So it's the USB data connection (the CHDKPTP connection), between the Pi and the Ixus that I'm unsure of.
Fortunately the depth we're looking at is less than 5mtrs. So pressure is not an issue.
FWIW, those black frames look suspiciously like hardware failure to me. 1/8 at f3.2, ISO800 should show *something* at 9:00 AM outdoors under almost any weather conditions at aus latitudes.
That will definitely make it easier to seal. But the pressure at a depth of 5 meters is about 1.5 atmospheres. So a leak in the bottom of your enclosure would allow the internal water level to go 1/3 of the way up the inside by the time the pressure equalized.Post some pics of your rig when you get it all together? It would be very cool to see.
but I did not notice a response from you? If one of your cameras is indeed flakey then sending it 5m down where you can't get at it does not seem like a good idea?
Regarding the black image, it would be interesting to see one of the original files if possible.
here's a link to the last, black frame which, on closer inspection, isn't 100% black.. ...curious!