I take most of my UW images in dark conditions with a low level or lack of ambient light using high ISO, a large aperture, slow shutter speed and stobes.
The OM-D is a great camera in that kind of environment thanks to the 3-axis image stabilization and good low-light performance.
However i have a problem with the built in flash when triggering the external strobes. Light is leaking out through the housing and dome causing backscatter in the center of the images. I'm using a Panasonic 8mm + Nauticam housing with the 4" fisheye dome.
This is only a problem in dark conditions described above. I have tried to reduce the power of the internal flash, but the it sometimes fails to trigger the strobes.
I have seen some LED thingy that can be used instead of the internal flash. Is anyone using this and have some experience from it?
The attached image is not the worst example since you have some surface light, but you can clearly see the backscatter and in darker conditions you will se stripes of backscatter like in the second image shot in the housing with strobes turned off against a white wall.
f/3,5 1/20 ISO800 @8mm