The whole question of lens sharpness...

Started Jun 12, 2013 | Discussions thread
Detail Man
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Re: The whole question of lens sharpness ...
In reply to olliess, Jun 21, 2013

olliess wrote:

Detail Man wrote:

olliess wrote:

Compare the heat/diffusion kernel to the (model) blur function of a lens.

Could you please state (or reference using URLs) both specific models of which you speak ?

A basic textbook on differential equations would be relevant here. If wiki counts you can look under "Fundamental Solutions" in Heat equation. You can also look at Fick's laws for diffusion. Then compare to the link given for Deconvolution.

Thanks for the links. But what about the "(model) blur function of a lens" ?

There is no such thing as a 'diffusion-type process.' The blur of a lens is simply a convolution with the PSF of the lens. If the PSF is exactly known, it can be exactly inverted with a deconvolution.

So what is a "diffusion-type process" ?

One that resembles diffusion in a mathematical sense.

First off, the problems of finite bandwidth, limited image extent, and noise will limit your ability to invert. And even you assume the PSF of the lens is known perfectly as a function of distance to the subject, it seems a stretch to assume that you know the distance to every point in the unblurred image.

Otherwise, it can be inverted to the degree it is known.

That's a far cry from a theoretically-guaranteed inversion.

Based upon such a criterion, the Hubble Space Telescope output would have remained unprocessed.

The HST output was greatly improved by deconvolution processing. It did not achieve perfection, nor would one expect it to, on purely theoretical grounds. Also consider the distance to subject for astronomical objects.

What is the specific significance of "distance to subject" ?

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