Predictive focusing for image scanning systems

Abstract

This invention discloses an apparatus for achieving predictive focusing in an image scanning system. The apparatus comprises an optical path-length changing plate and an image sensor. In one embodiment, the plate comprises a plurality of path-length changing members. The plate further includes a central region configured to provide a substantially constant change in optical path length across the central region, allowing an image passing therethrough to be in-focus captured. Having a light receiving surface, each path-length changing member is configured to provide a substantially non-uniform change in optical path length across the light receiving surface, allowing a focus plane of the image to be tilted such that the image projected onto the imaging sensor can be used for predicting an amount of optical adjustment required to achieve focusing. By using more than one path-length changing member, predictive focusing is achievable with more than one direction of focus-plane tilting.