JP4418650B2 - Zoom lens and image projection apparatus having the same - Google Patents

Description

【００６４】
で表示される。但しｒは近軸曲率半径である。尚、例えば「ｅ−Ｚ」の表示は「１０^-Z」を意味する。
【００６５】
前述の各条件式１〜４と数値実施例１〜３における諸数値との関係を表４に示す。
【００６６】
【外１】

【００６７】
【外２】

【００６８】
【外３】

【００６９】
【外４】

【００７０】
図７は、本発明のズームレンズを反射型の液晶プロジェクター（画像投射装置）に適用した実施形態の要部概略図である。
【００７１】
照明手段１０１からの出射光束は、ビームスプリッタ１０２によって反射され反射型の液晶表示パネル１０３に入射して反射される、この後液晶表示パネル１０３で光変調された光束はビームスプリッタ１０２を通し、ズームレンズ１０４に入射し、ズームレンズ１０４によって液晶表示パネル１０３に基づく画像情報をスクリーン１０５に投射している。
【００７２】
図８は本発明のズームレンズを撮像装置に適用した実施形態の要部概略図である。本実施形態ではビデオカメラ、フィルムカメラ、デジタルカメラ等の撮像装置に撮影レンズとして前述したズームレンズを用いた例を示している。図８においては被写体９の像をズームレンズ８で感光体７に結像し、画像情報を得ている。
【００７３】
【発明の効果】
本発明によれば、レンズ系全体の小型化を図りつつ、ズーミングに伴う諸収差を良好に補正し、画面全体にわたり良好なる光学性能を有した広画角でバックフォーカスの長いズームレンズを達成することができる。
【図面の簡単な説明】
【図１】 実施形態１のズームレンズを用いた画像投射装置の要部概略図
【図２】 数値実施例１のズームレンズをｍｍ単位で表わしたときの物体距離１．８ｍのときの収差図
【図３】 実施形態２のズームレンズを用いた画像投射装置の要部概略図
【図４】 数値実施例２のズームレンズをｍｍ単位で表わしたときの物体距離１．８ｍのときの収差図
【図５】 実施形態３のズームレンズを用いた画像投射装置の要部概略図
【図６】 数値実施例３のズームレンズをｍｍ単位で表わしたときの物体距離１．８ｍのときの収差図
【図７】 画像投射装置を反射型の液晶プロジェクターに適用したときの要部概略図
【図８】 光学機器の実施形態の要部概略図
【符号の説明】
Ｌ１ 第１レンズ群
Ｌ２ 第２レンズ群
Ｌ３ 第３レンズ群
Ｌ４ 第４レンズ群
Ｌ５ 第５レンズ群
Ｌ６ 第６レンズ群
ＬＣＤ 液晶表示装置（像面）
ＧＢ 硝子ブロック(色合成プリズム)
Ｓ Ｓａｇｉｔｔａｌ像面の倒れ
Ｍ Ｍｅｒｉｄｉｏｎａｌ像面の倒れ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a zoom lens, for example, a compact zoom lens that maintains good pupil matching with an illumination system when projecting an image displayed on a liquid crystal display element having a long back focus, and in particular, It is suitable for a mobile liquid crystal projector.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, various liquid crystal projectors (image projection apparatuses) that use an image display element such as a liquid crystal display element to project an image displayed on the display element onto a screen surface have been proposed.
[0003]
In particular, liquid crystal projectors have been widely used for conferences and presentations as devices capable of projecting images from a personal computer or the like on a large screen. In recent years, miniaturized liquid crystal projectors for home theaters have been popularized, and the size of liquid crystal display elements tends to be miniaturized.
[0004]
With regard to such a liquid crystal projector, there are roughly two types, one of which is a transmissive liquid crystal projector that projects a modulated image that has been transmitted through the liquid crystal display element by color synthesis, and the other is the back side of the liquid crystal display element. Is a reflection type liquid crystal projector that projects a modulated image reflected by the mirror.
[0005]
In a three-plate type liquid crystal projector using three liquid crystal display elements, a space for arranging elements such as a dichroic prism and a polarizing plate for synthesizing color light modulated by the liquid crystal display element is provided between the liquid crystal display element and the projection lens. It is necessary to provide the projection lens with a certain length of back focus.
[0006]
In such a liquid crystal projector, a negative lead type zoom lens preceded by a lens group having a negative refractive power is widely used. The negative lead type zoom lens has features such as being relatively easy to widen the angle and maintaining good optical performance at close-up shooting distances, but on the other hand, it is a lens group that moves during zooming. The amount of movement increases and aberration fluctuations increase accordingly, and it is difficult to achieve a high zoom ratio, and further, it is difficult to widen the angle while suppressing various aberrations.
[0007]
As a projection optical system used for a color liquid crystal projector,
-The pupil on the liquid crystal display element (reduction) side is at infinity in order to minimize the effect of the angle dependency of the color composition film provided on the dichroic prism and to ensure good pupil matching with the illumination system. A so-called telecentric optical system,
・ When combining and projecting pictures (images) of three color liquid crystal display elements on the screen, the pixels of each color are displayed on the screen so that the characters on the computer do not appear double and the sense of resolution and quality are not compromised. It must be superimposed over the entire area. Therefore, the color shift (magnification chromatic aberration) occurring in the projection lens is corrected well in the visible light band,
-The distortion is sufficiently corrected so that the projected image is not distorted and unsightly (especially if there is a sudden change in distortion at the periphery and middle, etc., the image quality deteriorates). Not preferred),
