From a quality/cost perspective, the AIs 50mm f1.8 and f2 are the best-built, sharpest and cheapest standard lenses for the FM3a. You can probably get one for $40 on the auction sites. The AF 50/1.8 is okay, but it doesn't have the wonderful tactile quality of the metal lenses, and is not as easy to focus. The 50mm f1.4 AIs is also great, but a bit more expensive, though you can probably get one for $150. Don't bother with the f1.2 unless you really like to spend money. It's not all that sharp wide open, and it's no better stopped down than cheaper versions, except maybe the 58mm f1.2, which is legendary and carries a legendary price tag. Hooray, in this case, the cheapest route is the best! That doesn't happen every day.