1. A scanning mechanism for scanning an image onto a detector array, comprising in combination: a first prism having a first wedge angle and a first index of refraction; a second prism having a second wedge angle and a second index of refraction and positioned behind said first prism; said second prism being tilted with respect to the axis of the detector array by a predetermined tilt angle; the tilt angle of said second prism and the indices of refraction and the wedge angles of each said prisms being selected to produce an elliptical pattern having a substantially flat configuration with two parallel lines which remain substantially parallel over the majority of the length of said elliptical pattern; the detector array including a column of stacked detector elements of uniform height with each detector element being spaced apart from one another by a distance equal to the height of the detector elements; said parallel lines of said elliptical pattern being separated by a distance equal to the height of the detector elements; and means for counterrotating said prisms whereby the image is scanned in an elliptical pattern onto the detector array by a 2:1 interlacing technique.