Etc. are needed.
[0008]
Recently, while there is a need for high screen brightness and high image definition, projectors equipped with small panels are strongly required to be compact and lightweight with emphasis on mobility. Furthermore, there is also a demand for specifications for increasing the brightness and wide angle of view that enable bright and large screen projection in a narrow room.
[0009]
Conventionally, a projection lens for a liquid crystal projector is composed of a total of six lens groups each consisting of a negative, positive, positive, negative, positive, and positive refractive power lens group in order from the enlargement side (front side). There is known a 6-group zoom lens that performs zooming by appropriately moving the lens group (for example, Patent Document 1). This 6-group zoom lens has the first, fourth, and sixth lens groups fixed, and moves the second, third, and fifth groups in the lens system during zooming from the wide-angle end to the telephoto end. This is a telecentric zoom lens that maintains a constant overall length and suppresses chromatic aberration and aberration fluctuations during zooming. However, this 6-group zoom lens does not have a sufficient back focus length for use in a reflective liquid crystal projector.
[0010]
In addition, as a projection lens for a liquid crystal projector, it is composed of a total of four lens groups consisting of lens groups of negative, positive, negative, and positive refractive power in order from the magnification side, and among these, a predetermined lens group is moved appropriately. There is known a four-group zoom lens that performs zooming (for example, Patent Document 2). In this four-group zoom lens, the first and fourth lens groups are fixed, and the second and third lens groups in the lens system are moved during zooming from the wide-angle end to the telephoto end. In addition, this is a telecentric zoom lens having a sufficiently long back focus and a relatively wide angle of view in consideration of a reflective liquid crystal projector. However, this four-group zoom lens has a relatively large open F value (hereinafter, F value represents open), so that sufficient brightness cannot be obtained.
[Patent Document 1]
JP 2001-108900 A [Patent Document 2]
Japanese Patent Laid-Open No. 2001-215410
[Problems to be solved by the invention]
Currently, there is a demand for a small mobile type liquid crystal projector. In addition, there is a demand for short-distance projection, which is a great advantage for home theaters, that is, a wider angle of view of a liquid crystal projector. In recent years, for the purpose of increasing the brightness of a projected image, a reflection type liquid crystal display element having a good aperture efficiency has been widely used.
[0012]
For the theme of miniaturization of liquid crystal projectors, the liquid crystal display element must first be made smaller. However, if the same resolution is desired, the aperture ratio of the liquid crystal display element is reduced and the ratio between the illuminated area and the size of the light source Since (= size of illuminated area / size of light source) decreases, the illumination efficiency generally decreases, and the brightness decreases even if the device can be miniaturized. Occurs.
[0013]
In the case of a transmissive liquid crystal display element, as the size of the liquid crystal display element is reduced, the aperture ratio is reduced by the drive circuit, and the amount of light is reduced. On the other hand, in the case of a reflective liquid crystal display element, the drive circuit can be installed on the back side of the panel, so that the aperture ratio is increased and a decrease in light amount can be suppressed. For this reason, in recent years, a bright zoom lens for a reflective liquid crystal projector with good aperture efficiency has been demanded in order to efficiently achieve high brightness. However, a reflection type liquid crystal projector is longer than a transmission type liquid crystal projector because a polarization separation optical system is inserted in addition to a color synthesis optical system such as a dichroic prism between a projection lens and a liquid crystal display element. A projection lens having a back focus is required.
[0014]
In addition to the above problem, in order to ensure screen illuminance that can be observed even under fluorescent light, a projection lens with a F-number (F number) of about 3.0 or more at the wide-angle end of a projection lens for a small projector Is desired.
[0015]
