Patent Publication Number: US-7911705-B2

Title: Projection lens and projector

Description:
This application is based on Japanese Patent Application No. 2008-169197 filed on Jun. 27, 2008, the contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT 
     1. Field of the Invention 
     The present invention relates to a projection lens for use in e.g. a projector having a zoom function, and more particularly to a projection lens for enlarging and projecting an image generated by e.g. a liquid crystal panel or a digital micromirror device onto a screen. 
     2. Description of the Related Art 
     There is widely known use of a glass material having an anomalous dispersion characteristic for correcting lateral chromatic aberration of a lens. Unlike a general glass material, the glass material having an anomalous dispersion characteristic has a feature that a graph representing a relation between a partial dispersion ratio and the Abbe number is greatly displaced from a straight line. 
     The partial dispersion ratio Pg, F; and the Abbe number Vd are respectively represented by the following conditional expressions.
 
 Pg,F =( ng−nF )/( nF−nC )
 
where ng is a refractive index with respect to g-line, nF is a refractive index with respect to F-line, and nC is a refractive index with respect to C-line.
 
 Vd =( nd− 1)/( nF−nC )
 
where nd is a refractive index with respect to d-line.
 
     In the specification, as compared with a dispersion characteristic of a general glass material, a lens element made of a glass material having relatively large refractive indexes with respect to red light and blue light is called as a lens element made of a glass material having an anomalous dispersion characteristic of Lang (hereinafter, simply called as “a lens element having Lang characteristic”); and a lens element made of a glass material having relatively small refractive indexes with respect to red light and blue light is called as a lens element made of a glass material having an anomalous dispersion characteristic of Kurz (hereinafter, simply called as “a lens element having Kurz characteristic”). 
     Specifically, a lens element made of an anomalous dispersion glass material has the following features. 
     i) In the case where a positive lens element having Lang characteristic is disposed on the reduction side of a diaphragm, lateral chromatic aberration occurs on the minus side. 
     ii) In the case where a positive lens element having Lang characteristic is disposed on the enlargement side of a diaphragm, lateral chromatic aberration occurs on the plus side. 
     iii) In the case where a negative lens element having Lang characteristic is disposed on the reduction side of a diaphragm, lateral chromatic aberration occurs on the plus side. 
     iv) In the case where a negative lens element having Lang characteristic is disposed on the enlargement side of a diaphragm, lateral chromatic aberration occurs on the minus side. 
     In the specification, the expression “lateral chromatic aberration occurs on the plus side” means that a projected image of red light or blue light is formed at a position closer to the center of a screen with respect to a projected image of green light; and the expression “lateral chromatic aberration occurs on the minus side” means that a projected image of red light or blue light is formed at a position closer to a periphery of a screen with respect to a projected image of green light. In the case where a lens element having Kurz characteristic is used, lateral chromatic aberration occurs in a reverse manner as described above. 
     In recent years, high magnification zoom lenses compatible with various photographing conditions have been demanded. In the case where the zoom ratio is increased in the high magnification zoom lenses, it is difficult to obtain an optimal lens arrangement that enables to minimize lateral chromatic aberration at both of the wide-angle end and the telephoto end. In order to satisfy the above requirement, an increased number of lens elements is required, and the production cost may be increased. 
     In the case where the zoom ratio is large, the positive power by a positive lens element is dominant at the wide-angle end where the power is increased among all the lens groups. In view of this, there is proposed an idea, wherein an optimal lens arrangement is set at the telephoto end, and a movable lens group is disposed in front of a diaphragm to suppress variation in telecentricity. In this arrangement, however, correction by the positive lens element may be excessive, and lateral chromatic aberration may occur on the plus side. 
     On the other hand, lateral chromatic aberration may occur on the minus side at the telephoto end. In other words, as a principle, lateral chromatic aberration is likely to occur on the plus side at the wide-angle end, and lateral chromatic aberration is likely to occur on the minus side at the telephoto end. 
     In order to correct the lateral chromatic aberration, U.S. Pat. No. 5,278,698, JP2004-109896, U.S. Pat. No. 7,170,691, and JP2005-43607 disclose zoom lenses, wherein a lens element having a large anomalous dispersion characteristic is arranged in a lens group having a large moving amount. 
     In the zoom lens recited in U.S. Pat. No. 5,278,698, since the moving amount of a lens group on the reduction side is large, telecentricity may vary by a zooming operation. 
     In the zoom lenses recited in JP2004-109896, U.S. Pat. No. 7,170,691, and JP2005-43607, the distance between a lens group having a maximum moving amount, and a diaphragm is not significantly changed during a zooming operation. Accordingly, the light flux passing position through the lens group is not significantly changed during the zoom operation, and lateral chromatic aberration which may vary by a zooming operation cannot be sufficiently corrected. In other words, in the zoom lenses recited in JP2004-109896, U.S. Pat. No. 7,170,691, and JP2005-43607, the effect of correcting lateral chromatic aberration is substantially the same between the wide-angle end and the telephoto end. Accordingly, a difference in lateral chromatic aberration between the wide-angle end and the telephoto end may remain unchanged, and fine lateral chromatic aberration correction cannot be performed in the entire zoom range. 
     SUMMARY OF THE INVENTION 
     In view of the above, it is an object of the present invention to provide a projection lens capable of sufficiently correcting lateral chromatic aberration at both of the wide-angle end and the telephoto end, with an increased zoom ratio, a less number of lens elements, and less variation in telecentricity. 
     A projection lens according to an aspect of the invention includes at least two movable lens groups to be moved in zooming, wherein one of the movable lens groups having a maximum moving amount includes at least one positive lens element having a positive power, the movable lens group having the maximum moving amount is arranged on an enlargement side with respect to a diaphragm, and is operable to move toward the diaphragm in zooming from a telephoto end to a wide-angle end, and the movable lens group having the maximum moving amount and the positive lens element satisfy the following conditional expressions (1) through (3)
 
 Pg,F+ 0.00181 Vd&gt; 0.652  (1)
 
0.5 &lt;Lr/L&lt; 0.8  (2)
 
1.2 &lt;Lsf/Lsr&lt; 5  (3)
 
where
 
Pg, F: a partial dispersion ratio of a lens glass material of the positive lens element,
 
Vd: an Abbe number of the lens glass material of the positive lens element,
 
Lr: a distance between an apex of a reduction-side lens surface in the movable lens group having the maximum moving amount, and an apex of a reduction-side lens surface in all the lens groups, in the case where the movable lens group having the maximum moving amount is moved to a position closest to the enlargement side in zooming,
 
L: a lens length of all the lens groups, in the case where the movable lens group having the maximum moving amount is moved to the position closest to the enlargement side in zooming,
 
Lsf: a distance between the apex of the reduction-side lens surface in the movable lens group having the maximum moving amount, and a surface of the diaphragm, in the case where the movable lens group having the maximum moving amount is moved to the position closest to the enlargement side in zooming, and
 
Lsr: a distance between the apex of the reduction-side lens surface in the movable lens group having the maximum moving amount, and the surface of the diaphragm, in the case where the movable lens group having the maximum moving amount is moved to a position closest to a reduction side in zooming.
 
