Abstract:
A projector lens system includes a negative first lens group and a positive second lens group. The first lens group comprises a first lens element that is formed as a negative meniscus lens element, a positive or negative second lens element, a negative third lens element, a positive fourth lens element that is cemented to or separated from the third lens element, and a negative fifth lens element. The first lens group satisfies condition (1) with respect to the refractive power thereof, and satisfies condition (2) with respect to the refractive power of the negative first lens element of the negative first lens group:
 
0.6&lt; f   w   /|f   I |&lt;1.0( f   I &lt;0)  (1)
 
0.3&lt; f   I   /f   1,1 &lt;0.7  (2)
       wherein   f w : focal length of the entire projector lens system at the wide-angle extremity;   f I : the focal length of the negative first lens group; and   f 1,1 : the focal length of the negative first lens element of the negative first lens group.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a projector lens system for projecting an image from a light bulb, especially a light bulb such as a digital micromirror device (herein after, DMD), which forms an image by changing directions of the micromirrors and the reflecting-direction of light rays. 
   2. Description of the Prior Art 
   In recent years, a DMD as a light bulb for a projector has become commercially viable, instead of liquid crystal display panels which have been widely used over many years. The DMD displays an image by arranging miniature micromirrors (mirror-surface elements) on a flat surface so as to correspond to pixels, and the angle of each mirror surface is mechanically controlled by employing micro-machine technology. Furthermore, the DMD has a faster response speed than a liquid crystal displays does, and can obtain a brighter image. Therefore the DMD is showing clear signs of wide popularization due to being suitable for achieving a miniaturized portable projector having high luminance and high image quality. As an example, Japanese Unexamined Patent Publication No.2001-51195 has taught an apparatus utilizing such a DMD. 
   In the case where a DMD is used in a projector apparatus as a light bulb, restrictions inherent to the DMD have to be imposed on the projector lens system. 
   The first restriction concerns the F-number of the projector lens system. Currently, when a DMD produces an image, the micromirrors are swiveled at an angle of ±12°; and by swiveling the micromirrors, effective reflection light rays (effective light rays) are separated from void reflection light rays (void light rays). Accordingly, in a projector utilizing a DMD as a light bulb, the following condition has to be met, i.e., it is required to use effective light rays only, and at the same time, not to use void light rays. By this condition, the F-number of the projector lens system can be determined, namely, the F-number is 2.4. Actually, since an increase of the amount of light rays as could as possible has been demanded, it is common practice to constitute the projector lens system having an F-number of 2.0, by considering a decrease of contrast within a range causing no adverse effects. 
   Furthermore, it should be understood that a condition like the above is established, provided that the light-bulb-side pupil of the projector lens system remains at a fixed position. Accordingly, in the case where the pupil position is variable, e.g., a zoom lens system, consideration has to be taken for optimizing the position of the pupil at the wide-angle extremity where brightness becomes generally lower due to loss in the amount of light rays. 
   The second restriction concerns the positional relationship between the DMD and the light-source system. In order to further miniaturize the projector lens system, it is preferable that the image circle of the projector lens system be as small as possible. Consequently, the position where the light source system, which inputs a projector light bundle to the DMD, is provided is limited, so that the light source system has to be positioned in substantially the same direction as the projector lens system (i.e., adjacent to each other) is, in order to make effective light rays from the DMD incident on the projector lens system. 
   Furthermore, the space between the light bulb and the most light-bulb-side lens element of the projector lens system (i.e., the back focal distance) is utilized for both the projector lens system and the light source system, so that a longer back focal distance has to be secured for the projector lens system, and at the same time, there is a need to make a lens system on the side of the light bulb smaller in order to secure sufficient light-guiding space from the light source system. This optical arrangement is equivalent to positioning the light-bulb-side pupil of the projector lens system in the vicinity of the rear of the projector lens system, from the viewpoint of the optical design for the projector lens system. 
   On the other hand, in order to improve the optical performance of the projector lens system, there is a need to use a large number of lens elements. However, if a large number of lens elements are employed in the projector lens system, the overall length thereof will become longer; and consequently, in the case of a lens system having the entrance pupil at a rearward portion thereof, the diameters of lens elements at a front portion thereof become larger. 
   Although there are restrictions as mentioned above in developing a projector apparatus, a projector apparatus employing a DMD as a light bulb is understood to be more advantageous than others not employing a DMD, in order to attain further miniaturization. Therefore currently, portable and compact apparatuses with a DMD, such as a data projector, etc., have been widely used. 
   In order to miniaturize the projector apparatus itself, there is obviously a high demand for the projector lens system to be miniaturized, and there is also a demand for an increase in the number of functions. Moreover, the projector&#39;s various aberrations should be corrected to satisfy the performance of a DMD. Furthermore, from the viewpoint of convenience, there are demands for zooming function with a large zoom ratio, and for having a large angle-of-view at the wide-angle extremity. 
   SUMMARY OF THE INVENTION 
   The present invention provides a projector apparatus which materializes a projector lens system being compact, having a wide angle-of-view, and having a high image-forming performance suitable for the characteristics of a light bulb, such as a DMD, which is arranged to form an image by changing the reflecting-direction of light rays. The projector apparatus of the present invention can project an image on a large screen with high picture quality even in a limited space, such as a small conference-room, etc. 
   According to an aspect of the present invention, there is provided a projector lens system which projects and enlarges an image from a light bulb of a projector display device onto a screen. 
   The projector lens system includes a first lens group having a negative refractive power (hereinafter, negative first lens group), a second lens group having a positive refractive power (hereinafter, positive second lens group), and a third lens group having a positive refractive power (hereinafter, positive third lens group), in this order from the projection side. 
   The negative first lens group includes a first lens element which is formed as a negative meniscus lens element having the convex surface facing toward the projection side, a positive or negative second lens element, a negative third lens element, a positive fourth lens element which is cemented to or separated from the third lens element, and a negative fifth lens element, in this order from the projection side. 
   The negative first lens group satisfies condition (1) with respect to the refractive power thereof, and satisfies condition (2) with respect to the refractive power of the negative first lens element thereof:
 
0.6 &lt;f   w   /|f   I |1.0  (1)
 
(Note: Absolute value is used due to f I &lt;0)
 
0.3 &lt;f   I   /f   1,1 &lt;0.7  (2)
 
wherein
         f w  designates the focal length of the entire the projector lens system at the wide-angle extremity;   f I  designates the focal length of the negative first lens group; and   f 1,1  designates the focal length of the negative first lens element of the negative first lens group.       

