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The Optical Precision Port—or OPP, as it will inevitably be called—is SEACAM’s water-corrected alternative to a dome port. It is a two-lens system, consisting of a thick front port—actually a lens, which is flat on the outside, but concave on the inside—and a matched correction lens (a positive lens) that screws on the front of the camera’s lens. And to get straight to what you want to know: I am happy to report that it works as advertised/hoped and with a custom port adapter could be used with any housing.

But should you be adding the OPP to your shopping list? We’ll circle back to that. To answer that for yourself, it is important to understand more about water-corrected optics. The OPP retails for a not insignificant €5,000 and currently is only approved for the Nikon (F-mount) 16–35mm lens. I would fully expect the similar Canon, Sony and Nikon Z lenses to be supported very soon, but within each system, it is best thought of as a specific solution for a specific wide rectilinear zoom. If you want to use the OPP, then you have to choose a lens it works with. Wider lenses like fisheyes and wider rectilinear lenses are not compatible, in part because they cannot accept the correction lens.

The new Optical Precision Port mounted on a SEACAM housing

The corrector port (left) and correction lens. The bulk of the setup above is the extension ring necessary for the Nikon AF-S 16–35mm f/4

How It Works

SEACAM’s OPP—which shares its acronym (although not what the abbreviation stands for!) with Naughty by Nature’s 90s hip hop track—is actually based on something properly old school, the Ivanoff Corrector Port. Patented in 1953 by French Professor Alexandre Ivanoff, this two-lens corrector (flat-concave port and matched convex lens attached to the camera lens) makes a land lens “water contact”, or in other words fully corrected for underwater use.
 

The OPP is designed to allow a land lens perform underwater EXACTLY the way it does on land. Thus, in theory, if a lens performs well on land and is compatible with the OPP, it will perform well underwater as well (Nikon Z8, Nikon AF-S 16–35mm f/4, SEACAM housing, dual SEACAM SEAFLASH 160D strobes, f/18, 1/25s, ISO 320)
 

The Corrector Port maintains the angle of view of the original lens, just as a dome port does, but without creating the curved/domed field of focus. This curved field isn’t a problem in the center of the image, but it causes the image to become increasingly soft, seen in our pictures as blurred details into the corners of the frame. We correct this characteristic of all dome ports by closing our aperture—bringing the curved field of focus within the increased depth of field. Therefore, the most obvious advantage of an Ivanoff-style port is that it preserves excellent image quality into the edges and corners of the frame, which is particularly noticeable at more open apertures. In addition, if the corrector is manufactured to high quality, with carefully selected and matched optics, the design will also correct other issues like chromatic aberration.
 

A Bit of History

The Ivanoff Corrector Port is also known as the Ivanoff–Rebikoff Corrector Port and the Aquar Correction Lens. Paris-born Dimitri Rebikoff bought the patent rights and these ports were only available from him during the 1950s to 1970s. I’ve always assumed the “r” at the end of Aquar was for Rebikoff, who always seems keen to blow his own (French) horn. If you are interested in learning more, look up Ivanoff and Rebikoff, as well as Yves-Jacques Le Grand, Paul Cherney and Dan Slater, who have all played important roles in the corrector port story thus far.
 

A pile of lenses, part of an arsenal of Ivanoff–Rebikoff Corrector Ports from the 1950s–1970s era. (Images courtesy of Doug Hankin)

Why Haven’t You Heard of These Correctors?

Ivanoff Corrector Ports have been around a long time but have never been widely known for a few reasons:

• Most importantly, they are more expensive than domes, being made of multiple elements of ground glass. The OPP sells for a little more than twice SEACAM’s Superdome, but I would argue that given the R&D and production costs compared to a dome, it is good value (compared to the dome). But, ultimately, it is the same lens behind it.

