>>2945942olympus pen f vintage lenses.
like the radioactive 40mm f1.4.
it was made for half frame film, so no need for speedbooster.
otherwise any of the first party prime is good. just check for optical condition, canon fdn 50 mm 1.4 is nice, but i prefer 50 1.7 from minolta or pentax. check out zhongyi lens turbo ii.