Abstract:
An image taking optical system including a main optical system for forming an object image; and an image splitting unit for dividing an image without re-forming the image formed by the main optical system. The image splitting unit includes sequentially from the object side a performance correcting optical system and an image splitting unit, and satisfies the following conditional equation: 
     
       
         −0.25&lt;φh×Ys&lt;0.25 
       
     
     
       
         0.8&lt;βh&lt;1.2 
       
     
     where φh represents the optical power of the performance correcting optical system, Ys represents the maximum image height by the image splitting unit, and βh represents the transverse magnification of the performance correcting optical system.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is based on Application No. 10-297931 filed in Japan, the content of which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a taking optical system for cameras, and specifically relates to a taking optical system having an image-splitting image sensing unit for sensing divisions or parts of an image formed by an exchangeable lens. 
     2. Description of Related Art 
     In conjunction with the popularization of personal computers in recent years, digital still cameras for taking images which are easily stored on floppy disks and the like have become widely used. With the increasing popularity of digital still cameras, there has been demand for enlargement of the photographic range, and concomitant demand for photographic lenses of various specifications. In the field of recording images on silver salt film, single lens reflex cameras have come to use a plurality of exchangeable taking lenses (exchangeable lenses), and there has been a corresponding demand for taking lenses of various specifications. 
     If exchangeable lenses for single lens reflex cameras can be used with digital still cameras using an photoelectric conversion element, it is possible to respond to the demand for such photographic lenses. One specific method, for example, arranges a direct photoelectric conversion element on the image forming plane of an exchangeable lens. Japanese Laid-Open Patent Application Nos. 63-205626 and 7-253537 disclose other methods wherein a condenser lens is arranged near the image plane of an exchangeable lens, and a relay optical system is provided for re-forming an image formed by the exchangeable lens. 
     In such methods which arrange a direct photoelectric conversion element on the image forming plane of an exchangeable lens, an extremely large photoelectric conversion element having a large number of pixels is required to obtain the full optical capabilities of the exchangeable lens by having a screen size similar to that of silver salt film. Such a large photoelectric conversion element is prohibitively expensive and difficult to apply to consumer products. 
     The constructions disclosed in Japanese Laid-Open Patent Application Nos. 63-205626 and 7-253537 are disadvantageous inasmuch as the taking optical system is greatly enlarged by the inposition of a relay optical system so as to re-form the image formed by the exchangeable lens. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an improved taking optical system for cameras. 
     Another object of the present invention is to provide a compact taking optical system for cameras capable of using exchangeable lenses, and which is suitable for producing high quality images. 
     These objects are attained by a taking optical system comprising a main optical system for forming an object image, and an image splitting unit for dividing an image without re-forming the image formed by the main optical system, wherein the image splitting unit comprises sequentially from the object side a performance correcting positive lens and a split prism, and satisfies the following conditional equation: 
     
       
         −0.25&lt;φh×Ys&lt;0.25 
       
     
     
