KR100585603B1 - Wide angle converter lens - Google Patents

Abstract

A wide-angle converter lens mounted to a master lens is disclosed.

The disclosed wide-angle converter lens is positioned on the object side of the master lens system and has a negative refractive power from the object side to the image in the wide-angle converter lens for shortening the focal length of the master lens system by constituting the afocal system as a whole. And a first lens, and a second lens having positive refractive power, wherein the first lens is a meniscus lens having a convex object-side surface, and the second lens has a relatively strong convex shape with respect to the image-side surface. It is characterized by satisfying the following conditional expression.

<Conditional expression>

Here, f1 is a focal length of the first lens, and R1 represents an effective radius of the first lens.

By the above configuration, the wide-angle converter lens of the present invention is well corrected for aberration and miniaturized.

Description

Wide angle converter lens

1 shows a front wide-angle converter lens disclosed in Japanese Patent Laid-Open No. 1993-264,901.

2 shows a front wide-angle converter lens disclosed in Japanese Patent Laid-Open No. 2001-255,460.

3A is a block diagram of a wide-angle converter lens according to the first embodiment of the present invention.

3B illustrates longitudinal spherical aberration, image curvature, and distortion aberration in the wide-angle converter lens according to the first embodiment of the present invention.

3C illustrates coma aberration in the wide-angle converter lens according to the first embodiment of the present invention.

4A is a block diagram of a wide-angle converter lens according to a second embodiment of the present invention.

4B illustrates longitudinal spherical aberration, image curvature, and distortion aberration in the wide-angle converter lens according to the second embodiment of the present invention.

4C illustrates coma aberration in the wide-angle converter lens according to the second embodiment of the present invention.

5A is a block diagram of a wide-angle converter lens according to a third embodiment of the present invention.

5B illustrates longitudinal spherical aberration, image curvature, and distortion aberration in the wide-angle converter lens according to the third embodiment of the present invention.

5C illustrates coma aberration in the wide-angle converter lens according to the third embodiment of the present invention.

6A is a block diagram of a wide-angle converter lens according to a fourth embodiment of the present invention.

6B illustrates longitudinal spherical aberration, image curvature, and distortion aberration in the wide-angle converter lens according to the fourth embodiment of the present invention.

6C illustrates coma aberration in the wide-angle converter lens according to the fourth embodiment of the present invention.

<Description of main part of drawing>

C ... wide-angle converter lens, M ... master lens

ST ... aperture, 50 ... first lens

53 ... second lens

The present invention relates to a wide-angle converter lens, and more particularly, to a high-performance wide-angle converter lens that constitutes an afocal system as a whole, widens the angle of view of the master lens system, and is well corrected for distortion aberration.

The wide-angle converter lens is mounted on the object side of the master lens for camera shooting, and serves to widen the field of view by simply shortening the focal length of the electric field without changing the F number.

1 shows a front wide-angle converter lens C disclosed in Japanese Patent Laid-Open No. 1993-264,901. This wide-angle converter lens C is attached to the master lens M and consists of two lenses. A first lens 10 having negative refractive power and a second lens 13 having positive refractive power are provided in order from the object side O to the image side I.

When the focal length of the first lens 10 is f ₁ , the effective radius of the first lens is R ₁ , and the refractive index of the first lens 10 is n ₁ , the first lens 10 has the following conditions: Satisfies

The wide-angle converter lens that satisfies the above Equation 1 has an apocal magnification of about 0.7, and the distortion aberration is well corrected, but it is difficult to miniaturize due to the small refractive power.

2 shows a front wide-angle converter lens disclosed in Japanese Patent Laid-Open No. 2001-255,460. The disclosed wide-angle converter lens C is mounted in front of the master lens M, and has a meniscus-shaped negative lens 20 having an object side O as a convex surface and an object side O compared to the image side I. It consists of the positive lens 22 which has a convex surface strong in ().

Here, the radius of curvature of the positive lens 20 is r ₁ , the focal length is f ₁ , the effective radius is ER ₁ , the thickness of the positive lens 20 d ₁ , the thickness of the negative lens 20 d ₃ , positive When the distance between the lens and the negative lens is d ₂ , the wide-angle converter lens satisfies the following condition.

