JP2004061677A - Rear focus lens and optical equipment using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a ghost and a flare generated by a device of a transmitted light quantity adjusting mechanism and an imaging element and to provide a rear focus lens which is suitable therefor. <P>SOLUTION: An aperture stop is arranged on the object side of a 3rd group and a transmitted light quantity adjusting mechanism is arranged on the image-plane side of the 3rd group; and the mechanism is arranged obliquely to an optical axis. <P>COPYRIGHT: (C)2004,JPO

Description

【００２５】
なる条件式を満足することを特徴としている。
【００２６】
条件式（１）は、前記フィルターの傾斜角度を規定する条件式である。第４群の焦点距離と横倍率が関係している。下限値を超えて角度が小さいとゴーストを撮影画面外に飛ばすことが困難となる。逆に上限値を超えて大きくなると、前記フィルターを配置するために、前記フィルターの前後に配置されるもの、たとえばレンズと接触しないように空間を確保しなければならなくなり、小型化に不利となってくるので好ましくない。
【００２７】
また、前記ズームレンズを小型化するには、前記第２群の焦点距離をｆ２としたとき、
０．１　＜｜ｆ_２／ｆ_Ｍ｜＜　０．５　・・・（２）
なる条件式を満足することを特徴とすることである。
【００２８】
条件式（２）は第２群の焦点距離（換言すればパワー）を適正にするための条件式である。条件式の上限値を超えて焦点距離が長くなると、収差補正上は好ましいが、所望のズーム比を得るためには第２群の移動量を大きくしなくてはならず、レンズ系全体の大型化を招き好ましくない。逆に下限値を超えるとペッツバール和が負に大きくなり、像面が倒れてくるので良好な光学性能を保つのが困難になる。
【００２９】
また、前記絞りとフィルター部材の光軸上の交点との距離をＬとしたとき、
０．１　＜　Ｌ／ｆＭ　・・・（３）
なる条件式を満足することを特徴とすることである。
【００３０】
条件式（３）はフィルター部材を適切に配置するための条件式である。条件式の下限値を超えると絞り位置と近くなり好ましくない。
【００３１】
また、前記第４群を移動させてフォーカスを行うことを特徴とすることである。従来の技術でも説明しているが、リアフォーカス式にすることにより、レンズの小型化、フォーカスの迅速化、消費電流の省エネ化を達成することが可能となる。
【００３２】
また、前記第３群の全体または一部のレンズを光軸方向に略垂直に移動させて、被写体像の像面移動を補正することを特徴とすることである。前記ズームレンズの場合、ズーミング作用において第３群は固定であり、防振機能を考慮した場合、制御を行なうのが容易である。
【００３３】
また、前記特長を有するズームレンズを搭載した光学機器は、ゴーストやフレアーの発生が少なく、小型化を達成することが可能となる。
【００３４】
次に、本発明の実施形態を図面を用いて具体的に説明する。
