I'm currently using a Sony A6300 with the 16-50mm zoom in a SeaFrogs housing (the last year's model with the fixed port), and while it works great within its performance envelope, the macro capability is... lacking, as the lens can't focus any closer than about 25cm, so I'm considering options:
- 30mm macro - would fit my current housing, and can focus down to 10cm from the sensor plane, so basically almost to the port glass, but I'm afraid that getting this close to small critters would be quite difficult, plus I'd lose the wide-angle capability.
- Wet diopter - Nauticam CMC-1 is quoted as having 46mm minimum working distance when in front of Sony 16-50mm, with the frame width being 26mm, but what is its maximum working distance? I read somewhere that for diopters, you take 1 meter and divide by diopter strength, so for a +15 diopter like CMC-1, it'd be 66mm, giving me a 2cm window into which the camera can focus - is that correct? What are the corresponding numbers for CMC-2?
- 90mm macro - it's the most powerful option, to be sure, but it's expensive ($1200 new, and it's hard to find used lenses around here - small country, small market - plus I'd need a new housing and port, although I'm probably getting that new housing anyway for the dry dome port and vacuum system capability), and as I understand it, quite difficult to use, as it focuses much slower than the little kit zoom while draining a lot of battery power - moving all that heavy glass back and forth isn't easy.
- 50mm macro - might be easier to use than 90mm, but I've seen some quite unflattering reviews, and I'm not sure how the part where it extends to focus will play with a port - what are the chances that, while retracted, it will start trying to focus on the port glass instead of the subject?
The flexibility afforded by wet lenses is really attractive - I have been on a dive where we saw a seahorse, followed by a whale shark - but I've never used a diopter, so I don't really know which way to go...