Hi everyone,

I'm setting up my Canon R6 Mark II inside a Nauticam NA-R6II housing (N120 port system) with the Canon 8–15mm f/4L fisheye lens and the Nauticam 180mm dome port.

I'm trying to confirm the correct extension ring for this configuration. I've seen different suggestions depending on dome size — does anyone know what Nauticam officially recommends for the 180mm dome?

Also, if anyone has used this lens with a Kenko 1.4x teleconverter behind the same dome, I'd really appreciate advice on the required extension ring length for that combo as well.

Thanks in advance!

3 hours ago, chemsdiving said:

Hi everyone,

I'm setting up my Canon R6 Mark II inside a Nauticam NA-R6II housing (N120 port system) with the Canon 8–15mm f/4L fisheye lens and the Nauticam 180mm dome port.

I'm trying to confirm the correct extension ring for this configuration. I've seen different suggestions depending on dome size — does anyone know what Nauticam officially recommends for the 180mm dome?

Also, if anyone has used this lens with a Kenko 1.4x teleconverter behind the same dome, I'd really appreciate advice on the required extension ring length for that combo as well.

Thanks in advance!

Hi chemsdiving,

For Canon EF lenses, Nauticam recommends the use of the Canon EF to Canon R adapter (see here: https://drive.google.com/file/d/1wjedtgAP1MCgmCFUYGYrGC7I_J7GPCiH/view) and then the appropriate extension, according to the Canon EF cards (see here: https://drive.google.com/file/d/1J-d1Phs2q3ZU3vu0TMNaUQtwJ8Pr_VG_/view)

For the 140mm and 230mm fisheye domes (approximate hemispheres) Nauticam recommends a 30mm N120 extension w/o TC and 50mm with the Kenko 1.4x TC (see link above)...

They do not recommend to use the Canon 8-15mm with the 180mm domeport, which is not a hemisphere but a smaller section of a sphere, optimized for rectilinear WA lenses. The extension should remain the same (30mm w/o TC and 50mm with 1.4x TC), longer extension (as required for optimal positioning) will result in vignetting and shorter extension is even worse (for theoretical optimum positioning of the lens)), but the optical quality may not be good enough (best is to inquire at Nauticam)...

Wolfgang

P.S.: I was using the Canon 8-15mm with the Nauticam 140mm fisheye domeport and with the Zen 170mm domeport (similar to the Nauticam 180mm domeport) with MFT cameras with the same extension for both domeports and the results were pleasing for both. The larger FF sensor may be different, however...

Edited June 24, 2025Jun 24 by Architeuthis

As Wolfgang has said, Nauticam do not recommend the 180mm dome with the fisheye as it is not a full sphere and requires the lens to be positioned well forward of the centre of curvature of the dome. Fisheyes are surprisingly tolerant of this, though I believe they will lose some field of view though you may be OK with this.

A bigger problem is that the dome shade is not removable on the 180mm I believe - which means you won't be able to use the circular fisheye (8mm) as the dome shade will be in the pic. The 140mm dome is the recommended dome for this lens, you need to be sure to order the version with the removable shade. The 230mm dome also works but it also is not quite a hemisphere, though the mis-positioning is not quite so bad compared to the 180mm as the 230mm is closer to a full hemisphere.

An alternative to the 140mm dome is the Zen 100mm dome, some people use this combo although the edges may not be as good as the 140mm dome. Again fisheyes are quite tolerant of smaller domes and the there is apparently no improvement using the bigger 230mm dome, probably as the lens has to be positioned a little forward of the centre of curvature. The 100mm dome is good for CFWA work as you can get closer to the subject.

On the question of the 1.4x TC this is included in the port charts and requires 20mm more extension and also the appropriate zoom gear if you choose to use one. The lens is either 8mm or 15mm on full frame, the in between focal lengths are oddly vignetted and some people just set the lens at 15mm and leave it there if not planning on using the 8mm end. It's all in the port charts for the recommended ports and this data is in the N120 EF port chart that Wolfgang linked.

Hi @chemsdiving ,

I use the Canon 8-15 and Kenko 1.4x TC with a FF body. The 140 works very well as it is both small for travel and hemispherical. The 30mm extension is needed for the lens with an additional 20mm needed for the TC. Unfortunately, different zoom gears are required for the lens alone vs the added TC.

I tried the lens with the 180 dome. Like others have said, it’s not the best choice due to the curvature. The 230 dome has traditionally been the go-to larger option. It also allows the best chance of clean split frames if that’s an interest.

