Patent Publication Number: US-2005140831-A1

Title: Projection optical system and projection television employing the same

Description:
BACKGROUND OF THE INVENTION  
      This application claims the benefit of Russian Patent Application No. 2003131819, filed on Oct. 30, 2003, in the Russian Patent and Trademark Office, the disclosure of which is incorporated herein in its entirety by reference.  
     FIELD OF THE INVENTION  
      The present invention relates to a projection optical system and a projection television (TV) employing the same. More particularly, the present invention relates to a projection optical system having a simplified lens system structure, thus reducing the manufacturing costs and satisfactorily correcting aberration, and to a projection television employing the projection optical system.  
     DESCRIPTION OF THE RELATED ART  
      A conventional projection lens system disclosed in U.S. Pat. No. 5,029,993 magnifies an image formed by a cathode ray tube (CRT) and then projects the magnified image on a screen.  FIG. 1  is a diagram illustrating the conventional projection lens system. Referring to  FIG. 1 , the conventional projection lens system includes a first lens  13  having relatively weak power, a second lens  14  having relatively strong focal power, a third lens  15  having at least one aspheric surface and having relatively weak focal power, and a fourth lens  16  having a concave surface facing toward a screen and having relatively strong power. The first through fourth lenses  13  through  16  are sequentially arranged between the screen and a picture tube face along an optical axis  19 .  
      The conventional projection lens system is divided into a lens module LM and an electron beam tube optical module OM. The lens module LM includes the first through third lenses  13  through  15 . The first and second lenses  13  and  14  are power lenses formed of plastic, and the third lens  15  is a power lens formed of glass. The electronic beam tube optical module OM includes the fourth lens  16 , which is C-shaped.  
      The conventional lens system, however, has complicated lens structures. In addition, since the conventional lens system is manufactured through compression molding, the manufacturing costs are high. Specifically, two plastic lenses of the conventional lens system should be formed to have at least one aspheric surface through press molding. In general, plastic lenses are manufactured with smaller tolerances than glass lenses, making it more complicated and costly to manufacture plastic lenses than to manufacture glass lenses.  
     SUMMARY OF THE INVENTION  
      The present invention provides a projection optical system which is less costly to manufacture and which satisfactorily corrects aberration, and a projection TV employing the projection optical system.  
      According to an aspect of the present invention, there is provided a projection optical system. The projection optical system includes a lens module, which itself comprises a plastic power lens and a hybrid lens. The hybrid lens is comprised of a spherical, biconvex, glass lens, and an aspheric lens layer formed on at least one face of the spherical lens. The projection optical system further includes an electron beam tube optical module, comprising a C-shaped aberration correction device, a window, and a coolant disposed between the window and the aberration correction device.  
      The aspheric lens layer may be formed of plastic.  
      The focal power of the hybrid lens may be 95-98% of the focal power of the projection optical system.  
      Both faces of the spherical lens may be symmetrical.  
      According to another aspect of the present invention, there is provided a projection TV. The projection TV includes an electron beam tube, which generates a color image and a projection optical system, which magnifies the color image and then projects the magnified color image on a screen. Here, the projection optical system may include a lens module and an electron beam tube optical module. The lens module includes a plastic power lens and a hybrid lens. The hybrid lens is comprised of a spherical, biconvex, glass lens and an aspheric lens layer formed on at least one face of the spherical lens. The electron beam tube optical module includes a C-shaped aberration correction device, a window, and a coolant disposed between the window and the aberration correction device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:  
       FIG. 1  is a diagram illustrating a conventional projection lens system disclosed in U.S. Pat. No. 5,029,993;  
       FIG. 2  is a diagram illustrating a projection optical system according to an exemplary embodiment of the present invention; and  
       FIG. 3  is a diagram illustrating a projection TV employing the projection optical system of  FIG. 2 , according to an exemplary embodiment of the present invention.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Referring to  FIG. 2 , a projection optical system  80  includes a lens module M 1  and an electron beam tube optical module M 2 .  
      The lens module M 1  includes a plastic power lens  52  and a hybrid lens  54 . The hybrid lens  54  is comprised of a spherical glass lens  54   a , which is a biconvex lens, and an aspheric lens layer  54   b , which is coated on at least one surface of the spherical glass lens  54   a.    
      Preferably, but not necessarily, both surfaces of the spherical glass lens  54   a  are symmetrical, and the aspheric lens layer  54   b  is formed of a plastic layer so that its aspheric surfaces face the electron beam tube optical module M 2 . The focal power of the hybrid lens  54  has a ratio of 0.95-0.98 to the focal power of the entire projection optical system.  
      The aspheric lens layer  54   b  has an aspheric surface expressed by Equation (1):  
             z   =         c   ⁢           ⁢     ρ   2         1   +       1   -       (     1   +   k     )     ⁢     c   2     ⁢     ρ   2               +       ∑     i   =   1     7     ⁢           ⁢       a   i     ⁢     ρ     2   ⁢   i                     (   1   )             
 
