I have been reading reviews about this lens and one thing I have noticed is that several reviewers state that they returned their first copy for sharpness or some other reason. Then the second copy was "tested" and preformed well.
What form of testing is done. Is there a recommended process, target and software?
When I Google 'lens testing software' there is a plethora of hits but nothing seems to jump out at me. Any suggestions?
The required tests depend on the intended use and the type of lens tested, e.g. a macro lens should be tested for close-up photography, perhaps field flatness, and is either expressed as a resolution value or an MTF curve, but resistance to glare could also be an important metric. Therefore, the tests should test those features that are important, and preferably deliver a quantifiable result. A program like Imatest
offers a range of tests, and those in the SFR (spatial frequency Response) category are most often used for resolution/MTF testing.
I get very positive feedback on a free resolution test target
that I created with several useful features in it, for both visual inspection of the results, and it can also produce a few quantifiable measurement values. One of those values is a parameter that can be used for optimal Capture sharpening
For resolution tests (which are useful to test for deviant performance) one typically tests the image center and the four corners for resolution. When one of the corners performs significantly worse than the others, and assuming that the focus procedure was very good, then the lens may suffer from decentering, and is a candidate for replacement or repair. I prefer to test by focusing separately on the individual corners, to make sure that they are good, and not allow the field curvature of lenses, or mis-alignment of the sensor, to muddle the optimal score that can be achieved, on non-flat
This will also produce good reference data for later inspection, e.g. after a drop.