Abstract:
A fixed focal-length lens system includes a negative first lens group, a positive second and third lens groups. The first and second lens groups move toward the object side during focusing from an object at infinity to an object at a close-up distance. The first lens group includes a negative lens element having a concave surface on the image side, at least two positive lens elements, and a negative lens element having a concave surface on the image side. The second lens group includes a negative lens element having a concave surface on the object side, and at least two positive lens elements. The third lens group includes at least one negative lens element, and at least one positive lens element. The following condition (1) is satisfied: 
       −0.3&lt; fG 2/ fG 1&lt;−0.05  (1),
 
     wherein fG1 and fG2 designate the focal lengths of the first and second lens groups.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a fixed focal-length lens system, which is capable of macro photography and includes an intermediate telephoto angle-of-view. 
       BACKGROUND ART 
       [0002]    Conventionally, if a typical photographing lens system, in which an infinite and low-magnification photographing distance is set as a design standard distance, is used as a macro lens system by performing focusing by advancing the entire lens system in order to shorten the close-up photographing distance, a large amount of aberration fluctuations occur during close-up photography, so that the optical quality is insufficient. Accordingly, in order to maintain a favorable optical quality for a photographing distance ranging from infinity through to a close-up distance, a macro lens system has been proposed that employs a so-called “floating method”, in which focusing is performed by moving a plurality of lens groups by differing amounts to suppress aberration fluctuations that occur during close-up photography. 
         [0003]    Patent Literature Nos. 1 through 4 each disclose a macro lens system which employs a floating method. In order to achieve a lens system that employs a floating method in a photographing apparatus, in which a further miniaturized image sensor is installed, in theory it is only necessary to scale down each numerical embodiment of the macro lens systems of Patent Literature Nos. 1 through 4. However, when such a scaled-down model is adjusted to lens element thicknesses and distances between lens elements that are determined with consideration of workability and assemblability, the balance of aberration corrections is lost, so that various aberrations increase and the optical quality becomes insufficient. 
         [0004]    In each macro lens system of Patent Literature Nos. 1 through 4, an aperture diaphragm is included within a focusing lens group, which moves during focusing. Therefore, when the macro lens system of each of Patent Literature Nos. 1 through 4 is applied to an interchangeable lens, in which a shutter unit is mounted within the lens body, that is typified by a non-reflex camera (mirrorless camera), the shutter unit must be moved with the lens body during focusing, unavoidably complicating and enlarging the floating mechanism. Furthermore, since motors or actuators are required to cater to the number and weight of the focusing lens group(s), the lens system that includes a lens barrel increases in size. 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         Patent Literature 1: Japanese Patent No. 4,996,151 
         Patent Literature 2: Japanese Patent No. 4,986,710 
         Patent Literature 3: Japanese Patent No. 3,429,562 
         Patent Literature 4: Japanese Unexamined Patent Publication No. 2009-145587 
       
     
       SUMMARY OF THE INVENTION 
     Technical Problem 
       [0009]    The present invention has been devised with consideration of the aforementioned problems, and an object of the present invention is to achieve a fixed focal-length lens system which is ideal for an interchangeable lens, in which a shutter unit is mounted within the lens body, that is typified by a non-reflex camera (mirrorless camera), includes an intermediate telephoto angle-of-view, has a simple and miniaturized focusing mechanism, the entire lens system is compact, can achieve a superior optical quality by favorably correct various aberrations, and is capable of macro photography. 
       Solution to Problem 
       [0010]    A fixed focal-length lens system is provided, including a negative first lens group, a positive second lens group and a positive third lens group, in that order from the object side, wherein the first lens group and the second lens group move toward the object side during focusing from an object at infinity to an object at a close-up distance. The first lens group includes a negative lens element having a concave surface on the image side, at least two positive lens elements, and a negative lens element having a concave surface on the image side, in that order from a side closest to the object to a side closest to the image. The second lens group includes a negative lens element having a concave surface on the object side, and at least two positive lens elements, in that order from the object side. The third lens group includes at least one negative lens element, and at least one positive lens element. The following condition (1) is satisfied: 
         [0000]      −0.3&lt; fG 2/ fG 1&lt;−0.05  (1),
 
         [0000]    wherein fG1 designates the focal length of the first lens group, and fG2 designates the focal length of the second lens group. 
         [0011]    The second lens group can be configured of a negative cemented lens, and at least one positive lens element, in that order from the object side. 
         [0012]    The second lens group can be configured of a negative cemented lens, and at least two positive lens elements, in that order from the object side. 
         [0013]    The cemented lens that is provided within the second lens group can be configured of a negative lens element and a positive lens element, in that order from the object side. 
         [0014]    It is desirable for the following conditions (2) and (3) to be satisfied: 
         [0000]        nd ( G 2 N )&lt;1.82(2) 
         [0000]      and 
         [0000]      ν d ( G 2 N )&lt;50  (3),
 
         [0000]    wherein nd(G2N) designates the refractive index at the d-line of the negative lens element that is provided closest to the object side within the second lens group, and νd(G2N) designates the Abbe number at the d-line of the negative lens element that is provided closest to the object side within the second lens group. 
         [0015]    It is desirable for the following condition (4) to be satisfied: 
         [0000]      Δ Pg,F ( G 2 N )&lt;0  (4),
 
         [0000]    wherein ΔPg, F(G2N) designates the anomalous dispersion of the negative lens element that is provided closest to the object side within the second lens group, wherein (A) ΔPg, F=0.002νd−0.6575+Pg,F: anomalous dispersion between the g-line and the F-line, and wherein (B) Pg, F=(N g −N F )/(N F −N C ): partial dispersion ratio between the g-line and the F-line. 
         [0016]    It is desirable for the following condition (5) to be satisfied: 
         [0000]      ν d ( G 2 P )&gt;80  (5),
 
         [0000]    wherein νd(G2P) designates the Abbe number at the d-line of at least one positive lens element of the positive lens elements provided within the second lens group. 
         [0017]    It is desirable for the fixed focal-length lens system of the present invention to satisfy the following condition (5′) from within the range of condition (5): 
         [0000]      ν d ( G 2 P )&gt;90  (5′).
 
         [0018]    The first lens group can be configured of a negative lens element having a concave surface on the image side, a positive lens element having a convex surface on the object side, a positive meniscus lens element having a concave surface on the image side, and a negative lens element having a concave surface on the image side, in that order from the object side. 
         [0019]    In the fixed focal-length lens system of the present invention, it is desirable for the following conditions (6) and (7) to be satisfied: 
         [0000]        nd ( G 1 P )&gt;1.70  (6),
 
         [0000]      and 
         [0000]      ν d ( G 1 P )&gt;45  (7),
 
         [0000]    wherein nd(G1P) designates the refractive index at the d-line of at least one positive lens element of the positive lens elements provided within the first lens group, and νd(G1P) designates the Abbe number at the d-line of at least one positive lens element of the positive lens elements provided within the first lens group. 
         [0020]    It is desirable for the following conditions (8) and (9) to be satisfied: 
         [0000]      0.5&lt; SF ( L 1)&lt;3  (8),
 
         [0000]      and 
         [0000]      ν d ( L 1)&gt;50  (9),
 
         [0000]    wherein SF(L1) designates the shaping factor of the negative lens element provided closest to the object side within the first lens group, SF(L1)=(L1R1+L1R2)/(L1R1−L1R2); L1R1 designates the radius of curvature of the surface on the object side of the negative lens element provided closest to the object side within the first lens group, L1R2 designates the radius of curvature of the surface on the image side of the negative lens element provided closest to the object side within the first lens group, and νd(L1) designates the Abbe number at the d-line of the negative lens element provided closest to the object side within the first lens group. 
         [0021]    It is desirable for the following condition (10) to be satisfied: 
         [0000]      Δ Pg,F ( G 1 N )&lt;0  (10),
 
