Fogged up viewfinder on E-M5...common? Solutions? Problem?

This is common - Robin Wong blogged about it for instance. The fogging is due to it being sealed a little too well combined with temperature differentials.

From Olympus website:
"When going from extremes in temperature (for example, moving from an air conditioned environment to a hot environment or vice versa), condensation may form inside the camera. Even though the E-M5 is weatherproof, it still may contain humid air because the camera needs to "breathe" to compensate for changes in internal pressure when lenses are zoomed, particularly long focal length zoom lenses. The condensation will disappear in a few minutes when the temperature of the camera has stabilized in relation to the shooting environment."

What's scary is if too much condensation builds up to vent properly... never had to deal with it though.

 

I've had this happen a few times to my E-M5 in the rain. It's always cleared OK and I've not experienced any adverse effect. I'm not convinced about the temperatures and condensation explanation though. That would imply it would happen in cold conditions too and I've never experienced this - only in the rain.

 

All enclosures need to breath, otherwise they would inflate or deflate with change in atmospheric pressure. We all fly don't we. Given that, the enclosure of the 'EM-whatever' will ingest the current atmospheric conditions... the rest needs no explanation.