Abstract:
An optical system focuses an object upon an image surface of a solid-state image device. The optical system has a master optical system and a condenser lens. The master optical system and the condenser lens both have positive optical power. The focusing optical system fulfills the following conditions: ##EQU1## where a represents the distance between the exit pupil of the master optical system and the image surface; 
     b represents the distance between the exit pupil of the entire optical system and the image surface; and 
     Y&#39; represents the maximum image height.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a taking optical system. More particularly, the present invention relates to a compact taking optical system suitable for use in a camera provided with a solid-state image device. 
     2. Description of the Prior Art 
     In a camera (for example, video camera or television camera) that shoots an object by directing a light beam incoming through a taking optical system to a solid-state image device such as a CCD (charge-coupled device) consisting of an array of light-sensing devices, a condensing microlens is provided on the light-receiving side of each of the light-sensing device to enhance its light-receiving efficiency. To make the most of the light-condensing ability of the microlenses, conventional taking optical systems are designed to have their exit pupil substantially at infinity (i.e. designed as an optical system that is substantially telecentric toward the image side). This is because, if a taking optical system has its exit pupil substantially at infinity, even an off-axial light beam strikes the light-sensing devices from a direction substantially perpendicular to the light-receiving surfaces of the light-sensing devices, and thus it is possible to make the most of the light-condensing ability of the microlenses. 
     The recent trend toward more compact cameras has been creating the need for taking optical systems having shorter overall lengths. However, as taking optical systems are made shorter, their exit pupil inevitably comes closer to the image surface; as the exit pupil comes closer to the image surface, the angle at which an off-axial light beam strikes the microlenses disposed at the periphery of an image deviates more from a right angle with respect to the light-receiving surfaces of the light-sensing devices. As a result, the light-condensing ability of the microlenses is impaired at the periphery of the image, and thus images shot by the solid-state image device suffer from uneven brightness between their central and peripheral portions. As described above, conventional taking optical systems are imperfect because, in them, it is not possible to reduce the overall length with the exit pupil placed at a substantially infinite position. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a taking optical system that has a relatively short overall length despite having its exit pupil substantially at infinity. 
     To achieve the above object, according to one aspect of the present invention, an optical system for focusing an object upon an image surface of a solid-state image device is provided with a master optical system having positive optical power, and a condenser lens having positive optical power and provided between the master optical system and the image surface of the solid-state image device. In addition, in this optical system, the following conditions are fulfilled: ##EQU2## 
     where 
     a represents a distance between an exit pupil of the master optical system and the image surface; 
     b represents a distance between an exit pupil of the entire optical system and the image surface; and 
     Y&#39; represents a maximum image height. 
     According to another aspect of the present invention, an optical system for focusing an object upon an image surface of a solid-state image device is provided with a master optical system having positive optical power, and a condenser lens having positive optical power and provided between the master optical system and the image surface of the solid-state image device. In addition, in this optical system, the following condition is fulfilled: ##EQU3## 
     where 
     a represents a distance between an exit pupil of the master optical system and the image surface; and 
     b represents a distance between an exit pupil of the entire optical system and the image surface. 
     According to still another aspect of the present invention, an optical system for focusing an object upon an image surface of a solid-state image device is provided with a master optical system having positive optical power, and a condenser lens having positive optical power and provided between the master optical system and the image surface of the solid-state image device. In addition, in this optical system, the following conditions are fulfilled: ##EQU4## 
     where 
     a represents a distance between an exit pupil of the master optical system and the image surface; 
     b represents a distance between an exit pupil of the entire optical system and the image surface; and 
     Y&#39; represents a maximum image height. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This and other objects and features of this invention will become clear from the following description, taken in conjunction with the preferred embodiments with reference to the accompanied drawings in which: 
     FIG. 1 is a diagram showing the lens construction of the taking optical system of a first embodiment of the present invention; 
     FIGS. 2A to 2C are diagrams showing the aberrations observed in the first embodiment; 
     FIG. 3 is a diagram showing the lens construction of the taking optical system of a second embodiment of the present invention; 
     FIGS. 4A to 4I are diagrams showing the aberrations observed in the second embodiment; 
     FIG. 5 is a diagram showing the lens construction of the taking optical system of a third embodiment of the present invention; 
     FIGS. 6A to 6C are diagrams showing the aberrations observed in the third embodiment; 
     FIG. 7 is a diagram showing the lens construction of the taking optical system of a fourth embodiment of the present invention; 
     FIGS. 8A to 8I are diagrams showing the aberrations observed in the fourth embodiment; 
     FIG. 9 is a diagram showing the lens construction of the taking optical system of a fifth embodiment of the present invention; 
     FIGS. 10A to 10I are diagrams showing the aberrations observed in the fifth embodiment; 
     FIG. 11 is a diagram showing the lens construction of the taking optical system of a sixth embodiment of the present invention; 
     FIGS. 12A to 12C are diagrams showing the aberrations observed in the sixth embodiment; 
     FIG. 13 is a diagram showing the lens construction of the taking optical system of a seventh embodiment of the present invention; 
     FIGS. 14A to 14I are diagrams showing the aberrations observed in the seventh embodiment; 
     FIG. 15 is a schematic diagram of the taking optical systems according to the present invention, in explanation of the conditions to be satisfied therein; and 
     FIGS. 16A to 16C are diagrams schematically showing an off-axial light beam striking the solid-state image device, in explanation of the action of the condenser lenses. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, taking optical systems embodying the present invention will be described with reference to the drawings. 
