Focus underwater when shooting video

I know I read about this somewhere before but have forgotten. When shooting video underwater on a DSLR with a lens such as the Tokina 10-17mm fisheye behind an 8 inch dome should focus be set at infinity with an F stop of around F8 in order to have pretty much everything in focus?

focus should be set to 12 in from the center of the dome (which would be more to the centerplane of the sensor) for an object that is at infinity. Anything close would require you to focus closer.

You would need to step down the lens in order for the center and side image to be both in focus since the camera lens focuses on a flat plane and the doe lens creates a circular planed image.

---------- Post Merged at 02:37 AM ---------- Previous Post was at 02:33 AM ----------

focus should be set to 12 in from the center of the dome (which would be more to the centerplane of the sensor) for an object that is at infinity. Anything close would require you to focus closer.

There are some that says a virtual image of such a such distance is created, as if it is like a inward curving TV screen, where all you have to do is keep it focused at that virtual image, but I've seen pictures where the closer subject still requires closer focus.

You would need to step down the lens in order for the center and side image to be both in focus since the camera lens focuses on a flat plane and the doe lens creates a circular planed image.