【００３５】
図１〜図３は各々後述する数値実施例１〜３のレンズ断面図、図４〜図６は各々後述する数値実施例１〜３のゴースト光路図である。
【００３６】
図１〜図３のレンズ断面図において、Ｌ１〜Ｌ４はそれぞれ第１〜４群、ＳＰは絞り、ＰはＣＣＤのフェースプレートやローパスフィルター等のガラスブロック、Ｉは像面、Ｆはフィルターである。本実施形態においては、広角端から望遠端への変倍に際して、図中の矢印のように第２群Ｌ２を像面側へ移動させると共に、変倍に伴う像面変動を第４群４を移動させて補正している。第１群Ｌ１、第３群Ｌ３、絞りＳＰは変倍に際し固定である。なお、第４群Ｌ４の変倍に伴う移動軌跡は物体距離によって異なり、図中実線で表された移動軌跡は無限遠物体の場合、破線で表された移動軌跡は至近物体の場合をそれぞれ表している。また、本実施形態のズームレンズは、第４群Ｌ４を光軸上移動させてフォーカスを行うリアフォーカス方式を採用している。
【００３７】
また、第３群Ｌ３を構成するレンズ面のうち、少なくとも１つの正レンズの片面または両面を非球面とすることである。これは、該第２群から発散で入ってくる光束を受け止める第３群中の正レンズに非球面のレンズを１つ以上配することにより光学性能の向上を図ることができる。
【００３８】
また、ズームレンズの広角端及び望遠端における全系の焦点距離をそれぞれｆｗ，ｆｔ、前記第ｉ群の焦点距離をｆｉとしたとき、
１．７２　＜　ｆ_１／ｆ_Ｍ＜　１．７７　…（４）
０．９　＜　ｆ_３／ｆ_Ｍ＜　１．３　…（５）
なる条件式の少なくとも１つを満足することが望ましい。
【００３９】
条件式（４）は、第１群の焦点距離を適正にするための条件式である。条件式の上限値を超えて焦点距離が長くなると、レンズ系全体の焦点距離が長くなり、レンズ全長の長大化を招き好ましくない。逆に下限値を超えると第１群の負担が大きくなり、良好な光学性能、特にテレ端の球面収差や色収差を悪化させて好ましくない。
【００４０】
条件式（５）は、第３群の焦点距離を適正にするための条件式である。条件式の上限値を超えて焦点距離が長くなると、第３群の負担が軽くなり収差補正上は好ましいが、第４群の負担が大きくなり第４群のレンズ枚数を増やしたり非球面レンズを配したりしなければならず、小型化が困難になってくる。逆に下限値を超えると第３群の負担が大きくなり、良好な光学性能、特に球面収差を悪化させて好ましくない。
【００４１】
条件式（４）〜（５）については、それぞれの条件式を満足することでそれぞれの作用効果を得ることができるが、全ての条件式を満足することが収差補正上望ましいのはここで言うまでもない。
【００４２】
（数値実施例）
次に、本発明の実施形態１〜３に各々対応する数値実施例１〜３を示す。各数値実施例においてｉは物体側からの光学面の順序を示し、Ｒｉは第ｉ番目の光学面（第ｉ面）の曲率半径、Ｄｉは第ｉ面と第ｉ＋１面との間の間隔、Ｎｉとνｉはそれぞれｄ線に対する第ｉ番目の光学部材の屈折率、アッベ数を示す。ｆは焦点距離、ＦｎｏはＦナンバー、ωは半画角である。実施例の計算において、ｔａｎωＭは、ＣＣＤ撮像素子の短辺方向の画角を使用している。またｋを離心率、Ｂ、Ｃ、Ｄ、Ｅ、Ｆを非球面係数、光軸からの高さｈの位置での光軸方向の変位を面頂点を基準にしてｘとするとき、非球面形状は、
ｘ＝（ｈ^２／Ｒ）／［１＋［１−（１＋ｋ）（ｈ／Ｒ）^２］^１／２］＋Ａｈ^２＋Ｂｈ^４
＋Ｃｈ^６＋Ｄｈ^８＋Ｅｈ^１０＋Ｆｈ^１２
で表示される。但しＲは曲率半径である。また、例えば「ｅ−Ｚ」の表示は「１０^−Ｚ」を意味する。又、各数値実施例における上述した条件式との対応を表１に示す。
【００４３】
【外１】

