I've noticed that my SMC Takumar 135 doesn't touch any of the pins on he mount; they're all completely exposed with the lens mounted. I have to wonder if that has something to do with it. I'm pretty sure my M50 covers them all - and stop-down metering works a treat with that.
... Then again, stop-down metering doesn't work with my Tokina big zoom thing, which attaches via an adaptor, which I think covers all the pins ... But perhaps isn't conductive.
Oh I don't know ;-) Av mode or Sunny16; that'll do.