I placed an order for a Sigma 8-16mm f/4.5-5.6 EX DG a few days ago - I'll still keep my DA15mm f/4, because it is
considerably smaller than the sigma zoom lens - and you can use filters on it. Even though the image quality from the DA15mm improves considerably in the corners on the K5IIs, it just makes the exceptionally high resolution from the centre of the lens stand out even more. The centre doesn't need sharpening - but the edges do. It is also a bit frustrating to be forced to go past the diffraction limit with the DA15*, on the K5IIs the whole idea or removing the AA filter is to capture as much detail as possible, the laws of physics are a harsh mistress.
P
entax K5IIs - DA15mm f/4 ED ASPH Limited 1/60th f/11 ISO 80
*IMO the absolute best performance from the DA15mm f/4 ED ASPH is achieved at f/11~f/16, to obtain the absolute best image quality on the K5IIs the ideal aperture range is f/4.5-f/5.6 - many of my best lenses happen to put in stellar performance at this aperture range,some lenses FA31,FA77 and 50mm f/1.2 are superb at f/2.8, but the DA 15mm f/4 forces you to stop down to f/11~f/16 equalise resolution across the frame - at f/16 diffraction is painfully obvious.
Last edited by Digitalis; 01-31-2013 at 05:56 PM.