   Condition (1) specifies an appropriate distribution of refractive power to the negative first lens group. This condition is necessary to achieve balance between the size of the entire projector lens system and requirements for appropriately correcting various aberrations. In addition to the above, condition (1) is for securing a back focal distance, since a space for providing an optical system(hereinafter, illuminating optical system) for illuminating a light bulb, such as a DMD, or the like, has to be provided. 
   In a projector lens system utilizing a DMD, the illuminating optical system is positioned so that the light rays therefrom are reflected on the surface of a DMD facing toward the projector lens system, and then the light rays from the DMD progress toward the projector lens system. Accordingly, the illuminating optical system is positioned in an area within the back focal distance, i.e., between the final surface of the most light-bulb-side lens group and the DMD. For example, in  FIGS. 1 and 3 , the light rays from the illuminating optical system run along the light path D 30  to the surface of a DMD, and thereafter, the light rays reflected by the surface of a DMD again run along the light path D 30  toward the projector lens system. This can be applied to the two-lens-group arrangement ( FIG. 1 ) and the three-lens-group arrangement (FIG.  3 ). 
   If the upper limit of condition (1) is exceeded, the negative refractive power of the first lens group becomes stronger; and accordingly, the refractive power of the positive second and positive third lens groups have to be made stronger. Consequently, it becomes difficult to achieve balance among various aberrations, and the optical performance of the projector lens system deteriorates. 
   If the lower limit of condition (1) is exceeded, the distance between the negative first lens group and the positive second lens group has to make longer, so that the size of the entire projector lens system becomes larger. As a result, the purpose of further miniaturization cannot be achieved, or the back focal distance cannot be secured. 
   Condition (2) relates to the distribution of refractive power in the negative first lens group under the condition that condition (1) is satisfied. Namely, it is particularly necessary to provide an appropriate negative refractive power to the first lens element of the negative first lens group in order to secure the back focal distance, and maintain balance among various aberrations. 
   If the upper limit of condition (2) is exceeded, it would be easy to satisfy requirements of the back focal distance, and to maintain balance among various aberrations; however, it becomes difficult to produce the negative first lens group, and the production costs thereof becomes higher. 
   If the lower limit of condition (2) is exceeded, it becomes difficult to secure the back focal distance, and to maintain balance among various aberrations. 
   In addition to the above, a radius of curvature of the light-bulb-side surface of the negative first lens element of the negative first lens group preferably satisfies condition (3); a radius of curvature of the projection-side surface of the negative fifth lens element of the negative first lens group preferably satisfies condition (4); Abbe numbers of glass materials used for lens elements of the negative first lens group except for the second lens element preferably satisfy condition (5); and a refractive index of a glass material used for the positive fourth lens element preferably satisfies condition (6):
 
−1.8 &lt;f   I   /r   12 &lt;−1.0  (3)
 
0.8 &lt;f   I   /r   19 &lt;1.7  (4)
 
15&lt;(ν 1,1 +ν 1,3 +ν 1,5 )/3−ν 1,4   (5)
 
1.7&lt;n 1,4   (6)
 
wherein
 
r 12  designates a radius of curvature of a light-bulb-side surface of the negative first lens element of the negative first lens group;
         r 19  designates a radius of curvature of the projection-side surface of the negative fifth lens element of the negative first lens group;   ν 1,1  designates the Abbe number of the negative first lens element of the negative first lens group;   ν 1,3  designates the Abbe number of the negative third lens element of the negative first lens group;   ν 1,4  designates the Abbe number of the positive fourth lens element of the negative first lens group;   ν 1,5  designates the Abbe number of the negative fifth lens element of the negative first lens group; and   n 1,4  designates the refractive index with respect to the d-line of the positive fourth lens element of the negative first lens group.       

   Condition (3) is for reducing coma and distortion under the condition that negative refractive power is given to the first lens element of the negative first lens group according to condition (2). Namely, by satisfying these two conditions (2) and (3), the first lens element becomes the shape of a meniscus lens element having a strong negative refractive power. 
   If the upper limit of condition (3) is exceeded, coma and distortion cannot sufficiently be reduced. 
   If the lower limit of condition (3) is exceeded, it is effective to reduce the occurrence of various aberrations; however, the curved-shape of the negative meniscus lens element becomes too sharp, so that producing the negative first lens element becomes difficult. 
   Condition (4) specifies the ratio of the combined focal length of the negative first lens group to the radius of curvature of the projection-side surface of the negative fifth lens element of the negative first lens group. This condition influences the correcting of spherical aberration and coma in the negative first lens group, and the effective diameter of the negative first lens element thereof (hereinafter, the front-lens diameter). 
   The projector lens system of the present invention is constituted as a zoom lens system which is required to have (i) a wider angle-of-view at the wide-angle extremity, and at the same time, to have (ii) a smaller front-lens diameter. It has been know that these two requirements (i) and (ii) are generally incompatible. More specifically, in order to correct aberrations and at the same time to make the front-lens diameter smaller, a bundle of light rays corresponding to an image point at a higher image height has to be passed at a lower height through lens elements provided on the projection side_in the negative first lens group. This arrangement is materialized by the negative third lens element and the negative fifth lens element in the negative first lens group. Particularly, the negative fifth lens element is arranged to characteristically work to satisfy these requirements, i.e., although the refractive power of the negative fifth lens element is weaker, the above requirements are satisfied by making the large convex surface toward the light bulb side; on the other hand, balance between having the small front-lens diameter and the correcting of spherical aberration and coma is maintained. 
   If the upper limit of condition (4) is exceeded, i.e., the radius of curvature of the projection-side surface of the negative fifth lens element is too small, degree of freedom with respect to the correcting of coma and spherical aberration becomes smaller. 
   If the lower limit of condition (4) is exceeded, the front-lens diameter has to make larger. 
   Condition (5) relates to the distribution of the Abbe numbers over the positive and negative lens elements of the negative first lens group; and more specifically, condition (5) is for suitably correcting chromatic aberration in the negative first lens group. By selecting glass materials for the positive and negative lens elements of the negative first lens group according to condition (5), refractive power is suitably distributed over the negative first lens group, and chromatic aberration can be adequately corrected. 
   If the lower limit of condition (5) is exceeded, refractive power of each lens element becomes extremely strong to correct chromatic aberration, so that various aberrations deteriorate. 
   Condition (6) is for determining field curvature, i.e., relates to the Petzval sum. In the negative first lens group, it should be understood that the fourth lens element which is the only and permanently positive lens element is very important to control the Petzval sum. In other words, it is important to make the Petzval sum smaller by making refractive power stronger, i.e., the value of the refractive index is set larger. 
   If the lower limit of condition (6) is exceeded, the Petzval sum becomes larger, so that field curvature becomes larger. Consequently, it becomes difficult to control the image, as desired, at an image height around the periphery of a lens element. 
   Furthermore, the second lens element of the negative first lens group is made from a resin material; and an aspherical surface is formed on at least the light-bulb-side surface thereof. The second lens element preferably satisfies condition (7) with respect to the refractive power.
 
 |f   I   /f   1,2 |&lt;0.25  (7)
 
wherein
         f 1,2  designates the focal length of the second lens element of the negative first lens group.       

   From the viewpoint of correcting distortion, forming an aspherical surface on both negative first lens element and the second lens element is effective; however, the diameter of these lens element, e.g., the second lens element having a smaller effective diameter, varies from 32.6 mm to 34.8 mm. The size of these lens elements is disadvantageous to utilize a current glass-molding process with respect to the production costs thereof. 
   If an aspherical lens element made of a resin material is employed, the disadvantage on costs is eliminated. Moreover, such an aspherical lens element is more preferably employed as the second lens element than as the first lens element exposed to outside of to projection lens system, since a lens surface made of a resin material is vulnerable to scratch, etc. 
   Accordingly, condition (7) specifies a range in which the second lens element made of a resin material maintains optical performance as a projector lens element. Here, in the case where a lens element is made of a resin material, consideration should be taken to (a) reduce the change in the refractive index due to the change in temperature and humidity, and to (b) maintain the thickness of the second lens element as uniform as possible (refer to, e.g., the second lens element L 12  shown in  FIG. 1 ) so that molding the second lens element can be made easier. In order to satisfy these considerations (a) and (b), it is necessary to weaken refractive power to be distributed to the second lens element. 
   If the lower limit of condition (7) is exceeded, refractive power distributed to the second lens element becomes excessively strong to maintain optical performance as a projector lens element. Consequently, optical performance cannot suitably be maintained when the change in temperature and humidity occurs. 
   Still further, the projector lens system can perform focusing by moving the negative first lens element through the positive fourth lens element toward the projection side, in accordance with the change in a projecting distance from infinity to a closer distance. The combined focal length of the first through fourth lens elements preferably satisfies condition (8):
 
0.2 &lt;f   I   /f   1,1-4 &lt;0.9  (8)
         wherein   f 1,1-4  designates the combined focal length of the negative first through positive fourth lens elements of the negative first lens group.       