• Second, for much of the history of underwater photography, there have been bigger fish to fry for improving our shots—technique, film stock, autofocus performance, strobe performance, ISO performance, sensor resolution, and so on. For example, in the era of the Nikonos RS camera, everyone respected the optical quality of the RS 13mm Fisheye, but most people chose to use a housed Nikon and the 16mm Fisheye with a dome, because the Nikonos RS camera was so limited by its painfully slow focus. The underwater photography market has only become focused on optics as these other issues have been solved and standards have become more exacting. It’s why I call the last decade the Optical Revolution in underwater photography, carrying on from the Digital Revolution of the decade before.

• Third, although Ivanoff Corrector Ports were sold from the late 1950s, underwater photography was still a very niche activity. The Nikonos viewfinder cameras (the more basic predecessors of the RS) increased its popularity and were swiftly accompanied from the late 1960s by the Nikonos 15mm wide angle—a fully corrected underwater lens, which made the Ivanoff look bulky.

• And finally, the Ivanoff Corrector Port works its magic on wide rectilinear—non-fisheye—lenses. Underwater photographers also learned that fisheyes not only work well behind dome ports—as their barrel distortion helps de-emphasize any corner issues, but also their barrel distortion combined with the ultra-wide view of fisheyes actually helps to create those high impact, forced perspective shots.

All that said, Ivanoff Correctors Ports have cropped up periodically in underwater photography. Most of Rebikoff’s products ended up on specialist survey or filming cameras, while smaller units appeared on several video housings in the 1990s and 2000s. Personally, the only one I have shot seriously, and possibly the only one previously produced for high quality artistic still photography, is a two-lens design from Carl Zeiss made for the Hasselblad medium format Super Wide Camera in the 1970/80s.
 

My Ivanoff Journey

In the late 1990s, I was gifted a medium format Hasselblad housing, and it came with the Zeiss-made Ivanoff Corrector Port. It was already a long-outdated system, but I got it running again and enjoyed the experience—and the challenges—of shooting medium format film underwater with a fully mechanical camera.
 

A Caribbean reef shark, photographed with a medium format film camera and a Carl Zeiss-made Ivanoff Corrector Port
 

By 2014, digital technology had matured and megapixels continued to climb. This prompted several serious underwater photographers to get interested in further improving their images with underwater corrected optics. I got hooked when I shot the Nikonos RS 13mm, converted by SEACAM to work on a Nikon DSLR. Some shots were transformed, while in others, the gains were only small. But they were there in every image I took and I wanted more! (The Nikonos RS 13mm has been my workhorse lens since 2014, first on my Nikon DSLRs, and then thanks to Isaac Szabo’s ingenious conversion, on my Sony mirrorless cameras.) I was also impressed with what I was seeing from Nauticam’s WWL wet lens, but this wasn’t compatible with DSLRs, so myself and others pushed Nauticam to make a port version that could be used on DSLRs. I tested the prototype called the WWL-Dry lens in 2016, which would be released as the WACP-1 in 2017.

Before this, though, wanting an accompaniment for my Nikonos 13mm, I returned to the Ivanoff Corrector Port from my Hasselblad. I had this adapted to my Subal housing and got it working well in 2015. I had hoped to be able to use it with my Nikon 16–35mm, but optically it was actually worse than a dome with that lens. But it worked fantastically well with the smaller Nikon 20mm, which I think was a better match with the correction lens.
 

The author’s personal Hasselblad Corrector Port, used to create a number of well-known underwater images, including one awarded in the Wildlife Photographer of the Year 2016, and a title image for BBC’s Blue Planet III
 

I shot this setup extensively, including using it to take a well-known image awarded in the Wildlife Photographer of the Year 2016, which has also gone on to be featured in their “best of” books Unforgettable Underwater Photography and 60 Years of Wildlife Photographer of the Year. Another image I shot with that setup has been used as the calling-card image for the BBC’s forthcoming Blue Planet III series. Suffice to say, I am a card-carrying member of the Ivanoff fan club, but I am also aware of the challenges of realizing the full potential from this solution.
 

An image from the old Ivanoff Corrector Port, now getting new life via the BBC’s Blue Planet III marketing!

