Users of cameras and eyeglasses will be familiar with the phenomenon of fogging, which occurs when one goes from a cold and dry place into a warm one. This occurs because air can hold about 7% more water per unit of volume for each ˚C of additional temperature. That means that air in warm places is naturally more laden with water than that in cold ones. When the water-laden air hits cool glass, it condenses into a fog that confounds the bespecktacled and shutterbugs.
The other night, I witnessed a special elaboration of this phenomenon unique to conditions including (a) a very cold and dry night (b) a fairly large volume of glass and (c) an instant transition to a warm and relatively humid coffee shop.
The normal fogging occurred, but it would not dissipate after several minutes of waiting. It was then that I noticed that the glass on which the fog had formed was cold enough to freeze it – leaving a thin sheet of ice of the lens. The remedy was a few minutes of huffing to melt the ice, followed by a few more waiting for evaporation.
I am a bit surprised not to have experienced this working with cameras in Finland or Estonia. Like getting mild frostbite walking home from a party, it seems to be an Ottawa experience.