I'm thinking about getting either a factory AI-d pre-ai 105 or a newer AI-S. Are they optically the same? I read somewhere that the AI-d lenses weren't true AI lenses, and sometimes threw off some camera bodies. Is this true? Also, what other differences are there? Coatings? I quite like the way my 50mm f1.4 pre-AI looks. The answer probably is to go with the AI-S lens, but for portrait work, what would you prefer?