     FIGS. 1, 3, 5, 7, 9, 11, 13 show the lens constructions of the taking optical systems of first to seventh embodiments, respectively. For the second, fourth, fifth, and seventh embodiments, which are each constructed as a zoom lens, the lens construction in their shortest focal length condition [W] is shown in the corresponding figures, and the movement of their constituent lens units Gr1 to Gr3 during zooming from the shortest focal length condition [W] to the longest focal length condition [T] is schematically indicated by arrows m1 to m3. In all of these lens construction diagrams, ri (i=1, 2, 3, . . . ) represents the radius of curvature of the i-th surface from the object side. In lens construction diagrams for the embodiments constructed as zoom lenses, di (i=1, 2, 3, . . . ) represents the i-th axial distance from the object side, though only those which vary with zooming appear in this figure. 
     The taking optical systems of the first to seventh embodiments are all used to form an object image on a solid-state image device, and are each constituted of, from the object side, a master optical system ML having positive optical power, a low-pass filter LP, and a condenser lens CL having positive optical power. The condenser lens CL is disposed between the master optical system ML and the solid-state image device and in the vicinity of the image surface of the solid-state image device, and its positive optical power acts such that the exit pupil of the taking optical system is placed substantially at infinity. The taking optical systems of the first, third, and sixth embodiments are each constructed as a single-focal-length lens, whereas those of the second, fourth, fifth, and seventh embodiments are each constructed as a zoom lens. 
     In the first embodiment, the master optical system ML is constituted of, from the object side, two positive meniscus lens elements with their convex surfaces facing toward the object side, a negative meniscus lens element with its concave surface facing toward the image side, an aperture diaphragm S, a negative meniscus lens element with its concave surface facing toward the object side, and a positive biconvex lens element. The condenser lens CL is composed of a plano-convex lens element with its convex surface facing toward the image side. 
     In the second embodiment, the master optical system ML is constituted of, from the object side, a first lens unit Gr1 composed of a negative biconcave lens element and a positive meniscus lens element with its convex surface facing toward the object side; a second lens unit Gr2 composed of a positive biconvex lens element, a negative meniscus lens element with its concave surface facing toward the image side, a positive biconvex lens element, and an aperture diaphragm S; and a third lens unit Gr3 composed of a positive meniscus lens element with its convex surface facing toward the image side and a negative meniscus lens element with its concave surface facing toward the object side. The condenser lens CL is composed of a plano-convex lens element with its convex surface facing toward the image side. Although the master optical system ML is constructed as an independent three-unit zoom lens having its own optical performance, it serves, during zooming, as the principal portion of a four-unit zoom lens constituted by the entire taking optical system which includes, as its fourth lens unit, the low-pass filter LP and the condenser lens CL that are fixed. 
     In the third embodiment, the master optical system ML is constituted of, from the object side, a negative meniscus lens element with its convex surface facing toward the object side, a positive biconvex lens element, an aperture diaphragm S, a negative biconcave lens element, a positive meniscus lens element with its convex surface facing toward the image side, and a positive biconvex lens element. The condenser lens CL is composed of a plano-convex lens element with its convex surface facing toward the image side. 
     In the fourth embodiment, the master optical system ML is constituted of, from the object side, a first lens unit Gr1 composed of a negative meniscus lens element with its concave surface facing toward the image side and a positive meniscus lens element with its convex surface facing toward the object side; and a second lens unit Gr2 composed of an aperture diaphragm S, a positive meniscus lens element with its convex surface facing toward the object side, and a negative meniscus lens element with its concave surface facing toward the object side. The condenser lens CL is composed of a plano-convex lens element with its convex surface facing toward the image side. Although the master optical system ML is constructed as an independent two-unit zoom lens having its own optical performance, it serves, during zooming, as the principal portion of a three-unit zoom lens constituted by the entire taking optical system which includes, as its third lens unit, the low-pass filter LP and the condenser lens CL that are fixed. 
     In the fifth embodiment, the master optical system ML is constituted of, from the object side, a first lens unit Gr1 composed of a doublet lens element produced by bonding together a negative meniscus lens element with its concave surface facing toward the image side and a positive meniscus lens element with its convex surface facing toward the object side, and a positive meniscus lens element with its convex surface facing toward the object side; a second lens unit Gr2 composed of a negative meniscus lens element with its concave surface facing toward the image side, a negative biconcave lens element, a positive biconvex lens element, and a negative meniscus lens element with its concave surface facing toward the image side; a third lens unit Gr3 composed of an aperture diaphragms S, a positive biconvex lens element, a negative meniscus lens element with its concave surface facing toward the object side, a positive biconvex lens element, and a negative meniscus lens element with its concave surface facing toward the object side. The condenser lens CL is composed of a plano-convex lens element with its convex surface facing toward the image side. Although the master optical system ML is constructed as an independent three-unit zoom lens having its own optical performance, it serves, during zooming, as the principal portion of a four-unit zoom lens constituted by the entire taking optical system which includes, as its fourth lens unit, the low-pass filter LP and the condenser lens CL that are fixed. 
     In the sixth embodiment, the master optical system ML is constituted of, from the object side, a positive biconvex lens element, two positive meniscus lens elements with their convex surfaces facing toward the object side, a negative meniscus lens element with its concave surface facing toward the image side, an aperture diaphragm, a doublet lens element produced by bonding together a positive biconvex lens element and a negative biconcave lens element, a negative meniscus lens element with its concave surface facing toward the image side, and a positive biconvex lens element. The condenser lens CL is composed of a plano-convex lens element with its convex surface facing toward the image side. 
