One easy way to combat any condensation is to leave all your gear outside, simple enough however if you are like me the thought of leaving over $10,000 worth of camera gear in your car or on hotel balcony can make you slightly twitchy and restless, then read on and I’ll tell you how you can avoid that horror scenario.
When going from hot to cold you will need to cool your equipment down, the best way is to throw some freezer packs into your camera bag in a separate compartment and then leave it closed. I use these from Amazon for $20 as they are super thin and can be placed anywhere inside. If you are staying in a hotel check the freezer (if you have one) is actually on when you arrive, then you can freeze your packs.
It’s worth noting batteries perform far worse in the cold so keep them warm for as long as possible or slip them into your packet with a hand warmer for example, these hand warmer packs from Eddie Bauer do the trick, can heat an entire compartment in another bag too and only cost around $30. A good alternative is keep them in the same pocket as your mobile phone as that will keep them just warm enough too. Check the heat from the heat warmers (which ever you choose) before you set off mind as they do get toasty.
Make sure your freezer pack is in with your camera for at least an hour before you head out. Pro note (i.e. I learned from this mistake), make sure you wrap the freezer pack inside a zip lock bag so your camera and lenses are not splashing around in water by the time you use them.
If you are in a hotel and have a fridge you can set the fridge on its highest temperature and place your camera and lens in there. Do not place your batteries in as well as they will under perform when you go to use them. Keep them charged at ambient temperature. When you’re ready to go place your cold camera into your bag at the very last moment before leaving the room. Use a freezer pack to keep it cold during transportation, you could take it out after you know the lens doesn’t fog up.
Doing all this should stop your equipment from fogging up, at least in some part when going from hot to cold temperatures. Do not open your bag again until you’re ready to start your photography.