Patent Publication Number: US-2006007402-A1

Title: Illumination lens system and projection system including the same

Description:
BACKGROUND OF THE INVENTION  
      This application claims the benefit of Korean Patent Application No. 10-2004-0052337, filed on Jul. 6, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.  
      1. Field of the Invention  
      Apparatuses consistent with the present invention relate to an illumination lens system and a projection system including the same, and more particularly to an illumination lens system, in which chromatic aberration and manufacturing expenses are reduced, and a projection system including the illumination lens system.  
      2. Description of the Related Art  
      Projection systems are generally classified into three-panel projection systems and single-panel projection systems depending on the number of display devices used to turn pixels on and off to control light emitted from a light source. The light source is a high-powered lamp which produces a color image. In a single-panel projection system, the structure of the optical system can be made smaller, in comparison to a three-panel projection system, but white light is separated into red (R), green (G), and blue (B) colors using a sequential method. Thus, the light efficiency of a single-panel projection system is ⅓ the light efficiency of a three-panel projection system. Therefore, efforts for increasing the light efficiency of single-panel projection systems have been made.  
      In a conventional single-panel projection system, a beam irradiated from a white light source is separated into RGB color beams using a color filter, and the RGB beams are sequentially transferred to a display device. The display device operates sequentially and forms an image.  
      As shown in  FIG. 1A , a conventional single-panel projection system includes a light source  100 ; a color wheel  115  that splits a beam emitted from the light source  100  into RGB color beams; an integrator  117  which shapes the RGB beams that have passed through the color wheel  115 ; a total reflection prism  125  which totally reflects the RGB beams that have passed through the integrator  117 ; and a display device  122  which receives the RGB beams reflected by the total reflection prism  125 , processes the RGB beams according to an input image signal, and forms a color image. The system further includes a projection lens unit  130  which enlarges and projects the color image formed by the display device  122  onto a screen.  
      An illumination lens system  120  which condenses the RGB beams that pass through the integrator  117  is disposed along a light path between the integrator  117  and the total reflection prism  125 .  
      The total reflection prism  125  includes an incidence prism  125   a  which totally reflects the beam emitted from the light source  100  onto the display device  122 ; and an emission prism  125   b  which transmits the beam reflected by the display device  122  to the projection lens unit  130 .  
      As shown in  FIG. 1B , the illumination lens system  120  is composed of first through fourth lenses  120   a ,  120   b ,  120   c , and  120   d . The exemplary design data of the first through fourth lenses  120   a ,  120   b ,  120   c , and  120   d  is shown in Table 1. Here, R denotes a radius curvature, Dn denotes the thickness of a lens or the distance between lenses, N denotes a refractive index, and v denotes an Abbe&#39;s number.  
                               TABLE 1                       Lens   Curvature   Thickness or   Refractive   Abbe&#39;s       Side   Radius (R)   Distance (Dn)   Index (N)   Number (v)                                                    0   ∞   3.50               S1   −9.91000   6.00   1.51680   64.2       S2   −10.42700   0.10           S3   ∞   5.00   1.51680   64.2       S4   −21.60000   33.00           S5   ∞   6.50   1.52500   64.2       S6   −23.19962   65.80           S7   98.28100   8.00   1.51680   64.2       S8   −54.76600   2.00           S9   ∞   22.64   1.51680   64.2       S10   ∞   0.00   1.51680   64.2       S11   ∞   −21.62   1.51680   64.2       S12   ∞   −4.80           S13   ∞   −2.74   1.47200   66.1       S14   ∞   −0.78           SIM   ∞                  
 
      The side S6 is aspherical whose definition is as follows.  
      When the X-axis is set as the optical axis in  FIG. 1B , and the Y-axis is set as a perpendicular direction from the optical axis, a forward direction of the beam is positive and can be expressed as described below. Here, x denotes a distance from the vertex of a lens to the optical axis, y denotes a distance toward the perpendicular direction from the optical axis, K denotes a conic constant, A, B, C, and D denote coefficients of an aspherical surface, and c denotes a reciprocal number (1/R) of the refractive radius in the vertex of lens.  
             x   =         cy   2       1   +       1   -       (     K   +   1     )     ⁢     c   2     ⁢     y   2               +     Ay   4     +     By   6     +     Cy   8     +     Dy   10               (   10   )             
 