     In the seventh embodiment, the master optical system ML is constituted of, from the object side, a first lens unit Gr1 composed of a doublet lens element produced by bonding together a negative meniscus lens element with its concave surface facing toward the image side and a positive biconvex lens element, and a positive meniscus lens element with its convex surface facing toward the object side; a second lens unit Gr2 composed of a negative meniscus lens element with its concave surface facing toward the image side, a negative biconcave lens element, a positive biconvex lens element, and a negative biconcave lens element; a third lens unit Gr3 composed of an aperture diaphragm S, two positive biconvex lens elements, and a negative biconcave lens element; and a fourth lens unit Gr4 composed of a positive biconvex lens element, a negative biconcave lens element, and a positive meniscus lens element with its convex surface facing toward the object side. The condenser lens CL is composed of a plano-convex lens element with its convex surface facing toward the image side. Although the master optical system ML is constructed as an independent four-unit zoom lens having its own optical performance, it serves, during zooming, as the principal portion of a five-unit zoom lens constituted by the entire taking optical system which includes, as its fifth lens unit, the low-pass filter LP and the condenser lens CL that are fixed. 
     In all of the first to seventh embodiments, the positive optical power of the condenser lens CL, which is disposed between the master optical system ML and the solid-state image device and in the vicinity of the image surface of the solid-state image device, acts such that the exit pupil of the taking optical system is placed substantially at infinity, as described previously. The condenser lens CL thus serves to shift the exit pupil of the taking optical system away from the image surface, and accordingly its use makes it possible to shorten the overall length of the taking optical system. In addition, the exit pupil of the taking optical system can be shifted away from the image surface with far less degradation of the imaging performance of the master optical system ML than in conventional constructions lacking the condenser lens CL. 
     The optical power of the condenser lens CL is determined in accordance with the position of the exit pupil of the master optical system ML. As the condenser lens CL has stronger optical power, it shifts the exit pupil of the taking optical system farther away. Therefore, as the exit pupil of the master optical system ML is closer to the image surface, the condenser lens CL needs to be given stronger power. In the second, fourth, fifth, and seventh embodiments, where the master optical system ML is a zoom lens, the exit pupil moves along the optical axis AX during zooming. In this case, therefore, it is preferable to additionally balance the exit pupil position in the shortest focal length condition [W] with that in the longest focal length condition [T]. 
     The conditions that need to be satisfied in the first to seventh embodiments will be described below. The variables and symbols used in these conditions and in their descriptions are illustrated in FIG. 15. In FIG. 15, PR represents the principal ray of the most off-axial light beam. 
     In the first and second embodiments, conditions (1) and (2) below are satisfied: ##EQU5## 
     where 
     a represents the distance between the exit pupil position Pa of the master optical system ML and the image surface I; 
     b represents the distance between the exit pupil position Pb of the taking optical system and the image surface I; and 
     Y&#39; represents the maximum image height. 
     Condition (1) defines the relation between the exit pupil position Pa of the master optical system ML and the maximum image height Y&#39;. By condition (1), the exit pupil position Pa of the master optical system ML is determined in accordance with the image-surface size of the solid-state image device. The exit pupil position Pa of the master optical system ML depends on the size of the master optical system ML. Specifically, as the exit pupil position Pa is placed farther from the image surface I, the overall length of the taking optical system becomes longer. If the exit pupil position Pa of the master optical system ML is so far from the image surface I that condition (1) is no more satisfied, the overall length of the master optical system ML is too long to be reduced even by providing the condenser lens CL. As a result, it is not possible to make the taking optical system compact enough. 
     Condition (2) defines the relation between the exit pupil position Pa of the master optical system ML and the exit pupil position Pb of the taking optical system, and represents how far the action of the condenser lens CL shifts the exit pupil away from the image surface I. If condition (2) is not satisfied, the exit pupil is shifted too far. This means that the optical power of the condenser lens CL is too strong, and, as a result, it is difficult to correct properly the curvature of field and distortion caused by the condenser lens CL itself. 
     In the first and second embodiments, it is preferable that condition (3) below be satisfied additionally: ##EQU6## 
     where 
     φC represents the optical power of the condenser lens CL; and 
     φM represents the optical power of the master optical system ML. 
     Condition (3) defines the ratio of the optical power of the condenser lens CL to that of the master optical system ML. When condition (3) is satisfied, it is possible to shift the exit pupil position Pb of the taking optical system far enough without unduly sacrificing proper correction of aberrations. If the lower limit of condition (3) is exceeded, the relative optical power of the condenser lens CL is too weak, and thus the exit pupil cannot be shifted far enough. As a result, it is difficult to place the exit pupil position Pb of the taking optical system substantially at infinity. If the upper limit of condition (3) is exceeded, the optical power of the condenser lens CL is too strong. As a result, it is difficult to correct properly the curvature of field caused by the condenser lens CL itself. 
     In the third to fifth embodiments, condition (4) below is satisfied: ##EQU7## 
     where 
     a represents the distance between the exit pupil position Pa of the master optical system ML and the image surface I; and 
     b represents the distance between the exit pupil position Pb of the taking optical system and the image surface I. 
     Condition (4) defines the relation between the exit pupil position Pa of the master optical system ML and the exit pupil position Pb of the taking optical system, and represents how far the action of the condenser lens CL shifts the exit pupil away from the image surface I. If condition (4) is not satisfied, the action of the condenser lens CL is too weak to shift the exit pupil far enough, and thus the use of the condenser lens CL does not lead to any improvement. In addition, since the taking optical system as a whole needs to be made larger, it is not possible to shorten its overall length. 
     In the third to fifth embodiments, it is preferable that conditions (5) and (6) below be satisfied additionally: ##EQU8## 
     where 
     Y&#39; represents the maximum image height; 
     LB represents the distance between the image-side end surface of the master optical system ML and the image surface I (for the embodiments in which the master optical system ML is a zoom lens, the minimum value throughout the entire zoom range is taken); 
     a min  represents the distance between the exit pupil position Pa of the master optical system ML and the image surface I (for the embodiments in which the master optical system ML is a zoom lens, the minimum value throughout the entire zoom range is taken); and 
     φC represents the optical power of the condenser lens CL. 
