Archived posting to the Leica Users Group, 2000/07/23
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Thanks for the clarification! I got it now!! Dan - ----- Original Message ----- From: "Chris Lee" <chrislee@mac.com> To: <leica-users@mejac.palo-alto.ca.us> Sent: Sunday, July 23, 2000 10:56 AM Subject: Re: [Leica] Diffraction limited; bo-ke > > 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 >