Actually, I always shoot in CINE MODE for exposure ... I find that it is too easy to blow out highlights with the other automated exposure modes. I started out shooting in 60i, and am now shooting in 30p.
We do a lot of macro photography in southern california, because, dive conditions are often too poor for wide angle, and fish or other larger scale marine life is scarce.
I have been doing some video macro, but, unless the nudi is actually doing something, it is like trying to do a video of a pretty rock or something. Not really much action and, to my taste, still photography is better suited to nudibranchs, etc.
I have, however, invested in some dive lights, so may take it up again soon
Would be interested to see a still of how the image looks with your stronger diopters behind a dome port.
I tried a +6 dry diopter combination and it worked out well behind the dome port. I was able to fill most of the frame with a 3" nudibranch with good focus. I left the lens at full-wideangle behind the dome port. The combination seemed to work ok. I then tried a +2 diopter on the second dive, and this did not have much effect. I can't recommend this low diopter as being much good.
Exposure is still a problem. I decided to go back to automatic "cine"mode on the HV30 which is full autoexposre with low gain with the shutter locked at 1/60. Unfortunately, I was deep in cold southern california waters with littel light. The footage is viewable, but undereposed a bit.
Next time I will try locking the exposure at f4 in aperature priority, or, better yet, mabe bring some lights.