This is a common problem in astronomy. Unfortunately acclimatizing wont help, unless you're going from cold to hot. The problem is down to the lens cooling to a temperature lower than the dew point of the night air (i'l spare you the complicated reason why). Generally, a dew shield helps delay it (basically a longer hood), but only heat will prevent it. You can buy dew straps which are basically heat matts that wrap around the circumferance, or just give it a blast from a hairdryer, you can get 12v jobbies that will run off of one of those portable car battery chargers. That might be too much kit for you, but astronomers tend to have them around for powering their mounts anyway...