Upgrade options: Fuji X-T4 vs Nikon Z6

Basil K wrote:

I have a Fuji X-H1, and a nice set of Fuji lenses. I love the Fuji colors, and increasingly I am actually shooting for the JPEGs almost as much as the raws - great colors and much less work in post-processing.
So I am not in hurry to upgrade, but I am considering upgrade options. I shoot a wide variety of photography. I do some event shooting, I do a lot of bird and wildlife photography (I really love that), and some studio portraits — I am considering going semi-professional (doing some paid work). But right now, I mostly shoot for pleasure.
My upgrade decision is driven by my bird photography in particular - I would like better autofocus. The X-H1 is good, I use the medium sized zone in the center of the sensor where the PDAF points are located, and the camera does alright as long as my subject is in the center of the frame. But I would like my next camera to have better autofocus, with the points across the whole frame. The Fuji X-T4 sounds attractive in this regard, but so do some other cameras.
My other wildlife photography concern is relates to high ISO performance. I shoot at a high shutter speed to freeze action when I am shooting birds. However, the results in high ISO pictures in most scenarios, unless it is a very bright scene (I usually set ISO to auto, capped at 6400). Would shooting with a full frame camera help me keep the ISO lower, and reduce the level of noise in my bird/wildlife photos? Is improved ISO performance worth a potential sacrifice of those amazing Fuji jpegs?

Long story short: If you use Fuji jpegs, stick with fuji. The Nikon will be a slight jump up in IQ, especially if you go for the Z7. But the Z6's image quality will not make your images noticeably more refined or anything. I'd say between Fuji 24mp and Nikon FF 24mp the difference in dynamic range, resolution, tonality is less than 10% and not really noticeable unless you start really zooming in.

Long story:

I've owned and shot with Nikon and Fuji almost exclusively since I switched to digital (from film) around 2010. It's always been a difficult decision as Nikon makes the best FF sensor SLRs, there are so many great (affordable) used lenses, and their SLRs work just as well in 2021 as they did in 1991.

For a while I was traveling a lot and shooting x-t2 and x100. Loved the size, the styling, the high quality and compact kit. EVF was novel at the time and welcomed. For travel this was a great set up. Then I started doing some comparisons to my Nikon d750 and the jump up in IQ was noticeable enough for me to adopt the Nikon for local commercial shooting where size wasn't such a concern. I had my eye on the Z7 but cannot imagine traveling with those big ass lenses (expensive too!) so I held off.

I just got an x-t4 and decided to compare to my old trusty d750. The sensor should be almost identical to the z6 but it's not backlit.

Comparing RAW files in capture one: there is a difference in IQ; the nikon hold maybe 5% more detail in the highlights and shadows. It has a little more dynamic range. when I set both files to linear response and match the exposure of the mid-tones, the highlights are a little hotter and the shadows a little deeper from the Fuji files.

However it's too small a difference to really make a difference and it's negated by the X-t4 image stabilization which is really good. THE IQ IS REALLY CLOSE between the two. If you really want to see a meaningful jump in IQ you need to go MF. I have the GFX50s. It is not a good birding camera but it's great when tonality and IQ are the priority.

Also keep in mind that ISO rating is not the same between Nikon and Fuji. If you meter with Fuji, and shoot with Nikon you will be overexposed. Nikon FF ISO 100 = Fuji ISO 160. The fuji needs about 2/3 stop higher iso setting to match the exposure of the nikon. In practice not a big deal, because opening up your lens's aperture 2/3 - 1 stop will give you a similar DOF as the nikon.

I imagine a z6 is going to be a little bit better than the x-t4 but not enough to warrant buying new, expensive, and bulky lenses. I'd rather go birding with the smaller x series telephotos any day of the damn week. Also, while IQ is important for birding it's not the most important thing, capturing the bird is the most important thing. With the Fuji, the whole kit will be a lot lighter and therefore easier to stabilize whether that's electronically or with a tripod. Also the little bit of extra DOF from the smaller sensor will probably be a good thing if you're shooting long lenses wide open.