JP4138439B2 - Zoom lens and image enlargement projection system, video projector, rear projector, and multivision system using the same - Google Patents

Description

【００６９】
【表２】

【００７０】
図３の各図はそれぞれ、実施例１の広角端の球面収差(mm)、非点収差(mm)、歪曲収差（％）を示しており、このことは以下の図７、１１についても同様である。図４の各図はそれぞれ、実施例１の望遠端の球面収差(mm)、非点収差(mm)、歪曲収差（％）を示しており、このことは以下の図８、１２についても同様である。図３、４から分るように、実施例１に係るズームレンズは良好な収差性能を示している。
【００７１】
（実施例２）
図５は、実施例２に係るズームレンズの広角端の構成図である。図６は、図５に示したズームレンズの望遠端の構成図である。図５に示したズームレンズ２０は、共役距離の長い側から見て、負屈折力の第１レンズ群２１（レンズ２１ａ〜２１ｆ）、正屈折力の第２レンズ群２２（レンズ２２ａ〜２２ｃ）、正屈折力の第３レンズ群２３（レンズ２３ａ〜２３ｃ）、正屈折力の第４レンズ群１４（レンズ２４ａ〜２４ｄ）の４群構成となっている。
【００７２】
また、広角端（図５）から望遠端（図６）の変倍に際して、第１レンズ群２１は共役距離の短い側に移動し、第２レンズ群２２は共役距離の長い側に移動し、第３レンズ群２３は共役距離の長い側に移動し、第４レンズ群２４は共役距離の長い側に移動する。
【００７３】
本実施例２は、広角端のＦ_NO＝２．３、焦点距離ｆ＝２１．３２、半画角＝３０．９°の設計例である。実施例２の前記式（１）〜（１０）の各値は下記の通りである。
式（１）ｂｆｗ／ｆｗ＝３．６６
式（２）ｆｗ／ｆ１ｇ＝−０．３７
式（３）ｆｗ／ｆ２ｇ＝０．０１
式（４）ｆｗ／ｆ３ｇ＝０．２２２
式（５）ｆｗ／ｆ４ｇ＝０．１７５
式（６）（１／ｆ１／ａｂｅ１）／（１／ｆｒｅａｒ）＝−０．００９
式（７）ｎｄ１１＝１．７８４
式（８）ｎｄ４＝１．８３４
式（９）νｄ４＝３７．３
式（１０）ｆ４ｒ／ｂｆｗ＝１．５６
次に具体的な数値を表３に示し、ズームデータを表４に示す。表３の例では、ｒ１〜ｒ１２が第１レンズ群、ｒ１３〜ｒ１９が第２レンズ群、ｒ２０〜ｒ２５が第３レンズ群、ｒ２６〜ｒ３３が第４レンズ群であり、ｒ１７は絞りである。
【００７４】
【表３】

【００７５】
【表４】

【００７６】
図７、８の各図はそれぞれ、実施例２の広角端の収差図、望遠端の収差図を示しており、実施例２に係るズームレンズは良好な収差性能を示していることが分かる。
【００７７】
（実施例３）
図９は、実施例３に係るズームレンズの広角端の構成図である。図１０は、図９に示したズームレンズの望遠端の構成図である。図９に示したズームレンズ２０は、共役距離の長い側から見て、負屈折力の第１レンズ群３１（レンズ３１ａ〜３１ｆ）、正屈折力の第２レンズ群３２（レンズ３２ａ〜３２ｃ）、正屈折力の第３レンズ群３３（レンズ３３ａ〜３３ｃ）、正屈折力の第４レンズ群３４（レンズ３４ａ〜３４ｄ）の４群構成となっている。
【００７８】
また、広角端（図９）から望遠端（図１０）の変倍に際して、第１レンズ群３１は共役距離の短い側に移動し、第２レンズ群３２は共役距離の長い側に移動し、第３レンズ群３３は共役距離の長い側に移動し、第４レンズ群３４は共役距離の長い側に移動する。
【００７９】
本実施例３は、広角端のＦ_NO＝２．４、焦点距離ｆ＝２８．９３、半画角＝３０．９°の設計例である。実施例３の前記式（１）〜（１０）の各値は下記の通りである。
式（１）ｂｆｗ／ｆｗ＝２．７９
式（２）ｆｗ／ｆ１ｇ＝−０．３８
式（３）ｆｗ／ｆ２ｇ＝０．２９
式（４）ｆｗ／ｆ３ｇ＝０．２４５
式（５）ｆｗ／ｆ４ｇ＝０．０９６
式（６）（１／ｆ１／ａｂｅ１）／（１／ｆｒｅａｒ）＝−０．０１２
式（７）ｎｄ１１＝１．７８４
式（８）ｎｄ４＝１．８３４
式（９）νｄ４＝３７．３
式（１０）ｆ４ｒ／ｂｆｗ＝３．７５
次に具体的な数値を表５に示し、ズームデータを表６に示す。表５の例では、ｒ１〜ｒ１２が第１レンズ群、ｒ１３〜ｒ１９が第２レンズ群、ｒ２０〜ｒ２７が第３レンズ群、ｒ２８〜ｒ３５が第４レンズ群であり、ｒ１５は絞りである。
【００８０】
【表５】