   Condition (8) is for determining a suitable traveling distance, with less fluctuations of aberrations, of the negative first lens element though the positive fourth lens element in the case where the first through fourth lens elements are independently moved from the negative fifth lens element. 
   In a lens system in which focusing is performed by moving the entire first lens group along the optical axis, the positional relationship between the second lens group and each lens element of the first lens group varies. The negative fifth lens element, as explained, is arranged to have a strong deflecting function with respect to a bundle of light rays corresponding to an image point at a higher image height, so that the negative fifth lens element largely influences image-forming performance on the periphery of the screen. More specifically, the change in the positional relationship between the negative fifth lens element and the second lens group appears as fluctuations of aberrations. Accordingly, in order to reduce fluctuations of aberrations due to a focusing distance, the lens elements to be moved upon focusing are preferably the negative first lens element through the positive fourth lens element. By determining the focal length of the lens elements to be used in focusing (i.e., the first through fourth lens elements, as a focusing lens group) according to the range defined in condition (8), a suitable traveling distance with less fluctuations of aberrations become possible. 
   If the upper limit of condition (8) is exceeded, refractive power of the focusing lens group becomes too strong, so that the traveling distance thereof becomes shorter. Consequently, a focus-adjusting operation becomes difficult, considering precision of the mechanism of the projector lens system. 
   If the lower limit of condition (8) is exceeded, the traveling distance of the focusing lens group becomes longer, so that fluctuations of aberrations become larger. 
   The second lens group includes a positive first lens element, a positive second lens element, a negative third lens element which is cemented to the positive second lens element, a negative fourth lens element, a positive fifth lens element which is cemented to the positive fourth lens element, and a positive sixth lens element. The positive first lens element and the positive sixth lens element of the second lens group preferably satisfy condition (9) with respect to the refractive power thereof; and the negative fourth lens element and the positive fifth lens element which are cemented preferably satisfy condition (10) with respect to the combined focal length thereof:
 
1.7 &lt;f   2,6   /f   2,1 &lt;3.0  (9)
 
−0.5 &lt;f   II   /f   2,4-5 &lt;0  (10)
         wherein   f 2,1  designates the focal length of the positive first lens element of the second lens group;   f 2,6  designates the focal length of the positive sixth lens element of the second lens group;   f II  designates the combined focal length of the second lens group; and   f 2,4-5 designates the combined focal length of the negative fourth lens element and the positive fifth lens element of the second lens group.       

   Condition (9) relates to the correcting of monochromatic aberration in the second lens group. The second lens group is arranged in a Gauss lens arrangement or a double Gauss lens arrangement. Accordingly, by providing a strong positive refractive power to the positive first lens element and the positive sixth lens element, refractive power is balanced over the second lens group with respect to various aberrations. This balance should not be adversely varied; however, in the case of the projector lens system of the present invention constituted as a zoom lens system, the positive first lens element of the second lens group has to converge the diverging light rays emitted from the negative first lens group. Therefore the positive first lens element is provided with a stronger refractive power than the positive sixth lens element is, within the range of condition (9). 
   If the upper limit of condition (9) is exceeded, i.e., the refractive power of the positive first lens element is too strong, degree of freedom on the correcting of various aberrations becomes smaller. 
   If the lower limit of condition (9) is exceeded, the converging function has to be shared by the positive first lens element, and by other lens elements of the second lens group as well, and the aberration balance of the entire second lens group is adversely varied. 
   Condition (10) is for correcting chromatic aberration and coma in the second lens group. More specifically, chromatic aberration is corrected by the combined surface of the negative fourth lens element and the positive fifth lens element which constitute cemented lens elements, although the refractive power of these cemented elements is relatively weaker, compared with refractive power of cemented lens elements in general. 
   If either the upper or lower limits of condition (10) are exceeded, the balance of chromatic aberration in the entire projector lens system is deteriorated. 
   Furthermore, in regard to the second lens group, a radius of curvature of the projection-side surface of the positive first lens element of the second lens group preferably satisfies condition (11); a relationship between the radius of curvature of the projection-side surface of the positive first lens element and a radius of curvature of the light-bulb-side surface of the positive sixth lens element preferably satisfies condition (12); a radius of curvature of the projection-side surface of the negative fourth lens element and a refractive power of the second lens group preferably satisfies condition (13); an Abbe number of a glass material used for each of the positive and negative lens elements preferably satisfies condition (14); and a refractive index of a glass material used for each positive lens element preferably satisfies condition (15):
 
1.0 &lt;f   II   /r   21 &lt;1.6  (11)
 
−1.5 &lt;r   21   /r   30 &lt;−0.6  (12)
 
−1.5 &lt;f   II   /r   26 &lt;−0.6  (13)
 
15&lt;(ν 2,1 +ν 2,2 +ν 2,5 +ν 2,6 )/4−(ν 2,3 +ν 2,4 )/2  (14)
 
0&lt;( n   2,1   +n   2,2 )/2−( n   2,5   +n   2,6 )/2  (15)
         wherein   r 21  designates a radius of curvature of the projection-side surface of the positive first lens element of the second lens group;   r 26  designates a radius of curvature of the projection-side surface of the negative fourth lens element thereof the second lens group;   r 30  designates a radius of curvature of the light-bulb-side surface of the positive sixth lens element thereof;   ν 2,1  designates the Abbe number of the positive first lens element thereof;   ν 2,2  designates the Abbe number of the positive second lens element thereof;   ν 2,3  designates the Abbe number of the negative third lens element thereof;   ν 2,4  designates the Abbe number of the negative fourth lens element thereof;   ν 2,5  designates the Abbe number of the positive fifth lens element there of;   ν 2,6  designates the Abbe number of the positive sixth lens element thereof;   n 2,1  designates the refractive index of the positive first lens element thereof with respect to the d-line;   n 2,2  designates the refractive index of the positive second lens element thereof with respect to the d-line;   n 2,5  designates the refractive index of the positive fifth lens element thereof with respect to the d-line; and   n 2,6  designates the refractive index of the positive sixth lens element thereof with respect to the d-line.       

