I have a lot of scopes from very old and cheap to quite expensive. Several are Zeiss, two of which are very old. One in particular I used for several years on a 270. During that period it seemed that I had bad weather everywhere I went. Lots of rain and snow and cold. I kept thinking I was going to have to go to a back up rifle as the weather was so bad particularly taking the gun from very cold into warm cabins. I never had a problem. But, I have only had one scope fog and Weaver replaced it even though it was very old with a lot of bluing missing.