       
         0.8&lt;βh&lt;1.2 
       
     
     where φh represents the optical power of the performance enhancing lens, Ys represents the maximum image height by the image-splitting unit, and βh represents the transverse magnification of the performance correcting lens. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and features of this invention will become clear from the following description taken in conjunction with the preferred embodiments with reference to the accompanying drawings, in which: 
     FIG. 1 shows the construction of the taking optical system of a first embodiment; 
     FIG. 2 shows the construction of the taking optical system of a second embodiment; 
     FIG. 3 shows the construction of the taking optical system of a third embodiment; 
     FIGS. 4 a  through  i  show aberration diagrams at infinity corresponding to the first embodiment; 
     FIGS. 5 a  through  i  show aberration diagrams at infinity corresponding to the second embodiment; 
     FIGS. 6 a  through  i  show aberration diagrams at infinity corresponding to the third embodiment; 
     FIG. 7 illustrates sensing of the respective halves of a split image by the photoelectric conversion element; and 
     FIG. 8 illustrates sensing of the total split image by the photoelectric conversion element. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The embodiments of the present invention are described hereinafter with reference to the accompanying drawings. FIGS. 1 through 3 show the constructions of the taking optical systems of the first through the third embodiments, respectively. Arrows in the drawings schematically represent the direction of movement of each lens element during the zooming operation described later. Each drawing shows conditions at the wide angle end during zooming. 
     In the first embodiment shown in FIG. 1, a main optical system unit L 1  is provided with an image-splitting image sensing unit U 1 . The left side in the drawing is the object side and the right side is the image side. In the drawing, the image-splitting image sensing unit U 1  comprises sequentially from the object side a performance correcting optical system A, a low-pass filter unit LPF, and an image-splitting prism P 1 . The performance correcting optical system A comprises sequentially from the object side a positive meniscus lens having a convex surface on the object side, and a negative meniscus lens having a concave surface on the image side. 
     The main optical system unit L 1  is a zoom lens comprising sequentially from the object side a first lens element Gr 1 , a second lens element Gr 2 , a third lens element Gr 3 , and a fourth lens element Gr 4 , wherein all lens elements move simply to the object side as indicated by the arrows in the drawing when zooming from the wide angle end to the telephoto end. 
     In the second embodiment shown in FIG. 2, a main optical system unit L 2  is provided with the image-splitting image sensing unit U 1 . Similar to the first embodiment, the left side of the drawing is the object side, and the right side is the image side. In the drawing, the main optical system L 2  is a zoom lens comprising sequentially from the object side a first lens element Gr 1 , a second lens element Gr 2 , a third lens element Gr 3 , and a fourth lens element Gr 4 , and all lens elements move simply to the object side as indicated by the arrows in the drawing when zooming from the wide angle side to the telephoto side. 
     In the third embodiment shown in FIG. 3, a main optical system unit L 3  is provided with an image-splitting image sensing unit U 2 . Similar to the first embodiment, the left side of the drawing is the object side, and the right side is the image side. In the drawing, the image-splitting image sensing unit U 2  comprises sequentially from the object side a performance correcting lens unit B, a low-pass filter LPF, and an image-splitting prism P 2 . The performance correcting lens unit B comprises sequentially from the object side a biconvex lens, a negative meniscus lens having a concave surface on the image side, and a biconcave lens. 
     The main optical system unit L 3  is a zoom lens comprising sequentially from the object side a first lens element Gr 1 , and a second lens element Gr 2 , wherein the first lens element Gr 1  moves once to the image side, then moves again to the object side, and the second lens element Gr 2  moves simply to the object side as indicated by the arrows in the drawing when zooming from the wide angle end to the telephoto end. The image-splitting unit U 1  also is applicable to the main optical system unit L 3 , and the image-splitting unit U 2  also is applicable to the main optical system units L 1  and L 2 . Accordingly, each of the main optical system units are mutually exchangeable. 
     Although a low-pass filter is disposed medially to the performance correcting lens and the image-splitting prism in the previously described embodiments, the low-pass filter also may be disposed medially to the image-splitting prism and a photoelectric conversion element described later. In this instance a low-pass filter unit is required for each of the divided light fluxes. The low-pass filter unit may be omitted, or a low-pass filter using a diffraction element may be used depending on the performance requirements. 
     The previously mentioned image splitting prism is described in detail below. FIGS. 7 and 8 schematically show the positional relationship of the image-splitting prism and the photoelectric conversion element. As shown in the drawings, the image-splitting prism P is formed by cementing two prisms on an inclined adhering surface S, and the adhering surface S is provided with a vacuum deposition layer which permits equally balanced transmission light and reflected light. 
     FIG. 7 illustrates sensing of the respective halves of a split image by the photoelectric conversion element. In the drawing, illumination is from the left side of the drawing along the optical axis X indicated by the dashed line. Light from a photographic object not shown in the illustration forms an image on a photoelectric conversion element  1  via light transmitted through the splitting prism P in the bottom half, and forms an image on the photoelectric conversion element  2  via light reflected by the splitting prism P in the top half. According to this construction, a compact photoelectric conversion element can be used, thereby reducing cost. The images from the top and bottom halves are joined electronically in, for instance, a known manner. 
     FIG. 8 illustrates sensing of the total split image by the photoelectric conversion element. In the drawing, illumination is from the left side of the drawing along the optical axis X indicated by the dashed line. Light from a photographic object not shown in the illustration forms an image on a photoelectric conversion element  1 ′ via all light transmitted through the splitting prism P, and forms an image on the photoelectric conversion element  2 ′ via all light reflected by the splitting prism P. At this time, the obtained image quality is greater than the original photoelectric conversion element due to the pixels of one photoelectric conversion element being offset relative to counterpart pixels of the other photoelectric conversion elements, thus attaining higher image quality through electronic image integration techniques. 
     FIGS. 9 and 10 disclose two other embodiments for sensing the total split image by photoelectric conversion elements. In FIG. 9, the respective portions of a split image by the photoelectric conversion element are taken from the middle and at the edges of the photoelectric conversion elements. In the drawing, illumination is from the left side of the drawing along the optical axis X indicated by the dashed line. Light from a photographic object not shown in the illustration forms an image on a photoelectric conversion element  1 ″ via light transmitted through the splitting prism P in the center portion, and forms an image on the photoelectric conversion element  2 ″ via light reflected by the splitting prism P in the edge portions adjacent the center portion. According to this construction, a compact photoelectric conversion element can be used, thereby reducing cost. The images from the different portions are joined electronically in, a known manner. 
     FIG. 10 illustrates sensing of the total split image by the photoelectric conversion element. In the drawing, illumination is from the left side of the drawing along the optical axis X indicated by the dashed line. Light from a photographic object not shown in the illustration forms an image on a photoelectric conversion element  1 ′″ via all light transmitted through the splitting prism P, and forms an image on the photoelectric conversion element  2 ′″ via light reflected by the splitting prism P. Additionally, light forms an image on a third photoelectric conversion element  3  via all light reflected by the splitting prism P in a direction different than the light reflected from the prism towards the second photoelectric conversion element  2 ′″. The light can be divided by wavelength (e.g., RGB). At this time, the obtained image quality is greater than the original photoelectric conversion element due to the separation of the color images, thus attaining higher image quality through electronic image integration techniques. However, it is also possible to separate the images on the three (or two using the embodiment of FIG. 8) photoelectric conversion elements, which are activated or read sequentially, for instance. In this manner, the speed required by the photoelectric conversion elements for taking images could be increased to one third the time taken to take three images using one photoelectric conversion element in this example. 
     The previously mentioned performance correcting optical system is described below. In general, when a glass is inserted in an aberration-corrected optical system, the light ray optical path length changes so as to produce a markedly adverse affect mainly on extra-axial performance and various types of aberration such as color aberration and curvature of field to the over side. Accordingly, when the aforesaid image-splitting prism is inserted on the image plane side relative to the independently used exchangeable lens, aberration degradation is generated. The performance correcting optical system functions to correct the aberration degradation generated by the insertion of the image splitting prism on the image plane side. 
     The performance correcting optical systems should satisfy the following conditions. It is desirable that the performance correcting optical system of each of the aforesaid embodiments satisfies conditional equation (1): 
     
