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Two male giant cuttlefish size each other up in shallow water off Western Australia. The Nikonos RS 13mm is the perfect optic for this dive. The cuttlefish are big, you can get close, and being able to shoot at wider apertures without losing image quality can be paramount in dark conditions
 

As many an underwater shooter can relate to, I’ve spent a long time searching for ways to improve my images, specifically on the gear front. I had been searching for the best option to shoot wide angle underwater but had a few criteria I needed to meet: I wanted something wide, small and sharp. Easier said than done! I had tried many iterations of rectilinear zooms whilst using my Ikelite housing and had never quite been satisfied with the image quality, especially in the corners. So when I decided to finally upgrade to a Nauticam system for my Sony Alpha 1, I knew that it was time to get serious about a wide-angle lens to complement it.

Around the same time, I began reading about the Nikonos RS fisheye lens, a legendary bit of glass that had been the pinnacle of optics in its day and had been carried into the digital realm with several conversion options for DLSRs. Designed specifically for underwater use, it didn’t need to be adapted with any fancy wet lenses or ports to be used in the water, and therefore came out on top when it came to image quality by a mile.
 

A school of oddly-named old wives. The wide fisheye field of view of the RS 13mm allows the entire school to be in frame while also capturing the sunball
 

An environmental portrait of a seahorse in soft coral. While it is a wide-angle lens, the incredibly small footprint of the RS 13mm allows a photographer to get nice and close even to small subjects while still putting them in context with the wide field of view
 

After trawling through all of the available online literature, I started to reach out to people who had shot the lens, picking their brains about the pros and cons of using the converted versions. I received overwhelmingly positive feedback from everyone that was shooting the RS 13mm, with most people claiming that it was the “sharpest lens they’ve ever used underwater.” It was around this time that I was put in contact with Isaac Szabo, a US-based underwater photographer and the pioneer of the Nikonos 13mm conversion for the mirrorless systems, specifically the Sony FE system (though it can be adapted to Nikon Z as well). Through meticulous research, and much trial and error, he had discovered that the glass elements of the old lens could be removed from their lens housing and fitted into a native Sony lens, acting as a “donor body” allowing the Nikonos optics to gain native Sony autofocus and aperture control, tricking the camera into thinking that its shooting with a 50mm prime.
 

A leafy seadragon moving through the shadows beneath a well-known jetty. Fisheye lenses are without a doubt the best for giving large views of the underwater world. However, their ability to focus right onto the glass also makes them extremely useful for close-focus wide angle, filling the frame with smaller creatures
 

A photographer and a broadclub cuttlefish share space. Being able to focus closely means less water between lens and subject, making for sharper subjects. The RS 13mm is already exceptionally sharp, and being right on top of your subject just boosts that even further
 

Understandably, I was hesitant at the idea, but after seeing the quality of images that people had shot with the converted lens, it was pretty evident that this was a top tier bit of equipment. It was only a few months later that a mint quality RS 13mm popped up for sale in Japan—for an eye-wateringly steep price tag. Due to how few of these lenses were made during production in the 1990s, there were already only a few thousand in circulation worldwide, but once the news got out that they could be converted to modern mirrorless cameras, the price for secondhand lenses skyrocketed to astronomical numbers quite quickly. I made the decision that it was unlikely the prices were going to drop anytime soon and purchased the one in Japan, and I had it sent directly to Isaac for its conversion.

Isaac was exceptionally helpful during this period, offering additional information and handy tips about the lens during the conversion. He is extremely patient and knowledgeable and his website goes into more detail about exactly how he does the conversion, for those interested. It didn’t take long until I was getting a notification on my phone that a first class parcel from the States was on its way to my doorstep in Western Australia, and I was beyond excited to take it for its first dive!

I have been shooting with the lens for about a year and a half now, and whilst I haven’t been underwater nearly as much as I would like in that time, I have been lucky enough to take it on half a dozen photography trips where it has served as my only wide-angle option. I figured it would be handy to add to the online library of information about shooting with this lens for those who are interested, hopefully giving some insight into its many pros and some of the hidden cons that this legendary piece of glass offers.
 

A pair of tomato clownfish sheltered in their host anemone with a bustling tropical reef behind. The RS 13mm is wonderfully resistent to flare. While flare can rear its ugly head, the RS 13mm seems far less prone to it than other wide-angle optics
 

An anemonefish eyes the RS 13mm from its host anemone—no doubt shocked by its sharpness!
 

