Hi,
I started to take UW photos at summer'09.
First without external strobe, but since Jan'10 I bought a Inon Z-240.
The first 3 photos where taken with internal flash (with Ikelite good difuser), and the 2 others where taken with Inon.
One of the things I like about A590, is the advantage of use manual mode (with external strobe, I use manual about 90% of the photos).
Of course, have to push one button to toggle between aperture and speed, and then use arrows buttons... takes some time, but it is usable...
With internal flash (and difuser), it have a real good colors (as you can see on first two)...
But external stobe is a must.
The Ikelite housing is very rought and a little big for the camera (it is the middle one, on size), but I like it.
Because it have a 67mm treat, you can use various macro and wide angle wet lens, without any adapters.
I hope I did help you
Good dives