       
         −0.25&lt;φh×Ys&lt;0.25  (1) 
       
     
     where φh represents the optical power of the performance correcting optical system, and Ys represents the maximum image height by the image-splitting prism. 
     Conditional equation (1) stipulates the optical power of the performance correcting optical system. When the lower limit of conditional equation (1) is exceeded, there is a pronounced negative tendency of distortion. Conversely, when the upper limit is exceeded, there is a marked positive tendency of distortion. 
     It is further desirable that the performance correcting optical systems of the aforesaid embodiments satisfies conditional equation (2) below: 
     
       
         0.8&lt;βh&lt;1.2  (2) 
       
     
     where βh represents the transverse magnification of the performance correcting optical system. 
     Conditional equation (2) stipulates the magnification of the performance correcting optical system. In this instance, magnification is nearly 1:1. When the lower limit of conditional equation (2) is exceeded, magnification becomes too small, back focus is reduced, and it becomes difficult to ensure adequate space for the splitting prism. Conversely, when the upper limit is exceeded, the screen size becomes larger and necessitates the use of a large screen photoelectric conversion element, thereby increasing cost. 
     It is desirable that the lens having the strongest positive optical power of the performance correcting optical system of the aforesaid embodiments satisfies conditional equation (3) below: 
     
       
         0.10&lt;φP×Ys&lt;0.60  (3) 
       
     
     where φP represents the optical power of the positive lens. 
     When the lower limit of conditional equation (3) is exceeded, the optical power is too weak, such that multiple positive power lenses are required to attain a desired aberration correction, thereby increasing cost. Conversely, when the upper limit is exceeded, the optical power becomes excessive and spherical aberration tends to fall markedly on the under side. 
     It is further desirable that the aforesaid positive lens satisfies conditional equations (4) and (5) below: 
     
       
         1.45&lt;NdP  (4) 
       
     
     
       
         30&lt;νdP  (5) 
       
     
     Where Nd represents the refractive index relative to the d-line, and vd represents the Abbe number. Conditional equations (4) and (5) stipulate the glass material of the positive lens, and are conditions which maintain suitable Petzval sum and color aberration. 
     It is desirable that the lens having the strongest negative optical power of the performance correcting optical system of the aforesaid embodiments satisfies conditional equation (6) below in addition to conditional equation (3): 
     
       
         −0.60&lt;φN×Ys&lt;−0.1  (6) 
       
     
     where φN represents the optical power of the negative lens. 
     When the upper limit of conditional equation (6) is exceeded, the optical power is too weak, such that multiple negative power lenses are required to attain a desired aberration correction, thereby increasing cost. Conversely, when the lower limit is exceeded, the optical power becomes excessive and spherical aberration tends to fall markedly on the over side (i.e., toward the positive side in an aberration diagram). 
     It is desirable that the aforesaid negative power lens satisfies conditional equation (7) and (8) below in addition to conditional equations (4) and (5). 
     