In the above configuration, the afocal magnification has a value of 0.9 or less, but there is a problem in that the distance between the wide-angle converter lens C and the master lens M is short. In order to sufficiently secure the distance between the wide-angle converter lens C and the master lens M, the lens is enlarged in size. In addition, aberration correction is difficult.

The present invention has been made to solve the above problems, and implements a wide-angle converter lens that can achieve affinity magnification of 0.75 or less, achieve a miniaturization and light weight, and the distortion aberration is well corrected to widen the field of view of the master lens system. The purpose is to provide.

In order to achieve the above object, the wide-angle converter lens according to the present invention is located on the object side of the master lens system, and constitutes an afocal system as a whole to reduce the focal length of the master lens system. A first lens having a negative refractive power from a side to an image side and a second lens having a positive refractive power, wherein the first lens is a meniscus lens having a convex object-side surface, and the second lens having an image-side surface. The object side surface has a relatively strong convex shape and is characterized by the following conditional expression.

<Conditional expression>

Here, f1 is a focal length of the first lens, and R1 represents an effective radius of the first lens.

The first lens and the second lens are characterized by satisfying the following conditional expression.

<Conditional expression>

Here, the thickness of the first lens is d ₁ , the thickness of the second lens is d ₃ , the distance between the first lens and the second lens is d ₂ , and the effective radius of the first lens is r _1. It is called.

When the Abbe number of the first lens is v1 and the Abbe number of the second lens is v2, the first and second lenses satisfy the following conditional expression.

<Conditional expression>

In order to achieve the above object, the wide-angle converter lens according to the present invention is located on the object side of the master lens system, and constitutes an afocal system as a whole to shorten the focal length of the master lens system. A first lens having a negative refractive power and a second lens having a positive refractive power from an image side to an image side, wherein the first lens is a meniscus lens having a convex object-side surface, and the second lens being an object side with respect to the image-side surface. The surface has a relatively strong convex shape and is characterized by the following conditional expression.

<Conditional expression>

Here, the thickness of the first lens is d ₁ , the thickness of the second lens is d ₃ , the distance between the first lens and the second lens is d ₂ , and the effective radius of the first lens is r _1. It is called.

The focal magnification of the wide-angle converter lens is characterized in that less than 0.75.

At least one surface of the second lens is aspherical.

Hereinafter, a wide-angle converter lens according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

Referring to FIG. 3A, the wide-angle converter lens C according to the present invention is located on the object side O of the master lens M. FIG.

The wide-angle converter lens C includes a first lens 50 having negative refractive power and a second lens 53 having positive refractive power, and form an afocal system as a whole.

The wide-angle converter lens according to the present invention is mounted on the object side of the master lens system and has an afocal magnification of 0.75 or less. The first lens 50 having the negative refractive power and the second lens 53 having the positive refractive power are arranged in the order of the image side I from the object side O. FIG.

The first lens 50 is a meniscus type having a convex surface on the object side, and the second lens 53 is a lens having a convex surface that is stronger on the object side O than the image side I, and at least one surface. It is provided with an aspherical surface.

In the focal system composed of the first lens 50 and the second lens, the distance between the two lenses is d, the focal length of the first lens is f ₁ , and the focal length of the second lens is f ₂ . Then, the following relation is established.

d` = `f_1` + `f_2

And when the focal magnification of an afocal system is m, the afocal magnification is as follows.

From the equations (3) and (4), the distance d between the first lens and the second lens may be expressed as follows.

d` = `f_2 (1-m)

Referring to the above equations, it is preferable to reduce the sum of the focal lengths of the two lenses and to increase the refractive power (= 1 / f ₂ ) of the second lens in order to miniaturize the afocal system. When the magnification of the afocal system is determined, if the refractive power of the second lens is large, the refractive power of the first lens is also large. However, when the refractive power of the first and second lenses is increased for miniaturization, it is difficult to correct aberration, in particular, correction of negative distortion aberration.