     These and other objects, features and advantages of the present invention will become more apparent upon reading the following detailed description along with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a lens arrangement diagram of a projection lens in accordance with the first embodiment of the invention. 
         FIG. 2  is an optical path diagram of the projection lens at a wide-angle end. 
         FIG. 3  is an optical path diagram of the projection lens in a middle focal length position. 
         FIG. 4  is an optical path diagram of the projection lens at a telephoto end. 
         FIGS. 5A and 5B  are diagrams showing effects of correcting lateral chromatic aberration of the projection lens in the first embodiment. 
         FIGS. 6A and 6B  are diagrams schematically showing effects of correcting lateral chromatic aberration of a projection lens as a conventional example. 
         FIGS. 7A through 7D  are aberration diagrams of Example 1 of the projection lens in accordance with the first embodiment. 
         FIGS. 8A through 8D  are aberration diagrams of Example 1 of the projection lens in accordance with the first embodiment. 
         FIGS. 9A through 9D  are aberration diagrams of Example 1 of the projection lens in accordance with the first embodiment. 
         FIG. 10  is a lens arrangement diagram of a projection lens in accordance with the second embodiment of the invention. 
         FIG. 11  is an optical path diagram of the projection lens in the second embodiment at a wide-angle end. 
         FIG. 12  is an optical path diagram of the projection lens in the second embodiment in a middle focal length position. 
         FIG. 13  is an optical path diagram of the projection lens in the second embodiment at a telephoto end. 
         FIGS. 14A through 14D  are aberration diagrams of Example 2 of the projection lens in accordance with the second embodiment. 
         FIGS. 15A through 15D  are aberration diagrams of Example 2 of the projection lens in accordance with the second embodiment. 
         FIGS. 16A through 16D  are aberration diagrams of Example 2 of the projection lens in accordance with the second embodiment. 
         FIG. 17  is a lens arrangement diagram of a projection lens in accordance with the third embodiment of the invention. 
         FIG. 18  is an optical path diagram of the projection lens in the third embodiment at a wide-angle end. 
         FIG. 19  is an optical path diagram of the projection lens in the third embodiment in a middle focal length position. 
         FIG. 20  is an optical path diagram of the projection lens in the third embodiment at a telephoto end. 
         FIGS. 21A through 21D  are aberration diagrams of Example 3 of the projection lens in accordance with the third embodiment. 
         FIGS. 22A through 22D  are aberration diagrams of Example 3 of the projection lens in accordance with the third embodiment. 
         FIGS. 23A through 23D  are aberration diagrams of Example 3 of the projection lens in accordance with the third embodiment. 
         FIG. 24  is a diagram showing the entire arrangement of a projector embodying the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
     The invention is now described, by way of example, with reference to the accompanying drawings. 
     First Embodiment 
     In this section, described is an example, wherein a projection lens in accordance with the first embodiment of the invention is applied to a projector.  FIG. 24  is a diagram showing the entire arrangement of a projector in accordance with the first embodiment.  FIG. 1  is a lens arrangement diagram of a projection lens in accordance with the first embodiment. 
       FIG. 2  is an optical path diagram of the projection lens at a wide-angle end.  FIG. 3  is an optical path diagram of the projection lens in a middle focal length position between the wide-angle end and a telephoto end.  FIG. 4  is an optical path diagram of the projection lens at the telephoto end. 
     As shown in  FIG. 24 , the projector includes a screen  2 , an image generator  3  for generating an image by modulating light, a projection lens  1  for projecting an image onto the screen  2 , a light source  4 , an illumination optical system  5  for guiding light from the light source  4  to the image generator  3 , a prism Pr constituted of e.g. a TIR prism for separating illumination light and projection light, and a controller  6  for controlling overall operations of the projector. A cover glass CG is mounted on a front surface of the image generator  3 . 
     As shown in  FIG. 1 , the projection lens  1  includes first through fifth lens groups Gr 1  through Gr 5  disposed in this order from the side of the screen  2  (enlargement side or light exit side); and the prism Pr disposed on the side of the image generator  3  (reduction side or light incident side) with respect to the fifth lens group Gr 5 . 
     The first lens group Gr 1  has a negative power, the second lens group Gr 2  has a positive power, the third lens group Gr 3  has a positive power, the fourth lens group Gr 4  has a negative power, and the fifth lens group Gr 5  has a positive power. The second through the fourth lens groups Gr 2  through Gr 4  serve as movable lens groups. In this embodiment, actuators (not shown) for moving the second through the fourth lens groups Gr 2  through Gr 4  along an optical axis toward the enlargement side or the reduction side are connected to the second through the fourth lens groups Gr 2  through Gr 4 , respectively. The controller  6  is connected to the actuators to control movement of the second through the fourth lens groups Gr 2  through Gr 4 . 
     In this embodiment, the third lens group Gr 3  serves as a movable lens group having a maximum moving amount, as compared with the second lens group Gr 2  and the fourth lens group Gr 4 . The first lens group Gr 1  is constituted of lens elements L 1  through L 4  in this order from the enlargement side. The second lens group Gr 2  is constituted of lens elements L 5  and L 6  in this order from the enlargement side. The third lens group Gr 3  is constituted of lens elements L 7  through L 9  in this order from the enlargement side. The fourth lens group Gr 4  is constituted of lens elements L 10  and L 11  in this order from the enlargement side. The fifth lens group Gr 5  is constituted of lens elements L 12  through L 17  in this order from the enlargement side, and a diaphragm S 1  disposed on the enlargement side with respect to the lens element L 12 . 
     The third lens group Gr 3  has at least one positive lens element having a positive power. In the example of  FIG. 1 , the lens element L 8  and the lens element L 9  correspond to positive lens elements. 
     The third lens group Gr 3  as a movable lens group having a maximum moving amount is moved toward the diaphragm S 1  in zooming from the telephoto end to the wide-angle end. In this embodiment, as shown in  FIG. 4 , at the telephoto end, the third lens group Gr 3  is moved to a position closest to the enlargement side, and as shown in  FIG. 2 , at the wide-angle end, the third lens group Gr 3  is moved to a position closest to the reduction side. 
     The third lens group Gr 3 , and the lens elements L 8  and L 9  satisfy the following conditional expressions (1) through (3).
 
 Pg,F+ 0.00181 Vd&gt; 0.652  (1)
 
0.5 &lt;Lr/L&lt; 0.8  (2)
 
1.2 &lt;Lsf/Lsr&lt; 5  (3)
 
where
 
Pg, F: a partial dispersion ratio of a lens glass material of the lens element L 8 , L 9 ,
 
Vd: the Abbe number of the lens glass material of the lens element L 8 , L 9 ,
 
Lr: a distance between the apex of a reduction-side lens surface in the third lens group Gr 3 , and the apex of a reduction-side lens surface in all the lens groups, in the case where the third lens group Gr 3  is moved to the position closest to the enlargement side in zooming (see  FIG. 4 ),
 
L: a lens length of all the lens groups, in the case where the third lens group Gr 3  is moved to the position closest to the enlargement side in zooming (see  FIG. 4 ),
 
Lsf: a distance between the apex of the reduction-side lens surface in the third lens group Gr 3 , and a surface of the diaphragm, in the case where the third lens group Gr 3  is moved to the position closest to the enlargement side in zooming (see  FIG. 4 ), and
 
Lsr: a distance between the apex of the reduction-side lens surface in the third lens group Gr 3 , and the surface of the diaphragm, in the case where the third lens group Gr 3  is moved to the position closest to the reduction side in zooming (see  FIG. 2 ).
 
     Preferably, the projection lens  1  may satisfy the conditional expression (1)′, in place of the conditional expression (1).
 
