What humans perceive as sharpness depends on at least 3 measureable
qualities (all affected by film as well):
Resolution: roughly what you call the "ability to pick out fine details"
Edge definition: roughly what you call "for the image not to be viewed
as soft when...." This is how sharply the edge between areas of
differing brightness is defined. Analogous to square wave response in audio.
Contrast: overall contrast can effect how sharp an image appears.
These things can be objectively measured. One problem is that different
people find different combinations of these factors to provide the
'sharpest' pictures for them. If we all had the same vision (eyes/mind),
there might be far fewer discussions and arguments about lenses. Another
problem is that the current state of optical design/materials forces
lens designers to make tradeoffs between these factors.
Edge definition is what sharpening tools like unsharp mask alter. They
have no positive impact on resolution, and can decrease it if overdone.
Image editing can improve edge definition and adjust contrast, but
cannot improve resolution.
These are all very often compromised by vibration and other movement
during the exposure, inaccurate focusing, inadequate DOF, flare from
inadequate shading, etc. A lot of stuff is blamed on lenses that isn't
attributable to them.
You have something more valuable than any of this stuff, a real
photographers 'eye'.
Moose
Bolty wrote:
I would agree with you that the unsharp mask or sharpening tool can add that
certain crispness to an image. I am talking about the ability of a lens to
pick out fine details and then for the image not be viewed as soft when
transferred to film, so I guess you would call it the resolving power of a
lens then. I would also say that film types and characteristics would have a
lot do with contrast and sharpness/resolving power eg Velvia to a high speed
film.
Is there a specific standard to test for these properties in a lens or is it
just on what we see?
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