         [0000]    wherein ΔPg, F(G1N) designates the anomalous dispersion of the negative lens element that is provided closest to the image side within the first lens group, wherein (A) ΔPg, F=0.002νd−0.6575+Pg,F: anomalous dispersion between the g-line and the F-line, and wherein (B) Pg, F=(N g −N F )/(N F −N C ): partial dispersion ratio between the g-line and the F-line. 
         [0022]    In the fixed focal-length lens system of the present invention, an aperture diaphragm can be positioned between the second lens group and the third lens group, wherein the aperture diaphragm remains stationary, with the third lens group, relative to the imaging plane during focusing from an object at infinity to an object at a close-up distance. 
         [0023]    Alternatively, an aperture diaphragm can be positioned between the first lens group and the second lens group, wherein the aperture diaphragm integrally moves toward the object side with the first lens group and the second lens group during focusing from an object at infinity to an object at a close-up distance. 
         [0024]    A fixed focal-length lens system of the present invention, in another embodiment, is configured of a negative first lens group, a positive second lens group and a positive third lens group, in that order from the object side. The first lens group includes four lens elements: a negative lens element, a positive lens element, a positive lens element and a negative lens element, in that order from the object side. The second lens group includes three lens elements: a negative lens element, a positive lens element and a positive lens element, in that order from the object side; or four lens elements: a negative lens element, a positive lens element, a positive lens element and a positive lens element, in that order from the object side. The third lens group includes two lens elements: a negative lens element and a positive lens element, in that order from the object side. An aperture diaphragm is positioned between the second lens group and the third lens group. During focusing from an object at infinity to an object at a close-up distance, the first lens group and the second lens group move toward the object side, and the aperture diaphragm remains stationary, with the third lens group, relative to the imaging plane. 
       Advantageous Effects of Invention 
       [0025]    According to the present invention, a fixed focal-length lens system can be achieved which is ideal for an interchangeable lens, in which a shutter unit is mounted within the lens body, that is typified by a non-reflex camera (mirrorless camera), includes an intermediate telephoto angle-of-view, has a simple and miniaturized focusing mechanism, the entire lens system being compact, can achieve a superior optical quality by favorably correct various aberrations, and is capable of macro photography. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0026]      FIG. 1  shows a lens arrangement of a first numerical embodiment of a fixed focal-length lens system, according to the present invention, at an infinite photographic position; 
           [0027]      FIG. 2  shows various aberrations that occurred in the arrangement of  FIG. 1 ; 
           [0028]      FIG. 3  shows lateral aberrations that occurred in the arrangement of  FIG. 1 ; 
           [0029]      FIG. 4  shows a lens arrangement of a first numerical embodiment of a fixed focal-length lens system, according to the present invention, at a minimum photographic position; 
           [0030]      FIG. 5  shows various aberrations that occurred in the arrangement of  FIG. 4 ; 
           [0031]      FIG. 6  shows lateral aberrations that occurred in the arrangement of  FIG. 4 ; 
           [0032]      FIG. 7  shows a lens arrangement of a second numerical embodiment of a fixed focal-length lens system, according to the present invention, at an infinite photographic position; 
           [0033]      FIG. 8  shows various aberrations that occurred in the arrangement of  FIG. 7 ; 
           [0034]      FIG. 9  shows lateral aberrations that occurred in the arrangement of  FIG. 7 ; 
           [0035]      FIG. 10  shows a lens arrangement of a second numerical embodiment of a fixed focal-length lens system, according to the present invention, at a minimum photographic position; 
           [0036]      FIG. 11  shows various aberrations that occurred in the arrangement of  FIG. 10 ; 
           [0037]      FIG. 12  shows lateral aberrations that occurred in the arrangement of  FIG. 10 ; 
           [0038]      FIG. 13  shows a lens arrangement of a third numerical embodiment of a fixed focal-length lens system, according to the present invention, at an infinite photographic position; 
           [0039]      FIG. 14  shows various aberrations that occurred in the arrangement of  FIG. 13 ; 
           [0040]      FIG. 15  shows lateral aberrations that occurred in the arrangement of  FIG. 13 ; 
           [0041]      FIG. 16  shows a lens arrangement of a third numerical embodiment of a fixed focal-length lens system, according to the present invention, at a minimum photographic position; 
           [0042]      FIG. 17  shows various aberrations that occurred in the arrangement of  FIG. 16 ; 
           [0043]      FIG. 18  shows lateral aberrations that occurred in the arrangement of  FIG. 16 ; 
           [0044]      FIG. 19  shows a lens arrangement of a fourth numerical embodiment of a fixed focal-length lens system, according to the present invention, at an infinite photographic position; 
           [0045]      FIG. 20  shows various aberrations that occurred in the arrangement of  FIG. 19 ; 
           [0046]      FIG. 21  shows lateral aberrations that occurred in the arrangement of  FIG. 19 ; 
           [0047]      FIG. 22  shows a lens arrangement of a fourth numerical embodiment of a fixed focal-length lens system, according to the present invention, at a minimum photographic position; 
           [0048]      FIG. 23  shows various aberrations that occurred in the arrangement of  FIG. 22 ; 
           [0049]      FIG. 24  shows lateral aberrations that occurred in the arrangement of  FIG. 22 ; 
           [0050]      FIG. 25  shows a lens arrangement of a fifth numerical embodiment of a fixed focal-length lens system, according to the present invention, at an infinite photographic position; 
           [0051]      FIG. 26  shows various aberrations that occurred in the arrangement of  FIG. 25 ; 
           [0052]      FIG. 27  shows lateral aberrations that occurred in the arrangement of  FIG. 25 ; 
           [0053]      FIG. 28  shows a lens arrangement of a fifth numerical embodiment of a fixed focal-length lens system, according to the present invention, at a minimum photographic position; 
           [0054]      FIG. 29  shows various aberrations that occurred in the arrangement of  FIG. 28 ; 
           [0055]      FIG. 30  shows lateral aberrations that occurred in the arrangement of  FIG. 28 ; 
           [0056]      FIG. 31  shows a lens arrangement of a sixth numerical embodiment of a fixed focal-length lens system, according to the present invention, at an infinite photographic position; 
           [0057]      FIG. 32  shows various aberrations that occurred in the arrangement of  FIG. 31 ; 
           [0058]      FIG. 33  shows lateral aberrations that occurred in the arrangement of  FIG. 31 ; 
           [0059]      FIG. 34  shows a lens arrangement of a sixth numerical embodiment of a fixed focal-length lens system, according to the present invention, at a minimum photographic position; 
           [0060]      FIG. 35  shows various aberrations that occurred in the arrangement of  FIG. 34 ; 
           [0061]      FIG. 36  shows lateral aberrations that occurred in the arrangement of  FIG. 34 ; 
           [0062]      FIG. 37  shows a first simplified movement diagram of the fixed focal-length lens system according to the present invention when focusing from the infinite photographic position to the minimum photographic position; and 
           [0063]      FIG. 38  shows a second simplified movement diagram of the fixed focal-length lens system according to the present invention when focusing from the infinite photographic position to the minimum photographic position. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0064]    As shown in the simplified movement diagrams of  FIGS. 37 and 38 , in each of the first through sixth numerical embodiments, the fixed focal-length lens systems of the present embodiments are configured of a negative first lens group G 1 , a positive second lens group G 2  and a positive third lens group G 3 , in that order from the object side. ‘I’ designates an imaging plane. 
         [0065]    In each of the first, second, fourth through sixth numerical embodiments, in the fixed focal-length lens system of the present embodiments, an aperture diaphragm S is positioned in between the second lens group G 2  and the third lens group G 3 , as shown in the simplified movement diagram of  FIG. 37 . During focusing from an object at infinity to an object at a close-up distance, the first lens group G 1  and the second lens group G 2  move (advance) toward the object side, and the aperture diaphragm S remains stationary, with the third lens group G 3 , relative to the imaging plane I. 
         [0066]    In the third numerical embodiment, in the fixed focal-length lens system of the present embodiment, an aperture diaphragm S is positioned in between the first lens group G 1  and the second lens group G 2 , as shown in the simplified movement diagram of  FIG. 38 . During focusing from an object at infinity to an object at a close-up distance, the aperture diaphragm S moves (advances) integrally with the first lens group G 1  and the second lens group G 2  toward the object side, and the third lens group G 3  remains stationary relative to the imaging plane I. 
         [0067]    Furthermore, an embodiment is possible in which, during focusing from an object at infinity to an object at a close-up distance, the third lens group G 3  moves (advances) toward the object side. In addition, an embodiment is possible in which, during focusing from an object at infinity to an object at a close-up distance, the aperture diaphragm S moves in the optical axis direction independently from the first through third lens groups G 1  through G 3 . 
         [0068]    In each of the first through sixth numerical embodiments, the first lens group G 1  is configured of a negative meniscus lens element  11  having a convex surface on the object side, a biconvex positive lens element  12 , a positive meniscus lens element  13  having a convex surface on the object side, and a biconcave negative lens element  14 , in that order from the object side. 