 where z denotes a longitudinal coordinate of the aspheric surface, c denotes a curvature of the aspheric surface, p denotes a radial coordinate of the aspheric surface, k denotes a conic constant, and a i  denotes an aspheric coefficient, which determines a deviation of the aspheric surface from a spherical surface of the aspheric lens layer  54   b  and which satisfies the following inequality: ai×a i+1 &lt;0. 
 
      The optical module M 2  includes an aberration correction device  62 , which is C-shaped, a window  66 , and a coolant  64 , which is disposed between the aberration correction device  62  and the window  66 .  
      The window  66  covers a fluorescent surface of a display device (e.g., an electron beam tube), which generates a color image. The coolant  64  cools down the display device. The aberration correction device  62 , which is in contact with the coolant  64 , diverges the color image, generated by the display device, along a predetermined optical path.  
      A color image output from the aberration correction device  62  is condensed passing through the hybrid lens  54  and then is directed to a screen S after passing through the plastic power lens  52 .  
       FIG. 3  is a diagram illustrating a projection TV employing the projection optical system  80  of  FIG. 2 , according to an exemplary embodiment of the present invention. Referring to  FIG. 3 , the projection TV includes an electron beam tube  70 , which generates a color image, and the projection optical system  80 , which magnifies the color image and then projects the magnified image on a screen S. The projection TV may further include a mirror  85 , which reflects the magnified image output from the projection optical system  80  toward the screen S.  
      The projection TV forms a color image by combining signals of different color beams (e.g., red, green, and blue beams) generated by the electron beam tube  70  together with the use of the projection optical system  80  and displays the color image on the screen S. The electron beam tube  70  is comprised of three sub-electron beam tubes, which respectively generate, e.g., red, green, and blue images.  
      As described above with reference to  FIG. 2 , the projection optical system  80  is divided into the lens module M 1  and the electron beam tube optical module M 2 . Referring to  FIG. 2 , the plastic power lens  52  has a concave surface facing toward the screen S or the mirror  85  and corrects a spherical aberration that is more likely to be generated as the aperture of the plastic power lens  52  increases.  
      The hybrid lens  54  is an optical device that magnifies a color image input from the electron beam tube  70 . Since the hybrid lens  54  is comprised of the spherical glass lens  54   a  having a high positive refracting power, and the aspheric lens layer  54   b , which is formed on at least one of the surfaces of the spherical glass lens  54   a , it can enhance the aberration correctability of the projection optical system.  
      The aberration correction device  62  is formed of a lens, which has a convex surface facing toward the screen S or the mirror  85  and has a concave surface facing toward the electron beam tube  70 , and thus can correct a field curvature and a distortion aberration.  
      As described above, the projection optical system according to the present invention has a lens module having simplified lens structures and has a reduced number of plastic lenses, thus decreasing the number of press molding processes for generating plastic lenses. In addition, the projection optical system according to the present invention enables a hybrid lens to be manufactured with a high tolerance by forming the hybrid lens to be composed of an aspheric plastic lens layer.  
      In addition, the projection TV according to the present invention, which employs the projection optical system according to the present invention, can satisfactorily correct a chromatic aberration and spherical aberration. Thus, the projection TV according to the present invention can provide high quality pictures. In addition, since the projection optical system according to the present invention has a reduced number of plastic lenses, the projection TV according to the present invention is less costly to manufacture.  
      Although the above exemplary embodiments of the present invention have been described, it will be understood by those skilled in the art that the present invention should not be limited to the described exemplary embodiments, but that various changes and modifications can be made within the spirit and scope of the present invention.