Patent Grant
7009780
1. Field of the Invention
The present invention relates to a zoom lens used in a silver-halide camera, a digital camera, a video camera or the like.
2. Description of the Related Art
Conventionally, in a zoom lens used in a silver-halide camera, a digital camera, a video camera or the like, it is known as a method for focusing from an object at the infinite distance to an object at a near distance to shift whole or a part of one unit out of lens units that change mutual spaces during a zooming operation (For example, refer to Japanese Patent Application Preliminary Publication (KOKAI) No. Hei 3-289612 or Japanese Patent Application Preliminary Publication (KOKAI) No. Hei 3-228008).
There is a type including four units having positive-negative-negative-positive power arrangement in order from the object side and performing focusing by shifting the positive first lens unit toward the object side, as in the method shown in KOKAI No. Hei 3-289612. Also, there is another type including three lens units having positive-negative-positive power arrangement in order from the object side and performing focusing by shifting forth the negative second lens unit toward the object side as in the method shown in KOKAI No. Hei 3-228008.
A zoom lens according to the present invention includes, in order from the object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a negative refractive power, and a fourth lens unit having a positive refractive power, wherein, during a magnification change from the wide-angle end through the telephoto end, the first lens unit and the fourth lens unit shift from the image-surface side toward the object side, a space between the first lens unit and the second lens unit increases, and spaces between individual lens units change, and wherein, during a focusing from an object at the infinite distance onto an object at a near distance, the second lens unit and the third lens unit individually shift independently.
Also, a zoom lens according to the present invention includes, in order from the object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a negative refractive power, and a fourth lens unit having a positive refractive power, wherein, during a magnification change from the wide-angle end through the telephoto end, the first lens unit and the fourth lens unit shift from the image-surface side toward the object side, a space between the first lens unit and the second lens unit increases, and spaces between the individual lens units change, wherein, during a focusing from an object at the infinite distance onto an object at a near distance, the second lens unit and the third lens unit individually shift independently, and wherein, for a focusing from an object at the infinite distance onto an object at any finite distance between the infinite distance and the proximate distance, amount of shift of the second lens unit and the third lens unit have predetermined values differing by zooming state.
Furthermore, a zoom lens according to the present invention includes, in order from the object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a negative refractive power, and a fourth lens unit having a positive refractive power, wherein, during a magnification change from the wide-angle end through the telephoto end, the first lens unit and the fourth lens unit shift from the image-surface side toward the object side, a space between the first lens unit and the second lens unit increases, and spaces between individual lens units change, wherein, during a focusing from an object at the infinite distance onto an object at a near distance, the second lens unit and the third lens unit individually shift independently, wherein, for a focusing from an object at the infinite distance onto an object at any finite distance between the infinite distance and the proximate distance, amount of shift of the second lens unit and the third lens unit have predetermined values differing by zooming state, and wherein the following condition is satisfied:
−2<X2w/X3W<0.5
where X2W is an amount of shift of the second lens unit and X3W is an amount of shift of the third lens unit for a focusing from the infinite distance to the proximate distance at the wide-angle end, upon a shift toward the image-surface side being given a positive value.
According to the present invention, it is possible to provide a zoom lens in which fluctuation of aberrations involved in focusing is stayed small and in which the proximate distance is designed sufficiently close without size increase of the lens system.
These features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments when taken in conjunction with the accompanying drawings.
Preceding the explanation of the embodiments shown in the drawings, function and effect of the present invention are described below.
Regarding a zoom lens according to the present invention, it is possible to achieve small fluctuation of aberrations involved in focusing and to design the proximate distance to be sufficiently close without size increase of the lens system, by performing focusing by way of shifting each of the plurality of lens units in the zoom lens independently for an optimum amount in each zoom state. To be specific, in a zoom lens including a positive first lens unit, a negative second lens unit, a negative third lens unit, and a positive fourth lens unit with the first lens unit and the fourth lens unit shifting toward the object side and a space between the first lens unit and the second lens unit increasing during a magnification change from the wide-angle end through the telephoto end, configuration is made so that the second lens unit and the third lens unit individually shift independently during a focusing from an object at the infinite distance onto an object at a near distance.