【００４４】
【外２】

【００４５】
【外３】

【００４６】
【表１】

【００４７】
次に本発明のズームレンズを撮影光学系として用いたビデオカメラの実施形態を図７を用いて説明する。
【００４８】
図７において、１０はビデオカメラ本体、１１は本発明のズームレンズによって構成された撮影光学系、１２は撮影光学系１１によって被写体像を受光するＣＣＤ等の撮像素子、１３は撮像素子１２が受光した被写体像を記録する記録手段、１４は不図示の表示素子に表示された被写体像を観察するためのファインダーである。上記表示素子は液晶パネル等によって構成され、撮像素子１２上に形成された被写体像が表示される。
【００４９】
このように本発明のズームレンズをビデオカメラ等の光学機器に適用することにより、ゴーストやフレアーの少ない、高変倍比で大口径で、高い光学性能を有する光学機器が実現できる。
【００５０】
【発明の効果】
以上説明したように、本発明によれば、
第３群の物体側に開口絞りを、第３群の像面側に透過光量を減衰するためのフィルターを配置し、前記フィルターと撮像素子とで発生するゴーストやフレアーを低減することおよびそれに適したズームレンズを実現することができる。
【図面の簡単な説明】
【図１】数値実施例１のズームレンズのレンズ断面図である。
【図２】数値実施例２のズームレンズのレンズ断面図である。
【図３】数値実施例３のズームレンズのレンズ断面図である。
【図４】数値実施例１のズームレンズのゴースト光路図である。絞りは開放から１段絞っている。
【図５】数値実施例２のズームレンズのゴースト光路図である。絞りは開放から１段絞っている。
【図６】数値実施例３のズームレンズのゴースト光路図である。絞りは開放から１段絞っている。
【図７】本発明のズームレンズをビデオカメラに適用した場合の実施形態を説明するための図である。
【符号の説明】
Ｌ１　第１群
Ｌ２　第２群
Ｌ３　第３群
Ｌ４　第４群
ＳＰ　絞り
Ｆ　フィルター
Ｐ　ガラスブロック
Ｉ　像面[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a transmission light amount adjusting device and a zoom lens of a photographing optical device having an optical member such as a filter that advances and retreats in an optical path of a photographing optical system.
[0002]
[Prior art]
When taking a picture with a still camera or a video camera, if the aperture diameter is too small when the subject is bright, there is a problem in that image quality is deteriorated due to diffraction and dust is reflected due to an increase in the depth of focus. Therefore, in order to prevent the aperture diameter from becoming too small, an ND filter is attached to the aperture blade of the taking lens, a plurality of aperture blades are driven to form an aperture, and the ND filter is made to enter the aperture aperture. There is something. Also, in order to prevent image deterioration caused by a cut surface of the ND filter in the middle of the optical path, the ND filter is independently advanced and retracted so that the ND filter can be automatically or manually switched between advanced and retracted. There is also.
[0003]
Japanese Patent Application Laid-Open No. 2000-305018 discloses an arrangement in which an ND filter integrated with a diaphragm device is disposed behind the third group and tilted.
[0004]
2. Description of the Related Art Conventionally, various types of zoom lenses used in photographic cameras and video cameras have been proposed, which employ a so-called rear focus method in which a lens group behind an object-side first lens group is moved to perform focusing. . This is because the rear focus method moves a relatively small and light lens group during focusing, so that a small driving force is required, and quick focusing is possible, which is compatible with the autofocus system. Because there is.
[0005]
As such a rear focus type zoom lens, for example, in JP-A-63-44614, a first lens unit having a positive refractive power and a second lens unit having a negative refractive power for zooming are arranged in order from the object side. And a third lens unit having a negative refractive power for correcting an image plane variation caused by zooming, and a fourth lens unit including a fourth lens unit having a positive refractive power. Is moved to focus.
[0006]
However, in such a configuration, the moving space of the third lens group must be secured, and the overall length of the lens tends to increase. JP-A-63-278013 also discloses a zoom lens composed of a first positive lens unit, a second negative lens unit, a third negative lens unit, and a fourth positive lens unit. The fourth group performs image plane correction and focusing. However, in these zoom systems using the negative third lens group, the divergent light from the second lens group is further diverged by the third lens group. In addition, the variation in aberration due to focusing tends to increase.
[0007]
JP-A-62-24213 and JP-A-63-247316, which are improved zoom types, have a first group of positive refractive power, a second group of negative refractive power, A zoom lens having four lens groups, a third lens group having a positive refractive power and a fourth lens group having a positive refractive power, performs zooming by moving the second lens group, and suppresses image plane fluctuation accompanying zooming. The fourth group is moved and corrected, and focusing is performed.
