JP2009186611A - Teleconverter lens, optical device, and method for extending focal length of master lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a teleconverter lens having high imaging performance, to provide an optical device having the same and to provide a method for extending a focal length of a master lens. <P>SOLUTION: The attachable/detachable teleconverter lens TC is attached to an image side of the master lens ML and used, and has a synthetic focal length which, when it is attached, is longer than the focal length of the master lens ML, the teleconverter lens TC has a first lens L1 having positive refractive power, a second lens L2 having negative refractive power, a third lens L3 having positive refractive power, and a fourth lens component having negative refractive power. The teleconverter lens has an aspherical surface on the first lens L1. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

Conventionally, a detachable teleconverter 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 63-234211 A

  Conventional teleconverter lenses have not had sufficient imaging performance.

  The present invention has been made in view of the above problems, and provides a teleconverter lens having high imaging performance, an optical apparatus having the teleconverter lens, and a method for expanding the focal length of a master lens.

  In order to solve the above problems, the present invention is a detachable teleconverter lens that is used by being mounted on the image side of a master lens, and the combined focal length when mounted is longer than the focal length of the master lens. The first lens includes a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, and a fourth lens component having a negative refractive power in order from the object side. A teleconverter lens having an aspherical surface is provided.

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

  Further, the present invention includes, in order from the object side, a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, and a fourth lens component having a negative refractive power. A method is provided in which a teleconverter lens having an aspherical surface is attached to the first lens on the image side of the master lens to enlarge the focal length of the master lens.

  ADVANTAGE OF THE INVENTION According to this invention, the teleconverter lens which has high image formation performance, the optical apparatus which has this, and the method of expanding the focal distance of a master lens can be provided.

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

  In general, the teleconverter 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 very difficult to correct aberrations. This becomes more prominent as the enlargement magnification is higher. Therefore, the higher the magnification, the better the optical performance.

  The teleconverter lens according to the present embodiment is a detachable teleconverter lens that is used by being mounted on the image side of the master lens and has a combined focal length that is longer than the focal length of the master lens. The first lens having positive refractive power, the second lens having negative refractive power, the third lens having positive refractive power, and the fourth lens component having negative refractive power are sequentially arranged. With this configuration, it is possible to realize a teleconverter lens that corrects spherical aberration satisfactorily and suppresses the occurrence of field curvature and coma, and has high imaging performance.

  In particular, when the first lens is configured to have an aspherical surface, the spherical aberration correction effect is significantly improved. A good combination of positive and negative lenses contributes to correction of longitudinal chromatic aberration.

  In the teleconverter lens according to the present embodiment, it is desirable that the fourth lens component has at least a positive lens and a negative lens. With this configuration, Petzval sum can be controlled, field curvature and coma can be corrected well, and lateral chromatic aberration can also be corrected well.

In the teleconverter lens according to the present embodiment, it is desirable that the lens group including the first, second, and third lenses satisfies the following conditional expression (1).
(1) −4.0 <β × TL / f1 <1.5
Where β is the magnification of the teleconverter lens, TL is the total length of the teleconverter lens, and f1 is the combined focal length of the lens group composed of the first, second, and third lenses.

  Conditional expression (1) is a relational expression of the magnification of the teleconverter lens, the total length of the teleconverter lens, and the combined focal length of the lens group including the first, second, and third lenses. The total length of the teleconverter lens is a distance on the optical axis from the most object side lens surface to the most image side lens surface of the teleconverter lens.

  If the lower limit value of conditional expression (1) is not reached, the negative power of the lens group becomes strong, and it becomes difficult to correct spherical aberration and Petzval sum, which is not desirable. If the upper limit of conditional expression (1) is exceeded, the positive power of the lens group will increase, making it difficult to correct curvature of field and coma, which is not desirable.

  In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (1) to −2.0. In order to further secure the effect of the embodiment, it is more preferable to set the lower limit of conditional expression (1) to −1.5. In order to secure the effect of the embodiment, it is preferable to set the upper limit of conditional expression (1) to 0.7. In order to further secure the effect of the embodiment, it is more preferable to set the upper limit of conditional expression (1) to 0.5.

In the teleconverter lens according to the present embodiment, it is desirable that the fourth lens component satisfies the following conditional expression (2).
(2) 0.75 <Np / Nn <0.95
Np is the refractive index of the d-line of the positive lens of the fourth lens component, and Nn is the refractive index of the d-line of the negative lens of the fourth lens component.