【００８１】
【表６】

【００８２】
図１１、１２の各図はそれぞれ、実施例３の広角端の収差図、望遠端の収差図を示しており、実施例３に係るズームレンズは良好な収差性能を示していることが分かる。
【００８３】
（実施の形態２）
図１３は、本発明の実施の形態２に係る映像拡大投写システム４０の構成図である。映像拡大投写システム４０は、実施の形態１のズームレンズで構成された投写レンズ４１、光学像を形成する空間光変調素子４２、光源４３を備えている。４４は、投写された映像のフォーカス面である。光源４３により照明される空間光変調素子４２に形成された光学像は、投写レンズ４１によってフォーカス面４４に拡大投写される。本実施の形態に係る映像拡大投写システム４０は、投写レンズ４１に前記実施の形態１のズームレンズを用いているので、歪みや色のにじみのすくない画面を得ることができる。
【００８４】
（実施の形態３）
図１４は、本発明の実施の形態３に係るビデオプロジェクター５０の構成図である。ビデオプロジェクター５０は、実施の形態１のズームレンズで構成された投写レンズ５１、光学像を形成する空間光変調素子５２、回転手段５３、光源５４を備えている。
【００８５】
空間光変調素子５２には、各々青、緑、赤の３種の光学像が時間的に分割されて形成される。回転手段５３は、青、緑、赤に対応したフィルターを回転させることで光学像を青、緑、赤の３色に時間的に制限する。
【００８６】
光源５４からの光は、回転手段５３によって青、緑、赤の３色に時間的に分解され、空間光変調素子５２を照明する。空間光変調素子５２には青、緑、赤の３種の光学像が時間的に分割されて形成され、投写レンズ５１によって拡大投写される。
【００８７】
投写レンズ５１に前記実施の形態１のズームレンズを用いているので、明るくて歪みや色のにじみの少ない映像が得られるビデオプロジェクターがコンパクトに実現できる。
【００８８】
（実施の形態４）
図１５は、本発明の実施の形態４に係るリアプロジェクター６０の構成図である。リアプロジェクター６０は、実施の形態３のビデオプロジェクター６１、光を折り曲げるミラー６２、透過型スクリーン６３、筐体６４を備えている。
【００８９】
ビデオプロジェクター６１から投写される映像はミラー６２によって反射され、透過型スクリーン６３に結像される。本実施の形態によれば、ビデオプロジェクター６１に実施の形態３のビデオプロジェクターを用いているので、高精細なリアプロジェクターがコンパクトに実現できる。
【００９０】
（実施の形態５）
図１６は、本発明の実施の形態５に係るマルチビジョンシステム７０の構成図である。本図に示したマルチビジョンシステム７０は、実施の形態３のビデオプロジェクター７１、透過型スクリーン７２、筐体７３、映像を分割する映像分割回路７４を備えている。
【００９１】
映像信号は映像分割回路７４によって加工分割されて複数台のビデオプロジェクター７１に送られる。ビデオプロジェクター７１から投写される映像は透過型スクリーン７２に結像される。本実施の形態によれば、ビデオプロジェクター７１に、実施の形態３のビデオプロジェクタを用いているので、映像のつなぎ目がなだらかにつながれ違和感のないマルチビジョンシステムがコンパクトに実現できる。
【００９２】
なお、実施の形態２〜５では、実施の形態１のズームレンズを映像拡大投写システム等に用いた例で説明したが、画像情報をフィルム、ＣＣＤ等の撮像手段面上に形成するビデオカメラ、フィルムカメラ、デジタルカメラ等の光学機器に用いてもよい。
【００９３】
【発明の効果】
以上のように本発明によれば、長いバックフォーカスを有しながら、コンパクトなズームレンズを提供することができ。また、本発明に係るズームレンズを用いることにより、明るく高精細な映像拡大投写システム、ビデオプロジェクター、リアプロジェクター、及びマルチビジョンシステムをコンパクトに実現できる。
【図面の簡単な説明】
【図１】本発明の実施の形態１に係るズームレンズの広角端の構成図
【図２】本発明の実施の形態１に係るズームレンズの望遠端の構成図
【図３】本発明の実施例１に係る広角端の収差図
【図４】本発明の実施例１に係る望遠端の収差図
【図５】本発明の実施例２に係るズームレンズの広角端の構成図
【図６】本発明の実施例２に係るズームレンズの望遠端の構成図
【図７】本発明の実施例２に係る広角端の収差図
【図８】本発明の実施例２に係る望遠端の収差図
【図９】本発明の実施例３に係るズームレンズの広角端の構成図
【図１０】本発明の実施例３に係るズームレンズの望遠端の構成図
【図１１】本発明の実施例３に係る広角端の収差図
【図１２】本発明の実施例３に係る望遠端の収差図
【図１３】本発明の実施の形態２に係る映像拡大投写システムの構成図
【図１４】本発明の実施の形態３に係るビデオプロジェクターの構成図
【図１５】本発明の実施の形態４に係るリアプロジェクターの構成図
【図１６】本発明の実施の形態５に係るマルチビジョンシステムの構成図
【符号の説明】
１０，２０，３０ ズームレンズ
１１，２１，３１ 第１レンズ群
１２，２２，３２ 第２レンズ群
１３，２３，３３ 第３レンズ群
１４，２４，３４ 第４レンズ群
１５ ガラスブロック
１６ 像面
１７ 絞り
４１，５１ 投写レンズ
４２，５２ 空間光変調素子
４３，５４ 光源
４４ 投写された映像のフォーカス面
５３ 回転手段
６１ ビデオプロジェクター
６２ ミラー
６３ 透過型スクリーン
６４，７３ 筐体
７４ 映像分割回路[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a zoom lens, and more particularly to a zoom lens for use in a projector or the like that enlarges and projects an image of a spatial light modulator on a screen.
[0002]
[Prior art]
In a projector using a reflective spatial modulation element of three primary colors of red, green, and blue, a prism for guiding illumination light and a color composition prism are arranged between the projection lens and the spatial modulation element. For this reason, the projection lens requires a long back focus. Since the color-combining prism has an incident angle dependency in spectral characteristics, an optical system that makes the pupil position on the short conjugate distance side sufficiently far from the spatial modulation element, that is, telecentricity is necessary.
[0003]
There is a zoom lens proposed in the following Patent Document 1 as a convex group leading four-group zoom lens whose long back focus and telecentricity do not change even by zooming. Further, as a convex group preceding third group zoom lens, for example, there is a zoom lens proposed in Patent Document 2 below, and as a concave group preceding fourth group zoom lens, for example, there is a zoom lens proposed in Patent Document 3 below.
[0004]
Furthermore, there is a demand to shorten the projection distance from the screen to the projector and use it in a small space, and a wide-angle zoom lens that can be used at a short projection distance is also demanded for the projection lens.
[0005]
[Patent Document 1]
Japanese Patent Laid-Open No. 10-161027
[0006]
[Patent Document 2]
JP 2001-215411 A
[0007]
[Patent Document 3]
JP 2002-131039 A
[0008]
[Problems to be solved by the invention]
However, in order to realize a long back focus and a wide angle, there has been a problem that the entire length of the zoom lens becomes long and the lens outer diameter, particularly, the lens outer diameter on the longer conjugate distance side becomes larger. In a large high-intensity projector that uses a large light source, the size of the lens has not been a major problem. However, even in such a high-intensity projector, a reduction in size and weight is required. For example, when used in a rental company, if it can be quickly installed alone by reducing the size and weight, it greatly affects the cost reduction.
[0009]
Further, the lens mount that is a lens holding structure has a lens focus mechanism and a shift mechanism, and the mechanism is complicated, and rigidity is required to suppress the tilt and vibration of the lens. The chassis to which the lens mount is fixed needs to be rigid enough to support the weight of the lens and the lens mount. If the projection lens can be reduced in size and weight, these lens mounts and chassis can be simplified and reduced in weight.
[0010]
In other words, reducing the size and weight of the projection lens can reduce not only the size and weight of the projection lens itself but also the components of the set, and can reduce the weight of large projectors that were previously difficult to install, It will be easy to install.
[0011]
On the other hand, the convex group leading three-group zoom lens proposed in Patent Document 2 has insufficient back focus, and the total length of the lens is about 11 times the wide-angle end focal length, making it difficult to reduce the size. In addition, the concave group leading four-group zoom lens proposed in Patent Document 3 is so dark that the F number is about 3.5, and the brightness cannot be secured.
[0012]
The present invention solves the above-described conventional problems, and in order to realize a bright, high-definition and compact projector, a compact zoom lens having a long back focus and a projector using the same are provided. The purpose is to provide.
[0013]
[Means for Solving the Problems]
  In order to achieve the above object, a first zoom lens of the present invention includes a first lens group having a negative refractive power and a positive refraction in order from the side having the long conjugate distance.PowerSecond lens group and positive refractionPower3rd lens group and positive refractionPowerThe first4With lens groupConsists ofWhen zooming from the wide-angle end to the telephoto end,1In the zoom lens in which the lens group, the second lens group, the third lens group, and the fourth lens group move along the optical axis, the first lens group moves monotonously to the short conjugate distance side, and the second lens group A lens group, the third lens group, and the third lens group.4The lens group monotonously moves to the longer conjugate distance side, and the diaphragm is located in the second lens group.2When moving along the optical axis together with the lens group, bfw is the air-converted back focus at the infinity of the zoom lens at the wide angle end, and fw is the focal length of the zoom lens at the wide angle end,
  2.5 <bfw / fw <4
It is characterized by satisfying the relationship.
[0014]
In the second zoom lens of the present invention, the focal length of the first negative lens when viewed from the side having the long conjugate distance is f1, the Abbe number is abe1, the refractive index of the d-line is nd11, and the second lens group at the wide-angle end. From the above, it is assumed that the combined focal length of the fourth lens group is frear.
−0.018 <(1 / f1 / abe1) / (1 / frear) <0
1.7 <nd11 <1.79
It is characterized by satisfying the relationship.
[0015]
In the third zoom lens according to the present invention, the configuration of four lenses from the side with the short conjugate distance is, in order from the side with the long conjugate distance, the negative meniscus lens, the positive lens, and the conjugate with the convex surface facing the side with the long conjugate distance. A negative meniscus lens with a convex surface facing the short side, a positive lens,
