Dome or flat Port?
It all depends on the lens you're using....
✓ If a lens can accept a screw on filter, then it should be shot through a flat port
✓ FLAT PORTS produce stunning imagery above water and underwater too, as these Art Brewer images show
✓ Underwater swimmer photos by firstname.lastname@example.org using a Slant-X, 5DM3 control back with a EF 100mm f:2.8 Macro USM lens in a flat port.
✓ FISHEYE LENSES with their 180° angle of view, have to be used in a dome port.
✓ Above the surface, a dome port is usually shot "wet".
✓ For above the surface imaging, you can use autofocus and shoot either wet or dry depending on your preference.
✓ Below the surface, a dome port becomes an optical element producing a "Virtual Image" that the lens needs to focus on.
✓ The 8" dome used on our Pro Dome ports creates a virtual image approximately 12.5" away from the outside surface of the dome.
✓ For underwater imaging, we recommend setting your focus between 12-15" for optimum results.
(This distance is within the close focusing range of most fisheye lenses.)