That is, there is a demand for a projection lens capable of projecting close distances with high brightness and high resolution and a sufficiently long back focus as a small and light reflective liquid crystal projector.
[0016]
The present invention is a projection lens for a liquid crystal projector, for example, having a wide angle of view and a long back focus, which corrects various aberrations caused by zooming while reducing the size of the entire lens system, and has good optical performance over the entire screen. An object of the present invention is to provide a zoom lens suitable for use.
[0017]
[Means for Solving the Problems]
The zoom lens of the present invention, (screen side in the case of the projection device, the object side in the case of imaging device) front (original side in the case of the projection apparatus, the image side in the case of imaging devices) behind the sequentially into, for zooming The first lens group having a negative refractive power, the second lens group having a positive refractive power, the third lens group having a negative refractive power, the fourth lens group having a negative refractive power, or a negative refractive power that does not move. the fifth lens group, for zooming is composed of a sixth lens unit having positive refractive power which does not move, during zooming from the wide-angle end to the telephoto end, the second, third, fourth, fifth lens group Are independently moved, and when the focal length of the first lens unit is f1, the air-converted back focus is bf, and the focal length of the entire system at the short focal length end (so-called wide angle end) is fw,
1.7 <bf / (| f1 | · fw) ^1/2 <2.3
It is characterized by satisfying the following conditions.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of a zoom lens according to the present invention will be described below with reference to the drawings.
[0019]
FIG. 1 is a schematic diagram of a main part of an image projection apparatus (liquid crystal video projector) using a zoom lens according to Embodiment 1 of the present invention. 2A and 2B show an object distance (distance from the first lens group) of 1.8 m when a numerical value of Numerical Example 1 described later corresponding to Embodiment 1 of the present invention is expressed in mm. It is an aberration diagram at the wide-angle end (short focal length end) and telephoto end (long focal length end).
[0020]
FIG. 3 is a schematic diagram of a main part of an image projection apparatus (liquid crystal video projector) using the zoom lens according to the second embodiment of the present invention. 4A and 4B show an object distance (distance from the first lens group) of 1.8 m when the numerical value of Numerical Example 2 described later corresponding to Embodiment 2 of the present invention is expressed in mm. It is an aberration diagram at the wide-angle end (short focal length end) and telephoto end (long focal length end).
[0021]
FIG. 5 is a schematic diagram of a main part of an image projection apparatus (liquid crystal video projector) using a zoom lens according to Embodiment 3 of the present invention. 6A and 6B show an object distance (distance from the first lens group) of 1.8 m when a numerical value of Numerical Example 3 described later corresponding to Embodiment 3 of the present invention is expressed in mm. It is an aberration diagram at the wide-angle end (short focal length end) and telephoto end (long focal length end).
[0022]
In the image projection apparatuses according to Embodiments 1 to 3 of FIGS. 1, 3, and 5, an original image (projected image) displayed on a liquid crystal panel LCD or the like is displayed on a screen surface S using a zoom lens (projection lens, projection lens) PL. The state of the enlarged projection is shown above.
[0023]
S is a screen surface (projection surface), and LCD is an original image (projected image) such as a liquid crystal panel (liquid crystal display element). The screen surface S and the original image LCD have a conjugate relationship. In general, the screen surface S has a longer conjugate point (first conjugate point) at the enlargement side (front side), and the original image LCD has a shorter distance. The second conjugate point (second conjugate point) corresponds to the reduction side (rear side).
[0024]
GB is a glass block such as a color synthesis prism, a polarizing filter, and a color filter.
[0025]
The zoom lens PL is attached to a liquid crystal video projector main body (not shown) via a connecting member (not shown). The liquid crystal display element LCD side after the glass block GB is included in the projector body.
[0026]