The negative meniscus lens on the longer conjugate distance side has a d-line refractive index of nd4, an Abbe number of νd4, the focal length of the four lenses is f4r, and an air-converted back that does not include a prism or cover glass at the wide-angle end. If the focus is bfw,
nd4> 1.75
νd4> 35
1 <f4r / bfw <4
It is characterized by satisfying the relationship.
[0016]
The image magnification projection system of the present invention includes a projection lens using each of the zoom lenses, and further includes a light source, and a spatial light modulation element that is illuminated with light emitted from the light source and forms an optical image, An optical image on the spatial light modulator is projected by the projection lens.
[0017]
The video projector of the present invention includes a projection lens using each of the zoom lenses, further includes a light source, means for temporally limiting light from the light source to three colors of blue, green, and red, and radiation from the light source. A spatial light modulation element that forms an optical image corresponding to three colors of blue, green, and red that is illuminated with the light and changes with time, and an optical image on the spatial light modulation element by the projection lens Is projected.
[0018]
A rear projector according to the present invention includes the deoprojector according to the present invention, a mirror that bends light projected from a projection lens, and a transmission screen that projects the projected light on an image.
[0019]
The multi-vision system of the present invention includes a plurality of systems each including the video projector of the present invention, a transmissive screen that projects projected light onto an image, and a housing, and further includes image division for dividing the image. A circuit is provided.
[0020]
  BookAccording to the first zoom lens of the present invention, the first lens group has negative power, and the pupil having the long conjugate distance is moved to the side having the long conjugate distance, so that the outer diameter of the first lens group can be reduced. In addition, the second to fourth lens groups move to the longer conjugate distance for good aberration correction in the entire zoom range from the wide-angle end to the telephoto end. The stop is in the second lens group and prevents the position of the pupil on the side with the short conjugate distance from fluctuating. According to this configuration, a compact zoom lens can be realized while realizing a long back focus.
[0021]
According to the second zoom lens of the present invention, the lateral chromatic aberration can be reduced. frear is the combined focal length of the second lens group to the fourth lens group at the wide-angle end, and represents an overcorrection amount of the blue magnification chromatic aberration of the second lens group to the fourth lens group. f1 / abe1 represents the amount of blue lateral chromatic aberration generated by the leading negative lens on the longer conjugate distance side. By satisfying the relational expression, an excessive correction of the blue lateral chromatic aberration occurring from the second lens group to the fourth lens group is caused by the blue lateral chromatic aberration occurring at the leading negative lens when viewed from the side having the long conjugate distance. The amount of generation can be canceled out, and the chromatic aberration of magnification can be kept small. nd11 is the refractive index of the d-line of the leading negative lens when viewed from the side with the long conjugate distance. The higher the refractive index, the greater the amount of blue lateral chromatic aberration generated. However, the higher the refractive index, the worse the blue internal transmittance and the blue brightness becomes darker. For this reason, the balance between the amount of chromatic aberration of magnification and the internal transmittance is achieved by the relational expression.
[0022]
According to the third zoom lens of the present invention, distortion and lateral chromatic aberration can be suppressed to a small level. A lens having a short conjugate distance generates large distortion and lateral chromatic aberration, and its power and shape are important for correction. For this reason, negative meniscus lenses having high ability to correct distortion aberration and lateral chromatic aberration are used for two of the four lenses from the side having the short conjugate distance. nd4 and νd4 are conditions for suppressing overcorrection of the lateral chromatic aberration of blue by the refractive index and Abbe number of the negative meniscus lens. f4r / bfw represents the ratio of the focal length of the four lenses from the side with the short conjugate distance and the air-converted back focus not including the prism or cover glass at the wide-angle end. This relates to the correction, the overall lens length, and the outer diameter of the lens on the longer conjugate distance side.
[0036]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[0037]
(Embodiment 1)
FIG. 1 is a configuration diagram of the zoom lens according to Embodiment 1 at the wide-angle end. FIG. 2 is a configuration diagram of the telephoto end of the zoom lens shown in FIG. The zoom lens 10 shown in FIG. 1 includes a first lens group 11 having a negative refractive power, a second lens group 12 having a positive refractive power, a third lens group 13 having a positive refractive power, and a positive lens when viewed from the side having a long conjugate distance. The fourth lens group 14 having a refractive power has a four-group configuration. Reference numeral 15 denotes a glass block such as a prism. Reference numeral 16 denotes an image plane, which is a film or a CCD in the case of an imaging system, and an LCD that is a spatial modulation element in the case of a projection apparatus. In the example of FIG. 1, the side having the long conjugate distance is the side opposite to the image plane 16 (the same applies to the following drawings).
[0038]
In zooming from the wide-angle end (FIG. 1) to the telephoto end (FIG. 2), the first lens group 11 moves to the short conjugate distance side, and the second lens group 12 moves to the long conjugate distance side. The third lens group 13 moves to the longer conjugate distance side, and the fourth lens group 14 moves to the longer conjugate distance side.
[0039]
The configuration of the first lens group 11 is a six-lens configuration including a negative lens 11a, a positive lens 11b, a negative lens 11c, a negative lens 11d, a negative lens 11e, and a positive lens 11f in this order from the longest conjugate distance.
[0040]
The second lens group 12 is a variable magnification lens group. The configuration of the second lens group 12 is a three-lens configuration including a negative lens 12a, a positive lens 12b, and a positive lens 12c from the side having the long conjugate distance. In order to ensure the back focus of the entire zoom lens, the second lens group 12 has a reverse telephoto configuration.
[0041]
The third lens group 13 has a relatively large positive refractive index, and has the effect of reducing the burden on the fourth lens group and moving the position of the diaphragm 17 to the longer conjugate distance side. The third lens group 13 moves slightly differently from the second lens group 12 and the fourth lens group 14 in order to suppress aberration fluctuations accompanying zooming from the wide-angle end to the telephoto end, that is, the third lens group. 13 does not move integrally with the second lens group 12 and the fourth lens group 14, and the amount of movement differs from these lens groups.
[0042]
The fourth lens group 14 is a variable magnification lens group. During zooming, the fourth lens group 14 moves in the same manner as the second lens group 12 so as to suppress a change in telecentricity due to zooming. Since the fourth lens group 14 greatly affects the distortion and the chromatic aberration of magnification, the fourth lens group 14 is configured to effectively suppress these aberrations. That is, in order from the long conjugate distance, a concave meniscus lens 14a and a positive lens 14b with a convex surface facing the long conjugate distance, a concave meniscus lens 14c with a convex surface facing the short conjugate distance, and a positive lens 14d are arranged. It has a configuration.
