Salted Line Flat Ports
Flat ports are generally preferred for surf and wave photography, where shooting occurs at or just above the water’s surface. While they can be used underwater, it’s important to note that flat ports reduce the effective angle of view by approximately 25–33% and introduce image magnification due to refraction. Interestingly, these characteristics make flat ports—especially those with a 67mm thread for “wet” close-up attachments—ideal for macro photography, where a narrower field of view and increased magnification are advantageous.

Salted Line Dome Ports
Dome ports are recommended for underwater and split-shot photography, as their curved design preserves the lens’s full angle of view. By compensating for light refraction underwater, dome ports prevent the magnification effect associated with flat ports. They are also effective above the water’s surface, particularly with ultra-wide-angle or fisheye lenses. For shooting with focal lengths longer than 35mm, however, a flat port is typically the better choice.

Understanding the strengths and limitations of each port type ensures you can capture sharp, distortion-free images both above and below the water’s surface.