JPH06324267A - Zoom lens having converter lens - Google Patents

Abstract

PURPOSE:To provide a zoom lens having a converter lens which is capable of simplifying the lens system and easily displacing the focal length of the whole system to a longer side by properly setting the lens system and the converter lens in a rear focus type zoom lens. CONSTITUTION:A main lens system is composed of a first group L1 of a positive refractive power, a second group L2 for variable power having a negative refractive power, a third group L3 of a positive refractive power and a fourth group L4 of a positive refractive power, and an aperture diaphragm SP is arranged in front of the third group L3. At the time of performing power variation from a wide angle end to a telescopic end, the second group L2 is moved to the image plane side shown by an arrow and the fluctuation of the image plane attending the power variation is corrected by moving the fourth group L4. At the time of performing power variation from the telescopic end to the super-telescopic end, the second group L2 is moved to the image plane side and the fourth group L4 to the object side by prescribed amounts as shown by arrows so as to narrow their interval and an attachable and detachable converter lens C having a negative refractive power is inserted to a space generated on the image plane side of the fourth group L4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens having a converter lens suitable for still cameras, cine cameras, video cameras and the like, and more particularly to a negative refracting power converter lens detachable on the image side of the main lens system. By attaching the, the focal length at the telephoto end of the entire system is displaced to a longer side, and the range of zooming is expanded.

[0002]

2. Description of the Related Art Conventionally, various methods for enlarging a variable power range of a zoom lens have been proposed. For example, a so-called rear converter method of expanding the focal length of the entire system by inserting a rear converter lens group having negative refractive power between the final lens surface of the zoom lens and the image surface, and a focal length in front of the zoom lens An afocal converter method (front converter method) has been proposed in which an infinite afocal converter lens group is attached to expand or reduce the focal length of the entire system.

In addition, an extender lens is detachably attached to a part of a relay lens which is fixed during zooming and which constitutes a zoom lens, so that the focal length range of the entire system is displaced to, for example, the long focal length side. There is a built-in extender system, which is proposed in, for example, Japanese Patent Application Laid-Open No. 2-85818.

[0004]

In the rear converter method, the tele ratio can be made relatively small, but it is necessary to satisfactorily correct various aberrations by the rear converter lens group alone. It becomes more complicated and larger. On the other hand, with the afocal converter method, both widening of the zoom lens system and widening of the zoom lens can be performed relatively easily, but since the lens group is mounted in front of the lens, the lens group tends to become large. is there.

In addition, in the built-in extender system, the extender lens itself can be constructed to be relatively small, and even if it is attached to the zoom lens, the entire lens system does not increase in size so much, but the lens configuration becomes complicated and aberration correction becomes difficult. There was a problem that it was difficult to secure the insertion space.

In addition, the rear focus type zoom lens has an advantage that the entire lens system is downsized and quick focusing is possible. However, in the rear focus type zoom lens, there is a problem that it is difficult to secure an insertion space in the method of mounting the converter lens behind the lens system and enlarging the focal length of the entire system to the longer side.

In the rear focus type zoom lens according to the present invention, the focal length of the entire system can be easily displaced to the longer side while simplifying the lens system by appropriately setting the lens system and the converter lens. An object of the present invention is to provide a zoom lens having a converter lens that can be used.

In particular, the present invention uses a part of the lens group of the variable power system at the telephoto end of the variable power system having a variable power lens group and a correction lens group for correcting and focusing the image plane due to the variable power. A converter lens that can be easily displaced to the longer super-telephoto end by moving and moving the lens surface of the variable power system so that the converter lens with negative refractive power is detachably attached. An object is to provide a zoom lens having the same.

[0009]

A zoom lens having a converter lens according to the present invention comprises: (1-1) a zoom lens group for performing zooming in order from the object side, and correction of image plane variation due to zooming. A variable power system having a focusing lens group for focusing, and when the variable power system is at the zoom position at the telephoto end, it is mounted on the image plane side of the variable power system to further increase the focal length of the entire system at the super telephoto end. It is characterized in that it has a detachable negative refractive power converter lens that can be displaced.

(1-2) In order from the object side, the first group of positive refractive power, the second group of negative refractive power, the third group of positive refractive power, and the fourth group of positive refractive power Has two lens groups, the second
The lens unit is moved to the image plane side to change the magnification from the wide-angle end to the telephoto end, and the image plane variation due to the magnification change is corrected by moving the fourth unit and moving the fourth unit. When the main lens system and the main lens system are at the zoom position at the telephoto end, at least one of the second lens group and the fourth lens group is moved on the optical axis and is attached to the image plane side of the fourth lens group. It has a detachable negative refractive power converter lens for displacing the focal length of the entire system to the longer super-telephoto end.