   Condition (11) relates to the shape of the positive first lens element of the second lens group. In particular, the projection-side surface of the positive first lens element converges strong diverging light rays emitted from the negative first lens group, and also needs to correct spherical aberration. Accordingly, the lens surface of the positive first lens element needs to have a strong refractive surface power. 
   If the upper limit of condition (11) is exceeded, a sufficient converging function is obtained; however, the under-corrected spherical aberration remains. 
   If the lower limit of condition (11) is exceeded, refractive power for converging the light rays emitted from the negative first lens group becomes insufficient, so that the converging function has to be shared by the positive first lens element, and by other lens elements in the second lens group as well. As a result, various aberrations deteriorate. 
   Condition (12), together with condition (11), is for correcting spherical aberration and various other aberrations in a well balanced manner. 
   If the upper limit of condition (12) is exceeded, the correcting of various aberrations become difficult. 
   If the lower limit of condition (12) is exceeded, the correcting of spherical aberration cannot be carried out. 
   Condition (13) relates to the shape of the negative fourth lens element of the second lens group. The shape of the projection-side surface of the negative fourth lens element is particularly important. Namely, the negative fourth lens element is arranged to correct the under-corrected spherical aberration occurred in the positive first lens element, to make a bundle of light rays concentric with respect to the diaphragm, and adequately correct coma. If the upper limit of condition (13) is exceeded, i.e., the radius of curvature of the projection-side surface of the negative fourth lens element of the second lens group becomes too large, the correcting of coma becomes difficult. 
   If the lower limit of condition (13) is exceeded, the correcting of spherical aberration becomes difficult. 
   Condition (14) relates to the distribution of the Abbe numbers used for the positive and negative lens elements in the second lens group. More specifically, this condition is for correcting chromatic aberration, and for maintaining a balance between chromatic aberration and various other aberrations. 
   If the lower limit of condition (14) is exceeded, the refractive power of each lens element to correct chromatic aberration becomes larger, which is disadvantageous for correcting spherical aberration and coma. 
   Condition (15) relates to the selection of an refractive index of a glass material used for each of the positive lens elements in the second lens group. In the second lens group, for the purpose of correcting spherical aberration, coma, and various other aberrations, the first lens element and the second lens element are required to have a stronger refractive power than the fifth lens element and the sixth lens element are. 
   Accordingly, the refractive index of a glass material to be selected for the first and second lens elements needs to be higher. 
   If the lower limit of condition (15) is exceeded, the correcting of spherical aberration and various other aberrations becomes difficult. 
   At least one of the projection-side surface of the positive first lens element and the light-bulb-side surface of the positive sixth lens element of the second lens group is preferably provided with an aspherical lens surface. 
   The above is because both the projection-side surface of the positive first lens element and the light-bulb-side surface of the positive sixth lens element largely influence the correcting of spherical aberration and coma. 
   Accordingly, by forming an aspherical surface on at least one of these surfaces, it is advantageous for correcting spherical aberration and coma, and further miniaturization and higher optical performance of the projector lens system become possible. 
   Furthermore, the third lens group is preferably constituted by one positive lens element only, and satisfies condition (16) with respect to the refractive power thereof:
 
0.20 &lt;f   w   /f   III &lt;0.27  (16)
         wherein   f III  designates the focal length of the third lens group.       

   In order to efficiently form an image on a screen with a bundle of light rays from a light bulb, such as a DMD, the angle of the principal ray of a bundle of light rays between the third lens group and the DMD has to be set in accordance with the characteristics of the illumination optical system. In many cases, the angle of the principal ray is set to be substantially telecentrical. In order to ensure such telecentricity, it is necessary to position the focal point of the third lens group in the vicinity of the exit pupil of the second lens group. This positional arrangement can be achieved by providing a refractive power of the third lens group within the range of condition (16). 
   If either the upper or lower limits of condition (16) are exceeded, the focal point of the third lens group cannot be positioned in the vicinity of the exit pupil of the second lens group, so that various aberrations deteriorate. 
   The present disclosure relates to subject matter contained in Japanese Patent Application No. 2003-59533 (filed on Mar. 6, 2003) which is expressly incorporated herein in its entirety. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be discussed below in detail with reference to the accompanying drawings, in which: 
       FIG. 1  shows a lens arrangement of a projector lens system according to a first embodiment of the present invention; 
       FIGS. 2A ,  2 B,  2 C,  2 D,  2 E,  2 F,  2 G,  2 H and  2 I show various aberrations occurred in the projector lens system of the first embodiment; 
       FIG. 3  shows a lens arrangement of a projector lens system according to a second embodiment of the present invention; 
       FIGS. 4A ,  4 B,  4 C,  4 D,  4 E,  4 F,  4 G,  4 H and  4 I show various aberrations occurred in the projector lens system of the second embodiment; 
       FIGS. 5A ,  5 B and  5 C show a change in field (diagram of astigmatism) of the second embodiment in the case where focusing is carried out, at the wide-angle extremity, by moving the negative first through positive fourth lens elements of the negative first lens group; 
       FIGS. 6A ,  6 B and  6 C show a change in field (diagram of astigmatism) of the second embodiment in the case where focusing is carried out, at the wide-angle extremity, by moving the negative first through positive fifth lens elements of the negative first lens group; 
       FIG. 7  shows a lens arrangement of a projector lens system according to a third embodiment of the present invention; 
       FIGS. 8A ,  8 B,  8 C,  8 D,  8 E,  8 F,  8 G,  8 H and  8 I show various aberrations occurred in the projector lens system of the third embodiment; 
       FIG. 9  shows a lens arrangement of a projector lens system according to a fourth embodiment of the present invention; 
       FIGS. 10A ,  10 B,  10 C,  10 D,  10 E,  10 F,  10 G,  10 H and  10 I show various aberrations occurred in the projector lens system of the fourth embodiment; 
       FIG. 11  shows a lens arrangement of a projector lens system according to a fifth embodiment of the present invention; and 
       FIGS. 12A ,  12 B,  12 C,  12 D,  12 E,  12 F,  12 G,  12 H and  12 I show various aberrations occurred in the projector lens system of the fifth embodiment. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The embodiments of the present invention will be described according to the drawings and tables. 
   A projector lens system of a projector display device according to each of the first through fifth embodiments includes a first lens group LG 1  and a second lens group LG 2 , in this order from the projection side; and a third lens group LG 3  is provided behind the second lens group LG 2  in all embodiments other than the first embodiment. 
   The first lens group LG 1  has a negative refractive power, and includes a first lens element L 11  which is formed as a meniscus lens having the convex surface facing toward the projection side and having a negative refractive power (hereinafter referred as a negative first lens element), a second lens element L 12  having a positive or negative refractive power, a negative third lens element L 13 , a positive fourth lens element L 14  which is cemented to or separated from the negative third lens element L 13 , and a negative fifth lens element L 15 . 
   The second lens group LG 2  has a positive refractive power, and includes a positive first lens element L 21 , a positive second lens element L 22 , a negative third lens element L 23  which his cemented to the positive second lens element L 22 , a negative fourth lens element L 24 , a positive fifth lens element L 25  which is cemented to the negative fourth lens element L 24 , and a positive sixth lens element L 26 . 
   The third lens group LG 3  has a positive refractive power, and includes one positive first lens element L 31  only. 
   Zooming is performed by moving the first lens group LG 1  and the second lens group LG 2  in an optical axis direction. Namely, the distances, which vary due to zooming, are defined as an distance D 20  between the light-bulb-side surface of the negative fifth lens element L 15  of the negative first lens group LG 1  and the projection-side surface of the positive first lens element L 21  of the second lens group LG 2 ; and a distance D 30  between the light-bulb-side surface of the positive sixth lens element L 26  of the second lens group LG 2  and a cover glass CG or the projection-side surface of the positive third lens element L 31  of the positive third lens group LG 3 . 
   On the other hand, the distances between lens groups related to focusing are described as a case where a projecting distance from the projection-side surface of the negative first lens element L 11  to the screen is set to 2 meters, as shown in  FIGS. 2B ,  2 E,  2 H,  4 B ( 5 B),  4 E,  4 H,  8 B,  8 E,  8 H,  10 B,  10 E,  10 H,  12 B,  12 E and  2 H; and in this case, the negative first lens element L 11  through the positive fourth lens element L 14  are moved upon focusing. 
   In addition to the focusing carried out under the above-described distance of 2 meters as shown in  FIG. 5B , cases where the distances are infinity and 1 meter are added as shown in  FIGS. 5A and 5C . 
   Also, in the second embodiment, cases where the negative first lens element L 11  through the negative fifth lens element L 15  are moved upon focusing are added with respect to infinity, 1 meter and 2 meters, as shown in  FIGS. 6A ,  6 B and  6 C. 
   In the case of focusing by moving the first lens element L 11  though the fourth lens element L 14 , a distance D 18  between the light-bulb-side surface of the fourth lens element L 14  and the projection-side surface of the fifth lens element L 15  varies. 
   In the case of focusing by moving the first lens element L 11  though the fifth lens element L 15 , the distance D 20  between the light-bulb-side surface of the fifth lens element L 15  of the first lens group and the projection-side surface of the first lens element L 21  of the second lens group varies. 
   Furthermore, a cover glass CG, which is a structural component of a light bulb such as a DMD, is provided between the third lens group LG 3  and the light bulb surface, between which a predetermined distance is formed In the first lens group LG 1 , the first lens element L 11  has a projection-side surface S 11  and a light-bulb-side surface S 12 , the second lens element L 12  has a projection-side surface S 13  and a light-bulb-side surface S 14 , the third lens element L 13  has a projection-side surface S 15  and a light-bulb-side surface S 16 , the fourth lens element L 14  has a projection-side surface S 17  and a light-bulb-side surface S 18 , and the fifth lens element L 15  has a projection-side surface S 19  and a light-bulb-side surface S 20 . 
   In the second lens group LG 2 , the first lens element L 21  has a projection-side surface S 21  and a light-bulb-side surface S 22 , the second lens element L 22  has a projection-side surface S 23  and a light-bulb-side surface (the surface cemented to the third lens element L 23 ) S 24 , the third lens element L 23  has a light-bulb-side surface S 25 , the fourth lens element L 24  has a projection-side surface S 26  and a light-bulb-side surface (the surface cemented to the fifth lens element L 25 ) S 27 , the fifth lens element L 25  has a light-bulb-side surface S 28 , and the sixth lens element L 26  has a projection-side surface S 29  and a light-bulb-side surface S 30 . 
   Furthermore, the cover glass CG has a projection side surface S 41  and a light-bulb-side surface S 42 . 
   In all the embodiments except for the first embodiment, the first lens element L 31  constituting the third lens group LG 3  has a projection-side surface S 31  and a light-bulb-surface S 32 . 
   In regard to an aspherical surface which is utilized in each embodiment, the aspherical surface, as well known in the art, can be defined by the following aspherical formula, assuming that the Z axis extends along the optical axis direction, and the Y axis extends along a direction perpendicular to the optical axis:
 
