Only as sure as the metadata on the file which read as I indicated. The shot was a RAW file and processed in Lightroom with Exposure at 1.93

Here is a shot I took of the Blue Moon. Z9 with 400mm F/4.5 at 1/200 sec., F7.1, ISO 64. Shot in DX mode and cropped small amount.

Here is a shot I took of the Blue Moon. Z9 with 400mm F4.5 lens @ 1/200 sec., F/7.1 ISO 64. Hand held shot in DX mode and cropped a bit

Buy the Nikon Z8 and use all of your current lenses with an adapter until you decide to convert to Z lenses.

I have shot in near darkness in the jungle without too much difficulty. Increase ISO, put camera in starlight mode and manually focus.

Agree, but I find the F mount lenses focus a bit quicker and sharper on the Z9 (and would guess on the Z8 as well). I am getting higher keeper rates on BIF with the Z9 and Z 400mm F4.5 then I do with the 500 PF mounted on the Z9. That one extra stop on the 400mm F/4.5 and the sensor on the Z9 make the difference.

To build on imagemeister's comment; he is correct. In my shooting the Z9 with the 400mm 4.5 and TC it is faster and yields sharper images, not to mention how much lighter and easier to handle the camera is.

You've taken pretty much the same route/option I did with the 300 PF, maxing it out with a TC. The advantage with the D850 in the mix is a larger sensor (allowing some cropping) and the ease of shooting in DX. My current strategy is to use my new Z400mm 4.5 on the Z9 -- extremely fast to focus and sharp and light -- overall a beautiful lens to handle. With the Z TC 1.4 on it, I am at 560mm (F/6.3) and much lighter and with a quick change using a function button I am in crop mode, still with 21mp and now an effective focal length of 780mm or so. Total weight with of lens and TC is 2.8# and w/Z9 camera, 5.8#'s. The 500mm PF with adapter (for Z9) and the 1.4TC is 7.2 #'s. Consider using the 400mm with Z8 and TC 1.4 the weight would be 4.8#'s. This is not a bad way to go. All the other options are heavier and more costly -- like the 600mm F/4 or the 800mm F/6.3. It's still a costly proposition.
Good luck in whatever you decide to do.
Michael

Good question. I have used the 500 PF as my long reach lens on the Z9. Firstly, since the Z9 (and the Z8) are very easy to setup a quick switch from FX to DX via one of the custom buttons, I very often first shoot in FZ mode to take advantage of all the MP the camera has, knowing I will usually crop a bird photo. Next, I hit my custom button to switch immediately (to get the same shot) but in DX mode. As far as IQ they seem to render equally. Also, to max out my 500PF I have shot periodically with a TC 1.4 on the Z9 (it works better, meaning acquires focus) much better than on the D850. The Z9 and the Z8 "help" F mount lenses to perform better. However, in the short time I have owned the Z9 and purchased the Z lenses, the Z lenses outperform their F mount counterparts on the Z body. Hope this helps.
Michael

I can only say having used the Z9 for six months, and given that the Z8 is a junior version with much the same power and features at a reduced weight of 30%, that the Z8 will outperform the D500 using F mount lenses with the adapter. I have owned the D500 and the 500mm pf as well as the D850 and can vouch for the performance of all of my F mounts with the Z9. It was a big improvement in IQ and focus acquisition. Good luck with your decision.

Some work for both. If you are going to continue to use XQD as well as CFexpress, make sure you get a reader that reads both. There are some.

You ain't seen nothin yet!!

Let me add to this string; Truly wealthy people can purchase the most expensive photographic equipment money can buy and produce truly unremarkable photography.

No it was not a kit lens.

Overall the D850 is a better camera. To get the reach you're talking about, just put it in DX mode. The cameras are somewhat redundant. I sold my D500. Now have the D850 and the Z9. Having so much fun with the Z9 that I haven't used the D850 since, but will take on a trip to the Amazon -- for two bodies.