Well that was weird - put the lens on again and it works fine, with or without lens OS on. She was taking bird pics and had it on Tv mode with a fast shutter, and it was good, but even when I put it on auto modes it was fine. The only thing I can think of the battery wasn't fully charged yesterday because she wanted to try the camera out - but I don't think that should make any difference..
update - I spoke too soon - for some reason the Sigma lens just randomly stops working completely. Some of the numbers will start flashing on the back screen (usually aperture) and nothing works. Cycle through modes etc, and nothing. Power the camera off and on again & everything works again, then will just stop. When it's doing this I can hear a whirring & sometimes clicking sound in either the lens or camera body. It definitely seems like there is some compatibility issues with this lens. I guess the lens could be faulty, but if I move it over to my K10 or Kx it works perfectly and I can't replicate the problem.
Last edited by Glen_S; 12-27-2015 at 01:54 PM.