The whole question of lens sharpness...

Started Jun 12, 2013 | Discussions thread
Detail Man
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Re: Counterexample
In reply to olliess, Jun 21, 2013

olliess wrote:

Alphoid wrote:

If you believe lens blur "resembles diffusion in a mathematical sense," can you please give a diffusion process, as per the links you gave, which has a PSF which is a solid octagon? It is trivial to design an optical system with this (I'll use your made-up terminology here for humor value) "blur function."

Look at how a 2-d heat kernel describes the spreading (by heat- or Fickian diffusion) of a point source. Now compare this to the blur kernel (PSF) of a lens.

(Again) what about the "(model) blur function of a lens" ? How is your model mathematically characterized ? What independent variables affect it, and how do they specifically affect it ?

It isn't the precise shape that is the resemblance. It's the existence of a kernel, which in the heat equation has time dependent radial spreading, and for the lens has focal distance dependent change (not necessarily just spreading).

The relevant spatial domain function is across the surface of the film/sensor plane, right ? The effects of de-focus represent additional factors affecting that 2-dimensional spatial domain function, right ? The commonality that you allude to relates to the fact that convolution(s) are required in order to determine a (linear, constant coefficient) system ouptut resulting from a forcing function, right ?

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