 Pg,F+ 0.00118 Vd&gt; 0.655  (1)′
 
     As shown in the optical path diagrams of  FIG. 2  and  FIG. 4 , in the third lens group Gr 3 , the light flux passing position can be set high at the telephoto end, and the light flux passing position can be set low at the wide-angle end by satisfying the conditional expression (3). 
     As shown in  FIG. 2 , at the wide-angle end, the light flux passing position of off-axis light in the third lens group Gr 3  is close to the light flux passing position of on-axis light. As a result, at the wide-angle end, the effect of refracting the off-axis light in the third lens group Gr 3  is substantially the same as the effect of refracting the on-axis light. Accordingly, at the wide-angle end, a difference in lateral chromatic aberration between the off-axis light, and light near the optical axis in the third lens group Gr 3  is small, and lateral chromatic aberration generated in the third lens group Gr 3  is small. 
     Generally, as shown in  FIG. 2  and  FIG. 4 , a projection lens is constructed in such a manner that the light flux width of off-axis light passing through the third lens group Gr 3  is increased at the telephoto end and decreased at the wide-angle end in order to secure a fast lens system in zooming as much as possible. Thereby, the effect of refracting off-axis light at the telephoto end is gradually increased in the off-axis direction, and accordingly, the effect of correcting lateral chromatic aberration can be gradually increased in the off-axis direction. Thus, an effect of correcting lateral chromatic aberration can be sufficiently obtained even at the intermediate imaging position between the on-axis position and the outermost off-axis position. 
     In the above arrangement, fabricating the lens elements L 8  and L 9  having a positive power in the third lens group Gr 3  into a lens element having a characteristic as represented by the conditional expression (1) enables to suppress generation and variation of lateral chromatic aberration from the wide-angle end to the telephoto end. The conditional expression (1) indicates that the lens glass material has Lang characteristic. 
     The projection lens  1  in this embodiment satisfies the conditional expression (4).
 
 ft/fw&gt; 1.3  (4)
 
where ft is a focal length of all the lens groups at the telephoto end, and fw is a focal length of all the lens groups at the wide-angle end.
 
     In the case where the conditional expression (4) is satisfied, in the conventional arrangement, a difference in lateral chromatic aberration between the telephoto end and the wide-angle end is likely to increase. However, the lateral chromatic aberration difference can be suppressed by satisfying the conditional expressions (1) through (3). 
     Thereby, the zoom ratio can be increased, and usage environment of the projection lens  1  can be made versatile. 
     The projection lens  1  in this embodiment satisfies the conditional expression (5).
 
|exp/ fw|&gt; 40  (5)
 
where exp is a paraxial exit pupil position relative to the reduction-side imaging position (i.e. the image generator  3 ), and fw is a focal length of all the lens groups at the wide-angle end.
 
     Thereby, telecentricity can be secured. If the left-side value of the conditional expression (5) is under the lower limit, particularly, the efficiency in combining colors by a dichroic prism or extracting illumination light by a TIR prism may be lowered, because the angle of off-axis light is unduly increased. 
     The projection lens  1  in this embodiment satisfies the conditional expression (6).
 
 Lsr/Lw&lt; 0.3  (6)
 
where Lsr is a distance between the diaphragm S 1 , and the apex of a reduction-side lens surface in the third lens group Gr 3 , in the case where the third lens group Gr 3  is moved to the position closest to the reduction side in zooming (see  FIG. 2 ), and Lw is a lens length of all the lens groups, in the case where the third lens group Gr 3  is moved to the position closest to the reduction side in zooming (see  FIG. 2 ).
 
     Thereby, at the wide-angle end, the third lens group Gr 3  is moved to a position close to the diaphragm S 1 , and the effect of correcting lateral chromatic aberration at the telephoto end can be increased, without changing the lateral chromatic aberration at the wide-angle end. 
     The projection lens  1  in this embodiment is constructed in such a manner that each of the first lens group Gr 1  and the second lens group Gr 2  disposed at a position closer to the enlargement side with respect to the third lens group Gr 3  includes at least one negative lens element, and the negative lens elements satisfy the conditional expression (1). In this embodiment, negative lens elements satisfying the conditional expression (1) are the lens element L 2  and the lens element L 5 . Preferably, at least one negative lens element to be provided in each of the first lens group Gr 1  and the second lens group Gr 2  may satisfy the conditional expression (1)′, in place of the conditional expression (1). 
     Thereby, lateral chromatic aberration at the wide-angle end can be reduced. Since lateral chromatic aberration at the telephoto end is corrected by the positive lens elements in the third lens group Gr 3 , and lateral chromatic aberration at the wide-angle end is corrected by the negative lens elements in the first lens group Gr 1  and the second lens group Gr 2 , lateral chromatic aberration in the entire zoom range can be corrected. Further, in this embodiment, the number of the lens elements L 1  through L 17  constituting all the lens groups is seventeen. Thus, the lens construction is simplified. 
     The number of the lens elements constituting each of the first through the fifth lens groups Gr 1  through Gr 5  is not limited to the one shown in  FIG. 1 , but may be the number other than the one shown in  FIG. 1 . 
       FIGS. 5A and 5B  are diagrams schematically showing effects of correcting lateral chromatic aberration of the projection lens  1  in this embodiment.  FIGS. 6A and 6B  are diagrams schematically showing effects of correcting lateral chromatic aberration of a projection lens as a comparative example. The projection lens  1  in this embodiment is constructed in such a manner that a movable lens group (third lens group Gr 3 ) having a maximum moving amount is moved toward the diaphragm in zooming from the telephoto end to the wide-angle end. On the other hand, the projection lens as a comparative example is constructed in such a manner that a movable lens group having a maximum moving amount is moved away from the diaphragm in zooming from the telephoto end to the wide-angle end. In other words, in the comparative example, the projection lens is constructed to reduce lateral chromatic aberration at the telephoto end, and correct lateral chromatic aberration at the wide-angle end by the movable lens group having the maximum moving amount. 
       FIGS. 5A and 6A  show effects of correcting lateral chromatic aberration at the telephoto end, and  FIGS. 5B and 6B  show effects of correcting lateral chromatic aberration at the wide-angle end, respectively. 
     In  FIGS. 5A and 5B , and  FIGS. 6A and 6B , the vertical axis indicates a magnitude of lateral chromatic aberration, and the horizontal axis indicates a distance from the optical axis of a projection lens. 
     In this embodiment, lateral chromatic aberration at the telephoto end is corrected by the third lens group Gr 3  satisfying the conditional expressions (1) and (3), but lateral chromatic aberration at the wide-angle end is not corrected. However, in this embodiment, lateral chromatic aberration at the wide-angle end is set small by fabricating the negative lens elements (lens elements L 2  and L 5 ) in the first lens group Gr 1  and the second lens group Gr 2  into a negative lens element satisfying the conditional expression (1), in other words, a lens element satisfying Lang characteristic. Accordingly, as is obvious from  FIGS. 5A and 5B , lateral chromatic aberration at both of the wide-angle end and the telephoto end is satisfactorily corrected. 
     On the other hand, in the case of  FIGS. 6A and 6B , the projection lens is constructed in such a manner that lateral chromatic aberration at the telephoto end is not generated, and lateral chromatic aberration at the wide-angle end is corrected by the third lens group Gr 3 . In the case of a projection lens, lens elements having substantially the same F-number are required to be arranged at the telephoto end and the wide-angle end. Accordingly, the light flux width at the wide-angle end is reduced, as compared with the light flux width at the telephoto end. If a light flux having a small light flux width is incident on a periphery of a lens element, the light flux is subjected to strong refraction, as compared with a light flux having a large light flux width. 
     Accordingly, as is obvious from  FIG. 6B , the effect of correcting lateral chromatic aberration is excessively imposed on the periphery of a lens element, and lateral chromatic aberration is not satisfactorily corrected. 
     Example 1 
     In this section, Example 1 of the projection lens  1  in accordance with the first embodiment is described. Construction data of lens elements in Example 1 is as follows. CR indicates a curvature radius of a lens surface of each lens element. T indicates a distance (on-axis distance between lens surfaces) between lens surfaces on the optical axis in an infinite focus position. Nd indicates a refractive index of each lens element with respect to d-line. Vd indicates the Abbe number of each lens element with respect to d-line. The lens surface attached with the symbol ri (i=1, 2, 3, . . . ) indicates the i-th lens surface from the enlargement side. 
     
