Condensation inside lens

If I see it right, a "normal" lens can't be air- and therefore moisture tight. The elements inside the lens are moving back and forth while focussing and adapting the focal length. Therefore one has to be aware of all large differences in temperature in the environment. It's pure physic, that warm air can hold more moisture without condensation that cold air (glasses are fogging, when you enter the warm pub from the cold street). And vice versa: Cold air can't hold that amount of moisture, than warm (in winter you have to rub your skin with a moisturizer cream because the cold air is drying out your dermis).

Changing from warm conditions to cold – so my experience and knowledge - is not as "dangerous" as coming from outside at -10° C/14 F into the well warmed appartment @ 21°C/69 F : The moisture in the air of the warm room will condense at once at the cold photo equipment – except, you are keeping it in the closed bag or even more in a closed shopping plastic bag and let it adapt the temperature for some hours. (This is to consider if you are invited to picture a "party" in cold seasons, coming from the cold car into the "steaming" party. You will have to "pre-heat" your equipment or transport it "heat" insulated from your own flat.)
The other way round: I know, that huntsmen are storing their weapons and hunting optics outside the warm hut in the cold, so that these precision instruments need not acclimatize when leaving the warm hut into the snow. Also the optics itself need to acclimatize with expand and contract.

If a lens shows fogging *inside* because of changing from warm to cold, there has to be before a lot of moisture in the warm environment – and getting into the lens. That never happen to my equipment. OR: Shortly before, you have moved from cold to warm, has used the cold/not acclimated camera, so that the moisture had been "breathed in" in the camera and lens and had there condensed!
   This causes a *very dangerous effect*: Fungus between the lenses, resp. inside the lens! (google it). That "desease" causes normally "trashiness" of the whole lens or have the lens sent in, disassembly the whole optics, clean it and reassemble. The most expansive variant, you can imagine...

In short: Normally it is not so "dangerous" to fetch the warm camera and optics to the cold outside because cold air does not contain much moisture. Normally no danger of condensation.
You always shout store and let the optics adapt the temperature difference in a moisture-tight bag/housinf if coming from rather cold conditions to warm rooms.