Hi Friends,

for some reason I happen to own an old Nikonos III + 15mm underwater lens which I got more than 10 years ago on ebay.

It's been a beloved pet project for me to dive this lens again on a full frame DSLM camera such as my R6 Mark II.

Mainly because of IQ and the very compact size.

I am aware that it's not a fisheye and equivalent to a 20mm lens, my favourite wide angle range underwater.

There are two versions.

The earlier one only fits on Nikonos I, ii and iii since it blocks the TTL-sensor of the Nikonos IV and V.
The earlier lens is told to be the better performer due to its retro focusing design.

This makes it even more mouthwatering after reading this optical benchmark done by Pawel Achtel from 2014 :

https://wetpixel.com/articles/test-optical-performance-of-nikonos-15mm-flat-and-dome-ports

It resulted in some cinema products: https://achtel.com/3deep/

I am also aware of this tinkering thread by @ianmarsh ( thank you Ian ! )
https://waterpixels.net/forums/topic/418-nikonos-15mm-service-manuals-and-schematics-was-do-15s-need-servicing/

I have some questions though, matching with my previous experience.

In the Nauticam Sony NEX-5 days and Nikonos NEX Adapter, the Version III would not mount on the crop camera as it's derriere would have hit the image sensor.

You needed to get a Nikonos 15mm in the V (five not three) version to make it work. I never did 🙃
If I remember correctly this was the reason why the III Version of the Nikon Nikonos UW-Nikkor 15mm f/2.8 would not mount on APS-C type.

Now will full frame and mirrorless I see that Nauticam has a Nikonos-Full-Frame Adapter in their portfolio, but it's just for the A7 Sony camera series, not for Canon.
https://www.nauticam.com/products/nikonos-adaptor-for-na-a7

In another thread together with @Phil Rudin and @Isaac Szabo that I recall but did not find we learned that Nauticam has different bayonet to camera flange distances between their brand housings.

Some SONY models seem to sit closer to the Nauticam Bayonet, especially closer than the Canon DSLMs.

Nauticams Nikonos Adapter for full frame just seems to work for A7/A7R/A7S System - anybody around using it with a 15mm lens and can report about the experience?

In my MARELUX the Canon R6 II sits even deeper inside the housing, which may provoke a collision with the two knobs for focus and aperture control.

I have exactly this set including the viewfinder: https://www.pacificrimcamera.com/rl/01394/01394.pdf

Seeking your advice and comment in hope to make my pet project come alive.

Edited May 8May 8 by Adventurer

The issue you up against is that many housing manufacturers opted set the camera back in the housing such that the lens mount of the adapter (EF -RF or ZTF) was in the same position relative to the port flange as the DSLR camera flange. Doing this means that the port charts and zoom/focus gears for DSLR lenses will be the same when adapted to mirrorless cameras. Sony never had this limitation as it was for the most part and was using short mirrorless flange distances from their first full frame mirrorless.

Looking up the flange distance for Nikonos it's 28mm, your Canon RF has a 20mm flange distance - in theory adaptable if there's no obstructions but I guess you've worked that one out! I think your fundamental problem is that the aperture knobs will stop you getting the nikonos deep enough into the adapter to reach focus. Have a look at the pic in this arrticle, scroll down to the pic of the mounted 15mm in hand and you will see the knobs extend beyond the outer diameter of the N100 mount shown here:

Interceptor121 Photography & Vid...

Nikkor UW15 on Sony Mirrorless for photography – Worth it?

Nauticam makes some really interesting adapters and ports for Sony cameras, one of them allows you to use vintage Nikkor lenses on full frame mirrorless cameras. I decided to source the UW15 as I a…

You've got a 125mm mount on the Marelux but the knobs would need to be inside the port flange to get close enough to the sensor it seems, it looks like the knobs extend past the 100mm port diameter by at least 10mm or more not leaving enough meat to allow you to recess them even with the 125mm port mount of the Marelux. The link also reviews using the 15mm lens on his Sony.

The adapter looks odd with those plates bolted to it, that's because there's not enough room to build it with a flange, so they bolt on two pieces so there is no flange under the knobs. The plates are what stop the adapter ring being pushed through the port. I'm guessing you need to remove them, mount the lens then replace them. There's only just enough room to mount this lens in the Nauticam setup and have it in the right position to reach focus.