       
         
           
               
             
               
                   
               
               
                 unit: mm 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 lens surface number 
                 CR 
                 T 
                 Nd 
                 Vd 
               
               
                   
               
               
                  1 
                 159.120 
                 10.101 
                 1.5168 
                 64.2 
               
               
                  2 
                 1150.457 
                 0.300 
               
               
                  3 
                 129.889 
                 5.000 
                 1.48749 
                 70.44 
               
               
                  4 
                 54.181 
                 13.898 
               
               
                  5 
                 408.230 
                 4.099 
                 1.62299 
                 58.12 
               
               
                  6 
                 60.318 
                 13.793 
               
               
                  7 
                 −388.564 
                 3.724 
                 1.60311 
                 60.69 
               
               
                  8 
                 85.750 
                 variable 
               
               
                  9 
                 −163.277 
                 4.000 
                 1.62004 
                 36.29 
               
               
                 10 
                 203.028 
                 2.172 
               
               
                 11 
                 167.910 
                 13.235 
                 1.713 
                 53.94 
               
               
                 12 
                 −84.834 
                 variable 
               
               
                 13 
                 −74.125 
                 3.752 
                 1.53172 
                 48.84 
               
               
                 14 
                 210.004 
                 2.288 
               
               
                 15 
                 254.435 
                 11.317 
                 1.48749 
                 70.44 
               
               
                 16 
                 −71.783 
                 0.353 
               
               
                 17 
                 145.364 
                 6.943 
                 1.497 
                 81.61 
               
               
                 18 
                 −368.970 
                 70.864 
                 39.285 
                 3.183 
               
               
                 19 
                 −268.508 
                 2.500 
                 1.497 
                 81.61 
               
               
                 20 
                 61.678 
                 3.864 
               
               
                 21 
                 74.377 
                 5.467 
                 1.6727 
                 32.17 
               
               
                 22 
                 463.777 
                 variable 
               
               
                 23 (diaphragm) 
                 infinite 
                 65.254 
               
               
                 24 
                 2648.586 
                 2.674 
                 1.6968 
                 55.46 
               
               
                 25 
                 110.620 
                 1.620 
               
               
                 26 
                 75.026 
                 8.886 
                 1.497 
                 81.61 
               
               
                 27 
                 −118.044 
                 15.000 
               
               
                 28 
                 101.694 
                 9.074 
                 1.497 
                 81.61 
               
               
                 29 
                 −104.836 
                 2.395 
               
               
                 30 
                 −88.294 
                 3.000 
                 1.8061 
                 40.72 
               
               
                 31 
                 63.381 
                 4.295 
               
               
                 32 
                 85.519 
                 7.998 
                 1.497 
                 81.61 
               
               
                 33 
                 −213.247 
                 0.800 
               
               
                 34 
                 73.913 
                 8.683 
                 1.497 
                 81.61 
               
               
                 35 
                 −209.000 
                 15.300 
               
               
                 36 
                 infinite 
                 85.000 
                 1.5168 
                 64.2 
               
               
                 37 
                 infinite 
                 3.000 
               
               
                 38 
                 infinite 
                 3.000 
                 1.48749 
                 70.44 
               
               
                 39 
                 infinite 
                 2.000 
               
               
                   
               
            
           
           
               
            
               
                 Various data on zooming 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 telephoto end 
                 middle 
                 wide-angle end 
               
               
                   
                   
               
               
                   
                 focal length 
                 42.51 
                 36.80 
                 31.10 
               
               
                   
                 F-number 
                 2.50 
                 2.50 
                 2.50 
               
               
                   
                 T8 
                 27.844 
                 26.379 
                 25.687 
               
               
                   
                 T12 
                 42.552 
                 72.356 
                 105.818 
               
               
                   
                 T22 
                 3.455 
                 6.695 
                 10.026 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
             
            
               
                 Pg, F 
                 0.5305 (L2, L8) 
                 0.5387 (L9) 
                 0.5871 (L5) 
               
               
                 Vd 
                  70.44 (L2, L8) 
                  81.61 (L9) 
                  36.29 (L5) 
               
               
                 CONDITIONAL 
                  0.658 (L2, L8) 
                  0.686 (L9) 
                  0.653 (L5) 
               
               
                 EXPRESSION (1) 
               
               
                 Lr 
                 215.82 
               
               
                 L 
                 381.20 
               
               
                 CONDITIONAL 
                  0.566 
               
               
                 EXPRESSION (2) 
               
               
                 Lsf 
                  86.15 
               
               
                 Lsr 
                  25.04 
               
               
                 CONDITIONAL 
                  3.44 
               
               
                 EXPRESSION (3) 
               
               
                 ft 
                  42.50 
               
               
                 fw 
                  31.09 
               
               
                 CONDITIONAL 
                  1.36 
               
               
                 EXPRESSION (4) 
               
               
                 exp 
                  38902 (TELE) 
                  38902 (WIDE) 
               
               
                 CONDITIONAL 
                   1250 (TELE) 
                   1250 (WIDE) 
               
               
                 EXPRESSION (5) 
               
               
                 Lw 
                 381.20 
               
               
                 CONDITIONAL 
                  0.066 
               
               
                 EXPRESSION (6) 
               
               
                   
               
            
           
         
       
     
