JP3342157B2 - Wide converter lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wide converter lens which is mounted in front of a photographing lens (also referred to as a master lens) (object side) to displace the focal length of the entire photographing system to a shorter one, and in particular to a photographic camera. The lens system suitable for mounting on a zoom lens or a single focal length lens, such as a zoom lens having a wide angle of view of 30 degrees or more and a half angle of view used in video cameras, is small in size and has high optical performance. The present invention relates to a wide converter lens having

[0002]

2. Description of the Related Art Conventionally, there have been proposed various front type wide converter lenses which are mounted in front of a photographing lens and change the focal length of the entire photographing system to a shorter one while keeping the focal plane of the whole system at a fixed position. Have been.

For example, in Japanese Patent Application Laid-Open No. Sho 59-204817, an afocal system is composed of five lenses, which are composed of a first lens unit having a negative refractive power and a second lens unit having a positive refractive power in order from the object side. A wide converter lens with a focal magnification of about 0.7 is proposed.

In Japanese Patent Application Laid-Open No. 63-253319, 3
A wide converter lens for a finder system or a small camera having an afocal magnification of about 0.6 times has been proposed.

In general, a front-type wide converter lens mounted in front of a photographing lens has an advantage that the F-number and focal plane of the entire system can be kept unchanged even when a wide converter lens is mounted.

[0006]

SUMMARY OF THE INVENTION Recent video cameras
In a still camera and the like, as a photographing lens (master lens) is reduced in size and weight, a wide converter lens to be attached to the lens is also required to be smaller and lighter.

However, when the photographing lens to which the wide converter lens is mounted has a wide angle of view, for example, a zoom lens having a photographing angle of view of 60 degrees or more at the wide angle end, the object of the wide converter lens is required to secure off-axis light flux. The effective diameter of the first lens unit on the side increases. For this reason, it is necessary to perform aberration correction by increasing the number of lenses in the first and subsequent lens units, and as a result, there has been a tendency for the wide converter lens as a whole to become larger.

For example, in Japanese Patent Publication No. 4-34722, a wide converter lens for mounting on a zoom lens (master lens) having a zoom ratio of 6 and a shooting angle of view of 53.2 degrees at the wide-angle end is composed of five lenses. ing.

According to the present invention, there is provided a two-lens as a whole which can be mounted on the object side of a wide-angle photographing lens by appropriately setting the lens configuration and can shift the focal length of the entire system to a shorter one. Provide a wide converter lens that has an afocal magnification of about 0.8, can maintain good optical performance of the entire system when mounted, and reduces the size and weight of the entire lens system. With the goal.

[0010]

A wide converter lens according to the present invention is mounted in front of a photographing lens and displaces the focal length of the entire system to a shorter one. In the wide converter lens, the wide converter lens is sequentially arranged from the object side. It has a first lens having a negative refractive power and a second lens having a positive refractive power, and constitutes an afocal system as a whole. The focal length of the i-th lens is fi, and the radius of curvature of the i-th lens surface is R
i, the refractive index of the material of the i-th lens with respect to the e-line is Ni, d.
When the Abbe number based on the line is νi and the effective diameter of the i-th lens surface is ai

[0011]

(Equation 2) It is characterized by satisfying certain conditions.

[0012]

1, 2 and 3 are sectional views of Examples 1, 2 and 3 when a wide converter lens according to the present invention is mounted in front of a taking lens (master lens).

In FIG. 1, reference numeral WC denotes a wide converter lens, which is composed of an afocal system. The first lens C1 having a negative refractive power and having a stronger negative refractive surface on the image surface side than the object side has both lens surfaces. Second lens C2 having a positive refractive power of a convex surface
Consists of M is a photographing lens (master lens), and FIG. 1 shows a case where a zoom lens is used.

F is a focus unit, V1 is a variator,
V2 is a compensator, and R is a relay lens. S
P is an aperture, G is a color separation prism or filter, etc.
In the figure, it is shown as a glass block.

In the present invention, in order to reduce the weight of the entire wide converter lens, a first lens C1 having a focal length f1 having a negative refractive power and a second lens having a focal length f2 having a positive refractive power are arranged in order from the object side. An afocal system having a magnification of about 0.8 times is constituted by the two sheets of C2.

Since the wide converter lens of the present invention is an afocal system, the object-side focal point of the first lens C1 and the object-side focal point of the second lens coincide with each other. If the principal point interval is e, e-f1 = f2 is satisfied. The afocal magnification is f1 / f2.

In general, a photographing lens itself is satisfactorily aberration-corrected by a photographing lens alone in order to photograph by itself.
Therefore, in order to obtain good overall optical performance when the wide converter lens is mounted, it is necessary to achieve good aberration correction with the wide converter lens alone.

