Z8 or new lens?

The old axiom is to date the camera but marry the glass. But with the AF improvements in the recent cameras Z9 and now the Z8 does this still hold? This is the question. I have a Z6 II with a Tamron 100-400mm. This combination is not the fastest to focus, misses focus regularly due to inconsistent focusing, and doesn't work very well with smaller and faster subjects - e.g., (small) BIF). But please don't get me wrong, I have learned to live with these limitations, and when this combination gets the shot - which it does often enough - I am quite satisfied with the results. In fact, I think the results are outstanding for a $700 lens.

So this is the question, if I had the ability to spend $ 3,000 and wanted to improve things like BIF, but also landscape photography, should I put this money toward a z8 (with its better AF and higher resolution), selling my Z6 II but hanging on to the Tamron. Or should I keep the Z6 II and get the better glass of the Z 100-400?

Note that I keep the upcoming Z 180/200-600 out of the picture since that is a much larger lens that I would not take along regularly as I do the 100-400mm.

Its a no brainer the Z8 not much use having a $3000 lens with misfocuses. and its just not focus perse its how accurate the AF is. when i got my
sony a74 its af is on another planet compared to any other camera i have ever owned. get the Z8.

I'd be inclined to agree however I would most probably rent a Z9 first, considering the fact for the Z8 to have the same AF capabilities, to see how it does with the lens before committing to such an expensive piece of equipment.

thats a good plan. i waited for the new tamron 28 75 G2 and the 70 180 before i picked up my a74. i predicted the z8 would be a mini z9 and i was right ,looks like a 10 year camera.

The world evolves on the one hand, and on the other hand lens technology is moving forward faster than some presume.

20 year old and even 30 year old design lenses (Nikon still seems to sell some new!) work as well as when new - provided the elements do not need an internal clean, relatively poor corner quality at wider than f5.6 is often accepted as OK, good flare resistance is taken as not high, and the lens is unlikely to achieve the optical resolution of recent lenses.

Some prefer the "look" achieved with these older lenses - which is fine but not what those like you who want the highest lens performance want from their budget.

For better or worse to get the best lenses performance, a shorter lens mount to sensor distance is needed than was possible with the mirror in a DSLR, a new lens mount able to transmit much more information between body and lens than is possible with Nikon AF-S or Canon EOS, multiple internal AF motors where beneficial, new glass types and new coatings all help.

Sony grabbed a lot of market share by going ML to produce some optically better lenses 5 years before Nikon and Canon, and Canon grabbed a lot of the Pro Sports market from Nikon years before Nikon introduced AF-S.

When better performing products are introduced many migrate, the older equipment passes to the second hand market and manufacturers who do not move quickly tend to loose market share.

Not everybody realises the indisputable fact that if you use a reasonable lens on a higher resolving sensor - you get higher image resolution.
You also get higher digital camera performance with BSI and stacked sensors - at an increased price point.

Step 1 if you go from 24 to 45 MP; the body on its own should have about 45% more image resolution. Step 2 is image resolution does not increase by 45% - and a reasonable expectation is around 20% with a relatively weak lens and maybe 27% with a very best lens.

To get a 20-27% resolution increase is unlikely upgrading lenses.
On the other hand in extremely low light due to the noise factor top pros believe a lower MP body such as a D5 or D6 produces better images than a Z9.

As you have noted getting small BIF is possible with a Z6 - provided you first develop the necessary skill.

My suggestion based on what you have written is trade to the Nikon 100-400S AND get the 1.4 converter first.
This lens has quite fast AF and double as a decent close up lens covering a 4 inch wide subject - before adding the converter.

In a perfect world you would have $6000 to get the Z9 as well.
The world is not always as perfect as we would like it to be.

I partially disagree.

My experience is lenses in general (not just £3000 ones) that do not need a service do not mis focus - PROVIDED the photographer follows the guidance Nikon provide to get accurate AF.
I find those who follow Nikon guidance do not have AF issues - and those who do not blame Nikon - with a HOWEVER - the range of subjects where AF can work well with DSLR's can be restrictive, and that ML AF acquisition may not be better than with a DSLR - WITHOUT subject type recognition.

Where AI recognises a person, or a face or an eye, or a dog, or a bird or a car it can often easily accurately detect subjects often a DSLR's cannot - but do not presume eye AF will choose a sheep or cow eye if the ear tag is brighter with greater contrast!

Over the years I have helped many with perceived AF problems achieve good AF success, only rarely have I encountered a situation the problem was defective equipment, and in consequence I do not buy into the current myth that older lenses cannot AF accurately.
In capable professional hands AF has always been good enough for pros - who tend to recognise those situations where (even with ML) manual focus can work better than AF.

For those who take photos of brick walls; the mortar joints indicate the skill of the wall builder - and bricklayers with lower skill levels tend not to continue in employment for very long.

I'd invest in Nikon Z 400mm F4.5 VR S @ $3K

I think you need a new date to get a better marriage.

Most people would say to get the lens as it is usually the right answer, but if you plan on shooting a lot of things like BIF, kids and sports, I would say the difference in capability for those subjects, the Z8 might be the better choice for right now. Its a do everything camera that should last you ten years. After getting it, you can think of nothing but lenses moving forward.

If the Z8 were less of an upgrade for those subjects over the Z6ii, lens would be the answer as usual, but the Z8 is a heck of an upgrade.

It really all depends on how much you value those subjects and how often you want to shoot them, and we cant guess or predict that, but the Z8 will never hold you back.

focus miss due to inconsistent focusing is the key. If it is the lens, and not operator error in the first place, then you better replace the lens first.
The lens can be the culprit.
It can be overblown expectations for difficult focusing situations. For example, initial focus acquisition for a small subject with wild background is a challenge.
From my experience with the Z7 II in real world and test situations, I expect that focus is very precise and consistent with a Z6 II . The improved AF system in a Z8/Z9 may give you improved focus acquisition speed and better focus tracking when challenged. I would not expect that plain focus precision for a static object could be much improved significantly over Z6 ... Z7 II .
Testing AF performance is not easy. Do you have other lenses to compare AF performance in a controlled setup?

Investing into a more expensive camera would increase the mismatch between lens and camera investment in your case. I would invest in lens in your situation.