There are many threads on this site showing the benefit of testing the flash/picture taking of camera and strobes once setup is complete and prior to reaching/entering the water. Simple things like leaving the lens cap on, forgetting to connect the hot shoe in some housings, etc. Simple to correct prior to diving, impossible to correct once underwater. I learned a new one last Sunday.
I was pool testing my newest purchase - a snoot. Once at the bottom of the pool, I discovered none of the controls on the back left side of my D90 would work. I could not review the previous image nor bring up the Menu. It was a bit frustrating but since I was only practicing on plastic fish, the frustration was limited.
Upon returning home and having it all dry, I could remove the back and manually work the buttons. Put the back on, it all looked perfect but the housing buttons would not fully depress the camera buttons on the left side.
I removed the camera, put it back in, put on the back, and all was perfect again.
Apparently, there is a slight amount of alignment flexibility that can prevent these buttons from working.
Just another reminder...do not just confirm focus/flash/strobe work in the hotel/on the boat, etc prior to getting to the water, also test the important buttons/knobs/switches to make certain it all works.
We can learn by others mistakes or insist on learning it the hard way. So there is my most recent lesson. Hope it helps.
dave
