Hi Marcus, Firstly, indeed lovely bokeh on these shots.
On CA, the estimable Erwin Puts says "Aberrations are often reduced when the lens is stopped down, because the marginal rays no longer contribute to the imaging errors. Laterial chromatic aberration is not diminished by stopping down the aperture and is very difficult to correct. The chromatic aberrations (lateral and longtitudinal) increase from the centre of the image towards its edges." "The focal length is linked to the magnification factor, and that is why a variation in the refractive index also causes a variation in magnification. This error is called lateral chromatic aberration and it mostly affects the reproduction of structures" So JCO is sort of half right. Longtitudinal aberrations will certainly be corrected by stopping down. But for a given focal length, I think you will notice longtitudinal CA (and the effect of stopping down) much more than lateral CA. D Marcus A. Hofmann wrote: > Thanks for the input, J.C. > > I really don't know much about the physics behind CA. But from the > shots I took at least it appears to not happen at shorter focal > lengths, and to not be as apparent even at 135mm when stopped down to > 3.5 or 4.0. From my simple understanding of how things work, and since > the CA mainly appears towards the borders of the frame, why wouldn't > stopping down the lens have an influence on that? > > > Marcus > > -- > Am 21.04.2008 um 19:09 schrieb J. C. O'Connell: > > >> CA usually cant be fixed by stopping down, its most likely >> some other problem. >> jco >> >> -----Original Message----- >> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf >> Of >> Marcus A. Hofmann >> Sent: Monday, April 21, 2008 11:20 AM >> To: Pentax-Discuss List Mail >> Subject: smc DA* f2.8/50-135mm Bokeh (PESO/GESO) >> >> >> One of the reasons I like the new 50-135mm so much is its oh so pretty >> bokeh. It suffers a bit from CA at maximum aperture in bright >> sunlight, though, so I like to stop it down just a little. Then the >> results are really nice. I have put up some "bokeh samples". I think >> these are some nice pictures. But then again, I may just not have a >> clue. ;-) >> >> http://www.ntony.net/fotos/album/pentax-50-135-bokeh >> >> If you don't have flash, or don't like flash, or want to be able to >> zoom in a little and gett bigger pictures, make that: >> >> http://www.ntony.net/fotos/album/html/pentax-50-135-bokeh >> >> C&C welcome, as always. >> >> >> Marcus >> >> >> >> -- >> PDML Pentax-Discuss Mail List >> PDML@pdml.net >> 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 >> PDML@pdml.net >> http://pdml.net/mailman/listinfo/pdml_pdml.net >> to UNSUBSCRIBE from the PDML, please visit the link directly above >> and follow the directions. >> > > > -- [EMAIL PROTECTED] http://members.iinet.net.au/~derbyc -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
