JP2011090346A - Front converter lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light-weight converter lens that is composed of relatively fewer lenses, while achieving high afocal magnification ratio at low cost. <P>SOLUTION: The front converter lens C is composed of a front group L1 with a positive refractive power and a back group L2 with a negative refractive power, and is attachable to a front of a main lens system M. The front group L1 has at least two positive lens and all of the lens are arranged with a certain interval, and the back group L2 is composed of the positive lens and negative lens. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a converter lens that is mounted in front (object side) of a photographic lens (main lens system) such as a digital still camera, a video camera, or a silver halide photographic camera to displace the focal length of the entire lens system.

  Conventionally, for example, Patent Document 1 proposes a front-type teleconverter lens (teleconverter) that is mounted in front of a photographing lens and changes the focal length of the entire system to the long focal length side.

  In many cases, a teleconverter has two lens groups, a front group having a positive refractive power and a rear group having a negative refractive power, arranged with a principal point interval that is the sum of the focal lengths of both lens groups. Consists of a focal system. Therefore, as the simplest lens system, a configuration in which one positive lens and one negative lens are arranged as in Patent Document 1 can be used. However, in order to obtain high optical performance, it is difficult to correct aberrations by using only two lenses.

  Patent Documents 2 and 3 are known as teleconverters in which the number of lenses is increased and aberrations are corrected.

JP 55-32046 A JP-A-4-191717 JP-A-6-289289

  The teleconverter disclosed in Patent Document 2 has a problem that it is difficult to correct various aberrations in the front group composed of only one lens when the afocal magnification is increased, and the front group includes two positive meniscuses. Aberrations are corrected by reducing the refractive power of each lens. However, the rear group is composed of only one negative lens, and correction of chromatic aberration is insufficient.

  In addition, the teleconverter disclosed in Patent Document 3 prevents deterioration of chromatic aberration by using only one positive lens in which the front group is made of low dispersion glass, but the afocal magnification is 1.3 times or less. Low.

  However, if the number of the front group having a large diameter is excessively increased for these corrections, the weight and cost are greatly increased.

  The present invention has been made in view of the above-described conventional example. An object of the present invention is to provide an inexpensive and lightweight converter lens having a relatively small number of constituent lenses while realizing a high afocal magnification.

  In order to achieve the above-mentioned object, the present invention comprises a front group having a positive refractive power and a rear group having a negative refractive power disposed behind the front group, and is detachable in front of the main lens system. The front group has two positive lenses, all the lenses are arranged at intervals (no cemented lens), and the rear group has a positive lens and a negative lens.

  According to the present invention, it is possible to realize an inexpensive and lightweight converter lens with a relatively small number of constituent lenses while realizing a high afocal magnification.

2 is a lens cross-sectional view of a teleconverter and a main lens system of Example 1. FIG. FIG. 6 is a diagram illustrating various aberrations of the system in which the teleconverter of Example 1 is mounted. 6 is a lens cross-sectional view of a teleconverter and a main lens system of Example 2. FIG. FIG. 7 is a diagram illustrating all aberrations of the system to which the teleconverter of Example 2 is mounted. 6 is a lens cross-sectional view of a teleconverter and a main lens system of Example 3. FIG. FIG. 10 is a diagram illustrating all aberrations of the system to which the teleconverter of Example 3 is mounted. It is an aberration diagram of only the main lens system. It is a principal part schematic diagram of a video camera.

  Embodiments of the converter lens of the present invention will be described below with reference to the drawings. The converter lens disclosed in the present embodiment is a teleconverter that is mounted in front of a photographing lens of a camera and displaces the focal length of the entire lens system in the longer direction.

  1, 3, and 5 are lens cross-sectional views when the teleconverters of Numerical Examples 1 to 3 are mounted on the object side (front) of the photographing lens (main lens system), respectively.

  2, 4 and 6 are graphs showing various aberrations in the state where the teleconverters of Numerical Examples 1 to 3 are mounted on the main lens system. Each of the numerical examples uses a common main lens system. FIG. 7 is a diagram showing various aberrations of the main lens system alone.

  In each lens cross-sectional view, the left side is the object side (front), and the right side is the image side (rear). C is a teleconverter, and M is a taking lens. The teleconverter C includes, in order from the object side, a front group L1 having a positive refractive power and a rear group L2 having a negative refractive power. In the taking lens M, SP is an aperture stop, P is an optical low-pass filter, an infrared cut filter, a glass block designed to correspond to a parallel plate existing in an optical path such as a cover glass, and I is a CCD sensor or CMOS. It is an image surface on which a photosensitive surface of a solid-state imaging device (photoelectric conversion device) such as a sensor is located.

  In each aberration diagram, c, d, f, and g represent c-line, d-line, f-line, and g-line, respectively, and ΔM and ΔS represent a meridional image surface and a sagittal image surface.