     Table 1 shows values of the conditional expressions (1) through (6) concerning the projection lens  1  in accordance with the first embodiment. Concerning the exit pupil position exp, a positive value indicates that the exit pupil position is on the enlargement side of a reduction-side image plane, and a negative value indicates that the exit pupil position is on the side opposite to the enlargement side of a reduction-side image plane. 
       FIGS. 7A through 9D  are aberration diagrams of the projection lens  1  as Example 1 having the above lens arrangement and construction data.  FIGS. 7A through 7D  are aberration diagrams at the wide-angle end.  FIGS. 8A through 8D  are aberration diagrams in the middle focal length position.  FIGS. 9A through 9D  are aberration diagrams at the telephoto end. Referring to  FIGS. 7A through 9D ,  FIGS. 7A ,  8 A, and  9 A show spherical aberrations and sine conditions;  FIGS. 7B ,  8 B, and  9 B show astigmatisms;  FIGS. 7C ,  8 C, and  9 C show distortion aberrations, and  FIGS. 7D ,  8 D, and  9 D show lateral chromatic aberrations. Each of the aberration diagrams show aberration at the reduction side. 
     In the spherical aberration diagrams, the solid line “d”, the one-dotted-chain line “g”, and the two-dotted chain line “C” respectively represent spherical aberration amounts (unit: mm) with respect to d-line, g-line, and C-line; and the broken line “sc” represents the amount (unit: mm) of dissatisfaction with respect to the sine condition. In the astigmatism diagrams, the lines “d”, “g”, and “C” in DT respectively represent astigmatism (unit: mm) on a meridional plane with respect to the corresponding emission lines; and the lines “d”, “g”, and “C” in DS respectively represent astigmatism (unit: mm) on a sagittal plane with respect to the corresponding emission lines. In the distortion aberration diagrams, the solid line represents a distortion (unit: %) with respect to d-line. In the lateral chromatic aberration diagrams, the line “g” (solid line) and the line “C” (broken line) respectively represent lateral chromatic aberration (unit: mm) with respect to d-line. 
     Second Embodiment 
       FIG. 10  is a lens arrangement diagram of a projection lens  1  in accordance with the second embodiment of the invention. Description on elements in the second embodiment substantially identical or equivalent to those in the first embodiment is omitted herein. As shown in  FIG. 10 , the projection lens  1  for use in a projector is constituted of a first lens group Gr 1  having a negative power, a second lens group Gr 2  having a positive power, a third lens group Gr 3  having a negative power, and a fourth lens group Gr 4  having a positive power. The second and the third lens groups Gr 2  and Gr 3  serve as movable lens groups, and the second lens group Gr 2  serves as a movable lens group having a maximum moving amount. 
     The first lens group Gr 1  is constituted of lens elements L 1  through L 6 . The second lens group Gr 2  is constituted of lens elements L 7  through L 9 . The third lens group Gr 3  is constituted of lens elements L 10  and L 11 . The fourth lens group Gr 4  is constituted of lens elements L 12  through L 17 , and a diaphragm S 1 . 
       FIG. 11  is an optical path diagram of the projection lens  1  at a wide-angle end.  FIG. 12  is an optical path diagram of the projection lens  1  in a middle focal length position.  FIG. 13  is an optical path diagram of the projection lens  1  at a telephoto end. 
     As shown in the optical path diagrams of  FIG. 11  and  FIG. 13 , in the second lens group Gr 2 , the light flux passing position can be set high at the telephoto end, and the light flux passing position can be set low at the wide-angle end by satisfying the conditional expression (3). 
     As shown in  FIG. 11 , at the wide-angle end, the light flux passing position of off-axis light in the second lens group Gr 2  is close to the light flux passing position of on-axis light. As a result, at the wide-angle end, the effect of refracting off-axis light in the second lens group Gr 2  is substantially the same as the effect of refracting on-axis light. Accordingly, at the wide-angle end, a difference in lateral chromatic aberration between the off-axis light, and light near the optical axis in the second lens group Gr 2  is small, and lateral chromatic aberration generated in the second lens group Gr 2  is small. 
     Generally, as shown in  FIG. 11  and  FIG. 13 , a projection lens is constructed in such a manner that the light flux width of off-axis light passing through the second lens group Gr 2  is increased at the telephoto end and decreased at the wide-angle end in order to secure a fast lens system in zooming as much as possible. Thereby, the effect of refracting off-axis light at the telephoto end is gradually increased in the off-axis direction, and accordingly, the effect of correcting lateral chromatic aberration can be gradually increased in the off-axis direction. Thus, an effect of correcting lateral chromatic aberration can be sufficiently obtained even at the intermediate imaging position between the on-axis position and the outermost off-axis position. 
     In the above arrangement, fabricating the lens elements L 8  and L 9  having a positive power in the second lens group Gr 2  into a lens element having a characteristic as represented by the conditional expression (1) enables to suppress generation and variation of lateral chromatic aberration from the wide-angle end to the telephoto end. 
     In this embodiment, the second positive lens element and the third positive lens element (lens elements L 8  and L 9 ) in the second lens group Gr 2  from the enlargement side have Lang characteristic; and the fourth negative lens element and the fifth negative lens element (lens elements L 4  and L 5 ) in the first lens group Gr 1  from the enlargement side have Lang characteristic. This is advantageous in effectively correcting lateral chromatic aberration at the wide-angle end. Also, similarly to the first embodiment, the projection lens  1  in accordance with the second embodiment satisfies the conditional expressions (1) through (6). Thereby, the effect of correcting lateral chromatic aberration at the telephoto end can be increased, without changing lateral chromatic aberration at the wide-angle end. Further, in this embodiment, the number of the lens elements L 1  through L 17  constituting all the lens groups is seventeen. Thus, the lens construction is simplified. 
     Example 2 
     In this section, Example 2 of the projection lens  1  in accordance with the second embodiment is described. Construction data of lens elements in Example 2 is described as follows. 
     
       
         
           
               
               
               
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 lens surface number 
                 CR 
                 T 
                 Nd 
                 Vd 
               
               
                   
                   
               
               
                   
                  1 
                 145.914 
                 13.688 
                 1.5168 
                 64.2 
               
               
                   
                  2 
                 4111.673 
                 0.300 
               
               
                   
                  3 
                 126.700 
                 5.000 
                 1.62299 
                 58.12 
               
               
                   
                  4 
                 59.838 
                 17.863 
               
               
                   
                  5 
                 −487.327 
                 4.000 
                 1.62299 
                 58.12 
               
               
                   
                  6 
                 69.775 
                 16.990 
               
               
                   
                  7 
                 −135.987 
                 3.500 
                 1.48749 
                 70.44 
               
               
                   
                  8 
                 110.920 
                 13.163 
               
               
                   
                  9 
                 −297.722 
                 4.000 
                 1.62004 
                 36.29 
               
               
                   
                 10 
                 182.301 
                 2.692 
               
               
                   
                 11 
                 167.869 
                 15.859 
                 1.713 
                 53.94 
               
               
                   
                 12 
                 −86.701 
                 variable 
               
               
                   
                 13 
                 −82.787 
                 3.500 
                 1.53172 
                 48.84 
               
               
                   
                 14 
                 158.884 
                 2.082 
               
               
                   
                 15 
                 168.714 
                 12.878 
                 1.48749 
                 70.44 
               
               
                   
                 16 
                 −77.261 
                 0.300 
               
               
                   
                 17 
                 143.584 
                 7.702 
                 1.497 
                 81.61 
               
               
                   
                 18 
                 −379.331 
                 variable 
               
               
                   
                 19 
                 −196.436 
                 2.500 
                 1.497 
                 81.61 
               
               
                   
                 20 
                 75.757 
                 20.746 
               
               
                   
                 21 
                 117.572 
                 6.032 
                 1.6727 
                 32.17 
               
               
                   
                 22 
                 34246.575 
                 variable 
               
               
                   
                 23 (diaphragm) 
                 infinite 
                 31.325 
               
               
                   
                 24 
                 −7727.975 
                 3.500 
                 1.48749 
                 70.44 
               
               
                   
                 25 
                 59.705 
                 3.113 
               
               
                   
                 26 
                 65.511 
                 10.307 
                 1.497 
                 81.61 
               
               
                   
                 27 
                 −120.777 
                 50.798 
               
               
                   
                 28 
                 118.670 
                 9.002 
                 1.497 
                 81.61 
               
               
                   
                 29 
                 −71.036 
                 1.607 
               
               
                   
                 30 
                 −76.120 
                 3.000 
                 1.8061 
                 40.72 
               
               
                   
                 31 
                 62.865 
                 4.142 
               
               
                   
                 32 
                 83.250 
                 7.796 
                 1.497 
                 81.61 
               
               
                   
                 33 
                 −260.727 
                 0.800 
               
               
                   
