Hey everyone,

One of the most important yet often overlooked parts of underwater photography is choosing the correct distance between your lens and the dome port. This is exactly what extension adapter rings do.

The Salted Line waterproof camera housings support a wide variety of lenses, from ultra-wide fisheyes to standard zooms. To achieve sharp corners and avoid vignetting or softness, you need to set the right optical distance. That is where our interchangeable Extension rings (V1, V2, V7 and V10) become really useful.

These lightweight polycarbonate adapters let you fine-tune your setup quickly and easily without having to buy a completely new Dome port every time you change lenses.

Why Extension Rings Matter

A Dome port delivers the best image quality when the lens sits at the precise optical distance from the curved glass. If the distance is wrong, you can get reduced sharpness in the corners, distortion, or dark vignetting. Extension rings solve this problem by adding exactly the right amount of length between the housing and the dome port.

The extension rings we discussed in the blog post are made specifically for Salted Line/Sea Frogs 6-inch and 8-inch dome ports and use the standard 90 mm bayonet mount. They are quick to swap, include spare O-rings, and come with a small tube of the original Silicone grease.

Our Extension Ring Lineup

Here is a clear breakdown of the most popular versions:

Important: On every Extension Ring product page, in the "Compatible Lenses" section you will find the full list of tested lenses with which the extension ring works perfectly. If your lens is not listed there - unfortunately, we have not tested it yet.

• V1 Extension Ring (23 mm) The shortest option. Perfect for many wide-angle prime lenses and compact zoom setups that need minimal extension.

See the full list of compatible lenses in the "Compatible Lenses" section on the product page.

• V7 Extension Ring (37 mm) It works extremely well with popular lenses such as the Sony FE 14mm F1.8 GM, Sony FE PZ 16-35mm F4 G, Sigma 18-50mm F2.8 zooms.

See the full list of compatible lenses in the "Compatible Lenses" section on the product page.

• V10 Extension Ring (61 mm) A longer ring that gives excellent results with certain zoom lenses that require more distance for optimal corner sharpness.

See the full list of compatible lenses in the "Compatible Lenses" section on the product page.

• V2 Extension Ring (88 mm) The longest in the range. Ideal for specific longer zoom lenses (for example Sony 16-35mm F2.8 GM) when maximum extension is needed.

See the full list of compatible lenses in the "Compatible Lenses" section on the product page.

Useful Information for Those Buying a Complete Kit: If you purchase a Camera Housing with Dome Port Kit (Dome Port + Extension Ring already included), the full list of tested lenses is also shown in the product description and in the "Compatible Lenses" section. 

All rings are fully interchangeable, so you can mix and match them with any of your Salted Line 6-inch or 8-inch dome ports.

How to Choose the Right Extension Ring

1. Check the recommended extension length for your specific lens (you will find this in the compatibility list on each dome port product page).
2. Most photographers start with the V7 (37 mm) because it covers the majority of popular wide-angle lenses.
3. If you shoot several different lenses, it is usually much more economical to buy one dome port plus a couple of extension rings instead of multiple complete dome assemblies.

Important note: Extension rings are designed only for dome ports and cannot be used with flat ports or stacked together.

Pro Tips from the Field

• Always apply a thin, even layer of the original silicone grease on the O-rings before installing the ring.

• Be sure to regularly grease both O-rings: the one between the extension ring and the housing, as well as the one between the extension ring and the dome port.

The Bottom Line

The right extension ring makes a noticeable difference in sharpness, especially in the corners of your images. Instead of buying a new dome port for every lens, you can simply swap the extension ring and keep getting maximum optical performance from your Salted Line waterproof camera housing.

If you already own a Salted Line dome port, adding one or two extension rings is one of the smartest and most cost-effective upgrades you can make.

Have questions about which extension ring works best with your lens and Salted Line waterproof camera housing? Feel free to email us at support@saltedline.com or message us on social media. We are always happy to give you a personal recommendation.

Stay safe, stay dry, and happy shooting!

- The Salted Line Team

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