Low Distortion Lens Using Double Plane Symmetric Element

Abstract

A low distortion lens suited for a wide variety of applications uses a double plane symmetry lens as part of a lens system to permit aberration correction to be optimized in the field of view of an associated sensor. Wide angle, Kepler telescopic and Galileo telescopic designs can be implemented. The design can be implemented using existing manufacturing techniques.

1 . A lens system having a different effective focal length in an X axis than in a Y axis comprising:
 a plurality of lens elements, configured in at least two groups and to have an image plane,   at least one of the lens elements having double plane symmetry in an optically active region wherein the effective focal length in the X axis is different than the effective focal length in the Y axis, and   wherein the respective X and Y effective focal lengths are configured to substantially match a ratio calculated from X and Y dimensions of a rectangular sensor positioned at the image plane.   
     
     
         2 . A lens system for creating an oval image at an image plane comprising:
 a plurality of lens elements configured for projecting an image having a oval shape onto an image plane, the lens elements comprising at least first and second groups, the first group being nearer an object plane and the second group nearer an image plane,   at least one of the groups configured to length that varics across provide a plurality of zones of different effective focal lengths whereby the effective focal length changes depending on the location with the field of view on a sensor.   
     
     
         3 . The lens system of  claim 2  wherein the relation defining the change in effective focal lengths is linear. 
     
     
         4 . The lens system of  claim 2  where the relation defining the change in effective focal length is a polynomial. 
     
     
         5 . The lens system of  claim 2  wherein the relation defining the change in effective focal length is an equation. 
     
     
         6 . The lens system of  claim 2  wherein the relation defining the change in effective focal length varies with the distance of a coordinate from the optical center of the image plane. 
     
     
         7 . The lens system of  claim 1  wherein the lens element having double plane symmetry in an optically active region has an effective focal length along the X axis that changes at a different rate such that lines parallel to the X axis in the object plane remain substantially straight in the image plane. 
     
     
         8 . The lens system of  claim 1  wherein the lens element having double plane symmetry has an effective focal length along the Y axis that changes at a different rate such that lines parallel to the Y axis in the object plane remain substantially straight in the image plane. 
     
     
         9 . A lens system for creating an image at an image plane having X and Y axes with reduced perspective aberration, the lens system having a different effective focal length in the X axis than in the Y axis and comprising:
 a plurality of lens elements configured as a wide angle lens for projecting an image having a shape onto an image plane, the lens elements comprising first and second groups, the first group being nearer an object plane and the second group nearer an image plane,   the second group comprising a lens element having double plane symmetry in the optically active region and positioned nearest the image plane,   the effective focal length of the lens system along the X axis being different than the effective focal length of the lens system along the Y axis such that an image projected at the image plane is not defined by the center of a circle.   
     
     
         10 . The lens system of  claim 9  further comprising at least one free form lens element in addition to the double symmetry lens element. 
     
     
         11 . The lens system of  claim 1  wherein total track is less than forty millimeters. 
     
     
         12 . The lens system of  claim 9  wherein total track is less than forty millimeters. 
     
     
         13 . The lens system of  claim 1  wherein the lens elements having double plane symmetry is not the last element. 
     
     
         14 . The lens system of  claim 1  wherein the X and Y effective focal lengths are configured to substantially optimize the modulation transfer function of the lens system at the corners of the sensor. 
     
     
         15 . The lens system of  claim 1  wherein the lens system is a wide angle lens. 
     
     
         16 . The lens system of  claim 2  wherein the at least one of the groups is configured to reduce perspective aberration. 
     
     
         17 . The lens system of  claim 2  wherein the shape of the projected image is defined by an axis. 
     
     
         18 . The lens system of  claim 2  wherein at least one of the lens elements is a double symmetry lens element. 
     
     
         19 . The lens system of  claim 9  wherein the rate of change of effective focal length along the X axis is different from rate of change of the effective focal length along the Y axis whereby perspective aberration is reduced.