When I moved from the D500 to the Z8, I had to sort out my wide-angle setup for full frame. Lenses: the 8–15 fisheye plus a Kenko 1.4× TC (the version that works on the Z8, see the Kenko TC thread), the Z 14–30 f/4, the Z 17–28 f/2.8 and the Z 20 f/1.8. None of them worked well with my old domes: an Aquatica 4" mini dome, an Aquatica 6" and an adapted Ikelite 8" that’s about 20 years old.

There’s a lot of good info here and on sites like interceptor121, but I couldn’t find a systematic, physics-based look at dome ports. Most sharpness tests are done on flat charts or brick walls. That mixes up lens sharpness and field curvature, and above water it tells you little about what happens behind a dome.

So I did my own tests. Because they focus close, the 8–15 and the 17–28 should be the best candidates for smaller domes, so I concentrated on those two. I measured:

• the field curvature of the 8–15 (with and without TC) and of the 17–28, using focus-shift series with the camera rotated around the entrance pupil on a nodal rail;

• the geometry of my domes, including the Howshot 140 (practically the same as the Nauticam 140, at about half the price) and the Sea&Sea 170AR on an adapter.

Lots of pictures, but the results are interesting:

• Sharpness: focused properly, both lenses are very sharp corner to corner at f/5.6.

• Diffraction: from about f/11 on, diffraction limits the sharpness. That’s physics, so no lens will do noticeably better at f/11 and smaller apertures.

• The TC: compared at the same effective focal length, it costs no measurable sharpness at f/5.6. In the corners the 8–15 with TC is even slightly better, because the TC only uses the centre of the fisheye’s image.

• Field curvature: neither lens has a flat field. The fisheye’s sharp surface is about halfway between a plane and a sphere, and the 17–28’s is much flatter. Behind a dome that actually helps, because the dome’s virtual image of a flat wall curves the same way.

All results, with tables and figures, are here: https://www.reefcolors.com/essays/equipment-wide-angle-photography/

Based on this I built an interactive dome port planner: https://www.reefcolors.com/essays/equipment-dome-port-planner/

You pick the dome, lens, extension rings, aperture, focal length and focus distance. It shows:

• how far the dome’s centre is from the lens’s entrance pupil, and the optimal extension;

• vignetting by the dome or the port;

• the closest focus and the depth of field;

• how much of a flat wall is sharp;

• lens data such as reproduction ratio and angle of view.

Right now it covers Nikon Z bodies in Aquatica housings and the lenses and domes I have or could measure. I’m happy to add other housings, lenses and domes if someone can provide the data, mainly port and extension dimensions, so let me know.

Please tell me if you find bugs or anything that looks odd.

My first pool shots agree well with the planner. Next up is a proper underwater test, with focus-shift series from a tripod in front of a tiled wall. That should show the combined effect of dome and lens on field curvature, sharpness and chromatic aberration, and give clean data for the domes.

Wolfram

Thanks for sharing this! It looks like a great resource.

I've seen using a 40mm extension on the Nauticam Z8 / 8-15mm / Kenko 1.4tc / 140mm dome combo. I'd like to see what your calculator reports.

I just measured my Nauticam Z8 system and the Z-Mount to Port Flange distance is 66.5mm. Probably accurate to at least 0.5mm as best I could determine after multiple measurements.

I also have a Zen170mm dome that I don't use much anymore but would like to see it represented to see what it can do.

Zen 170mm specs: