Aspherical blur filter for reducing artifacts in imaging apparatus

Claim 1

An electronic imaging apparatus for producing an image signal representing the image of an object disposed on an optical axis, said apparatus comprising: (a) an image sensor located at a fixed position along said optical axis, said sensor comprising a two-dimensional array of photosites and being adapted to produce said image signal representing the image of said object projected onto said photosites; (b) a zoom lens located at a fixed position along said optical axis, said zoom lens having a plurality of focal lengths and being adapted to project said image of said object onto said photosites; and (c) a blur filter located at a fixed position along said optical axis for limiting high spatial frequency image information in the projected image to reduce undersampling artifacts, said blur filter comprising a transparent optical element having an aspherical surface defined by the equation, δ=rS/(ψW(n-1)), where δ is the slope angle, measured from a line perpendicular to the optical axis, at each point on the aspherical surface; r is the radius, measured from the optical axis, at which the slope angle of each of said points is measured; ψ is the distance between the zoom lens and the aspherical surface measured along the optical axis; W is the maximum dimension of the photosite array measured in a direction perpendicular to the optical axis; and n is the refractive index of said transparent optical element, so as to produce, on the photosites, a blur disc pattern for each point source of said object, wherein said blur disc pattern has a substantially constant radius for each of said plurality of focal lengths of said zoom lens.