I have only really used this lens behind the 4" Zen dome and would love to see images and hear your thoughts about using it with a bigger dome (8"). crop sensor canon.

I have used the Tokina few times with Zen DP170 with Oly MFT camera. It worked very good, although the DP170 is nit a hemispherical domeport, but a smaller section of a sphere. The example images are in the old forum.

See here for the Nauticam recommendations: https://drive.google.com/file/d/1veVw6bFyoFx3JdFk-vo7He2jTde-xaTo/view