[0011]

1 is an explanatory view of a paraxial refractive power arrangement of a zoom lens according to the present invention, FIGS. 2 and 3 are lens cross-sectional views of Numerical Embodiments 1 and 2 which will be described later, and FIGS. Are aberration diagrams at the telephoto end and the super telephoto end of Numerical Example 1 of the present invention, and FIGS. 6 and 7 are aberration charts at the telephoto end and the super telephoto end of Numerical Example 2 of the present invention.

In FIG. 1, (A) is the wide-angle end for the first variable magnification, (B) is the telephoto end for the first variable magnification, that is, the wide-angle end for the second variable magnification, and (C) is the telephoto end for the second variable magnification. FIG. 7 is an optical layout diagram at a zoom position at an end, that is, a super-telephoto end.

L1 is a first lens group having a positive refractive power, L2 is a second lens group (magnifying lens group) having a negative refractive power for zooming, L3 is a third lens group having a positive refractive power, and L4 is a positive lens group. It is the 4th group (correction lens group) of refractive power. SP is an aperture stop, which is arranged in front of the third lens unit L3. The first lens unit L1 to the fourth lens unit L4 form a main lens system.

At the time of zooming (first zooming) from the wide-angle end in FIG. 1 (A) to the telephoto end in FIG. 1 (B), the second lens group is moved to the image plane side as indicated by the arrow, and zooming is performed. The image plane variation due to is corrected by moving the fourth lens unit.

At the time of zooming (second zooming) from the telephoto end in FIG. 1 (B) to the super telephoto end in FIG. 1 (C), the second lens unit is moved toward the image plane side and the fourth lens unit is moved as indicated by the arrow. Is moved linearly toward the object side by a predetermined amount so that the distance between both lens groups becomes narrow. Then, a detachable converter lens C having a negative refracting power is inserted in a space formed on the image side of the fourth lens unit.

As a result, the space in the lens system is effectively utilized, and a super-telephoto system having a focal length longer than the focal length at the telephoto end in FIG. 1B is obtained.

In this embodiment, from the telephoto end of FIG.
In the second magnification change to the super-telephoto end in (C), only the zoom position at the super-telephoto end in FIG. 1C is used, not in the variable power range.

In the present embodiment, when the second magnification is changed, the second
At least one lens group of the fourth group or the fourth group may be moved non-linearly so as to match the image plane position at the first magnification change and be used in the entire magnification change range.

Further, at the time of zooming from the telephoto end shown in FIG. 1B to the super telephoto end shown in FIG. 1C, at least one of the second lens group and the fourth lens group may be moved. .

As described above, in this embodiment, the second lens unit is zoomed from the zoom position at the telephoto end of the first lens unit, and the space produced when the fourth lens unit is moved to the object side is used to form the converter lens. By removably inserting C, the space in the lens system is efficiently used, and the variable power range is expanded with almost no increase in the total lens length.

The zoom lens of this embodiment employs a rear focus type in which the fourth lens unit is moved on the optical axis for focusing. The solid curve 4a and the dotted curve 4b of the fourth group shown in the same figure represent image plane fluctuations due to zooming from the wide-angle end to the telephoto end when focusing on an object at infinity and a near object, respectively. The movement locus for correction is shown. The first and third groups are fixed during zooming and focusing.

In the present embodiment, the fourth lens unit is moved to correct the image plane variation due to zooming, and the fourth lens unit is moved to perform focusing. Curve 4 in the figure
As shown in a and 4b, the zoom lens is moved so as to have a convex locus toward the object side during zooming from the wide-angle end to the telephoto end.
As a result, the space between the third group and the fourth group is effectively used, and the total lens length is effectively shortened.

In the present embodiment, for example, when focusing from an object at infinity to a near object at the telephoto end, the fourth lens unit is moved forward as indicated by a straight line 4c in the figure.

In the present embodiment, the focal lengths of the fourth lens group and the converter lens are set to f4 and fc, respectively, in order to increase the predetermined focal length at the super-telephoto end and to obtain high optical performance over the entire screen with little aberration variation. Then, it is preferable to satisfy the condition of 0.5 <| fc / f4 | <1.5 (1).