[0008]
Japanese Patent Application Laid-Open No. 63-29718 discloses a zoom lens having a first lens unit having a positive refractive power and a negative lens, a negative lens, and a positive lens. A second group which is sometimes movable and mainly controls the magnification, a third group which has a positive refractive power and includes an aspheric surface, and an image which has a positive refractive power with a slightly large air gap and has a positive refractive power A zoom lens composed of a fourth group that corrects surface fluctuation and moves for focusing is disclosed.
[0009]
Japanese Patent Application Laid-Open No. 5-72472 discloses a fixed first lens unit having positive refractive power and a second lens unit having negative refractive power in order from the object side. An aspheric zoom lens having a third group of refractive power and a fourth group of positive refractive power that moves on the optical axis to maintain the image plane position is disclosed. In the zoom lens disclosed in this publication, the second group includes a meniscus negative lens, a biconcave lens, and a positive lens, the third group includes a single lens having one or more aspheric surfaces, and the fourth group includes one lens. It is composed of a lens having an aspherical surface or more.
[0010]
On the other hand, in U.S. Pat. No. 4,299,454, at least two lenses including a first positive lens unit, a second negative lens unit, and a rear positive lens unit having a positive refractive power in order from the object side, and including a negative lens unit. A zoom lens in which the group is moved to perform zooming and the second negative lens group is constituted by the first and second negative lenses and the positive doublet from the object side is disclosed, but the third lens group moves. This complicates the mechanism. U.S. Pat. No. Re. 32,923 discloses a first positive lens unit, a second negative lens unit, a stop, a third positive lens unit, and a fourth positive lens unit arranged in this order from the object side. A four-lens group moves in the same direction at the time of zooming, and a stop has a fixed zoom lens at the time of zooming.
[0011]
JP-A-7-270684 and JP-A-7-318804 disclose a first lens unit having a positive refractive power and a fixed first lens unit, a second lens unit having a negative refractive power and a variable power, and a positive lens unit. A third lens unit having a refractive power and a fourth lens unit having a positive refractive power that moves on the optical axis to maintain the image plane position and perform focusing, and the second lens unit includes four single lenses. Are disclosed.
[0012]
JP-A-5-060974 discloses a first lens unit having a positive refractive power and a fixed first lens unit, a second lens unit having a negative refractive power and a variable power, and a third lens unit having a positive refractive power and fixed from the object side. Disclosed is a short length variable power lens having a fourth lens unit having a positive refractive power that moves on the optical axis in order to maintain a group and an image plane position and perform focusing.
[0013]
JP-A-11-305124 discloses a first lens unit having a positive refractive power and a fixed first lens unit, a second lens unit having a negative refractive power and a third lens unit having a positive refractive power and fixed from the object side. Disclosed is a short length variable power lens having a fourth lens unit having a positive refractive power that moves on the optical axis in order to maintain a group and an image plane position and perform focusing.
[0014]
However, all of the above publications do not disclose a zoom lens in which a filter for attenuating the amount of transmitted light and a diaphragm device are separately provided, and the filter is disposed obliquely to reduce ghost and flare.
[0015]
[Problems to be solved by the invention]
According to the present invention, an aperture stop is arranged on the object side of the third group, and a filter for attenuating the amount of transmitted light is arranged on the image plane side of the third group, and ghost and flare generated by the filter and the image sensor are reduced. And to provide a zoom lens suitable for it.
