Image pickup apparatus and zoom lens

Abstract

An image pickup apparatus having a plurality of image pickup modes and a zoom lens for use with the image pickup apparatus is configured such that, even if the dimension of an effective screen region of an image pickup element changes as a result of changeover of the image pickup mode, the change of the angle of view is moderated and good aberration correction can be achieved in any of the image pickup modes. In an image pickup apparatus ( 1 ), an additional lens set (G 5 ) having a positive refractive power is positioned most adjacent the image side with respect to a zoom lens ( 2 ) for movement to and from a position on an optical axis of the zoom lens. Upon changeover of an image pickup mode, the additional lens set is moved to or away from the position on the optical axis to reduce or extend the focal length range of the zoom lens thereby to moderate the variation of the angle of view caused by a difference in dimension of the effective screen region of an image pickup element ( 12 ) when any different image pickup mode is selected. Further, the movement of the additional lens set to or from the position on the optical axis is detected to set the states of components in accordance with any image pickup mode.

1 - 8 . (canceled)  
   
   
       9 . An image pickup apparatus which includes a zoom lens and an image pickup element and has a first image pickup mode and a second image pickup mode which can be arbitrarily selected upon image pickup by said image pickup apparatus, said image pickup apparatus being configured such that, when the first image pickup mode is selected, an image pickup plane of said image pickup element is used over a range as great as possible as an effective screen region and individual information obtained from each of pixels of said image pickup element is extracted as information of one pixel to form an image, but when the second image pickup mode is selected, said image pickup plane of said image pickup element is used over a smaller range than that when the first image pickup mode is selected as an effective screen region and information obtained by mixing information obtained from each plurality of adjacent ones of the pixels of said image pickup element is extracted as information of one pixel to form an image having a pixel pitch rougher than that of the image obtained in the first image pickup mode, characterized in that 
 a normally fixed optical low pass filter is disposed on an optical axis between said zoom lens and said image pickup element, that    said zoom lens includes, at a position nearest to the image side, an additional lens set having a positive refractive index and provided for movement to and from a position on the optical axis and a movable optical low pass filter mounted for integral movement with said additional lens set, that    said additional lens set and said movable optical low pass filter are moved, in response to changeover from the first image pickup mode to the second image pickup mode, to the respective positions position on the optical axis to shift a focal length range of said zoom lens to the shorter side and provide a low pass effect corresponding to the rougher pixel pitch but are moved, in response to changeover from the second image pickup mode to the first image pickup mode, from the respective positions on the optical axis to shift the focal length range to the longer side thereby to moderate a variation of an angle of view which is caused by a difference in dimension of the effective screen region of said image pickup element when the first image pickup mode is selected and when the second image pickup mode is selected and provide a low pass effect corresponding to the finer pixel pitch, and that    states of pertaining components of said image pickup apparatus are set in conformity with the first image pickup mode or the second image pickup mode in response to detection of the movement of said additional lens set and said movable optical low pass filter to or from the respective positions on the optical axis.    
   
   
       10 . An image pickup apparatus according to  claim 9 , characterized in that 
 said zoom lens further includes a plurality of fixed lens sets each having a normally fixed position and a movable lens set having a movable position, and that    said fixed lens sets and said image pickup element are retained integrally on a fixed lens barrel such that the positional relationship between said fixed lens sets and said image pickup element is fixed so as to keep an image forming position fixed irrespective of whether said additional lens set and said movable optical low pass filter are positioned on the optical axis or moved from the optical axis.    
   