                 34 
                 76.999 
                 9.968 
                 1.497 
                 81.61 
               
               
                   
                 35 
                 −114.817 
                 15.300 
               
               
                   
                 36 
                 infinite 
                 85.000 
                 1.5168 
                 64.2 
               
               
                   
                 37 
                 infinite 
                 3.000 
               
               
                   
                 38 
                 infinite 
                 3.000 
                 1.48749 
                 70.44 
               
               
                   
                 39 
                 infinite 
                 2.000 
               
               
                   
                   
               
            
           
           
               
            
               
                 Various data on zooming 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 telephoto end 
                 middle 
                 wide-angle end 
               
               
                   
                   
               
               
                   
                 focal length 
                 42.51 
                 36.80 
                 31.10 
               
               
                   
                 F-number 
                 2.50 
                 2.50 
                 2.50 
               
               
                   
                 T12 
                 64.135 
                 87.520 
                 119.446 
               
               
                   
                 T18 
                 68.375 
                 36.046 
                 4.048 
               
               
                   
                 T22 
                 4.016 
                 12.960 
                 13.031 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
             
            
               
                 Pg, F 
                 0.5305 (L4, L8) 
                 0.5387 (L9) 
                 0.5871 (L5) 
               
               
                 Vd 
                  70.44 (L4, L8) 
                  81.61 (L9) 
                  36.29 (L5) 
               
               
                 CONDITIONAL 
                  0.658 (L4, L8) 
                  0.686 (L9) 
                  0.653 (L5) 
               
               
                 EXPRESSION (1) 
               
               
                 Lr 
                 237.02 
               
               
                 L 
                 424.67 
               
               
                 CONDITIONAL 
                  0.558 
               
               
                 EXPRESSION (2) 
               
               
                 Lsf 
                 101.66 
               
               
                 Lsr 
                  46.35 
               
               
                 CONDITIONAL 
                  2.19 
               
               
                 EXPRESSION (3) 
               
               
                 ft 
                  42.51 
               
               
                 fw 
                  31.10 
               
               
                 CONDITIONAL 
                  1.36 
               
               
                 EXPRESSION (4) 
               
               
                 exp 
                   7241 (TELE) 
                   7241 (WIDE) 
               
               
                 CONDITIONAL 
                   232 (TELE) 
                   232 (WIDE) 
               
               
                 EXPRESSION (5) 
               
               
                 Lw 
                 424.67 
               
               
                 CONDITIONAL 
                  0.109 
               
               
                 EXPRESSION (6) 
               
               
                   
               
            
           
         
       
     
     Table 2 shows values of the conditional expressions (1) through (6) concerning the projection lens  1  in accordance with the second embodiment. Concerning the exit pupil position exp, a positive value indicates that the exit pupil position is on the enlargement side of a reduction-side image plane, and a negative value indicates that the exit pupil position is on the side opposite to the enlargement side of a reduction-side image plane. 
       FIGS. 14A through 16D  are aberration diagrams of the projection lens  1  as Example 2 having the above lens arrangement and construction data.  FIGS. 14A through 14D  are aberration diagrams at the wide-angle end.  FIGS. 15A through 15D  are aberration diagrams in the middle focal length position.  FIGS. 16A through 16D  are aberration diagrams at the telephoto end. Referring to  FIGS. 14A through 16D ,  FIGS. 14A ,  15 A, and  16 A show spherical aberrations;  FIGS. 14B ,  15 B, and  16 B show astigmatisms;  FIGS. 14C ,  15 C, and  16 C show distortion aberrations, and  FIGS. 14D ,  15 D, and  16 D show lateral chromatic aberrations. 
     Third Embodiment 
       FIG. 17  is a lens arrangement diagram of a projection lens  1  in accordance with the third embodiment of the invention. Description on elements in the third embodiment substantially identical or equivalent to those in the first and the second embodiments is omitted herein. As shown in  FIG. 17 , the projection lens  1  for use in a projector is constituted of a first lens group Gr 1  having a negative power, a second lens group Gr 2  having a positive power, a third lens group Gr 3  having a positive power, a fourth lens group Gr 4  having a negative power, a fifth lens group Gr 5  having a positive power, and a sixth lens group Gr 6  having a positive power. The second through the fifth lens groups Gr 2  through Gr 5  serve as movable lens groups, and the third lens group Gr 3  serves as a movable lens group having a maximum moving amount. 
     The first lens group Gr 1  is constituted of lens elements L 1  through L 4 . The second lens group Gr 2  is constituted of lens elements L 5  and L 6 . The third lens group Gr 3  is constituted of lens elements L 7  through L 9 . The fourth lens group Gr 4  is constituted of lens elements L 10  and L 11 . The fifth lens group Gr 5  is constituted of lens elements L 12  through L 16 , and a diaphragm S 1 . The sixth lens group Gr 6  is constituted of a lens element L 17 . 
       FIG. 18  is an optical path diagram of the projection lens  1  at a wide-angle end.  FIG. 19  is an optical path diagram of the projection lens  1  in a middle focal length position.  FIG. 20  is an optical path diagram of the projection lens  1  at a telephoto end. 
     As shown in the optical path diagrams of  FIG. 18  and  FIG. 20 , in the third lens group Gr 3 , the light flux passing position can be set high at the telephoto end, and the light flux passing position can be set low at the wide-angle end by satisfying the conditional expression (3). 
     As shown in  FIG. 18 , at the wide-angle end, the light flux passing position of off-axis light in the third lens group Gr 3  is close to the light flux passing position of on-axis light. As a result, at the wide-angle end, the effect of refracting off-axis light in the third lens group Gr 3  is substantially the same as the effect of refracting on-axis light. Accordingly, at the wide-angle end, a difference in lateral chromatic aberration between the off-axis light, and light near the optical axis in the third lens group Gr 3  is small, and lateral chromatic aberration generated in the third lens group Gr 3  is small. 
     Generally, as shown in  FIG. 18  and  FIG. 20 , a projection lens is constructed in such a manner that the light flux width of off-axis light passing through the third lens group Gr 3  is increased at the telephoto end and decreased at the wide-angle end in order to secure a fast lens system in zooming as much as possible. Thereby, the effect of refracting off-axis light at the telephoto end is gradually increased in the off-axis direction, and accordingly, the effect of correcting lateral chromatic aberration can be gradually increased in the off-axis direction. Thus, an effect of correcting lateral chromatic aberration can be sufficiently obtained even at the intermediate imaging position between the on-axis position and the outermost off-axis position. 
     In the above arrangement, fabricating the lens elements L 8  and L 9  having a positive power in the third lens group Gr 3  into a lens element having a characteristic as represented by the conditional expression (1) enables to suppress generation and variation of lateral chromatic aberration from the wide-angle end to the telephoto end. 
     In this embodiment, the second positive lens element and the third positive lens element (lens elements L 8  and L 9 ) in the third lens group Gr 3  from the enlargement side have Lang characteristic; and the second negative lens element (lens elements L 2 ) in the first lens group Gr 1  from the enlargement side, and the first negative lens element (lens element L 5 ) in the second lens group Gr 2  from the enlargement side have Lang characteristic. This is advantageous in effectively correcting lateral chromatic aberration at the wide-angle end. 
     Similarly to the first and the second embodiments, the projection lens  1  in accordance with the third embodiment satisfies the conditional expressions (1) through (6). 
     Thereby, the effect of correcting lateral chromatic aberration at the telephoto end can be increased, without changing lateral chromatic aberration at the wide-angle end. Further, in this embodiment, the number of the lens elements L 1  through L 17  constituting all the lens groups is seventeen. Thus, the lens construction is simplified. 
     Example 3 
     In this section, Example 3 of the projection lens  1  in accordance with the third embodiment is described. Construction data of lens elements in Example 3 is described as follows. 
     