[0016]
[Means for Solving the Problems]
To achieve the above object, the present invention provides
In order from the object side, there are four lens groups of 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. A zoom lens that moves the second lens unit to the image plane side to change the magnification from the wide-angle end to the telephoto end, and corrects the image plane fluctuation caused by the zooming by moving part or all of the fourth unit. An aperture stop is provided on the object side of the third group, and a filter member for attenuating the amount of transmitted light is provided on the image plane side of the third group. The filter member is arranged obliquely with respect to the optical axis. It is characterized by doing.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
The amount of light reflected by the filter is considerably large, and appears as a ghost in a photographed image, and significantly degrades the quality. By making the filter oblique with respect to the optical axis, it is possible to fly the light reflected by the filter out of the photographing screen, thereby preventing ghost light from being generated. In particular, providing an aperture stop on the object side of the third group as in the present invention is advantageous for miniaturization.
[0018]
Further, it is preferable that the filter member has a configuration in which the transmittance varies depending on the location of the filter. Although a single-density filter has been used in the past, when the camera system is configured with a single-density filter, for example, a large difference between the amount of light passing through a part without a filter and the amount of light passing through a certain part occurs, and an image is taken. Light quantity unevenness occurs on the screen.
[0019]
Further, the filter member is formed of a multilayer film. When a density change is made by a filter, the density change can be freely controlled to some extent, and the thickness of the filter necessary for giving a density can be reduced by forming the filter with a multilayer film. Thereby, the influence of the filter inserted into the photographing optical system is reduced, and the deterioration of the optical performance is reduced.
[0020]
Further, the multilayer film has a structure having a layer for reducing reflection. Conventionally, the presence of a flat plate such as a filter in a photographing optical system has caused ghost and flare. Therefore, it is possible to reduce a ghost and a flare by forming an antireflection film by forming the filter into a multilayer film structure.
[0021]
Further, the filter member is configured to be insertable and retractable into and out of the optical path by an external operation. This allows the photographer to intentionally participate in the removal of ghosts and flares, thereby improving usability.
[0022]
Further, the filter member is characterized in that the filter member is vertically inclined with respect to the photographing screen. Usually, in the case of shooting with a camera, in particular, shooting of a moving image such as a video camera, when a recorded image is reproduced and viewed, it is viewed with a TV monitor. At this time, the upper side photographed by the camera coincides with the upper side of the monitor. At this time, the light source that most influences the ghost generated by the filter is sunlight, light, or the like, and these light sources are often stochastically located above the screen. Therefore, by tilting the filter up and down, it is possible to effectively fly out of the shooting screen. Although it is possible to fly while tilting left and right, it is not preferable because the tilt angle becomes large.
[0023]
Further, when the inclination angle of the filter member is θ, the focal length of the fourth group is f ₄ , and the lateral magnification and the angle of view at the focal length f _M are β _4M and ω _M , respectively,
tan ⁻¹ [0.4 · f _M · tan ω _M · (1+ | β _4M |) / f ₄ ] <θ <15
... (1)
However,
[0024]
(Equation 2)