         [0069]    In each of the first through fourth and sixth numerical embodiments, the second lens group G 2  is configured of a biconcave negative lens element  21 , a biconvex positive lens element  22 , a biconvex positive lens element  23 , and a biconvex positive lens element  24 , in that order from the object side. The surface on the image side of the biconcave negative lens element  21  is cemented to the surface on the object side the biconvex positive lens element  22  to forma cemented lens having a negative refractive power. Each of the biconvex positive lens element  22 , the biconvex positive lens element  23  and a biconvex positive lens element  24  is formed from a low-dispersion glass ED lens having large positive anomalous dispersion characteristics. 
         [0070]    In the fifth numerical embodiment, the second lens group G 2  is configured of a biconcave negative lens element  21 ′, a biconvex positive lens element  22 ′, and a biconvex positive lens element  23 ′, in that order from the object side. The surface on the image side of the biconcave negative lens element  21 ′ is cemented to the surface on the object side of the biconvex positive lens element  22 ′ to form a cemented lens having a negative refractive power. The biconvex positive lens element  22 ′ is formed from a low-dispersion glass ED lens having large positive anomalous dispersion characteristics. 
         [0071]    In each of the first through fourth and sixth numerical embodiments, the third lens group G 3  is configured of a negative meniscus lens element  31  having a convex surface on the object side, and a positive meniscus lens element  32  having a convex surface on the object side, in that order from the object side. 
         [0072]    In the fifth numerical embodiment, the third lens group G 3  is configured of a negative meniscus lens element  31  having a convex surface on the object side, and a biconvex positive lens element  32 , in that order from the object side. 
         [0073]    In the fixed focal-length lens system of the present embodiments, the entire lens system is divided into the negative first lens group G 1 , the positive second lens group G 2  and the positive third lens group G 3 ; and the first lens group G 1  and the second lens group G 2  have been configured to have a retrofocus lens relationship. Furthermore, the fixed focal-length lens systems of the present embodiments are capable of macro photography and include an intermediate telephoto angle-of-view. 
         [0074]    The first lens group G 1  is configured of a negative lens element  11  having a concave surface on the image side, two positive lens elements  12  and  13 , and a negative lens element  14  having a concave surface on the image side, in that order from the object side. Furthermore, the number of positive lens elements provided in the middle of the lens group is not limited to two; three or more positive lens elements can be provided therein. It is necessary to strengthen the positive refractive power of at least two of the lens elements (including the positive lens elements  12  and  13 ) that are provided in the middle of the lens group, in order to miniaturize the lens system, whereby spherical aberration, axial chromatic aberration, coma and astigmatism occur in large amounts. However, in the present embodiments, by providing the negative lens element  11 , having a concave surface on the image side, on the object side of the at least two lens elements that are provided in the middle of the lens group (closest to the object side within the first lens group G 1 ), spherical aberration, axial chromatic aberration, coma and astigmatism can be favorably corrected while suitably maintaining a backfocus. Furthermore, by providing the negative lens element (biconcave negative lens element)  14 , having a concave surface on the image side, on the image side of the at least two lens elements that are provided in the middle of the lens group (closest to the image side within the first lens group G 1 ), coma and astigmatism can be favorably corrected. By forming the positive lens element that is provided closest to the image side within the first lens group G 1  (the positive lens element  13  in the present embodiments) to approach a concentric lens profile about the aperture diaphragm S, the change in incident angle on the lens elements from the axial light rays to the outermost peripheral abaxial light rays can be suppressed, and occurrence of astigmatism can be suppresses as much as possible. 
         [0075]    The second lens group G 2  is configured of a negative lens element  21  ( 21 ′) having a concave surface on the object side, and at least two positive lens elements  22 ,  23  and  24  ( 22 ′ and  23 ′), in that order from the object side. The negative lens element  21  ( 21 ′) that is provided closest to the object side within the second lens group G 2  and the positive lens element  22  ( 22 ′) constitute a negative cemented lens. Astigmatism can be favorably corrected by forming the negative lens element  21  ( 21 ′) of the cemented lens to have a profile having a concave surface on the object side. Furthermore, by forming the positive lens element  22  ( 22 ′) of the cemented lens to have a profile having a convex surface on the object side, spherical aberration and coma can be favorably corrected. Furthermore, by providing at least one positive lens element  23  and  24  ( 23 ′) on the image side of the cemented lens, axial chromatic aberration, spherical aberration and coma throughout the entire lens system can be favorably corrected. In the case where a glass material having a large Abbe number is selected for the positive lens element provided on the image side of the cemented lens in order to favorably correct chromatic aberration, the refractive index is lowered, and spherical aberration and coma tend to increase. Accordingly, by providing the two positive lens elements  23  and  24  on the image side of the cemented lens, as in the first through fourth and sixth numerical embodiments, spherical aberration and coma can be effectively suppressed. Furthermore, the number of positive lens elements on the image side of the cemented lens is not limited to one or two; it is also possible to provide three or more positive lens elements. 
         [0076]    In each of the first through sixth numerical embodiments, in order to favorably correct various aberrations, the third lens group G 3  is configured of two lens elements: the negative lens element  31  and the positive lens element  32 . By forming the negative lens element  31  to have a profile having a convex surface on the object side, coma and astigmatism can be favorably corrected. By forming the positive lens element  32  to have a concave surface on the image side, spherical aberration and coma can be favorably corrected. Furthermore, there is freedom in the arrangement order of the negative lens element  31  and the positive lens element  32  within the third lens group G 3 ; it is possible to reverse the positions thereof. In addition, it is possible to provide two or more negative lens elements and/or two or more positive lens elements within the third lens group G 3 . 
         [0077]    The fixed focal-length lens system of the present embodiments employs a so-called “floating method” in which, during focusing from an object at infinity to an object at a close-up distance, the third lens group G 3  remains stationary relative to the imaging plane I, and the first lens group G 1  and the second lens group G 2  move (advance) toward the object side. According to this configuration, miniaturization of the entire lens system including the lens barrel, and a superior optical quality can both be achieved. Furthermore, by also moving (advancing) the third lens group G 3  toward the object side, during focusing from an object at infinity to an object at a close-up distance, in addition to the first lens group G 1  and the second lens group G 2 , occurrence of astigmatism and field curvature can be suppressed, and fluctuations in aberrations from an infinite photographic position to a minimum photographic position can be reduced. 
         [0078]    From the viewpoint of balancing out aberration corrections, there is no difference in having the position of the aperture diaphragm S provided between the second lens group G 2  and the third lens group G 3  (first, second and fourth through sixth numerical embodiments) from being provided between the first lens group G 1  and the second lens group G 2  (third numerical embodiment). 
         [0079]    In the case where the aperture diaphragm S is provided at a fixed location between the second lens group G 2  and the third lens group G 3 , and focusing is carried out using the first lens group G 1  and the second lens group G 2 , the exit pupil does not change since the effective f-number at the minimum photographic position does not change (the effective f-number does not change in accordance with the photographic distance); hence, although spherical aberration and coma at the minimum photographic distance easily remain, in the case of a miniature optical system that has a small aperture, this arrangement is extremely advantageous with respect to a diffraction phenomenon in which the resolving power does not improve even if the aberrations are favorably corrected. Furthermore, even when the fixed focal-length lens system is applied to an interchangeable lens, in which a shutter unit is mounted within the lens body, that is typified by a non-reflex camera (mirrorless camera), since the shutter unit does not need to be moved with the focusing lens(es) during focusing, a compact mechanical system can be achieved. 
         [0080]    In the case where the aperture diaphragm S is provided between the first lens group G 1  and the second lens group G 2 , the aperture diaphragm S must also move during focusing, which although enlarges the lens barrel, this arrangement is advantageous for correcting spherical aberration and coma at the minimum photographic distance since the effective f-number becomes larger during focusing. 
         [0081]    Condition (1) specifies the ratio of the focal length of the first lens group G 1  to the focal length of the second lens group G 2 . By satisfying condition (1), the entire lens system can be made compact, and various aberrations such as spherical aberration and coma can be favorably corrected to thereby achieve a superior optical quality. 
         [0082]    If the upper limit of condition (1) is exceeded, the negative refractive power of the first lens group G 1  becomes too weak, so that the balance is lost between the aberrations that occur in the first lens group G 1  and the aberrations that occur in the second lens group G 2 , which is provided with a strong positive refractive power in order to miniaturize the lens system, thereby worsening the aberrations that occur over the entire lens system. Furthermore, in order to correct aberrations, the number of lens elements are required to be increased, thereby enlarging the entire lens system. 