       
         
           
               
               
               
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 lens surface number 
                 CR 
                 T 
                 Nd 
                 Vd 
               
               
                   
                   
               
               
                   
                  1 
                 174.384 
                 9.446 
                 1.5168 
                 64.2 
               
               
                   
                  2 
                 1547.341 
                 0.300 
               
               
                   
                  3 
                 132.570 
                 5.000 
                 1.48749 
                 70.44 
               
               
                   
                  4 
                 53.374 
                 13.591 
               
               
                   
                  5 
                 359.021 
                 4.000 
                 1.62299 
                 58.12 
               
               
                   
                  6 
                 58.083 
                 13.862 
               
               
                   
                  7 
                 −415.638 
                 3.500 
                 1.60311 
                 60.69 
               
               
                   
                  8 
                 94.635 
                 variable 
               
               
                   
                  9 
                 −178.335 
                 4.000 
                 1.62004 
                 36.29 
               
               
                   
                 10 
                 198.416 
                 2.379 
               
               
                   
                 11 
                 171.982 
                 3.076 
                 1.713 
                 53.94 
               
               
                   
                 12 
                 −86.487 
                 variable 
               
               
                   
                 13 
                 −72.250 
                 3.687 
                 1.53172 
                 48.84 
               
               
                   
                 14 
                 260.421 
                 2.329 
               
               
                   
                 15 
                 340.086 
                 11.202 
                 1.48749 
                 70.44 
               
               
                   
                 16 
                 −69.818 
                 0.300 
               
               
                   
                 17 
                 138.701 
                 6.841 
                 1.497 
                 81.61 
               
               
                   
                 18 
                 −464.59 
                 variable 
               
               
                   
                 19 
                 −258.385 
                 2.500 
                 1.497 
                 81.61 
               
               
                   
                 20 
                 61.303 
                 4.044 
               
               
                   
                 21 
                 73.952 
                 5.559 
                 1.6727 
                 32.17 
               
               
                   
                 22 
                 467.530 
                 variable 
               
               
                   
                 23 (diaphragm) 
                 infinite 
                 62.147 
               
               
                   
                 24 
                 −3327.012 
                 2.500 
                 1.6968 
                 55.46 
               
               
                   
                 25 
                 117.293 
                 1.380 
               
               
                   
                 26 
                 72.058 
                 8.862 
                 1.497 
                 81.61 
               
               
                   
                 27 
                 −119.257 
                 15.000 
               
               
                   
                 28 
                 99.844 
                 8.249 
                 1.497 
                 81.61 
               
               
                   
                 29 
                 −106.812 
                 2.523 
               
               
                   
                 30 
                 −85.559 
                 3.000 
                 1.8061 
                 40.72 
               
               
                   
                 31 
                 62.568 
                 4.301 
               
               
                   
                 32 
                 85.163 
                 8.099 
                 1.497 
                 81.61 
               
               
                   
                 33 
                 −180.309 
                 variable 
               
               
                   
                 34 
                 74.475 
                 8.598 
                 1.497 
                 81.61 
               
               
                   
                 35 
                 −226.364 
                 15.300 
               
               
                   
                 36 
                 infinite 
                 85.000 
                 1.5168 
                 64.2 
               
               
                   
                 37 
                 infinite 
                 3.000 
               
               
                   
                 38 
                 infinite 
                 3.000 
                 1.48749 
                 70.44 
               
               
                   
                 39 
                 infinite 
                 2.000 
               
               
                   
                   
               
            
           
           
               
            
               
                 Various data on zooming 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 telephoto end 
                 middle 
                 wide-angle end 
               
               
                   
                   
               
               
                   
                 focal length 
                 42.51 
                 36.80 
                 31.10 
               
               
                   
                 F-number 
                 2.50 
                 2.50 
                 2.49 
               
               
                   
                 T8 
                 29.512 
                 28.687 
                 28.992 
               
               
                   
                 T12 
                 42.998 
                 72.617 
                 106.029 
               
               
                   
                 T18 
                 69.384 
                 37.949 
                 3.335 
               
               
                   
                 T22 
                 3.466 
                 6.637 
                 9.568 
               
               
                   
                 T33 
                 5.564 
                 5.035 
                 3.000 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
             
            
               
                 Pg, F 
                 0.5305 (L2, L8) 
                  0.5387 (L9) 
                 0.5871 (L5) 
               
               
                 Vd 
                  70.44 (L2, L8) 
                  81.61 (L9) 
                  36.29 (L5) 
               
               
                 CONDITIONAL 
                  0.658 (L2, L8) 
                  0.686 (L9) 
                  0.653 (L5) 
               
               
                 EXPRESSION (1) 
               
               
                 Lr 
                 215.17 
               
               
                 L 
                 381.20 
               
               
                 CONDITIONAL 
                  0.564 
               
               
                 EXPRESSION (2) 
               
               
                 Lsf 
                  84.95 
               
               
                 Lsr 
                  25.00 
               
               
                 CONDITIONAL 
                  3.39 
               
               
                 EXPRESSION (3) 
               
               
                 ft 
                  42.50 
               
               
                 fw 
                  31.10 
               
               
                 CONDITIONAL 
                  1.36 
               
               
                 EXPRESSION (4) 
               
               
                 exp 
                  −4696 (TELE) 
                  −73447 (WIDE) 
               
               
                 CONDITIONAL 
                   151 (TELE) 
                   2361 (WIDE) 
               
               
                 EXPRESSION (5) 
               
               
                 Lw 
                 381.20 
               
               
                 CONDITIONAL 
                  0.066 
               
               
                 EXPRESSION (6) 
               
               
                   
               
            
           
         
       
     
     Table 3 shows values of the conditional expressions (1) through (6) concerning the projection lens  1  in accordance with the third embodiment. Concerning the exit pupil position exp, a positive value indicates that the exit pupil position is on the enlargement side of a reduction-side image plane, and a negative value indicates that the exit pupil position is on the side opposite to the enlargement side of a reduction-side image plane. 
       FIGS. 21A through 23D  are aberration diagrams of the projection lens  1  as Example 3 having the above lens arrangement and construction data.  FIGS. 21A through 21D  are aberration diagrams at the wide-angle end.  FIGS. 22A through 22D  are aberration diagrams in the middle focal length position.  FIGS. 23A through 23D  are aberration diagrams at the telephoto end. Referring to  FIGS. 21A through 23D ,  FIGS. 21A ,  22 A, and  23 A show spherical aberrations;  FIGS. 21B ,  22 B, and  23 B show astigmatisms;  FIGS. 21C ,  22 C, and  23 C show distortion aberrations, and  FIGS. 21D ,  22 D, and  23 D show lateral chromatic aberrations. 
     The following is a summary on the projection lens and the projector embodying the invention having the above arrangement. 
     (1) A projection lens according to an aspect of the invention is a projection lens constructed to perform a zooming operation by movable lens groups along an optical axis. The projection lens includes at least two movable lens groups to be moved in zooming, wherein one of the movable lens groups having a maximum moving amount includes at least one positive lens element having a positive power, the movable lens group having the maximum moving amount is arranged on an enlargement side with respect to a diaphragm, and is operable to move toward the diaphragm in zooming from a telephoto end to a wide-angle end, and the movable lens group having the maximum moving amount and the positive lens element satisfy the following conditional expressions (1) through (3)
 
