Nikonos Conversion System For Nauticam, Seacam and Subal

Project Finalized: Nikonos RS Lenses for DSLRs

A few months ago I came up with a new idea in order to improve underwater photography. The Nikonos RS lenses that were produced 20 years ago had a very high reputation regarding optical quality.

But these lenses could only be used with the Nikonos RS amphibic camera (that essentially was a stripped F70 film camera in a very small waterproof housing). In order to protect its’ proprietary system Nikon developed a unique electronic protocol not compatible with usual Nikon F cameras. This crippled the spreading of the whole system. Lenses and camera were quite expensive. Not only that: Nikon made a crucial mistake that meant the end of the whole project. The RS was using bright red o-rings that were made of silicone. Today colored o-rings have become standard but in the early 90s it was a big deal. As experienced uw-photographers might know a silicone o-ring must never be used with grease that contains silicone or otherwise the o-ring will swell. Nikon didn’t inform their users properly about it and so people flooded their housings. This was the main reason why the Nikonos RS project was stopped in 1996.

After that a lot of quality conscious photographers were missing Nikonos lenses on usual Nikon SLRs and their housings. With the advantages of digital photography nearly everyone – who has used the RS system – switched to conventional uw-housings with domeports.

But still the lenses remained and it was a matter of time before someone had the idea to adapt them on DSLRs. Actually I did exactly that. You can read more about the evolution in my previous articles.

Finalizing the Conversion

By end of September I have accomplished the Nikonos conversion system for three major housing manufacturers. It is a two staged process: First the lens is converted and electronically modified so that all necessary functions like AF, shutterspeed and f-stops, exposure mode and metering, Liveview AF, exposure compensation, etc. work. The lens has to be sent in to us for service.

The second stage is an appropriate adapter that on one side seals the port opening of the housing as a normal extension ring would do. And on the other side works as a mount for the RS-lens and is made like the original bayonet of the Nikonos RS camera. In order to overcome any potential problems with original Nikonos o-rings we have supplied a proprietary o-ring that works with any o-ring grease and is reinforced for additional safety.

We have tried and tested all adapters personally to a depth of 60m and they have worked successfully. More depth should be possible but we didn’t test it.  The adapters are made of 100% marine grade aluminium and come in black color as standard. We have made the mounting as user friendly as possible and will provide a detailed instruction manual.


The Nauticam mount is the most comfortable of all housings. Simply put the RS adapter into the housing as you would do with a normal port, turn the red lever and lock the port. Since it’s the largest opening of all housings it is even possible to have a look at the focus scale of the 13mm RS fisheye lens that is calibrated for underwater. The 28mm will also work with the adapter. Nauticam is the only housing providing enough space for the 50mm macro lens though we didn’t test it but will do so soon.


We’ve made adapters for Seacam housings since we got various requests for it. But in order to house the RS lens you have to remove focus wheel, zoom wheel and lens release lever inside the housing. We have tried it with a D800 housing and it is a matter of seconds. Take two small screwdrivers and remove the small metal washers that hold the focus- and zoom-wheel. Then remove the lens release lever with a hex key and screw in our custom made lever for AF-mode control. With a D4 you’ll probably have to remove the FN lever on the other side of the housing with a hex key. All controls can be replaced instantly when switching to usual lenses behind ports. We will provide a detailed instruction manual on how to do it. While the removal of focus wheel and lens release can be considered a minor drawback, the zoom wheel might be important for switching lenses on a boat. However it is the only way to house an optical superior lens in a Seacam housing. The Seacam housing can accommodate the 13mm and the 28mm lens.


The adapter for Subal (Type 4) works without restrictions: Open the port lock on newer housing models. Swing the lens release lever out of the way and pull the spring loaded zoom control wheel to the side. Screw in the RS adapter from 9 o’clock to 12 o’clock and engage the port lock. That’s all. Subal provides enough space for 13mm and 28mm lens.

How to mount the RS lens

Again this is relatively easy but might take time getting used to. With usual housing-lens-port combinations you have two bayonets that are not connected: camera-lens and housing-port. With the Nikonos Conversion System you have three and all are linked together: camera-lens, lens-adapter and adapter-housing. This is a more complicated setup. We have provided markers on the adapters to make aligning as easy as possible.

Sea & Sea and Aquatica?

We got various requests for Sea & Sea but unfortunately the port mount is too small for the 13mm lens with adapter. I also got a request for Aquatica and so if there are others who’d like to use this setup feel free to ask any questions.

And the 20-35mm RS zoom lens?

Unfortunately the 20-35 is too large to be accommodated by any current housing port. I’ve already electronically modified one prototype so that it can communicate with regular Nikon DSLRs and I’m working on a very special solution that will be presented after new-year holiday.

Test Results

We have tested the 13 mm with the Nikon D3s and the D800 and especially the 36 megapixels are good to exploit the most of underwater optics. I have uploaded some simple pool shots for further examination and there are more tests to come:

Basically the 13mm lens is much better than the 16mm Fisheye Nikkor with any domeport, virtually free from chromatic aberration, offering way more resolution, sharpness and contrast across the entire frame.

We have made tests with the 10.5mm DX Nikkor (that is optically superior to the 16mm) and state of the art 9” domes (Zen/Subal and Seacam). Here the 13mm is better in terms of resolution, contrast, sharpness and lack of chromatic aberrations. In the corners the sharpness is similar but this is a comparison between DX/9” dome and FX/4” dome.

We have examined the reason why the 13mm is so much better and apart from the coating the dome of the 13mm is not a typical dome but a real lens with varying thickness at different areas. Other advantages are the very small size comparable to a minidome and its’ weight of only 1kg. The close focus is only 7cm or 4cm (w/o rear filter holder) from dome surface giving DOF from glass/water interface at smaller apertures. It’s also possible to mount magic filters.

I think a great goal has been achieved and it’s a sensation that after 20 years it is possible to use the optical capabilities of RS lenses on new Nikon DSLRs. The Nikonos Conversion System is ready to ship. Expect a turnaround time of 3-4 weeks depending on the country you live. And feel free to ask any questions.

A red sea star 5 cm away from the dome surface