First time I have experienced this failure and would not have believed it if I hadn't seen it. (also captured on video)
Conditions: mid 40's, raining, heavy cloud cover. While down at PFC in Vegas earlier this week I was doing some structure clearing training. One of the dudes on the team runs a G17, RMR type2. After moving into position prior to punching out to engage a reasonably far target from behind a barricade he purposefully exhaled his breath, pistol was in a compressed high ready.
As he punched out after his intentional breath, he couldn't find the dot. He pulled back behind cover after realizing the dot was being impacted by the system being fogged from his breath. Took about 12 seconds for the system to clear and dot to become useful again. We stopped the series to dig into the failure. The objective lens was obviously obscured but the failure was the emitter itself. We handed him my pistol with an RCR to perform the same test, rear lens was fogged just the same but dot was not completely obscured. Performed the same set of circumstances with my second rig running 509T2 with the same result.
This was a perfect storm of technique, conditions, equipment but a result is a result regardless. This could obviously be trained out of him BUT it highlights a shortcoming of an open emitter system in this condition set.
Something to test yourself but figured this info could be lifesaving for some of you.
To that note, everyone on the team is moving to an enclosed emitter optic immediately.