         [0083]    If the lower limit of condition (1) is exceeded, the negative refractive power of the first lens group G 1  becomes too strong, so that a strong refractive power arrangement is required within the first lens group G 1  for miniaturization purposes, thereby increasing spherical aberration and coma. Furthermore, the overall degree of retrofocus becomes too strong, thereby enlarging the entire length of the lens system. 
         [0084]    Condition (2) specifies the refractive index at the d-line of the negative lens element  21  ( 21 ′) which is positioned closest to the object side within the second lens group G 2 . By satisfying condition (2), the Petzval sum can be favorably corrected while field curvature and astigmatism in particular can be favorably corrected at the minimum photographic distance, thereby achieving a superior optical quality. 
         [0085]    If the upper limit of condition (2) is exceeded, the correction of the Petzval sum becomes insufficient, so that large amounts of field curvature and astigmatism occur, especially at the minimum photographic distance. 
         [0086]    Condition (3) specifies the Abbe number at the d-line of the negative lens element  21  ( 21 ′) which is positioned closest to the object side within the second lens group G 2 . By satisfying condition (3), axial chromatic aberration can be favorably corrected, thereby achieving a superior optical quality. 
         [0087]    If the upper limit of condition (3) is exceeded, correction of axial chromatic aberration becomes insufficient, so that axial chromatic aberration increases, especially at the minimum photographic distance. 
         [0088]    Condition (4) specifies the anomalous dispersion characteristics of the negative lens element  21  ( 21 ′) which is positioned closest to the object side within the second lens group G 2 . By satisfying condition (4), even when a glass material having a large positive anomalous dispersion is used in the positive lens elements  22 ,  23  and  24  ( 23 ′ and  24 ′) within the second lens group G 2 , axial chromatic aberration is favorably corrected and a superior optical quality is achieved. 
         [0089]    If the upper limit of condition (4) is exceeded, when a glass material having a large positive anomalous dispersion is used for the positive lens elements  22 ,  23  and  24  ( 23 ′ and  24 ′) within the second lens group G 2 , correction of axial chromatic aberration becomes insufficient. 
         [0090]    Condition (5) specifies the Abbe number at the d-line of at least one of the positive lens elements  22 ,  23  and  24  ( 23 ′ and  24 ′) within the second lens group G 2 . Since the position of the light rays that pass through the second lens group G 2  is high at both the infinite photographic distance and the minimum photographic distance, by including within the second lens group G 2  a positive lens element that has a large color-correction effect and a large anomalous dispersion which satisfy condition (5), axial chromatic aberration and lateral chromatic aberration can be effectively corrected, thereby achieving a superior optical quality. 
         [0091]    If a positive lens element that satisfies condition (5) is not included within the second lens group G 2 , correction of axial chromatic aberration and lateral chromatic aberration becomes insufficient. 
         [0092]    Condition (6) specifies the refractive index at the d-line of at least one of the positive lens elements  12  and  13  provided within the first lens group G 1 . By including a positive lens element that satisfies condition (6) within the first lens group G 1 , spherical aberration, coma and the Petzval sum can be favorably corrected, and various aberrations can be favorably corrected, especially at the minimum photographic distance, thereby achieving a superior optical quality. 
         [0093]    If a positive lens element that satisfies condition (6) is not included within the first lens group G 1 , correction of spherical aberration, coma and the Petzval sum becomes insufficient, so that various aberrations increase, especially at the minimum photographic distance. 
         [0094]    Condition (7) specifies the Abbe number at the d-line of at least one of the positive lens elements  12  and  13  provided within the first lens group G 1 . By including a positive lens element that satisfies condition (7) within the first lens group G 1 , lateral chromatic aberration can be favorably corrected and a superior optical quality can be achieved. 
         [0095]    If a positive lens element that satisfies condition (7) is not included within the first lens group G 1 , correction of lateral chromatic aberration becomes insufficient. 
         [0096]    Condition (8) specifies the shaping factor of the negative lens element  11  that is positioned closest to the object side within the first lens group G 1 . By satisfying condition (8), the entire lens system can be made compact, and coma and lateral chromatic aberration can be favorably corrected, thereby achieving a superior optical quality. 
         [0097]    If the upper limit of condition (8) is exceeded, the refractive power of the negative lens element  11  becomes too weak, so that the negative lens element  11  must be provided at a further forward position in order to obtain a sufficient diverging effect, and since the overall length of the lens system and the effective diameter increase, miniaturization cannot be achieved. 
         [0098]    If the lower limit of condition (8) is exceeded, the refractive power of the negative lens element  11  becomes too strong, so that due to the light bundle dispersing by a great amount, coma and lateral chromatic aberration increase. 
         [0099]    Condition (9) specifies the Abbe number at the d-line of the negative lens element  11  which is positioned closest to the object side within the first lens group G 1 . By satisfying condition (9), the overall lens system can be made compact and lateral chromatic aberration can be favorably corrected, thereby achieving a superior optical quality. 
         [0100]    If the lower limit of condition (9) is exceeded, a large amount of lateral chromatic aberration occurs. Furthermore, in order to correct lateral chromatic aberration, the number of lens elements within the first lens group G 1  would need to be increased, thereby enlarging the entire lens system. 
         [0101]    Condition (10) specifies the anomalous dispersion characteristics of the negative lens element  11  that is provided closest to the image side within the first lens group G 1 . By satisfying condition (10), axial chromatic aberration can be favorably corrected to thereby achieve a superior optical quality. 
         [0102]    If the upper limit of condition (10) is exceeded, correction of axial chromatic aberration becomes insufficient. 
       EMBODIMENTS 
       [0103]    Specific numerical embodiments will be herein shown. In the various aberration diagrams, lateral aberration diagrams, and the tables, the d-line, g-line and C-line show aberrations at their respective wave-lengths; S designates the sagittal image, M designates the meridional image, FNO. designates the f-number, f designates the focal length of the entire optical system, W designates the half angle of view (°), Y designates the image height, fB designates the backfocus, L designates the overall length of the lens system, r designates the radius of curvature, d designates the lens thickness or distance between lenses, N(d) designates the refractive index at the d-line, and ν(d) designates the Abbe number with respect to the d-line. The unit used for lengths is defined in millimeters (mm). The values for the f-number, the focal length, magnification, the half angle-of-view, the image height, the backfocus, the overall length of the lens system, and the distance d between lenses which changes during focusing are shown in the following order: infinite photographic position, intermediate photographic position (finite photographic position), and minimum photographic position. An aspherical lens element is not used in any of the first through sixth numerical embodiments. 
       Numerical Embodiment 1 
       [0104]      FIGS. 1 through 6  and Tables 1 and 2 show a first numerical embodiment of the fixed focal-length lens system according to the present invention.  FIG. 1  shows the lens arrangement at the infinite photographic position,  FIG. 2  shows various aberrations thereof,  FIG. 3  shows the lateral aberrations thereof,  FIG. 4  shows the lens arrangement at the minimum photographic position,  FIG. 5  shows various aberrations thereof, and  FIG. 6  shows the lateral aberrations thereof. Table 1 shows the lens surface data, and Table 2 shows various lens-system data. 
         [0105]    The fixed focal-length lens system of the first numerical embodiment is configured of a negative first lens group G 1 , a positive second lens group G 2 , and a positive third lens group G 3 , in that order from the object side. The aperture diaphragm S is positioned in between the second lens group G 2  and the third lens group G 3 . During focusing from an object at infinity to an object at a close-up distance, the first lens group G 1  and the second lens group G 2  move toward the object side, and the aperture diaphragm S remains stationary, with the third lens group G 3 , relative to the imaging plane I. An optical filter OP is provided between the third lens group G 3  and the imaging plane I. 
         [0106]    The first lens group G 1  is configured of a negative meniscus lens element  11  having a convex surface on the object side, a biconvex positive lens element  12 , a positive meniscus lens element  13  having a convex surface on the object side, and a biconcave negative lens element  14 , in that order from the object side. The biconcave negative lens element  14  is formed from a glass material having negative anomalous dispersion characteristics by using, e.g., OHARA S-NBM51. 
         [0107]    The second lens group G 2  is configured of a biconcave negative lens element  21 , a biconvex positive lens element  22 , a biconvex positive lens element  23 , and a biconvex positive lens element  24 , in that order from the object side. The surface on the image side of the biconcave negative lens element  21  and the surface on the object of the biconvex positive lens element  22  are cemented to each other to form a cemented lens having a negative refractive power. The biconcave negative lens element  21  is formed from a glass material having negative anomalous dispersion characteristics by using, e.g., OHARA S-NBM51. Each of the biconvex positive lens element  22 , the biconvex positive lens element  23  and the biconvex positive lens element  24  is formed from a low-dispersion glass ED lens having large positive anomalous dispersion characteristics. 
         [0108]    The third lens group G 3  is configured of a negative meniscus lens element  31  having a convex surface on the object side, and a positive meniscus lens element  32  having a convex surface on the object side, in that order from the object side. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 SURFACE DATA 
               