     Condition (5) defines the ratio of the distance LB between the image-side end surface of the master optical system ML and the image surface I to the maximum image height Y&#39;. By condition (5), the distance LB between the image-side end surface of the master optical system ML and the image surface I is determined in accordance with the image-surface size of the solid-state image device. If the distance LB between the image-side end surface of the master optical system ML and the image surface I is so short that condition (5) is no more satisfied, it is difficult to arrange the low-pass filter LP and the condenser lens CL between the image-side end surface of the master optical system ML and the image surface I. 
     Condition (6) defines the relation between the optical power of the condenser lens CL and the exit pupil position Pa of the master optical system ML. From condition (6), it is known that, as the exit pupil position Pa of the master optical system ML is farther from the image surface I, the optical power φC of the condenser lens CL needs to be weaker, and that, as the exit pupil position Pa of the master optical system ML is closer to the image surface I, the optical power qC of the condenser lens CL needs to be stronger. When condition (6) is satisfied, the exit pupil position Pb of the taking optical system is placed within an appropriate range. 
     If the optical power of the condenser lens CL is so weak that the lower limit of condition (6) is exceeded, the action of the condenser lens CL is too weak, and thus the exit pupil cannot be shifted far enough. In this case, in order to place the exit pupil position Pb of the taking optical system within an appropriate range, the exit pupil position Pa of the master optical system ML needs to be shifted farther away from the image surface I. As a result, the taking optical system needs to be made larger. If the optical power of the condenser lens CL is so strong that the upper limit of condition (6) is exceeded, the action of the condenser lens CL is too strong, and thus the exit pupil is shifted too far. As a result, not only the exit pupil position Pb of the taking optical system is placed too far away from the image surface I, but also it is difficult to correct aberrations (in particular, curvature of field and distortion). 
     In the sixth and seventh embodiments, conditions (7) and (8) below are satisfied: ##EQU9## 
     where 
     a represents the distance between the exit pupil position Pa of the master optical system ML and the image surface I; 
     b represents the distance between the exit pupil position Pb of the entire optical system and the image surface I; and 
     Y&#39; represents the maximum image height. 
     Condition (7) defines the relation between the exit pupil position Pa of the master optical system ML and the maximum image height Y&#39;. By condition (7), the exit pupil position Pa of the master optical system ML is determined in accordance with the image-surface size of the solid-state image device. If the exit pupil position Pa of the master optical system ML is so close to the image surface I that condition (7) is no more satisfied, the condenser lens CL needs to be given stronger optical power so that the exit pupil position is shifted farther away. As a result, aberrations (in particular, curvature of field and distortion) become too great to be corrected properly. 
     Condition (8) defines the relation between the exit pupil position Pa of the master optical system ML and the exit pupil position Pb of the taking optical system, and represents how far the action of the condenser lens CL shifts the exit pupil away from the image surface I. If condition (8) is not satisfied, the exit pupil position is shifted too far. This means that the optical power of the condenser lens CL is too strong, and, as a result, it is difficult to correct the curvature of field and distortion caused by the condenser lens CL itself. 
     As described earlier, in a taking optical system in which the master optical system ML is a zoom lens, and in which the exit pupil therefore moves along the optical axis AX during zooming, it is preferable to balance the exit pupil position in the shortest focal length condition [W] with that in the longest focal length condition [T]. Accordingly, in the ninth embodiment, it is preferable that condition (9) below be satisfied additionally: ##EQU10## 
     where 
     φC represents the optical power of the condenser lens CL; 
     φW represents the optical power of the taking optical system when it is in the shortest focal length condition [W]; and 
     φT represents the optical power of the taking optical system when it is in the longest focal length condition [T]. 
     Condition (9) defines the relation between the optical power of the condenser lens CL and the zoom ratio (φW/φT) of the taking optical system. When condition (9) is satisfied, it is possible to balance the exit pupil position Pb in the shortest focal length condition [W] with that in the longest focal length condition [T]. If the lower limit of condition (9) is exceeded, the refractive power of the condenser lens CL is too weak relative to the zoom ratio, with the result that the exit pupil cannot be shifted far enough in the longest focal length condition [T] or in the shortest focal length condition [W]. If the upper limit of condition (9) is exceeded, the refractive power of the condenser lens CL is too strong relative to the zoom ratio, with the result that the exit pupil is shifted too far, i.e. past infinity, causing an off-axial light beam 3 to enter the microlenses 2 in a way as illustrated in FIG. 16C. In this case, since the off-axial light beam 3 enters the microlenses from a direction that is not perpendicular to the light-receiving surfaces of the light-sensing devices, the light-condensing ability of the microlenses is impaired. 
     FIGS. 16A to 16C show how an off-axial light beam 3 that has exited from the taking optical system strikes a solid-state image device (such as a CCD) 1 having microlenses 2 disposed on its light-receiving surface. FIG. 16A illustrates the path the off-axial light beam 3 takes when the condenser lens CL is not provided; FIG. 16B illustrates the ideal path the off-axial light beam 3 takes when the condenser lens CL is provided; FIG. 16C illustrates the path the off-axial light beam 3 takes when the condenser lens CL has excessively strong optical power φC. 
     Tables 1 to 7 list the construction data of the taking optical systems of the first to seventh embodiments (FIGS. 1, 3, 5, 7, 9, 11 and 13), respectively. 
