I am using a somewhat dated (very dated?) Sony A7R III / Seacam rig and after seeing the success some members are having with the Canon 8-15 I'm considering giving it a try. I was particularly intrigued by this thread where @jjmochi described using the 8-15 with a 2X TC to have a zoomable +/- 15-30mm. I'm wondering if anyone is using the 8-15mm with the 2X TC in a Seacam housing with a Seacam SD dome port. I use the Sony 28mm / Fisheye Converter in my current rig and it's a fine setup, but I'm looking for the versatility of a zoom if possible.

In principle the way to do this is fairly easy, you just need to work out the right extension. I see the Seacam port chart mentions that is using a converted lens with Metabones to use to the PVL25 extension and that the zoom ring is a special. To that you would need to add extension equivalent to the thickness of the converter in question. Presumably you use the recommended Canon extension with the PVL 25, but you would need to confirm that with Seacam and also ask them if they can help you with a zoom ring, otherwise you would need to have one printed.

I would also add that the compact dome or one of the fisheye ports would be more flexible for this setup if you want to do CFWA as you can get quite a bit closer.