  Conditional expression (2) is a relational expression of the refractive index of the glass material.

  If the lower limit of conditional expression (2) 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 (2) 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 (2) to 0.80. In order to secure the effect of the embodiment, it is preferable to set the upper limit of conditional expression (2) to 0.90.

  In the teleconverter lens according to this embodiment, the aspheric surface is preferably a composite aspheric surface made of resin.

  The composite aspherical surface is easy to manufacture and can reduce the cost.

  In the teleconverter lens according to this embodiment, the aspheric surface is preferably a glass mold aspheric surface.

  An aspherical surface having a large difference with respect to the spherical surface can be produced by the glass mold.

Moreover, it is desirable that the teleconverter lens according to this embodiment satisfies the following conditional expression (3).
(3) 1.4 <β
Where β is the magnification of the teleconverter lens.

  Conditional expression (3) defines the magnification at which the teleconverter lens expands the focal length of the master lens in the infinitely focused state.

  If the lower limit of conditional expression (3) is not reached, the magnification will be insufficient and the teleconverter lens will not function.

  In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (3) to 1.7.

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

(First embodiment)
FIG. 1 is a diagram illustrating a configuration in which the teleconverter lens TC according to the first example is mounted on the master lens ML.

  The teleconverter lens TC according to the first example includes, in order from the object side, a biconvex positive lens L1, a biconcave negative lens L2, a positive meniscus lens L3 having a convex surface facing the object side, and a biconcave. A cemented negative lens (corresponding to the fourth lens component) of a negative lens L4 having a shape and a positive lens L5 having a biconvex shape, a positive meniscus lens L6 having a concave surface facing the object side, and a concave surface facing the object side And a negative meniscus lens L7. The lens surface on the image plane I side of the positive lens L1 is an aspherical surface.

  Table 1 below lists specifications of the master lens ML and the teleconverter lens TC according to the first example attached to 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 (Aspheric data), the aspheric 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 + A12 × y ¹²

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, FNO (ML) is the F number of the master lens, β is the magnification of the teleconverter lens, R is the shooting distance, f is the telephoto lens to the master lens FNO is the teleconverter lens F number, 2ω is the angle of view of the teleconverter lens (unit: “°”), Y is the image height of the teleconverter lens, TL is the total length of the teleconverter lens Bf represents the back focus, and f1 represents the combined focal length of the lens group including the positive lens L1, the negative lens L2, and the positive meniscus lens L3. The total length of the teleconverter lens is a distance on the optical axis from the most object side surface of the teleconverter lens to the most image side surface.

  (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 82.51
4 -978.065 0.20
5 133.636 15.00 1.49782 82.51
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 82.51
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 19.28
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 70.40
22 -53.035 14.50
23 ∞ 7.00
24 ∞ 2.00 1.51680 64.10
25 ∞ 35.25
26 190.253 4.00 1.62004 36.26
27 * -32.496 0.50
28 -58.846 2.00 1.81600 46.62
29 26.744 1.30
30 30.456 5.10 1.63980 34.56
31 113.724 11.00
32 -36.658 2.00 1.88300 40.76
33 32.008 11.60 1.56732 42.70
34 -24.336 10.40
35 -115.327 9.00 1.58913 61.16
36 -28.151 0.10
37 -48.064 2.50 1.88300 40.76
38 -247.647 (Bf)
Image plane ∞

(Aspheric data)
27th surface κ = 1.0000
A4 = 1.37729E-05
A6 = -4.74420E-09
A8 = -2.76001E-11
A10 = 1.97596E-13
A12 = -0.40561E-15

(Various data)
f (ML) = 294.0
FNO (ML) = 2.88
β = 2
R = ∞
f = 583.7
FNO = 5.72
2ω = 4.24
Y = 21.60
TL = 59.5
Bf = 52.36
f1 = -175.6

(Values for conditional expressions)
(1) β × TL / f1 = −0.678
(2) Np / Nn = 0.833
(3) β = 1.985

  FIG. 2 is a diagram illustrating various aberrations of the teleconverter lens 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 the d-line (λ = 587.6 nm), and g represents the 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.

  It can be seen from the respective aberration diagrams that the teleconverter lens 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 teleconverter lens TC according to the second example is mounted on the master lens ML.