If the lower limit of conditional expression (1) is exceeded and the refracting power of the converter lens becomes too strong, it becomes difficult to correct various aberrations such as axial chromatic aberration and field curvature, and it becomes difficult to obtain high optical performance. come. Further, if the refractive power of the converter lens becomes too weak beyond the upper limit, the expansion ratio of the focal length of the entire system when the converter lens is mounted becomes small, which is not good.

Next, numerical examples of the present invention will be shown. In the numerical examples, Ri is the radius of curvature of the i-th lens surface in order from the object side, Di is the i-th lens thickness and air gap from the object side, and Ni and νi are respectively from the object side of the i-th lens. The refractive index of glass and the Abbe number.

In addition, R26 and R2 in the numerical value embodiment 1
7. R19 and R20 in Numerical Example 2 are glass blocks such as face plates and filters.

The aspherical shape has an X axis in the optical axis direction, an H axis in the direction perpendicular to the optical axis, a positive light traveling direction, and R as a paraxial radius of curvature,
When A, B, C, D, and E are aspherical coefficients, respectively

[0029]

[Equation 1] Or

[0030]

[Equation 2] It is expressed by

Numerical Example 1 f = 1 fno = 1: 1.85 to 4.5 2 ω = 53.3 ° to 3.9 ° R 1 = 7.060 D 1 = 0.17 N 1 = 1.80518 ν 1 = 25.4 R 2 = 3.305 D 2 = 0.78 N 2 = 1.51633 ν 2 = 64.2 R 3 = -11.023 D 3 = 0.03 R 4 = 2.619 D 4 = 0.44 N 3 = 1.62299 ν 3 = 58.2 R 5 = 7.520 D 5 = Variable R 6 = 4.336 D 6 = 0.11 N 4 = 1.66672 ν 4 = 48.3 R 7 = 0.967 D 7 = 0.53 R 8 = -1.292 D 8 = 0.11 N 5 = 1.69680 ν 5 = 55.5 R 9 = 1.271 D 9 = 0.31 N 6 = 1.84666 ν 6 = 23.9 R10 = 29.382 D10 = Variable R11 = (Aperture) D11 = -0.19 R12 = 6.990 D12 = 0.28 N 7 = 1.58313 ν 7 = 59.4 R13 = -4.538 D13 = 0.02 R14 = 2.114 D14 = 0.41 N 8 = 1.51633 ν 8 = 64.2 R15 =- 8.861 D15 = 0.08 R16 = -3.181 D16 = 0.11 N 9 = 1.80518 ν 9 = 25.4 R17 = -10.290 D17 = Variable R18 = 5.016 D18 = 0.11 N10 = 1.84666 ν10 = 23.9 R19 = 1.860 D19 = 0.06 R20 = 2.669 D20 = 0.30 N11 = 1.65844 ν11 = 50.9 R21 = -4.090 D21 = 0.02 R22 = 2.988 D22 = 0.24 N12 = 1.51633 ν12 = 64.2 R23 = -201.264 D23 = variable R24 = -1.854 D24 = 0.13 N13 = 1.49171 ν13 = 57.4 R25 = 2.822 D25 = 0.50 R26 = ∞ D26 = 0.94 N14 = 1.51633 ν14 = 64 .2 R27 = ∞ Aspheric coefficient R24 A = 4.06123 × 10 ^-2 B = 1.1489 × 10 ⁰ C = -6.0738
4 x 10 ⁰ R25 A = 3.21419 x10 ^-2 B = 1.52108 x10 ⁰ C = -8.7715
4 x 10 ⁰

[0032]