If the focusing be made by shifting forth the second lens unit as stated above at the wide-angle end, it would be necessary, for the purpose of setting the proximate distance to be sufficiently close, to secure a wide space between the first lens unit and the second lens unit under the condition where the infinite distance is in focus. As a result, a lens diameter of the first lens unit would be rendered large. In addition, shift of the second lens unit would cause the problem of large fluctuation of astigmatism, distortion or the like. According to the present invention, the focusing is made by shifting forth mainly the third lens unit at the wide-angle end, to dispense with an extra space between the first lens unit and the second lens unit and to stay fluctuation of aberrations small. In addition, by shifting back the second lens unit toward the image-surface side by an amount smaller than the amount of shift of the third lens unit at the same time as the third lens unit is shifted forth toward the object side, fluctuation of aberrations involved in the shift of the third lens unit can cancel. Here, it is preferable to satisfy the following condition:
−2<X2w/X3W<0.5 (1)
where X2W is an amount of shift of the second lens unit and X3W is an amount of shift of the third lens unit for the focusing at the wide-angle end, with a shift toward the image-surface side being given a positive value.
Condition (1) specifies a ratio of the amount of shift of the second lens unit to the amount of shift of the third lens unit for the focusing. If the upper limit of Condition (1) is exceeded, the amount of shift of the second lens unit toward the object side is large, to result in a large lens diameter of the first lens unit and increase in fluctuation of aberrations during the focusing, as stated above. If the lower limit of Condition (1) is not reached, the amount of shift back toward the image-surface side of the second lens unit is large, to result in increase in amount of shift of the third lens unit, for a shift of the imaging position caused by the shift of the second lens unit is in the opposite direction to the focusing.
Here, the case where X2W/X3W=0 is explained. Upon designing focusing to be performed by shifting the second lens unit and the third lens unit for respectively independent amount at any position other than the wide-angle end, the configuration can be made so that the second lens unit is not shifted in a focusing at the wide-angle end.
It is much preferable to satisfy the following condition (1′):
−1<X2W/X3W<0.3 (1′)
Furthermore, if the following condition (1″) is satisfied, good focusing operation can be achieved over the full zooming range while precluding a large lens diameter of the first lens unit.
−0.8<X2W/X3W<−0.01 (1″)
Also, for a magnification change, a space between the first lens unit and the second lens unit should be sufficiently wide at the telephoto end. Thus, in order to achieve compact design of the length of the entire zoom lens, it is desirable that a space between the second lens unit and the third lens unit is small. In this case, it is desirable that the focusing is performed by shifting forth both of the second lens unit and the third lens unit. At the telephoto end, the space between the first lens unit and the second lens unit is large and the field angle is small. Thus, since fluctuation of aberrations involved in the shift of the second lens unit is small, the above-mentioned problem at the wide-angle end is not raised, and the proximate distance can be designed sufficiently small without degradation of performance.
In order to configure a system in which spaces for zooming are efficiently used and in which performance fluctuation caused by focusing is small, it is preferable that the second lens unit shifts toward the image side at the wide angle end and toward the object side at the telephoto end during a focusing from an object at the infinite distance onto an object at a finite distance.
In such an inner focus method, amount of shift of focusing lens unit(s) for a focusing onto a certain finite distance inevitably varies with zooming position, irrespective of whether a single lens unit or a plurality of lens units are used for focusing.
In a case where focusing is performed by a single lens unit, once the paraxial power arrangement of the entire system is determined, amount of shift of the focusing lens unit is uniquely determined by the object distance.
According to the present invention, in a case where focusing is performed by shifting a plurality of lens units independently, distribution ratio of amount of shift among the respective lens units may be arbitrarily selected. In this case, for realizing a smooth moving mechanism, it is desirable that, for a focusing from an object at the infinite distance onto an object at a certain finite distance, amount of shift of the second lens unit continuously changes as a zooming state changes from the wide-angle end through the telephoto end.
