Dome Ports vs. Flat Ports: What the Results Actually Look Like
Mar 11, 2019
The best way to understand the difference between dome ports and flat ports is to see it. This article is a visual guide — real photos taken with Outex dome and flat ports in comparable conditions, with brief explanations of what you're seeing and why it happens.
For the full technical explanation of how dome ports work, why glass outperforms acrylic, and how to choose between the 120mm and 180mm dome, see:
- Dome Ports vs. Flat Ports: Advantages, Differences, and When to Use Each
- Outex Dome Port Guide: 120mm vs. 180mm
Flat Port vs. Dome Port: Side-by-Side Comparison
The image below shows the same scene shot with a flat port (left) and a dome port (right) using a 16mm lens. Notice the distortion and edge softness in the flat port image vs. the corrected, sharper result from the dome.
Left: flat port. Right: dome port. Same scene, same camera, same lens (16mm). The dome port corrects the edge distortion and restores continuity across the waterline.
Outex Pro Kit with flat port (left) and dome port (right) side by side. Dome ports come pre-packaged in a neoprene protective case.
What Dome Ports Fix: Refraction and Magnification
When light crosses from air into water it bends — a phenomenon called refraction. This makes subjects appear approximately one quarter closer and one third larger than they actually are, and creates visual discontinuity at the waterline in split-level shots.
Refraction in action: the pencil appears bent at the air-water boundary. Dome ports compensate for this effect across the full image frame.
Flat ports do not correct for this refraction, which is why they produce more distortion — particularly at the edges of the frame and across the waterline. Dome ports reposition the virtual image of the subject, reducing magnification and restoring sharpness edge-to-edge.
The two images below show the same subject shot with a flat port (Outex 82mm) and a dome port (Outex Dome 100mm):
Canon 16-35mm + Outex flat port 82mm — by Satiro Sodre.
Canon 15mm + Outex Dome 100mm — by Julie Thies. Note the improved edge sharpness and color accuracy with the dome port.
Split-Level Photography: Dome 120mm vs. Dome 180mm
Split-level (half above, half below water) shots are where dome ports make the most dramatic difference. The larger the dome, the greater the separation between the lens and the waterline — which means less distortion and easier focus across both planes simultaneously.
Both images below were taken with the same camera and lens (Canon 6D + Sigma 12-24mm f/4), in similar conditions. The only variable is dome size:
Canon 6D + Sigma 12-24mm f/4 — Outex Dome 120mm. Good split-level result; requires precise control of focal length, aperture, and proximity.
Canon 6D + Sigma 12-24mm f/4 — Outex Dome 180mm. Greater focal parity above and below the waterline; easier to achieve in a wider range of conditions.
Depth of field is a key creative tool in split-level work. A shallower depth of field can be used to deliberately emphasise the disparity between the two planes — which can itself serve the story being told:
The disparity between above and below water focus planes is used deliberately here to tell the story. Shot with Outex Dome 120mm.
Real-World Results: Dome 120mm in Use
The images below were shot by community ambassadors Paul Toma and John Starrett, all using the Outex Dome 120mm. Wide-angle lenses (below 24mm focal length) are recommended for underwater and split-level work.
Split-level shot using Outex Pro Kit + Dome 180mm.
When to Use a Flat Port Instead
Flat ports are lighter, more compact, and less expensive than dome ports. They perform well underwater and are the better choice when:
- Shooting above water — rain, mist, beach, sand, or any surface condition
- Shooting at longer focal lengths underwater (above 24mm)
- Portability and weight are the priority
- Split-level photography is not the goal
Outex flat ports are also nano-coated with an oleophobic and hydrophobic film to reduce water droplet adhesion — an advantage over dome ports, which can adhere to water in less predictable ways above the surface. Learn more about managing water drops in the water drop management FAQ.
The Outex system is fully modular — flat ports and dome ports are interchangeable across all covers and accessories. You can own both and switch depending on your shoot.
Ready to Add a Dome Port to Your Kit?
Both the Dome 120mm and Dome 180mm are available as complete kits in Accessories, or as individual components in Parts. Both work with any lens and any Outex cover.