       
         1.55&lt;NdN  (7) 
       
     
     
       
         45&lt;νdN  (8) 
       
     
     Conditional equations (7) and (8) stipulate the glass material of the negative lens, and are conditions which maintain suitable Petzval sum and color aberration. 
     When an aspherical surface is used in the performance correcting optical system, it is desirable that the aspherical surface satisfies conditional equation (9) below: 
      −0.01&lt;( X−X   0 )/( N′−N )&lt;−0.0001  ( 9)   
     where X represents the displacement in the optical axis direction at height Y of the effective optical path diameter expressed in equation (a) below, X 0  represents the displacement in the optical axis direction at height Y of the effective optical path diameter expressed by equation (b) below, N′ represents the refractive index of the aspherical surface on the image side, and N represents the refractive index of the aspherical surface on the object side. The equations below express the surface shape of the aspherical surface described later. 
     The performance correcting optical systems of the present invention corrects performance degradation arising from the insertion of glass, and the performance degradation is mainly the degradation of extra-axial performance. When an aspherical surface is provided, it object is mainly for correcting extra-axial performance, such that conditional equation (9) may be evaluated at a representative screen height of 0.7 which influences extra axial flux. The aspherical surface is particularly effective in dealing with curvature of field and distortion. 
     When the lower limit of conditional equation (9) is exceeded, curvature of field falls to the over side and there is a marked tendency of pin-cushion distortion. Conversely, when the upper limit is exceeded, curvature of filed fall to the under side and there is a pronounced tendency of barrel distortion. When a plurality of aspherical surfaces are used, the other aspherical surfaces combine other aberrations regardless of whether or not conditional equation (9) is satisfied. 
     The structure of the taking optical system of the present invention is described below by way of specific examples with construction data and aberration diagrams. The first through the third examples correspond to the previously described first through the third embodiments, and the lens structural diagrams (FIGS.  1 ˜ 3 ) showing the first through the third embodiments respective show the lens structures of the first through the third examples corresponding therewith. 
     In the examples, the reference symbol ri (i=1,2,3 . . .) represents the radius of curvature of the No. i surface counting from the object side, di (i=1,2,3 . . .) represents the axial distance of the No. i surface counting from the object side, Ni (i=1,2,3 . . .) and vi (i=1,2,3 . . .) respectively represent the refractive index on the d-line and the Abbe Number of the No. i lens counting from the object side. In each example, the focal length of the main optical system, the total system focal length f, the total system F-number FNO, the spacing between the first lens element and the second lens element, the spacing between the second lens element and the third lens element, the spacing between the third lens element and the fourth lens element, and the spacing between the last lens element of the main optical system unit and the performance correcting lens unit correspond sequentially from the left to values at the wide angle end (W), intermediate focal length (M), and telephoto end (T). In each example, surfaces marked by an asterisk (*) appended to the radius of curvature are aspherical surfaces, and the equations expressing the surface shape of the aspherical surfaces are defined below: 
     
       
         X=X 0 +ΣAiY 2   (a) 
       
     
     
       
         Xo=Cy 2 /{1+(1−εC 2 Y 2 ) ½ }  (b) 
       
     
     where X represents the displacement from a reference surface in the optical axis direction, Y represents the height in a direction perpendicular to the optical axis, C represents the paraxial curvature, ε represents the secondary curvature parameter, and Ai represents the aspherical coefficient of the i order. 
     
       
         
               
             
               
               
               
               
             
               
               
               
             
               
               
               
               
             
               
               
               
             
               
               
               
               
             
               
               
               
             
               
               
               
               
             
               
               
             
               
               
               
               
             
               
             
           
               
                 EMBODIMENT 1 
               
             
             
               
                   
               
               
                 L1 = 22.5 mm ˜ 50.5 mm ˜ 78.0 mm Focal length of main optical system 
               
               
                 f = 20.2 mm ˜ 45.5 mm ˜ 70.2 mm Focal length of toal optical system 
               
               
                 FNO = 4.10 ˜ 5.23 ˜ 5.67 F number 
               
             
          
           
               
                 [Radius of 
                   
                 [Refractive 
                   
               
               
