JP2004078103A - Zoom lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an FB regulation mechanism without requiring energization in manual focusing and without mechanical complication for a zoom lens having two focusing means; front lens manual focusing and rear autofocusing. <P>SOLUTION: The zoom lens consists of, successively from an object side, a positive first group moving during manual focusing, a second group taking charge of zooming, a third group, and a positive fourth group including a group moving during autofocusing. The fourth group is divided to two groups; an FR and BR, one of which is defined as an autofocusing group and the other as an FB group, and for which lateral magnification ranges and achromatism ranges respectively optimum for these groups are set. <P>COPYRIGHT: (C)2004,JPO

Description

【００１５】
実施例２は以下の表２に示すとおりである。
【００１６】
【表２】

【図面の簡単な説明】
【図１】実施例１の広角端の断面図
【図２】実施例２の広角端の断面図
【図３】実施例１の広角端の収差図
【図４】実施例１のＭＦ時望遠端の無限遠（＝　ＡＦ時望遠端の無限遠）の収差図
【図５】実施例１のＭＦ時望遠端の２．５ｍの収差図
【図６】実施例１のＭＦ時望遠端の１ｍの収差図
【図７】実施例１のＡＦ時望遠端の２．５ｍの収差図
【図８】実施例１のＡＦ時望遠端の１ｍの収差図
【図９】実施例２の広角端の収差図
【図１０】実施例２のＭＦ時望遠端の無限遠（＝　ＡＦ時望遠端の無限遠）の収差図
【図１１】実施例２のＭＦ時望遠端の２．５ｍの収差図
【図１２】実施例２のＭＦ時望遠端の１ｍの収差図
【図１３】実施例２のＡＦ時望遠端の２．５ｍの収差図
【図１４】実施例２のＡＦ時望遠端の１ｍの収差図[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a zoom lens used for a photographing lens of a video camera, a television camera, and the like, and in particular, allows a focus operation and a zoom operation to be performed both manually (manual) and automatically (electrically), and then allows lens exchange. Related to zoom lenses.
[0002]
[Prior art]
Generally, in many photographing lenses, at least a part of a lens group constituting a lens system is moved in an optical axis direction in order to focus on a subject.
[0003]
In the zoom lens dealt with in the present application, a method of moving the first lens group on the object side, so-called front lens focus, is one of the methods. In this front lens focus method, the front lens for focusing moves independently of the zoom unit that controls the change of the focal length, and the amount of movement of the front lens is constant regardless of the zoom position. It has the feature that quick zooming is possible while keeping it constant. However, there is a disadvantage in that a large amount of power is required for electric focusing for moving the heaviest front lens in the zoom lens, and rapid focusing cannot be performed. However, manual focusing (MF) eliminates this disadvantage.
[0004]
Another focus adjustment method of a zoom lens is a rear focus method. This is a method of performing focusing by moving a part of the rear lens group in the zoom lens system. The rear focus method is characterized in that the focusing lens group is smaller and lighter than the front lens focus method, so that quick focusing is possible, there is no change in the overall length, and there is little change in the center of gravity.
However, since the amount of movement for focusing changes with changes in zoom, if zooming is performed with the subject distance kept constant, the lens group must be moved for focusing at the same time as zooming. And there is a drawback that rapid zooming cannot be performed. However, if an automatic focus detection device is used, this drawback is eliminated, and since the focusing lens group is small and lightweight, quick focusing can be performed by electric power. Suitable for.
[0005]
For the purpose of effectively utilizing the features of the above two focus methods, various zoom lenses have been proposed that can be used both as the front lens MF and the rear AF with respect to conventional photographing lenses such as video and television cameras. (Patent Gazette No. 25661637, Jiko 62-43286)
[0006]
[Problems to be solved by the invention]
On the other hand, most broadcast television cameras use an interchangeable lens system. It is well known that in the interchangeable lens system, FB adjustment at the wide-angle end is indispensable.
[0007]
Considering how to perform this FB adjustment in the above-described zoom lens that can be used for both the front lens MF and the rear AF, it is optically easy to use the rear AF group and the FB group, and the lens always receives power supply. It is clear that there is no hindrance during AF. However, at the time of MF, it is necessary to always energize the rear AF group that does not originally require power supply to perform FB adjustment, which wastes power. Or, in order to mechanically perform FB adjustment to avoid this, a complicated mechanical structure for finely adjusting the rear AF group together with the AF mechanism is required.
[0008]
[Means for Solving the Problems]
In a zoom lens having a positive first lens unit that moves in order of manual focus in order from the object side, second and third lens units that control a change in focal length (zoom), and a positive fourth lens unit that further moves in the case of autofocus. The fourth group is composed of two groups, a front group FR and a rear group BR, one of which is a movable group for autofocus, and the other is a flange back adjustment group which is moved in the optical axis direction. By providing an independent group and eliminating the need for energization during MF, and by providing the FB adjustment mechanism as a separate mechanism from the AF movement mechanism, a zoom lens with a simple configuration that does not complicate the entire mechanical system is provided.
[0009]
At this time, the air gap between the front group FR and the rear group BR in the fourth group is L, the imaging magnification of the front group is βFR, the imaging magnification of the rear group is βBR, and the emission magnification of the front group is βBR. When the effective beam diameter is φFR, 3> | (1−βFR ＾ 2) * βBR ＾ 2 |> 0.5
1-βBR ＾ 2> 0.5
1.5 * φFR>L> 0.7 * φFR
Is satisfied.
[0010]
Further, each of FR and BR is composed of at least two positive lenses and at least one negative lens, and the average of Abbe numbers of the positive lenses constituting FR and BR is νpFR, νpBR, and the average of Abbe numbers of the negative lenses. When νnFR and νnBR are set, νpFR−νnFR> 15
νpBR−νnBR> 28
It is characterized by satisfying.
Numerical range 3> | (1−βFR ＾ 2) * βBR ＾ 2 |> 0.5
1-βBR ＾ 2> 0.5
Indicates the amount of movement of the imaging plane when FR and BR move on the optical axis. If the amount of movement exceeds the minimum value, the efficiency of both the AF operation and FB adjustment deteriorates. And the size of the mechanical system increases. On the other hand, if the value exceeds the maximum value, the efficiency is increased, but the sensitivity is too strong and a highly accurate moving mechanism is required, which also results in an increase in the size and cost of the mechanical system.
[0011]
1.5 * φFR>L> 0.7 * φFR
Indicates an interval between FR and BR. The upper limit is determined by the length required when designing an optical system such as a built-in extender to be insertable. The lower limit value is determined from both the necessary movement amount at the telephoto end of the AF group and the space for incorporating the drive mechanisms of AF and FB.
About 0.7 times φFR is suitable from experience. Also, νpFR−νnFR> 15
νpBR−νnBR> 28
Is a formula for achromatism of each of FR and BR. If the lower limit of each is exceeded, not only does the achromatism of a normal relay system become insufficient, but also the fluctuation of chromatic aberration when moving for AF and FB. It becomes too large and cannot be put to practical use.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
[0013]
【Example】
Example 1 is as shown in Table 1 below.
[0014]
[Table 1]