[0043]
As described above, according to the present invention, a compact zoom can be achieved while ensuring a back focus by adopting a four-group zoom configuration of negative, positive, positive, and positive refractive power when viewed from the side having a long conjugate distance. The lens is realized. Hereinafter, the zoom lens 10 will be described more specifically. The zoom lens 10 is based on a two-group zoom composed of negative and positive. The two-group zoom is suitable for a wide angle and has a feature that a long back focus can be easily obtained. However, it is difficult to achieve a large zoom and a large aperture, and the back focus changes due to zooming from the wide-angle end to the telephoto end, and the F-number changes.
[0044]
The so-called positive power leading zoom lens of positive, negative, positive, positive, positive, negative, negative, and positive four-group zoom, or positive, negative, and positive three-group zoom has a long conjugate distance on the pupil side. Since it is located on the side where the conjugate distance is short, the outer diameter of the positive first lens group becomes large when the angle is widened. Furthermore, in order for telecentricity not to change by zooming, it is necessary to place a stop in the positive lens group on the side with the shortest conjugate distance in any configuration, and it is difficult to suppress distortion variation due to zooming. It is.
[0045]
In order to obtain a projection lens of a projector, it is necessary to have a small distortion and a small chromatic aberration of magnification in order to obtain high image quality, and a reduction in size is desired for ease of installation.
[0046]
Therefore, in the present embodiment, a negative power head type zoom configuration is used, and the outer diameter of the negative first lens group is suppressed to be compact by positioning the pupil on the longer conjugate distance side. Furthermore, by positioning the aperture position on the longer conjugate distance side, the pupil can be moved to the longer conjugate distance side, so that the outer diameter of the negative first lens group 11 can be made compact.
[0047]
The aperture position determines telecentricity and is important for optical arrangement. In order to realize a long back focus, telecentricity, and an arrangement of a diaphragm located on the long side of the conjugate distance, it is important to arrange a positive power as close to the diaphragm as possible. In order to satisfy the above, the positive power of the second lens group and the third lens group is larger than the positive power of the fourth lens group 14.
[0048]
A basic zoom lens produces a negative distortion at the wide-angle end and a positive distortion at the telephoto end than at the wide-angle end. In order to suppress fluctuation due to distortion magnification, it is desirable that each lens group due to magnification change monotonously. For example, in the positive, negative, positive, and positive four-group zoom, when the positive first lens unit is fixed during zooming and the magnification of the negative second lens unit moves across the same magnification, the positive third lens The group is at the same position at the wide-angle end and the telephoto end, and has the maximum amount of movement between the wide-angle end and the telephoto end. In this case, the distortion generated in the positive third lens group is substantially the same at the wide-angle end and the telephoto end, and it is impossible to suppress distortion variation due to zooming in the entire lens system.
[0049]
In the present embodiment, the second lens group 12 to the fourth lens group 14 are arranged so as to be used at a minus reduction magnification so that the magnification is not sandwiched by magnification. In this way, in the present embodiment, in zooming from the wide angle end to the telephoto end, the first lens group 11 monotonously moves from the long conjugate distance side to the short side, and from the second lens group 12 to the first one. The four lens group 14 monotonously moves from the short side of the conjugate distance to the long side. With the configuration as described above, the variation in distortion due to zooming from the wide-angle end to the telephoto end can be effectively suppressed.
[0050]
In a zoom lens in which the back focus fluctuates, the F-number fluctuates unless the aperture is varied by zooming. The F number variation is proportional to the back focus variation. In order to reduce the fluctuation amount of the F number, the fluctuation amount of the back focus may be reduced.
[0051]
In the present embodiment, the absolute value of the magnification of the second lens group 12 to the fourth lens group 14 is reduced. However, if this magnification is reduced, the overall length of the lens increases, and a long back focus cannot be secured. Therefore, in the present embodiment, when the second lens group 12 is viewed from the side having the long conjugate distance, a long back focus is ensured by forming the lens 12a with a negative refractive power and a lens 12b with a positive refractive power. ing.
[0052]
The present embodiment satisfies the following expression (1), where bfw is the air-converted back focus at infinity at the wide angle end and fw is the focal length of the zoom lens 10 at the wide angle end.
(1) 2.5 <bfw / fw <4
Expression (1) defines the back focus at the wide-angle end with respect to the focal length at the wide-angle end, and defines the necessary back focus of the projection lens used in the projector. In particular, when a reflective element is used as the spatial modulation element, a prism block for introducing illumination light is disposed between the projection lens and the spatial modulation element in addition to the color synthesis prism. For this reason, the projector projection lens requires a long back focus. If the lower limit of Expression (1) is exceeded, a necessary space cannot be obtained between the projection lens and the spatial modulation element, and the projector cannot be configured. If the upper limit is exceeded, the overall length and outer diameter of the lens will increase, making it impossible to reduce the size.
[0053]
Hereinafter, in the present embodiment, a configuration preferable for optical performance will be described. First, in the second lens group 12, when viewed from the side with the long conjugate distance, the first lens has a negative refractive power, and the second lens from the side with the long conjugate distance has a positive refractive power, and at least 3 It consists of more than one lens. In this way, a long back focus can be secured by using a lens having negative and positive refractive power when viewed from the side having the long conjugate distance. In the example of FIG. 1, the second lens group 12 has a three-lens configuration, but may have a configuration of four or more lenses as long as the negative lens and the positive lens are arranged in this order from the side with the long conjugate distance.
[0054]
Next, when zooming from the wide-angle end to the telephoto end, the second lens group 12 and the fourth lens group 14 make the same movement on the optical axis from the shorter conjugate distance side to the longer side. Since the diaphragm 17 is disposed in the second lens group 12, the telecentricity does not change during zooming from the wide-angle end to the telephoto end when the fourth lens group 14 moves in the same manner as the second lens group 12. . Further, the lens barrel structure can be simplified, which is advantageous for ensuring accuracy and reducing costs.
[0055]
Next, the focal length of the first lens group 11 is f1g, the focal length of the second lens group 12 is f2g, the focal length of the third lens group 13 is f3g, the focal length of the fourth lens group 14 is f4g, and the wide-angle end. When the focal length of the zoom lens is fw, it is preferable that the following expressions (2) to (5) are satisfied.