[0025]
It is characterized by satisfying the following conditional expression.
[0026]
Conditional expression (1) is a conditional expression that defines the tilt angle of the filter. The focal length and the lateral magnification of the fourth group are related. When the angle is smaller than the lower limit, it is difficult to fly the ghost out of the shooting screen. Conversely, if the size exceeds the upper limit, the filter must be provided before and after the filter, for example, a space must be ensured so as not to come into contact with the lens in order to dispose the filter, which is disadvantageous for miniaturization. Is not preferred.
[0027]
In order to reduce the size of the zoom lens, when the focal length of the second group is f2,
_{0.1 <| f 2 / f M} | <0.5 ··· (2)
Characterized by satisfying the following conditional expression:
[0028]
Conditional expression (2) is a conditional expression for making the focal length of the second lens unit (in other words, power) appropriate. If the focal length becomes longer than the upper limit of the conditional expression, it is preferable in terms of aberration correction, but in order to obtain a desired zoom ratio, the amount of movement of the second lens unit must be increased, and the overall size of the lens system becomes large. This is not preferred. Conversely, if the value exceeds the lower limit, the Petzval sum becomes negatively large and the image plane falls, so that it becomes difficult to maintain good optical performance.
[0029]
Further, when the distance between the stop and the intersection on the optical axis of the filter member is L,
0.1 <L / fM (3)
Characterized by satisfying the following conditional expression:
[0030]
Conditional expression (3) is a conditional expression for appropriately disposing the filter member. Exceeding the lower limit of the conditional expression is undesirable because it approaches the stop position.
[0031]
Further, the focus is performed by moving the fourth group. As described in the related art, the use of the rear focus type makes it possible to achieve downsizing of the lens, quick focus, and energy saving of current consumption.
[0032]
Further, it is characterized in that the whole or a part of the lens of the third group is moved substantially perpendicularly to the optical axis direction to correct the image plane movement of the subject image. In the case of the zoom lens, the third group is fixed in the zooming operation, and control is easy to perform in consideration of the image stabilizing function.
[0033]
In addition, an optical device equipped with a zoom lens having the above-described features is less likely to generate ghost and flare, and can achieve downsizing.
[0034]
Next, embodiments of the present invention will be specifically described with reference to the drawings.
[0035]
1 to 3 are lens sectional views of Numerical Examples 1 to 3 described later, respectively, and FIGS. 4 to 6 are ghost optical path diagrams of Numerical Examples 1 to 3 described later.
[0036]
1 to 3, L1 to L4 denote first to fourth groups, SP denotes an aperture, P denotes a glass block such as a CCD face plate or a low-pass filter, I denotes an image plane, and F denotes a filter. . In the present embodiment, at the time of zooming from the wide-angle end to the telephoto end, the second lens unit L2 is moved to the image plane side as indicated by the arrow in the figure, and the image plane fluctuation due to zooming is changed by the fourth lens unit 4. It is moved and corrected. The first lens unit L1, the third lens unit L3, and the stop SP are fixed during zooming. The moving trajectory accompanying zooming of the fourth unit L4 varies depending on the object distance, and the moving trajectory indicated by a solid line in the drawing represents an infinitely distant object, and the moving trajectory indicated by a broken line represents a close-up object. ing. In addition, the zoom lens of the present embodiment employs a rear focus method in which the fourth unit L4 is moved on the optical axis to perform focusing.
[0037]
Further, one or both surfaces of at least one positive lens among the lens surfaces constituting the third lens unit L3 are aspherical. This is because the optical performance can be improved by arranging one or more aspherical lenses on the positive lens in the third group that receives the divergent light beam from the second group.
[0038]
When the focal lengths of the entire system at the wide-angle end and the telephoto end of the zoom lens are fw and ft, respectively, and the focal length of the i-th unit is fi,
_{1.72 <f 1 / f M <} 1.77 ... (4)
_{0.9 <f 3 / f M <} 1.3 ... (5)
It is desirable to satisfy at least one of the following conditional expressions.
[0039]
Conditional expression (4) is a conditional expression for making the focal length of the first lens unit appropriate. If the focal length becomes longer than the upper limit of the conditional expression, the focal length of the entire lens system becomes longer, which undesirably leads to a longer overall lens length. Conversely, when the value exceeds the lower limit, the burden on the first lens unit increases, and good optical performance, particularly, spherical aberration and chromatic aberration at the telephoto end is undesirably deteriorated.
[0040]
Conditional expression (5) is a conditional expression for making the focal length of the third lens unit appropriate. When the focal length is longer than the upper limit of the conditional expression, the load on the third group is reduced, which is preferable for aberration correction. However, the load on the fourth group is increased, and the number of lenses in the fourth group is increased. And it becomes difficult to reduce the size. Conversely, when the value exceeds the lower limit, the burden on the third lens unit increases, and good optical performance, particularly, spherical aberration is undesirably deteriorated.
[0041]
Regarding the conditional expressions (4) and (5), the respective functions and effects can be obtained by satisfying the respective conditional expressions. However, it is needless to say that satisfying all the conditional expressions is desirable for aberration correction. No.
[0042]
(Numerical example)
Next, Numerical Examples 1 to 3 respectively corresponding to Embodiments 1 to 3 of the present invention will be described. In each numerical example, i indicates the order of the optical surface from the object side, Ri is the radius of curvature of the i-th optical surface (i-th surface), Di is the distance between the i-th surface and the (i + 1) -th surface, Ni and νi represent the refractive index and Abbe number of the i-th optical member with respect to the d-line, respectively. f is the focal length, Fno is the F number, and ω is the half angle of view. In the calculation of the embodiment, tan ωM uses the angle of view in the short side direction of the CCD image sensor. When k is the eccentricity, B, C, D, E, and F are aspherical coefficients, and the displacement in the optical axis direction at the position of height h from the optical axis is x with respect to the surface vertex, the aspherical surface The shape is
^{x = (h 2 / R)} / [1+ [1- (1 + k) (h / R) 2] 1/2] + Ah 2 + Bh 4
+ Ch ⁶ + Dh ⁸ + Eh ¹⁰ + Fh ¹²
Displayed with. Here, R is a radius of curvature. Further, for example, "e-Z" means ^{"10 -Z".} Table 1 shows the correspondence between the numerical expressions and the conditional expressions described above.
[0043]
[Outside 1]

