50 1.88300 40.76
37 -80.004 (Bf)
Image plane ∞

(Aspheric data)
34th surface κ = 1.0000
A4 = 1.32520E-05
A6 = 1.02370E-08
A8 = 0.00000E + 00
A10 = 0.00000E + 00

(Various data)
f (ML) = 294.001
FNO (ML) = 2.89
f (ML + CL) = 582.0
R = ∞
S = 38.7
f1 = -64.9
f2 = 467.5
FNO = 5.7
2ω = -4.3
Y = 21.6
Bf = 53.2
D = 2.49
TL = 43.17
fc = 335.50
fn = -61.68
Np1 = 1.62588
Nn = 1.88300
Np2 = 1.56732

(Values for conditional expressions)
(1) D / TL = 0.058
(2) (-fn) /fc=0.184
(3) Np1 / Nn = 0.863
(4) Np2 / Nn = 0.833
(5) β = 1.97

FIG. 6 is a diagram illustrating various aberrations when the converter lens CL according to Example 3 is focused at infinity.
It can be seen from the respective aberration diagrams that the converter lens CL according to the third example has excellent imaging performance with various aberrations corrected well.

(Fourth embodiment)
FIG. 7 is a diagram illustrating a configuration in which the converter lens CL according to the fourth example is mounted on the master lens ML.

  The converter lens CL according to the fourth example includes, in order from the object side, a first lens group G1 having negative refractive power and a second lens group G2 having negative refractive power.

  The first lens group G1 includes, in order from the object side, a biconvex positive lens L1, a biconcave negative lens L2, and a biconvex positive lens L3.

  The second lens group G2 includes, in order from the object side, a cemented positive lens of a biconvex positive lens L4, a biconcave negative lens L5, and a biconvex positive lens L6, and a positive surface with a concave surface facing the object side. It comprises a meniscus lens L7 and a negative meniscus lens L8 with a concave surface facing the object side. The image-side lens surface of the positive meniscus lens L7 is aspheric.

  Table 4 below lists specifications of the master lens ML and the converter lens CL according to the fourth example attached to the image side of the master lens ML.

(Table 4)

(Surface data)
Surface number rd nd νd
Object ∞ ∞
1 ∞ 4.00 1.51680 64.10
2 ∞ 0.60
3 173.866 12.00 1.49782 82.52
4 -978.065 0.20
5 133.636 15.00 1.49782 82.52
6 -464.694 5.00 1.80411 46.54
7 332.918 46.30
8 99.554 3.50 1.74400 45.00
9 55.631 15.90 1.49782 82.52
10 -1371.060 29.55
11 -169.969 2.70 1.51680 64.10
12 67.285 4.51
13 -192.927 7.00 1.80384 33.89
14 -43.081 2.80 1.58913 61.09
15 83.887 19.21
16 (Aperture) ∞ 1.70
17 194.039 5.80 1.51860 69.98
18 -90.958 3.10
19 -43.595 3.50 1.79504 28.56
20 -64.790 7.60
21 -175.804 6.70 1.48749 70.41
22 -53.035 14.50
23 ∞ 3.63
24 ∞ 2.00 1.51680 64.10
25 ∞ 38.62
26 49.516 5.00 1.62004 36.26
27 -73.947 0.27
28 -82.701 1.50 1.81600 46.62
29 26.746 3.21
30 139.929 4.18 1.67270 32.11
31 -111.051 3.00
32 120.000 6.91 1.72342 37.95
33 -22.968 2.00 1.88300 40.76
34 27.016 8.42 1.56732 42.70
35 -46.582 6.39
36 -59.851 5.84 1.58913 61.16
37 * -28.452 0.10
38 -34.892 2.50 1.88300 40.76
39 -115.137 (Bf)
Image plane ∞

(Aspheric data)
37th surface κ = 1.0000
A4 = 1.22110E-05
A6 = 5.14870E-09
A8 = 0.00000E + 00
A10 = 0.00000E + 00

