Maybe me. For visible light, you can use the rule that the Airy disk, in
microns, equals the f#. For high magnification, the effective f# is f*(m+1);
so if the lens is used at a magnification of 10, the effective f# at the
marking of f/2 will be f/22. The Airy disk will be about 20micron, or
1/50mm, making modulation transfer fall off pretty dramatically by 25
cycles/mm.
Paul Farrar
----- Original Message -----
From: "William Biesele" <biesele@xxxxxxxx>
To: <olympus@xxxxxxxxxxxxxxx>
Sent: Wednesday, February 05, 2003 4:11 PM
Subject: Re: [OM] Mythical Olympus 4/3 systems and depth of field
> Didn't someone here claim the 20mmF2 macro was diffraction limited at F2?
>
> Quoting Thomas Heide Clausen <T.Clausen@xxxxxxxxxxxx>:
>
> > I think it has something to do with diffraction, i.e. some physical
> > properties of light entering through a "small enough hole". However I
> > am sure that we have someone on the list who are much more capable
> > into optics and physics than me, so I will not pretend to know a
> > whole lot on the how and why of that.
> >
> > However......this is what I know on the topic...
> >
> > I read somewhere about that good lenses have an optimal
> > apeture from which they are "diffraction limited". I.e. that
> > diffraction is the singlemost important degrading factor of a lens -
> > meaning that a lens couldn't get better (since diffraction is a
> > result from a law of physics, not something a lens producer can fix
> > by designs and coatings - contrary to e.g. flare and chromatic
> > abbreation). The very best such lenses should be "diffraction
> > limited" at their full apeture (I've only ever heard of enlarger
> > lenses that claimed to be diffraction limited at full apeture, but
> > then again, I am not an optical engineer), whereas most (i.e. those
> > we can afford) are diffraction limited at some smaller apeture. I
> > have a Pentax 77mm/1.8 limited, which is said to be quite good at
> > that respect: I've read that it is "diffraction limited" from when
> > stopped down 1/2 stop or so.
> >
> > I have no idea how true the above is (so please feel free to
> > enlighten me), if it is true how to measure/test it. And I have no
> > clue how our beloved Zuiko glass test in this respect.
> >
> > Was that as close to a non-answer as possible? :)
> >
> > --thomas
> >
> >
> > On Wed, 05 Feb 2003 17:55:14 +0000
> > Roger Wesson <roger@xxxxxxxxxxxxxxxxxxxxxxx> wrote:
> >
> > > There's an inverse relation between the size of your aperture and
> > > maximum theoretical lens resolution. The smaller your aperture the
> > >
> > > coarser your best possible resolution becomes.
> > >
> > > Roger
> > >
> > > R. Jackson wrote:
> > >
> > > > Really? I wasn't aware of that. Do you know why that occurs?
> > > >
> > > > -Rob (big fan of Group F64)
> > > >
> > > > On Wednesday, February 5, 2003, at 01:40 AM, Winsor Crosby
> > > > wrote:
> > > >
> > > >> 35mm starts to soften at F16 or F22.
> > >
> > >
> > >
> > > < This message was delivered via the Olympus Mailing List >
> > > < For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
> > > < Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
> > >
> >
> >
> > --
> >
> > -------------------------------------------
> > Thomas Heide Clausen
> > Civilingeniør i Datateknik (cand.polyt)
> > M.Sc in Computer Engineering
> >
> > E-Mail: T.Clausen@xxxxxxxxxxxx
> > WWW: http://www.cs.auc.dk/~voop
> > -------------------------------------------
> >
> > < This message was delivered via the Olympus Mailing List >
> > < For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
> > < Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
> >
> >
>
>
>
> < This message was delivered via the Olympus Mailing List >
> < For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
> < Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
>
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