Final note: The vacuum check system may extend all the way back to the 70's. I'm asking around to find out more....
I think you will find that doing a vacuum check to ensure that the seals on submersible enclosures are functioning correctly goes back a very long way. I spent a large chunk of my life as a Submarine Engineer Officer in the Australian Navy. The last thing we did before going to sea and diving after an extended period in harbour for maintenance was to close all the hatches, pull a vacuum inside the submarine and monitor over a period of time to ensure that none of the seals on hatches, periscopes etc were leaking air into the boat. This has been a standard maintenance procedure in submarines for a long time. If a vacuum check is good to keep me dry when the submarine dives (water in the people tank is not a good thing ) it's good enough to ensure my camera stays dry when I take it diving.
I think Retra's web site was a little out of date when I ordered my Retra Pro. At that time the angled adapter was offered as an optional extra and I ordered mine without it. When I received it, it was fitted with the angled adapter.
The angled adapter is good in that it allows you to align the LSD so that the aiming light in the strobe is shining on the centre of the light collector in the LSD. This ensures that the beam from the aiming light is a bright as possible and accurately shows where the beam from the flash will fall. The only downside I found was that because the angled adapter is clear to allow you to align the strobe's aiming light on the light collector, it does allow some light from the strobe to escape. Depending on strobe position this can allow escaping strobe light to light the background of your shot. For example:
Although it can work to your advantage as shown in these two shots, in general it doesn't.
However it is easy to fix the strobe side leakage problem. Once I had determined the optimum position for the LSD on the strobe I put an alignment mark on the LSD and the strobe and covered the clear adapter with duct tape.
While I do use a Nauticam housing I am using Subal mount dome ports/extensions with a Nauticam/Subal converter. Therefore, I can't answer your question directly based on what I'm using. The Teleplus Pro 300 is 19mm long so you'll need an extension ring as close to 19mm as possible. I add a Subal 18mm extension ring when using the teleconverter but in your case it looks like the best fit is the Nauticam 20mm extension ring:
While those lenses may fit inside the dome and work without and extension ring the results will be less than satisfactory (distortion, soft edges etc) because the entrance pupil of the lens will not be aligned with the centre of the dome. There's more information here:
Flatworms do have a "head" (for want of a better word) but it is not clearly visible all the time. Here's a couple of shots showing the "head", it's the inverted V shaped bit at the front end. Use this in your composition as you would rhinphores with nudibranchs:
I probably didn't word it quite right, Philippines I've been to once, and Bali I'm probably doing next year. I'm really just looking for something where I can jump off a direct flight from Singapore and jump into the water (more or less), stay there for a couple of days, then come home. Does such a place exist? Tell me if I'm dreaming!
Fly direct to Manado via Silk Air (approx 3 hours from memory) and you can be diving in Bunaken and/or Lembeh.