🔍 Why Optical Glass Domes Outperform Flat Ports Underwater

There are several factors that make domes outperform flat ports underwater, including the physics of how light travels at a different speeds over air versus water, magnification, refraction, and field of view. For underwater or split-level imaging (half over, half underwater) Outex dome ports outperform flat ports because they correct for all those distortions. In addition, Outex optical glass ports are better than acrylic or plastic ports. They are optically superior (clearer, sharper), vastly more scratch resistant, and less susceptible to reflections and glare. While there are complicated optical variables at play such as virtual-images, we’re summarizing the key benefits below:

Advantages of Domes over Flat Ports

1. Refraction and Field of View

• Flat Ports:
  When light passes from water → glass → air (your camera lens), it bends due to refraction as light travels slower thru water than air. A flat port magnifies the image by 25%~33% and narrows the field of view. A wide-angle lens behaves more like a normal lens underwater, rather than presenting that wide-angle perspective.
• Dome Port:
  A dome port acts as a “refractive corrector.” Because of its curved shape, it places the optical center of the dome at the same point as the entrance pupil of the lens, restoring the lens’s natural angle of view. That means your wide-angle lens remains wide underwater.

@JR deSouza

2. Distortion and Edge Sharpness

• Flat Port:
  With wide-angle lenses, a flat port causes soft edges, blurring, and chromatic aberration. The water-to-glass angle varies across the port, so off-axis rays bend unevenly.
• Dome Port:
  A dome equalizes these angles, minimizing distortion. You still need to stop down the lens for sharpness (f/8 or higher), but edges are far cleaner.

@Damon Loble

3. Split-Level (Over-Under) Photography

• Flat Port:
  A flat surface doesn’t allow water to “cling” smoothly, so the waterline is jittery and irregular. It also magnifies and distorts the underwater portion differently from the above-water portion, making split shots look awkward.
• Dome Port:
  A dome creates a smooth, natural transition at the waterline. The curved surface helps hold a stable meniscus (waterline curve), giving that clean, cinematic “half-in/half-out” look. It also balances magnification above and below water so both halves look proportional.

@Jessica Haydahl

4. Close Focus Wide Angle (CFWA)

• Flat Port:
  You can’t get close with a wide-angle lens because of magnification and distortion. This often leaves you with too much water between subject and camera, reducing clarity and contrast.
• Dome Port:
  Domes allow you to get physically close to your subject while still capturing the full scene. This shortens the water column, improving color, sharpness, and contrast — essential for dramatic reef, wreck, or model shots.

@Matt Addington

✅ In short:

• Flat ports are fine for macro (where magnification actually helps).
• Dome ports are essential for wide-angle, split-level, and creative underwater shots because they restore your lens’s natural field of view, reduce distortion, and handle the waterline beautifully.

🔍 Why Optical Glass Domes Outperform Acrylic Domes

1. Optical Clarity & Sharpness

• Acrylic:
  Acrylic isn’t perfectly optically neutral — it scatters light slightly, reducing contrast and sharpness. Over time, micro-scratches from salt, sand, and cleaning make this worse.
• Optical Glass:
  High-quality glass (like the kind used in camera lenses & Outex ports) has superior transparency and doesn’t scatter light the same way. It maintains full resolution, contrast, and sharpness edge to edge — especially important for today’s high-megapixel sensors.

@Paul Toma

2. Scratch Resistance

• Acrylic:
  Soft and easily scratched. Even wiping with the “wrong” cloth or touching sand in the water can leave visible marks that show up in your photos and videos. Scratches near the center of the dome are particularly destructive.
• Glass:
  Much harder, far more scratch-resistant. You can clean it like a normal lens (carefully) without worrying about hairline scratches ruining your shoot. For professionals shooting in harsh conditions (surf, sand, travel), this is a massive advantage.

@Craig Coker

3. Reflections & Flare

• Acrylic:
  Acrylic domes generally don’t have advanced coatings. This makes them more prone to reflections, glare, and chromatic aberrations, especially in split-level shots with bright skies and dark underwater scenes.
• Glass:
  Optical glass domes can be treated with anti-reflective and hydrophobic coatings, reducing glare, flare, and ghosting. They also shed water droplets more effectively, which is crucial for split-level shots.

@Dan M Lee

4. Durability & Longevity

• Acrylic:
  Lightweight, cheaper, but degrades with scratches, UV, and exposure. Many divers treat them as semi-disposable, replacing every few years.
• Glass:
  Heavier and more expensive, but lasts virtually forever if not cracked. For serious photographers and filmmakers, it’s a long-term investment.

5. Professional Credibility

• Many pro underwater shooters, broadcasters, and production houses insist on glass domes because they can trust them to deliver consistent, uncompromised results on high-value projects (documentaries, commercial shoots, Olympic sports, etc.).

@JR deSouza

Another advantage of the Outex Domes:

In addition, Outex ports (flat and domes), which are all made of optical glass, conform to each lens, which positions them optimally for optical results. The Dome itself is universally compatible, and the adaptors and clamps position them to conform to each other. In other words, the dome adaptors and clamps position the dome in accordance to the physical specifications of each lens, positioning them for ideal imaging results. 

By contrast, most lenses, "float" inside other hard case housings, so you may end up with vignetting, or other impediments to use. With Outex you know the positioning and fit will match to optimize the imaging characteristics of the specific lens being used, delivering the best results each time.

✅ Summary:

• Acrylic domes = lightweight, cheaper, okay for casual use, prone to scratches and optical compromises.
• Optical glass domes = sharpest, most durable, scratch-resistant, and professional-grade — the standard for anyone shooting serious underwater or split-level content.