  In the teleconverter C of the present embodiment, the principal point interval between the front group L1 and the rear group L2 is substantially equal to the sum of the focal lengths of the front group L1 and the rear group L2, thereby forming a substantially afocal system as a whole. is doing.

  Then, by arranging two positive lenses in the front group L1, mainly spherical aberration and astigmatism are corrected favorably. Further, by arranging a positive lens and a negative lens in the rear group L2, chromatic aberration generated in the front group L1 is effectively canceled.

  In the teleconverter C of the present embodiment, in order to perform better aberration correction, the image side surface of the positive lens disposed closest to the object side has a convex shape. If the image side surface of the positive lens located closest to the object side has a concave shape, this positive lens needs to have a smaller radius of curvature of the object side surface in order to maintain the desired refractive power. At a small telephoto end, the angle formed between the off-axis incident light beam and the object side surface of the positive lens disposed closest to the object side becomes steep. As a result, the chromatic aberration of magnification becomes large and correction in the rear group L2 becomes difficult. For this reason, in the present embodiment, the image side surface of the positive lens disposed closest to the object side is convex, and the occurrence of lateral chromatic aberration is suppressed to a level that can be corrected by the rear group L2.

In addition, since the positive lens placed on the most object side, which has a large effective diameter, generates a large amount of various aberrations, the positive lens placed on the most object side has a larger radius of curvature (reducing the refractive power). It is desirable to reduce the occurrence of various aberrations. For this reason, in this embodiment, the radius of curvature of the image side surface of the positive lens disposed closest to the object side is RI, and the radius of curvature of the object side surface of the positive lens disposed closest to the image side of the front group is RO. and when,
| RI | >> | RO | (1)
Is set to satisfy the following conditions.
Furthermore,
5 <| RI / RO | (2)
It is more preferable that the above condition is satisfied, and the teleconverter of this embodiment satisfies this condition. If the object side surface of the positive lens arranged closest to the object side is convex, | RI | can be increased while maintaining positive refractive power.
Further, in the teleconverter of this embodiment, when the focal length of the front group L1 and the focal length of the rear group L2 are fP and fN,
1.5 <| fP / fN | <3.0 (3)
Is satisfied.

Conditional expression (3) defines the afocal magnification of the teleconverter. If the upper limit value of conditional expression (3) is exceeded, the chromatic aberration generated in the front group L1 becomes too large, so that correction of only the rear group L2 is insufficient and image quality deteriorates greatly. If the lower limit of conditional expression (3) is exceeded, the amount of various aberrations generated in the front group L1 decreases, and the necessity of the lens configuration proposed in the present embodiment becomes low. The range of conditional expression (3) is
1.6 <| fP / fN | <2.6 (3a)
And even better.

  Next, numerical data of numerical examples 1 to 3 are shown. In each numerical example, Ri is the radius of curvature of the i-th surface (i-th surface) in order from the object side, Di is the distance between the i-th surface and the (i + 1) -th surface, and Ni and νi are d-lines, respectively. The refractive index and Abbe number of the optical member used as a reference are shown. Numerical data of the main lens system (photographing lens M) is also shown. In the numerical data of the main lens system, the two planes closest to the image side are the surfaces constituting the glass block GB provided by design as described above. F is a focal length, Fno is an F number, and ω is a half angle of view.

  The aspherical shape is the X axis in the optical axis direction, the H axis in the direction perpendicular to the optical axis, the light traveling direction is positive, R is the paraxial radius of curvature, k is the conic constant, and B, C, D, E, and F are respectively Aspheric coefficient

It is expressed by the following formula. “E ± Z” means “× 10 ^{± Z} ”.

Table 1 shows the relationship between the above-described conditional expressions and numerical examples.
(Numerical example 1)
1.64 times
R 1 = 50.964 D 1 = 9.00 N 1 = 1.487490 ν1 = 70.2
R 2 = -224.857 D 2 = 0.30
R 3 = 37.531 D 3 = 4.00 N 2 = 1.487490 ν2 = 70.2
R 4 = 54.080 D 4 = 15.00
R 5 = -243.690 D 5 = 2.00 N 3 = 1.846660 ν3 = 23.9
R 6 = -100.901 D 6 = 1.50 N 4 = 1.834000 ν4 = 37.2
R 7 = 36.891 D 7 = 3.80

(Numerical example 2)
1.98 times
R 1 = 47.743 D 1 = 14.64 N 1 = 1.496999 ν 1 = 81.5
R 2 = -6539.459 D 2 = 0.98
R 3 = 39.131 D 3 = 5.62 N 2 = 1.496999 ν 2 = 81.5
R 4 = 65.714 D 4 = 18.33
R 5 = 829.088 D 5 = 3.01 N 3 = 2.003300 ν 3 = 28.3
R 6 = 21.205 D 6 = 4.92
R 7 = 26.029 D 7 = 4.01 N 4 = 1.922860 ν 4 = 18.9
R 8 = 40.003 D 8 = 3.80

