sea and sea dome port help please, canon 17-40mm

Interesting you you rate the sea & sea optical glass as one of the best domes, isn't this only about 6-7" diameter? I have read the large sea & sea fisheye dome is optically better than their glass offering. I do prefer glass domes though for durability. I did plan to get a zen 9" dome and an adapter made for my sea and sea rig but on arrival of the sea&sea fisheye dome I was quite impressed so it would be silly not to give it a good trial hence asking the questions here

I have the large Sea & Sea acyllic dome and it is one of the best but, with the Tokina, the smaller optical glass dome excels. Can't tell you why. Maybe it's the perfection of the curve or the position of the lens node or both.

I know it's been a while since this post was published but I have shot a lot with the 5DmkII with the Canon 17-40mm using the Sea & Sea housing with the large acrylic dome port and the 40 extention and for this lens it is the best combo. The small dome with extention and the large dome w/o extention all led to poor image sharpness in the corners. The 15mm with no extention and the 8" port is a great combo and had no problems with sharpness issues.