Articles

A head-on composition showing off more of the batfish's habitat. The curved port restores the normal field of view of the lens behind it, to match the field-of-view on land
 

Some of the earliest lessons you learn as an underwater photographer focus on or revolve around gear. Starting out, at least some gear is an absolute necessity, and let’s be honest, it is really easy to find yourself “needing” more as you grow. You’ll likely reach the point where you have, at the least, one setup for macro and another for wide angle.

You’ll have learned that flat ports and diopters are for macro or super macro, and that dome ports are for wide angle. These generalizations make sense starting out and even experienced shooters might not question, “Is a flat port the right tool?” There are a lot of commonly-agreed-upon lens and port combinations, so luckily we don’t have to reinvent the wheel when matching lenses to ports.

But what if you wanted to try a lens that falls outside of these common lens/port configurations? For example, maybe you have a very specific shot in mind that you are trying to optimize for, or maybe you just like to experiment. What do you do if your subject doesn’t quite match either your macro or wide setup? Can a flat port be the wrong choice here? 
 

Even classically wide-angle subjects like marine iguanas can be photographed with short macro lenses and a curved macro port!

Right vs Wrong 

It’s a little nuanced, but there is not really a right or wrong here, just shades of gray. If I say wrong, what I’m really implying is a suboptimal solution. At the end of the day, if you are happy with your images, that really is all that matters. I genuinely believe that making images that you enjoy should always trump any pixel-peeping. 

With that disclaimer out of the way, a flat port can certainly be the less optimal solution in some situations. The alternative is a curved or semi-dome port, which, unlike traditional domes and mini-domes, is a much smaller section of the hemisphere. Imagine an 8-inch dome that had the top inch or two (or so) cut off—that is the type of curvature we’re talking about here.
 

My custom-made dome port using Subal extension rings and semi-dome glass
 

A sheephead biting at my dome port is not a new encounter, but being able to fill the frame with more of the fish is new compared to similar images taken with a fisheye
 

Let’s dive into a few of the scenarios where I reach for a curved port over a flat port:

• Shooting textures or patterns 

  • If you care about having sharp edge-to-edge details, a curved port can far exceed a flat port.

  • Seriously, the 60mm behind a curved port gives some of the sharpest images I’ve ever shot underwater, exceeding the Nauticam WACP and at the least, rivaling the Nikonos RS 13mm .

• Wider field-of-view while shooting the same lens

  • A 60mm behind a curved port will have a wider field of view compared to a flat port, with improved depth of field. With a flat port, the field-of-view is reduced by about 25%.

  • Essentially, this gives you the equivalent of a new lens. This is especially helpful if subjects are large enough that you’re forced to back up to frame, leading to lower quality light or increased backscatter.  

  • This is also a great way to include more habitat with your images.

• Shooting lenses that are wider than 60mm 

  • I’ve had a lot of fun shooting less-standard lenses such as the Tokina 35mm macro or Nikon 40mm macro. These lenses perform poorly behind flat ports, but add new perspectives to subjects when used with a curved port. 

  • These lenses do perform acceptably behind mini-domes, but with a caveat. The “shape” of the in-focus area will be very curved. Optically, this is very much expected, but my personal opinion is it leads to a less-pleasing effect on images. 

• Creative freedom of composition

  • This edge-to-edge sharpness allows me to place subjects anywhere in the frame, without having to worry about the details getting smeared. 

As a bit of an anecdote, I do open up my aperture much more with a curved port. Unlike a full dome port, where you stop down in order to get acceptable corners, for a curved port you only need to stop down to get your subject in focus. This allows me to shoot closer to each lens “sweet spot” for maximum sharpness.

Although corner-to-corner detail is not a necessity for every shot, it is much simpler with a curved port 

Trade-offs of Curved Ports

If curved ports give you edge-to-edge sharpness, and let you shoot new lenses or perspectives, what are the downsides? For starters, they are largely unheard of and current manufacturers don’t offer them for just about any housings.  

The first curved port I was able to get my hands on was made and discontinued by Subal well over a decade ago. It took quite some time to even track one down, and it wasn’t the more optimal model (DP54B); it was the DP115B. This meant in addition to needing a Type 3 to 4 adapter, it was substantially longer and as a result, harder to pack on trips. 

Availability and the extra space needed to pack on trips are about the only trade-offs. Using a diopter is more or less out of the question. In practice, the 60mm is able to focus on the glass of my curved port, so a diopter doesn’t add much here. I don’t really see this as a trade-off, but more of a consideration when gearing up for a dive. Instead of trying to shoot tiny nudibranchs with my 60mm and curved port, I simply look for larger subjects.
 

A large female nautilus on a lengthy jellyfish. Although the curved port did help fit more of the animal, it is not without limits
 

A large red octopus on the move through the eelgrass. The curved port and size of the subject matched really well, giving adequate space to the octopus to capture more natural behavior in its habitat

DIY/Technical Notes

I’m a bit of a tinkerer at heart, so I took an interest in learning how ports are made—by ripping several of them apart—before trying to build one myself. About half of the images in this article were taken with a self-made design. I also spent a good amount of time reading up on optics. There is quite a bit to learn, and I certainly won’t call myself an expert or even an amateur—that’s why I’ve largely skirted around trying to explain the underlying physics here.

What does seem clear to me is the reason flat ports and dome ports have remained unchanged for decades (and decades): They are simple, generic solutions with a generally fixed price point. The consensus is generally that they work well enough, even if they are unlikely to be the most optimal solution available. 

In the case of a curved port, though, we’re not talking about the same exponential jump in cost that you get when discussing wet-corrected optics. This, in my opinion, puts them into the realm of a “must-consider” tool to—for me personally—a “must-have” tool.
 

A female nautilus shares a salp chain with several smaller nautiluses (likely males)
 

To follow along with Aaron and to see more of his fantastic images, please follow him on Instagram and visit his website, www.d1ver.com.