The lost field of view compared to air depends on the water between the port and the back of the wet lens. Say that in air that distance is 2mm once you put it with water that becomes 2*1.339=2.678
As the camera has a focal multiplier of 2.7 is like you zoomed in additional 1.83 mm at 35mm equivalent so you are now at 30mm before hitting the lens and not anymore 28mm as you were in air. This explains why you still loose some field of view
End of the lesson!
not sure how you get focal multipler of 2.7 or 2.678. But if an object looks bigger, it should look like it is closer, not farther away.
There is a point where when you have a wider lens, all you are going to see is vignetting from the edge of the wet lens. I am not sure how your housing/lens relationship interact with the wet lens, but with mine, even if I pull the wet lens forward 5mm, there is no vignetting in its widest setting, so there is a little bit of extra built into the wet lens.
Anyway, flat port multipler is not linear. If you put an object 0.1mm in front of a flat port, it will not magically look 1.33x bigger. If it does, any object that is stuck to the front of your mask, then suddenly pulled away ever so slightly, will have a drastic jump in image size, which it don't.
For a port to wet lens and port to camera lens of 2mm, and a nodal point of 26mm (which seems to be my camera's nodal point), the magnification effect by the water is only 1.016, which is 1.6%. That is too small to account for any variation in field of view (this doesnt take into account of the subject getting demagnified when the light goes from air to water medium of the rear of the wet lens(like looking at one's eyes thru scuba mask).
Slightly different topic, but I wonder whether it is feasible to convert my S&S DX-1G wet lens to a Nauticam RX100 housing. It works well with that 24mm lens and has the inner lens diameter 42mm, which seems big enough. The S&S plastic bayonet unscrews and a well centered 67 to 50 something step up ring will fit using the original screws with some careful drilling.
Is that likely to work?
//O
I guess you have to see what the S&S wet lens' rear element's OD and the image size it throws out (should be pretty much the diameter of the rear element at close range. Should be larger than your camera's lens, and it should be able to mount very close to the rear port. The exit pupil has to be a bit larger than the camera's front element. Putting a cameraphone's lens 1 inch behind the wet lens will produce much better result than putting a large format camera's lens at the same distance.
