Tokina 11-16 and small subal dome port

Got very bored yesterday and was playing about in a bathtub full of water trying to get my 11-16 to work and it fits (very very snug fit) behind a subal dp 84 dome port with a +3 dioptre and seems to work reasonably well without vignetting throught the range - not sure how sharp it will be (trying to take photos with one hand of my other hand!) but am going diving this weekend so will try and get some shots then. interestingly if you reverse the zoom ring on th 10-17 and add a 1.4x TC this also works behind the same port and lets you zoom through the whole range