In this embodiment, when the wide converter lens WC is mounted on the zoom lens M, the off-axis light flux enters the first lens highest on the optical axis when the zoom lens is zoomed to the wide-angle end. Correction of external aberration becomes important. When the zoom lens is zoomed to the telephoto end, the on-axis light flux is incident on the second lens at the highest position on the optical axis. At this time, it is important to correct spherical aberration.

Therefore, in the present embodiment, the first lens C1 is a negative lens having concave surfaces on both sides, and the second lens C2 is a positive lens having both convex surfaces. It is composed of a lens and the above-mentioned conditional expressions (1) to
Each element is set so as to satisfy (8).

As a result, the amount of aberration generated by the wide converter lens itself is reduced, and the optical performance of the entire photographing system when attached to the master lens is kept good throughout the zoom range, and a small and lightweight wide converter lens is achieved.

Next, the technical meaning of each of the above conditional expressions will be described.

Conditional expression (1) relates to the ratio of the focal length of the first lens to the focal length of the second lens, and defines the afocal magnification as a wide converter lens. If the lower limit of conditional expression (1) is exceeded, the widening effect of the wide converter lens aimed at by the present invention cannot be sufficiently obtained. On the other hand, when the value exceeds the upper limit, the afocal ratio becomes too large, and it becomes difficult to perform satisfactory aberration correction.

Conditional expression (2) defines the ratio between the focal length of the second lens and the effective diameter of the final lens surface. Second
When the master lens to be mounted is a zoom lens, the effective diameter of the final lens surface of the lens is substantially equal to the effective diameter of the axial light beam at the telephoto end. Conditional expression (2) represents the aperture ratio of the second lens, and indicates the degree of difficulty of aberration correction at the telephoto end.

In conditional expression (2), if the lower limit of the conditional expression (2) is exceeded, the power (refractive power) of the second lens increases, and from the relationship of conditional expression (1), the power of the first lens also increases. It becomes difficult. Conversely, if the upper limit is exceeded,
This is not good because the power of the second lens becomes too small and the entire lens system becomes large.

Conditional expression (3) defines the shape factor of the first lens having a negative refractive power. When the master lens is a zoom lens, in order to reduce distortion on the wide-angle side, it is preferable that the master lens has a meniscus shape concentric with the principal ray, that is, the shape factor is smaller.

However, in this lens shape, since the power of the lens surface on the image surface side of the first lens is increased, spherical aberration on the telephoto side is extremely excessively generated, and correction becomes difficult. In order to correct spherical aberration on the telephoto side, it is preferable that both the object-side lens surface and the image-side lens surface have shapes having negative power, that is, the shape factor is close to zero. However, this shape increases the barrel distortion on the wide-angle side.

Conditional expression (3) shows the lens shape of the first lens capable of appropriately correcting distortion on the wide-angle side and spherical aberration on the telephoto side. If the lower limit value is exceeded, spherical aberration on the telephoto side increases. Conversely, if the value exceeds the upper limit, the barrel distortion on the wide-angle side increases, which is not good.

Conditional expression (4) defines the shape factor of the second lens having a positive refractive power. When the master lens is a zoom lens, the second lens corrects the distortion generated by the preceding first lens on the wide-angle side by the refraction effect of the lens surface on the object side, and also corrects the distortion of the preceding first lens on the telephoto side. Excessive spherical aberration generated on the concave lens surface on the strong image side is corrected.

In order to effectively perform these corrections under the condition regarding the lens shape of the first lens in the conditional expression (3), both the object-side lens surface and the image-side lens surface must be positive. And the curvature of the lens surface on the object side must be greater than the curvature of the lens surface on the image side.

Conditional expression (4) expresses this condition by a shape factor. If the upper limit of conditional expression (4) is exceeded, correction of distortion by the preceding first lens on the wide-angle side becomes insufficient. Conversely, if the lower limit value is exceeded, the overcorrected spherical aberration by the preceding first lens on the telephoto side is insufficiently corrected, which is not good.

Conditional expression (5) relates to the ratio of the radius of curvature of the image-side lens surface of the first lens to the radius of curvature of the object-side lens surface of the second lens, and is mainly based on the image-side lens surface of the first lens. An over-spherical aberration mainly generated is generated on the object-side lens surface of the second lens to generate an under-spherical aberration, and particularly when the master lens is a zoom lens, the spherical aberration on the telephoto side thereof is favorably corrected. Things. Conditional expression (5)
Exceeds the upper limit, excessive spherical aberration by the first lens on the telephoto side is overcorrected. Conversely, if the lower limit is exceeded, the correction becomes insufficient, which is not good.

