Thnx for the answer Walt. I must say my Tamron 18-250 had no problem at all. And if it was just my own sigma 17-70 I might have thought it is an incident and I have a bad copy temperaturewise. But my brother had the same problem withe that lens at the same day. He uses the 350 also. I was just wondering if anyone ever had similar problems. Maybe I should address myself to Sigma itself and ask.
All the others, thnx for answering
Cheers shooting, too bad the snow has nearly gone.