I was wondering if there would also be the additional advantage of less condensation risk. Lower pressure means lower partial pressure of water vapour, unless the pressure drop is too small to be significant.
There should be less condensation risk while diving, since more humid air is sucked out, causiing less overall humidity in the Housing.
This is however only an issue for plastic Housings.
The 2nd part of condensation is when opening the Housing at the surface. The Air is generally warmer at the surface compared to the water..
With a vacuum system, more air will rush in when opening the Housing after a dive. That gives us a faster temp change, this causes a condensation as well.
If it is only a theoretical problem or a a "real" issue???
An easy way to get around this should be to leave the Camera in the Housing a bit longer than normal.
Nikon D800, Nikon 60, 105, 16-35, Sigma 15, Nauticam D800, Zen 230mm, Subsee +5 & +10, 2*INON Z240