I quickly tried the 3.5" and 4.33" domes with a 30mm extension on the EM-5 and the 9-18mm and a good +4 topside diopter.
I did not upload the pictures but the findings:
- the 3.5" dome just sits too close (maybe a mm) from the lens and diopter. The result is just unacceptable unless you close to F11 or so.
- the 4.33" dome is acceptable once you correct for distortions (both chromatic and focal). Good results at f8.
However the 4" semidome still behaves better and for some reason it can focus much closer (like 20% or 25% better magnification). Good even wide open!
Maybe with 2 20mm extensions make the 4.33 worthwhile but at this point I do not see a reason to use the 3.5" or 4.33" domes with the 9-18mm.
The trials have shown that at least a +2 diopter will make the 9-18mm lens work well in the 4" semidome. I wished I had known before as I have used this lens underwater very seldom....!
This port can now be used with good results for the 9-18mm, 60mm macro, and 12-50mm lenses. A DIY macro adapter or the expensive flip holder would make it even more versatile. I am thinking the 12-50mm in this port with the new SMC nauticam macro lens would probably be better than the same lens in the super expensive flat port offered by Nauticam to use the lens macro function. I never liked much the 12mm focal length behind a flat port and with an equivalent expensive 4" port and SMC macrolens you could get real macro and reasonable wide angle with this port.
Has anybody tried the 12-50 with the powerful SMC lens?