Archived posting to the Leica Users Group, 1997/12/10

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Subject: Re: [Leica] diffraction limited lens: the theory
From: Patrick Sobalvarro <pgs@best.com>
Date: Wed, 10 Dec 1997 00:28:01 -0800 (PST)
 
Thanks, Erwin, for your explanatory post.  However, your message gives
the wrong impression about the phenomenon of diffraction itself.

   Date: Sun, 7 Dec 1997 19:14:28 +0100
   From: Erwin Puts <imxputs@knoware.nl>

   First some theory. The phenomenon of diffraction: if a wave encounters a
   barrier that has an opening of dimensions similar to the wavelength, then
   the wave will flare out into the region behind the barrier.

Diffraction will happen whenever part of a wavefront is blocked by a
barrier, regardless of its shape or size.

If diffraction only happened when a wavefront encountered an opening
of dimensions similar to the wavelength, we as photographers would
never encounter it, because the wavelengths of visible light are from
400nm - 700nm, or about one-half of one-thousandth of a millimeter.

This is a very small pinhole.  For a 50mm lens, it corresponds to
f/100000.

- -Patrick