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Abstract

Enhanced performance of an uneven surface image transfer apparatus is provided by using a well-defined convergent field of illumination that is nominally focussed at the stop of an imaging lens. An integrated optical system exhibiting such enhanced performance includes an aspheric illuminating lens that directs radiant energy onto a presentation platen from which fingerprint or bar code images are transferred to an external image sensing device, such as a charged coupled device chip. An evanescent wave image is totally internally reflected (TIR) off of the platen along an optical path including a plurality of TIR surfaces to achieve a predetermined optical path length. One or more of the TIR surfaces may be curved to reduce or eliminate astigmatism and geometric distortion. An aspheric imaging lens having a split-axis aperture stop transfers the image rays to the image sensing device. The split axis aperture stop has its stop axes on opposite sides of the nominal focal point of the aspheric illuminating lens. The image transfer apparatus has utility with surfaces that are uneven in the sense that there is coded image data in the form of spatial or intensity contrasts, such as bar codes.

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First Claim