Nikonos Conversion System – V2

Two years ago we have presented our lens project to quality conscious underwater photographers and achieved higher optical standards compared to regular lens port combinations. For the first time we had to manufacture those things we usually were talking of, a much harder task. There was a lot of work and trial & error involved. But at the end it worked out and was sold to the demanding customer. By now we have expanded our system to almost all housing brands.

Those who know the size of the Nikonos lenses and that of different port openings also should know that in order to mount the lens as a whole (to achieve highest optical quality and to retain the Nikonos look) you’ll need an adaptor for your housing and also that these adaptors might be too small for all lenses, depending on port size. Since we have constructed adaptors for most manufacturers here’s an overview of lenses suited to housing brands.



Aquatica is one of the last additions to our line up. The adaptor is sturdily built and suited for Aquatica typical using and cold water diving. It can handle 13mm fisheye and 28mm prime lens. The zoom wheel has to be removed, an easy task with a screwdriver and few seconds of time.

BS Kinetics

German manufacturer of carbon made uw-housings with a large variety of housings. For Nikon’s full frame models we can also offer adaptor for 13mm and 28mm lenses. It was one of the first requests after our initial series.

ewa marine

is a manufacturer of splash bags suited to the needs of apnea divers. We received a request from our coworker Peter De Hueber who is an apnea uw – cameraman (and responsible for the great photographs of this article). He wanted maximum optical quality paired with lightness, so we made it and with that setup he achieved great results. The ewa marine can handle Nikonos 13mm and 28mm. The fisheye is used for model shooting while the 28mm serves for fish photography. The adaptor has to be manually fixed and should stay permanently on ewa marine bag.


Nikonos conversion was very well received from users and Nauticam is perfectly suited for it. Nauticam is one of the few brands which port opening is large enough for all Nikonos lenses, including 50mm macro and 20-35 zoom. Also no removal of parts is necessary. At first our Nauticam adaptor didn’t support large 20-35mm, but we’ve made it work a year ago.

nju system

is our own brand of universal underwater housings. One of our first design goals was the unrestricted use of Nikonos lenses. Our large port opening is showing the red framed distance information (which also won’t get scratched) on the RS 20-35mm and all other Nikonos lenses. Since our housings are electronically controlled we can focus lenses manually via software getting the same performance as original Nikonos RS camera.

Sea & Sea

Thumbs up for Sea & Sea, their port opening supports all Nikonos RS lenses: 13mm, 20-35mm, 28mm and 50mm. But the removal of zoom wheel is necessary, quite easy to handle.


We made adaptors for some Seacam pro – photographers, but Seacam bought an alternative concept from someone who defrauded it from us (more on that later). Still we expanded our line-up to include 13mm, 28mm and lately the 50mm macro. In order to house adaptor and lens the removal of zoom-wheel and focus wheel is necessary, something that can be done with two screwdrivers and a few seconds of time. The 50mm macro is very well acclaimed with Seacam photographers who own Nikonos lenses.


We received full support from this German manufacturer of small and light uw-housings. Sealux adaptor currently takes 13mm and 28mm, but with a little tweaking on future housing models it should be possible to include 50mm macro and 20-35mm zoom lens. Removal of zoom wheel and sunshade on 13mm lens is necessary. All you need is a small screwdriver.


Also one of our firsts, Subal type 4 Nikonos adaptor supports 13mm and 28mm and there’s no need to remove components.

Hugyfot and Ikelite?

We have examined it and by now there are following problems: Hugyfot’s strobe control is in the way, in order to mount adaptor properly it has to be removed and mounted differently. We will re-examine it on the next trade show and then see if we can proceed or not.

SLRs are mounted on backplate of Ikelite housings meaning that the distance between camera’s bayonet and housings’ is varying and (as it seems) too long, but if you’ve got an Ikelite housing and want Nikonos conversion feel free to contact us and then we can check if it works at all.

2. Lenses:

From top-left clockwise: 13mm fisheye, 20-35mm zoom, 28mm and 50mm macro

13mm fisheye

The Nikonos RS fisheye lens is the star of the line with a lens design still used today. It offers more resolution and sharpness over the whole frame than any lens-port combination regardless of dome-port size. The front lens is only 4” in diameter and is a specifically engineered underwater-lens for the optically altered fisheye. With stopped down aperture it is possible to touch objects with dome and still get sharp image. It’s also very light, weighing only 1 kg.

13mm lenses are hard to get, especially after our conversion service has started. However we still have a supply of optics if demanded. Prices have climbed from 1.000 € to 1.500-2.000 €. We – too – have the possibility to repair/replace front lens which might get scratched after years of use.