                 Curvature] 
                 [Axial Distance] 
                 Index (Nd)] 
                 [Abbe Number(νd)] 
               
               
                   
               
               
                 r1 = 138.245 
                   
                   
                   
               
               
                   
                 d1 = 1.300 
                 N1 = 1.83350 
                 ν1 = 21.00 
               
               
                 r2 = 54.039 
               
               
                   
                 d2 = 6.090 
                 N2 = 1.58913 
                 ν2 = 61.11 
               
               
                 r3 = −242.248 
               
               
                   
                 d3 = 0.100 
               
               
                 r4 = 30.432 
               
               
                   
                 d4 = 4.500 
                 N3 = 1.75450 
                 ν3 = 51.57 
               
               
                 r5 = 61.106 
               
             
          
           
               
                   
                 d5 = 1.870 ˜ 14.942 ˜ 22.023 
                   
               
             
          
           
               
                 r6 = 50.477 
                   
                   
                   
               
               
                   
                 d6 = 1.000 
                 N4 = 1.83400 
                 ν4 = 37.05 
               
               
                 r7 = 10.300 
               
               
                   
                 d7 = 4.800 
               
               
                 r8 = −37.077 
               
               
                   
                 d8 = 1.000 
                 N5 = 1.75450 
                 ν5 = 51.57 
               
               
                 r9 = 19.409 
               
               
                   
                 d9 = 0.210 
               
               
                 r10 = 16.272 
               
               
                   
                 d10 = 3.700 
                 N6 = 1.79850 
                 ν6 = 22.60 
               
               
                 r11 = −42.917 
               
               
                   
                 d11 = 0.917 
               
               
                 r12 = −16.998 
               
               
                   
                 d12 = 1.300 
                 N7 = 1.69680 
                 ν7 = 56.47 
               
               
                 r13 = −83.356 
               
             
          
           
               
                   
                 d13 = 9.767 ˜ 4.197 ˜ 1.780 
                   
               
             
          
           
               
                 r14 = ∞ 
                   
                   
                   
               
               
                 (diaphragm) 
               
               
                   
                 d14 = 0.800 
               
               
                 r15 = 24.573 
               
               
                   
                 d15 = 3.200 
                 N8 = 1.61720 
                 ν8 = 54.00 
               
               
                 r16 = −28.989 
               
               
                   
                 d16 = 0.100 
               
               
                 r17 = 28.797 
               
               
                   
                 d17 = 4.800 
                 N9 = 1.51680 
                 ν9 = 64.20 
               
               
                 r18 = −12.357 
               
               
                   
                 d18 = 1.339 
                 N10 = 1.80741 
                 ν10 = 31.59 
               
               
                 r19 = 105.532 
               
             
          
           
               
                   
                 d19 = 5.400 ˜ 1.669 ˜ 1.089 
                   
               
             
          
           
               
                 r20 = 28.973 
                   
                   
                   
               
               
                   
                 d20 = 4.760 
                 N11 = 1.58267 
                 ν11 = 46.43 
               
               
                 r21 = −19.633 
               
               
                   
                 d21 = 1.588 
               
               
                 r22* = 
               
               
                 −167.579 
               
               
                   
                 d22 = 0.040 
                 N12 = 1.51790 
                 ν12 = 52.31 
               
               
                 r23 = −167.579 
               
               
                   
                 d23 = 1.400 
                 N13 = 1.80741 
                 ν13 = 31.59 
               
               
                 r24 = 29.320 
               
             
          
           
               
                 d24 = 4.180 ˜ 17.541 ˜ 22.191 
                   
               
             
          
           
               
                 r25 = 32.298 
                   
                   
                   
               
               
                   
                 d25 = 4.194 
                 N14 = 1.62346 
                 ν14 = 32.23 
               
               
                 r26 = 1607.174 
               
               
                   
                 d26 = 2.540 
               
               
                 r27 = 171.729 
               
               
                   
                 d27 = 1.100 
                 N15 = 1.84666 
                 ν15 = 23.82 
               
               
                 r28* = 31.216 
               
               
                   
                 d28 = 2.500 
               
               
                 r29 = ∞ 
               
               
                   
                 d29 = 3.200 
                 N16 = 1.51680 
                 ν16 = 64.20 
               
               
                 r30 = ∞ 
               
               
                   
                 d30 = 0.500 
               
               
                 r31 = ∞ 
               
               
                   
                 d31 = 13.800 
                 N17 = 1.51680 
                 ν17 = 64.20 
               
               
                 r32 = ∞ 
               
             
          
           
               
                 [Aspherical coefficient of 22th surface (r22)] 
               
