By: Todd Winner
There are a lot of decisions when it comes to choosing the right dome port for your camera and lenses. Is a glass dome better than acrylic? What’s the proper size to use with a particular lens? These are just a few of the questions we will cover in this article as well as explain how to use the Nauticam port charts to make an informed decision.
Glass vs. Acrylic
- Image quality: Both glass and acrylic perform very well and optical are very similar underwater.
- Price: The decisions between the two is often made on price. Acrylic domes tend to be about half the price or less of a similar sized glass dome.
- Flare: Glass handles flares and shooting into the sun much better than acrylic. If your shooting style includes the sun in many of your wide angle shots than try to stick with glass. Acrylic domes often show reflections in these type of images.
- Depth: Acrylic domes have deeper depth ratings compared to glass domes. Most acrylic domes are capable of 150m compared to 100m for glass. You should always check the actual depth rating of your dome as some, especially the larger domes, can have significantly shallower maximum depths.
- Durability: Glass is much harder to nick or scratch but minor damage to acrylic domes can usually be repaired with polishing kits.
- Balance: Glass domes tend to be better balanced and weighted underwater. Acrylic domes, especially the larger size ones, tend to tilt port up due to the buoyancy of the port.
- Splits: Glass tends to shed water better for split images but you can still receive good results with acrylic.
In this image you can see the reflection of the lens. This was shot with an acrylic port. For this image, glass would have been a better choice.
All domes are sharp in the center, so when we are comparing the image quality of domes we are concerned more with the corners and edges. In general the larger the dome the better the corner sharpness. Knowing this, it seems like the solution is to use the largest dome possible but this is not always necessary, practical or the best solution. Smaller sensor cameras can use smaller domes and still retain good image quality. This is also more practical as most users of smaller sensor cameras are concerned with size. Fisheye lenses can also use smaller domes and still retain acceptable corners. In fact, in most cases a small dome is preferred over a large dome for a fisheye. This is because fisheye lenses are able to focus extremely close and the smaller dome allows us to get physically closer to our subject. This makes them better suited for close focus wide angle and the smaller size has less drag and is easier to use in tight spaces. Rectilinear lenses will benefit from a larger size dome but you want to use what is appropriate for your sensor size and focal length. Split images also benefit from a larger size dome, creating a thinner meniscus or water line. Whenever your image contains important information in the corners it’s a good idea to stop down to retain good detail. f/8 is recommended for APS-C and M4/3 and f/13 is recommended for full frame sensors.
Small domes work well with fisheye lenses allowing you to get close to your subject and fill a large portion of the frame with it.
Using the correct extension has a huge impact on image quality. Each lens is different so it is important to know the proper length for each of your lenses. Luckily for us Nauticam is constantly testing lenses and publishes their recommendations for extensions, ports and gears in their port charts.
Large domes are usually the best choice for split images.
Circular fisheye lens like the popular Canon EF 8-15mm f/4L Fisheye USM and Nikon AF-S Fisheye Nikkor 8-15mm f/3.5-4E ED require a dome port with a removable shade. The shade must be removed before shooting at the 8mm end of the zoom range.
Circular fisheye images require a dome port with a removable shade.
Nauticam makes five different size port openings. Typically you will use the same size ports as the opening on your housing but there are are a number of step-up and step-down rings to use ports with different openings. This is most common with mirrorless systems that can use DSLR lens from other manufactures with adapters.
- N200 found on some Cinema housings
- N120 found on DSLR, some full frame Mirrorless housings, Medium Format and some Cinema housings
- N100 found on Sony full frame Mirrorless housings
- N85 found on APS-C and M4/3 Mirrorless housings
- N50 found on some compact housings
Nauticam Port Charts
This is a great resource to get the necessary information needed to set up a lens correctly. You can find the port charts in the learn section or in the footer of the nauticam.com site. Here is direct link: https://www.nauticam.com/pages/port-charts This is also a good place to start if you are thinking about purchasing a lens for underwater use. Chances are if it is a lens that performs well underwater it has already been tested and is on the chart. Start by finding the correct chart for the housing you are using.
Below is a page from the N120 Canon system Port chart. The first column shows the lens. The second shows zoom and focus gears. The third shows port bases like a step up extension. The fourth has the recommended extension length. The fifth has the recommended port often designating one as the most optimal with an asterisk if there is more than one choice. The last column shows accessories that work with that set up like flip adapters or the wet wide lens.