28mm prime

is a small and fast lens suitable for fish photography. It weighs only 500g but has higher optical performance than a 16-35mm@35mm behind a 9” dome. A close focus distance of 0,25m enables portrait shots of small to medium sized fish. Lens also features fastest AF of all Nikonos RS optics because of small size. 28mm are easy to get, they cost between 200 € to 700 € depending on condition.

50mm macro

This is the only Nikonos RS lens featuring a flat port. Meaning it can also be used on air but also signaling that there should be no improvement in optical quality compared to regular lens-port combinations (we didn’t test yet, but will check). Still it’s the most sought after Nikonos lens for conversion after the 13mm. It’s surprisingly compact and weighs only 1 kg and offers good close focusing distance for pros paired with standard focal length suited for medium sized fish. Not suited for fast moving small fish that need speedy AF tracking, but for most other macro to medium fish subjects. Also quite easy to get, prices start from 300 € and end at 800 €. We have successfully replaced scratched front lenses that plague cheaper offerings.

20-35mm zoom

This is the first and only underwater zoom ever made, groundbreaking when it was announced 20 years ago. Loosely based on the 20-35mm land zoom design it features a large front lens specifically engineered for the zoom sitting behind. It has wider angle compared to RS 28mm, but AF is slower due to size of moving lenses. Its’ angle of view is more of a normal zoom by today’s means, but still a sought after rarity selling for well over 1.000 € on the used lens market. It would be of more interest to demanding uw-photographers, but its’ sheer size makes it unfavorable for most port openings. Image resolution is higher than any 24-70mm/2.8 type lens sitting behind 9” dome can offer. It weighs 1800g.

Conversion System

Our conversion is a two stepped process. On one side we need to modify lenses to work with today’s digital SLRs. The lens has to be sent in to us for conversion and servicing and it usually takes 3 weeks. We also do repair and replacement of scratched front lenses. Now the lens works with Nikon SLR but it’s not waterproof with housing, so you’ll need an additional adaptor for port opening. These are made of marine grade alloy and come hard anodized in black color.

3. Critics and competition

When you make something new there is always someone who disregards your work or wants to profit from it or both. So we were bullied by a quite uncomfortable guy from Slovenia.

In the last months a different way of doing Nikonos conversion has emerged based on the 13mm fisheye. It takes apart the 13mm lens and uses the front dome, the fisheye is sheathed in a self-made enclosure and the whole setup is used in a classical lens/port combination manner.

They also criticized our approach in their articles. Before we go into technical matters let’s first recall how this guy received his knowledge.

I was approached by him some two years ago when we presented our conversions and adapters for Subal and Nauticam and were interested in expanding our line up. He pretended he was interested in buying a lens with conversion but wanted to have a look at it first if it works at all. At our first meeting he demanded lens conversion service as a gift(!), afterwards he lent us his Seacam housing because he wanted an adaptor, soon after he stalked one of our suppliers for spare parts who informed us. Caught in the act he demanded these parts from us to make it on his own. It was funny, somehow he believed that since he and I had to live together in a communist country I owed him something. Afterwards I learnt that he managed to copy our conversion and – though he claims to have no commercial interest – sell his concept to Seacam.

Here are his main critical points and our answer to it:

Q. “The Nikonos lenses were designed for rugged underwater cameras. By adding an adapter to the system, there is a possibility that a hydrostatic pressure could affect a much more delicate modern digital camera and could thereby hinder its operation or even damage it.

A. Nikon’s F bayonet is made for all Nikon lenses since 1959, the RS is no exception and neither are modern digital cameras. There are some details to be taken care of which we have solved two years ago.

Q. “In the case of minor defects on the O-ring between the adapter and the lens, the adapter would be in a function of a funnel, which means it would be leading water directly to the camera and would consequently destroy it. In the case of minor defects on the O-ring of the dome port, only a little water would be accumulated at the bottom of the underwater housing and would thus keep the camera dry and undamaged.

A. That is always the case with defect o-rings, we use improved o-rings and haven’t had a single customer’s flood.

Q. “Mounting the lens and the adapter is more time consuming and more complicated than the installation of conventional ports.”

A. Simply not true and only a matter of taste. Lens is better optically centered with lens-adaptor approach. Also the possibility to manually focus is much easier with nju system housings.

Q. “In the case of SEACAM underwater housing (for D800), zoom gears, manual focus gears, and lens release levers should be removed in order to insert the adapter. This means that some important housing functions would be lost. Removing the RS lens from the camera would be particularly awkward as the adapter prevents finger access to the lens release button, which would therefore make it necessary to open the housing back-cover and press the button from behind.”

A. Maybe that was the status two years ago, because only the zoom and focus wheel need to be removed. Removing RS lens from Seacam housing is very easy and works as usual. Removing or retaining zoom and focus function is also easy and can be accomplished in 30 seconds on D800 housing.