[0015]
Example 2 is as shown in Table 2 below.
[0016]
[Table 2]

[Brief description of the drawings]
FIG. 1 is a cross-sectional view at the wide-angle end according to the first embodiment. FIG. 2 is a cross-sectional view at a wide-angle end according to the second embodiment. FIG. 3 is an aberration diagram at the wide-angle end according to the first embodiment. FIG. 5 is an aberration diagram at the telephoto end at MF in Example 1 and 2.5 m at the telephoto end at MF in Example 1. FIG. 6 is 1 m at the telephoto end at MF in Example 1. FIG. 7 is an aberration diagram at a telephoto end of 2.5 m at the time of AF in Example 1. FIG. 8 is an aberration diagram of 1 m at a telephoto end of AF in Example 1. FIG. 9 is a diagram at the wide-angle end of Example 2. FIG. 10 is an aberration diagram at the MF telephoto end at infinity (= AF at the telephoto end infinity) according to the second embodiment. FIG. 11 is a 2.5 m aberration diagram at the MF telephoto end in the second embodiment. FIG. 12 is an aberration diagram at 1 m at the telephoto end in MF according to the second embodiment. FIG. 13 is an aberration diagram at 2.5 m at the telephoto end in AF according to the second embodiment. Aberration diagram

Claims (2)

In a zoom lens having a positive first lens unit that moves in order of manual focus in order from the object side, second and third lens units that control a change in focal length (zoom), and a positive fourth lens unit that further moves in the case of autofocus. ,
The fourth unit is a two-unit configuration including a front unit FR and a rear unit BR, one of which is a movable unit for autofocus, and the other is a flange back adjustment unit which is moved in the optical axis direction. Where L is the air interval, βFR is the imaging magnification of the front group, βBR is the imaging magnification of the rear group, and φFR is the effective beam diameter on the exit side of the front group. 3> | (1−βFR ＾ 2) * βBR ＾ 2 |> 0.5
1-βBR ＾ 2> 0.5
1.5 * φFR>L> 0.7 * φFR
A zoom lens that satisfies certain conditions. FR and BR are each composed of at least two positive lenses and at least one negative lens. The average Abbe numbers of the positive lenses constituting each of FR and BR are νpFR and νpBR, and the average Abbe number of the negative lenses is vnFR. , ΝnBR, νpFR−νnFR> 15
νpBR−νnBR> 28
The zoom lens according to claim 1, wherein the following condition is satisfied.

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