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Hi @veronac
Your 12-100mm (24-200mm full frame equivalent) lens is too narrow for proper CFWA.
Your 9-18mm (18-36mm FF equivalent) sounds like the better one, provided it lets you focus very close with the dome you have. Can I suggest you do some tests in the water, try focusing closer and closer to the glass, and see how close you can get tack-sharp pictures. Make sure your strobe light reaches the subject, don’t worry about backscatter when doing those tests.
Basically, the 100° FOV you can get when zooming out, combine with very close focusing (within 10cm of the glass) would be a good CFWA combo.
If you’re feeling like shopping a bit, with your system (OM System mirrorless / AOI housing), I’d be looking at getting a real fisheye lens (180° FOV) which would pair nicely with one of the 4 inch AOI mini domes. With this combo, you’d get all the field of view you want, and focusing ability right on the glass.