I will give an example how optical design and superior flare reduction in the mechanical design can conflict. The SMCK 105/2.8 AND SMCK120/2.8 are same optical design with the SMCK120 just scaled up. What this means is optically the SMCK120 would have a larger image circle than the SMCK105/2.8 BUT since both lenses have built in rectangular baffles in the back designed only for the 24mmx36mm full frame film format, you cant use either on larger than 24x36mm formats and the 120SMCK usable image circle is NOT any larger than the 105mm because of the baffle limitations which were intentional and improve perfomance when used on the 24x36mm format as designed.
JC O'Connell (mailto:[email protected]) "Honesty is the first chapter in the book of wisdom" - Thomas Jefferson -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of John Francis Sent: Wednesday, April 29, 2009 1:09 PM To: Pentax-Discuss Mail List Subject: Re: image circle of DA lenses: how much smaller than FF? On Wed, Apr 29, 2009 at 01:35:09PM -0300, Luiz Felipe wrote: > I was looking for data on the available 180~200mm 2.8 lenses for K and > EF mounts, and found some story about how the DA* 200 2.8 is related to > the former 200mm full frame and so it possibly would cover said full > frame. > > That got me wondering if one of the tech-oriented actually knows the > image circle dimensions for the DA lenses, and how much is missing. I > know the difference should be proportional to the difference from APS-C > to 24x36mm, but would like ko know the size and borderline falloff > evolution on the DA lenses. > > Just wondering, TIA. :-) > > LF Above some focal length (well below 200mm) it's likely that just about any lens will have an image circle easily large enough to cover 36x24mm. But, as Ned Bunnell point out in his blog entry on the forthcoming camera, there's a difference between covering an image circle and covering it well. The DA lenses are not designed for sensors of that size, so things such as corner resolution, distortion, etc. may not be sufficiently high. (There again, as he also mentions, some older lenses may also fall short in that regard, even though they were designed for use on film cameras). -- 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. -- 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.
