I have this lens again, and may have it for the rest of the year. Did some testing with it, compared to the Canon FDn 50 1.2L and 1.4.
Sharpness, hands down, it kicks ass.
extremely flat plane (no curvature)
Very bright for a 1.8 lens, maybe little or no T loss compared to lenses in test, stays bright throughout the whole test, consistently brighter than the canons at the same settings.
extremely clean bokeh. Doesnt have nearly the blur power, however what it blurs, there is no bokeh fringing, and easily handles busy backgrounds. 5mm seems to make a difference, 2-3 degrees narrower if I had to guess. This can be a pro or con depending how you operate.
high contrast at any aperture
best at F8
Canon FDn 50mm F1.4
Sharpness good center, edges a little soft wide open, doesnt really catch up to ZE till f4
fairly flat plane (no curvature)
T stop around the same or maybe even a tad less than ZE55.
busy bokeh with complicated background
some contrast lost wide open and CA, however good as zeiss by F2
best at F11, about as good as the ze throughout the frame
Canon FDn 50mm F1.2L
Similar to the F1.4 in sharpness, however, stopping down to 1.4, it's very good already.
has some field curvature
T stop is a good 2/3 brighter than the ZE55
busy bokeh with complicated background, very similar to the 1.4, however a little more blur
some contrast lost wide open and CA, however good as zeiss by F1.4
best at F11, nearly catches the ze except for the far corners, not really sure due to curvature issues.
50L wins, not only is aperture wide, it has good transmission.
bokeh and blur
50L, Ze55, 50 1.4 in that order. Technically, zeiss is cleanest, however less busy backgrounds, the difference is quite noticeable.
Ze55, 50 1.4/50L tie
Ze55, 50L, 50 1.4, all fairly good
Ze55 since it's a little brighter, 50 1.4, 50L (field curvature may affect closer subjects).
color cast (subjective feeling)
50mm F1.4, extremely neutral, borderline cool.
50L tad warm
Ze55 tad warm
50 1.4 $100, average 1.4 lens, very good F2 lens
50L $700, average 1.2 lens, very good F1.4 lens
ZE55 $740, excellent 1.8 lens