hi hunker
I have no experience with the 50 1.7 MD lens.
However, I have bought a couple of cheap M42 and tamron adaptall lenses which I have tried to use with my a580 (using adapters of course) but with unhappy results.
I have a minolta 50 1.7 AF, which I bought through ebay, and I'm extremely satisfied with it. To me, changing from f3.5 in the kit-lens to a f1.8 was the next best thing after buying the slr
To continue with what Thomas said, you'll be using a 1.8 for low light situations, and for a shallow depth of field, and in both cases, i find that the extra help by the camera via AF is extremely helpful. And you always have the MF function available if you want to.
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Sony α580 dSLR
Tamron 17-50 2.8, Sony 18-55 kit lens, Minolta AF 50mm 1.7, Minolta 28-105mm xi zoom, Minolta 35-70mm 3.5-4.5, Minolta 75-300mm 4.5-5.6
Kata 3n1-22
My short photostream:
ivandegi