Conditional expression (6) relates to the ratio of the radius of curvature of the object-side lens surface of the first lens to the radius of curvature of the image-side lens surface of the second lens, and mainly relates to the object-side lens surface of the first lens. The purpose is to generate the over distortion on the image side lens surface of the second lens by the generated under distortion, and to satisfactorily correct the distortion on the wide angle side particularly when the master lens is a zoom lens.

When the value exceeds the upper limit of conditional expression (6), distortion on the wide-angle side is corrected well, but it becomes difficult to correct spherical aberration on the telephoto side. Conversely, when the value exceeds the lower limit, distortion on the wide-angle side is satisfied. Is not good because of insufficient correction.

The conditional expressions (7) and (8) relate to the refractive indexes of the materials of the first lens and the second lens, respectively. Conditional expression (7) is for selecting a material having a refractive index as high as possible to make the first lens group one, and for making the curvature loose. If the refractive index falls below the lower limit of conditional expression (7), the curvature of the lens surface of the first lens becomes strong, and it becomes difficult to correct distortion on the wide-angle side.

Conditional expression (8) is used to reduce the refractive index of the material of the second lens to cancel the negative Petzval sum generated in the first lens, and to increase the curvature to some extent to correct distortion and spherical aberration. belongs to. If conditional expression (8) is not satisfied, it becomes difficult to satisfactorily correct distortion and spherical aberration.

The conditional expressions (9) and (10) relate to the Abbe numbers of the materials of the first lens and the second lens. Conditional expression (9) is for maximizing the Abbe number as much as possible in order to suppress negative axial chromatic aberration since the first lens has strong negative power. If the Abbe number of the material of the first lens deviates from the conditional expression (9), it becomes difficult to satisfactorily correct axial chromatic aberration.

Conditional expression (10) mainly relates to the Abbe number of the second lens for correcting axial chromatic aberration generated in the first lens. If the lower limit of conditional expression (10) is exceeded, axial chromatic aberration will be under-corrected.

Next, numerical examples of the wide converter lens of the present invention and a photographing lens (master lens) to which the wide converter lens is attached will be described.

In the numerical examples, Ri is the radius of curvature of the i-th lens surface in order from the object side, and Di is the i-th lens surface from the object side.
The second lens thickness, the air gap, and Ni and νi are the refractive index and Abbe number of the glass of the ith lens in order from the object side.

Table 1 shows the relationship between the above-described conditional expressions and various numerical values in the numerical examples.

Numerical Embodiment 1 is an example in which the first lens is made of glass having a high refractive index. The curvature of each lens surface can be made relatively gentle, and distortion at the wide-angle end is corrected to be small.

In Numerical Examples 2 and 3, the refractive index of the material of the second lens is selected to be a glass having a somewhat low but large Abbe number, and chromatic aberration is corrected well. The master lens is a high-magnification, wide-field-of-view zoom lens with a zoom ratio of 13, a half angle of view of 31.5 degrees at the wide-angle end, an F-number of 1.6 at the wide-angle end, and an F-number of 1.9 at the telephoto end. .

