Q: When I travel to my stalking grounds in a warm car my scope’s lenses fog up in the cold weather. What, if anything, can 
I do to stop this? It’s a real nuisance and very irritating when I want to get out in the field

Bruce Potts offers some solutions

A: It can indeed be a real pain 
when you get to your shooting grounds after a long drive and then, when you remove the rifle from its 
case, the scope’s lenses fog over 
with condensation in the colder air.

If it is just the external surfaces that 
are fogging or showing signs of condensation, it is not too bad.

A bigger problem

It is when the internal of the scope fogs 
that you have a bigger problem on your hands. This means that the scope’s seals have failed and the inert gas used to purge the scope to keep it dry has escaped. This will require repair 
by the manufacturer.

The likely cause

However, it is more likely that the rifle is warm from the car and it is simply the change in temperature causing the problem. To prevent this, keep the rifle in the case but put it in the coldest part of the car — for example, the boot — and then when you arrive at the shoot bring it out and unzip it and let it acclimatise a while to the new temperature. Also open the scope’s 
flip-up covers if it has them.

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Be patient

It is best to wait until the condensation does not form any more, as you know what will happen — a deer will walk out and you won’t be able to see it, and it is dangerous too. I also always have a small scope cloth in a pouch that attaches to the sling so I can keep the scope clear if necessary as I stalk.