I have been trying to use my Nikon D2Xs outdoors in the cold weather and it stops focusing within about 5 to 10 min. The rest of the camera seems to function properly. I have a D100 for a back up that works but isnt 1/2 the camera. I have made sure it is not building up condensation. Battery power isnt the problem, I carry a few extras. I thought at first it may be a lens problem but the result is the same with other lenses. I need it to work in the cold air for portrait and sport photos. Is there any advice for cold weather use?