L1 is a first lens group having negative refractive power, L2 is a second lens group having positive refractive power, L3 is a third lens group having negative refractive power, and L4 is a fourth lens group having negative or positive refractive power. , L5 is a fifth lens group having a negative refractive power, and L6 is a sixth lens group having a positive refractive power. The fourth lens unit L4 has a negative refractive power in the first and third embodiments and a positive refractive power in the second embodiment. ST is a stop, which is provided in the second lens unit L2.
[0027]
In each embodiment, when zooming from the wide-angle end to the telephoto end, the second lens unit L2 and the third lens unit L3 are directed to the screen S side as indicated by arrows, and the fourth lens unit L4 and the fifth lens unit L5 are the original image LCD. Each side is moved independently. For zooming, the first lens unit L1 and the sixth lens unit L6 do not move. However, focusing is performed by moving the first lens unit L1 on the optical axis. The focusing may be performed by moving the display panel LCD.
[0028]
Each lens surface is provided with a multilayer coating, which prevents a reduction in illuminance on the screen surface S.
[0029]
2, 4, and 6, G indicates the aberration at the wavelength of 550 nm, R indicates the wavelength at 620 nm, and B indicates the aberration at the wavelength of 450 nm, and S (tilt of the sagittal image plane) and M (tilt of the meridional image plane) indicate Both show aberrations at a wavelength of 550 nm. Y is the image height and Fno is the F number.
[0030]
Next, features of each embodiment will be described.
[0031]
Each embodiment has a total of six lens groups, and is characterized in that at least four lens groups are moved during zooming from the wide-angle end to the telephoto end.
[0032]
In each embodiment, a negative lead type configuration preceded by a lens unit having a negative refractive power facilitates ensuring a wide angle of view and a long back focus. In addition, the variation of aberration due to zooming is corrected by using a movable lens group for zooming as four components, and a wide optical performance is obtained over the entire zooming range.
[0033]
For zooming, both the first and sixth lens groups are fixed with respect to the image plane (LCD) so that the total zoom length is unchanged. As a result, the robustness of the projection lens unit is ensured, and the change in weight balance is reduced by fixing the lens group (first lens group) having a large effective diameter during zooming, which is advantageous in terms of mechanism. I am doing so.
[0034]
When the focal length of the first lens unit L1 is f1, the air equivalent back focus is bf, and the focal length of the entire system at the wide angle end is fw,
1.7 <bf / (| f1 | · fw) ^1/2 <2.3 (1)
Is satisfied.
[0035]
Conditional expression (1) is a condition for obtaining a sufficiently long back focus at the same time as realizing a wide angle of view. If the upper limit is exceeded, the refractive power of the first lens unit L1 becomes too strong, and it becomes difficult to correct aberrations especially in off-axis rays. On the other hand, if the lower limit is exceeded, the power of the first lens unit L1 (reciprocal of the focal length) becomes weak, so that the lens diameter tends to increase, and the entire lens length becomes longer, which is not preferable from the mechanical structure.
[0036]
When the focal lengths of the first lens group 1L1 and the second lens group L2 are f1 and f2, respectively.
0.5 <| f1 | / f2 <0.9 (2)
Is satisfied.
[0037]
Conditional expression (2) appropriately sets the relationship between the second lens unit L2 and the first lens unit L1, which are the main variable magnification lens units. If the upper limit is exceeded, the variation in aberrations during zooming becomes large, and correction thereof becomes difficult. If the lower limit is exceeded, the amount of movement of the second lens unit L2 will increase during zooming, making it difficult to reduce the size.
[0038]
Further, when the focal length of the entire system at the wide angle end is fw and the focal length of the fourth lens group is f4,
10 <| f4 | / fw <40 (3)
Is satisfied.
[0039]
Conditional expression (3) is a condition that prescribes the magnification of the correction lens group (compensator) L4 that corrects fluctuations in the imaging position accompanying zooming. If the lower limit is exceeded, the refractive power of the fourth lens unit L4 becomes too strong, and the back focus becomes longer than necessary, which makes it difficult to achieve compactness. On the contrary, if the upper limit is exceeded, the refractive power of the fourth lens unit L4 becomes too weak, and the amount of movement in zooming increases, which is not preferable.