 Z =( Y   2   /r )[1+{1−(1 +K )( Y/r ) 2 } 1/2   ]+AY   4   +BY   6   +CY   8   +DY   10. 
 
Namely, the aspherical surface is a curved surface obtained by rotating the curved line defined by the above formula about the optical axis. The shape of the aspherical surface is defined by a paraxial radius of curvature r, a conic constant K, and higher-order aspherical surface coefficients A, B, C and D.
 
[Embodiment 1]
 
   The numerical values of a first embodiment of the compact wide-angle projector lens system are shown in Table 1. 
     FIG. 1  shows a lens arrangement of a projector lens system according to the first embodiment. 
     FIGS. 2A through 2I  show various aberrations occurred in the projector lens system of the first embodiment. 
   In the table and drawings, f designates the focal length of the entire projector lens system; F NO  designates the F-number; 2ω designates the full angle of view of the projector lens system; and b f  designates the back focal distance which is the reduced distance, at the wide-angle extremity, from the light-bulb-surface S 30  of the positive sixth lens element L 26  of the second lens group LG 2  to the image plane; R designates the radius of curvature, D designates the lens-element thickness or distance between lens elements, N d  designates the refractive index with respect to the d-line, and ν d  designates the Abbe number. 
   In the aberration diagrams, CA 1 , CA 2 , CA 3  and CA 4  designate an aberration curve at the following respective wavelengths: CA 1 =550.0 nm, CA 2 =486.1 nm, CA 3 =640.0 nm and CA 4 =435.8 nm. Furthermore, S designates the sagittal image, and M designates the meridional image. 
   
     
       
             
           
             
             
             
             
             
           
             
             
             
             
             
           
         
             
               TABLE 1 
             
           
           
             
                 
             
             
               f = 20.49˜26.41˜34.84 
             
             
               Fno = 2.07˜2.33˜2.70 
             
             
               2ω = 65.65°˜52.70°˜40.96° 
             
             
               bf = 42.12 
             
           
        
         
             
               Surf. No. 
               R 
               D 
               Nd 
               νd 
             
             
                 
             
           
        
         
             
               S11 
               41.806 
               1.70 
               1.80420 
               46.50 
             
             
               S12 
               19.421 
               4.60 
               — 
               — 
             
             
               S13* 
               339.559 
               3.22 
               1.50914 
               56.41 
             
             
               S14* 
               146.858 
               11.82 
               — 
               — 
             
             
               S15 
               −37.830 
               1.59 
               1.49700 
               81.61 
             
             
               S16 
               176.091 
               0.53 
               — 
               — 
             
             
               S17 
               55.888 
               6.00 
               1.80518 
               25.46 
             
             
               S18 
               −638.362 
               6.10 
               — 
               — 
             
             
               S19 
               −22.304 
               1.20 
               1.69680 
               55.46 
             
             
               S20 
               −30.294 
               21.90˜11.13˜2.10 
               — 
               — 
             
             
               S21* 
               26.674 
               6.70 
               1.66910 
               55.40 
             
             
               S22* 
               −58.835 
               0.88 
               — 
               — 
             
             
               S23 
               52.722 
               2.40 
               1.69680 
               55.46 
             
             
               S24 
               64.463 
               1.15 
               1.75520 
               27.53 
             
             
               S25 
               27.180 
               8.11 
               — 
               — 
             
             
               S26 
               −34.072 
               1.07 
               1.80610 
               33.27 
             
             
               S27 
               76.559 
               5.92 
               1.48749 
               70.45 
             
             
               S28 
               −25.425 
               0.10 
               — 
               — 
             
             
               S29 
               138.095 
               4.56 
               1.51760 
               63.50 
             
             
               S30* 
               −36.649 
               38.70˜46.10˜56.67 
               — 
               — 
             
             
               S41 
               ∞ 
               3.00 
               1.51680 
               64.20 
             
             
               S42 
               ∞ 
               — 
               — 
               — 
             
             
                 
             
             
               *designates the aspherical surface which is rotationally symmetrical with respect to the optical axis.  
             
