Enemy #2: Condensation
This is a problem for shooters in warm climates as well. Way back when, I used to be a cruise ship photographer. We would come into tropical ports like Cozumel Mexico and had to be the first ones off the gangway. We did this in order to set-up for shooting the passengers on the pier with the ship in the background. Frustratingly, we would lose the first 20% of passengers and would have to stand idly by as they passed. Why? Well we would grab our cameras from our heavily air-conditioned photo lab and burst outside into 90°f weather. Immediately, the prism, mirror, lens elements and who-knows-what other delicate innards would fog up. In places like the inside of the viewfinder and inner elements of the lens, one can’t simply wipe the moisture off with a cloth. So we would have to loiter on the pier, looking awfully bored. We could have alleviated that situation by getting up a bit earlier and exposing our cameras to the warmer air before we went ashore. But that would require us getting up earlier and if you know anything of the drinking habits of the average cruise ship photographer, you would understand that our late-night “habits” preclude that from happening.
We tried the old plastic bag method to allow the cold air to mix with the warm air on the surface of the bag rather than the camera, but it did not work as well as theorized. The bags are not 100% airtight and puddles of condensing water on the inside of the bag is probably more harmful than not using the bag at all.
With cold, all of the problems are reversed. The camera is fine and dandy until you walk back in to your toasty warm house and then your lens immediately begins to look like Jack Frost sneezed all over it. Here the bag trick is a bit more successful as the moisture builds up on the outside. Just be sure to place your camera gear in the bag prior to going back into the warm interior of your home.
Currently my personal method for dealing with extreme climate transitions is to avoid them completely. This requires making controlled and stepped temperature increases when moving from climate to climate. Sometimes you can go from cold to warm very gradually at the end of a winter expedition by not jumping into a warm car, but rather slowly bring up the heat and keeping a careful eye on your optical goods.
On the other end of the thermometer, during my ship days, we found that by standing in the open bulkhead when the gangway was positioned, and not sprinting off into the hot sticky weather, we could minimize the fogging with this impromptu temperature transition zone.