My conclusions so far regarding the optical qualities of the 28mm Nokton:
Good:
Sharpness from wide open in most of the frame from infinity to about 1 meter.
Sharpness wide open in the center, even at MFD (0.5 meter).
Flare and ghosting is very well suppressed.
Great sun-stars when stopped down a bit.
Bokeh in the central image area.
Transition zone in the central image.
Average:
Optical vignetting. Sometimes this will be visible is you look for it.
Overall bokeh behavior.
Bokeh-balls, or points of light behind the plane of focus, creates balls of light with a highlighted edge, when the lens is wide open. In the central area, these outlinings are minimized when stopping down to f/2.8 or more.
Bad:
Sharpness away from center at or near MFD.
Bokeh away from center at certain distances: Transition zone well away from the center of the image, when structures with lines pointing to the center of the image sometimes yields "double-drawing" (looks like a shaken image) instead of just blurring.
Wide open and well away from the center, bokeh balls become more or less squares with highlighted edges. The outlining of the bokeh balls (or squares) away from center never disappears when stopping down.