In view of this point, the preferred range of the focal length of the first lens to be small in size and to satisfactorily correct the aberration is determined according to the effective radius.

The first lens 50 preferably satisfies the following conditions.

Here, f1 represents a focal length of the first lens, and r ₁ represents an effective radius of the first lens 50.

Equation 6 shows the ratio of the focal length f ₁ and the effective radius r ₁ of the _first lens, and the focal length of the lens is determined according to the effective radius size of the lens. When the condition of Equation 6 is satisfied, a compact lens system in which spherical aberration, astigmatism, chromatic aberration, and distortion aberration is well corrected can be realized.

When the upper limit value of Equation 6 is exceeded, the refractive power of the first lens is weakened, so it is difficult to realize miniaturization of the converter lens. Conversely, when the value is equal to or lower than the lower limit of the expression (6), the refractive power of the first lens is increased, which makes it difficult to correct the distortion aberration.

On the other hand, the afocal magnification can also be defined as the ratio between the incident pupil and the exit pupil of the lens system. A wide-angle converter lens having an apocalypical magnification of 0.75 or less has a light beam having a height of one light beam incident in parallel with the optical axis from an infinitely distant object. The lens is configured to be 1.33 times or more the height of the light beam incident in parallel to the master lens system. The distance from the master lens system to the converter lens is determined so that the combined focal length after mounting the converter lens is 0.75 times or less of the focal length of the master lens system.

Next, the thickness of the first lens 50 is d ₁ , the thickness of the second lens 53 is d ₃ , and the distance between the first lens 50 and the second lens 53 is d ₂ . When the effective radius of the first lens 50 is r ₁ , it is preferable to satisfy the following conditions for miniaturization of the lens system.

Equation 7 is the sum of the thickness d ₁ (d ₃ ) of the first lens 50 and the second lens 53 and the distance d ₂ between the two lenses and the effective radius r ₁ of the first lens. It shows the ratio of. When the upper limit value of the condition according to Equation 7 is exceeded, it is difficult to correct the chromatic aberration of magnification, and conversely, when the value is lower than the lower limit value, the radius of curvature of the object-side of the second lens becomes smaller and the correction of astigmatism is difficult, and other aberration correction is performed. It becomes difficult to form aspherical surfaces.

Next, as a condition regarding the material of the lens, spherical aberration, image curvature, magnification chromatic aberration, etc. are corrected by using a material having a low dispersion of high refractive index in the first lens 50, and the second lens 53 uses a plastic material. It is preferable to use. When the Abbe number of the first lens is ν ₁ and the Abbe number of the second lens is ν ₂ , it is preferable that the following conditional expression is satisfied.

When the upper limit value of Equation 8 is exceeded, it is difficult to control longitudinal chromatic aberration, and when it has a value lower than or equal to the lower limit, correction of magnification chromatic aberration and coma aberration is difficult. In particular, when the second lens 53 is made of a plastic material, when the above Equation 8 is satisfied, a small wide-angle converter lens having sufficiently corrected magnification chromatic aberration can be obtained.

Next, the definition of the aspherical surface provided in the embodiment of the present invention is as follows.

The aspherical surface can be expressed by the following equation with the X-axis as the optical axis direction and the Y-axis as the direction perpendicular to the optical axis direction. Where x is the distance from the vertex of the lens in the optical axis direction, y is the distance in the direction perpendicular to the optical axis, K is the conic constant, A, B, C, D is the aspherical coefficient, c represents the inverse of the radius of curvature (1 / R) at the vertex of the lens, respectively.

In this way, the aspherical lens can be appropriately arranged to mass-produce while lowering the manufacturing cost of the zoom lens.

The following shows embodiments of the wide-angle converter lens according to the present invention. Hereinafter, R denotes a radius of curvature, dn (n denotes a natural number) denotes the center thickness of the lens or an interval between the lens and the lens, N _d denotes a refractive index, and ν _d denotes an Abbe number.