      Coefficients of the aspherical side S8 are K=0.0, A=0.112753E-04, B=−0.665984E-8, C=0.112495E-9, and D=−0.262361E-12. In Table 1, S9, S10, S11, S12, S13, and S14 indicate the respective sides of the total reflection prism  125  and the display device  122 .  
      Referring to  FIG. 2 , calculation of the chromatic aberration of the illumination lens system of  FIG. 1B  is based on five fields a, b, c, d, and e when the beam is emitted from the integrator  117 . The coordinates of each field are shown in Table 2.  
                                       TABLE 2                                   a   b   c   d   e                                                            X coordinate   0.00000   −1.09602   −3.92444   1.09602   3.92444       Y coordinate   0.00000   3.92444   1.09602   −3.92444   −1.09602                  
 
      With reference to the aberration diagram of  FIG. 2 , even if the conventional illumination lens system employs an expensive aspherical lens, chromatic aberration still occurs. The chromatic aberration results in a reduction of an illumination margin when the beam emitted from the integrator  117  is irradiated onto the display device  122 . That is, a beam that is output from the integrator  117  and has a shape corresponding to the shape of the display device  122  must be uniformly irradiated onto the display device  122 . However, a large amount of chromatic aberration reduces the beam which is effectively irradiated onto the display device  122 , thereby lowering image quality.  
      The conventional illumination system further costs a great deal of money due to its use of an aspherical surface.  
     SUMMARY OF THE INVENTION  
      An exemplary embodiment of present invention provides an illumination lens system, in which chromatic aberration and expenses are reduced, and a projection system including the illumination lens system.  
      According to an aspect of the present invention, there is provided a projection system comprising: a light source; a color filter separating beams emitted from the light source into colored beams; an illumination lens system comprising first through third lens groups that condense the colored beams, the second lens group comprising a double lens comprising a first lens having a highly disperse and negative refractive power and a second lens having a low disperse and positive refractive power; a display device processing the beam emitted from the illumination lens system in response to an input signal and forming a color image; and a projection lens unit enlarging the color image formed by the display device and projecting the color image onto a screen.  
      The projection system further comprising a total reflection prism between the illumination lens system and the display device condensing the beam emitted from the illumination lens system toward the display devices, and directing the beam reflected by the display device toward the projection lens unit.  
      The projection system further comprising a concave mirror between the illumination lens system and the display device condensing the beam emitted from the illumination lens system onto the display device.  
      According to another aspect of the present invention, there is provided an illumination lens system that is employed in a projection system and condenses a beam emitted from a light source onto a display device that forms an image, comprising: first through third lens groups, the second lens group comprising, a double lens comprising a first lens having a highly disperse and negative refractive power and a second lens having a low disperse and positive refractive power.  
      When f1 is the effective focal distance of the first lens group, f3 is the effective focal distance of the third lens group, and d is the distance between the principal plane of the first lens group and the principal plane of the third lens group, the illumination lens system may satisfy the following conditions:  
       0.8   ≤     d       f   1     +     f   3         ≤   1.2       
 
      The projection system may further include a beam shaper that shapes the beam emitted from the light source so that the beam has a cross-sectional shape corresponding to the shape of the display device, where m is the size of the beam emitted from the display device, f1 is the effective focal distance of the first lens group, and f3 is the effective focal distance of the third lens group, such that the illumination lens system satisfies the following condition:  
         0.8   ⁢   m     ≤       f   3       f   1       ≤     1.2   ⁢   m         
 
