Something I have never heard of before and never experienced is lens fogging. The only exception is going from an air conditioned room into the cold. So when watching this video I was quite surprised to see the chap using electric lens warmers. Is that a thing? In Australia of all places at 2 degrees at night it,is not something I would have thought would be needed. Certainly here in Blighty I can honestly not think of a time, even at -9, that I have had an issue. I have also shot inside the artic circle with wind chill at -38c and not had a problem although my Sony tog friend got through a suitcase of batteries before his EVF gave up due to the cold.