[0040]
The sixth lens unit L6 includes one or more positive lenses, and when the Abbe number of the Abbe numbers of the materials of the one or more positive lenses is ν6p,
ν6p <30 (4)
Is satisfied.
[0041]
Conditional expression (4) is a condition when a highly dispersed material is used for the positive lens. By using a positive lens whose convex surfaces are both high-dispersion and high-refractive-power lenses, telecentricity is imparted to the image surface, and at the same time, the occurrence of high-order chromatic aberration of magnification occurring in the fifth lens unit L5 is suppressed. It is working. If the upper limit is exceeded, the dispersion becomes low and it becomes difficult to sufficiently correct the lateral chromatic aberration. Further, generally used glass tends to have a low refractive power as it becomes a low dispersion glass. It becomes difficult to obtain.
[0042]
In order to correct aberrations and reduce the overall size of the apparatus, it is preferable to set the numerical ranges of the conditional expressions (1) to (4) as follows.
[0043]
1.9 <bf / (| f1 | · fw) ^1/2 <2.2 ·· (1a)
0.55 <| f1 | / f2 <0.8 (2a)
11 <| f4 | / fw <38 (3a)
ν6p <28 (4a)
In each embodiment, in order from the front to the rear, the first lens unit L1 has a positive lens whose convex surfaces are convex, a meniscus negative lens with a convex surface facing forward, two negative lenses, and a convex surface rearward. It is composed of a meniscus positive lens. In this way, the positive lens is disposed in front of the first lens unit L1, and the distortion aberration mainly at the zoom position at the wide angle end is corrected favorably.
[0044]
Further, in order to suppress high-order lateral chromatic aberration, a material having a large chromatic dispersion (small Abbe number) is used for the rearmost positive lens having a small off-axis ray height. The three negative lenses disposed between the two positive lenses of the first lens unit L1 have the refractive powers divided on the lens surfaces of the three negative lenses, so that distortion, astigmatism, The above-described shape is used so that coma aberration is minimized.
[0045]
The second lens unit L2 includes a positive lens, a negative lens, a stop, and a positive lens whose convex surfaces are convex (embodiments 1 and 3), or a positive lens, a negative lens whose convex surfaces are convex, The positive lens, the stop, and both lens surfaces are configured as convex positive lenses (Embodiment 2).
[0046]
The third lens unit L3 includes a lens in which a negative lens whose concave surfaces are concave and a positive lens whose convex surfaces are convex.
[0047]
The second lens unit L2 and the third lens unit L3 play the role of the main variable power lens unit and are given a large refractive power. For this reason, a glass material with a high refractive index is used for the positive lens to reduce aberration fluctuations such as Petzval sum and spherical aberration during zooming. When a large aperture is required and a high resolving power is required, the depth of the rear image surface becomes shallow, and when the curvature of field and astigmatism at the intermediate image height and the like are large, the resolution is rapidly deteriorated. For this reason, the second lens unit L2 is configured as described above, thereby correcting the Petzval sum to be small.
[0048]
In particular, in the case of color blurring, in order to satisfactorily correct lateral chromatic aberration in the visible light broadband, the positive lens is efficiently corrected by using a lanthanum heavy flint material having anomalous dispersion.
[0049]
The aperture stop ST exists in the second lens unit L2 and moves together with the second lens unit L2 during zooming, and suppresses fluctuations in off-axis aberrations during zooming.
[0050]
The fourth lens unit L4 includes a negative lens whose concave surfaces are concave and a positive lens whose convex surfaces are convex.
[0051]
The fourth lens unit L4 plays a role of correcting the movement of the focus surface accompanying zooming. The magnification of the fourth lens unit L4 is equal to or greater than the entire zooming range (zoom range), and the zoom lens moves backward during zooming from the wide-angle end to the telephoto end.
[0052]
The fifth lens unit L5 includes, in order from the front to the rear, a negative lens, a positive lens whose convex surfaces are convex, and a meniscus negative lens whose convex surfaces are directed rearward. Each of these lenses is independent or two or more. It includes a cemented lens with a lens attached.
[0053]