(2) -0.45 <fw / f1g <-0.3
(3) 0.01 <fw / f2g <0.3
(4) 0.18 <fw / f3g <0.29
(5) 0.05 <fw / f4g <0.2
Expression (2) defines the focal length of the first lens group 11 by the ratio of the focal lengths at the wide angle end. If the lower limit is exceeded, the Petzval sum cannot be corrected, and field curvature and astigmatism increase. If the upper limit is exceeded, the back focus cannot be secured. If the back focus is tried to be secured, the overall optical length of the entire zoom lens becomes large, and the outer diameter of the first lens group becomes large.
[0056]
Expression (3) defines the focal length of the second lens group 12 by the ratio of the focal lengths at the wide-angle end. When the lower limit is exceeded, coma increases, and when the upper limit is exceeded, back focus cannot be secured.
[0057]
Expression (4) defines the focal length of the third lens group 13 by the ratio of the focal lengths at the wide-angle end. When the lower limit is exceeded, the aperture position moves to the short conjugate distance side. The outer diameter increases. If the upper limit is exceeded, spherical aberration cannot be corrected.
[0058]
Expression (5) defines the focal length of the fourth lens group 14 by the ratio of the focal lengths at the wide-angle end. If the lower limit is exceeded, back focus cannot be secured. If the upper limit is exceeded, distortion and lateral chromatic aberration cannot be corrected.
[0059]
Next, when viewed from the long conjugate distance side, the focal length of the first negative lens 11a is f1, the Abbe number is abe1, the refractive index of the d-line is nd11, and the second lens group 12 to the fourth lens at the wide angle end. When the combined focal length of the group 14 is “frear”, it is preferable that the following expressions (6) and (7) are satisfied.
(6) -0.018 <(1 / f1 / abe1) / (1 / frear) <0.0
(7) 1.70 <nd11 <1.79
When the second lens group 12 to the fourth lens group 14 correct the chromatic aberration, the blue lateral chromatic aberration is overcorrected. The first negative lens 11a as viewed from the side having the long conjugate distance cancels the overcorrection of the blue lateral chromatic aberration.
[0060]
Equation (6) is the relationship between the amount of chromatic aberration of blue magnification of the first negative lens and the amount of overcorrection of chromatic aberration of blue magnification of the second lens group to the fourth lens group when viewed from the side having the long conjugate distance. Represents. Exceeding the lower limit results in insufficient correction of chromatic aberration of blue magnification and insufficient correction of chromatic aberration of red magnification. If the upper limit is exceeded, the blue lateral chromatic aberration will increase with overcorrection.
[0061]
The first negative lens 11a as viewed from the side having the long conjugate distance preferably has a high refractive index and a small Abbe number. However, the glass glass material as described above has a characteristic that the internal transmittance deteriorates. Expression (7) is the regulation of the refractive index of the leading negative lens 11a. If the lower limit is exceeded, the overcorrection of the chromatic aberration of the blue magnification cannot be reduced, and if the upper limit is exceeded, the internal transmittance becomes lower. The balance becomes worse.
[0062]
Next, when viewed from the side with the short conjugate distance, the four lenses (14a to 14d) are configured in order from the side with the long conjugate distance, the negative meniscus lens 14a and the positive lens 14b with the convex surface facing the side with the long conjugate distance. The negative meniscus lens 14c and the positive lens 14d have convex surfaces facing the short conjugate distance side, the refractive index of the d-line of the negative meniscus lens 14a on the long conjugate distance side is nd4, the Abbe number is νd4, and the conjugate distance is From the short side, if the focal length of the four lenses is f4r and the back focus in terms of air not including the prism or cover glass at the wide-angle end is bfw, the following expressions (8) to (10) may be satisfied. preferable.
(8) nd4> 1.75
(9) νd4> 35
(10) 1 <f4r / bfw <4
By directing the convex surfaces of the two negative meniscus lenses in different directions, it is advantageous for reducing chromatic aberration of magnification and distortion. For correction of distortion, the negative meniscus lens 14a having a convex surface facing the longer conjugate distance acts effectively, and for the magnification chromatic aberration, the negative meniscus lens 14c having the convex surface directed to the shorter conjugate distance acts effectively. .
[0063]
Expression (8) represents the refractive index of the d-line of the negative meniscus lens on the longer conjugate distance side, and the field curvature increases when the lower limit is exceeded. Equation (9) represents the Abbe number of the negative meniscus lens on the longer conjugate distance side, and the chromatic aberration of magnification increases when the lower limit is exceeded. In the formula (9), it is more preferable that νd4> 40 is satisfied.
[0064]
Expression (10) indicates that the focal length of the four lenses from the side having the short conjugate distance is larger than the air-converted back focus not including the prism or the cover glass at the wide-angle end, and the F-number light beam is the conjugate distance. This indicates that when the light enters the four lenses from the short side of the lens, it is used in a convergent state toward the short side of the conjugate distance. If the lower limit is exceeded, the outer diameter of the lens on the long side of the conjugate distance increases. , Distortion, and chromatic aberration of magnification increase. If the upper limit is exceeded, the total lens length increases, and the back focus cannot be secured.
[0065]
Next, it is preferable that all lenses having positive refractive power constituting the third lens group 13 and the fourth lens group 14 are configured with an Abbe number of 80 or more. The third lens group 13 and the fourth lens group 14 have positive refracting power, and the principal ray is greatly bent to ensure telecentricity, resulting in large chromatic aberration. In particular, the chromatic aberration of magnification increases. If all the lenses having positive refractive power constituting the third lens group 13 and the fourth lens group 14 are 80 in the Abbe number, the chromatic aberration of magnification can be reduced.
[0066]
In addition, although the structure which satisfy | fills said Formula (6)-(7) and the structure which satisfy | fills Formula (8)-(10) were demonstrated on the assumption that it applies to the structure which each satisfy | fills said Formula (1), respectively. Even if the present invention is applied to a configuration that does not satisfy the above formula (1), the effect of satisfying each of the above formulas can be obtained.
[0067]
Example 1
Hereinafter, Example 1 according to Embodiment 1 will be described. The lens configuration of Example 1 is the same as the configuration of FIGS._NO= 2.5, focal length f = 27.84, half angle of view = 30.9 °. Each value of the formulas (1) to (10) in Example 1 is as follows.
Formula (1) bfw / fw = 2.78
Formula (2) fw / f1g = −0.39
Formula (3) fw / f2g = 0.277
Formula (4) fw / f3g = 0.228
Formula (5) fw / f4g = 0.09
Formula (6) (1 / f1 / abe1) / (1 / frear) = − 0.011
Formula (7) nd11 = 1.784
Formula (8) nd4 = 1.835
Formula (9) νd4 = 37.3
Formula (10) f4r / bfw = 3.94
Next, specific numerical values are shown in Table 1, and zoom data are shown in Table 2. In Table 1, ri (mm) is the radius of curvature of each lens surface, di (mm) is the lens thickness or inter-lens spacing, ni is the refractive index of each lens at the d-line, and νi is the Abbe of each lens at the d-line. Is a number. The same applies to Tables 3 and 5 below. In the example of Table 1, r1 to r12 are a first lens group, r13 to r19 are a second lens group, r20 to r27 are a third lens group, r28 to r35 are a fourth lens group, and r15 is a stop.
[0068]
[Table 1]

