Originally Posted by kthung 
I didnt know that! How??
The lens should have an auto/manual switch. Set it to Auto and the lens will always be wide open regardless of aperture ring setting. Set the camera on Av. You can then focus wide open with the lens if you want. Then switch the lens to Manual. The aperture will now change by moving the aperture ring, and the light meter will see the changes as you make them. So it acts kind of like it should. Exposure compensation works too. Metering switches to center-weighted automatically if it was on multi-segment.
Focus can get tricky at this point because the viewfinder will get darker at small apertures, and depth of field will increase. Different lens brands have different switches placed for film cameras, maybe not conveniently located.
As for the OP's original question, I would make sure the A50/1.7 stays on the A setting, because it has a weak spot when switched off of A. There's no reason to ever take it off A on a DSLR anyway, and it will work fine for a long time. The only A lens that I ever saw with a focus problem was dropped; even still, I fixed it and it was fine. I have a 45 year-old Takumar that focuses perfectly and smoothly, and I expect it could outlast me.