      In an exemplary embodiment, the illumination lens system may comprise only spherical lenses. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above aspects and features of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:  
       FIG. 1A  is a schematic diagram of a conventional projection system;  
       FIG. 1B  is a schematic diagram of an illumination lens system included in the projection system illustrated in  FIG. 1A ;  
       FIG. 2  is a diagram illustrating fields used to calculate chromatic aberration of the illumination lens system illustrated in  FIG. 1B ;  
       FIG. 3  the chromatic aberration of the illumination lens system illustrated in  FIG. 1B ;  
       FIG. 4A  is a schematic diagram of a projection system according to an embodiment of the present invention;  
       FIG. 4B  illustrates a modified example of the projection system according to an embodiment of the present invention;  
       FIG. 5  is a schematic diagram of an illumination lens system according to a first exemplary embodiment of the present invention;  
       FIG. 6  illustrates the chromatic aberration of the illumination lens system illustrated in  FIG. 5 .  
       FIG. 7  is a schematic diagram of an illumination lens system according to a second exemplary embodiment of the present invention;  
       FIG. 8  illustrates the chromatic aberration of the illumination lens system of  FIG. 7 .  
       FIG. 9  is a schematic diagram of an illumination lens system according to a third exemplary embodiment of the present invention;  
       FIG. 10  illustrates the chromatic aberration of the illumination lens system illustrated in  FIG. 9 .  
       FIG. 11  is a schematic diagram of an illumination lens system according to a fourth exemplary embodiment of the present invention;  
       FIG. 12  illustrates the chromatic aberration of the illumination lens system illustrated in  FIG. 11 . 
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION  
      Referring to  FIG. 4A , the projection system includes a light source  5 ; a color filter  8  which separates light emitted from the light source  5  into colored beams; and a display device  30  which processes the colored beams passing through the color filter  8  in response to an input signal and forms a color image. A projection lens unit  35  enlarges and projects the color image formed in the display device  30  onto a screen (not shown).  
      The color filter  8  may be, for example, a color wheel. An ultraviolet filter  7  is disposed on the light path between the light source  5  and the color filter  8 , and a beam shaper  10  that shapes the beam emitted from the light source  5  is disposed on the light path between the color filter  8  and the display device  30 . The beam shaper  10  may be an integrator, a light tunnel, or a glass rod. The beam shaper  10  shapes the beam so that the beam has a cross-sectional shape corresponding to the shape of the display device  30  and a uniform intensity.  
      A total reflection prism  33  directs the beam emitted by the beam shaper  10  toward the display device  30 , and directs the beam reflected by the display device  30  toward the projection lens unit  35 .  
      With additional reference to  FIG. 5 , an illumination lens system  20 A including first through third lens groups I, II, and III condenses beams on a light path between the beam shaper  10  and the total reflection prism  33 . The second lens group II includes a double lens including a first lens  23  having a highly disperse negative refractive power and a second lens  24  having a low disperse positive refractive power.  
      The total reflection prism  33  creates different optical paths for the beam incident on the display device  30  and the beam reflected by the display device  30 . The total reflection prism  33  may have first and second prisms  33   a  and  33   b  opposite each another. The first prism  33   a , which is an incidence prism, totally reflects the incident beam directly onto the display device  30 , and the second prism  33   b , which is an emission prism, transmits the beam reflected by the display device  30  directly to the projection lens unit  35 .  
      Alternatively, as shown in  FIG. 4B , the total reflection prism  33  may include a concave mirror  40  that reflects and condenses the beam emitted from the illumination lens system  20 A onto a display device such that the display device  43  emits light along an optical axis parallel to the optical axis of the illumination lens system  20 A. A projection lens unit  45  enlarges and projects a color image formed by the display device  43  onto a screen S.  
      The display devices  30  and  43  may be reflection type liquid crystal displays (LCDs) or deformable micromirror devices (DMDs).  
      Although not shown in the figures, at least one light-path converter which changes the path of the colored beams is disposed between the color filter  8  and the display device  30  or  43 .  
      Referring to  FIG. 5 , the illumination lens system  20 A according to an exemplary embodiment of the present invention includes the first through third lens groups I, II, and III which are disposed from an objective side to an image side. The second lens group II includes a double lens comprising a first lens  23  having a highly disperse and negative refractive power and a second lens  24  having a low disperse and positive refractive power.  
      When the effective focal distance of the first lens group I is f1, the effective focal distance of the third lens group I is f3, and the distance from the principal plane of the first lens group I to the principal plane of the first lens group III is d, the illumination lens system  20 A may satisfy the following conditions:  
             0.8   ≤     d       f   1     +     f   3         ≤   1.2           (   2   )             
 
      When the illumination lens system  20 A has a value bigger than the maximum value, the beam incident on the display device  30  has such a large amount of diversion that the illumination lens system  20 A departs from the telecentric system. When the illumination lens system  20 A has a value smaller than the minimum value, the beam incident on the display device  30  has such a large amount of condensation that the illumination lens system  20 A is not utilized.  
      When the ratio of the size of the beam incident on the illumination lens system  20 A and the size of the beam emitted from the display device  30  is m, the illumination lens system  20 A may satisfy the following condition:  
               0.8   ⁢   m     ≤       f   3       f   1       ≤     1.2   ⁢   m             (   3   )             
 
      If the illumination lens system  20 A has a value exceeding the maximum value, the beam incident on the display device  30  has such a large amount of radiation that the illumination lens system  20 A cannot be utilized. If the illumination lens system  20 A has a value smaller than the minimum value, the beam incident on the display device  30  has a very large amount of condensation.  
      The design data of an illumination lens system  20 A according to a first exemplary embodiment of the present invention is as follows.  
      Here, R denotes a radius of curvature of a lens, Dn (n is a natural number) denotes the thickness of a lens or the distance between lenses, N denotes a refractive index, and v denotes an Abbe&#39;s number.  
                               TABLE 3                       Lens   Curvature   Thickness or   Refractive   Abbe&#39;s       Side   Radius (R)   Distance (Dn)   Index (N)   Number (v)                                                    0   ∞   4.04               S1   −27.75407   10.00   1.65844   50.9       S2   −11.79481   26.00           S3   58.25637   2.00   1.72825   28.3       S4   20.25800   11.70   1.58913   61.3       S5   −29.91033   64.21           S6   37.82266   6.40   1.51680   64.2       S7   ∞   19.69   1.51680   64.2       S8   ∞   0.00   1.51680   64.2       S9   ∞   −22.74   1.51680   64.2       S10   ∞   −3.00           S11   ∞   −3.00   1.47200   66.1       S12   ∞   −0.47           SIM   ∞                  
 
