Date the Bodies, Marry the Glass ..............Love the way you put it.
Yes image file quality and glass has been the back bone for me, i use the D850 and the Z9.
Why did i get the Z9..........
1) sensor has VR that can benefit my collection of the FX glass.
2) tilt screen for water level in rapids or other low ground level shots.
3) silent shutter.
4) endless shutter use, unlike the limitations of DSLRS.
5) optional frame rate and focus acquisition speed.
6) all stacked into a 46 mp sensor similar to but not ultimately as brilliant as the D850 LOL.
7) two card slots the same.
8) i can use FX or Z glass.
9) i can use my D4s D5 D6 batteries as well.
10) basically its a D850 on steroids.
More and more, I detect the D6 and Z9 share a great deal of secret-sauce, as much as this is possible across their distinctly different
bauplan.
The tracking is a nice option but not the deal maker for me, i would have bought it anyway for the other reasons.
What i don't like about the Z9
1) prematurely released as unripened fruit, i believe after 12 months its ripened somewhat and improved.
Agreed that the camera released in December 2021 is distinctly different from a Z9 running on the firmware of late April, August, or November 2022.
To add all along, the majority of award winning features have been part of the Z9, since the day it launched,
4 5 examples include the Electronic shutter; rapid frame rates, high quality HE*RAW, the unique Sensor Shield, the superb EVF, and deep-learning based AF.
In & amongst these changes/additions, I suspect there's been a fairly long learning curve for many Z9 owners; this is true for me certainly, as I enjoy experimenting with alternative settings/tweaks. So it is hard to separate these two factors. Bottom line IME my hand muscles struggle to remember the simplest in new reflex actions!
It's a Pro Nikon ILC so it has similar Al-Mg chassis etc as in the D5, D6 and a gripped D850. I would much rather have the in built cooling heatsink and weatherproofing of the Z9 than any of the slightest compromise on these features.
3) can be very complicated to use to its potential.
For those who upgraded from the earlier Nikon ILCs, we probably have evolved with the incremental changes, and so there were no big leaps with retooling. Fundamentally the DSLRs are nonetheless relatively simple to use. The hybrid focusing of the D5 Triumvirate extended the AF modes to multiple options on the go i.e. using AFMode+AFON and similar custom functions. Most of us probably rely on 2-3 AF Modes with a DSLR such as the D850, however; and the standard solution to tricky subjects was toggling between Single-Point and a wider coverage dynamic mode or Group, or perhaps AutoAF.
Besides the excellent Recall Shooting Functions in both D6 and Z9, the D6 is the first DSLR in which I often use 3D mode (as on the Z9), as the D6 Eye & Face recognition works across many species, even some birds surprisingly. So in this case, 10 months with the Z9 has lead me to reconsider and modify how I have grown to setup and shoot the D6!
The Z9 runs a lap ahead of the D6 (and 2 or more laps in front of the D5, D850) with its Subject-Recognition, especially thanks to the robust eye-detect software. This leap forward seems to be a common strength of the flagship MILCs, including the new
Fuji APC Pro MILC. Being cast in AI software, we can expect the designers will continue to improve these incrementally ie Firmware patches/updates in respective camera systems. At least for Nikon, the next big leap likely lies in the new advances in R&D that will be enabled with new hardware (stacked sensors, with fully electronic shutters + EXPEED8 etc]
Overall, I've found learning and fine-tuning the Z9 to have been stimulating and it's a most rewarding imaging instrument. As with the overlaps in added firmware features and the new & diversified Menus and AF system in the Z9, the new Z Nikkors have also had a major impact on my photography. In particular, I suggest 2022 will "...be remembered - among the wildlife lens geeks at least - as the year of the '
Democratization of the 800 Prime'..."
4) menu system used to be easy simple and now to deep and complicated for someone like myself.
Added functionality demands more interfaces, with deeper menu dives. The increased options have improved the Z9 customization options compared to the DSLRs - much improved in my experience, which is distinctly parochial and centred mostly on the AF. I don't use networking, video nor flash....
5) the focusing system, unless vastly improved in the 3.01 update i find it can be a hit and miss, but that's also possibly partly in play due to my struggling a little with the steepish learning curve.
6) i wish they would introduce the group focusing like in DSLRS
I find the Custom Area AF modes - one of Nikon's great ideas - are very similar in use across the Z9 and D6, and I no longer use the D5 - D850 style Group AF mode in the D6. However, when turned ON, the Z9 AI software dominates the CA modes, which is a major advantage over the DSLRs (and other Zeds, IME). In fact CA1*1 is a force to be reckoned with photographing wildlife. Saying farewell to AFFT is another huge positive of MILC AF, especially with fickle zooms and/or TC combo's.
EDIT: no ways do I find Z9 AF hit & miss. On the contrary for wildlife subjects. Hybrid focusing works very well, interleaving the key AFmodes (usually CA1*1 or Single-Point with 3D and/or Auto etc) and leveraging Recall Focus Distance(s). The big challenge is training muscle memory. True a D6 is impossible to beat in dense clutter at a fleeting subject e.g. a warbler hopping and hiding in the reeds, but with the right technique I've proved the Z9 delivers and with much higher hit rate in sharp images. Obviously, silent shooting is yet another unique MILC feature with a Z9 for wildlife.
7) i wish it was a little friendlier to use, but from what i hear that's mirror less regardless of brand.
According to the consensus from much discussion on this, again one factor is the sensor based AF in MILCs with its propensity to grab backgrounds [the common solution is leveraging Recall Focus Distance(s) ], which is a major reason for Hybrid-focusing.
OTTH it's clear MILC architecture is opening up more and more interfaces and features eg video, which all builds up the diversity of operations/settings that are now made possible. More challenging to learn but no free lunches here, as everywhere. The spin off of MILC is there's more options and more to learn etc. We have yet to see where and how Nikon engineers build on the scope enabled with 'just' an electronic shutter in future cameras.
Finally i feel the Z9 is great, i am intrigued as to what the Z8 will be or bring.
Only an opinion
My responses are a summary of empirical experience and much reading of the industry literature, as reliably as I can ascertain, recall the above.