For split level shots, there seems to be no large dome option for my Nauticam GH4 with Panasonic 8mm fisheye.
I take over unders with my 4.3" dome but wanted to have a play with something larger, so I decided to make my own.
I found a second hand Ikelite 8" dome, and a Ikelite super wide port body for $150AU ( good deal! )
I sanded the Ikelite body port to fit onto a Nauticam 3.5" mini dome, I used aqua polymer knead glue to attach them together. The 8" dome screws onto this, using the original ikelite o-ring.
So there are now 2 domes the lens shoots through, which might affect image quality slightly, but not noticeable.
I used two brackets attaching the heavy dome securely to the housing for extra strength.
And it works, image quality is great, no chromatic aberration or negative effects at all.
Split image is straight from the camera, showing minimal vignetting.
5510.11.jpg 9.97KB 3 downloads
36131__63470.1402963547.1280.1280.jpg 37.35KB 8 downloads
keand32.jpg 91.27KB 3 downloads
knead.jpg 140.96KB 3 downloads
housing2.jpg 93.86KB 4 downloads
housing3.jpg 194.78KB 3 downloads
housing.jpg 96.19KB 2 downloads
overunder.jpg 311.83KB 2 downloads