Also, I think you are adding noise in your post processing.
I suggest with the Inon lens not working below about f4 as the corners will go soft unless you modified your port like I did and I recommend against it, it became a major engineering undertaking with little gain.
SouthFla says;
"I processed and made a handful of 13x19 prints of a few of my favorite ones. I just don't think the small camera sensor can handle the detail of all the underwater world has to offer. While the prints were "nice" they just weren't WOW. The lack of fine detail was pretty evident to me, and the noise reduction clearly took away from some of the detail."
You are not going to get a 13X19 print from an A590 that will satisfy you, the Nikonos could of course cover a wall form a projector with a sharp image, yes, you are expecting to much from what is essentially a toy camera by comparison to a Nikonos.
I suggest:
1. Shoot at ISO100
2. Underexpose (for ambient) by about .5 to 1.0 stops and use your strobe to lighten up the subject
3. Try to keep your dome away from the sun (hard to do)
4. Look for shots were the dynamic range does not go from a sun ball to deep black
5. Ask your fish to be still, works for me because my double hose reg does not scare them like you guys with the hub caps in the face noise makers
.
This is close to what I am trying to do, f5.6 at 1/60:
This is an example of not quite getting it, I was to far from my subject but I did manage to get the sun under control, had I moved in closer it would have worked:
Underexposed on purpose, I like it, y'all may not:
This shot is similar to what you are getting, it is OK but it is too light, washed out, I should have stopped down a bit more and maybe turned my strobe down a bit:
Just trying to help. BTW, I use a Sekonic Marine meter to verify exposures especially in manual mode with my 570 which is as I think you know, set up like your 590 rig. BTW, the 590 due to the increase in MP from 7 to 8 did pick up a bit of noise, several testers have noted this but also stated it was acceptable for this class of camera.
N