View Full Version : condensation on GND filters

28th of November 2009 (Sat), 22:37
I was out in some cooler weather in the mountains (high 30's, low 40's) and I noticed that my GND filters mounted on the front of my lens started fogging up. They had been out for quite a while (about 45 min) before they started fogging, which I thought was odd because I would have assumed that they had already adjusted in temperature. How come this happened?

29th of November 2009 (Sun), 21:02
Same reason your car gets dew or frost on the windshield in the fall/winter. As they cool below the dew point, moisture in the air condenses on them. That's actually why things fog up when you come inside - the moist air condenses on the cold stuff because the cold lens is below the dew point of the warm, humid, inside air.