Right off the bat, it’s sharp—like… really, really sharp. So sharp, in fact, that it rivals some of my Sony GM lenses when shooting above water for image quality and the details that it renders when paired with my Alpha 1 still blow me away each time I shoot it. But to me, the most impressive part of this sharpness isn’t how well it resolves 50 megapixels at f/14; it’s how sharp it is all the way open at its maximum aperture of f/1.8. Being able to shoot at f/1.8 underwater and still retain impressive image quality on a wide-angle lens is something that just really hasn’t been possible prior to Isaac’s mirrorless RS 13mm, so it has opened a whole new category of creative images that I can capture underwater, with beautifully rendered bokeh and artistically out-of-focus foregrounds and backgrounds.
 

Most “rules” in wide-angle underwater photography suggest closing down your aperture. This improves sharpness, especially at the edges of the frame and most wide optics give terrible image quality at wide apertures. Isaac’s RS 13mm conversion allows photographers to shoot wide open at f/1.8 and retain image quality! While it won’t be quite as sharp across the frame as if you shot at f/8, for example, you can certainly shoot wide open and add some wonderfully unique wide-angle pictures to your portfolio
 

The RS 13mm focuses right to the glass, meaning you can shoot from infinity all the way to whatever is touching the front dome of the lens. Considering how small the front element is, this means you can squeeze it into some pretty epic spots, allowing you to shoot razor-sharp close-focus wide-angle (CFWA) images with ease. 

The autofocus system is both accurate and fast. It doesn’t hunt and search for focus like some of my older rectilinear setups did when shooting through acrylic domes. When paired with the newer generation of Sony Alpha cameras that utilize phase detection autofocus, it simply locks onto a subject and tracks it with no issues at all, allowing me to focus on more important things like composition or lighting.

It’s absolutely tiny, about the height of a can of Coke! Small is great whilst you’re in the water, allowing you to be more streamlined whilst swimming in strong currents or on snorkels, tucking the lens into small nooks and crannies, or whilst getting right up close to a shy animal when it’s essential to not have a massive reflective element on the front of your camera to scare it away. Optics like the Nauticam EMWL are quite a bit smaller on the front end, but I would confidently say that the RS 13mm is smaller than most people's standard macro setups, which is incredibly handy for travel as well. Packing it away into carry-on baggage with ease, you won’t be lugging around a 10lb port and lens combo if you choose the Nikonos RS 13mm.
 

A classic reef scene. While this is the type of image that could certainly be captured with a regular fisheye lens and a dome port, the sharpness of the RS 13mm is unmatched, especially by other optics that are so tiny
 

The field of view that this lens offers is impressive. With no native full-frame fisheye available in the Sony FE system, I had never had the privilege of shooting with a fisheye, so I was blown away with just how much you can capture with this lens in one frame. Its 170 degrees of coverage means you can fit a lot in your shot, allowing you to frame smaller animals in creative ways, getting super close and still showing the environment that it lives in. This is especially handy for poor visibility dives, as it allows you to minimize the amount of water that you are shooting through, giving the appearance of better viz in your images and encountering fewer particles to be turned into pesky backscatter.
 

Because the RS 13mm is so small, in certain scenarios you can get a quasi-probe lens type aesthetic by squeezing it into tight spaces like between the arms of a soft coral
 

The aforementioned super-wide field of view contributes to pretty much the only negative that I have found with the Nikonos RS 13mm so far and hopefully it can help with your decision making if you’re thinking about taking the plunge and purchasing one. I’ll preface this by saying the following isn’t actually an indictment of the lens itself, it is an issue with fisheye lenses in general.

If you’re like me and don’t have access to unlimited money to spend on camera gear, then you’ll be wanting to make sure that your choice of wide-angle lens is as versatile as possible. This is where the Nikonos RS 13mm may fall short, as it is simply too wide for some genres of underwater photography. If you talk to any experienced underwater photographer, they will tell you that a fisheye cannot be the only wide-angle option in your kit bag, as it may be too wide to capture things like sharks, rays, whales, etc., which often keep their distance. Whilst perfect for this job if they come in close, there are some scenarios where the rectilinear lens without the barrel distortion will always look better regardless of proximity to your subject. So my advice to you if you are looking at this lens being your only option for wide angle is that you need to be aware you will be limiting yourself in some scenarios—scenarios that shooting with something like the Nauticam WACP will give you a significant advantage, allowing you to zoom in and capture tighter frames on the same dive as wide angles.

Having said all that, if you’ve shot with a fisheye before and know what you’re getting yourself into regarding the type of image that they produce, then this is hands down the best option currently available on the market to help you create beautiful, unique underwater images in such a small form factor.
 

An impressive pair of male giant cuttlefish battle for mating rights, right in front of the author’s Nikonos RS 13mm!
 

To see more of Lewis’ amazing underwater and wildlife work, please give him a follow on Instagram and visit his website, www.huntingforparadise.com.