About ten or twelve years ago or so I bought a used Zeiss Diatal-C 4x32, used, in Paris. Some idiot had glued their 26mm continental size rings to this 1" tube 'scope with Araldite. The rings eventually came off but they left a ring or Araldite around the 'scope tube in the two places where the rings were. I had read that Araldite doesn't like being frozen. So this Zeiss went in the deep freeze for one day, then two days, then three days trying to enable me to remove the Araldite. It did eventually work with enabling me to pick off the Araldite. But what I can say is that after you'd taken a half a minute and wiped the ice from the front and back lens the 'scope worked perfectly. No fogging at all. Ever since then I've used nothing but Zeiss 'scopes.
Some people apparently rub the lens with a cut potato.
Use butler creeks or other lens covers. I sit in my fox box in -20c and below with scope lenses uncovered without issue, although the moderator and barrel that stick out of the shooting opening get a nice coat of ice.....
And, dont breathe on the lenses.
Yup , rule number one if you're hunting in the cold . When we're out in the late season , I leave my rifle , cased , in the back of the truck . I hunt in some pretty remote country though , I wouldn't recommend doing it in the UK lol .
A leather doeskin? or thin sheet rubber cover held onto the scopes mid body with a cable tie it is homemade looks like shiite but is like a flip off cover for the front lens? works for me and we do get -10C. When you are in a shooting position it falls away naturally
You have to make sure your breath doesn’t go near the scope. It’s very easy when getting set up to breath all over the eyepiece. See through lense covers can also help. Keep on an wit them off at last moment. I have never with flip up scope covers - they just break. More of an issue can be snow.
Or use open sights - they can never fog or get disabled by snow.