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>A sharply focused image contains the most > contrast. Since the non-APO lens puts the focused light of different > wavelengths in different planes, the auto focus will probably not work > accurately. I could not autofocus with the Sigma lens. > > Mark Bailey > Rockford, IL > I dangerously assume that you had the f5.6 version of the lens. f5.6 is typically the slowest aperture that any autofocus camera will work with, and does not always work well.. Autofocus cameras use a phase matching system to determine the focus, basically matching multiple images together to determine correct focus. I may be incorrect, but the APO feature of the lens is less likely a cause of autofocusing failure, than the slow lens. Rick ======================================================= -> SPORRS: 'Serious Photographers Of Railroad Related Subjects' -> Web Site: http://www.anet-stl.com/acphotog/sporrs/ -> Message © 1998 SPORRS® - All Rights Reserved =======================================================