[Wide Converter Lens] <Numerical Example 1> R 1 = -961.351 D 1 = 2.80 N 1 = 1.73852 ν 1 = 49.8 a 1 = 112.803 R 2 = 157.859 D 2 = 27.03 a 2 = 103.645 R 3 = 185.016 D 3 = 19.03 N 2 = 1.51678 ν 2 = 54.7 a 3 = 87.366 R 4 = -270.185 a 4 = 90.679 <Numerical Example 2> R 1 = -602.952 D 1 = 2.80 N 1 = 1.68108 ν 1 = 50.7 a 1 = 112.523 R 2 = 91.253 D 2 = 34.94 a 2 = 97.160 R 3 = 141.197 D 3 = 13.22 N 2 = 1.54212 ν 2 = 59.5 a 3 = 83.427 R 4 = -200.510 a 4 = 81.967 <Numerical example 3> R 1 = -602.486 D 1 = 2.80 N 1 = 1.68082 ν 1 = 55.3 a 1 = 112.005 R 2 = 90.157 D 2 = 34.43 a 2 = 96.687 R 3 = 138.465 D 3 = 13.16 N 2 = 1.52736 ν 2 = 64.6 a 3 = 83.500 R 4 = -188.075 a 4 = 82.337 [Master lens] <Numerical example> R 1 = 705.470 D 1 = 2.50 N 1 = 1.81264 ν 1 = 25.4 R 2 = 90.710 D 2 = 5.80 R 3 = 528.960 D 3 = 6.20 N 2 = 1.49845 ν 2 = 81.6 R 4 = -189.480 D 4 = 0.17 R 5 = 103.400 D 5 = 12.24 N 3 = 1.43496 ν 3 = 95.1 R 6 = -136.990 D 6 = 0.17 R 7 = 52.570 D 7 = 10.34 N 4 = 1.69979 ν 4 = 55.5 R 8 = 219.360 D 8 = Variable R 9 = 71.980 D 9 = 1.00 N 5 = 1.88814 ν 5 = 40.8 R10 = 17.870 D10 = 3.75 R11 = -110.470 D11 = 0.80 N 6 = 1.80811 ν 6 = 46.6 R12 = 78.620 D12 = 3.80 R13 = -15.560 D13 = 1.00 N 7 = 1.77621 ν 7 = 49.6 R14 = 121.380 D14 = 3.52 N 8 = 1.93306 ν 8 = 21.3 R15 = -31.110 D15 = Variable R16 = -24.590 D16 = 0.90 N 9 = 1.77621 ν 9 = 49.6 R17 = -36.260 D17 = 4.30 N10 = 1.81265 ν10 = 25.4 R18 = -269.500 D18 = Variable R19 = (Aperture) D19 = 2.84 R20 = -176.460 D20 = 3.96 N11 = 1.76168 ν11 = 27.5 R21 = 40.580 D21 = 0.17 R22 = 90.990 D22 = 10.86 N12 = 1.48915 ν12 = 70.2 R23 = -23.600 D23 = 1.30 N13 = 1.83932 ν13 = 37.2 R24 = -54.300 D24 = 21.69 R25 = -1049.550 D25 = 6.25 N14 = 1.60548 ν14 = 60.7 R26 = -47.850 D26 = 0.17 R27 = 95.900 D27 = 1.65 N15 = 1.81265 ν15 = 25.4 R28 = 31.110 D28 = 9.07 N16 = 1.48915 ν16 = 70.2 R29 = -220.140 D29 = 0.17 R30 = 41.330 D30 = 5.74 N17 = 1.48915 ν17 = 70.2 R31 = 208.110 D31 = 8.27 R32 = ∞ D32 = 65.00 N18 = 1.51825 ν18 = 64.2 R33 = 値 Value when a wide converter lens is attached, wide converter lens Distance between the master lens is 10.

F _NO 1.6 to 1.9

[0045]

[Table 1]

[0046]

As described above, according to the present invention, by appropriately setting the lens configuration, the wide-angle photographing lens is mounted on the object side, and the focal length of the entire system is displaced to the shorter side. As a whole, it consists of two lenses, has an afocal magnification of about 0.8, can maintain good optical performance of the entire system when mounted, and is also compact and lightweight as a whole lens system. , A wide converter lens can be achieved.

[Brief description of the drawings]

FIG. 1 is a lens cross-sectional view when a wide converter lens according to Numerical Example 1 of the present invention is mounted on a master lens.

FIG. 2 is a lens cross-sectional view when a wide converter lens according to Numerical Example 2 of the present invention is mounted on a master lens.

FIG. 3 is a lens cross-sectional view when a wide converter lens according to Numerical Example 3 of the present invention is mounted on a master lens.

FIG. 4 is an aberration diagram at a wide-angle end when the wide converter lens according to Numerical Example 1 of the present invention is mounted on a master lens.

FIG. 5 is an aberration diagram at a telephoto end when the wide converter lens according to Numerical Example 1 of the present invention is mounted on a master lens.

FIG. 6 is an aberration diagram at a wide angle end when the wide converter lens according to Numerical Example 2 of the present invention is mounted on a master lens.

FIG. 7 is an aberration diagram at a telephoto end when the wide converter lens according to Numerical Example 2 of the present invention is mounted on a master lens.

FIG. 8 is an aberration diagram at a wide-angle end when the wide converter lens according to Numerical Example 3 of the present invention is mounted on a master lens.

FIG. 9 is an aberration diagram at a telephoto end when the wide converter lens according to Numerical Example 3 of the present invention is mounted on a master lens.

[Explanation of symbols]

 WC wide converter lens M master lens C1 first lens C2 second lens F focus group V variator C compensator R relay lens group g g line ee line ΔS sagittal image plane ΔM meridional image plane

Claims (1)

(57) [Claims] 1. A wide converter lens mounted in front of a photographing lens and displacing the focal length of the entire system to a shorter one, wherein the wide converter lens and a first lens having a negative refractive power and a positive refraction in order from the object side. The second lens has a second lens having a power and constitutes an afocal system as a whole. The focal length of the i-th lens is fi, and the radius of curvature of the i-th lens surface is R.
i, the refractive index of the material of the i-th lens with respect to the e-line is Ni, d.
When the Abbe number based on the line is νi, and the effective diameter of the i-th lens surface is ai. A wide converter lens that satisfies certain conditions.