Also, it is desirable that, for a focusing from an object at the infinite distance onto an object at a certain finite distance, amount of shift of the third lens unit continuously changes as a zooming state changes from the wide-angle end through the telephoto end. In addition, if the configuration is made so that the third lens unit is shifted from the image side toward the object side during a focusing from an object at the infinite distance onto an object at a certain finite distance with its amount of shift increasing as a zooming state is changed from the wide-angle end through the telephoto end, a smooth moving mechanism can be much easily realized. In this configuration, effect of compensation for aberrations by shift of the second lens unit does not abruptly changes dependent on a zooming state, and thus a zoom lens in a good balance as a whole is achieved.
Also, upon expressing a shift of a focus lens by a function curve corresponding to f(Z)+g(L), which curve has a cam shape, where f(Z) and g(L) are cam rotation angle for zooming and cam rotation angle for focusing, respectively, upon taking zooming position Z and object distance L as parameters, it is desirable that distribution ratio of amount of shift for focusing between the respective lens units in each zooming position is set so that each of the second lens unit and the third lens unit can be expressed by an independent function curve corresponding to f(Z)+g(L).
Also, in a case where a focusing is performed by the second and third lens units in a zoom lens having positive-negative-negative-positive arrangement of refractive power with amount of shift of the second lens unit being small at the wide-angle end and increasing as a zooming state changes toward the telephoto side as set forth above, it is desirable that the cam curve of the second lens unit has an extreme value.
Also, it is much preferable to satisfy the following condition (2):
0.001<D12W/D12T<0.1 (2)
where D12W is a space between the first lens unit and the second lens unit at the wide-angle end under the condition where the infinite distance is in focus, and D12T is a space between the first lens unit and the second lens unit at the telephoto end under the condition where the infinite distance is in focus.
If the lower limit of Condition (2) is not reached, the space between the first lens unit and the second lens unit at the wide-angle end is so small that frames of the lens units are likely to interfere. On the other hand, if the upper limit is exceeded, the space between the first lens unit and the second lens unit at the wide-angle end is wide, to render the lens diameter of the first lens unit large.
It is much preferable to satisfy the following condition (2′):
0.005<D12W/D12T<0.07 (2′)
It is still much preferable to satisfy the following condition (2″):
0.01<D12W/D12T<0.05 (2″)
Also, it is preferable to satisfy the following condition (3)
3.0<D23w/D23T<20.0 (3)
where D23W is a space between the second lens unit and the third lens unit at the wide-angle end under the condition where the infinite distance is in focus, and D23T is a space between the second lens unit and the third lens unit at the telephoto end under the condition where the infinite distance is in focus.
Condition (3) specifies a ratio of the space between the second lens unit and the third lens unit at the wide-angle end to the space between the second lens unit and the third lens unit at the telephoto end. If the lower limit of Condition (3) is not reached, variation of the space between the second lens unit and the third lens unit in zooming is small, to less contribute to compensation, by change of the space between the second lens unit and the third lens unit, for fluctuation of aberrations. On the other hand, if the upper limit is exceeded, the space between the second lens unit and the third lens unit at the wide-angle end is large, to less contribute to compact design of the entire length at the wide-angle end.
It is much preferable to satisfy the following condition (3′):
4.0<D23W/D23T<10.0 (3′)
It is still much preferable to satisfy the following condition (3″):
5.0<D23w/D23T<7.0 (3″)
Also, it is preferable to satisfy the following condition (4):
0.7<X2T/X3T<1.5 (4)
where X2T is an amount of shift of the second lens unit for a focusing from the infinite distance onto the proximate distance at the telephoto end, and X3T is an amount of shift of the third lens unit for the focusing from the infinite distance onto the proximate distance at the telephoto end.
Condition (4) specifies a ratio of the amount of shift of the second lens unit to the amount of shift of the third lens unit for the focusing at the telephoto end. If the lower limit of Condition (4) is not reached, the amount of shift of the second lens unit in the focusing is small, and thus the second lens unit and the third lens unit are likely to interfere, to make it difficult to shorten the proximate distance. On the other hand, if the upper limited is exceeded, the amount of shift of the third lens unit in the focusing becomes small, and thus contribution of the third lens unit to the focusing is reduced.
