I should probably mention that I am by no means an expert in dome-port optics but what I know is that the length of your extension ring (ring that goes between housing and dome) is extremely important for overall sharpness/ability to focus (see the lens chart).
I always shoot with the 10-17 and a very small 4" dome and I love it, because of the strong curvature of the small dome you do get unsharp image corners at high apertures. If you want to have the corners tack sharp then you need to stop down to f.8 or lower, but then again, how important is it really that the corners are totally 100% sharp?
Hehe, think of that gorgeous shark over-under shot with the one eye above the surface, teeth clearly showing, almost bumping the dome with his snout, while the sun is setting in the background, now tell me if you really care about having tack-sharp corners
As far as I can see, the only major disadvantage of using a small dome such as my 4" mini-dome is that over-unders are basically impossible to get right, for that you need a bigger dome, I believe a 8" or even a 9,5" is preferred by most.
With a 8" or 9,5" dome of course then it would be impossible/very hard to get close-focus-wide-angle shots of critters :/
It seems there is never a perfect choice that is great for everything but I guess the 6" dome is a good choice to start out with!
Happy bubbles, Morten
- Kenr likes this