By arranging a lens having a strong negative refractive power at a position where the incident height of the axial light beam in front of the fifth lens unit L5 arranged on the reduction side when viewed from the aperture stop ST is the smallest, efficiency is improved. The Petzval sum is kept small. Furthermore, by using two or three bonded lenses, it is easy to correct chromatic aberration of magnification, and each lens has a relatively small curvature, which reduces the sensitivity that tends to cause manufacturing problems. Yes.
[0054]
In each embodiment, the fifth lens unit L5 is composed of three bonded lenses, and a strong negative refractive power is given to two lenses having a small curvature with a positive lens having a convex surface between both lens surfaces. Yes. This strong negative refractive power effectively reduces the Petzval sum. Moreover, it plays the role which suppresses a magnification chromatic aberration by using a bonded lens. Further, since the main plane position can be arranged on the liquid crystal display element LCD side, it is advantageous to secure good telecentric performance and back focus with respect to the pupil.
[0055]
The sixth lens unit L6 includes a positive lens having convex lens surfaces. This positive lens has a high refractive index in the glass material in order to gently bend the light bounced up by a lens unit having a negative refractive power disposed on the reduction side from the aperture stop ST so as to have good telecentric performance. It is preferable to use a material, which makes it easy to reduce the Petzval sum. In addition, the sixth lens unit L6 uses a positive lens having high refractive power and high dispersion, and provides telecentricity to the image surface, and at the same time, generation of high-order chromatic aberration of magnification that occurs in the negative lens of the fifth lens unit L5. It works to suppress
[0056]
In order to reduce the size of the entire optical system, the refractive power of each lens group needs to be increased. In order to correct an increase in various aberrations accompanying an increase in refractive power at this time, it is preferable to employ at least one aspheric lens inside the projection lens PL. Specifically, in Embodiment 3 in FIG. 5, the lens surface on the front side of the fourth negative lens in the first lens unit L1 from the front is an aspherical surface.
[0057]
The aspherical surface is preferably composed of a glass mold type or a replica, but may be a plastic aspherical lens depending on the resolution target and the sensitivity of the aspherical lens. Although it depends on the aberration to be removed, it is as far as possible from the position of the aperture stop ST such as the first, fifth, or sixth lens group in order to satisfactorily correct off-axis aberrations such as field curvature and astigmatism. It is effective to adopt the position.
[0058]
The aperture stop ST is originally preferably provided with a movable stop group. However, considering the production requirements such as the addition of a cam groove, the aperture stop ST is disposed in the variable power lens group such as the second or third lens group. According to this, aberration variations during zooming can be corrected efficiently.
[0059]
As described above, according to each embodiment, a long back having a large aperture, good telecentric performance on the reduction side, high resolution, low distortion, and good correction of lateral chromatic aberration in the visible light broadband. A retrofocus zoom lens having a focus can be realized. Furthermore, a large screen image of 60 inches can be obtained at a projection distance as short as 1.8 m.
[0060]
Numerical Examples 1 to 3 corresponding to the numerical data of the zoom lenses of Embodiments 1 to 3, respectively, are shown below. In each numerical example, i indicates the order of optical surfaces from the enlargement side (front side), ri is the radius of curvature of the i-th optical surface (i-th surface), and di is the i-th surface and the (i + 1) -th surface. , Ni and νi represent the refractive index and Abbe number of the material of the i-th optical member with respect to the d-line, respectively. f is a focal length, and Fno is an F number.
[0061]
In addition, the three surfaces closest to the reduction side in Numerical Examples 1 to 3 are surfaces constituting a glass block GB corresponding to a color synthesis prism, a face plate, various filters, and the like.
[0062]
Also, when k is a conic constant, A, B, C, and D are aspheric coefficients, and the displacement in the optical axis direction at the position of the height h from the optical axis is x with respect to the surface vertex, the aspheric shape is ,
[0063]
[Expression 1]

