The problem I see here is more about including the light appliance. It adds a "hot spot" on DSLRs cameras that are not so good on extreme values (as can be seen here with the posterisation effect) ! No, the real drawback of such a framing with the light appliance is that it fools your metering system (matrix, average, spot ?) by trying to find a mean value between the very dark shirt (dress?) and the very white hot spot ! As it can't, you loose all details in the shadows AND in the hot spot...
Framing without the appliance would have given at f/1.4 and with a "normal" speed an ISO value that would have kept the shadows correctly illuminated and less noise even at a higher ISO...!
Then there is the focus problem with the shallow DoF (what settings for AF do you use ?) that might have been corrected by manual focus... :-) "What can I do, What can I write, Against the fall of Night". A.E. Housman
I do find with the 50mm that I have more trouble focussing it on AF than with other lenses. But when I switch to manual focus I always mess it up even if it looks right in the viewfinder. Ad astra per aspera
