NX20: Testing Minolta MC/MD Lenses

Recently I described, generally, my experience using Minolta MC/MD manual focus lenses on the NX20.  Results were over all strikingly good, though I noted isolated problems of the sort mentioned by others.  Lately I conducted more careful tests of my lenses, checking them at each aperture stop.  Lighting conditions  regrettably varied, but otherwise it was a decent experiment.

Results are charted below.  For each lens, I divide the imaging results into three simple categories:  bad, acceptable, good.  Each category, per lens, is defined by the brightest aperture which belongs in that result.  "x" means that category does not apply.  The problems revealed came in three types:  serious ghosting, poor focus (perhaps really extreme ghosting?), and very poor contrast.

bad  acceptable  good        f=focus   g=ghosting  c=contrast (not with flash)

Sigma 8/4:            4f      8        11

Rokkor 16/2.8:      2.8f    5.6      8

Sigma 18/2.8:        x       2.8g   4

Rokkor 24/2.8:       x        x       2.8

Vivitar S1 28/1.9:   x       1.9c   2.8

Rokkor 35/1.8:       x        x      1.8

Rokkor 50/1.2:       x        x      1.2

Rokkor 58/1.2:       x        x      1.2

Rokkor 85/1.7:       x        x      1.7

Vivitar S1 90/2.5:   x        x      2.5       22c

Soligor 135/2:        x        x      2         22c

Vivitar S1 200/3:    x        x      3         22c

Rokkor 300/4.5:     x        x     4.5

Tokina 400/5.6:     x        x      5.6

Which means:

1)      The Sigma 8/4 and Rokkor 16/2.8 (both fisheyes) generate blurry-looking images wide open.  This behavior puzzles me.  Is there an obvious explanation?  Stopped down to 8/5.6 respectively they deliver fair images, that might require some modest sharpening; stopped down still more, and they're fine.

2)      The Sigma 18/2.8 exhibits definitely eye-catching ghosting wide open, but that vanishes totally at the next stop.

3)      All of my Rokkor lenses from 24/2.8 to 85/1.7 are great throughout their ranges.  So is the Vivitar Series 1 28/1.9, except that, surprisingly (for one of my favorite and most used lenses), it presents markedly poor contrast wide open.  Stop down by one and the effect disappears; furthermore, the contrast problem is entirely erased by easy post-processing.

4)      The next three-- Vivitar Series 1 90/2.5 macro (used here as a telephoto), Soligor 135/2, Vivitar Series 1 200/3-- operate on the exact same pattern.  All are fine from wide open, yet exhibit that poor contrast problem associated with the 28, but in these cases only stopped down all the way.  A dab of processing perfects them.

5)      My Rokkor and Tokina long telephoto lenses are both great at every stop.

I get the impression that I've done pretty well for myself with this new camera/old lenses combination.  If my fisheyes weren't so lousy wide open I'd be completely content.  Even those, however, deliver superb results, as long as I don't use them at full speed.