What mode is your camera most often in? Why?

So, you are lucky! You can recreate that time!   

Just put your camera in Av, select ISO 400, use for processing one of these RAW converters that emulate film (there are good ones) and there you are!

Only,  don't put the card into a developer bath, bless you want to spend a lot of money...  

Actually, I am semi-serious: if that is what worked best for you, ever, why not use it?

BTW: I saw yesterday an exhibition of B&W photos from the 60s-70s - what an excellent collection!

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Antonio http://ferrer.smugmug.com/