Olympus 12-45 F4 suitable for UW photograhy?

On the 12-50, I think you can assign a button function to go close-up. I am not sure about the extreme close-up. If you go to menu and select the fish icon and assign it to a button it will zoom in from wide to tele, once activated. It seems to focus about 12 inches.

That is correct, but you can’t access the true macro range without the physical switch on the lens barrel, which is why the dedicated Nauticam port and gear are so complicated. 

If you don't have the Nauticam dedicated port available then the the magnification of the 12-50 is quite low and the 12-40 lens does better.  Even with the switch activated it's only 0.36x, while the 12-40 achieves 0.3x and the 12-45 gets 0.25x.

You can use wet lenses on the 12-50 of course but the CMC-1 only gets to 0.8x at the unusable working distance of 14mm  on the Nauticam flat port.  The working distance is better with  the Nauticam 4"dome and their special flip holder.  But probably irrelevant for AOI housings.

I couldn't find the max magnification for the 12-50 without flipping the macro switch but I expect it's probably similar to the 12-45 lens and the 12-45 behind a 4"dome is probably more versatile than the 12-50 behind a flat port and is certainly a sharper lens on land.  You only miss out on using wet lenses with that solution. 

19 hours ago, Interceptor121 said:

Uhm I think you are the one missing the point

I can't believe I'm arguing with a stranger on the internet about what exactly the premise was of my own post.  The point is that people who already own a dome for the 8mm but who want to shoot the 12-45 underwater may not need to buy a second dome.  My test shots lie about halfway between shooting a grid and shooting in the real world; lines seem straight and text is crisp and legible right out to the edges.  Other's results may vary, but I'm perfectly happy shooting this combo vs. buying (and traveling) with a dome designed for mediocre 1st generation M43 zooms like the 14-42 and 9-18.  To my knowledge, nobody is making a dome specifically for the 12-45, so anything out there is a compromise.

I can't believe I'm arguing with a stranger on the internet about what exactly the premise was of my own post.  The point is that people who already own a dome for the 8mm but who want to shoot the 12-45 underwater may not need to buy a second dome.  My test shots lie about halfway between shooting a grid and shooting in the real world; lines seem straight and text is crisp and legible right out to the edges.  Other's results may vary, but I'm perfectly happy shooting this combo vs. buying (and traveling) with a dome designed for mediocre 1st generation M43 zooms like the 14-42 and 9-18.  To my knowledge, nobody is making a dome specifically for the 12-45, so anything out there is a compromise.