Lenses and sharpening

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?
--
Alfred Molon

Olympus E-series DSLRs and micro 4/3 forum at
http://tech.groups.yahoo.com/group/MyOlympus/
http://myolympus.org/ photo sharing site