(Numerical Example 3)
2.51 times
R 1 = 86.372 D 1 = 16.47 N 1 = 1.433870 ν1 = 95.1
R 2 = -361.663 D 2 = 10.00
R 3 = 52.557 D 3 = 8.28 N 2 = 1.433870 ν2 = 95.1
R 4 = 113.013 D 4 = 36.10
R 5 = -181.942 D 5 = 4.19 N 3 = 1.922860 ν3 = 18.9
R 6 = -57.843 D 6 = 3.48 N 4 = 2.003300 ν4 = 28.3
R 7 = 52.764 D 7 = 3.80

(Main lens system)
f = 46.728
R 1 = 45.439 D 1 = 1.05 N 1 = 1.846660 ν1 = 23.9
R 2 = 21.972 D 2 = 4.42 N 2 = 1.603112 ν2 = 60.6
R 3 = -175.910 D 3 = 0.17
R 4 = 18.527 D 4 = 2.68 N 3 = 1.772499 ν3 = 49.6
R 5 = 49.994 D 5 = 15.72
R 6 = 40.310 D 6 = 0.60 N 4 = 1.846660 ν4 = 23.9
R 7 = 6.119 D 7 = 2.00
R 8 = -15.571 D 8 = 0.60 N 5 = 1.772499 ν5 = 49.6
R 9 = 15.571 D 9 = 1.70
R10 = 14.649 D10 = 2.27 N 6 = 1.846660 ν6 = 23.9
R11 = -11.573 D11 = 0.07
R12 = -10.432 D12 = 0.60 N 7 = 1.772499 ν7 = 49.6
R13 = 49.276 D13 = 0.65
R14 = 9.009 D14 = 2.13 N 8 = 1.693500 ν8 = 53.2
R15 = 146.263 D15 = 1.25
R16 = ∞ (aperture) D16 = 2.62
R17 = 17.860 D17 = 0.60 N 9 = 1.846660 ν9 = 23.9
R18 = 7.660 D18 = 0.45
R19 = 14.925 D19 = 1.34 N10 = 1.603112 ν10 = 60.6
R20 = -247.566 D20 = 5.54
R21 = 11.668 D21 = 2.74 N11 = 1.712995 ν11 = 53.9
R22 = -9.023 D22 = 0.50 N12 = 1.846660 ν12 = 23.9
R23 = -46.321 D23 = 3.32
R24 = ∞ D24 = 2.40 N13 = 1.516330 ν13 = 64.1
R25 = ∞

R14 (Aspherical)
K = -1.86050e-01
B = -1.18491e-04 C = -6.43582e-07 D = 6.57163e-11 E = -1.34365e-12

  Next, an embodiment of an imaging apparatus capable of mounting the converter lens of the present invention in front of the photographing optical system will be described with reference to FIG.

  In FIG. 8, 10 is a video camera body, 11 is a photographic optical system, 12 is a solid-state image sensor (photoelectric conversion element) such as a CCD sensor or a CMOS sensor that receives a subject image formed by the photographic optical system 11, and 13 is an image sensor. A memory for recording information corresponding to the subject image photoelectrically converted by the element 12, 14 a viewfinder for observing the subject image displayed on a display element (not shown), and 15 a converter lens of the present invention. The display element is constituted by a liquid crystal panel or the like, and a subject image formed on the image sensor 12 is displayed.

  By configuring the converter lens of the present invention so as to be detachable in front of the photographing optical system of such an imaging apparatus such as a video camera, the focal length of the entire optical system can be displaced.

C Teleconverter M Photography lens (main lens system)
L1 front group L2 rear group SP aperture stop P glass block I image plane d d line g g line c c line f f line ΔM d line meridional ΔS d line sagittal

Claims (6)

  A front converter lens composed of a front group having a positive refractive power and a rear group having a negative refractive power disposed behind the front group, and is detachable in front of the main lens system. A front converter lens having a positive lens, wherein all the lenses are spaced apart, and the rear group includes a positive lens and a negative lens.   2. The front converter lens according to claim 1, wherein the image side surface of the positive lens disposed closest to the object side has a convex shape. When the radius of curvature of the image side surface of the positive lens disposed closest to the object side is RI, and the radius of curvature of the object side surface of the positive lens disposed closest to the image side of the front group is RO,
｜ RI ｜ ＞ ｜ RO ｜
The front converter lens according to claim 1, wherein the following condition is satisfied. When the radius of curvature of the image side surface of the positive lens disposed closest to the object side is RI, and the radius of curvature of the object side surface of the positive lens disposed closest to the image side of the front group is RO,
5 <| RI / RO |
The front converter lens according to claim 1, wherein the following condition is satisfied.   The front converter lens according to claim 1, wherein the object side surface of the positive lens arranged closest to the object side has a convex shape. When the focal length of the front group and the focal length of the rear group are fP and fN, respectively,
1.5 <| fP / fN | <3.0
The front converter lens according to claim 1, wherein the following condition is satisfied.

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