there is very little you can do to keep the outside from fogging.there are some things you can use that will help.one is a spray called "parkers perfect".it works as good as any of the others.another is a anti fog paste like stuff. just wipe it on and wipe it off.it works but not for long.one thing i have tried that helps a great deal is wrapping a scarf around and over my mouth. it prevents you from breathing directly onto the scope