     In the construction data of all of the embodiments, the following symbols are used: ri (i=1, 2, 3, . . . ) represents the radius of curvature of the i-th surface from the object side; di (i=1, 2, 3, . . . ) represents the i-th axial distance from the object side; Ni (i=1, 2, 3, . . . ) and νi (i=1, 2, 3, . . . ) respectively represent the refractive index (Nd) and Abbe number (νd) for d-lines of the i-th lens element from the object side; f and FNO respectively represent the focal length and f-number of the entire optical system. Note that, for those axial distances which vary with zooming (variable distances), and for the focal length f and f-number FNO of the entire optical system, three values are listed together which are, from the left, the value in the shortest focal length condition [W], the value in the middle focal length condition [M], and the value in the longest focal length condition [T]. 
     Moreover, in the construction data of all of the embodiments, a surface marked with an asterisk (*) in its radius-of-curvature column is an a spherical surface, whose surface curve is defined by formula (AS) below: ##EQU11## 
     where 
     X represents the displacement from the reference surface of the X-axis direction; 
     Y represents the height in a direction perpendicular to the optical axis; 
     C represents the paraxial curvature; 
     ε represents the quadric surface parameter; and 
     Ai represents the aspherical coefficient of the i-th order. 
     Table 8 lists the values corresponding to conditions (1) to (3) in the first and second embodiments. Note that, for the second embodiment, in which the master optical system ML is a zoom lens, the values as observed in the shortest focal length condition [W] are listed. In practice, the distances a and b and the optical power φM vary with zooming. However, since the zoom lens of the second embodiment is of the type in which the aperture diaphragm S moves monotonically toward the object side during zooming from the shortest focal length condition [W] to the longest focal length condition [T], conditions (1) to (3) are most difficult to comply with in the shortest focal length condition [W]. In other words, in the second embodiment, if conditions (1) to (3) are satisfied in the shortest focal length condition [W], they are satisfied over the entire zoom range. 
     Table 9 lists the values corresponding to conditions (4) to (6) in the third to fifth embodiments. Note that, for the fourth and fifth embodiments, in which the master optical system ML is a zoom lens, the values as observed in the shortest focal length condition [W] are listed. In practice, the distances a, b, and LB vary with zooming. However, since the zoom lenses of the fourth and fifth embodiments are of the type in which the aperture diaphragm S moves monotonically toward the object side during zooming from the shortest focal length condition [W] to the longest focal length condition [T], conditions (4) to (6) are most difficult to comply with in the shortest focal length condition [W]. In other words, in the fourth and fifth embodiments, if conditions (4) to (6) are satisfied in the shortest focal length condition [W], they are satisfied over the entire zoom range. Note that the distance a is shortest in the shortest focal length condition [W] throughout the entire zoom range, and the distance a in that condition is represented as a min . 
     Table 10 lists the values corresponding to conditions (7) to (9) in the sixth and seventh embodiments. Note that, for the seventh embodiment, in which the master optical system ML is a zoom lens, the values as observed in the shortest focal length condition [W] are listed. In practice, the distances a and b vary with zooming. However, since the zoom lens of the seventh embodiment is of the type in which the aperture diaphragm S moves monotonically toward the object side during zooming from the shortest focal length condition [W] to the longest focal length condition [T], conditions (7) to (9) are most difficult to comply with in the shortest focal length condition [W]. In other words, in the seventh embodiment, if conditions (7) to (9) are satisfied in the shortest focal length condition [W], they are satisfied over the entire zoom range. 
     FIGS. 2A to 2C, 4A to 4I, 6A to 6C, 8A to 8I, 10A to 10I, 12A to 12C, and 14A to 14I show the aberrations observed in the first to seventh embodiments, respectively. For the embodiments which are constructed as a zoom lens, the aberrations as observed in three different focal length conditions are separately shown. Specifically, for the second, fourth, fifth, and seventh embodiments, FIGS. 4A to 4C, 8A to 8C, 10A to 10C, and 14A to 14C illustrate the aberrations appearing in the shortest focal length condition [W], FIGS. 4D to 4F, 8D to 8F, 10D to 10F, and 14D to 14F illustrate the aberrations appearing in the middle focal length condition [M], and FIGS. 4G to 4I, 8G to 8I, 10G to 10I, and 14G to 14I illustrate the aberrations appearing in the longest focal length condition [T]. In all of these aberration diagrams, a solid line (d) represents the aberration for d-lines, a broken line (SC) represents the sine condition, and a broken line (DM) and a solid line (DS) represent the astigmatism on the meridional and sagittal planes, respectively. 
     As described above, according to the present invention, it is possible to place the exit pupil of a taking optical system far away from the image surface even when the taking optical system is made more compact. Accordingly, it is possible to realize a taking optical system that has a relatively short overall length despite having its exit pupil substantially at infinity. By use of such a taking optical system, it is possible to prevent images shot by a solid-state image device from becoming dimmer at their peripheral portion than at their central portion, that is, it is possible to obtain uniform brightness in such images. 