             
          
           
               
                   
                 Surf. No. 
                 r 
                 d 
                 N(d) 
                 ν d 
               
               
                   
                   
               
             
          
           
               
                   
                  1 
                 93.279 
                 1.000 
                 1.49700 
                 81.6 
               
               
                   
                  2 
                 12.089 
                 5.404 
               
               
                   
                  3 
                 19.009 
                 3.287 
                 1.72916 
                 54.7 
               
               
                   
                  4 
                 −34.417 
                 0.100 
               
               
                   
                  5 
                 13.573 
                 2.073 
                 1.81600 
                 46.6 
               
               
                   
                  6 
                 19.915 
                 1.786 
               
               
                   
                  7 
                 −52.240 
                 1.000 
                 1.61340 
                 44.3 
               
               
                   
                  8 
                 8.724 
                 3.221 
               
               
                   
                  9 
                 −8.863 
                 1.000 
                 1.61340 
                 44.3 
               
               
                   
                 10 
                 24.506 
                 2.789 
                 1.49700 
                 81.6 
               
               
                   
                 11 
                 −13.220 
                 0.100 
               
               
                   
                 12 
                 60.224 
                 2.568 
                 1.43875 
                 95.0 
               
               
                   
                 13 
                 −13.295 
                 0.100 
               
               
                   
                 14 
                 32.652 
                 2.485 
                 1.43875 
                 95.0 
               
               
                   
                 15 
                 −21.880 
                 d15 
               
               
                   
                 16(diaphragm) 
                 ∞ 
                 2.200 
               
               
                   
                 17 
                 51.961 
                 1.000 
                 1.65412 
                 39.7 
               
               
                   
                 18 
                 15.785 
                 0.859 
               
               
                   
                 19 
                 19.813 
                 2.618 
                 1.77250 
                 49.6 
               
               
                   
                 20 
                 348.818 
                 13.259  
               
               
                   
                 21 
                 ∞ 
                 1.050 
                 1.51633 
                 64.1 
               
               
                   
                 22 
                 ∞ 
                 — 
               
               
                   
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 VARIOUS LENS-SYSTEM DATA 
               
             
          
           
               
                   
                 Infinite 
                 Intermediate 
                 Minimum 
               
               
                   
                 Photographic 
                 Photographic 
                 Photographic 
               
               
                   
                 Position 
                 Position 
                 Position 
               
               
                   
                   
               
             
          
           
               
                   
                 FNO. 
                 2.8 
                 2.8 
                 2.8 
               
               
                   
                 f 
                 18.00 
                 18.75 
                 19.18 
               
               
                   
                 Magnification 
                 0.000 
                 −0.217 
                 −0.333 
               
               
                   
                 W 
                 15.8 
                 13.0 
                 11.6 
               
               
                   
                 Y 
                 5.00 
                 5.00 
                 5.00 
               
               
                   
                 fB 
                 1.00 
                 1.00 
                 1.00 
               
               
                   
                 L 
                 50.70 
                 55.89 
                 58.67 
               
               
                   
                 d15 
                 1.800 
                 6.991 
                 9.766 
               
               
                   
                   
               
             
          
         
       
     
       Numerical Embodiment 2 
       [0109]      FIGS. 7 through 12  and Tables 3 and 4 show a second numerical embodiment of the fixed focal-length lens system according to the present invention.  FIG. 7  shows the lens arrangement at the infinite photographic position,  FIG. 8  shows various aberrations thereof,  FIG. 9  shows the lateral aberrations thereof,  FIG. 10  shows the lens arrangement at the minimum photographic position,  FIG. 11  shows various aberrations thereof, and  FIG. 12  shows the lateral aberrations thereof. Table 3 shows the lens surface data, and Table 4 shows various lens-system data. 
         [0110]    The lens arrangement of the second numerical embodiment is the same as that of the lens arrangement of the first numerical embodiment. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 SURFACE DATA 
               
             
          
           
               
                   
                 Surf. No. 
                 r 
                 d 
                 N(d) 
                 ν d 
               
               
                   
                   
               
             
          
           
               
                   
                  1 
                 40.272 
                 1.000 
                 1.56384 
                 60.7 
               
               
                   
                  2 
                 13.043 
                 3.631 
               
               
                   
                  3 
                 19.288 
                 3.399 
                 1.77250 
                 49.6 
               
               
                   
                  4 
                 −41.615 
                 0.261 
               
               
                   
                  5 
                 13.950 
                 1.979 
                 1.77250 
                 49.6 
               
               
                   
                  6 
                 18.983 
                 1.917 
               
               
                   
                  7 
                 −74.991 
                 1.000 
                 1.61340 
                 44.3 
               
               
                   
                  8 
                 8.971 
                 3.210 
               
               
                   
                  9 
                 −8.275 
                 1.000 
                 1.61340 
                 44.3 
               
               
                   
                 10 
                 32.585 
                 2.721 
                 1.49700 
                 81.6 
               
               
                   
                 11 
                 −12.389 
                 0.100 
               
               
                   
                 12 
                 71.065 
                 3.122 
                 1.43875 
                 95.0 
               