           
        
       
     
   
   Aspherical surface data (the aspherical surface coefficients not indicated are zero (0.00)). 
   Aspherical Surface Coefficients 
                                           S13   K = 0.376158 × 10 3     A = 0.673786 × 10 −4     B = −0.152616 × 10 −6                 C = 0.516285 × 10 −9     D = −0.535296 × 10 −12         S14   K = 0.510936 × 10 2     A = 0.584010 × 10 −4     B = −0.196316 × 10 −6                 C = 0.675631 × 10 −9     D = −0.127628 × 10 −11         S21   K = 0.225323   A = −0.636685 × 10 −5     B = −0.336434 × 10 −8                 C = 0.137668 × 10 −10     D = −0.338975 × 10 −13         S22   K = −0.364182 × 10   A = 0.974482 × 10 −5     B = −0.281257 × 10 −8         S30   K = −0.171317 × 10 2     A = −0.363413 × 10 −4     B = 0.184683 × 10 −6                 C = −0.578782 × 10 −9     D = 0.936511 × 10 −12                      
[Embodiment 2]
 
   The numerical values of a second embodiment of the compact wide-angle projector lens system are shown in Table 2. The signs and symbols in the table and drawings are the same as those of the first embodiment, and the wavelength values of CA 1 , CA 2 , CA 3  and CA 4  are also the same as those of the first embodiment. 
     FIG. 3  shows a lens arrangement of a projector lens system according to the second embodiment. 
     FIGS. 4A through 4I  show various aberrations occurred in the projector lens system of the second embodiment. 
   In the second embodiment and thereafter, the back focal distance b f  is the reduced distance, at the wide-angle extremity, from the light-bulb-surface S 32  of the positive lens element L 31  of the positive third lens group LG 3  to the image plane 
   Furthermore, in order to show fluctuations of aberrations due to the movement of the lens groups upon focusing, the numerical values of the distances which vary upon focusing at the wide-angle extremity are shown in Table 3. 
   In connection with Table 3,  FIGS. 5A ,  5 B and  5 C show a change in field (diagram of astigmatism) in the case where focusing is carried out, at the wide-angle extremity, by moving the negative first lens element L 11  through the positive fourth lens element L 14  of the negative first lens group. 
   For the purpose of comparing with  FIGS. 5A  to  5 C,  FIGS. 6A ,  6 B and  6 C show a change in field (diagram of astigmatism) in the case where focusing is carried out, at the wide-angle extremity, by moving the negative first lens element L 11  through the positive fifth lens element L 15  of the negative first lens group; 
   In the second embodiment, the zoom ratio of the projector lens system is 1.94, which is larger than the other embodiments; however, in the case where the negative first lens element L 11  through the positive fourth lens element L 14  are moved to perform focusing, fluctuations of aberrations are reduced, which indicates that the focusing of this way is appropriate. 
   
     
       
             
           
             
             
             
             
             
           
             
             
             
             
             
           
         
             
               TABLE 2 
             
           
           
             
                 
             
             
               f = 20.50˜28.07˜39.77 
             
             
               Fno = 2.07˜2.39˜2.90 
             
             
               2ω = 65.63°˜50.30°˜36.70° 
             
             
               bf = 3.11 
             
           
        
         
             
               Surf. No. 
               R 
               D 
               Nd 
               νd 
             
             
                 
             
           
        
         
             
               S11 
               42.336 
               1.80 
               1.80420 
               46.50 
             
             
               S12 
               20.470 
               5.37 
               — 
               — 
             
             
               S13* 
               1395.401 
               4.90 
               1.50914 
               56.41 
             
             
               S14* 
               4122.679 
               12.80 
               — 
               — 
             
             
               S15 
               −25.058 
               1.50 
               1.49700 
               81.61 
             
             
               S16 
               628.979 
               0.20 
               — 
               — 
             
             
               S17 
               68.401 
               3.12 
               1.80518 
               25.46 
             
             
               S18 
               −213.323 
               6.57 
               — 
               — 
             
             
               S19 
               −19.207 
               1.20 
               1.58913 
               61.25 
             
             
               S20 
               −24.216 
               26.28˜12.77˜2.00 
               — 
               — 
             
             
               S21* 
               25.653 
               6.78 
               1.69350 
               53.54 
             
             
               S22* 
               −57.172 
               0.20 
               — 
               — 
             
             
               S23 
               115.192 
               3.25 
               1.69680 
               55.46 
             
             
               S24 
               −78.903 
               1.00 
               1.59551 
               39.23 
             
             
               S25 
               28.413 
               6.37 
               — 
               — 
             
             
               S26 
               −26.720 
               2.00 
               1.67270 
               32.17 
             
             
               S27 
               71.919 
               6.20 
               1.49700 
               81.61 
             
             
               S28 
               −27.589 
               0.20 
               — 
               — 
             
             
               S29* 
               −500.000 
               3.79 
               1.48749 
               70.45 
             
             
               S30* 
               −32.727 
               38.00˜47.57˜62.36 
               — 
               — 
             
             
               S31 
               −100.000 
               3.50 
               1.83400 
               37.34 
             
             
               S32 
               −44.000 
               0.70 
               — 
               — 
             
             
               S41 
               ∞ 
               3.00 
               1.51680 
               64.20 
             
             
               S42 
               ∞ 
               — 
               — 
               — 
             
             
                 
             
             
               *designates the aspherical surface which is rotationally symmetrical with respect to the optical axis.  
             
           
        
       
     
   
   Aspherical surface data (the aspherical surface coefficients not indicated are zero (0.00)). 
   Aspherical Surface Coefficients 
   
     
       
             
             
             
             
           
         
             
                 
             
           
           
             
               S13 
               K = −0.100000 × 10 3   
               A = 0.521546 × 10 −4   
               B = −0.732367 × 10 −7   
             
             
                 
                 
               C = 0.222631 × 10 −9   
               D = −0.679169 × 10 −13   
             
             
               S14 
               K = −0.100000 × 10 3   
               A = 0.421670 × 10 −4   
               B = −0.119066 × 10 −6   
             
             
                 
                 
               C = 0.382188 × 10 −9   
               D = −0.757078 × 10 −12   
             
             
               S21 
               K = 0.758444 
               A = −0.786718 × 10 −5   
               B = −0.106818 × 10 −7   
             
             
                 
                 
               C = −0.195533 × 10 −10   
               D = −0.710529 × 10 −13   
             
             
               S22 
               K = −0.523125 × 10 
               A = 0.108758 × 10 −4   
               B = −0.399958 × 10 −8   
             
             
                 
                 
               C = −0.475537 × 10 −10   
               D = 0.149969 × 10 −12   
             
             
               S29 
               K = −0.100000 × 10 3   
               A = 0.408166 × 10 −5   
               B = −0.117530 × 10 −7   
             
             
                 
                 
               C = 0.185982 × 10 −9   
               D = −0.162667 × 10 −12   
             
             
               S30 
               K = −0.130886 × 10 2   
               A = −0.321784 × 10 −4   
               B = 0.198124 × 10 −6   
             
             
                 
                 
               C = −0.472368 × 10 −9   
               D = 0.123930 × 10 −11   
             
             
                 
             
           
        
       
     
   
                                                                                               TABLE 3                       Distance   ∞   2 m   1 m                                    Change in the distances upon focusing with the       negative first lens element L11 through the positive fourth       lens element L14:                D18   5.83   6.57   7.32           D20   26.28   26.28   26.28           D30   38.00   38.00   38.00            Change in the distances upon focusing with the negative       first lens element L11 through the negative fifth lens       element L15:                D18   5.83   5.83   5.83           D20   26.28   26.68   27.08           D30   38.00   38.00   38.00                        
[Embodiment 3]
 
   The numerical values of a third embodiment of the compact wide-angle projector lens system are shown in Table 4. The signs and symbols in the table and drawings are the same as those of the first embodiment, and the wavelength values of CA 1 , CA 2 , CA 3  and CA 4  are also the same as those of the first embodiment. 
     FIG. 7  shows a lens arrangement of a projector lens system according to the third embodiment. 
     FIGS. 8A through 8I  show various aberrations occurred in the projector lens system of the third embodiment. 
   