The only way I can see to use it with a Canon mirrorless would be to find a housing with a shorter camera flange to port flange distance if one exists. Either that or convert to Sony, You might be able to engineer something but it may work out cheaper to change brands 😂

I see that Aquatica utilise an external RF-EF extension to EF lenses on RF mount mirrorless cameras. Indicates their camera is closer to the front of the housing but is it close enough?

I use the Nikonos 15mm lens quite regularly (but I don't always tag the lens in keywords, so it is hard to share a gallery of images). I just use it on Nauticam's stock adapter. It is the lens I have owned from new (30+ years). Here are a few recent ones:

1 hour ago, Chris Ross said:

Looking up the flange distance for Nikonos it's 28mm, your Canon RF has a 20mm flange distance - in theory adaptable if there's no obstructions but I guess you've worked that one out

Great Info Chris, where did you look that up? What is the source? Official from Nikon / Canon?
I did my own measurement and got 19mm on my Canon RF.

Indeed the extruding knobs are going to be an issue.

I am thinking about cutting or replacing them to be able to move the port adapter more inside.

13 minutes ago, Alex_Mustard said:

I use the Nikonos 15mm lens quite regularly (but I don't always tag the lens in keywords, so it is hard to share a gallery of images). I just use it on Nauticam's stock adapter. It is the lens I have owned from new (30+ years). Here are a few recent ones:

Thanks @Alex_Mustard for sharing your wonderful images.

They are indeed dent sharp and extra-immersive.

I also find it very interesting that it seems flexible enough to shoot medium sized fish portraits.
Obviously due to the small min. focussing distance.

Just to make sure: the parrotfish shot are also the the 15mm Nikonos and not a Nikonos Macro?

May I ask what aperture you mainly shoot it ?
There is an old rumor that @ F8 everything usually is sharp with that lens.

Edited May 8May 8 by Adventurer

9 hours ago, Adventurer said:

Great Info Chris, where did you look that up? What is the source? Official from Nikon / Canon?
I did my own measurement and got 19mm on my Canon RF.

Indeed the extruding knobs are going to be an issue.

I am thinking about cutting or replacing them to be able to move the port adapter more inside.

Google reveals multiple sources stating it is 20mm including a Canon website. I recall reading somewhere that a straight measurement to the surface of the sensor stack is not what you use, rather you want the sensor surface. The sensor on cameras with in body stabilization is also mobile and some of them apparently have a parked position to allow cleaning without damaging the IS mechanism which could change the sensor position??

Though if you have measured using something like a depth gauge (not a ruler and straight edge) it should work for physically placing the camera body correctly.

It sounds like quite the project! with some precision machining required. The ID of the adapter recess you can use will be set by the ID of the port o-ring minus 2x the wall thickness you need to use, which you could judge from the wall thickness marelux uses. I'm thinking it might something like 110mm ID you have available (4mm O-ring plus 3mm wall thickness and rounded down). Some type of flexible drive shaft might be the way to control the focus and aperture.

Not that I'm trying to discourage you but it seems to me switching to Sony or at least researching a housing that places the sensor closer to the port flange might be a lot less work.

15 hours ago, Chris Ross said:

Though if you have measured using something like a depth gauge (not a ruler and straight edge) it should work for physically placing the camera body correctly.

Well yes that's what I did, but of course with shutter closed, which might explain the 1 mm offset. Good to reflect a little bit on that. Also the IBIS can make the sensor wobble a lot which might be interesting.

Having said that, the Nikonos bayonet is also kind-off weird and allows you to shift the lense a little back and forth when properly mounted. I guess the water pressure will always push that lens towards sensor direction. But overall there might be some tolerante for the focus plane.

Edited May 9May 9 by Adventurer

On 5/9/2025 at 4:58 PM, Adventurer said:

Well yes that's what I did, but of course with shutter closed, which might explain the 1 mm offset. Good to reflect a little bit on that. Also the IBIS can make the sensor wobble a lot which might be interesting.

Having said that, the Nikonos bayonet is also kind-off weird and allows you to shift the lense a little back and forth when properly mounted. I guess the water pressure will always push that lens towards sensor direction. But overall there might be some tolerant for the focus plane.

As far as I know for infinity focus you need to be quite precise in air, The UW situation is probably similar for the Nikonos as you probably want something close to infinity focus on that lens while a land lens inside a dome is probably more forgiving as it is focusing quite close when used UW behind a dome.