               
                   
                 13 
                 −12.682 
                 0.100 
               
               
                   
                 14 
                 34.209 
                 3.012 
                 1.49700 
                 81.6 
               
               
                   
                 15 
                 −26.316 
                 d15 
               
               
                   
                 16(diaphragm) 
                 ∞ 
                 2.586 
               
               
                   
                 17 
                 47.168 
                 1.662 
                 1.65412 
                 39.7 
               
               
                   
                 18 
                 15.387 
                 2.712 
               
               
                   
                 19 
                 24.367 
                 1.753 
                 1.81600 
                 46.6 
               
               
                   
                 20 
                 184.031 
                 12.780  
               
               
                   
                 21 
                 ∞ 
                 1.050 
                 1.51633 
                 64.1 
               
               
                   
                 22 
                 ∞ 
                 — 
               
               
                   
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 VARIOUS LENS-SYSTEM DATA 
               
             
          
           
               
                   
                 Infinite 
                 Intermediate 
                 Minimum 
               
               
                   
                 Photographic 
                 Photographic 
                 Photographic 
               
               
                   
                 Position 
                 Position 
                 Position 
               
               
                   
                   
               
             
          
           
               
                   
                 FNO. 
                 2.8 
                 2.8 
                 2.8 
               
               
                   
                 f 
                 22.00 
                 22.30 
                 22.46 
               
               
                   
                 Magnification 
                 0.000 
                 −0.217 
                 −0.333 
               
               
                   
                 W 
                 12.9 
                 10.8 
                 9.8 
               
               
                   
                 Y 
                 5.00 
                 5.00 
                 5.00 
               
               
                   
                 fB 
                 1.00 
                 1.00 
                 1.00 
               
               
                   
                 L 
                 51.80 
                 56.44 
                 58.92 
               
               
                   
                 d15 
                 1.800 
                 6.445 
                 8.929 
               
               
                   
                   
               
             
          
         
       
     
       Numerical Embodiment 3 
       [0111]      FIGS. 13 through 18  and Tables 5 and 6 show a third numerical embodiment of the fixed focal-length lens system according to the present invention.  FIG. 13  shows the lens arrangement at the infinite photographic position,  FIG. 14  shows various aberrations thereof,  FIG. 15  shows the lateral aberrations thereof,  FIG. 16  shows the lens arrangement at the minimum photographic position,  FIG. 17  shows various aberrations thereof, and  FIG. 18  shows the lateral aberrations thereof. Table 5 shows the lens surface data, and Table 6 shows various lens-system data. 
         [0112]    The lens arrangement of the third numerical embodiment is the same as that of the lens arrangement of the first numerical embodiment except for the following point: 
         [0113]    (1) The aperture diaphragm S is positioned in between the first lens group G 1  and the second lens group G 2 , and the aperture diaphragm S moves with the first lens group G 1  and the second lens group G 2  toward the object side during focusing from an object at infinity to an object at a close-up distance. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 SURFACE DATA 
               
             
          
           
               
                   
                 Surf. No. 
                 r 
                 d 
                 N(d) 
                 ν d 
               
               
                   
                   
               
             
          
           
               
                   
                  1 
                 63.562 
                 1.000 
                 1.48749 
                 70.2 
               
               
                   
                  2 
                 11.981 
                 4.593 
               
               
                   
                  3 
                 18.014 
                 3.274 
                 1.72916 
                 54.7 
               
               
                   
                  4 
                 −34.660 
                 0.100 
               
               
                   
                  5 
                 14.376 
                 1.995 
                 1.81600 
                 46.6 
               
               
                   
                  6 
                 21.603 
                 1.765 
               
               
                   
                  7 
                 −48.220 
                 1.000 
                 1.61340 
                 44.3 
               
               
                   
                  8 
                 9.158 
                 1.361 
               
               
                   
                  9(diaphragm) 
                 ∞ 
                 1.400 
               
               
                   
                 10 
                 −8.580 
                 1.000 
                 1.61340 
                 44.3 
               
               
                   
                 11 
                 21.064 
                 2.832 
                 1.49700 
                 81.6 
               
               
                   
                 12 
                 −13.049 
                 0.100 
               
               
                   
                 13 
                 85.505 
                 3.224 
                 1.49700 
                 81.6 
               
               
                   
                 14 
                 −13.990 
                 0.100 
               
               
                   
                 15 
                 42.887 
                 2.310 
                 1.43875 
                 95.0 
               
               
                   
                 16 
                 −20.872 
                 d16 
               
               
                   
                 17 
                 48.657 
                 1.000 
                 1.65412 
                 39.7 
               
               
                   
                 18 
                 16.978 
                 0.854 
               
               
                   
                 19 
                 22.498 
                 1.886 
                 1.74320 
                 49.3 
               
               
                   
                 20 
                 177.055 
                 14.130  
               
               
                   
                 21 
                 ∞ 
                 1.050 
                 1.51633 
                 64.1 
               
               
                   
                 22 
                 ∞ 
                 — 
               
               
                   
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 6 
               
             
             
               
                   
               
               
                 VARIOUS LENS-SYSTEM DATA 
               
             
          
           
               
                   
                 Infinite 
                 Intermediate 
                 Minimum 
               
               
                   
                 Photographic 
                 Photographic 
                 Photographic 
               
               
                   
                 Position 
                 Position 
                 Position 
               
               
                   
                   
               
             
          
           
               
                   
                 FNO. 
                 2.8 
                 3.1 
                 3.2 
               
               
                   
                 f 
                 20.00 
                 20.29 
                 20.43 
               
               
                   
                 Magnification 
                 0.000 
                 −0.150 
                 −0.217 
               
               
                   
                 W 
                 14.2 
                 12.8 
                 12.2 
               
               
                   
                 Y 
                 5.00 
                 5.00 
                 5.00 
               
               
                   
                 fB 
                 1.00 
                 1.00 
                 1.00 
               
               
                   
                 L 
                 49.97 
                 53.42 
                 54.96 
               
               
                   
                 d16 
                 4.000 
                 7.448 
                 8.989 
               
               
                   
                   
               
             
          
         
       
     
       Numerical Embodiment 4 
       [0114]      FIGS. 19 through 24  and Tables 7 and 8 show a fourth numerical embodiment of the fixed focal-length lens system according to the present invention.  FIG. 19  shows the lens arrangement at the infinite photographic position,  FIG. 20  shows various aberrations thereof,  FIG. 21  shows the lateral aberrations thereof,  FIG. 22  shows the lens arrangement at the minimum photographic position,  FIG. 23  shows various aberrations thereof, and  FIG. 24  shows the lateral aberrations thereof. Table 7 shows the lens surface data, and Table 8 shows various lens-system data. 
         [0115]    The first lens group G 1  is configured of a negative meniscus lens element  11  having a convex surface on the object side, a biconvex positive lens element  12 , a positive meniscus lens element  13  having a convex surface on the object side, and a biconcave negative lens element  14 , in that order from the object side. The biconcave negative lens element  14  is formed from a glass material having negative anomalous dispersion characteristics by using, e.g., HOYA E-ADF10. 
         [0116]    The second lens group G 2  is configured of a biconcave negative lens element  21 , a biconvex positive lens element  22 , a biconvex positive lens element  23 , and a biconvex positive lens element  24 , in that order from the object side. The surface on the image side of the biconcave negative lens element  21  and the surface on the object of the biconvex positive lens element  22  are cemented to each other to form a cemented lens having a negative refractive power. The biconcave negative lens element  21  is formed from a glass material having negative anomalous dispersion characteristics by using, e.g., HOYA E-ADF10. Each of the biconvex positive lens element  22 , the biconvex positive lens element  23  and the biconvex positive lens element  24  is formed from a low-dispersion glass ED lens having large positive anomalous dispersion characteristics. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 7 
               
             
             
               
                   
               
               
                 SURFACE DATA 
               
             
          
           
               
