In article ,
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?

Defects in lenses rarely produce a Gaussian blur or haze that can be
corrected with an unsharp mask. It's a complex mess with too many
variables to compensate for.

It's better to buy a higher quality lens if you're spending lots of time
on correction. Some mid-range lenses can be nearly perfect within a
reduced range of aperture and focal length. Sharpness charts can help
you decide what works for you. Around f/2, stabilization becomes more
practical than a larger aperture for low light hand-held photography.

If you're talking about the Canon 70-300 DO IS USM, there's a magic
aperture somewhere near f/6. The next step is to apply a small amount
of a large diameter unsharp mask to remove the haze. Don't let the
camera use small apertures. 300m at f/40 takes a picture of the fresnel
lens :P

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