<Example 1>

The first embodiment is shown in FIG. 3A and has an apocalation magnification m = 0.75.

     if      Radius (R)     Thickness (dn) N _D ν _D      S1   14.67800    0.80000    1.83400   37.34      S2    5.33100    3.57000      S3    9.15800    2.02000    1.58547   29.9      S4   -69.33400    3.10988    Aspherical surface coefficient S3 K: -1.6258E + 1 A: 2.7387E-3 B: -1.5344E-4 C: 7.6389E-6 D: -1.7729E-7    Aspheric surface coefficient S4 K: 2.2536E + 2 A: -4.0176E-5 B: -2.7212E-6 C: -1.5031E-7 D: -7.2605E-9

The results of measuring longitudinal spherical aberration, image curvature and distortion aberration of the converter lens configured as described above are shown in FIG. 3B, and coma aberration is shown in FIG. 3C. According to this result, it can be seen that the aberration is well corrected.

<Example 2>

A second embodiment is shown in Fig. 4A, with apocalation magnification m = 0.725.

      if     Radius (R)     Thickness (dn) N _D ν _D       S1   15.90000   0.75000    1.83400    37.34       S2    5.82700   4.18000       S3   11.31100   2.89000    1.58547    29.9       S4  -45.47500   3.80000     Aspherical surface coefficient S3 K: 2.6901E-1 A: 7.4081E-5 B: 2.4734E-6 C: -6.6883E-7 D: 3.4187E-8     S4 Surface Aspheric Coefficient K: 8.0950E + 1 A: -1.2591E-4 B: 5.8433E-8 C: -3.3903E-7 D: 3.8070E-8

The results of measuring longitudinal spherical aberration, image surface curvature, and distortion aberration of the converter lens according to the second embodiment are shown in FIG. 4B, and coma aberration is shown in FIG. 4C.

<Example 3>

A third embodiment is shown in FIG. 5A, with apocalation m = 0.75.

    if     Radius (R)     Thickness (dn) N _D ν _D      S1   16.23200    0.80000   1.83400   37.34      S2    5.36800    3.28000      S3    9.09600    2.19000   1.58547   29.9      S4   -45.55900    3.22000     Aspherical surface coefficient S3 K ::-5.0155E-1 A: 1.0685E-3 B: -2.5755E-5 C: -8.6833E-7 D: 1.2714E-7     Aspherical surface coefficient S4 K: -1.2711E + 2 A: 9.1691E-4 B: -1.3243E-4 C: 7.6680E-6 D: -1.0664E-7

Longitudinal spherical aberration, image curvature, and distortion aberration of the converter lens according to the third embodiment are shown in FIG. 5B, and coma aberration is shown in FIG. 5C.

<Example 4>

A fourth embodiment is shown in Fig. 6A, with an apocalation m = 0.75.

      if     Radius (R)    Thickness (dn) N _D ν _D       S1   14.9060   0.80000    1.752742    33.12       S2    5.30700   3.52000       S3    8.82500   2.06000    1.607000    27.59       S4  -80.91700   3.11000     Aspherical surface coefficient S3 K: -2.0236E-1 A: 0.3408E-3 B: 0.6322E-5 C: 0.3930E-6 D: 0.1711E-8

The results of measuring longitudinal spherical aberration, image curvature and distortion aberration of the converter lens according to the fourth embodiment are shown in FIG. 6B, and coma aberration is shown in FIG. 6C.

On the other hand, the master lens (M) to which the wide-angle converter lens according to the invention is mounted may have the following configuration. The master lens M includes five lenses of the third, fourth, fifth, sixth, and seventh lenses 55, 57, 59, 61, and 63, the infrared filter 65, and the cover glass 67. An example configuration is shown. In addition, an aperture stop ST is disposed between the third lens 55 and the fourth lens 57. In the following, f denotes the combined focal length of the lens system, Fno denotes the F number, 2ω denotes the angle of view, R denotes the radius of curvature, and dn (n denotes the natural number) denotes the center thickness of the lens or the distance between the lens and the lens. , N _D represents a refractive index and ν _D represents an Abbe's number, respectively.

