A focus changing apparatus for an optical scanner which increases the depth of the field of the optical scanner. The focus changing apparatus is optically located between a laser source and a scan mirror and includes a plurality of alternating curved and flat facets. Alternatively, a piezoelectric deformable...http://www.google.com.au/patents/US6053409?utm_source=gb-gplus-sharePatent US6053409 - Dynamic focusing apparatus for an optical imaging system using a deformable mirror
