Sony APS-C lenses for blackwater?

I did a couple of blackwater dives with my Sony A6300 recently, and found that the 90mm (the only macro lens that I have) is somewhat too slow and prone to focusing on particles in the water, while the 16-50mm is fast, but doesn't have the needed macro capability - I could shoot the baby squids and jellyfish, but not much else.

Between Sony 30mm f/3.5, Sony 50mm f/2.8 and Zeiss Touit 50mm f/2.8, which one would be the optimal choice? I was told by a D500 user that 60mm macro is the most optimal choice for them, but I haven't seen either of the Sony 50mm options being praised for speed, so I'm actually leaning towards the 30mm - it's small, relatively cheap, the comparably wide FoV should aid with subject acquisition, and focus should be snappy. Is there anything that I'm missing with this line of reasoning? I just signed up for a blackwater-focused liveaboard trip, and I want to be fully equipped before I head out

Depends on how small your creatures are, the 30mm does 1:1 but that is right up on the port glass, min working distance is around 24mm.  Maybe a weak diopter on the 16-50 might be an option?

Give it a try with the Nauticam CMC-2 with the 16-55. You'll find the working distance to be doable, and certainly better and more unique than either of the 50mm offerings. 

Dunno, I was specifically cautioned against using diopters, what with how much everything moves around. Looking at Nauticam port chart (I use a SeaFrogs housing, but it shouldn't make a difference), working distance for CMC-2 with 16-50mm is listed as 69-121mm - just two inches of range. I don't have one of those fancy add-on viewfinders, so I'm using the screen to frame and focus, and I imagine that losing the ability to acquire a subject from a distance, then move in while keeping it in the field of view will make life that much harder. It's also more expensive than a SEL30M35, albeit not by much.

I think it will depend on how big the critters are my m43 Panasonic macro lens gets 1:1 at 25mm from the lens, while 1:2 is at 55mm from the lens - the Sony lens will have working distances in the same ball park as this as the focal length is the same.  So on APS-C you would have a 50mm subject filling the frame about 55mm out from the lens more or less.  If they are mostly 50mm and bigger then you might be in with a chance.

Have you considered the canon 60mm 2.8 macro on an adaptor?  I found it focus's well, and is pretty easy to get hold of.  Fully capable of adding diopters to as well?

AFAIK the autofocus speed of A6300 with adapted lenses isn't brilliant (it's much better on the newer bodies like A6400 or A7RIV), but it'd be interesting to hear from someone who has the experience with that specific combination.

I got it to run on my A6500, due to covid haven't had much use of it underwater but where I have haven't had too many issues.  I also have a Sony 90mm, and the 60mm is much more forgiving and seems to hunt less.

if you can wait, over the next few weeks to should get some use from the 60mm in the lovely crystal clear waters of the English channel... so very similar to blackwater...

My trip is in November, so no great hurry

Which adapter are you using?

I used the Canon 60mm macro via Metabones adapter on the A6300 for a couple years, and it focused fine for me (though I've never done blackwater shooting). Later on I used it on the A6500, and I didn't notice any difference in performance (I believe the A6300 and A6500 share the same AF system). Now I use the Sony 90mm on an A7R II, and overall I'd say the focus is slower and more prone to hunting than the Canon 60mm (though I also don't think the A7R II focus system is as good as that of the A6300/A6500). Anyway, like lostloki said, I think you'd probably be happy with the performance of the adapted Canon 60mm. For what it's worth, the Canon 35mm macro and Tokina 10-17mm fisheye also worked well on those bodies.

Thank you, that does sound encouraging. I'll be on the lookout for good deals on a used Metabones IV and a Canon 60mm. Looking at physical specs, those two together are about 35mm shorter than the Sony 90mm, so they should fit into the same port, albeit without the possibility of adding diopters.