 Pg,F+ 0.00181 Vd&gt; 0.652  (1)
 
0.5 &lt;Lr/L&lt; 0.8  (2)
 
1.2 &lt;Lsf/Lsr&lt; 5  (3)
 
where
 
Pg, F: a partial dispersion ratio of a lens glass material of the positive lens element,
 
Vd: an Abbe number of the lens glass material of the positive lens element,
 
Lr: a distance between an apex of a reduction-side lens surface in the movable lens group having the maximum moving amount, and an apex of a reduction-side lens surface in all the lens groups, in the case where the movable lens group having the maximum moving amount is moved to a position closest to the enlargement side in zooming,
 
L: a lens length of all the lens groups, in the case where the movable lens group having the maximum moving amount is moved to the position closest to the enlargement side in zooming,
 
Lsf: a distance between the apex of the reduction-side lens surface in the movable lens group having the maximum moving amount, and a surface of the diaphragm, in the case where the movable lens group having the maximum moving amount is moved to the position closest to the enlargement side in zooming, and
 
Lsr: a distance between the apex of the reduction-side lens surface in the movable lens group having the maximum moving amount, and the surface of the diaphragm, in the case where the movable lens group having the maximum moving amount is moved to a position closest to a reduction side in zooming.
 
     In the above arrangement, the conditional expression (3) means that the distance between the movable lens group having the maximum moving amount, and the diaphragm is variable during a zooming operation. Thereby, the light flux passing position can be greatly changed during a zooming operation. This is advantageous in producing a projection lens having an increased effect of correcting lateral chromatic aberration at either one of the telephoto end and the wide-angle end. 
     In the case where a projection lens is incorporated in a projector, it is necessary to minimize a change in light fastness by a zooming operation. As a result, the light flux width at the telephoto end where the focal length is long can be increased, as compared with the wide-angle end where the focal length is short. 
     In correcting lateral chromatic aberration at the wide-angle end where the light flux width is small, the correction amount may be increased at a periphery of a lens element, as compared with the center of the lens element. As a result, lateral chromatic aberration may remain at a portion near the center of a screen. In view of this, it is desirable to correct lateral chromatic aberration at the telephoto end. In the above arrangement, the movable lens group having the maximum moving amount is constructed to move toward the diaphragm in zooming from the telephoto end to the wide-angle end, and the conditional expression (1) is defined to correct lateral chromatic aberration at the telephoto end. 
     Specifically, the conditional expression (1) means that the positive lens element having an anomalous dispersion characteristic in the movable lens group having the maximum moving amount has Lang characteristic. This enables to increase the effect of correcting lateral chromatic aberration at the telephoto end in the plus direction. 
     Further, the conditional expression (2) means that the movable lens group having the maximum moving amount is arranged at a position closer to the enlargement side among all the lens groups. This arrangement facilitates correction of lateral chromatic aberration. Further, this arrangement enables to suppress variation in telecentricity by a zooming operation. 
     (2) Preferably, the projection lens may satisfy the conditional expression (4)
 
 ft/fw&gt; 1.3  (4)
 
where
 
ft: a focal length of the projection lens at the telephoto end, and
 
fw: a focal length of the projection lens at the wide-angle end.
 
     In the above arrangement, the conditional expression (4) means that the zoom ratio is large. Thereby, usage environment of the projection lens can be made versatile. 
     (3) Preferably, the projection lens may satisfy the following conditional expression (5)
 
|exp/ fw|&gt; 40  (5)
 
where
 
exp: a paraxial exit pupil position, and
 
fw: a focal length of the projection lens at the wide-angle end.
 
     In the above arrangement, the conditional expression (5) means that telecentricity is defined. If the left-side value of the conditional expression (5) is under the lower limit, the angle of off-axis light may be increased. An increased angle of off-axis light may lower the efficiency particularly in combining colors by a dichroic prism or extracting illumination light by a TIR prism. 
     (4) Preferably, the projection lens may satisfy the conditional expression (6)
 
 Lsr/Lw&lt; 0.3  (6)
 
where
 
Lsr: the distance between the apex of the reduction-side lens surface in the movable lens group having the maximum moving amount, and the surface of the diaphragm, in the case where the movable lens group having the maximum moving amount is moved to the position closest to the reduction side in zooming, and
 
Lw: a lens length of all the lens groups at the wide-angle end.
 
     In the above arrangement, the conditional expression (6) means that the movable lens group having the maximum moving amount is close to the diaphragm at the wide-angle end. This enables to increase the effect of correcting lateral chromatic aberration at the telephoto end, without changing lateral chromatic aberration at the wide-angle end. 
     (5) Preferably, the projection lens may include at least one negative lens element having a negative power on the enlargement side with respect to the movable lens group having the maximum moving amount, and a lens glass material of the negative lens element may satisfy the conditional expression (1). 
     In the above arrangement, lateral chromatic aberration at the wide-angle end can be reduced, and the effect of correcting lateral chromatic aberration at the telephoto end can be increased in the movable lens group having the maximum moving amount. Thereby, lateral chromatic aberration in the entire zoom range can be reduced. This is advantageous in obtaining an optimal lens arrangement in correcting lateral chromatic aberration at the wide-angle end. 
     (6) Preferably, in the projection lens, the lens group provided at an end of the projection lens corresponding to the enlargement side may have a negative power. 
     In the above arrangement, since the lens group provided at an end of the projection lens corresponding to the enlargement side has a negative power, correction of lateral chromatic aberration is facilitated. 
     (7) Preferably, in the projection lens, the lens groups may be constituted of a first lens group having a negative power, a second lens group having a positive power, a third lens group having a positive power, a fourth lens group having a negative power, and a fifth lens group having a positive power in the order from the enlargement side, the second lens group, the third lens group, and the fourth lens group may be the movable lens groups, and the third lens group may be the movable lens group having the maximum moving amount. 
     (8) Preferably, in the projection lens, the lens groups may be constituted of a first lens group having a negative power, a second lens group having a positive power, a third lens group having a negative power, and a fourth lens group having a positive power in the order from the enlargement side, the second lens group and the third lens group may be the movable lens groups, and the second lens group may be the movable lens group having the maximum moving amount. 
     (9) Preferably, in the projection lens, the lens groups may be constituted of a first lens group having a negative power, a second lens group having a positive power, a third lens group having a positive power, a fourth lens group having a negative power, a fifth lens group having a positive power, and a sixth lens group having a positive power in the order from the enlargement side, the second lens group, the third lens group, the fourth lens group, and the fifth lens group may be the movable lens groups, and the third lens group may be the movable lens group having the maximum moving amount. 
     (10) Preferably, in the projection lens, the number of lens elements constituting all the lens groups may be eighteen or less. 
     The above arrangement enables to produce a projection lens at a less cost. 
     (11) A projector according to another aspect of the invention includes an image generator for generating an image; a light source for emitting light; an illumination optical system for guiding the light from the light source to the image generator; and the projection lens having one of the arrangements recited in (1) through (10), and for enlarging and projecting the image generated by the image generator as a light image onto a screen surface. 
     The above arrangement enables to provide a projector incorporated with the projection lens having one of the arrangements recited in (1) through (10). 
     Although the present invention has been fully described by way of example with reference to the accompanying drawings, it is to be understood that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention hereinafter defined, they should be construed as being included therein.