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Take your pick. I see Canon, Pentax, other Nikons, etc.

The D750 is not a strong low light performer by today's standards. For example, here is is against the Sony A7M3 :

Not sure about other brands but Kenko tubes do support screw-drive AF on Nikon.

he says "how high?":

So, as you said, you don't need the IPTC Preset Manager; it's just convenient. Page 138 of the Menu Guide

You said so above. The Artists and Copyright are standard Exif tags (Comment is not).

You may be fueling the "confusion"; Artist and Copyright do not go into the Makernote; they are all standard Exif tags. Only UserComment goes into the MakerNote. And IPTC tags are standard, not in ...

No, IPTC is there: But the OP has *not* demonstrated that Auto embed during shooting is turned on.

This is absolutely relevant. You may have failed to embed the information; which would be your error.

Well yes; can you provide a picture of yours to check what you have done? (It can be anything.)

I don't have a D500 in front of me. Can you send an out of the camera files that I can run through my inspection tool? I assume you have Auto embed turned on?

I don't know of any Nikon camera that populates IPTC tags. The Copyright and Artist tags do get populated.

This isn't true of modern lenses; many have internal focus and some don't extend (from the image plane) at all. For a good example see Optics Primer - Focusing by Lowering Focal Length

Interesting result : The best Panasonic I have tested so far. About 2/3 stop above the DC-GX9 (If you have a camera that I haven't tested I'd love to hear from you to collect the required raw files.)

Once again, if you say so, and just barely. Once again that is a global (entire frame) technique. The hallmark of "computational imaging" is that it treats different parts of the image differently.

I invented Photographic Dynamic Range (PDR) so can be quite sure what the intent is. Reminds me of 1st year law school. It's hard to prove a negative; I'm satified it is so.

If you like. But certainly not at the level of sophistication that is now available in certain smartphones.

That isn't the intent. Once SNR is high enough for an acceptable image higher values do not improve Image Quality (IQ). (You probably disagree.) The comment above applies here too. Perhaps you can ...

These techniques aren't "computational imaging" they are all variations of High Dynamic Range (HDR). Computational Imaging is image processing that generally take a single frame and applies ...

Really; what cameras?