     
                       TABLE 1______________________________________&lt;&lt; Embodiment 1 &gt;&gt;f = 6.2FNO = 4.5Radius of  Axial     Refractive AbbeCurvature  Distance  Index      Number______________________________________r1 =    3.220          d1 =   0.800                      N1 = 1.79952                               ν1 = 42.24r2 =   23.087          d2 =   0.100r3 =    2.476          d3 =   0.400                      N2 = 1.77250                               ν2 = 49.62r4 =    2.961          d4 =   0.250r5 =   15.216          d5 =   0.150                      N3 = 1.80518                               ν3 = 25.43r6 =    1.868          d6 =   0.500r7 = ∞ (ApertureDiaphragmS)          d7 =   0.700r8 =  -1.515          d8 =   0.250                      N4 = 1.58340                               ν4 = 30.23r9 =  -1.665          d9 =   0.100r10 =  13.547          d10 =  0.650                      N5 = 1.69680                               ν5 = 55.53r11 = -4.548          d11 =  0.500r12 =∞          d12 =  3.600                      N6 = 1.51680                               ν6 = 64.20 . . . LPr13 =∞          d13 =  0.200r14 =∞          d14 =  0.800                      N7 = 1.75450                               ν7 = 51.57 . . . CLr15 =-10.870______________________________________ 
    
     
                       TABLE 2______________________________________&lt;&lt; Embodiment 2 &gt;&gt;f = 8.2 ˜ 15.0 ˜ 27.0FNO = 4.1 ˜ 6.1 ˜ 8.24Radius of Axial       Refractive AbbeCurvature Distance    Index      Number______________________________________r1 =  -47.224         d1 =    0.500 N1 = 1.80100                                ν1 =                                     46.54r2 =   5.757         d2 =    0.700r3 =   6.528         d3 =    1.450 N2 = 1.83350                                ν2 =                                     21.00r4 =   14.092         d4 =    7.139 ˜                 4.470 ˜                 1.735r5* =  3.715         d5 =    1.250 N3 = 1.57885                                ν3 =                                     69.57r6* = -63.854         d6 =    0.100r7 =  308.501         d7 =    0.981 N4 = 1.84666                                ν4 =                                     23.82r8 =   4.385         d8 =    0.435r9 =   8.637         d9 =    1.095 N5 = 1.65446                                ν5 =                                     33.86r10 =  -7.370         d10 =   0.569r11 = ∞ (Ap- erture Dia- phragm S)         d11 =   3.351 ˜                 1.809 ˜                 1.784r12* = -18.214         d12 =   1.000 N6 = 1.58340                                ν6 =                                     30.23r13 =  -6.471         d13 =   1.000r14 =  -3.812         d14 =   0.310 N7 = 1.78831                                ν7 =                                     47.32r15 = -21.539         d15 =   0.200 ˜                 7.111 ˜                15.172r16 = ∞         d16 =   4.000 N8 = 1.51680                                ν8 =                                     64.20 . . .                                     LPr17 = ∞         d17 =   0.200r18 = ∞         d18 =   0.800 N9 = 1.77250                                ν9 =                                     49.77 . . .                                     CLr19 = -11.111______________________________________[Aspherical Coefficients]______________________________________     r5: ε =             1.0000     A4 =  -0.81615 × 10.sup.-3     A6 =    0.84500 × 10.sup.-4     A8 =  -0.77756 × 10.sup.-4     A10 =   0.13292 × 10.sup.-4     A12 = -0.12185 × 10.sup.-5     r6: ε =             1.0000     A4 =    0.18470 × 10.sup.-2     A6 =  -0.10277 × 10.sup.-4     A8 =  -0.47766 × 10.sup.-4     A10 =   0.82440 × 10.sup.-5     A12 = -0.84956 × 10.sup.-6     r12: ε =             1.0000     A4 =    0.12450 × 10.sup.-2     A6 =  -0.17142 × 10.sup.-3     A8 =    0.58540 × 10.sup.-4     A10 = -0.64512 × 10.sup.-5     A12 =   0.35323 × 10.sup.-6______________________________________ 
    
     
                       TABLE 3______________________________________&lt;&lt; Embodiment 3 &gt;&gt;f = 6.2FNO = 3.5Radius of  Axial     Refractive AbbeCurvature  Distance  Index      Number______________________________________r1 =  9.168          d1 =   0.434                      N1 = 1.58313                               ν1 = 59.38r2* =221.093          d2 =   4.156r3 =  6.633          d3 =   1.427                      N2 = 1.78590                               ν2 = 44.19r4 = -28.421          d4 =   1.613r5 = ∞ (ApertureDiaphragmS)          d5 =   1.117r6 =  -4.272          d6 =   0.434                      N3 = 1.84666                               ν3 = 23.89r7 =  12.396          d7 =   0.124r8 = -81.560          d8 =   1.000                      N4 = 1.79952                               ν4 = 42.24r9 =  -4.425          d9 =   0.0r10 =121.374          d10 =  1.000                      N5 = 1.78590                               ν5 = 44.19r11 = -8.077          d11 =  2.000r12 =∞          d12 =  4.300                      N6 = 1.51680                               ν6 = 64.20 . . . LPr13 =∞          d13 =  2.000r14 =∞          d14 =  1.100                      N7 = 1.51680                               ν7 = 64.20 . . . CLr15 =-10.767______________________________________[Aspherical Coefficients]     r2: ε =           1.0000     A2 =  0.15479     A4 =  0.25578 × 10.sup.-2     A6 =  0.65957 × 10.sup.-4     A8 =  0.30586 × 10.sup.-5     A10 = 0.15978 × 10.sup.-6______________________________________ 
    
     
