Re: [Leica] Diffraction limited; bo-ke

["Dan Post" <dpost@triad.rr.com>]

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
>