[0069]
[Table 2]

[0070]
3 shows the spherical aberration (mm), astigmatism (mm), and distortion aberration (%) at the wide angle end of Example 1, and this also applies to FIGS. 7 and 11 below. It is. 4 shows the spherical aberration (mm), astigmatism (mm), and distortion (%) at the telephoto end of Example 1, and this also applies to FIGS. 8 and 12 below. It is. As can be seen from FIGS. 3 and 4, the zoom lens according to Example 1 shows good aberration performance.
[0071]
(Example 2)
FIG. 5 is a configuration diagram of the zoom lens according to the second embodiment at a wide angle end. FIG. 6 is a block diagram of the zoom lens shown in FIG. 5 at the telephoto end. The zoom lens 20 shown in FIG. 5 has a first lens group 21 (lenses 21a to 21f) having a negative refractive power and a second lens group 22 (lenses 22a to 22c) having a positive refractive power when viewed from the side having a long conjugate distance. The third lens group 23 (lenses 23a to 23c) having positive refracting power and the fourth lens group 14 (lenses 24a to 24d) having positive refracting power are provided.
[0072]
In zooming from the wide-angle end (FIG. 5) to the telephoto end (FIG. 6), the first lens group 21 moves to the short conjugate distance side, and the second lens group 22 moves to the long conjugate distance side, The third lens group 23 moves to the longer conjugate distance side, and the fourth lens group 24 moves to the longer conjugate distance side.
[0073]
In the second embodiment, F at the wide-angle end_NO= 2.3, focal length f = 21.32, half angle of view = 30.9 °. Each value of the formulas (1) to (10) in Example 2 is as follows.
Formula (1) bfw / fw = 3.66
Formula (2) fw / f1g = −0.37
Formula (3) fw / f2g = 0.01
Formula (4) fw / f3g = 0.222
Formula (5) fw / f4g = 0.175
Formula (6) (1 / f1 / abe1) / (1 / frear) = − 0.009
Formula (7) nd11 = 1.784
Formula (8) nd4 = 1.835
Formula (9) νd4 = 37.3
Formula (10) f4r / bfw = 1.56
Next, specific numerical values are shown in Table 3, and zoom data is shown in Table 4. In the example of Table 3, r1 to r12 are a first lens group, r13 to r19 are a second lens group, r20 to r25 are a third lens group, r26 to r33 are a fourth lens group, and r17 is a stop.
[0074]
[Table 3]

