Unexpected problem with the 5D

So we’re on vacation on Hilton Head Island, just getting used to my new 5D. I was out shooting with the 24-105 - twilight to early evening. The 24-105 had been on the camera since they both came out of the box.

The temperature was probably 86 degrees. Not hot, but fairly high humidity.

I’ve got my 17-40 with me, so I switched lenses. No problem with that. The 17-40 is awesome with full frame, BTW. When I’m done, I go back to our rental house, which has the A/C running on high. The temperature in the house was in the low 70’s with, I presume, low humidity.

The next night, we head to the beach to shoot the sun going down. Basically the same outside conditions, so I put the camera in a plastic bag for about 10, to adjust to the temperature change. When I took it out a tiny bit of condensation formed on the lens, but dissipated within 1 minute or so.

So, here comes the problem: the mirror fogged & would not clear. I finally gave up after about 45 minutes. When I got back to the house, I took off the lens & used the rocket blower on the inside. The mirror finally cleared.

Here’s what I think happened: When I changed lenses outside, the night before, I trapped high humidity inside the camera. During the next day, the air inside the camera cooled (but not enough to develop condensation). Next night out into the heat, I get condensation inside the camera that won’t go away (even after a controlled move from cold environment to hot).

Does this make sense or have I got the science messed up?

If so, it adds another issue to the condensation problem. May one needs to switch lenses in a cold environment after switching in a hot, humid one.

Sorry for the long post. Maybe others will learn from my mistake.

For something like the house to the beach, I would think that having the camera in a camera bag would be good enough to get it acclimated to the humidity.

Is it possible that perhaps the plastic bag actually prevented the camera from NATURALLY acclimating itself to the surrounding humidity?

The only time I had my camera/lens fog up was when I went in some kind of green house at the botanic gardens. It was stupid humid in there and I had to walk out of there to clear out my camera.

No, because the lens was fine, for the most part.

I think the camera, itself, being sealed prevented the humidity level from equalizing when back in the low indoor humidity

Same problem, in reverse, when back out in the heat. High humidity (& low temperate) trapped inside the camera with the body itself providing a measure of insulation

I think I could have fixed the problem by removing the lens, but I was not inclined to do so at the beach. There was some breeze, although I did not detect blowing sand.

As a former resident of Savannah, I can predict that the humidity was around 90-95%, which might be outside the operating parameters for the camera. Don't know though.

Im not saying this is what happened, but your reasoning is off a little bit.

If you trapped hot humid air in the mirror box and then took the camera inside, the condensation would have formed in the camera overnight as it cooled.
If no condensation formed over night, taking it outside to where it is warmer would not cause it to magically form.

You could be right. That's why I posted the question. Maybe it just takes a long time for the camera to adjust to the temperature.

My stategy for the rest of the vacation was to store the camera gear in the trunk of the car. The car was in a carport & the temperatures never got too hot. Never got higher than the upper 80's in the trunk.