Gang, By the generosity of Pentax Norway I have both the DA* and the FA* 200 on loan for the week-end. I will do some more testing today before I post any pics, but yesterday I went about testing the alledged Purple Fringing (PF)problem with some classigal twig-against-sky shots. My results indicate that the DA* does indeed exhibit more PF than do the FA*, at both f/2.8 and f/4.
However, things doesn't look entirely good for the FA* either. When fringing show up, there is just as much cyan fringing as there is PF. I do not know much optical theory, so I shall not attempt any authoritative explanation. But I can guess, can't I? :-) If I understand this article correctly: http://www.vanwalree.com/optics/chromatic.html colour-correcting a lens for all colours simultaneously is a compromise even with the most advanced optical designs ("ultra-achromatic", etc.). So with all reservations about my understanding being correct, this is what I believe goes on: One route of design compromise can be to correct the lens very accurately for green, and let blue and red deviate some. Put blue and red fringing together, and you see purple in your shots. This seems to be what Pentax has targeted with the DA* design. Another route of compromise can be to sacrifice some correction of green for a better correction of blue and red. The result is less purple fringing but some cyan/green fringing. This "balanced" approach seems to be behind the FA*. Anyway, from a practical approach the question is which to prefer? -Is this like "pest or cholera", or "chocolate or vanilla"? My preliminary conclusion is that if you shoot frequently at f/2.8 (eg. portraits or indoor sports) and want to avoid post-processing, then the FA* will look better. If you have the time and/or inclination to post-process, however, the pure-purple fringing of the DA* will be easier to deal with than the mixed aberrations of the FA*. In an ideal world there would be no aberrations, of course. But in an ideal world we'd also have peace in our time... :-) My son has just agreed to act as model for some large-aperture portraits this afternoon, against a substantial (to him) monetary compensation...lol... that boy has economic talent... If anyone reading this soon after posting, I may have opportunity to shoot some other motifs on request. Weather is lousy, though. Heavy overcast and chance of rain. The full report with most likely be posted on my website, to make room for the hi-res pics. Best, Jostein -- http://www.alunfoto.no/galleri/ http://alunfoto.blogspot.com -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
