Tom - That's a really lovely shot ... congratulations! I haven't done any testing on the new 16-35 F4, and have no reason to doubt the port extension suggestions that SEACAM Austria suggests. I personally have the 16-35 II, and Canon Professional Services didn't have loaners on the F4 version last time I asked. But, I'm off the road for a while now so maybe I can put the testing back on my radar. BTW ... the Superdome is a far better solution it appears (and we would expect) than the wideport. Thanks for sharing Tom.
Thank you! Looking forward to your test results. Thus far I used the wideport only for the initial shots in the creek that was just inches deep (post #7, above). The pix taken since with this lens have all been done with the superdome thanks in part to all the rain we have had recently (very dry earlier) so most creeks have been deep.