This is my first post and I would like to ask you for advice. I have many years in photography but few as underwater photographer. Underwater, mainly like angular photography. Especially shipwrecks. I usually photograph in Spain at depths of 50-60m with a Lumix GX8 (M4 / 3) + Zuiko 8mm f1.8 + nauticam + Zen 170mm. Sometimes I use a Leica 15mm 1.7 that works perfect with that dome. But basically I use 8mm for wrecks. The advantage of that sensor with that optics is that it allows me to shoot at f2 or even f1.8 at -50m at 250 iso (this is not as bright as the Red Sea) and I get sharpness throughout the frame, including the corners . I'm thinking about acquiring a nauticam for my 5DmkIII and a Sigma 15mm to get a better definition for a project I'm working on. 5D sensor will offer me more quality but I have some doubts. I'm going to lose depth of field, f stop .. I can increase the ISO but I'm not sure if I'll get a significant win by forcing it to shoot at least f8 to not have terrible corners with what it entails to increase the ISO and lower the speed shutter. My idea was to buy the same dome ZEN 170mm. Nauticam recommends the dome 140mm for the sigma 15 but I think I will get better definition in the corners with the ZEN.