To make it a bit more explicit, as David's question originally was, if
wave mechanics really does matter: Yes, it does. For explaining the
relation of N.A./filling the BFP and resolution/size of focus you have
to use wave optics. (Finding this out was actually the achievement of
Ernst Abbe). Alternatively one can still regard light as a stream of
particles (photons) that move along "rays". But then one has to take
into account the quantum mechanical behaviour of the particles, and this
gets even less intuitive.

Joachim

Christian Soeller wrote:
>
> David Knecht wrote:
>
> > filled is the sum of the two intensity profiles.  Where does this
> > logic go wrong, or is it simply that you can't explain it unless
> > getting into Fourier and wave mechanics.
>
> It seems to me that your logic *completely* ignores the wave nature of
> light (only talking about rays) and therefore your logic seems to have
> no chance of explaining things which *absolutely require* the wave
> nature of light be taken into account.
>
>   Christian

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  Joachim Walter, Dipl. Phys.
  Institut für Anthropologie und Humangenetik LMU München
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