It is much preferable to satisfy the following condition (4′):
0.8<X2T/X3T<1.3 (4′)
It is still much preferable to satisfy the following condition (4″);
0.9<X2T/X3T<1.1 (4′)
In each of the examples above, the upper limit value alone or the lower limit value alone may be specified. Also, a plurality of the conditional expressions may be satisfied simultaneously.
In reference to the drawings and numerical data, the embodiments of the zoom lens according to the present invention are described below.
First Embodiment
As shown in
The first lens unit G11 is composed of, in order from the object side X, a negative first lens L11, a positive second lens L12, and a positive third lens L13. The first lens L11 and the second lens L12 form a cemented lens.
The second lens unit G12 is composed of, in order from the object side X, a negative fourth lens L14, a negative fifth lens L15 with its image-side concave surface being aspherical, a negative sixth lens L16, and a positive seventh lens L17.
The third lens unit G13 is composed of, in order from the object side X, a positive eighth lens L18, and a negative ninth lens L19 with its object-side concave surface being aspherical.
The fourth lens unit G14 is composed of, in order from the object side X, a positive tenth lens L110 with its image-side concave surface being aspherical, a positive eleventh lens L111, a negative twelfth lens L112, a positive thirteenth lens L113, and a negative fourteenth lens L114. Of these lenses, the twelfth lens, the thirteenth lens, and the fourteenth lens form a cemented lens.
The stop S is arranged between the third lens unit G13 and the fourth lens unit G14. The infrared absorption filter FL1, the lowpass filter FL2, and the cover glass FL3 of the CCD or CMOS sensor are arranged on the image side of the fourth lens unit G14 in this order toward the image pickup surface P.
The numerical data of the optical members constituting the zoom lens according to the first embodiment are shown below.
In the numerical data of the first embodiment, r1, r2, . . . denote radii of curvature of the respective lens surfaces, d1, d2, . . . denote thicknesses of or airspaces between the respective lenses, nd1, nd2, . . . are refractive indices of the respective lenses or airspaces ford-line rays, Vd1, vd2, . . . are Abbe's numbers of the respective lenses, Fno. denotes F-number, and f denotes a focal length of the entire system. Values of r, d, and f are in millimeters.
It is noted that an aspherical surface is expressed by the following equation:
z=(y2/r)/[1+{1−(1+K)(y/r)2}1/2]+A4y4+A6y6+A8y8+A10y10
where z is taken along the direction of the optical axis, y is taken along a direction intersecting the optical axis at right angles, a conical coefficient is denoted by K, and aspherical coefficients are denoted by A4, A6, A8, and A10.
These reference symbols are commonly used in the numerical data of the subsequent embodiments also.
aspherical coefficients
(variable space in focusing)
Second Embodiment
As shown in
The first lens unit G21 is composed of, in order from the object side X, a negative first lens L21, a positive second lens L22, and a positive third lens L23. The first lens L21 and the second lens L22 form a cemented lens.
The second lens unit G22 is composed of, in order from the object side X, a negative fourth lens L24, a negative fifth lens L25 with its image-side concave surface being aspherical, a negative sixth lens L26, and a positive seventh lens L27.
The third lens unit G23 is composed of, in order from the object side X, a negative eighth lens L28, a positive ninth lens L29 with its image-side convex surface being aspherical, and a negative tenth lens L210. The eighth lens L28 and the ninth lens L29 form a cemented lens.
The fourth lens unit G24 is composed of, in order from the object side X, a positive eleventh lens L211 with its image-side concave surface being aspherical, a negative twelfth lens L212, a negative thirteenth lens L213, a negative fourteenth lens L214, and a positive fifteenth lens L215. Each lens of the fourth lens unit G24 is constructed as a singlet lens. The stop S is arranged between the third lens unit G23 and the fourth lens unit G24. The image pickup surface P is arranged on the image side of the fourth lens unit G24.