               
                 ε = 0.10000 × 10 
               
               
                 A4 = −0.11449 × 10 −3   
               
               
                 A6 = −0.40063 × 10 −6   
               
               
                 A8 = 0.19296 × 10 −11   
               
               
                 A10 = −0.80550 × 10 −11   
               
               
                 A12 = 0.60989 × 10 −13   
               
               
                 [Aspherical coefficient of 28th surface (r28)] 
               
               
                 ε = 0.10000 × 10 
               
               
                 A4 = −0.41378 × 10 −6   
               
               
                 A6 = 0.10694 × 10 −7   
               
               
                 A8 = −0.23259 × 10 −10   
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
             
               
               
               
             
               
               
               
               
             
               
               
               
             
               
               
               
               
             
               
               
               
             
               
               
               
               
             
               
               
             
               
               
               
               
             
               
             
           
               
                 EMBODIMENT 2 
               
             
             
               
                   
               
               
                 L3 = 22.5 mm ˜ 60.0 mm ˜ 156.0 mm Focal  
               
               
                 length of main optical system 
               
               
                 f = 20.2 mm ˜ 54.0 mm ˜ 140.4 mm Focal length of total optical system 
               
               
                 FNO = 4.65 ˜ 5.55 ˜ 5.85 F number 
               
             
          
           
               
                 [Radius of 
                   
                 [Refractive 
                   
               
               
                 Curvature] 
                 [Axial Distance] 
                 Index (Nd)] 
                 [Abbe Number(νd)] 
               
               
                   
               
               
                 r1 = 92.166 
                   
                   
                   
               
               
                   
                 d1 = 1.400 
                 N1 = 1.83350 
                 ν1= 21.00 
               
               
                 r2 = 56.497 
               
               
                   
                 d2 = 6.150 
                 N2 = 1.49310 
                 ν2 = 83.58 
               
               
                 r3 = −319.060 
               
               
                   
                 d3 = 0.100 
               
               
                 r4 = 39.303 
               
               
                   
                 d4 = 4.650 
                 N3 = 1.60311 
                 ν3 = 60.74 
               
               
                 r5 = 109.947 
               
             
          
           
               
                   
                 d5 = 1.500 ˜ 18.054 ˜ 32.384 
                   
               
             
          
           
               
                 r6* = 109.947 
                   
                   
                   
               
               
                   
                 d6 = 1.300 
                 N4 = 1.76683 
                 ν4 = 49.47 
               
               
                 r7 = 14.774 
               
               
                   
                 d7 = 4.500 
               
               
                 r8 = −32.796 
               
               
                   
                 d8 = 0.900 
                 N5 = 1.75450 
                 ν5 = 51.57 
               
               
                 r9 = 28.512 
               
               
                   
                 d9 = 0.080 
               
               
                 r10 = 23.140 
               
               
                   
                 d10 = 2.950 
                 N6 = 1.83350 
                 ν6 = 21.00 
               
               
                 r11 = −104.975 
               
               
                   
                 d11 = 0.600 
               
               
                 r12 = −62.052 
               
               
                   
                 d12 = 0.800 
                 N7 = 1.69680 
                 ν7 = 56.47 
               
               
                 r13 = 51.335 
               
             
          
           
               
                   
                 d13 = 15.741 ˜ 7.622 ˜ 1.500 
                   
               
             
          
           
               
                 r14 = ∞ 
                   
                   
                   
               
               
                 (diaphragm) 
               
               
                   
                 d14 = 0.500 
               
               
                 r15 = 18.507 
               
               
                   
                 d15 = 3.850 
                 N8 = 1.51742 
                 ν8 = 52.15 
               
               
                 r16 = −56.171 
               
               
                   
                 d16 = 0.080 
               
               
                 r17 = 18.468 
               
               
                   
                 d17 = 3.250 
                 N9 = 1.48749 
                 ν9 = 70.44 
               
               
                 r18 = −360.023 
               
               
                   
                 d18 = 1.650 
               
               
                 r19 = −26.148 
               
               
                   
                 d19 = 0.900 
                 N10 = 1.84666 
                 ν10 = 23.82 
               
               
                 r20 = 58.214 
               
             
          
           
               
                   
                 d20 = 6.550 ˜ 3.307 ˜ 0.700 
                   
               
             
          
           
               
                 r21 = 16.626 
                   
                   
                   
               
               