                       TABLE 4______________________________________&lt;&lt; Embodiment 4 &gt;&gt;f = 6.2 ˜ 9.7 ˜ 17.5FNO = 4.1 ˜ 4.9 ˜ 5.8Radius of Axial       Refractive AbbeCurvature Distance    Index      Number______________________________________r1 =  65.392         d1 =    1.000 N1 = 1.61293                                ν1 =                                     36.96r2 =  6.877         d2 =    3.000r3* = 29.403         d3 =    2.400 N2 = 1.84666                                ν2 =                                     23.82r4* =208.263         d4 =   27.096 ˜                12.747 ˜                 1.667r5 = ∞ (Aper-ture Dia-phragm S)         d5 =    1.800r6 =  4.249         d6 =    2.900 N3 = 1.61800                                ν3 =                                     63.39r7 =  50.171         d7 =    1.500r8* = -4.854         d8 =    1.000 N4 = 1.84666                                ν4 =                                     23.82r9* =-11.465         d9 =    3.000 ˜                 5.253 ˜                10.203r10 =∞         d10 =   4.300 N5 = 1.51680                                ν5 =                                     64.20 . . .                                     LPr11 =∞         d11 =   2.500r12 =∞         d12 =   1.200 N6 = 1.58913                                ν6 =                                     61.11 . . .                                     CLr13 =-14.286______________________________________[Aspherical Coefficients]______________________________________     r3: ε =             1.0000     A4 =  -0.19608 × 10.sup.-4     A6 =    0.21880 × 10.sup.-5     A8 =  -0.80228 × 10.sup.-8     A10 = -0.76205 × 10.sup.-9     A12 =   0.43686 × 10.sup.-11     r4: ε =             1.0000     A4 =  -0.15833 × 10.sup.-3     A6 =  -0.65843 × 10.sup.-6     A8 =    0.19636 × 10.sup.-7     A10 = -0.17223 × 10.sup.-8     A12 = -0.90220 × 10.sup.-11     r8: ε =             1.0000     A4 =    0.40439 × 10.sup.-2     A6 =    0.47048 × 10.sup.-4     A8 =    0.13896 × 10.sup.-5     A10 =   0.85541 × 10.sup.-9     A12 =   0.65927 × 10.sup.-11     r9: ε =             1.0000     A4 =    0.56004 × 10.sup.-2     A6 =    0.27703 × 10.sup.-3     A8 =    0.38550 × 10.sup.-5     A10 =   0.15857 × 10.sup.-8     A12 =   0.67739 × 10.sup.-11______________________________________ 
    
     
                       TABLE 5______________________________________&lt;&lt; Embodiment 5 &gt;&gt;f  = 4.1 ˜ 7.3 ˜ 14.1FNO = 4.1 ˜ 5.2 ˜ 5.7Radius of  Axial      Refractive AbbeCurvature  Distance   Index      Number______________________________________r1 =     20.833          d1 =   0.800  N1 = 1.84666                                 ν1 =                                     23.82r2 =     14.925          d2 =   2.700  N2 = 1.58913                                 ν2 =                                     61.11r3 =    186.013          d3 =   0.100r4 =     23.993          d4 =   1.700  N3 = 1.62280                                 ν3 =                                     56.88r5 =     68.710          d5 =   0.800 ˜                 2.143 ˜                 8.690r6* =    41.212          d6 =   0.800  N4 = 1.78831                                 ν4 =                                     47.32r7 =     2.719          d7 =   1.350r8 =   -20.759          d8 =   0.800  N5 = 1.78831                                 ν5 =                                     47.32r9 =     8.362          d9 =   0.050r10 =    5.009          d10 =  1.500  N6 = 1.75000                                 ν6 =                                     25.14r11 = -128.660          d11 =  0.050r12 =    82.283          d12 =  0.800  N7 = 1.80741                                 ν7 =                                     31.59r13 =    26.630          d13 =  4.358 ˜                 1.606 ˜                 0.350r14 = ∞ (Aper- ture Dia- phragm S)          d14 =  0.350r15 =    3.483          d15 =  2.200  N8 = 1.67790                                 ν8 =                                     55.38r16 =  -4.170          d16 =  0.150r17 =  -3.558          d17 =  0.800  N9 = 1.80518                                 ν9 =                                     25.43r18 =  -63.536          d18 =  0.100r19 =    13.447          d19 =  1.000 N10 = 1.58144                                ν10 =                                     40.89r20 =  -11.678          d20 =  0.250r21* =  -7.226          d21 =  1.150 N11 = 1.78831                                ν11 =                                     47.32r22 =  -18.720          d22 =  1.000 ˜                 3.852 ˜                 5.508r23 = ∞          d23 =  4.300 N12 = 1.51680                                ν12 =                                     64.20 . . .                                     LPr24 = ∞          d24 =  0.400r25 = ∞          d25 =  1.500 N13 = 1.51680                                ν13 =                                     64.20 . . .                                     CLr26 =  -7.521______________________________________[Aspherical Coefficients]______________________________________     r6: ε =             1.0000     A4 =  -0.14369 × 10.sup.-3     A6 =    0.19790 × 10.sup.-4     A8 =  -0.15019 × 10.sup.-6     A10 =   0.40488 × 10.sup.-8     A12 = -0.16614 × 10.sup.-8     r21: ε =             1.0000     A4 =  -0.74934 × 10.sup.-2     A6 =    0.18143 × 10.sup.-2     A8 =  -0.23089 × 10.sup.-2     A10 =   0.92684 × 10.sup.-3     A12 = -0.14570 × 10.sup.-3______________________________________ 
    
     