Yes, Zen does make a 100 mini dome for the 8-15, but take note it is not the same dome as that for the Tokina 10-17. The 8-15 model is specifically designed for the 8-15. As a bonus, it also has a shade that is removable and replaceable underwater when you may decide to make a circular frame.

One big note, the Zen 100 is not at all a good choice for use with a TC. The edges smear badly which often ruins the image.

Hope this help!

Chip

Thanks @ChipBPhoto for your input. I have the 180mm and would like to know what you did´nt like about it. I use it with a fujifilm xt3 and it´s very sharp in my opinion.

18 hours ago, Architeuthis said:

Hi chemsdiving,

For Canon EF lenses, Nauticam recommends the use of the Canon EF to Canon R adapter (see here: https://drive.google.com/file/d/1wjedtgAP1MCgmCFUYGYrGC7I_J7GPCiH/view) and then the appropriate extension, according to the Canon EF cards (see here: https://drive.google.com/file/d/1J-d1Phs2q3ZU3vu0TMNaUQtwJ8Pr_VG_/view)

For the 140mm and 230mm fisheye domes (approximate hemispheres) Nauticam recommends a 30mm N120 extension w/o TC and 50mm with the Kenko 1.4x TC (see link above)...

They do not recommend to use the Canon 8-15mm with the 180mm domeport, which is not a hemisphere but a smaller section of a sphere, optimized for rectilinear WA lenses. The extension should remain the same (30mm w/o TC and 50mm with 1.4x TC), longer extension (as required for optimal positioning) will result in vignetting and shorter extension is even worse (for theoretical optimum positioning of the lens)), but the optical quality may not be good enough (best is to inquire at Nauticam)...

Wolfgang

P.S.: I was using the Canon 8-15mm with the Nauticam 140mm fisheye domeport and with the Zen 170mm domeport (similar to the Nauticam 180mm domeport) with MFT cameras with the same extension for both domeports and the results were pleasing for both. The larger FF sensor may be different, however...

Thanks a lot for your answer.

Edited June 25, 2025Jun 25 by chemsdiving

180mm glass will be fine for central part of an image. out of center parts will suffer from CA and loss of sharpness because the light will come through more extreme angle through the glass. And that glass has some thickness... just think about it. That'a why 140mm dome with more curvy glass will introduce less of these. Obviously more you zoom in with TC less of these artifacts will be an issue because you will be using only central part of the dome and the light will come to lens under not so big angle... just physics. Look up my thread with lab examples.

10 hours ago, chemsdiving said:

Thanks @ChipBPhoto for your input. I have the 180mm and would like to know what you did´nt like about it. I use it with a fujifilm xt3 and it´s very sharp in my opinion.

Thanks a lot for your answer.

The 180 is a very fine dome made with high-quality glass. It does very well with a rectilinear lens such as the Fuji 10-24 or similar.

The Canon fisheye lens is a different design due to the 180 degree FoV. Like @RomiK shared, it has to do with the curvature of the dome glass and how light passes through. That is why you do not see it as a recommended dome for fisheye lenses. When a TC is added to a fisheye, it removes some of the native fisheye effect and starts to approach what a wide rectilinear lens will produce.

Again, the 180 dome is high quality. It just doesn’t have the correct curvature for a true fisheye lens.

To clarify further a dome in itself is not sharp, the results you get are the combination of the specific lens and the dome. Some rectilinear lenses will work better in the 180mm dome than others. For example the Canon EF 16-35 lenses are quite soft in the corners with the 180mm dome and work much better in the 230mm dome, but even there the corners have some softness. The newer Sony lenses in this zoom range actually perform quite well behind the 180mm dome.

It's not that the 8-15 won't work with a 180mm dome it just won't be as good particularly in the corners compared to the 140mm. Depending on your usage (if you are shooting big animals in open water with only water in the corners for example) you might find you are happy with the results.

Typically the port charts show that the 180mm dome needs 10mm less extension than the 230mm dome. However the limitation when deciding extension with the 8-15/180mm dome will be vignetting rather than placing the entrance pupil correctly. The geometry of the dome which is not a full hemisphere means that the entrance pupil is forward of the optimal position to avoid vignetting. The dome is designed such that a lens at the centre of curvature can see the field of a 16mm rectilnear lens. Any wider and it needs to move forward to avoid the vignette.

What this means in simple terms is that you will need at least 10mm less extension but will need to test to check if it vignettes which can be checked on land.

Even if you do this you will only be able to use the lens at 15mm, it will vignette badly and the dome port shade will appear in the image if you try to use the lens at 8mm.