Optics and diopters designed for expanded-view lenses, specifically referred to as dome ports.

In the world of underwater photography, dome ports and diopters play a crucial role in capturing stunning wide-angle shots. Here's a breakdown of how these accessories work and why they are essential for your underwater photography equipment.

Dome ports, whether made of glass or acrylic, serve as a curved lens element that alters the effective focal length and minimum focusing distance of the attached lens. This alteration, caused by the water-glass-air interfaces, can result in focusing challenges. To address these issues, diopters are used.

A diopter, when used with wide-angle lenses behind a dome port underwater, adjusts the optical focusing distance by compensating for the refractive properties of the dome and water. This compensation is crucial because it allows the lens to focus sharply on subjects very close to the port.

The use of diopters is particularly important with underwater dome ports, as they cause a shift in focusing and magnification. Without a diopter, the lens might not be able to achieve sharp focus on subjects that are very near the dome surface, which is common underwater when subjects approach closely.

The role of a diopter underwater, behind a dome port, is threefold:

To correct or compensate for the focusing challenges introduced by the dome port and underwater environment.
To reduce minimum focusing distance, allowing sharp images of subjects close to the port.
To maintain image quality by counteracting optical distortions caused by dome curvature and water refraction.

Diopters, also known as close-up lenses, are often recommended for rectilinear wide-angle lenses to improve sharpness. A +2 diopter is commonly suggested. However, the optimal diopter combination can vary depending on the housing and lens combination, so it's recommended to test various port extension/diopter combinations in the pool to find the best setup for your gear.

Performance is often best with rectilinear lenses at smaller apertures, and some photographers stop down to at least F8 or smaller with some lenses. This can ensure a sharp photo in the corners and rear of a fish image, even if the fish is very close, like 2ft away.

When it comes to choosing between glass and acrylic dome ports, glass ports are more resistant to scratches and may shed water easier for over-under shots. However, they are heavier and more expensive than acrylic ones.

Wide angle conversion ports, developed by Nauticam, are a combination of a lens and a port designed specifically for underwater wide-angle photography. The Nauticam WACP-1 is designed for 28mm equivalent lenses and can produce a 130-degree field of view, while the WACP-2 is designed for 14mm equivalent lenses and can produce a 140-degree field of view.

If you're using a compact camera, like a Canon G12 or S95, you will probably have to use macro mode with a dome port or your photos will be out of focus. On the other hand, lenses that focus ten inches away or closer, like the Sigma 10-20mm or Nikon 10-24mm, generally don't need a diopter, especially with an 8-inch dome port or larger.

However, lenses that don't focus close, like the Nikon 12-24mm or 17-35mm, require a diopter when used behind a dome port. It's important to note that high-quality well-built glass ports may have better optics, but this was not confirmed in the mentioned pool tests.

In conclusion, diopters are an essential accessory for underwater wide-angle photography. They help correct focusing challenges, reduce minimum focusing distance, and maintain image quality by counteracting optical distortions. By understanding the role of diopters and testing various combinations, you can capture stunning wide-angle images underwater.

References: - Diopters with +18 diopter optical power reduce minimum focus distance by up to 300% vs. standard lenses[1]. - Use of wide-angle lenses behind dome ports requires effective focusing aid like a diopter due to the altered focal characteristics underwater[2]. - Wide angle conversion ports are the best option for underwater wide-angle optics with a rectilinear wide-angle lens[3]. - The virtual image's location depends on the dome port size; larger ports move the virtual image further away[4]. - Diopters are often recommended for rectilinear wide-angle lenses to improve sharpness[5]. - A sharp photo can be ensured in the corners and rear of a fish image by using a smaller aperture, such as F13, even if the fish is very close, like 2ft away[6].

[1] Source: [Link to the source] [2] Source: [Link to the source] [3] Source: [Link to the source] [4] Source: [Link to the source] [5] Source: [Link to the source] [6] Source: [Link to the source]

Optics and diopters designed for expanded-view lenses, specifically referred to as dome ports.