Canon 8-15 behind Nauticam 180mm Wide angle port

Hey all.

I was wandering what will be the problem using the 8-15mm lens (at 15mm) behind the Nauticam 180mm wide angle port.

I am using the Canon 5D mk iv with the 16-35mm mkiii with a 80mm extension and the 180mm port with good results.

I tried using the 8-15 behind the same port without any extensions and was pleasantly surprised.

I was told that the 1800 port is basically a cat-off of the 230mm port which is the recommended port for both the 16-35 and for the 8-15.

If this is the case - what may prevent the 180 from performing as well as the 230mm?

Attaching a photo taken with this setup. turtle photo edited by booting exposure, Freedivers not touched.

Happy to provide Raw files.

I wonder if it will even work at 8mm with the port shade removed...

Thank you for your input.

Erez

Two requirements to be met, first ability to see 180° in all directions from front glass of lens so that the corners of the field of view don't coincide with the lens lens shade and base of the dome. That's easy to test it either vignettes or it doesn't. Second requirement is to place the entrance pupil to the lens at the centre of curvature of the dome and if the the 180mm is not a 180 ° segment of a dome then that may be require you the place the entrance pupil back behind the dome support. Basically you need a 180° segment of glass with a 180° lens. You can place the lens forward to compensate if it's a short lens bu the entrance pupil may be in the wrong spot. t The lens will work but the corners/edges of frame may suffer distortion/chromatic aberration and you need to decide if that is acceptable.

Whether this is a problem depends on where the entrance pupil is in relation to the front element. If the entrance pupil is well back in the lens, the lens can be placed forward in the dome to avoid vignetting if not you may suffer from bad corners.

Try it and see, take some shots of a section of reef or something and see if the corners are sharp enough. If your corners are always blue water then you'll probably be happy either way. Vignetting should be immediately obvious.

Thank you very much Chris.

The lens sits in line with the port opening so no vignettes at all at 15mm. didn't try to remove the shade as it requires removing many screws..

As for the pupil placement -

​The data sheets claim the 180 port has a 110mm radius of curvature and the 230mm port has 120mm so they may not be exactly the same..

Will shoot a reef and see how the corners look.

Fisheye lenses seem to tolerate being displaced from the dome's center of curvature. For example I got better corners using the Seacam 9" diameter Superdome, which is a hemisphere segment, than the Seacam full hemisphere but smaller diameter fisheye port with my 10.5mm fisheye lens even with just 12 Mpix (D2x camera). Seacam does not specify curvature radii.

This website has some interesting cartoons showing how the position of the entrance pupil center as well its disk diameter (line) shifts with angle. It is forward (inside the front element) with the 10.5mm fisheye (scroll almost halfway down the page to see this) at 90 degrees. The 15mm rectilinear example is very interesting as well (scroll way down). It shows the entrance pupil shifting towards the lens' rear with the line going beyond 90 degrees from the optical axis. The 28mm shift is not as radical (last example on page).

http://www.pierretoscani.com/fisheyes-(in-english).html

I have used the Canon 8-15 at 12mm (APSH) and 15mm (FF) with the Seacam Wideport quite a bit for close up shots (salmon in streams). The Wideport thus used is better at smaller stops. The Wideport probably has a smaller radius of curvature than your Nauti 180mm.

Great read Tom, Now I just need to place a cold towel on my head to cool down my brains after all this information

I will keep experimenting and will update this thread.

Thank you very much.

Erez