[Table 1] │fc / f4│ = 0.69 Numerical Example 2 f = 1 fno = 1: 1.4 to 4.5 2 ω = 53.9 ° to 4.2 ° R 1 = 7.673 D 1 = 0.15 N 1 = 1.80518 ν 1 = 25.4 R 2 = 3.115 D 2 = 0.75 N 2 = 1.62299 ν 2 = 58.2 R 3 = -10.997 D 3 = 0.03 R 4 = 2.388 D 4 = 0.38 N 3 = 1.65844 ν 3 = 50.9 R 5 = 4.269 D 5 = variable R 6 = 2.858 D 6 = 0.08 N 4 = 1.88300 ν 4 = 40.8 R 7 = 0.950 D 7 = 0.48 R 8 = -1.084 D 8 = 0.08 N 5 = 1.60311 ν 5 = 60.7 R 9 = 1.529 D 9 = 0.29 N 6 = 1.84666 ν 6 = 23.8 R10 = -57.081 D10 = Variable R11 = (Aperture) D11 = 0.22 R12 = 2.389 D12 = 0.55 N 7 = 1.58313 ν 7 = 59.4 R13 = -6.402 D13 = 1.16 R14 = 2.359 D14 = 0.09 N 8 = 1.84666 ν 8 = 23.8 R15 = 1.154 D15 = 0.77 N 9 = 1.58313 ν 9 = 59.4 R16 = -3.150 D16 = Variable R17 = 12.436 D17 = 0.15 N10 = 1.48749 ν10 = 70.2 R18 = 1.482 D18 = 0.45 R19 = ∞ D19 = 0.78 N11 = 1.51633 ν11 = 64.2 R20 = ∞ Aspheric coefficient R12 K = -5.50299 × 10 ^-1 L = -2.14710 × 10 ^-2 M =
3.62241 × 10 ^-3 N = -2.31215 × 10 ^-3 R15 K = -3.14981 × 10 ^-1 L = 1.55333 × 10 ^-2 M =-
4.82497 × 10 ^-3 N = -7.71808 × 10 ^-3 R18 A = 1.15418 × 10 ^-1 B = -4.02657 × 10 ^-1 C =
1.84551 × 10 ^-2

[0033]

[Table 2] | Fc / f4 | = 1.05

[0034]

As described above, according to the present invention, in the rear focus type zoom lens, by appropriately setting the lens system and the converter lens, the lens system can be simplified and the focal length of the entire system can be easily adjusted. It is possible to achieve a zoom lens having a converter lens that can be displaced in the long direction.

In particular, according to the present invention, at the telephoto end of the variable power system having the variable power lens group and the correction lens group for correcting and focusing the image plane accompanying the variable power, a part of the variable power system is provided. By moving the lens group and detachably mounting a converter lens having a negative refractive power on the image side of the variable power system, the focal length of the entire system can be easily displaced to a longer super telephoto end. A zoom lens with a converter lens can be achieved.

[Brief description of drawings]

FIG. 1 is an explanatory view of a paraxial refractive power arrangement of a zoom lens according to the present invention.

FIG. 2 is a lens cross-sectional view of Numerical Example 1 of the present invention.

FIG. 3 is a lens cross-sectional view of Numerical Example 2 of the present invention.

FIG. 4 is an aberration diagram at a telephoto end according to Numerical Example 1 of the present invention.

FIG. 5 is an aberration diagram at a super telephoto end according to Numerical Example 1 of the present invention.

FIG. 6 is an aberration diagram at a telephoto end according to Numerical Example 2 of the present invention.

FIG. 7 is an aberration diagram at a super telephoto end according to Numerical Example 2 of the present invention.

[Explanation of symbols]

 L1 1st group L2 2nd group L3 3rd group L4 4th group C converter lens SP diaphragm

Claims (4)

[Claims] 1. A variable power system having a variable power lens group for performing variable power in order from the object side, and a correction lens group for correcting and focusing the image plane due to the variable power, and the variable power system at the telephoto end. And a detachable negative-refractive-power converter lens that is mounted on the image plane side of the variable power system to displace the focal length of the entire system to a longer super-telephoto end. Zoom lens with a characteristic converter lens. 2. Four lens groups, a first group having a positive refractive power, a second group having a negative refractive power, a third group having a positive refractive power, and a fourth group having a positive refractive power, in order from the object side. And moving the second lens group toward the image plane side to perform zooming from the wide-angle end to the telephoto end, and moving the fourth lens group to correct the image plane variation due to zooming and A main lens system for focusing by moving the group, and when the main lens system is at the zoom position at the telephoto end, at least one lens group of the second group and the fourth group is moved on the optical axis and the fourth group is moved. And a detachable negative refracting power converter lens which is mounted on the image plane side to displace the focal length of the entire system to a longer super-telephoto end, and a zoom lens having a converter lens . 3. At the time of displacement from the telephoto end to the super telephoto end, at least one lens group of the second group or the fourth group is moved in a direction in which the distance between the second group and the fourth group becomes narrower. A zoom lens having the converter lens according to claim 2. 4. The condition of 0.5 <| fc / f4 | <1.5 is satisfied when the focal lengths of the fourth lens unit and the converter lens are f4 and fc, respectively. Or a zoom lens with 3 converter lenses.