f; 5.6 Fno; 2.8 2ω; 62.43      if      Radius (R)    Thickness (dn) N _D ν _D      S5    infinity   0.550000    1.51680    64.20      S6    infinity   1.230000      ST    infinity   0.280000      S7    5.35700   1.290000   1.83500    43.0      S8   -26.7340   0.790000      S9   -3.50000   0.500000   1.84700    23.8      S10   15.89600   0.180000      S11   -40.8120   2.190000   1.74300    49.3        K: 0.00000 A: 0.574890E-2 B: -0.353319E-2 C: 0.793086E-3 D: -0.513107E-4      S12   -2.72000   0.100000        K: -1.532735 A: -0.149553E-1 B; 0.370413E-2 C: -0.753572E-3 D: 0.598484E-4      S13    2.60100   0.800000  1.60700    27.6        K: -5.745605 A: -0.105599E-1 B: -0.319804E-2 C: 0.4203106E-3 D: -0.110990E-4      S14   2.08600   1.581000        K: -1.547321 A: -0.407695E-1 B: 0.280992E-2 C: -0.127053E-3 D: 0.463035E-5      S15    infinity   0.550000   1.51680    64.20      S16    infinity   0.200000      S17    infinity   0.500000   1.51680    64.20      S18    infinity   1.000000      SI    infinity   0.000000

The wide-angle converter lens according to the embodiment satisfies the conditions according to Equations 6, 7, and 8, which are summarized as follows.

  Example 1  Example 2   Example 3   Example 4  Equation 6    1.81    1.75    1.74    1.80  Equation 7    1.11    1.21    1.10    1.12  Equation 8    1.24    1.24    1.24    1.21

By satisfying the equations (6), (7) and (8) in the wide-angle converter lens, the aberration can be well corrected and at the same time miniaturized.

As described above, the wide-angle converter lens according to the present invention is mounted on a master lens for photographing to easily shorten the focal length of the master lens, and aberrations are well corrected, including two lenses, a negative lens and a positive lens, Miniaturization is possible.

Claims (7)

A wide-angle converter lens positioned on an object side of a master lens system and configured to shorten a focal length of the master lens system by forming an afocal system as a whole. A first lens having a negative refractive power from an object side to an image side, and a second lens having a positive refractive power, wherein the first lens is a meniscus lens having a convex object side surface, and a second lens having an image side surface A wide-angle converter lens having a relatively strong convex shape on an object side surface and satisfying the following conditional expression. <Conditional expression>

Here, f1 is a focal length of the first lens, and R1 represents an effective radius of the first lens. The method of claim 1, And the first lens and the second lens satisfy the following conditional expressions. <Conditional expression>

Here, the thickness of the first lens is d ₁ , the thickness of the second lens is d ₃ , the distance between the first lens and the second lens is d ₂ , and the effective radius of the first lens is r _1. It is called. The method according to claim 1 or 2, And when the Abbe number of the first lens is v1 and the Abbe number of the second lens is v2, the first and second lenses satisfy the following conditional expression. <Conditional expression>

A wide-angle converter lens positioned on an object side of a master lens system and configured to shorten a focal length of the master lens system by forming an afocal system as a whole. A first lens having a negative refractive power from an object side to an image side, and a second lens having a positive refractive power, wherein the first lens is a meniscus lens having a convex object side surface, and a second lens having an image side surface An object-side surface has a relatively strong convex shape, and satisfies the following conditional expression. <Conditional expression>

Here, the thickness of the first lens is d ₁ , the thickness of the second lens is d ₃ , the distance between the first lens and the second lens is d ₂ , and the effective radius of the first lens is r _1. It is called. The method of claim 4, wherein And when the Abbe number of the first lens is v1 and the Abbe number of the second lens is v2, the first and second lenses satisfy the following conditional expression. <Conditional expression>

The method according to claim 1, 2, 4 or 5, A wide-angle converter lens, characterized in that the focal magnification of the wide-angle converter lens is 0.75 or less. The method according to claim 1, 2, 4 or 5, The second lens is a wide-angle converter lens, characterized in that at least one surface is formed of a plastic material of aspherical surface.

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