                   
                 d21 = 4.550 
                 N11 = 1.51742 
                 ν11 = 52.15 
               
               
                 r22 = −24.842 
               
               
                   
                 d22 = 3.350 
               
               
                 r23* = −19.913 
               
               
                   
                 d23 = 1.300 
                 N12 = 1.76683 
                 ν12 = 49.47 
               
               
                 r24* = 
               
               
                 1607.252 
               
               
                   
                 d24 = 0.950 
               
               
                 r25 = 222.986 
               
               
                   
                 d25 = 1.250 
                 N13 = 1.67339 
                 ν13 = 29.25 
               
               
                 r26 = −85.731 
               
             
          
           
               
                 d26 = 1.731 ˜ 20.594 ˜ 35.822 
                   
               
             
          
           
               
                 r27 = 32.298 
                   
                   
                   
               
               
                   
                 d27 = 4.194 
                 N14 = 1.62346 
                 ν14 = 32.23 
               
               
                 r28 = 1607.174 
               
               
                   
                 d28 = 2.540 
               
               
                 r29 = 171.729 
               
               
                   
                 d29 = 1.100 
                 N15 = 1.84666 
                 ν15 = 23.82 
               
               
                 r30* = 31.216 
               
               
                   
                 d30 = 2.500 
               
               
                 r31 = ∞ 
               
               
                   
                 d31 = 3.200 
                 N16 = 1.51680 
                 ν16 = 64.20 
               
               
                 r32 = ∞ 
               
               
                   
                 d32 = 0.500 
               
               
                 r33 = ∞ 
               
               
                   
                 d33 = 13.800 
                 N17 = 1.51680 
                 ν17 = 64.20 
               
               
                 r34 = ∞ 
               
             
          
           
               
                 [Aspherical coefficient of 6th surface (r6)] 
               
               
                 ε = 0.10000 × 10 
               
               
                 A4 = −0.29128 × 10 −6   
               
               
                 A6 = −0.53706 × 10 −7   
               
               
                 A8 = 0.71320 × 10 −9   
               
               
                 A10 = −0.37618 × 10 −11   
               
               
                 A12 = 0.57958 × 10 −14   
               
               
                 [Aspherical coefficient of 23th surface (r23)] 
               
               
                 ε = 0.10000 × 10 
               
               
                 A4 = 0.19235 × 10 −4   
               
               
                 A6 = −0.43123 × 10 −6   
               
               
                 A8 = 0.66528 × 10 −8   
               
               
                 A10 = −0.11019 × 10 −9   
               
               
                 A12 = −0.35292 × 10 −12   
               
               
                 [Aspherical coefficient of 24th surface (r24)] 
               
               
                 ε = 0.10000 × 10 
               
               
                 A4 = 0.11942 × 10 −3   
               
               
                 A6 = −0.11184 × 10 −6   
               
               
                 A8 = 0.44019 × 10 −8   
               
               
                 A10 = −0.31761 × 10 −10   
               
               
                 A12 = −0.77476 × 10 −12   
               
               
                 [Aspherical coefficient of 30th surface (r30)] 
               
               
                 ε = 0.10000 × 10 
               
               
                 A4 = −0.41378 × 10 −6   
               
               
                 A6 = 0.10694 × 10 −7   
               
               
                 A8 = −0.23259 × 10 −10   
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
             
               
               
               
             
               
               
               
               
             
               
               
             
               
               
               
               
             
           
               
                 EMBODIMENT 3 
               
             
             
               
                   
               
               
                 L3 = 28.8 mm 39.6 mm 54.4 mm Focal length of main optical system 
               
               
                 f = 28.8 mm 39.6 mm 54.3 mm Focal length of total optical system 
               
               
                 FNO = 4.1 ˜ 4.87 ˜ 5.77 F number 
               
             
          
           
               
                 [Radius of 
                   
                 [Refractive 
                   
               
               
                 Curvature] 
                 [Axial Distance] 
                 Index (Nd)] 
                 [Abbe Number(νd)] 
               
               
                   
               
               
                 r1 = 43.616 
                   
                   
                   
               
               
                   
                 d1 = 1.400 
                 N1 = 1.67003 
                 ν1= 47.15 
               
               
                 r2 = 16.000 
               
               
                   
                 d2 = 6.100 
               
               
                 r3 = −89.833 
               
               
                   
                 d3 = 1.200 
                 N2 = 1.74400 
                 ν2 = 44.93 
               
               
                 r4 = 90.321 
               
               
                   
                 d4 = 1.100 
               
               
                 r5 = 29.006 
               
               
                   
                 d5 = 3.200 
                 N3 = 1.70055 
                 ν3 = 30.11 
               
               
                 r6 = 125.790 
               
             
          
           
               
                   
                 d6 = 24.105 ˜ 11.294 ˜ 2.000 
                   
               
             
