So my 17-40 has something wrong with it (probably just needs cleaning) were when it gets cold it stops focusing properly. This last weekend I was shooting relay for life so I obviously needed it to work, so I came up with the idea of rapping a bandana around it with a hand warmer stuff between to keep it warm. And low and behold it worked .
In my first round of testing it didn't work since I was putting the lens in a seal container and the handwarmer needs oxygen to work, but after just putting it outside it worked perfectly .
Just wanted to show a creative way of solving a gear problem.
Here are some shots from the freezer test.