[0044]
[Outside 2]

[0045]
[Outside 3]

[0046]
[Table 1]

[0047]
Next, an embodiment of a video camera using the zoom lens of the present invention as a photographic optical system will be described with reference to FIG.
[0048]
7, reference numeral 10 denotes a video camera main body, 11 denotes a photographing optical system constituted by the zoom lens of the present invention, 12 denotes an image pickup device such as a CCD for receiving a subject image by the photographing optical system 11, and 13 denotes an image pickup device 12 receiving light. A recording unit 14 for recording the subject image is a finder for observing the subject image displayed on a display element (not shown). The display element includes a liquid crystal panel or the like, and displays a subject image formed on the imaging element 12.
[0049]
Thus, by applying the zoom lens of the present invention to an optical device such as a video camera, an optical device with little ghost and flare, a high zoom ratio, a large aperture, and high optical performance can be realized.
[0050]
【The invention's effect】
As described above, according to the present invention,
An aperture stop is arranged on the object side of the third lens group, and a filter for attenuating the amount of transmitted light is arranged on the image plane side of the third lens group, to reduce ghosts and flares generated by the filter and the image sensor, and suitable for it. Zoom lens can be realized.
[Brief description of the drawings]
FIG. 1 is a lens cross-sectional view of a zoom lens according to Numerical Example 1.
FIG. 2 is a sectional view of a zoom lens according to a second numerical example;
FIG. 3 is a sectional view of a zoom lens according to a third numerical example;
FIG. 4 is a ghost optical path diagram of the zoom lens according to Numerical Example 1. The aperture is one stop down from the full aperture.
FIG. 5 is a ghost optical path diagram of the zoom lens according to Numerical Example 2. The aperture is one stop down from the full aperture.
FIG. 6 is a ghost optical path diagram of the zoom lens according to Numerical Example 3. The aperture is one stop down from the full aperture.
FIG. 7 is a diagram illustrating an embodiment in which the zoom lens of the present invention is applied to a video camera.
[Explanation of symbols]
L1 First group L2 Second group L3 Third group L4 Fourth group SP Aperture F Filter P Glass block I Image plane

Claims (12)

In order from the object side, there are 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. A zoom lens that moves the second lens unit to the image plane side to perform zooming from the wide-angle end to the telephoto end, and corrects image plane fluctuations caused by zooming by moving part or all of the fourth lens unit. An aperture stop is provided on the object side of the third group, and a filter member for attenuating the amount of transmitted light is provided on the image plane side of the third group. The filter member is disposed obliquely with respect to the optical axis. Zoom lens characterized by doing. The zoom lens according to claim 1, wherein the filter member has a different transmittance depending on a location. The zoom lens according to claim 1, wherein the filter member is formed of a multilayer film. The zoom lens according to claim 3, wherein the multilayer film has a layer that reduces reflection. The zoom lens according to any one of claims 1 to 4, wherein the filter member is configured to be inserted and retracted into and out of an optical path by an operation from outside. The zoom lens according to claim 1, wherein the filter member is vertically inclined with respect to a shooting screen. When the inclination angle of the filter member is θ, the focal length of the fourth group is f4, and the lateral magnification and the angle of view at the focal length fM are β4M and ωM, respectively,
tan-1 [0.4 · fM · tan ωM · (1+ | β4M |) / f4] <θ
However,

The zoom lens according to any one of claims 1 to 6, wherein the following conditional expression is satisfied. When the focal length of the second group is f2,
0.1 <| f2 / fM | <0.5
The zoom lens according to any one of claims 1 to 7, wherein the following conditional expression is satisfied. When the distance between the stop and the intersection on the optical axis of the filter member is L,
0.1 <L / fM
The zoom lens according to any one of claims 1 to 8, wherein the following conditional expression is satisfied. The zoom lens according to claim 1, wherein focusing is performed by moving the fourth group. 11. The apparatus according to claim 1, wherein the whole or a part of the lens of the third group is moved substantially perpendicularly to an optical axis direction to correct a movement of an image plane of a subject image. 12. Zoom lens. An optical apparatus comprising the zoom lens according to claim 1.

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