Just to confuse you even further, I choose the following options for the EM-10 in a Nauticam housing:
Nauticam 4" wide angle port for the following lenses:
- Oly 9-18mm with nauticam zoom ring and a +2 diopter for better corner sharpness
- Oly 60mm (no need for zoom gear as AF is fast and reliable). No corner distortion with this lens and wide-angle port. I also made a DIY flip diopter holder for the CMC for about $10. But Nauticam also sells a flip diopter holder for this port for about $400.
eventually, I added the following:
Nauticam 4.33" dome for for a Samyang/Rokinon 7.5mm fisheye lens. I use the zoom gear for the 9-18mm lens to manual focus the lens. But, aperture is set pre-dive. Thus, I can only adjust with SS and ISO during the dive.
Had a very limited budget but I find this set-up adequate for most shooting conditions (fisheye, wide angle and macro).
Hope this helps.