Patent ID: 7369304

Claim:
An automatic focusing method for an optical system, comprising: performing an initial coarse focus action along a focal axis at a scan position corresponding to a point on a surface of a slide; and respectively performing a plurality of subsequent fine focus actions along a plurality of focal axes at a plurality of scan positions corresponding to different points on the slide surface, wherein the performance of at least one of the fine focus actions comprises obtaining images of the slide, each of which has a two-dimensional array of pixels, at a plurality of coordinates within a predetermined range along the respective focal axis, and selecting one of the plurality of coordinates as a fine in-focus coordinate based on an examination of the pixel arrays of the images, wherein the slide comprises at least three fiducial points, and the method further comprises determining positions of the at least three fiducial points, and determining a scan axis slope, index axis slope, and focus intersect of a global focal plane based on the positions of the at least three fiducial points, wherein the Performance of the at least one of the fine focus actions comprises estimating an initial coordinate along the respective focal axis as a function of the global focal plane.