Alfred Molon wrote:
Sometimes a soft lens can be very effectively compensated by some
unsharp mask in post processing and you get a sharp, natural looking
image.

But sometimes no matter how much sharpening you apply or what parameters
you choose, you get that unnatural, "sharpened" look.

It probably depends on the unsharpness of the lens, its (spatial)
frequency response or whether the sharpness is caused by the lens glass
itself (i.e. lens not being sharp enough), inaccurate focus or some
motion blur.

For instance I have a 70-300 lens which at the tele end generates a bit
soft images, which however respond well to unsharp masking in post-
processing. But that's not the case for the another lens I have (a mid-
range one).

Has somebody analysed this (i.e. how to best sharpen an image, what
unsharpness can be eliminated in post-processing)? Is there perhaps some
web page with details?

Sharpening up the focus can be done to a limited extent.
UnSharp Mask is probably the most limited of various
sharpening tools. Likewise any sort of "smart sharpen"
that tries to isolate tonal edges will be less useful.

A true (not what Adobe labels as HP) high pass sharpen
tool will be fairly good. The problem is that most
image editors do not let the user set all the
parameters, and often limit user configuration to just
an amount.

One better option might be wavelet sharpen.

But probably the most useful would be Richardson-Lucy
Deconvolutional sharpening. Using just standard default
filters (Gaussian and perhaps exponantial) for the point
spread function should work better than other sharpen
tools, but it would also be possible to develop a very
accurate point spread function for any given specific
lens (think of the Hubble Telescope), and that would be
very significantly better than other methods.

--
Floyd L. Davidson http://www.apaflo.com/
Ukpeagvik (Barrow, Alaska)