SEACAM OPP Arrives at DEMA

The SEACAM OPP was announced at DEMA 2025. I was very excited by this product and curious to see what a modern design could deliver. I was also really pleased to see SEACAM go in their own direction with the OPP, adding a new option to the market. Too often underwater manufacturers simply copy each other. Nauticam created and have dominated the corrector port market over the last decade, and it is good for us all that SEACAM didn’t simply make a silver WACP.

However, I had concerns. The sample images released on the SEACAM website in 2025 along with the OPP weren’t encouraging. While they were strong photos, they did not show the exemplary edge-of-the-frame sharpness that the OPP should deliver. And given that superior edge-to-edge optical performance is the raison d’être of the Ivanoff, I was worried. Furthermore, my own struggles to get the 16–35mm to perform added to my concern about this new solution.
 

The OPP in Raja Ampat

Fortunately, the chance to try the production version of the OPP came up in March 2026 when I was running a workshop in Raja Ampat, Indonesia, that included six days at the fabulous Sorido Bay Resort. Not only is Sorido Bay, on Kri Island, a wonderful place to stay, right at the heart of the famous Dampier Strait, it is also the home of the Raja Ampat Seacam Center (RASC). The RASC provides rental gear, the latest SEACAM products, and at key times during the year, SEACAM Ambassadors on site to help you. Our group had the pleasure of newly minted Ambassador Don Silcock for company, who had done most of the development diving with the OPP. Don kindly lent me his OPP setup—Nikon Z8, Nikon 16–35mm f/4, SEACAM housing, OPP and SEACAM 160D strobes—for a few test dives.
 

The OPP mounted on a SEACAM Nikon Z8 housing, fresh off a dive in Raja Ampat, Indonesia
 

The author, Alex Mustard (left), holds Don Silcock’s SEACAM Z8 setup, complete with the Optical Corrector Port
 

The OPP’s two lenses are decent chunks of optical glass, but the system is not heavy in the water, and well balanced with SEACAM’s buoyancy port extension. SEACAM highlights on their website that the OPP is travel friendly—not that heavy (3kg/6.6lb total), nor big, and being modular, easier to pack. Keep in mind, though, that on many trips, you will likely take the OPP as an extra, because there is still a need for a dome port for other lenses—and for over-unders. The fact that the OPP is considerably smaller than a SEACAM Superdome in diameter, and focuses close, definitely allows you to shoot smaller subjects, and I found it impressively versatile underwater, able to shoot bigger scenes down to portraits of medium-sized fish.
 

Baitfish swirl over a coral head near Sorido Bay Resort in Raja Ampat, Indonesia. Note the lack of barrel distortion and how much “flatter” the image looks than if it had been taken with a fisheye. Previously, this sort of picture with a rectilinear lens would have required a huge dome port and a quite stopped down aperture. The SEACAM OPP has a much smaller footprint than a big dome and produces better image quality, especially along the edges of the frame, at the same or wider apertures (Nikon Z8, Nikon AF-S 16–35mm f/4, SEACAM housing, dual SEACAM SEAFLASH 160D strobes, f/13, 1/100s, ISO 400)

Image Quality

The OPP gives exactly the same view as using the 16–35mm behind a dome port, but it definitely delivers on image quality across the frame. I believe that edge-of-frame quality is particularly important with a rectilinear lens: While fisheye lenses project a picture that emphasizes the central area of the picture, rectilinear wide angle lenses project an image that puts more emphasis on the corners of the frame.
 

As the crop in the lower image shows, the OPP produces images that are sharp and detailed in the center, much the same as those produced when using a dome
 

In the central area of the frame, I don’t believe the OPP is any different from using a dome. It is sharp and detailed, as I would expect the 16–35mm to be behind a dome. Where the OPP excels is that it maintains very impressive quality right across the frame. The image quality right in the corner isn’t perfect, but I feel it is as good as you would expect the 16–35mm to deliver with a similar composition on land. When the aperture is opened up, even as far as f/5, the edge-of-frame performance remains very impressive, greatly exceeding what a dome port would produce in my experience.
 

