<title>Versatile anamorphic electronic fingerprinting: design and manufacturing considerations</title>

Abstract

Many electronic fingerprinting devices are required to have a distortion-free high-contrast imaging capability, with diffraction-limited resolution. That is, no software correction of image distortion is allowed, and all fingerprint scaling correction must be accomplished with optical components. For such systems, a minimum of four key requirements must be satisfied simultaneously in the optical design: (1) Total internal reflection (TIR) at the fingerprinting surface; (2) Optical compensation for producing zero distortion; (3) Variable anamorphic scaling capability in two axes for producing correct image sizing; (4) Diffraction-limited imagery across the entire field of view. In the mechanical design for manufacture and assembly of the imaging system, generally a number of mechanical implementations are needed to provide for each of alignment. Thus a strong interaction between the optical designer, the mechanical engineer, and the marketing company which dictates the system specification is essential all throughout the design process. In this paper we present several optical design principles involved with electronic fingerprinting. A discussion of the Scheimpflug condition, its attendant keystone distortion, tilted object and image planes to assist the correction of distortion, tilted lens elements to assist in the correction of defocus, and variable anamorphic prism pairs (or cylinders) will illustrate how a unified design solution is arrived at for a complex imaging system. Illumination concepts involving TIR and non-TIR approaches are also discussed.