The only problems with Leupolds I've seen, is nil, while 'almost' every Zeiss exposed to a wet 10 day hunt has fogged. Swaroski's also stayed clear, as did Bushnel 3200's and 4200's.
I have seen guys come in from a day's -35 moose hunt with their cheap muzzleloading production rifles (I'm being nice calling them rifles), remove the barrel from the stock and shove the breech, including the ocular lense of a 4X Leuy into almost boiling hot water right off the top of a wood stove, yet never saw one fog or fail - frightening to watch.