Rain X anti fog or something simular might work. If your talking about the lens fogging over from the heat of your eye when it's cold.

My best suggestion would be to get a better scope with better coatings. I've even had cheaper scopes that fog up inside (the scope) when the temp changes. My walmart binocs do that. I got mad and threw them out of my blind last year.[:@]

I had a BSA contender that used to do what you are talking about though. I would shoulder it to aim, and after a few seconed the picture would start to get blurry. I pull my head back and look and the lens was fogged over. Not a very good scope for winter hunting in michigan.

Paul