Test images showing edge/corner of frame sharpness at different apertures. Top: The OPP at f/13, showing the whole frame and a crop of the bottom-left corner, demonstrating excellent detail right up to the edge of the frame, which in my opinion very much matches the lens’ performance on land in my opinion. Middle: The OPP at f/7.1. At this aperture, in a close-focus shot like this, an image captured using a dome would be heavily compromised at the edges. The OPP again still only shows minor softening of the image in the very extreme corner of the frame. Bottom: The OPP at f/5. Even with a very open aperture for a wide-angle shot, the OPP still produces excellent image quality across the frame. Corner softening is noticeable, but does not compromise the image
 

It is important to stress that we typically use a closed aperture to shoot wide-angle underwater for more reasons than helping corner sharpness with dome ports. The majority of wide-angle photos are scenic images, where both the foreground and background are important parts of the composition, and like a hyperfocal landscape photo, all elements should ideally be in focus. In wide-angle shooting, we achieve this by closing the aperture. How much depends on the sensor size and how close our foreground subject is.

If you are a full-frame photographer, then you may shoot as open as f/8 for more distant subjects (like pelagics), f/11 for medium range subjects (fish schools), f/13 for reef scenery, and f/16 for close focus wide angle, to keep foregrounds and backgrounds in focus. If most of your wide-angle shooting is in the f/11–f/16 range, then the OPP’s strength will be less obvious in your images. However, if you shoot a lot of pelagics, or in deeper/darker environments (wrecks, deep reefs, cenotes, etc.), where you need to sacrifice the hyperfocal look simply because of a lack of light, then the OPP will be a highly valuable ally. And, of course, it would also be ideal for adding open-aperture wide-angle shots to your portfolio.
 

Wide-angle lenses, when shot at open apertures, can give a unique aesthetic that can be hard to replicate. However, most wide-angle setups underwater fall apart when shot wide open. Water-contact optics like the Nikonos RS 13mm, Nauticam WACP series, and of course SEACAM’s OPP, allow you to shoot wider apertures while retaining excellent image quality (Nikon Z8, Nikon AF-S 16–35mm f/4, SEACAM housing, dual SEACAM SEAFLASH 160D strobes, f/4, 1/50s, ISO 125)
 

I wasn’t able to do back-to-back tests against a dome port, but those of you in the market for the OPP will likely already have a 16–35mm and dome and a feeling of where you are and are not happy with the performance. Furthermore, the crux of whether you will buy the OPP will depend on how you personally value the improvement over what you currently get. Some will see the OPP as a must-have, a lens that gives them the best possible 16–35mm underwater, with image quality gains (sometimes big, sometimes small) in every image they take. Others will see the OPP as an unjustifiable expense, being totally content with the 16–35mm behind their dome. In addition, the OPP will also be rated individually based on how much you shoot with the 16–35mm compared to other wide-angle options.
 

While rectilinear lenses have fallen out of favor in recent times thanks to optics like the Nauticam WWL or WACP, SEACAM’s OPP might bring them back into vogue. A new (old) perspective to wide-angle images with improved image quality—what’s not to like? (Nikon Z8, Nikon AF-S 16–35mm f/4, SEACAM housing, dual SEACAM SEAFLASH 160D strobes, f/13, 1/125s, ISO 400)

The Elephants in the Room

So far, we’ve considered the OPP in terms of its performance relative to dome ports. But, of course, there are already plenty of other underwater corrected optics in the sea, especially those made by Nauticam. Nauticam’s WACP-2 is perhaps closest to the OPP, being predominantly rectilinear in look. It is the biggest, most expensive (Backscatter list it for $11K), and least commonly seen of Nauticam’s optics. It is also different from the OPP because despite its mostly rectilinear look, it significantly increases the field of view of your wide-angle lens. I’ve shot it mostly with the Nikon Z 14–30mm, where is offers a massive 140° coverage, compared with the 107° maximum of the 16–35mm with the OPP. However, the sheer size of the WACP- 2 means that few people can travel with one (I’ve only had three turn up on my workshops), but I did see that SEACAM Ambassador Laurent Ballesta shoots with one—as SEACAM themselves shared a picture of him using it on their social media earlier this year. Ultimately, the WACP-2 is more than twice the weight and nearly twice the price of the OPP.