                   
                 Surf. No. 
                 r 
                 d 
                 N(d) 
                 ν d 
               
               
                   
                   
               
             
          
           
               
                   
                  1 
                 49.997 
                 1.000 
                 1.48749 
                 70.2 
               
               
                   
                  2 
                 11.790 
                 4.904 
               
               
                   
                  3 
                 19.484 
                 3.061 
                 1.74100 
                 52.7 
               
               
                   
                  4 
                 −34.537 
                 0.103 
               
               
                   
                  5 
                 13.653 
                 2.027 
                 1.81600 
                 46.6 
               
               
                   
                  6 
                 18.584 
                 1.711 
               
               
                   
                  7 
                 −54.876 
                 1.000 
                 1.61310 
                 44.4 
               
               
                   
                  8 
                 9.175 
                 2.976 
               
               
                   
                  9 
                 −8.572 
                 1.000 
                 1.61310 
                 44.4 
               
               
                   
                 10 
                 32.812 
                 2.821 
                 1.49700 
                 81.6 
               
               
                   
                 11 
                 −12.593 
                 0.153 
               
               
                   
                 12 
                 84.638 
                 2.688 
                 1.43500 
                 95.0 
               
               
                   
                 13 
                 −13.078 
                 0.100 
               
               
                   
                 14 
                 36.610 
                 2.533 
                 1.43875 
                 95.0 
               
               
                   
                 15 
                 −21.582 
                 d15 
               
               
                   
                 16(diaphragm) 
                 ∞ 
                 2.209 
               
               
                   
                 17 
                 45.603 
                 1.395 
                 1.65412 
                 39.7 
               
               
                   
                 18 
                 16.441 
                 1.385 
               
               
                   
                 19 
                 22.314 
                 2.090 
                 1.77250 
                 49.6 
               
               
                   
                 20 
                 156.779 
                 13.795  
               
               
                   
                 21 
                 ∞ 
                 1.050 
                 1.51633 
                 64.1 
               
               
                   
                 22 
                 ∞ 
                 — 
               
               
                   
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 8 
               
             
             
               
                   
               
               
                 VARIOUS LENS-SYSTEM DATA 
               
             
          
           
               
                   
                 Infinite 
                 Intermediate 
                 Minimum 
               
               
                   
                 Photographic 
                 Photographic 
                 Photographic 
               
               
                   
                 Position 
                 Position 
                 Position 
               
               
                   
                   
               
             
          
           
               
                   
                 FNO. 
                 2.8 
                 2.8 
                 2.8 
               
               
                   
                 f 
                 20.00 
                 20.53 
                 20.82 
               
               
                   
                 Magnification 
                 0.000 
                 −0.217 
                 −0.333 
               
               
                   
                 W 
                 14.2 
                 11.8 
                 10.7 
               
               
                   
                 Y 
                 5.00 
                 5.00 
                 5.00 
               
               
                   
                 fB 
                 1.00 
                 1.00 
                 1.00 
               
               
                   
                 L 
                 50.80 
                 55.87 
                 58.57 
               
               
                   
                 d15 
                 1.800 
                 6.866 
                 9.574 
               
               
                   
                   
               
             
          
         
       
     
       Numerical Embodiment 5 
       [0117]      FIGS. 25 through 30  and Tables 9 and 10 show a fifth numerical embodiment of the fixed focal-length lens system according to the present invention.  FIG. 25  shows the lens arrangement at the infinite photographic position,  FIG. 26  shows various aberrations thereof,  FIG. 27  shows the lateral aberrations thereof,  FIG. 28  shows the lens arrangement at the minimum photographic position,  FIG. 29  shows various aberrations thereof, and  FIG. 30  shows the lateral aberrations thereof. Table 9 shows the lens surface data, and Table 10 shows various lens-system data. 
         [0118]    The lens arrangement of the fifth numerical embodiment is the same as that of the lens arrangement of the first numerical embodiment except for the following points: 
         [0119]    (1) The second lens group G 2  is configured of biconcave negative lens element  21 ′, a biconvex positive lens element  22 ′, and a biconvex positive lens element  23 ′, in that order from the object side. The surface on the image side of the biconcave negative lens element  21 ′ is cemented to the surface on the object side of the biconvex positive lens element  22 ′ to form a cemented lens having a negative refractive power. The biconvex positive lens element  22 ′ is formed from a low-dispersion glass ED lens having large positive anomalous dispersion characteristics. 
         [0120]    (2) The positive lens element  32  of the third lens group G 3  is a biconvex positive lens element instead of being a positive meniscus lens element having a convex surface on the object side. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 9 
               
             
             
               
                   
               
               
                 SURFACE DATA 
               
             
          
           
               
                   
                 Surf. No. 
                 r 
                 d 
                 N(d) 
                 ν d 
               
               
                   
                   
               
             
          
           
               
                   
                  1 
                 24.963 
                 1.000 
                 1.62041 
                 60.3 
               
               
                   
                  2 
                 11.203 
                 6.606 
               
               
                   
                  3 
                 14.561 
                 3.018 
                 1.77250 
                 49.6 
               
               
                   
                  4 
                 −55.473 
                 0.100 
               
               
                   
                  5 
                 16.848 
                 2.111 
                 1.77250 
                 49.6 
               
               
                   
                  6 
                 26.541 
                 1.142 
               
               
                   
                  7 
                 −53.663 
                 1.000 
                 1.61340 
                 44.3 
               
               
                   
                  8 
                 8.768 
                 2.964 
               
               
                   
                  9 
                 −8.646 
                 1.000 
                 1.54814 
                 45.8 
               
               
                   
                 10 
                 12.764 
                 3.301 
                 1.43875 
                 95.0 
               
               
                   
                 11 
                 −9.766 
                 0.100 
               
               
                   
                 12 
                 23.472 
                 2.584 
                 1.61800 
                 63.4 
               
               
                   
                 13 
                 −19.071 
                 d13 
               
               
                   
                 14(diaphragm) 
                 ∞ 
                 2.100 
               
               
                   
                 15 
                 68.674 
                 1.000 
                 1.60342 
                 38.0 
               
               
                   
                 16 
                 12.356 
                 2.132 
               
               
                   
                 17 
                 13.953 
                 3.008 
                 1.62041 
                 60.3 
               
               
                   
                 18 
                 −262.977 
                 12.984  
               
               
                   
                 19 
                 ∞ 
                 1.050 
                 1.51633 
                 64.1 
               
               
                   
                 20 
                 ∞ 
                 — 
               
               
                   
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 10 
               
             
             
               
                   
               
               
                 VARIOUS LENS-SYSTEM DATA 
               
             
          
           
               
                   
                 Infinite 
                 Intermediate 
                 Minimum 
               
               
                   
                 Photographic 
                 Photographic 
                 Photographic 
               
               
                   
                 Position 
                 Position 
                 Position 
               
               
                   
                   
               
             
          
           
               
                   
                 FNO. 
                 2.8 
                 2.8 
                 2.8 
               
               
                   
                 f 
                 20.00 
                 20.74 
                 21.08 
               
               
                   
                 Magnification 
                 0.000 
                 −0.150 
                 −0.217 
               
               
                   
                 W 
                 14.3 
                 12.5 
                 11.7 
               
               
                   
                 Y 
                 5.00 
                 5.00 
                 5.00 
               
               
                   
                 fB 
                 1.00 
                 1.00 
                 1.00 
               
               
                   
                 L 
                 50.00 
                 53.65 
                 55.28 
               
               
                   
                 d13 
                 1.800 
                 5.449 
                 7.079 
               
               
                   
                   
               
             
          
         
       