[0064]
Is displayed. Where r is the paraxial radius of curvature. For example, the display of “e-Z” means “10 ^−Z ”.
[0065]
Table 4 shows the relationship between the above-mentioned conditional expressions 1 to 4 and various numerical values in the numerical examples 1 to 3.
[0066]
[Outside 1]

[0067]
[Outside 2]

[0068]
[Outside 3]

[0069]
[Outside 4]

[0070]
FIG. 7 is a schematic view of a main part of an embodiment in which the zoom lens of the present invention is applied to a reflective liquid crystal projector (image projection apparatus).
[0071]
The light beam emitted from the illuminating means 101 is reflected by the beam splitter 102, is incident on the reflective liquid crystal display panel 103 and is reflected, and the light beam which has been light-modulated by the liquid crystal display panel 103 passes through the beam splitter 102 and zooms. The light enters the lens 104, and image information based on the liquid crystal display panel 103 is projected onto the screen 105 by the zoom lens 104.
[0072]
FIG. 8 is a schematic diagram of a main part of an embodiment in which the zoom lens of the present invention is applied to an imaging apparatus. In the present embodiment, an example in which the zoom lens described above is used as a photographing lens in an imaging apparatus such as a video camera, a film camera, or a digital camera is shown. In FIG. 8, the image of the subject 9 is formed on the photoconductor 7 by the zoom lens 8 to obtain image information.
[0073]
【The invention's effect】
According to the present invention, while reducing the size of the entire lens system, various aberrations due to zooming are corrected well, and a zoom lens having a wide angle of view and a long back focus having excellent optical performance over the entire screen is achieved. be able to.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a main part of an image projection apparatus using a zoom lens according to a first embodiment. FIG. 2 is an aberration diagram when the zoom lens according to Numerical Example 1 is expressed in mm units when the object distance is 1.8 m. FIG. 3 is a schematic diagram of a main part of an image projection apparatus using a zoom lens according to a second embodiment. FIG. 4 is an aberration diagram when the zoom lens according to numerical example 2 is expressed in mm and the object distance is 1.8 m. FIG. 5 is a schematic diagram of a main part of an image projection apparatus using a zoom lens according to a third embodiment. FIG. 6 is an aberration diagram when the zoom lens according to numerical example 3 is expressed in millimeters when the object distance is 1.8 m. FIG. 7 is a schematic diagram of a main part when the image projection apparatus is applied to a reflective liquid crystal projector. FIG. 8 is a schematic diagram of a main part of an embodiment of an optical apparatus.
L1 1st lens group L2 2nd lens group L3 3rd lens group L4 4th lens group L5 5th lens group L6 6th lens group LCD Liquid crystal display device (image surface)
GB glass block (color synthesis prism)
S Sagittal image plane collapse M Meridional image plane collapse

Claims (9)

In order from the front to the rear, for zooming , the first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a negative or positive refractive power having a negative refractive power are used. the fourth lens group, the fifth lens unit having a negative refractive power, for zooming is constructed from a sixth lens unit having a positive refractive power as a stationary, during zooming from the wide-angle end to the telephoto end, the second, third The third, fourth, and fifth lens groups move independently . When the focal length of the first lens group is f1, the back focal point of air is bf, and the focal length of the entire system at the short focal length end is fw,
1.7 <bf / (| f1 | · fw) ^1/2 <2.3
A zoom lens characterized by satisfying   The first lens group is a positive lens in which both lens surfaces are convex in order from the front to the rear. 2. The zoom lens according to claim 1, comprising a meniscus negative lens having a convex surface facing forward, two negative lenses, and a meniscus positive lens having a convex surface facing backward. When the focal lengths of the first lens group and the second lens group are f1 and f2, respectively.
0.5 <| f1 | / f2 <0.90
The zoom lens according to claim 1, wherein the zoom lens according to claim 1 is satisfied. When the focal length of the entire system at the short focal length end is fw and the focal length of the fourth lens group is f4,
10 <| f4 | / fw <40
The zoom lens according to claim 1, wherein the zoom lens satisfies the following. The sixth lens group is composed of one or more positive lenses, and when the Abbe number of the Abbe numbers of the materials of the one or more positive lenses is ν6p,
ν6p <30
The zoom lens according to claim 1, wherein the zoom lens satisfies the following.   The fifth lens group includes, in order from the front to the rear, a negative lens, a positive lens whose convex surfaces are convex, and a meniscus-shaped lens whose convex surfaces are directed rearward. These lenses are independent or two or more lenses. A zoom lens according to any one of claims 1 to 5, further comprising a cemented lens bonded together.   The zoom lens according to claim 1, further comprising one or more aspheric lenses.   It has an image display element and the zoom lens of any one of Claim 1-7, The original image displayed on this image display element is projected on a screen surface using this zoom lens. A featured image projection apparatus.   8. An optical apparatus characterized in that image information is formed on an imaging means surface using the zoom lens according to any one of claims 1 to 7.

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