Archived posting to the Leica Users Group, 2000/07/23
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]> The 35 Summicron is fiarly good wide open, better than 95% of the lenses out > there, and Leica designs its lenses so that there is minimal abberations > wide open- one of the reasons they are so expensive. They are designe to > perform well wide open and so you may find the in focus portion of a shot > taken at f2 is as sharp as one at f5,6. Diffraction limiting, it seems, is > inherent in any lens with an aperture- essentiall all of them, since to let > the light through, there logically has to be a hole! > How the diffraction around that hole handled- whether it is wide open or > very small, determines the diffraction limiting of the image. I have seen > some lenses that at f5,6 are quite low in contrast, and I have had to assume > that the placement of the aperture, and the internal contruction of the lens > had a lot to do with it. > Dan ( Still trying to get that 'perfect' negative!) Post Hi Dan, Diffraction-limited is a very specific term that is used to describe a very small group of lenses where the optical aberration is so well corrected that the only (internal) source of image degradation is diffraction. On the other hand, diffraction affects every lens--good or bad. But on cheaper lenses the effects may not be as noticeable because the optical system itself introduces a relatively large amount of aberration. These lenses are "limited by diffraction", as all lenses are. But we don't call them "diffraction-limited". Regards, Chris