Travelling with the Nauticam 230 dome is a pain. The 6" cast acrylic Ritchie dome I made is not as good but can be used with Sigma 15 and Nikon 18mm without extension. I am considering a 170 dome. Anyone compared the Zen and Athena domes? I would be using it with the 15mm Sigma (with compromised placement since the 170 is not a hemisphere, but fisheye's are forgiving) and a wide rectilinear, probably 18mm Nikon. If and when I return to crop-sensor from a D800 I will use the Tokina 10-17 with it.