                       TABLE 6______________________________________&lt;&lt; Embodiment 6 &gt;&gt;f = 27.8FNO = 3.1Radius of  Axial     Refractive AbbeCurvature  Distance  Index      Number______________________________________r1 =    13.591          d1 =   1.300                       N1 = 1.49310                                ν1 = 83.58r2 = -207.339          d2 =   0.100r3 =    8.737          d3 =   1.400                       N2 = 1.49310                                ν2 = 83.58r4 =    34.207          d4 =   0.100r5 =    7.341          d5 =   1.100                       N3 = 1.72000                                ν3 = 52.14r6 =    15.351          d6 =   0.300r7 =    23.959          d7 =   0.800                       N4 = 1.72100                                ν4 = 33.40r8 =    4.826          d8 =   2.000r9 = ∞ (ApertureDiaphragmS)          d9 =   1.900r10 =   59.048          d10 =  1.100                       N5 = 1.75520                                ν5 = 27.51r11 = -12.134          d11 =  0.450                       N6 = 1.72000                                ν6 = 50.31r12 =   11.119          d12 =  1.000r13 =   16.168          d13 =  0.450                       N7 = 1.58144                                ν7 = 40.89r14 =   7.363          d14 =  5.000r15 =   9.974          d15 =  1.100                       N8 = 1.48749                                ν8 = 70.44r16 = -35.920          d16 =  2.000r17 =∞          d17 =  4.300                       N9 = 1.51680                                ν9 = 64.20 . . . LPr18 =∞          d18 =  0.200r19 =∞          d19 =  0.800                      N10 = 1.75450                               ν10 = 51.57 . . . CLr20 = -33.333______________________________________ 
    
     
                       TABLE 7______________________________________&lt;&lt; Embodiment 7 &gt;&gt;f = 6.9 ˜ 16.0 ˜ 41.6FNO = 4.6 ˜ 5.5 ˜ 5.8Radius of Axial       Refractive AbbeCurvature Distance    Index      Number______________________________________ r1 =    33.615     d1 =    0.400    N1 = 1.84666                              ν1 =                                   23.82 r2 =    14.109     d2 =    1.840    N2 = 1.61720                              ν2 =                                   54.00 r3 =  -59.729     d3 =    0.050 r4 =    10.291     d4 =    1.200    N3 = 1.62280                              ν3 =                                   56.88 r5 =    25.185     d5 =    0.550 ˜             5.665 ˜             9.859 r6* =    25.185     d6 =    0.300    N4 = 1.75450                              ν4 =                                   51.57 r7 =    2.603     d7 =    1.100 r8 =  -12.769     d8 =    0.240    N5 = 1.75450                              ν5 =                                   51.57 r9 =    9.194     d9 =    0.040 r10 =    4.737     d10 =   1.050    N6 = 1.83350                              ν6 =                                   21.00 r11 = -163.921     d11 =   0.400 r12 =  -5.633     d12 =   0.250    N7 = 1.69680                              ν7 =                                   56.47 r13 =    73.561     d13 =   2.537 ˜             1.547 ˜             0.350 r14 = ∞ (Aper-   ture Dia-   phragm   S)     d14 =   1.100 r15 =    5.230     d15 =   1.700    N8 = 1.51823                              ν8 =                                   58.96 r16 =  -20.825     d16 =   0.050 r17 =    5.598     d17 =   1.850    N9 = 1.51742                              ν9 =                                   52.15 r18 =  -8.354     d18 =   0.450 r19 =  -4.499     d19 =   0.300   N10 = 1.84666                              ν10 =                                   23.82 r20 =    27.274     d20 =   1.200 ˜             0.610 ˜             0.370 r21 =    5.444     d21 =   2.050   N11 = 1.51742                              ν11 =                                   52.15 r22 =  -4.493     d22 =   0.650r23* =  -6.624     d23 =   0.300   N12 = 1.80100                              ν12 =                                   46.54r24* =    6.830     d24 =   0.300 r25 =    4.576     d25 =   1.150   N13 = 1.59270                              ν13 =                                   35.45 r26 =    50.278     d26 =   3.300 ˜             7.680 ˜            10.447 r27 = ∞     d27 =   4.300   N14 = 1.51680                              ν14 =                                   64.20 . . .                                   LP r28 = ∞     d28 =   3.200 r29 = ∞     d29 =   1.000   N15 = 1.51680                              ν15 =                                   64.20 . . .                                   CL r30 =  -15.385______________________________________[Aspherical Coefficients]______________________________________     r6: ε =             1.0000     A4 =    0.24608 × 10.sup.-3     A6 =    0.15327 × 10.sup.-3     A8 =  -0.49879 × 10.sup.-4     A10 =   0.61788 × 10.sup.-5     A12 = -0.27828 × 10.sup.-6     r23: ε =             1.0000     A4 =  -0.59350 × 10.sup.-2     A6 =    0.40581 × 10.sup.-3     A8 =  -0.21348 × 10.sup.-3     A10 =   0.50637 × 10.sup.-5     A12 =   0.17793 × 10.sup.-5     r24: ε =             1.0000     A4 =    0.21671 × 10.sup.-3     A6 =    0.60883 × 10.sup.-3     A8 =  -0.95912 × 10.sup.-4     A10 = -0.14691 × 10.sup.-5     A12 =   0.10474 × 10.sup.-5______________________________________ 
    
     
                       TABLE 8______________________________________&lt;&lt; Actual Values of Conditions (1), (2), and (3) &gt;&gt;   Cond. (1): Cond. (2):                       Cond. (3):   a/Y&#39;       |b/a|                       φC/φM______________________________________Emb. 1    2.42         1.90     0.438Emb. 2 [W]     2.73         1.77     0.591______________________________________ 
    
     
                       TABLE 9______________________________________&lt;&lt; Actual Values of Conditions (4), (5), and (6) &gt;&gt;   Cond. (4): Cond. (5):                       Cond. (6):   |b/a|              Y&#39;/LB    φC · a.sub.min______________________________________Emb. 3    1.99         0.360    0.687Emb. 4 [W]     1.88         0.303    0.659Emb. 5 [W]     2.96         0.469    0.887______________________________________ 
    
     
                       TABLE 10______________________________________&lt;&lt; Actual Values of Conditions (7), (8), and (9) &gt;&gt;  Cond. (7): Cond. (8):                      Cond. (9):  a/Y&#39;       |b/a|                      φC · φW/φT______________________________________Emb. 6   7.03         1.74     --Emb. 7   [W]7.00      [W]2.40  0.203______________________________________