Re: Airy disc & contrast (TECH-3D digest 210)

[T3D Bob Howard <bobh@xxxxxxxxxxxxxxxxxx>]

RE: John B. says he thought contrast was a function of aperture, but 
if this were true, stopping down would increase contrast. What may be 
confusing is the adage that wide open has more abberations than 
stopping down a bit and stopping down too far gets into diffraction, 
but these are not necessarily changing the core of the Airy disc. The 
core may be a function of the exact plane of focus. I.e. slightly 
defocused enlargers center but "blurs" flare rings. And exact focus 
has small core and flary rings? In cameras we rarely focus the real 
image but a substitute ground glass or rangefinder cam system, so 
these can be offset from the true film plane a bit. I am sure by spot 
diagrams (which are representations of the airy disc.) computers can 
jiggle curvatures and indices of glass to get different Airy disc 
look! 
 I am just reading now by accident, Richard P. Feynman's "QED, The 
Strange Theory of Light and Matter" (QED = Quantam Electro Dynamics).
These four lectures explain how light and other physics can be fully 
explained on a particle basis so no need for a duality of wave and 
particle theories. The "wave" idea works for gross dimensions so is 
handy crutch. This book is from the Princeton University Press, 
Princeton Science LIbrary 1985, seventh printing 1988 with 
corrections. ISBN 0-691-02417-0.
I can see how Feynman was revereed as a great teacher and explainer 
as well as discoverer. He was most famous for 'stirring things up'! 
BobH


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