   
       11 . An image pickup apparatus according to  claim 9 , characterized in that 
 said zoom lens includes, in order from the object side, a first lens set having a positive refractive index and having a normally fixed position, a second lens set having a negative refractive index and movable along the optical axis to principally perform power variation, a third lens set having a positive refractive index and having a normally fixed position, a fourth lens set having a positive refractive index and movable along the optical axis to perform correction of a variation of the image position and focusing, said additional lens set having a positive refractive index, and said movable optical low pass filter, that    said first lens set includes, in order from the object side, a cemented lens of a first lens in the form of a concave meniscus lens having a convex face directed to the object side and a second lens in the form of a convex lens, and a third lens in the form of a convex meniscus lens having a convex face directed to the object side, that    said second lens set includes, in order from the object side, a cemented lens of a fourth lens in the form of a concave lens, a fifth lens in the form of a biconcave lens and a sixth lens in the form of a convex lens, that    said third lens set includes a seventh lens in the form of a biconvex lens having faces at least one of which is an aspheric face, that    said fourth lens set includes, in order from the object side, a three-element cemented lens of an eighth lens in the form of a convex lens, a ninth lens in the form of a concave lens and a tenth lens in the form of a convex lens, and at least one of a face of said fourth lens set most adjacent the object side and a face of said fourth lens set most adjacent the image side is formed as an aspheric face, that    said additional lens set includes, in order from the object side, a cemented lens of a biconvex lens whose face on the object side is formed as an aspheric face and a biconcave lens, that    said movable optical low pass filter is held integrally with said additional lens set on the image side with respect to said additional lens set for movement to and from the position on the optical axis, that    said additional lens set and said movable optical low pass filter shift the focal length range of said zoom lens between when said additional lens set and said movable optical low pass filter are positioned on the optical axis and when said additional lens set and said movable optical low pass filter are positioned outside the optical axis, and that    said image pickup apparatus satisfies conditions of      0.7<Σ5 /fw 2<2.5  0.11< fw 2·( n 52− n 51)/ r 52<−0.085  0.003<Δ5/ fw 2<0.01  2.5< f 4/ fw 2<5    where Σ5 is the total thickness of said additional lens set, fw2 the focal length at the wide angle end of the lens system including said first to fourth lens sets and said additional lens set, n51 the refractive index of the biconvex lens of said additional lens set on a “d” line, n52 the refractive index of said biconcave lens of said additional lens set on the “d” line, r52 the radius of curvature of the interface of said additional lens set, and ΔA5 the amount of deformation of the aspheric face of said additional lens set from a generating face at a position of an effective radius (the deformation amount is in the positive where the deformation amount is provided on the image side), and f4 the focal length of said fourth lens set.    
   
   
       12 . A zoom lens which includes, in order from the object side, a first lens set having a positive refractive index and having a normally fixed position, a second lens set having a negative refractive index and movable along an optical axis to principally perform power variation, a third lens set having a positive refractive index and having a normally fixed position, a fourth lens set having a positive refractive index and movable along the optical axis to perform correction of a variation of the image position and focusing, an additional lens set having a positive refractive index, and a movable optical low pass filter, characterized in that 
 said first lens set includes, in order from the object side, a cemented lens of a first lens in the form of a concave meniscus lens having a convex face directed to the object side and a second lens in the form of a convex lens, and a third lens in the form of a convex meniscus lens having a convex face directed to the object side, that    said second lens set includes, in order from the object side, a cemented lens of a fourth lens in the form of a concave lens, a fifth lens in the form of a biconcave lens and a sixth lens in the form of a convex lens, that    said third lens set includes a seventh lens in the form of a biconvex lens having faces at least one of which is an aspheric face, that    said fourth lens set includes, in order from the object side, a three-element cemented lens of an eighth lens in the form of a convex lens, a ninth lens in the form of a concave lens and a tenth lens in the form of a convex lens, and at least one of a face of said fourth lens set most adjacent the object side and a face of said fourth lens set most adjacent the image side is formed as an aspheric face, that    said additional lens set includes, in order from the object side, a cemented lens of a biconvex lens whose face on the object side is formed as an aspheric face and a biconcave lens, that    said movable optical low pass filter is held integrally with said additional lens set on the image side with respect to said additional lens set for movement to and from the position on the optical axis, that    said additional lens set and said movable optical low pass filter shift the focal length range of said zoom lens between when said additional lens set and said movable optical low pass filter are positioned on the optical axis and when said additional lens set and said movable optical low pass filter are positioned outside the optical axis, and that    said zoom lens satisfies conditions of      0.7<Σ5 /fw 2<2.5  0.11< fw 2·( n 52− n 51)/ r 52<−0.085  0.003<Δ5/ fw 2<0.01  2.5< f 4/ fw 2<5    where Σ5 is the total thickness of said additional lens set, fw2 the focal length at the wide angle end of the lens system including said first to fourth lens sets and said additional lens set, n51 the refractive index of the biconvex lens of said additional lens set on a “d” line, n52 the refractive index of said biconcave lens of said additional lens set on the “d” line, r52 the radius of curvature of the interface of said additional lens set, and Δ5 the amount of deformation of the aspheric face of said additional lens set from a generating face at a position of an effective radius (the deformation amount is in the positive where the deformation amount is provided on the image side), and f4 the focal length of said fourth lens set.