[0075]
[Table 4]

[0076]
Each of FIGS. 7 and 8 shows an aberration diagram at the wide-angle end and an aberration diagram at the telephoto end of Example 2, and it can be seen that the zoom lens according to Example 2 shows good aberration performance.
[0077]
(Example 3)
FIG. 9 is a configuration diagram of the zoom lens at the wide-angle end according to the third embodiment. FIG. 10 is a configuration diagram of the zoom lens shown in FIG. 9 at the telephoto end. 9, the first lens group 31 (lenses 31a to 31f) having a negative refractive power and the second lens group 32 (lenses 32a to 32c) having a positive refractive power are viewed from the side having a long conjugate distance. The third lens group 33 (lenses 33a to 33c) having positive refractive power and the fourth lens group 34 (lenses 34a to 34d) having positive refractive power are provided.
[0078]
In zooming from the wide-angle end (FIG. 9) to the telephoto end (FIG. 10), the first lens group 31 moves to the short conjugate distance side, and the second lens group 32 moves to the long conjugate distance side, The third lens group 33 moves to the longer conjugate distance side, and the fourth lens group 34 moves to the longer conjugate distance side.
[0079]
In Example 3, F at the wide-angle end_NO= 2.4, focal length f = 28.93, half angle of view = 30.9 °. Each value of the formulas (1) to (10) in Example 3 is as follows.
Formula (1) bfw / fw = 2.79
Formula (2) fw / f1g = −0.38
Formula (3) fw / f2g = 0.29
Formula (4) fw / f3g = 0.245
Formula (5) fw / f4g = 0.096
Formula (6) (1 / f1 / abe1) / (1 / frear) = − 0.012
Formula (7) nd11 = 1.784
Formula (8) nd4 = 1.835
Formula (9) νd4 = 37.3
Formula (10) f4r / bfw = 3.75
Next, specific numerical values are shown in Table 5, and zoom data is shown in Table 6. In the example of Table 5, r1 to r12 are the first lens group, r13 to r19 are the second lens group, r20 to r27 are the third lens group, r28 to r35 are the fourth lens group, and r15 is the stop.
[0080]
[Table 5]

[0081]
[Table 6]

[0082]
11 and 12 show the aberration diagrams at the wide-angle end and the telephoto end of Example 3, respectively, and it can be seen that the zoom lens according to Example 3 shows good aberration performance.
[0083]
(Embodiment 2)
FIG. 13 is a configuration diagram of an image enlargement projection system 40 according to Embodiment 2 of the present invention. The image enlargement / projection system 40 includes a projection lens 41 configured by the zoom lens according to the first embodiment, a spatial light modulation element 42 that forms an optical image, and a light source 43. Reference numeral 44 denotes a focus plane of the projected image. The optical image formed on the spatial light modulator 42 illuminated by the light source 43 is enlarged and projected onto the focus surface 44 by the projection lens 41. Since the image enlargement / projection system 40 according to the present embodiment uses the zoom lens according to the first embodiment as the projection lens 41, it is possible to obtain a screen that is not distorted or blurring of color.
[0084]
(Embodiment 3)
FIG. 14 is a configuration diagram of a video projector 50 according to Embodiment 3 of the present invention. The video projector 50 includes a projection lens 51 configured by the zoom lens according to the first embodiment, a spatial light modulation element 52 that forms an optical image, a rotation unit 53, and a light source 54.
[0085]
In the spatial light modulator 52, three types of optical images of blue, green, and red are formed by being temporally divided. The rotation unit 53 temporally limits the optical image to three colors of blue, green, and red by rotating a filter corresponding to blue, green, and red.
[0086]
The light from the light source 54 is temporally decomposed into three colors of blue, green, and red by the rotating means 53 and illuminates the spatial light modulator 52. Three types of optical images of blue, green, and red are temporally divided and formed on the spatial light modulation element 52 and enlarged and projected by the projection lens 51.
[0087]
Since the zoom lens according to Embodiment 1 is used as the projection lens 51, a video projector that can obtain a bright image with less distortion and color blur can be realized in a compact manner.
[0088]
(Embodiment 4)
FIG. 15 is a configuration diagram of a rear projector 60 according to Embodiment 4 of the present invention. The rear projector 60 includes the video projector 61 according to the third embodiment, a mirror 62 that bends light, a transmission screen 63, and a housing 64.
[0089]
The image projected from the video projector 61 is reflected by the mirror 62 and formed on the transmissive screen 63. According to the present embodiment, since the video projector of the third embodiment is used as the video projector 61, a high-definition rear projector can be realized in a compact manner.
[0090]
(Embodiment 5)
FIG. 16 is a configuration diagram of a multivision system 70 according to Embodiment 5 of the present invention. The multi-vision system 70 shown in the figure includes the video projector 71, the transmissive screen 72, the housing 73, and the video dividing circuit 74 that divides the video according to the third embodiment.
[0091]
The video signal is processed and divided by the video dividing circuit 74 and sent to a plurality of video projectors 71. An image projected from the video projector 71 is formed on the transmission screen 72. According to the present embodiment, since the video projector according to the third embodiment is used as the video projector 71, a multi-vision system in which the joints of the images are smoothly connected and there is no sense of incongruity can be realized in a compact manner.
[0092]
In the second to fifth embodiments, the example in which the zoom lens according to the first embodiment is used in an image enlargement projection system or the like has been described. However, a video camera that forms image information on an imaging means surface such as a film or a CCD, You may use for optical apparatuses, such as a film camera and a digital camera.
[0093]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a compact zoom lens while having a long back focus. Further, by using the zoom lens according to the present invention, a bright and high-definition video enlargement projection system, a video projector, a rear projector, and a multivision system can be realized in a compact manner.
[Brief description of the drawings]
FIG. 1 is a configuration diagram at the wide-angle end of a zoom lens according to Embodiment 1 of the present invention;
FIG. 2 is a configuration diagram of a telephoto end of a zoom lens according to Embodiment 1 of the present invention.
FIG. 3 is an aberration diagram at the wide-angle end according to Embodiment 1 of the present invention.
FIG. 4 is an aberration diagram at the telephoto end according to Embodiment 1 of the present invention.
FIG. 5 is a configuration diagram at the wide-angle end of a zoom lens according to Embodiment 2 of the present invention;
FIG. 6 is a configuration diagram of a telephoto end of a zoom lens according to Embodiment 2 of the present invention.
FIG. 7 is an aberration diagram at the wide-angle end according to Example 2 of the present invention.
FIG. 8 is an aberration diagram at the telephoto end according to Example 2 of the present invention.
FIG. 9 is a configuration diagram at the wide-angle end of a zoom lens according to Embodiment 3 of the present invention;
FIG. 10 is a configuration diagram of a telephoto end of a zoom lens according to Embodiment 3 of the present invention.
FIG. 11 is an aberration diagram at the wide-angle end according to Example 3 of the present invention.
FIG. 12 is an aberration diagram at the telephoto end according to Example 3 of the present invention.
FIG. 13 is a configuration diagram of an image enlargement projection system according to Embodiment 2 of the present invention.
FIG. 14 is a configuration diagram of a video projector according to a third embodiment of the invention.
FIG. 15 is a configuration diagram of a rear projector according to a fourth embodiment of the invention.
FIG. 16 is a configuration diagram of a multivision system according to a fifth embodiment of the present invention.
[Explanation of symbols]
10, 20, 30 Zoom lens
11, 21, 31 First lens group
12, 22, 32 Second lens group
13, 23, 33 Third lens group
14, 24, 34 Fourth lens group
15 Glass block
16 Image plane
17 Aperture
41, 51 projection lens
42,52 spatial light modulator
43, 54 light source
44 Focus plane of the projected image
53 Rotating means
61 Video projector
62 Mirror
63 Transmission screen
64, 73 housing
74 Video division circuit