The Nauticam WACP-1 is $4.8K on Backscatter and clearly a direct competitor to the OPP on price, angle of view, open aperture performance, and across-the-frame image quality. The 16–35mm with OPP has a field of view (FOV) range of 107–63°, which is beaten by the WACP-1, which gives a FOV of 130–59° with the old Nikon AF-S 28–70mm f/2.8 and 130–81° with the newer Nikon Z 24–50mm f/4–6.3. However, despite being a bit cheaper, the WACP-1 is about a kilogram (2.2lb) heavier and bulkier to pack than the OPP.
 

SEACAM’s OPP commands a premium price tag, but then again it is a premium product. For those who shoot wrecks, models, big animals, sports, and so on, the OPP could be a valuable addition to the gear bag (Nikon Z8, Nikon AF-S 16–35mm f/4, SEACAM housing, dual SEACAM SEAFLASH 160D strobes, f/13, 1/125s, ISO 500)
 

Nauticam fans would counter by pointing out that Nauticam offer a range of smaller, lighter options, such as the WACP-C and the WWL series, which offer the same FOV as the WACP-1 with smaller, cheaper optics, and with only a small drop in image quality. I especially like the Nikon Z8 with the WWL-C, which is $1.3K and weighs just a kilogram (2.2lb). Nauticam also make the FCP-1 lens, which is the ultimate for flexibility, with an FOV range with the 24–50mm of 170–87°, but it doesn’t quite match the WACP-1 or OPP for image quality right across the frame.
 

Final Thoughts

The OPP is a great new addition to the underwater photographer’s menu of water-corrected lenses, offering a unique option at a reasonable size, weight and price for the high-end market that it is aimed at. It would require a custom port adapter to work on non-SEACAM housings, but these are easy enough to source. I’d wager it is the best quality Ivanoff Corrector Port ever produced and delivers excellent image quality across the frame, with a large performance advantage over a dome port in this regard at apertures f/8 and wider. At present, it only works with the Nikon AF-S 16–35mm f/4, but I would expect similar lenses from Sony and Canon to be supported officially soon. Still, it will probably remain incompatible with other wide-angle optics.

The OPP will obviously appeal to photographers that are dedicated 16–35mm shooters, especially those that shoot pelagics, caves and wrecks, or shoot in other low-light conditions, where the advantage of the optics in more open aperture shooting will be more telling. I can also see it appealing strongly to pool photographers, working with models and covering sports. If you are already satisfied with how the 16–35mm performs in all situations with your dome, then the OPP is not for you. While distinct, the OPP covers a very similar range of subjects, with similar quality across the frame over a wide a range of apertures to Nauticam’s WACP-1 (and wider WACP and WWL family of lenses). Given the similarities, owning both would be hard to justify.

Overall, I really enjoyed shooting the OPP, was very impressed with its performance, size, handling, and versatility. And as a Sony shooter currently, I look forward to news on its compatibility with Sony lenses.
 

While it currently only works with the Nikon AF-S 16–35mm lens, the SEACAM OPP promises to be compatible with a longer list of lenses in the future (Nikon Z8, Nikon AF-S 16–35mm f/4, SEACAM housing, dual SEACAM SEAFLASH 160D strobes, f/7.1, 1/80s, ISO 125)
 

About the Reviewer: Alex Mustard is the author of the popular Underwater Photography Masterclass book, as well as over 900 articles and 200 magazine cover shots. His photos have been awarded extensively, including in nine different categories in the Wildlife Photographer of the Year contest. Nissan built the NV200 concept car specifically for his underwater photography. He has a PhD in marine ecology and in 2018 was awarded an MBE by Queen Elizabeth II for “services to underwater photography.”