(Various data)
f (ML) = 294.001
FNO (ML) = 2.89
f (ML + CL) = 582.0
R = ∞
S = 38.7
f1 = -150.8
f2 = -160.5
FNO = 5.7
2ω = -4.3
Y = 21.6
Bf = 50.0
D = 3.00
TL = 49.32
fc = 1897.08
fn = -83.73
Np1 = 1.72342
Nn = 1.88300
Np2 = 1.56732

(Values for conditional expressions)
(1) D / TL = 0.061
(2) (-fn) /fc=0.044
(3) Np1 / Nn = 0.915
(4) Np2 / Nn = 0.833
(5) β = 1.96

FIG. 8 is a diagram illustrating various aberrations when the converter lens CL according to Example 4 is in focus at infinity.
From each aberration diagram, it can be seen that the converter lens CL according to Example 4 has various aberrations corrected satisfactorily and has excellent imaging performance.

(5th Example)
FIG. 9 is a diagram illustrating a configuration in which the converter lens CL according to the fifth example is mounted on the master lens ML.

  The converter lens CL according to Example 5 includes, in order from the object side, a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power.

  The first lens group G1 includes, in order from the object side, a biconvex positive lens L1 and a biconcave negative lens L2.

  The second lens group G2 includes, in order from the object side, a cemented positive lens of a biconvex positive lens L3, a biconcave negative lens L4, and a biconvex positive lens L5, and a positive surface with a concave surface facing the object side. It comprises a meniscus lens L6 and a biconcave negative lens L7.

  Table 5 below lists specifications of the master lens ML and the converter lens CL according to the fifth example attached to the image side of the master lens ML.

(Table 5)

(Surface data)
Surface number rd nd νd
Object ∞ ∞
1 ∞ 4.00 1.51680 64.10
2 ∞ 0.60
3 173.866 12.00 1.49782 82.52
4 -978.065 0.20
5 133.636 15.00 1.49782 82.52
6 -464.694 5.00 1.80411 46.54
7 332.918 46.30
8 99.554 3.50 1.74400 45.00
9 55.631 15.90 1.49782 82.52
10 -1371.060 29.55
11 -169.969 2.70 1.51680 64.10
12 67.285 4.51
13 -192.927 7.00 1.80384 33.89
14 -43.081 2.80 1.58913 61.09
15 83.887 19.21
16 (Aperture) ∞ 1.70
17 194.039 5.80 1.51860 69.98
18 -90.958 3.10
19 -43.595 3.50 1.79504 28.56
20 -64.790 7.60
21 -175.804 6.70 1.48749 70.41
22 -53.035 14.50
23 ∞ 3.63
24 ∞ 2.00 1.51680 64.10
25 ∞ 38.62
26 82.235 5.00 1.62004 36.26
27 -146.695 2.68
28 -726.932 1.50 1.81600 46.62
29 21.704 2.68
30 27.564 11.00 1.63980 34.56
31 -17.932 2.00 1.88300 40.76
32 47.494 9.25 1.51742 52.31
33 -25.996 4.14
34 -35.907 5.26 1.58913 61.16
35 -23.885 0.10
36 -45.558 2.50 1.88300 40.76
37 433.303 (Bf)
Image plane ∞

(Various data)
f (ML) = 294.001
FNO (ML) = 2.89
f (ML + CL) = 581.4
R = ∞
S = 38.7
f1 = -40.6
f2 = 84.1
FNO = 5.7
2ω = 4.2
Y = 21.6
Bf = 49.3
D = 2.68
TL = 46.10
fc = 47.03
fn = -71.01
Np1 = 1.63980
Nn = 1.88300
Np2 = 1.51742

(Values for conditional expressions)
(1) D / TL = 0.058
(2) (−fn) /fc=1.510
(3) Np1 / Nn = 0.871
(4) Np2 / Nn = 0.806
(5) β = 1.95

FIG. 10 is a diagram illustrating various aberrations when the converter lens CL according to Example 5 is focused at infinity.
From each aberration diagram, it can be seen that the converter lens CL according to Example 5 has various aberrations corrected satisfactorily and has excellent imaging performance.

