I have a vortex and a Leica, both don't work well in A fog, but I haven't noticed either fogging up inside. I have to say I'm not impressed with my vortex 1000 at all, the only reason I don't throw it up against a tree is because its easier to work with one hand then my older leica. I only use my vortex now for short range bow hunting. I'd look at a more reliable brand, I'll never buy vortex again.