          
           
               
                 r7 = ∞ 
                   
                   
                   
               
               
                 (diaphragm) 
               
               
                   
                 d7 = 1.000 
               
               
                 r8 = 32.893 
               
               
                   
                 d8 = 2.400 
                 N4 = 1.69100 
                 ν4 = 54.75 
               
               
                 r9 = −68.245 
               
               
                   
                 d9 = 0.150 
               
               
                 r10 = 16.011 
               
               
                   
                 d10 = 3.500 
                 N5 = 1.62280 
                 vS = 56.88 
               
               
                 r11 = 34.207 
               
               
                   
                 d11 = 2.300 
               
               
                 r12 = −108.225 
               
               
                   
                 d12 = 4.000 
                 N6 = 1.80518 
                 ν6 = 25.43 
               
               
                 r13 = 15.185 
               
               
                   
                 d13 = 2.100 
               
               
                 r14 = 161.817 
               
               
                   
                 d14 = 2.000 
                 N7 = 1.63980 
                 ν7 = 34.55 
               
               
                 r15 = −25.266 
               
             
          
           
               
                 d15 = 8.545 ˜ 16.053 ˜ 26.472 
                   
               
             
          
           
               
                 r16 = 44.996 
                   
                   
                   
               
               
                   
                 d16 = 4.154 
                 N8 = 1.62396 
                 ν8 = 32.18 
               
               
                 r17 = −129.963 
               
               
                   
                 d17 = 1.607 
               
               
                 r18 = 413.440 
               
               
                   
                 d18 = 1.000 
                 N9 = 1.85000 
                 ν9 = 40.04 
               
               
                 r19 = 64.990 
               
               
                   
                 d19 = 2.981 
               
               
                 r20 = −119.252 
               
               
                   
                 d20 = 1.000 
                 N10 = 1.84666 
                 ν10 = 23.82 
               
               
                 r21 = 92.550 
               
               
                   
                 d21 = 1.626 
               
               
                 r22 = ∞ 
               
               
                   
                 d22 = 3.500 
                 N11 = 1.51680 
                 ν11 = 64.20 
               
               
                 r23 = ∞ 
               
               
                   
                 d23 = 0.500 
               
               
                 r24 = ∞ 
               
               
                   
                 d22 = 15.000 
                 N12 = 1.51680 
                 ν12 = 64.20 
               
               
                 r25 = ∞ 
               
               
                   
               
             
          
         
       
     
     FIGS. 4 through 6 are aberration diagrams at infinity corresponding to the first through third embodiments, respectively, and in each diagram the top level shows the wide angle end (W), the middle level shoes the intermediate focal length (M), and the bottom level shows the telephoto end (T). In the spherical aberration diagrams, the solid line d represents the d-line, the w dashed line (sc) represents the sine condition. In the aspherical aberration diagrams, the solid line DS and the dashed line DM represent the astigmatism of the sagittal surface and the meridional surface, respectively. Examples 1 through 3 satisfy conditional equations (1) through (8). Table 1 below shows values corresponding to conditional equations (1) (3), and (6) of the performance correcting lens units A and B. 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 OPTICAL SYSTEM A 
                 OPTICAL SYSTEM B 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 φh × Ys 
                 −0.0093 
                 −0.0920 
               
               
                 φP × Ys 
                 0.250 
                 0.272 
               
               
                 φN × Ys 
                 −0.292 
                 −0.293 
               
               
                   
               
             
          
         
       
     
     Values which satisfy conditional equation (9) are shown below. Y is the maximum image height of the aspherical surface. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 (Embodiment 1,2) 
               
             
          
           
               
                   
                 HEIGHT 
                 (X-X0)/(N′-N) 
               
               
                   
                   
               
               
                   
                 0.70 Y 
                 −0.00116 
               
               
                   
                   
               
             
          
         
       
     
     The optical surfaces of the optical systems of the previously described embodiments are all surfaces utilizing a deflection action of the light rays via refraction by surfaces having different refractive indices, but the present invention is not limited to this arrangement inasmuch as lenses using a deflection action of rays via diffraction at predetermined parameters and optical surfaces of a refraction/diffraction hybrid type also may be used insofar as such surfaces are included within the essential scope of the present invention. 
     Although the present invention has been fully described by way of examples with reference to the accompanying drawings, it is to be noted that various changes and modification will be apparent to those skilled in the art. For instance, the invention has been described with reference to electronic imaging devices such as CCDs. However, the invention is useful for other imaging medium, such any size or type of electronic imaging devices or chemical imaging devices or films. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention, they should be construed as being included therein.