  FIG. 11 is a diagram showing various aberrations when the master lens ML is focused at infinity.

  In addition, although the master lens ML showed the same thing in each said Example, this master lens ML is only an example and the structure of the master lens ML is not limited to this.

  As described above, according to the present embodiment, it is possible to provide a converter lens having a high magnification and a high imaging performance that can be sufficiently applied to a digital still camera.

  Next, a camera equipped with the converter lens according to this embodiment will be described. In addition, although the case where the converter lens which concerns on 1st Example is mounted is demonstrated, it is the same also in another Example.

  FIG. 12 is a diagram illustrating a configuration of a camera including the converter lens CL according to the first example.

  In FIG. 12, a camera 1 is a digital single-lens reflex camera including a master lens ML as a photographing lens 2 and a converter lens CL according to the first embodiment attached to the master lens ML. 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 out of the optical path, and light from the subject (not shown) reaches the image sensor 7. 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 master lens ML as the photographing lens 2 on the camera 1 and the converter lens CL according to the first embodiment attached to the master lens ML, 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.

  Although the two-group configuration is shown in the embodiment, the present invention can be applied to other group configurations such as a three-group configuration. Further, a configuration in which a lens or a lens group is added to the most object side, or a configuration in which a lens or a lens group is added to the most image side may be used.

  A single lens group, a plurality of lens groups, or a partial lens group or the entire converter lens 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 addition, the lens group or the partial lens group is moved so as to have a component in a direction perpendicular to the optical axis, or is rotated (swayed) in the in-plane direction including the optical axis to reduce image blur caused by camera shake. A vibration-proof lens group to be corrected may be used. In particular, it is preferable that at least a part of the second lens group is an anti-vibration lens group.

  Further, 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.

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

  In the present embodiment, the magnification is about 1.4 to 2.5.

  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 the present invention is not limited to this.

ML master lens CL converter lens G1 first lens group G2 second lens group L1 positive lens L2 negative lens L3 positive lens I image plane 1 camera

Claims (11)

A detachable converter lens used on the image side of the master lens,
A converter lens comprising at least a cemented lens having a positive refractive power including at least a positive lens, a negative lens, and a positive lens.   The converter lens according to claim 1, further comprising a first lens having a positive refractive power and a second lens having a negative refractive power in order from the most object side. 3. The converter lens according to claim 1, wherein the converter lens includes a first lens group and a second lens group in order from the object side, and satisfies the following conditions.
0.01 <D / TL <0.25
However,
D: Distance from the most image side surface of the first lens group to the most object side surface of the second lens group TL: Light from the most object side lens surface of the converter lens to the most image side lens surface Axis distance The converter lens according to claim 1, wherein the cemented lens satisfies the following condition.
0.02 <(− fn) / fc <2.00
However,
fc: Composite focal length of the cemented lens fn: Focal length of the negative lens of the cemented lens The converter lens according to any one of claims 1 to 4, wherein the cemented lens satisfies the following condition.
0.75 <Np1 / Nn <0.95
However,
Nn: Refractive index of the d-line of the negative lens of the cemented lens Np1: Refractive index of the d-line of the object-side positive lens cemented to the negative lens of the cemented lens The converter lens according to claim 1, wherein the cemented lens satisfies the following condition.
0.70 <Np2 / Nn <0.95
However,
Nn: Refractive index of the d-line of the negative lens of the cemented lens Np2: Refractive index of the d-line of the positive lens on the image side cemented to the negative lens of the cemented lens The converter lens according to claim 1, wherein the following condition is satisfied.
1.40 ≦ β
However,
β: magnification of the converter lens   The converter lens according to claim 1, wherein the converter lens has an aspherical surface.   The converter lens according to claim 1, wherein the converter lens has an aspheric surface on the image side of the cemented lens.   An optical device comprising the converter lens according to claim 1.   A method of enlarging the focal length of a master lens by attaching a converter lens including at least a positive lens, a negative lens, and a cemented lens having a positive refractive power to the image side of the master lens.

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