I'm shooting a Canon T2i/550D in a Nauticam housing. I've already got the great 10-17 Tokina FE in the Zen 100mm dome, but I'm looking at adding a rectilinear wide angle for some variation. After much consideration of stepping up to full frame (have an unhoused 5D3 I use above water) or across to M43 for smaller size, I've decided I'm going to stick with my current system for a while longer. I figure I can always reuse a good dome on a future housing.
Most of my diving is done locally in Puget Sound where I mostly shoot macro and occasionally CFWA. However, the driving factor for a new lens option is that I'm booked on a Red Sea liveaboard at the end of the summer where there will be wrecks and larger pelagics like dolphins and sharks.
A lot of the info out there is for Nikon or full frame setups, but these appear to be the options for Canon APS-C:
Canon 10-22: Some people seem to be using it but I haven't been able to find much info about how well it works. It focuses down to 24cm which seems fairly good and it can take diopters to firm up corners. I used to own this lens, but sold it a while back when I moved to full frame above water.
Sigma 10-20: Lots of folks using this too, but many seem to be Nikon shooters which makes me wonder if it just fills a gap in Nikon's lineup better. Also focuses down to 24cm. Sounds very similar to the Canon, but unsure what the differences are.
Sigma 8-16: Looks interesting in that it's so wide. Also focuses down to 24cm. I'm a bit worried that it may be too wide for my purposes. It also seems like getting good corners may be more difficult due to the width and lack of ability to take diopters.
Tokina 11-16: Concerning that this only focuses to 30cm. I've used this above water before, but ended up with the Canon to get more range. Not sure this is really an option.
I'd really prefer something that does well without a diopter, but can take one when I really need improved corners for a great image.
What are others using and how happy are you with it?
As far domes, my impression is that at least an 8 inch dome is required for any of these lenses. That size dome already seems massive compared to my 100mm Zen, but beautiful photos require some suffering I suppose. I'm considering the 8.5" Nauticam acrylic dome, although I'd be up for spending some extra money for glass if it makes sense.
What would work best here? 200mm? or can you get away with the new Zen 170mm in some cases? I think the 230mm and 9+" domes are probably beyond my bulk and budget restrictions.