     
       Numerical Embodiment 6 
       [0121]      FIGS. 31 through 36  and Tables 11 and 12 show a sixth numerical embodiment of the fixed focal-length lens system according to the present invention.  FIG. 31  shows the lens arrangement at the infinite photographic position,  FIG. 32  shows various aberrations thereof,  FIG. 33  shows the lateral aberrations thereof,  FIG. 34  shows the lens arrangement at the minimum photographic position,  FIG. 35  shows various aberrations thereof, and  FIG. 36  shows the lateral aberrations thereof. Table 11 shows the lens surface data, and Table 12 shows various lens-system data. 
         [0122]    The lens arrangement of the sixth numerical embodiment is the same as that of the lens arrangement of the fourth numerical embodiment. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 11 
               
             
             
               
                   
               
               
                 SURFACE DATA 
               
             
          
           
               
                   
                 Surf. No. 
                 r 
                 d 
                 N(d) 
                 ν d 
               
               
                   
                   
               
             
          
           
               
                   
                  1 
                 45.438 
                 1.000 
                 1.48749 
                 70.2 
               
               
                   
                  2 
                 12.873 
                 4.776 
               
               
                   
                  3 
                 19.323 
                 3.835 
                 1.74100 
                 52.7 
               
               
                   
                  4 
                 −39.441 
                 0.333 
               
               
                   
                  5 
                 13.958 
                 1.935 
                 1.81600 
                 46.6 
               
               
                   
                  6 
                 18.048 
                 1.749 
               
               
                   
                  7 
                 −48.952 
                 1.000 
                 1.61310 
                 44.4 
               
               
                   
                  8 
                 9.756 
                 2.892 
               
               
                   
                  9 
                 −8.385 
                 1.000 
                 1.61310 
                 44.4 
               
               
                   
                 10 
                 18.153 
                 2.833 
                 1.49700 
                 81.6 
               
               
                   
                 11 
                 −13.057 
                 0.100 
               
               
                   
                 12 
                 62.807 
                 2.824 
                 1.49700 
                 81.6 
               
               
                   
                 13 
                 −14.128 
                 0.100 
               
               
                   
                 14 
                 41.312 
                 2.595 
                 1.49700 
                 81.6 
               
               
                   
                 15 
                 −23.712 
                 d15 
               
               
                   
                 16(diaphragm) 
                 ∞ 
                 2.277 
               
               
                   
                 17 
                 45.872 
                 1.140 
                 1.65412 
                 39.7 
               
               
                   
                 18 
                 15.600 
                 0.920 
               
               
                   
                 19 
                 22.515 
                 2.103 
                 1.77250 
                 49.6 
               
               
                   
                 20 
                 332.369 
                 13.539  
               
               
                   
                 21 
                 ∞ 
                 1.050 
                 1.51633 
                 64.1 
               
               
                   
                 22 
                 ∞ 
                 — 
               
               
                   
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 12 
               
             
             
               
                   
               
               
                 VARIOUS LENS-SYSTEM DATA 
               
             
          
           
               
                   
                 Infinite 
                 Intermediate 
                 Minimum 
               
               
                   
                 Photographic 
                 Photographic 
                 Photographic 
               
               
                   
                 Position 
                 Position 
                 Position 
               
               
                   
                   
               
             
          
           
               
                   
                 FNO. 
                 2.8 
                 2.8 
                 2.8 
               
               
                   
                 f 
                 20.00 
                 20.50 
                 20.78 
               
               
                   
                 Magnification 
                 0.000 
                 −0.217 
                 −0.333 
               
               
                   
                 W 
                 14.2 
                 11.7 
                 10.6 
               
               
                   
                 Y 
                 5.00 
                 5.00 
                 5.00 
               
               
                   
                 fB 
                 1.00 
                 1.00 
                 1.00 
               
               
                   
                 L 
                 50.80 
                 55.86 
                 58.56 
               
               
                   
                 d15 
                 1.800 
                 6.856 
                 9.558 
               
               
                   
                   
               
             
          
         
       
     
         [0123]    The values of each condition for each embodiment are shown in Table 13. The numerical values corresponding to condition (5) show values for the positive lens element that has the largest Abbe number at the d-line out of the positive lens elements  22 ,  23  and  24  ( 22 ′ and  23 ′) provided within the second lens group G 2 . The numerical values corresponding to condition (6) show values for the positive lens element that has the smallest refractive index at the d-line out of the positive lens elements  12  and  13  provided within the first lens group G 1 . The numerical values corresponding to condition (7) show values for the positive lens element that has the smallest Abbe number at the d-line out of the positive lens elements  12  and  13  provided within the first lens group G 1 . 
         [0000]    
       
         
               
               
               
               
               
             
           
               
                   
                 TABLE 13 
               
               
                   
                   
               
             
             
               
                   
                   
                 Embod. 1 
                 Embod. 2 
                 Embod. 3 
               
               
                   
                   
               
               
                   
                 Cond. (1) 
                 −0.21 
                 −0.14 
                 −0.12 
               
               
                   
                 Cond. (2) 
                 1.61340 
                 1.61340 
                 1.61340 
               
               
                   
                 Cond. (3) 
                 44.27 
                 44.27 
                 44.27 
               
               
                   
                 Cond. (4) 
                 −0.00650 
                 −0.00650 
                 −0.00650 
               
               
                   
                 Cond. (5) 
                 94.94 
                 94.94 
                 94.94 
               
               
                   
                 Cond. (6) 
                 1.72916 
                 1.77250 
                 1.72916 
               
               
                   
                 Cond. (7) 
                 46.60 
                 49.60 
                 46.60 
               
               
                   
                 Cond. (8) 
                 1.30 
                 1.96 
                 1.46 
               
               
                   
                 Cond. (9) 
                 81.60 
                 60.70 
                 70.20 
               
               
                   
                 Cond. (10) 
                 −0.00650 
                 −0.00650 
                 −0.00650 
               
               
                   
                   
               
               
                   
                   
                 Embod. 4 
                 Embod. 5 
                 Embod. 6 
               
               
                   
                   
               
               
                   
                 Cond. (1) 
                 −0.16 
                 −0.12 
                 −0.14 
               
               
                   
                 Cond. (2) 
                 1.61310 
                 1.54814 
                 1.61310 
               
               
                   
                 Cond. (3) 
                 44.36 
                 45.78 
                 44.36 
               
               
                   
                 Cond. (4) 
                 −0.00800 
                 0.00120 
                 −0.00800 
               
               
                   
                 Cond. (5) 
                 95.00 
                 94.94 
                 81.55 
               
               
                   
                 Cond. (6) 
                 1.74100 
                 1.77250 
                 1.74100 
               
               
                   
                 Cond. (7) 
                 46.60 
                 49.60 
                 46.60 
               
               
                   
                 Cond. (8) 
                 1.62 
                 2.63 
                 1.79 
               
               
                   
                 Cond. (9) 
                 70.20 
                 60.30 
                 70.20 
               
               
                   
                 Cond. (10) 
                 −0.00800 
                 −0.00650 
                 −0.00800 
               
               
                   
                   
               
             
          
         
       
     
         [0124]    As can be understood from Table 13, the first through sixth numerical embodiments satisfy conditions (1) through (10). As can be understood from the various aberration diagrams, the various aberrations are relatively well corrected. 
       INDUSTRIAL APPLICABILITY 
       [0125]    The fixed focal-length lens system of the present invention is ideal for use in a photographing apparatus such as a digital camera, etc., and is especially suitable for an interchangeable lens, in which a shutter unit is mounted within the lens body, that is typified by a non-reflex camera (mirrorless camera). 
       REFERENCE SIGNS LIST 
       [0000]    
       
         G 1  Negative first lens group 
           11  Negative lens element 
           12  Positive lens element 
           13  Positive lens element 
           14  Negative lens element 
         G 2  Positive second lens group 
           21  Negative lens element 
           22  Positive lens element 
           23  Positive lens element 
           24  Positive lens element 
           21 ′ Negative lens element 
           22 ′ Positive lens element 
           23 ′ Positive lens element 
         G 3  Positive third lens group 
           31  Negative lens element 
           32  Positive lens element 
         S Aperture diaphragm 
         OP Optical filter 
         I Imaging plane