Claims (10)

In order from the longer conjugate distance, the first lens group having a negative refractive power , the second lens group having a positive refractive power , the third lens group having a positive refractive power , and the fourth lens group having a positive refractive power . In the zoom lens in which the first lens group, the second lens group, the third lens group, and the fourth lens group move along the optical axis upon zooming from the wide angle end to the telephoto end,
The first lens group monotonously moves to a side having a short conjugate distance, the second lens group, the third lens group, and the fourth lens group monotonously moves to a side having a long conjugate distance. Located within the second lens group, upon zooming, the diaphragm moves on the optical axis together with the second lens group,
When the back focal length of the zoom lens at the infinity at the wide angle end is bfw and the focal length of the zoom lens at the wide angle end is fw,
2.5 <bfw / fw <4
A zoom lens characterized by satisfying the above relationship. In the second lens group, the first lens has a negative refractive power and the second lens has a positive refractive power when viewed from the side having the long conjugate distance, and is composed of three or more lenses. The zoom lens according to claim 1 .   3. The zoom lens according to claim 1, wherein the second lens unit and the fourth lens unit make the same movement on the optical axis from the shorter conjugate distance side to the longer side when zooming from the wide-angle end to the telephoto end. Zoom lens. The focal length of the first lens group is f1g, the focal length of the second lens group is f2g, the focal length of the third lens group is f3g, the focal length of the fourth lens group is f4g, and the zoom lens at the wide angle end. If the focal length of is fw,
−0.45 <fw / f1g <−0.3
0.01 <fw / f2g <0.3
0.18 <fw / f3g <0.29
0.05 <fw / f4g <0.2
The zoom lens according to claim 1, wherein the zoom lens satisfies the following relationship. The focal length of the first negative lens when viewed from the side having the long conjugate distance is f1, the Abbe number is abe1, the refractive index of the d-line is nd11, and the combined focal length of the second lens group to the fourth lens group at the wide angle end is If it is “frear”,
−0.018 <(1 / f1 / abe1) / (1 / frear) <0
1.7 <nd11 <1.79
The zoom lens according to claim 1, wherein the following relationship is satisfied. The configuration of four lenses from the side having the short conjugate distance is, in order from the side having the long conjugate distance, a negative meniscus lens having a convex surface facing the long conjugate distance, a positive lens, and a negative surface having the convex surface facing the short conjugate distance. Meniscus lens, positive lens,
The negative meniscus lens having the long conjugate distance has a d-line refractive index of nd4, an Abbe number of νd4, a focal length of the four lenses of f4r, and an air-converted back that does not include a prism or a cover glass at the wide-angle end. If the focus is bfw,
nd4> 1.75
νd4> 35
1 <f4r / bfw <4
The zoom lens according to claim 1, wherein the following relationship is satisfied. A projection lens using the zoom lens according to any one of claims 1 to 6 , further comprising a light source, and a spatial light modulation element that is illuminated with light emitted from the light source and forms an optical image, An image enlargement and projection system, wherein the projection lens projects an optical image on the spatial light modulator. A projection lens using the zoom lens according to any one of claims 1 to 6 , further comprising a light source, means for temporally limiting light from the light source to three colors of blue, green, and red, and the light source A spatial light modulation element that forms an optical image corresponding to three colors of blue, green, and red that is illuminated with light emitted from the light source and that changes with time, and is arranged on the spatial light modulation element by the projection lens. A video projector that projects an optical image. 9. A rear projector comprising: the video projector according to claim 8; a mirror that bends light projected from a projection lens; and a transmission screen that projects the projected light on an image. 9. A video projector according to claim 8 , a plurality of systems including a transmissive screen for projecting projected light on an image, and a housing, and further comprising an image dividing circuit for dividing the image. A featured multivision system.

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