At what point is it too cold to go out in the cold with a camera? (just curious)
I usually quit by about -25C or so. That's when exposed skin easily freezes. Starting around -20C, I find that my camera's AF speed slows significantly and the motor starts sounding a bit strained. When I was still shooting film, around -20C, you have a much higher chance of tearing the sprockets. At -30C, static discharge becomes a big problem since that will ruin your film.
We were shooting the Rosy Finches in New Mexico last winter on top of the Sandia Crest, 13,000 ft up, -15C but winds 50km/h or stronger. I think I lasted about 1hr or so, but the cameras and lenses were fine.
If you're planning a trip up north during the winter, and expect to hit -35C to -40C, it's recommended to send the camera body and lenses in for the extreme cold treatment. Basically, they will remove all the lubricants as they will all harden. That also renders the camera and lens useless for normal use in warmer climates.
