Have been using the 600mm lately for animal shots and have noticed something new as far as problems are concerned. This lens has on occasion color fringed in orange-red when stopped down and the shot is high contrast. What I'm seeing now at f/5.6 is a green fringe and sometimes violet. These two colors are traditionally not corrected in telephotos and appear as secodary spectrum in high contrast, out of focus areas. There is no question that this is longitudinal chromatic aberration and not lateral chromatic. The areas in focus never color fringe.It is better to use this lens stopped down to f/11 or more. My suggestion to Pentax is that they redesign this lens as an f/6.7 either using normal glass and making it superachromatic(and affordable) or makiing it APO using ED glass. SR

-- Steve Rasmussen (srasmuss@flash.net), April 17, 1999