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Owning or having owned A*'s and M*'s for 67 and F*'s and FA*'s, my perception is that the A* and M* off-white exterior finish is the toughest, F* cream color is a bit softer than that and the FA* silver is the softest and easiest to scratch. Funny, the oldest finish is the better finish for ruggedness. Note that the scratches on FA* lenses tend not to expose bare metal as the others do, but only exposes the black primer underneath. That said, it appears that the FA* primer coat is quite rugged. So I guess someday all my FA* silver lenses will be black?