     
       
             
           
             
             
             
             
             
           
             
             
             
             
             
           
         
             
               TABLE 4 
             
           
           
             
                 
             
             
               f = 20.46˜27.10˜34.78 
             
             
               Fno = 2.07˜2.41˜2.80 
             
             
               2ω = 65.34°˜51.69°˜41.47° 
             
             
               bf = 3.12 
             
           
        
         
             
               Surf. No. 
               R 
               D 
               Nd 
               νd 
             
             
                 
             
           
        
         
             
               S11 
               33.293 
               2.00 
               1.80610 
               33.27 
             
             
               S12 
               19.757 
               5.00 
               — 
               — 
             
             
               S13* 
               360.804 
               4.43 
               1.50914 
               56.41 
             
             
               S14* 
               74.067 
               15.05 
               — 
               — 
             
             
               S15 
               −23.402 
               1.50 
               1.49700 
               81.61 
             
             
               S16(17) 
               32.513 
               4.19 
               1.80518 
               25.46 
             
             
               S18 
               −141.071 
               4.95 
               — 
               — 
             
             
               S19 
               −17.318 
               2.50 
               1.50518 
               25.46 
             
             
               S20 
               −22.631 
               17.87˜8.52˜2.16 
               — 
               — 
             
             
               S21* 
               28.534 
               6.08 
               1.66910 
               55.40 
             
             
               S22* 
               −68.651 
               4.00 
               — 
               — 
             
             
               S23 
               51.012 
               2.80 
               1.69680 
               55.46 
             
             
               S24 
               145.297 
               1.89 
               1.80518 
               25.46 
             
             
               S25 
               35.542 
               4.00 
               — 
               — 
             
             
               S26 
               −46.619 
               1.00 
               1.80610 
               33.27 
             
             
               S27 
               42.190 
               6.00 
               1.48749 
               70.45 
             
             
               S28 
               −31.395 
               0.10 
               — 
               — 
             
             
               S29 
               149.021 
               4.30 
               1.51760 
               63.50 
             
             
               S30* 
               −35.920 
               38.00˜47.48˜58.44 
               — 
               — 
             
             
               S31 
               −100.000 
               3.50 
               1.83400 
               37.34 
             
             
               S32 
               −42.443 
               0.70 
               — 
               — 
             
             
               S41 
               ∞ 
               3.00 
               1.51680 
               64.20 
             
             
               S42 
               ∞ 
               — 
               — 
               — 
             
             
                 
             
             
               *designates the aspherical surface which is rotationally symmetrical with respect to the optical axis.  
             
           
        
       
     
   
   Aspherical surface data (the aspherical surface coefficients not indicated are zero (0.00)). 
   Aspherical Surface Coefficients 
                                           S13   K = 0.389395 × 10 3     A = 0.731879 × 10 −4     B = −0.194798 × 10 −6                 C = 0.663439 × 10 −9     D = −0.831076 × 10 −12         S14   K = 0.180617 × 10 2     A = 0.656650 × 10 −4     B = −0.276611 × 10 −6                 C = 0.105738 × 10 −8     D = −0.274290 × 10 −11         S21   K = 0.644345   A = −0.445869 × 10 −5     B = −0.501870 × 10 −8                 C = −0.171719 × 10 −12     D = −0.201427 × 10 −13         S22   K = −0.526651 × 10   A = 0.100175 × 10 −4     B = −0.347760 × 10 −8         S30   K = −0.161748 × 10 2     A = −0.344867 × 10 −4     B = 0.199889 × 10 −6                 C = −0.639136 × 10 −9     D = 0.124645 × 10 −11                      
[Embodiment 4]
 
   The numerical values of a fourth embodiment of the compact wide-angle projector lens system are shown in Table 5. The signs and symbols in the table and drawings are the same as those of the first embodiment, and the wavelength values of CA 1 , CA 2 , CA 3  and CA 4  are also the same as those of the first embodiment. 
     FIG. 9  shows a lens arrangement of a projector lens system according to the fourth embodiment. 
     FIGS. 10A through 10I  show various aberrations occurred in the projector lens system of the fourth embodiment. 
   
     
       
             
           
             
             
             
             
             
           
             
             
             
             
             
           
         
             
               TABLE 5 
             
           
           
             
                 
             
             
               f = 20.49˜26.54˜34.84 
             
             
               Fno = 2.07˜2.39˜2.82 
             
             
               2ω = 65.52°˜52.67°˜41.43° 
             
             
               bf = 3.12 
             
           
        
         
             
               Surf. No. 
               R 
               D 
               Nd 
               νd 
             
             
                 
             
           
        
         
             
               S11 
               36.354 
               1.50 
               1.80420 
               46.50 
             
             
               S12 
               19.240 
               4.70 
               — 
               — 
             
             
               S13* 
               −1178.675 
               2.52 
               1.50914 
               56.41 
             
             
               S14* 
               108.288 
               8.51 
               — 
               — 
             
             
               S15 
               −70.418 
               1.50 
               1.48749 
               70.45 
             
             
               S16 
               56.812 
               3.22 
               — 
               — 
             
             
               S17 
               36.686 
               4.21 
               1.80518 
               25.46 
             
             
               S18 
               962.797 
               12.60 
               — 
               — 
             
             
               S19 
               −22.369 
               1.20 
               1.77250 
               49.62 
             
             
               S20 
               −45.658 
               17.30˜9.04˜2.37 
               — 
               — 
             
             
               S21* 
               27.081 
               6.00 
               1.69350 
               53.54 
             
             
               S22* 
               −59.550 
               0.67 
               — 
               — 
             
             
               S23 
               29.126 
               3.69 
               1.63854 
               55.45 
             
             
               S24 
               678.818 
               1.03 
               1.71736 
               29.50 
             
             
               S25 
               18.188 
               5.44 
               — 
               — 
             
             
               S26 
               −25.443 
               1.11 
               1.62588 
               35.74 
             
             
               S27 
               −1311.448 
               3.93 
               1.51680 
               64.20 
             
             
               S28* 
               −26.837 
               1.52 
               — 
               — 
             
             
               S29 
               −102.054 
               4.55 
               1.58913 
               61.25 
             
             
               S30 
               −24.384 
               38.00˜46.46˜58.07 
               — 
               — 
             
             
               S31 
               −73.529 
               3.50 
               1.83400 
               37.34 
             
             
               S32 
               −37.060 
               0.70 
               — 
               — 
             
             
               S41 
               ∞ 
               3.00 
               1.51680 
               64.20 
             
             
               S42 
               ∞ 
               — 
               — 
               — 
             
             
                 
             
             
               *designates the aspherical surface which is rotationally symmetrical with respect to the optical axis.  
             
           
        
       
     
   
   Aspherical surface data (the aspherical surface coefficients not indicated are zero (0.00)). 
   Aspherical Surface Coefficients 
                                           S13   K = −0.632843 × 10 5     A = 0.114298 × 10 −3     B = −0.393675 × 10 −6                 C = 0.123347 × 10 −8     D = −0.182823 × 10 −11         S14   K = 0.389146 × 10 2     A = 0.108471 × 10 −3     B = −0.447785 × 10 −6                 C = 0.129272 × 10 −8     D = −0.260624 × 10 −11         S21   K = 0.405991   A = −0.852607 × 10 −5     B = −0.163933 × 10 −7                 C = 0.240787 × 10 −10     D = −0.138186 × 10 −12         S22   K = −0.365067 × 10   A = 0.801662 × 10 −5     B = −0.119792 × 10 −7         S28   K = −0.695081   A = 0.661517 × 10 −5     B = 0.289296 × 10 −7                 C = −0.492831 × 10 −10     D = −0.174230 × 10 −12                      
[Embodiment 5]
 
   The numerical values of a fifth embodiment of the compact wide-angle projector lens system are shown in Table 6. The signs and symbols in the table and drawings are the same as those of the first embodiment, and the wavelength values of CA 1 , CA 2 , CA 3  and CA 4  are also the same as those of the first embodiment. 
     FIG. 11  shows a lens arrangement of a projector lens system according to the fifth embodiment. 
     FIGS. 12A through 12I  show various aberrations occurred in the projector lens system of the fifth embodiment. 
   
