Alright, its dark here, so I had to adjust the exposure on some of the photos really quickly.
I've also took some photos with the camera from within the housing:
With the h100m67(type 2) screwed directly to the meikon housing port, the vignetting almost disappears by 30mm. I next unscrewed the h100 and placed some step up/down rings to simulate a bayonet adapter. results were not good. I had to zoom in ALOT before the vignetting goes away, and clearly(pun unintended), the quality and clarity of the image becomes almost unusable. In fact, I had to zoom in until it was close to the FOV of the 24mm flat port without wet lens, so it renders the additional wet lens almost useless.
This test/result demonstrates that the distance between the housing port and rear element of the wet lens also plays an important role.
As the h100 I have is a m67 type 2(rear element flush with m67 threads), I will be ordering a type 1 screw ring(rear element protrudes out from m67 threads) to see if I can get the rear element even closer to the housing glass. I would eventually like to adapt the h100 into a LD bayonet mount.
Interesting. You also have to take account of the gap being filled with water instead of air, thus causing more magnification, thus less vignetting. Not sure how much of that would be true since in my last camera setup, I had no vignetting so that was never an issue.
Here is how the lens fits on the RX100's plastic housing:
rx100_28mm.jpg 67.03KB 5 downloads
You can see that the lens sits much further back probably 7-8mm from the rear of the glass port (at 28mm, when zoomed to 33mm (or 12mm, as picture specs indicates)), it is maybe a mm or 2 further back. It seems that Meikon was on a learning process in their design of housings, with the earlier housing the least thought out in terms of design and lacking the most features.
Strangely, the beveled recess of that lens port mates perfectly with the UWL-100 28AD's rear lens protrusion. I did some measurements of the type 2 vs the bayonet mount depth and if I put a type 2 mount on the 28AD, the 2 lenses could mate almost perfectly once it is screwed down, avoiding the vignetting from the UWL-100, and being a much smaller lens. I tried to do the swap, but my screwdriver stripped and didn't want to do harm to the screws, so I will be using the UWL-100 for the upcoming trip.