As promised, I've done some informal tests with the Pentax T132 Achromatic 2-element close-up diopter on the FA*80-200/2.8 and compared it with the Sigma 180mm f/3.5 Macro. I shot newsprint on mat board, manual exposure, 1s @ f/8 on both lenses, ISO 200. The Pentax only gets to around 1:2 magnification and I positioned the Sigma so as to get almost exactly the same magnification for this test. (Obviously, the Sigma could get all the way to 1:1, but I wanted to see comparable application of the two lenses.)
Mini view of entire frame (for reference): http://www.robertstech.com/temp/mini.jpg (88kb) 100% magnification crops: http://www.robertstech.com/temp/sigmaCenterCorner.jpg (149kb) http://www.robertstech.com/temp/pentaxCenterCorner.jpg (143kb) My observations: The Pentax actually appears sharper in the center. Personally, I'm going to attribute that to focus discrepancy, given the magnification and relatively dim room light I was working in. Still an astonishing performance for a zoom lens with an add-on diopter! Of course, the Pentax lens sold, when new, for almost double the price of the Sigma, but I'm still very impressed. The Sigma is drastically sharper in the corner. Way to much to attribute to a non-perpendicular target or something like that. It could be field flatness or just better corner resolution, both of which I'd expect from a dedicated macro lens. Though the Sigma is not a small lens by any means, the Pentax is much larger and heavier. Of course, the Pentax is half a stop faster and zooms from 80mm to 200mm. The zoom is a real boon when you're shooting plant macros in the field and don't want to have to mess around with moving the tripod to back up or move in to the subject. Still, in the configuration tested, the Sigma will get double the magnification of the Pentax, so I may get the Canon 500D achromatic diopter (+2) and see how that fares... -- 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.
