50/1 and 50/2 APO are both 50s but are very different in design and it shows in the resulting images; neither is a replacement for the other, IMO. Both stay sharp wide open at close distances (or any distance for that matter) because of floating element design. The 50/1 has veiling and fringing wide open (but not enough to affect its resolving power) and i see why it's among the most expensive in its lineup; the APO, OTOH...is so good for its price it makes me wonder if Cosina priced it incorrectly...