I expect and depending on what type of tip your depth gauge has that it wouldn't hurt the sensor to touch it gently when doing the measurement. The main thing would be to de-grease it I would think - but of course at your own risk.

But if I'm not mistaken where you want your precision is the difference between the lens flange distance of a Canon RF versus a Nikonos. Assuming the figures are correct with 28mm for Nikonos and 20mm for Canon RF. You want the flange on the Adapter 8mm in front of the camera's lens flange.

You probably do not want to use the Mk I (non N) version of the Nikonos 15mm lens for the same reason why adapting many older Leica rangefinder lenses is not such a hot idea. Especially since the Sony cams reportedly have a thick cover glass over the sensor (discussed on Leica forums). This is because the lens is way too close to the sensor so that the light rays hit the sensor at an acute angle in the corners (leads to optical issues such as vignetting, color shits), i.e. the lens is NOT telecentric. Even many film (i.e. older) SLR lenses are not telecentric enough. This was discussed ad nauseum on internet forums in the early digital days (2 decades ago now!). I suspect that even the 15N lens may have issues (it is slightly retrofocus, the opposite of what was stated in post #1, but not to the same extent as SLR lenses (mirror box clearance need being greater than the TTL metering parts (metering first introduced with the N-IV, not the N-V)).

I use a later-generation 15mm with a Sony A7C in the nauticam housing with the stock adapter. One thing to be aware of - the lens, due to it's short focal length, is extremely sensitive to its flange distance (distance to sensor) being exactly correct. The difficulty with the nauticam adapter system is that it does not come into contact with the camera, and manufacturing tolerances by Nauticam just aren't precise enough to ensure perfect lens positioning. Not that their tolerances are bad - the system just requires it to be exact (±0.1mm or less) or else it doesn't work well. Some folks have gotten lucky and it's spot on from the get-go, others not so. When I first got my setup, it would not focus beyond about 1-2m underwater because the flange distance was too long, i.e. the lens was positioned too far away from the sensor. I had the lens serviced and checked by Devon at Pacific Housing Repair so it wasn't a lens problem. I solved the issue by filing a bit of plastic from the front of the camera plate that secures the body inside the housing. My copy needed exactly 0.5mm filed off (yes, it's that sensitive). Once I did that, it worked flawlessly. I still retain full use of all housing buttons and dials. Just be aware of this if you try to make it work. Like Alex's images demonstrate, once you get the lens dialed and get used to manual focusing with it, it produces seriously excellent images.

gracias Will,seguí tu ejemplo y el enfoque ha mejorado muchísimo,solo limando 0.5mm pero aún no acaba de ir bien..la distancia mínima de enfoque es ahora unos 60cm,,si pongo f8 y enfoque a 1m la camara enfoca de 1.5m a infinito,,no se si he limado demasiado la zapata de la cámara o si tengo que limar un poco más,,seguiré haciendo pruebas,,entre ellas adaptar una lente sea sea 17mm para nikonos que no creo que quepa en el adaptador nauticam pero lo intentaré ajustar....,,gracias.mi cámara es una sony A7R2,

On 8/5/2025 at 14:57, Adventurer said:

Excelente información, Chris, ¿dónde la buscaste? ¿Cuál es la fuente? ¿Oficial de Nikon/Canon?
Hice mis propias mediciones y obtuve 19 mm en mi Canon RF.

De hecho, las perillas de extrusión van a ser un problema.

Estoy pensando en cortarlos o reemplazarlos para poder mover el adaptador del puerto más hacia el interior.

Gracias@Alex_Mustardpor compartir tus maravillosas imágenes.

De hecho, son muy nítidos y muy inmersivos.

También me parece muy interesante que parezca lo suficientemente flexible como para fotografiar retratos de peces de tamaño mediano,
obviamente gracias a su corta distancia mínima de enfoque.

Solo para asegurarme: ¿Las fotos del pez loro también son con la Nikonos de 15 mm y no con una Nikonos Macro? ¿

Puedo preguntar con qué apertura la usas principalmente?
Dicen que a F8 todo suele salir nítido con ese objetivo.

Bueno,viendo que Alex aún no ha contestado,te diré que yo uso ambos 15mm,la versión 1 (tuve que rebajar las ruedas de mando) y la versión 2,en ambas usando f8 y distancia a 1m la profundidad de campo es muy aceptable,aunque para fotografías de primer plano a 25cm yo uno f11 o superior,espero te sirva de referencia,un saludo.