Q. “There is practically no depth limit. Since the front lens element is relatively small and very thick (at the thinnest point in the middle is 8 mm thick), it would withstand a depth of several hundred meters.”

A. Same holds true for original RS lens. It’s been made for 100m and has withstood much more.

Ok, there are some critics to be taken care of. At the beginning of our design process we also had the idea to take lens apart but soon were halted by a Nikonos owner who made following objections:

1. Lenses incl. front domes are better optically (centered) in an integral lens design like original RS than in lens-port combinations

2. Nikonos was a very well received product in the uw – photographers’ community, 20 year old lenses are still very worthy and won’t loose on value unless dismantled. Compared to the value of a 20 year old housing it is better to temporarily remove some components from housing than to take lens apart.

3. The Nikonos lens is universally applicable since it can be used on different housing brands with adaptors – also one of our main goals from beginning.

But we have also heard funny arguments against our concept and in a more radical tone, like:

Q. adaptor means to put something together that doesn’t work together

A. any screw- or bayonet mount is also an adaptor combined with a port, a dismantled lens also needs adapters to be put together and joined with camera. Also you might know about the huge success of Sony’s e-mount cameras where one of its’ main advantage lies in the use of third party lenses via adaptors.

Q. only the Nikon R-UW AF Fisheye Nikkor 13mm is (because of its’ optical quality) worth of being used with Seacam housings, all other lenses are optically inferior and 20 years old and very heavy and that is the reason Nikon let them die.

A. That is very shortsighted, the main point is that the 13mm is the only lens type widely used in today’s underwater photography, this is its’ main advantage compared to other RS lenses. The other common lens type used today is a zoom and those feature a wider angle than Nikonos could offer in the 90s. But ANY Nikonos lens is smaller and better suited to luggage restrictions than a large 9” dome port (those weigh 3.5 kg incl. extension rings and heavy zoom) or a large flat port with many extensions and focus rings (1.5 kg incl. macro lens). Also all wide angle Nikonos lenses feature the same high optical quality like RS Fisheye lens, and are useful in their domain which is fish-photography. High quality standard focal length lenses (Zeiss, Sigma Art, Schneider-Kreuznach) are a new trend in photography and Nikonos fits in that approach. We will soon prove the optical advantage of our concept over all focal lengths. Size advantage easily goes to underwater lenses, not lens-port combinations.

Another point which directly involves Seacam and Nikonos lenses: 13mm, 28mm and especially 50mm are top heavy and thus good balanced with Seacam’s large and back-heavy viewfinders. I was a Seacam shooter for 7 years and used their S45 viewfinder – which featured a great image, but in combination with a large dome or long flat-port the setup became very back heavy and required constant pressure while photographing. So a Nikonos lens to equalize the negative buoyancy of viewfinder on the back might be a dive-comfortable way to go.

Additionally I’d like to stress the advantages in optical quality. An integral lens design where all elements are in one lens is the optimum since lens elements are ideally centered and aligned with camera sensor. Also the camera should rest on a stable saddle/slide, a tripod screw on a platform is always prone to lose grip over time and can’t provide optimal and constant center for camera. A lens/adaptor on such housing solves this problem since it fixes lens on camera and aligns sensor, but if you feel the need to dismantle lens then neither have you got optimal center for camera, nor for port. Not a good idea from an optician’s point of view…

4. O-rings

One of the main problems of Nikonos RS lenses were their red o-rings made of silicone which were fragile in handling and the reason why the RS project was a financial loss and finally stopped (not because lenses were heavy). They couldn’t stand silicone-grease, this knowledge – which is more common today – was very rare in the 90s.

We use reinforced RS o-rings with a slightly thicker but softer silicone which seals better than original and come in the same orange color.

Our adaptors also have this visible orange o-ring on their black anodized alloy body. They are very soft and easy to handle.

5. Maintenance and servicing

When converting lenses one must not forget that they may need maintenance. For example the zoom mechanism of 20-35mm should be serviced when lens is converted. Also some lenses may have a scratched front glass or dome. We have already repaired and replaced scratched front lenses.

6. Verdict

Nikonos lenses have changed uw-photography technique. They offer higher optical quality and smaller size. They are also highly adaptable to housings. Fisheye 13mm and prime 28mm fit all ports, the larger macro 50mm and zoom 20-35mm are suited for larger port openings. Our own housing line has been designed to mount all RS lenses and provide access to functions like manual focusing and distance information. If you have read my report on Photokina,

high quality lenses in standard focal lengths from Zeiss, Sigma and Schneider-Kreuznach have emerged as a new trend in photography. The Nikonos lenses fit in the same approach for divers.