  The teleconverter lens TC according to the second example includes, in order from the object side, a biconvex positive lens L1, a biconcave negative lens L2, a positive meniscus lens L3 having a convex surface facing the object side, and a biconcave. A cemented negative lens (corresponding to the fourth lens component) of a negative lens L4 having a shape and a positive lens L5 having a biconvex shape, a positive meniscus lens L6 having a concave surface facing the object side, and a concave surface facing the object side And a negative meniscus lens L7. The lens surface on the image plane I side of the positive lens L1 and the lens surface on the object side of the negative meniscus lens L7 are aspheric.

  Table 2 below shows specification values of the master lens ML and the teleconverter lens TC according to the second example attached to 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 82.51
4 -978.065 0.20
5 133.636 15.00 1.49782 82.51
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 82.51
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 19.28
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 70.40
22 -53.035 14.50
23 ∞ 7.00
24 ∞ 2.00 1.51680 64.10
25 ∞ 35.25
26 96.962 4.00 1.62004 36.26
27 * -35.801 0.10
28 -62.149 2.00 1.81600 46.62
29 27.900 1.60
30 42.730 5.10 1.63980 34.56
31 2076.849 11.00
32 -33.251 2.00 1.88300 40.76
33 28.837 12.60 1.56732 42.70
34 -23.751 9.00
35 -94.722 9.00 1.58913 61.16
36 -26.895 0.10
37 * -48.165 2.50 1.88300 40.76
38 -267.134 (Bf)
Image plane ∞

(Aspheric data)
27th surface κ = 1.0000
A4 = 1.10288E-05
A6 = -8.37933E-09
A8 = 5.16039E-11
A10 = -3.03346E-13
A12 = 0.69998E-15
37th surface κ = 1.0000
A4 = -3.06183E-07
A6 = -2.24982E-10
A8 = 3.38434E-13
A10 = 2.80452E-15
A12 = 0

(Various data)
f (ML) = 294.0
FNO (ML) = 2.88
β = 2
R = ∞
f = 583.7
FNO = 5.72
2ω = 4.24
Y = 21.60
TL = 59.0
Bf = 52.98
f1 = -314.0

(Values for conditional expressions)
(1) β × TL / f1 = −0.376
(2) Np / Nn = 0.833
(3) β = 1.985

  FIG. 4 is a diagram illustrating various aberrations of the teleconverter lens according to Example 2 when focused on infinity.

  From the respective aberration diagrams, it can be seen that the teleconverter lens according to Example 2 has various aberrations corrected well and has excellent imaging performance.

(Third embodiment)
FIG. 5 is a diagram showing a configuration in which the teleconverter lens TC according to the third example is mounted on the master lens ML.

  The teleconverter lens TC according to the third example includes, in order from the object side, a biconvex positive lens L1, a biconcave negative lens L2, a positive meniscus lens L3 having a convex surface facing the object side, and a biconcave. A cemented negative lens (corresponding to the fourth lens component) of a negative lens L4 having a shape and a positive lens L5 having a biconvex shape, and a cemented lens having a negative lens L6 having a biconcave shape and a positive lens L7 having a biconvex shape; Consists of. The lens surface on the object side of the positive lens L1 is an aspherical surface.

  Table 3 below lists specifications of the master lens ML and the teleconverter lens TC according to the third example attached to 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 82.51
4 -978.065 0.20
5 133.636 15.00 1.49782 82.51
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 82.51
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 19.28
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 70.40
22 -53.035 14.50
23 ∞ 7.00
24 ∞ 2.00 1.51680 64.10
25 ∞ 35.25
26 * 89.082 4.00 1.62004 36.26
27 -71.546 0.50
28 -369.513 2.00 1.81600 46.62
29 21.705 1.00
30 22.002 5.10 1.63980 34.56
31 85.928 8.80
32 -38.814 2.00 1.88300 40.76
33 32.616 8.00 1.56732 42.70
34 -61.867 25.40
35 -1077.482 2.50 1.88300 40.76
36 79.250 13.50 1.58913 61.16
37 -37.725 (Bf)
Image plane ∞

(Aspheric data)
26th surface κ = 1.0000
A4 = -1.78023E-06
A6 = -9.34033E-10
A8 = -3.79037E-12
A10 = -6.83172E-15
A12 = 0

(Various data)
f (ML) = 294.0
FNO (ML) = 2.88
β = 2
R = ∞
f = 583.7
FNO = 5.72
2ω = 4.22
Y = 21.54
TL = 72.8
Bf = 42.00
f1 = -726.4

(Values for conditional expressions)
(1) β × TL / f1 = −0.200
(2) Np / Nn = 0.833
(3) β = 1.985

  FIG. 6 is a diagram illustrating various aberrations when the teleconverter lens according to Example 3 is in focus at infinity.