     
       
             
           
             
             
             
             
             
           
             
             
             
             
             
           
         
             
               TABLE 6 
             
           
           
             
                 
             
             
               f = 20.50˜27.13˜34.85 
             
             
               Fno = 2.07˜2.40˜2.78 
             
             
               2ω = 65.43°˜51.73°˜41.42° 
             
             
               bf = 3.11 
             
           
        
         
             
               Surf. No. 
               R 
               D 
               Nd 
               νd 
             
             
                 
             
           
        
         
             
               S11 
               53.961 
               1.55 
               1.80518 
               25.46 
             
             
               S12 
               20.813 
               4.23 
               — 
               — 
             
             
               S13* 
               136.815 
               6.91 
               1.58300 
               30.05 
             
             
               S14* 
               446.191 
               13.38 
               — 
               — 
             
             
               S15 
               −26.652 
               2.24 
               1.49700 
               81.61 
             
             
               S16(17) 
               30.659 
               6.46 
               1.80518 
               25.46 
             
             
               S18 
               −527.770 
               5.35 
               — 
               — 
             
             
               S19* 
               −16.675 
               2.26 
               1.50914 
               56.41 
             
             
               S20 
               −21.684 
               19.42˜9.15˜2.10 
               — 
               — 
             
             
               S21* 
               27.149 
               6.20 
               1.70154 
               41.15 
             
             
               S22* 
               −102.364 
               2.44 
               — 
               — 
             
             
               S23 
               57.409 
               4.06 
               1.60311 
               60.69 
             
             
               S24 
               −67.042 
               1.00 
               1.64769 
               33.84 
             
             
               S25 
               43.478 
               3.77 
               — 
               — 
             
             
               S26 
               −44.870 
               2.00 
               1.76182 
               26.61 
             
             
               S27 
               30.491 
               6.22 
               1.51680 
               64.20 
             
             
               S28 
               −40.047 
               0.10 
               — 
               — 
             
             
               S29 
               248.740 
               3.80 
               1.51680 
               64.20 
             
             
               S30* 
               −35.989 
               38.00˜47.01˜57.52 
               — 
               — 
             
             
               S31 
               −100.000 
               3.50 
               1.83400 
               37.34 
             
             
               S32 
               −41.926 
               0.70 
               — 
               — 
             
             
               S41 
               ∞ 
               3.00 
               1.51680 
               64.20 
             
             
               S42 
               ∞ 
               — 
               — 
               — 
             
             
                 
             
             
               *designates the aspherical surface which is rotationally symmetrical with respect to the optical axis.  
             
           
        
       
     
   
   Aspherical surface data (the aspherical surface coefficients not indicated are zero (0.00)). 
   Aspherical Surface Coefficients 
   
     
       
             
             
             
             
           
         
             
                 
             
           
           
             
               S13 
               K = −0.290056 × 10 3   
               A = 0.575052 × 10 −4   
               B = −0.112235 × 10 −6   
             
             
                 
                 
               C = 0.418545 × 10 −9   
               D = −0.513328 × 10 −12   
             
             
               S14 
               K = 0.686271 × 10 3   
               A = 0.365126 × 10 −4   
               B = −0.917797 × 10 −7   
             
             
                 
                 
               C = 0.358076 × 10 −9   
               D = −0.105402 × 10 −11   
             
             
               S19 
               K = −0.312349 
               A = −0.726388 × 10 −5   
               B = −0.276078 × 10 −7   
             
             
                 
                 
               C = −0.128642 × 10 −10   
               D = −0.543465 × 10 −12   
             
             
               S21 
               K = 0.973726 
               A = −0.538604 × 10 −5   
               B = −0.142938 × 10 −7   
             
             
                 
                 
               C = 0.252059 × 10 −11   
               D = −0.127605 × 10 −12   
             
             
               S22 
               K = −0.249011 × 10 
               A = 0.994834 × 10 −5   
               B = −0.361827 × 10 −8   
             
             
                 
                 
               C = −0.299959 × 10 −10   
               D = 0.964089 × 10 −13   
             
             
               S30 
               K = −0.173255 × 10 2   
               A = −0.338162 × 10 −4   
               B = 0.237688 × 10 −6   
             
             
                 
                 
               C = −0.811852 × 10 −9   
               D = 0.182309 × 10 −11   
             
             
                 
             
           
        
       
     
   
   Table 7 shows the numerical values for each of conditions (1) through (16) in each of the first through fifth embodiments. 
   
     
       
             
             
             
             
             
             
           
             
             
             
             
             
             
           
         
             
               TABLE 7 
             
             
                 
             
             
                 
               Embod. 1 
               Embod. 2 
               Embod. 3 
               Embod. 4 
               Embod. 5 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               Cond. (1) 
               0.73 
               0.71 
               0.86 
               0.88 
               0.80 
             
             
               Cond. (2) 
               0.60 
               0.57 
               0.37 
               0.44 
               0.60 
             
             
               Cond. (3) 
               −1.44 
               −1.42 
               −1.21 
               −1.22 
               −1.24 
             
             
               Cond. (4) 
               1.26 
               1.51 
               1.38 
               1.05 
               1.54 
             
             
               Cond. (5) 
               35.73 
               37.66 
               21.32 
               30.06 
               29.04 
             
             
               Cond. (6) 
               1.81 
               1.81 
               1.81 
               1.81 
               1.81 
             
             
               Cond. (7) 
               0.06 
               0.01 
               0.13 
               0.12 
               0.08 
             
             
               Cond. (8) 
               0.65 
               0.73 
               0.69 
               0.32 
               0.75 
             
             
               Cond. (9) 
               1.99 
               2.71 
               1.82 
               1.93 
               1.96 
             
             
               Cond. (10) 
               −0.23 
               −0.26 
               −0.26 
               −0.12 
               −0.37 
             
             
               Cond. (11) 
               1.32 
               1.40 
               1.17 
               1.19 
               1.26 
             
             
               Cond. (12) 
               −0.73 
               −0.78 
               −0.79 
               −1.11 
               −0.75 
             
             
               Cond. (13) 
               −1.03 
               −1.35 
               −0.72 
               −1.27 
               −0.76 
             
             
               Cond. (14) 
               30.80 
               29.56 
               31.84 
               25.99 
               27.34 
             
             
               Cond. (15) 
               0.18 
               0.20 
               0.18 
               0.11 
               0.14 
             
             
               Cond. (16) 
               — 
               0.23 
               0.24 
               0.24 
               0.24 
             
             
                 
             
           
        
       
     
   
   As can be understood from Table 7, the numerical values of each of the first through fifth embodiments satisfy each of conditions (1) through (16). Furthermore, as can be understood from the aberration diagrams of each embodiment, the various aberrations can be adequately corrected. 
   According to the present invention, a projector lens system, which is compact, has a wide angle-of-view, and has a high image-forming performance suitable for a light bulb such as a DMD, is achieved; and a projector apparatus with the projector lens system can be made compact, and can attain high picture quality. 
   Obvious changes may be made in the specific embodiments of the present invention described herein, such modifications being within the spirit and scope of the invention claimed. It is indicated that all matter contained herein is illustrative and does not limit the scope of the present invention.