This embodiment specifies a zoom lens having focal length of 14.71{tilde over ( )}53.88 mm, F-number of 2.85{tilde over ( )}3.75, and 2ω=74.58°{tilde over ( )}23.49°.
aspherical coefficients
(variable space in focusing)
Third Embodiment
As shown in
The first lens unit G31 is composed of, in order from the object side X, a negative first lens L31, a positive second lens L32, and a positive third lens L33. The first lens L31 and the second lens L32 form a cemented lens.
The second lens unit G32 is composed of, in order from the object side X, a negative fourth lens L34, a negative fifth lens L35, a negative sixth lens L36 with its image-side concave surface being aspherical, and a positive seventh lens L37.
The third lens unit G33 is composed of, in order from the object side X, a negative eighth lens L38, a positive ninth lens L39, and a negative tenth lens L310 with its object-side concave surface being aspherical. The eighth lens L38 and the ninth lens L39 form a cemented lens.
The fourth lens unit G34 is composed of, in order from the object side X, a positive eleventh lens L311 with its image-side concave surface being aspherical, a negative twelfth lens L312, a positive thirteenth lens L313, a negative fourteenth lens L314, and a positive fifteenth lens L315. Of these lenses of the fourth lens unit, each pair of the twelfth lens L312 and the thirteenth lens L313, and the fourteenth lens L314 and the fifteenth lens L315 form a cemented lens. The stop S is arranged between the third lens unit G33 and the fourth lens unit G34. The infrared absorption filter FL1, the filter FL2, and the lowpass filter FL3 are arranged behind the fourth lens unit G34. In addition, the cover glass FL4 is arranged on the image pickup surface P formed of a CCD or CMOS sensor.
This embodiment specifies a zoom lens having focal length of 14.69{tilde over ( )}53.09 mm, F-number of 2.85{tilde over ( )}3.57, and 2ω=74.34°{tilde over ( )}23.7°.
aspherical coefficients
(variable space in focusing)
Fourth Embodiment
As shown in
The first lens unit G41 is composed of, in order from the object side X, a negative first lens L41, a positive second lens L42, and a positive third lens L43. The first lens L41 and the second lens L42 form a cemented lens.
The second lens unit G42 is composed of, in order from the object side X, a negative fourth lens L44, a negative fifth lens L45, a negative sixth lens L46, and a positive seventh lens L47.
The third lens unit G43 is composed of, in order from the object side X, a negative eighth lens L48 with its object-side convex surface being aspherical, a positive ninth lens L49, and a negative tenth lens L410. The eighth lens L48 and the ninth lens L49 form a cemented lens.
The fourth lens unit G44 is composed of, in order from the object side X, a positive eleventh lens L411 with its object-side convex surface being aspherical, a negative twelfth lens L412, a positive thirteenth lens L413 with its object-side convex surface being aspherical, a negative fourteenth lens L414, and a positive fifteenth lens L415. Each pair of the twelfth lens L412 and the thirteenth lens L413, and the fourteenth lens L414 and the fifteenth lens L415 form a cemented lens. The stop S is arranged between the third lens unit G43 and the fourth lens unit G44. On the image side of the lens L415 of the fourth lens unit G44, arranged is the flare cut stop S2 that is shaped substantially as a rectangle, followed by the infrared absorption filter FL1, the filter FL2, the lowpass filter FL3, and the cover glass FL4 arranged in this order toward the image pickup surface P. Also, the image pickup surface P is formed of a CCD or CMOS sensor.
This embodiment specifies a zoom lens having focal length of 14.69{tilde over ( )}53.09 mm, F-number of 2.85{tilde over ( )}3.57, and 2ω=74.34°{tilde over ( )}23.70°.
aspherical coefficients
(variable space in focusing)
The above-described zoom lenses according to the present invention are applicable to silver-halide or digital, single-lens reflex cameras. An application example of these is shown below.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-134803 | May 2003 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5144488 | Endo et al. | Sep 1992 | A |
| 5737128 | Usui | Apr 1998 | A |
| 5898525 | Suzuki | Apr 1999 | A |
| 6002528 | Tomita | Dec 1999 | A |
| 20020063970 | Uzawa et al. | May 2002 | A1 |
| Number | Date | Country |
|---|---|---|
| 03-289612 | Dec 1991 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20050041305 A1 | Feb 2005 | US |
