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 8 hours ago8 hr 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 1 hour ago1 hr by Adventurer