Just in case anyone is interested... as the light is good here today I had another look at the Minolta 50mm f1.2 v Minolta 50mm f1.4 v Sony 55mm f1.8...
At 100%
In the centre of the frame the f1.2 is a tad soft wide open and the f1.4 looks quite good wide open. The f1.2 displays a little more glow/bloom/fringing.
Things are just about equal at f2 with maybe just a slight nod in favour of the f1.4 and from then on the f1.2 is sharp enough in the centre of the frame and there's really not a lot if anything in it between the two lenses.
The 55mm f1.8 is sharp from f1.8.
At the edges of the frame the f1.2 can't quite match the f1.4 at any aperture up to f4 at which point I stopped.
The 55mm f1.8 is much shaper than both the older lenses at the edges and is better at f1.8 than the older lenses at f4.
The 55mm may be better in the corners at f4 than at f1.8 but even at 100% there's not much in it, if anything. It's a very good lens and sharpness seems to be maintained across the frame very impressively.
As I said the other day... if looking to buy the Minolta 50mm f1.2 or f1.4 the smart move would be the f1.4 as it's just... better. The f1.2 gives you f1.2 so there's that in its favour but nothing else that I can see
It's worth it to me though just to use now and again
For whole image shots for viewing on screen and I'd imagine in quite large prints too the old Minolta lenses are ok
and indeed performance in the centre of the frame stands up quite well to pixel peeping from f2 onwards. The f1.2 isn't as good as the f1.4 but both are IMVHO good enough even at the edges for whole images.
The 55mm f1.8 is just... very impressive
PS. After all these lens changes I checked the sensor at f22 and there's a hint of a dust bunny here and there at 100% but honestly nothing to worry about and definitely no defined dark blobs. What a change from my Canon DSLR's!