My 2 psi.
If you go with your choice 1 add a +2 diopter, it's a great option but is it super sharp all the ways to corners? It's acceptable . This is with a glass zen semi dome and the orginal EM-5 with 9-18 and a +2
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I don't have the Oly 8mm M Zuiko, I do have the 8mm Zuiko with MMF-3 behind the 170mm Olympus dome that is also glass and it's nice that I can use it or the Oly 7-14 without changing anything but the lens with the focus ring. I shoot the 7-14 more and this shot of Edd was with 7-14 . I could also throw the Oly 8-25 in this and it is REALLY tempting.
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I also have the Pan 8mm on an older Pen housing that makes a GREAT super compact travel set up but is also a PITA to change ports so when travel with I am limited to only 8mm fisheye, and I'm weird in that it not my favorite look (most like it)
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So basically, I HAVE great options at hand.. you know what I am VERY tempted to do, because my gut is telling me I will get more enjoyment and also equal or even better quality? The silly 12-42 3.5-5.6 EZ behind a flat port and the AOI UWL-09 PRO (but I suspect the non pro would make me happy but hate acrylic domes because I do scratch them) with the quick release system that would also give me options like using a close up lens to change and adjust style of shooting which for reef diving is simply awesome. This is what your post made me immediately think would be the best answer to your question
Do I need to do anything at all? Hmmm.. not really but I have to say I really want to try both the 8-25 and the UWL-09 Pro routes. That is why I have some of my old strobes up for sale right now... because going to try both then see.