Archived posting to the Leica Users Group, 1997/12/05

[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]

Subject: Re: [Leica] RE: soft focus vs out -of- focus in an ultimate sharpness world
From: "Patrick G. Sobalvarro" <pgs@sobalvarro.org>
Date: Fri, 05 Dec 1997 20:57:40 -0800

At 07:47 AM 12/5/97 -0600, Eric Welch wrote:
>Well, I'll defer to the optical experts who hang out with lens designers.
>They say that focal length does effect diffraction. There are lots of
>factors that are involved in diffraction in a lens system. One of them,
>according to the folks I've read from in the photographic press, is the
>angle of incidence of the light hitting the aperture. 

Tell me about these optical experts.  Who are they?  Can you cite sources
for your contention that diffraction at a fixed aperture is reduced in
lenses with longer focal lengths as compared to those with shorter focal
lengths?  If in fact the experts you cite aren't mistaken (and lots of
photography "experts" are confused about things like the difference between
diffraction and refraction), then I can learn something from them, and I'd
like to.

Here are my sources:

"Optics," Second Edition, Eugene Hecht.  1987, Addison-Wesley.  This is a
text I used in an undergraduate course -- it presents optics from the point
of view of classical wave theory.  The resolution formula is presented
here, as well as its derivation.

"Image Clarity: High-Resolution Photography," John B. Williams.  1990,
Focal Press.  The resolution formula is also presented here, although no
derivation is given.

- -Patrick

P.S. I'll be in Boston for the next week and a half, so my reading of my
mail will be a little spotty.  But I'm interested in hearing about your
sources, even if I don't reply right away.