Imaging system

Abstract

The invention relates to an imaging system in which, while high image quality is maintained with the influence of diffraction minimized, the quantity of light is controlled, and which enables the length of the zoom lens to be cut down. The imaging system comprises a zoom lens comprising a plurality of lens groups G 1 and G 2 wherein the spacing between individual lens groups is varied to vary a focal length and an aperture stop located in an optical path for limiting at least an axial light beam diameter, and an electronic image pickup device I located on the image side of the zoom lens. The aperture stop has a fixed shape, and a filter S 2 for performing light quantity control by varying transmittance is located on an optical axis of a space located at a position different from that of a space in which the aperture stop is located.

1 . An imaging system comprising a zoom lens comprising a plurality of lens groups and an aperture stop located in an optical path for limiting at least an axial light beam diameter, and an electronic image pickup device located on an image side of the zoom lens, wherein:
 said zoom lens comprises at least a first lens group having negative refracting power, and a second lens group having positive refracting power and located just after the first lens;   a spacing between the first lens group having negative refracting power and the second lens group having positive refracting power becomes narrower at a telephoto end than at a wide-angle end of said zoom lens;   said aperture stop has a fixed shape;   said aperture stop is located between an image-side surface in the first lens group having negative refracting power and an object-side surface in the second lens group having positive refracting power;   said aperture stop is such that a position where a perpendicular going from said aperture stop down to the optical axis intersects the optical axis is found within a lens medium in the lens groups;   when said focal length is varied, said aperture stop moves together with the positive lens group;   said aperture stop and said lens group of positive refracting power are positioned more on the object side at the telephoto end than at the wide-angle end;   a filter for implementing light quantity control by varying transmittance is located on the optical axis; and   said filter for implementing light quantity control is located on an image plane side with respect to said lens group of positive refracting power.   
   
   
       2 . The imaging system according to  claim 1 , wherein said light quantity control filter comprises at least one transmitting surface wherein a central portion thereof has a transmittance higher than that of a marginal portion thereof. 
   
   
       3 . The imaging system according to  claim 1 , wherein said light quantity control filter is tiltable with respect to the optical axis. 
   
   
       4 . The imaging system according to  claim 1 , wherein said aperture stop is located in contact with the object-side surface in the second lens group. 
   
   
       5 . The imaging system according to  claim 1 , wherein said aperture stop is formed of an aperture plate having an aperture on an optical axis side. 
   
   
       6 . The imaging system according to  claim 1 , wherein said first lens group having negative refracting power is located nearest to the object side of the zoom lens. 
   
   
       7 . The imaging system according to  claim 1 , wherein said zoom lens comprises, in order from the object side thereof, the first lens group having negative refracting power and the second lens group having positive refracting power, wherein lens groups movable for zooming are defined by only two lens groups: the first lens group having negative refracting power and the second lens group having positive refracting power. 
   
   
       8 . The imaging system according to  claim 1 , wherein said plurality of lens groups consist of, in order from the object side thereof, only two lens groups: the first lens group having negative refracting power and the second lens group having positive refracting power. 
   
   
       9 . The imaging system according to  claim 1 , wherein said light quantity control filter is located in an air space just after the second lens group having positive refracting power, and when the focal length is varied, said light quantity control filter moves together with the second lens group. 
   
   
       10 . The imaging system according to  claim 1 , wherein the aperture stop is located in a variable space, both lens surfaces just before and just after the aperture stop are concave on image sides thereof, and the aperture stop has a funnel-form outside shape concave on the image side off and off an optical axis. 
   
   
       11 . The imaging system according to  claim 1 , wherein said light quantity filter can be inserted in or de-inserted from an optical path. 
   
   
       12 . The imaging system according to  claim 11 , wherein, upon retracting from an optical axis, said light quantity control filter fluctuates in such a direction that a filter surface comes close to the optical axis. 
   
   
       13 . An imaging system comprising a zoom lens comprising a plurality of lens groups and an aperture stop located in an optical path for limiting at least an axial light beam diameter, and an electronic image pickup device located on an image side of the zoom lens, wherein:
 said zoom lens comprises at least a first lens group having negative refracting power, and a second lens group having positive refracting power and located just after the first lens;   a spacing between the first lens group having negative refracting power and the second lens group having positive refracting power becomes narrower at the telephoto end than at a wide-angle end of said zoom lens;   said aperture has a fixed shape;   said aperture stop is located between an image-side surface in the first lens group having negative refracting power and an object-side surface in the second lens group having positive refracting power;   said aperture stop is such that a position where a perpendicular going from said aperture stop down to the optical axis intersects the optical axis is found within a lens medium in the lens group;   when said focal length is varied, said aperture stop moves together with the positive lens group;   said aperture stop and said lens group of positive refracting power are positioned more on the object side at the telephoto end than at the wide-angle end;   a shutter is located in the optical axis; and   said shutter is located on an image plane side with respect to said lens group of positive refracting power.   
   
   
       14 . The imaging system according to  claim 13 , wherein said aperture stop is located in contact with the object-side surface in the second lens groups. 
   
   
       15 . The imaging system according to  claim 13 , wherein said aperture stop is formed of an aperture plate having an aperture on an optical axis side. 
   
   
       16 . The imaging system according to  claim 13 , wherein said first lens group having negative refracting power is located nearest to the object side of the zoom lens. 
   
   
       17 . The imaging system according to  claim 13 , wherein said zoom lens comprises, in order from the object side thereof, the first lens group having negative refracting power and the second lens group having positive refracting power, wherein lens groups movable for zooming are defined by only two lens groups: the first lens group having negative refracting power and the second lens group having positive refracting power. 
   
   
       18 . The imaging system according to  claim 13 , wherein said plurality of lens groups consists of, in order from the object side thereof, only two lens groups: the first lens group having negative refracting power and the second lens group having positive refracting power. 
   
   
       19 . The imaging system according to  claim 13 , wherein said aperture stop is located in an air space just before the lens group having positive refracting power. 
   
   
       20 . The imaging system according to  claim 13 , wherein said shutter is located in an air space just after the second lens group having positive refracting power, and wherein when the focal length is varied, said shutter moves with the second lens group. 
   
   
       21 . The imaging system according to  claim 13 , wherein said aperture stop is located in a variable space, both lens surfaces just before and just after the aperture stop are concave on images sides thereof, and said aperture stop has a funnel-form outside shape concave on the image side.