      In Table 3, S8, S9, S10, S11, and S12 indicate the respective surfaces of the total reflection prism  33  and the display device  30 .  FIG. 6  illustrates the chromatic aberration of the illumination lens system  20 A shown in  FIG. 5 . The chromatic aberration is obtained when a lens is imaged in the display device  30 ,  43 .  
      An illumination lens system  20 B according to a second exemplary embodiment of the present invention is illustrated in  FIG. 7 . The design data of the illumination lens system  20 B illustrated in  FIG. 7  is as follows.  
                               TABLE 4                       Lens   Curvature   Thickness or   Refractive   Abbe&#39;s       Side   Radius (R)   Distance (Dn)   Index (N)   Number (v)                                                    0   ∞   4.826505               S1   −22.05139   7.00   1.74397   44.9       S2   −11.17675   26.00           S3   74.12738   2.00   1.75520   27.6       S4   34.74362   0.77           S5   46.77763   8.29   1.66162   53.4       S6   −29.04246   62.88           S7   37.82266   6.40   1.56124   63.9       S8   435.18490           SIM   ∞                  
 
       FIG. 8  illustrates the chromatic aberration of the illumination lens system  20 B illustrated in  FIG. 7 . Although the illumination lens system  20 B does not use an aspherical surface, the chromatic aberration is improved.  
       FIG. 9  illustrates an illumination lens system  20 C according to a third exemplary embodiment of the present invention. The exemplary design data of the illumination lens system  20 C illustrated in  FIG. 9  is as follows.  
                               TABLE 5                       Lens   Curvature   Thickness or   Refractive   Abbe&#39;s       Side   Radius (R)   Distance (Dn)   Index (N)   Number (v)                                                    0   ∞   4.00               S1   −28.99107   10.00   1.74428   44.1       S2   −11.42240   23.00           S3   −254.05314   4.19   1.71251   47.6       S4   −21.72603   2.00   1.75520   27.6       S5   −27.77453   50.009           S6   42.61221   5.89   1.74397   44.6       S7   ∞           SIM   ∞                    
       FIG. 10  illustrates the chromatic aberration of the illumination lens system  20 C illustrated in  FIG. 9 .  
       FIG. 11  is a schematic diagram of an illumination lens system  20 D according to a fourth exemplary embodiment of the present invention. Table 6 indicates exemplary design data of the illumination lens system  20 D illustrated in  FIG. 11 . In the fourth embodiment of the present invention, a first lens group I includes a first lens  21  and a second lens  22 , a second lens group II includes a third lens  23  and a fourth lens  24 , and a third lens group III includes a fifth lens group  25 .  
                               TABLE 6                       Lens   Curvature   Thickness or   Refractive   Abbe&#39;s       Side   Radius (R)   Distance (Dn)   Index (N)   Number (v)                                                    0   ∞   6.00               S1   −56.34802   8.00   1.55828   64.1       S2   −13.06447   0.10           S3   −69.95719   5.00   1.74589   40.5       S4   −30.53232   30.13           S5   95.49207   2.00   1.75520   27.6       S6   21.65923   11.700   1.65748   54.0       S7   −38.88080   55.00           S8   31.18209   6.40   1.55756   48.0       S9   89.53555   2.00           S10   ∞       SIM   ∞                    
       FIG. 12  illustrates the chromatic aberration of the illumination lens system  20 D according to the fourth embodiment of the present invention.  
      It can be seen from  FIG. 12  that the chromatic aberration is greatly improved in the illumination lens system  20 D illustrated in  FIG. 11 . The chromatic aberration is improved without using an aspherical lens, and therefore expenses are reduced and an increased illumination margin of the beam irradiated on the display device is obtained.  
      As described above, the illumination lens system according to the exemplary embodiments of the present invention can improve the chromatic aberration without using an aspherical lens, resulting in a reduction in the manufacturing expenses.  
      In a projection system including an illumination lens system with improved chromatic aberration, an illumination margin of a beam incident on a display device is increased, and therefore the performance of the illumination projection system is improved and image quality is improved.  
      While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the following claims.