Re: diffraction curiosity questions

Murray,

You're asking an awful lot here. A message board is a difficult place
to cover several lectures worth of material regarding physical optics.

One statement I can quickly clarify is in regards to a photographer's
hunt for diffraction limited optics. The diffraction limit of an
optical system defines the smallest point that can be formed at the
image plane. The derived equation for the diameter of this
fundamental spot is 2.44 * (wavelength) * F/# . It can be derived
from fourier optics techniques and wave theory (if you consider the
two topics to be separate). 88% of the energy that would form this
point is contained within this circle.

So why do photographers care about the size of a diffraction limited
spot, or if a system is diffraction limited at all? An optical system
can create distortions in the image (the general term we use is
aberrations, and distortion is a particular type of aberration). A
diffraction limited system is one that is free of all aberrations and
is therefore producing the best images possible limited only the
barriers of physics. In a scenario where the pixels of your detector
are small enough (say 1/2 the size or less of the diffraction limited
spot) the diffraction limit directly defines the resolution an imaging
system is capable of.

You may recall back to the early days of Hubble. The optics weren't
tested properly initially which led to improper manufacturing which
created a terrible amount of spherical aberration. The images were
blurry until additional optics were put in place to reverse the
effects spherical aberration and restore the telescope to diffraction
limited imaging quality, and thus maximizing the resolution of the
system.

If you in Ann Arbor and want to talk optics over a beer I'm around. I
think there is also an active OSA group here too but I haven't
attended their meetings.

Cheers,
Philip
.

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