  From the respective aberration diagrams, it can be seen that the teleconverter lens according to Example 3 has excellent imaging performance with various aberrations corrected well.

  FIG. 7 is a diagram showing various aberrations when the master lens ML is focused at infinity.

  In the first, second, and third examples, the same master lens is shown. However, this master lens is only an example, and the configuration of the master lens is not limited to this.

  As described above, according to the present embodiment, it is possible to provide a teleconverter lens that has a high magnification performance and a high imaging performance that is sufficiently compatible with a digital still camera.

  Next, a camera equipped with the teleconverter lens according to this embodiment will be described. Although the case where the teleconverter lens according to the first example is mounted will be described, the same applies to other examples.

  FIG. 8 is a diagram illustrating a configuration of a camera including the teleconverter lens according to the first example.

  In FIG. 8, a camera 1 is a digital single-lens reflex camera including a master lens ML as a photographing lens 2 and a teleconverter lens TC according to the first example 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 teleconverter lens TC 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.

  In the embodiment, a three-sheet and one-component configuration is shown, but the present invention can also be applied to a configuration in which other lenses or lens components are added.

  Alternatively, the lens group or the partial lens group may be vibrated in a direction perpendicular to the optical axis so as to correct an image blur caused by camera shake. In particular, the fourth lens component is preferably an anti-vibration lens group.

  The lens surface may be an aspherical surface. The aspherical surface may be any of an aspherical surface by grinding, a glass mold aspherical surface in which a glass is formed into an aspherical shape, or a composite aspherical surface in which a resin is formed in an aspherical shape on the glass surface.

  If each lens surface is provided with an antireflection film having a high transmittance in a wide wavelength range, flare and ghost can be reduced and high contrast and high optical performance can be achieved.

  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 a figure which shows the structure which mounted | wore the master converter ML with the teleconverter lens TC which concerns on 1st Example. FIG. 6 is a diagram illustrating various aberrations of the teleconverter lens according to Example 1 when focusing on infinity. It is a figure which shows the structure which mounted | wore the master converter ML with the teleconverter lens TC which concerns on 2nd Example. FIG. 12 is a diagram illustrating various aberrations of the teleconverter lens 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 teleconverter lens TC which concerns on 3rd Example. FIG. 12 is a diagram illustrating various aberrations of the teleconverter lens according to Example 3 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 teleconverter lens which concerns on 1st Example.

Explanation of symbols

ML master lens TC teleconverter lens L1 positive lens L2 negative lens L3 positive meniscus lens L4 negative lens L5 positive lens I image plane 1 camera

Claims (9)

A detachable teleconverter lens that is used by being mounted on the image side of the master lens, and the combined focal length when mounted is longer than the focal length of the master lens,
In order from the object side, a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, and a fourth lens component having a negative refractive power are provided. A teleconverter lens having an aspherical surface.   The teleconverter lens according to claim 1, wherein the fourth lens component includes at least a positive lens and a negative lens. The teleconverter lens according to claim 1 or 2, wherein a lens group including the first, second, and third lenses satisfies the following condition.
−4.0 <β × TL / f1 <1.5
However,
β: Magnification magnification of the teleconverter lens TL: Total length of the teleconverter lens f1: Composite focal length of the lens group composed of the first, second, and third lenses The teleconverter lens according to claim 2 or 3, wherein the fourth lens component satisfies the following condition.
0.75 <Np / Nn <0.95
However,
Np: refractive index of d-line of the positive lens of the fourth lens component Nn: refractive index of d-line of the negative lens of the fourth lens component   The teleconverter lens according to claim 1, wherein the aspheric surface is a composite aspheric surface made of resin.   The teleconverter lens according to any one of claims 1 to 4, wherein the aspheric surface is a glass mold aspheric surface. The teleconverter lens according to any one of claims 1 to 6, wherein the following condition is satisfied.
1.4 <β
However,
β: magnification of the teleconverter lens   An optical apparatus comprising the teleconverter lens according to claim 1.   In order from the object side, a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, and a fourth lens component having a negative refractive power are provided. A method in which a teleconverter lens having an aspherical surface is mounted on the image side of a master lens to enlarge the focal length of the master lens.

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