I’m often asked for a camera/housing/lens combination that works for freediving; photographing whales, dolphins or pelagic fish. The optimal optical performance might be with a superdome and the very best view of the groundglass might be with an S180 viewfinder. But, together they are rather big and heavy, with considerable water resistance. Sometimes, it doesn’t matter how good the view is if you can’t get to where the animal is (and back to the surface). In these situations, smaller may be better.
Here is the S180. Note that it is heavy because it contains a lot of very high quality glass, prisms, and very little air to contribute any buoyancy to offset the weight.
Here is the Pro viewfinder. Much less weight, and with a wide port or a fisheye port, a very streamlined housing package. The Pro viewfinder still offers a very nice view of the focus screen and viewfinder information, not enlarged like the S180 or S45, but still quite adequate for focus and composition on quickly moving subjects and reading viewfinder LED.
Now, consider a lens and port combination for this application, the Tokina 10-17 and fisheye port. See image explanation at bottom of each test photo:
CONCLUSION – For blue water work, or any wide angle situation where smaller size and minimal mass is important, the Tokina 10-17, fisheye port, and Pro viewfinder is an excellent option. Note that the lens will vignette on full frame Canon camera (1DsMKII/III) and even on the 1.25 crop MKII/III. It is perfect for any of the Nikon 1.5 cropped sensor camera such as the D2X or D300.