As Gavin said - Godox is your goto - for Fuji and Nikon use
Use the pro commander for your camera manufacturer to drive the other flash units wirelessly
Full HSS and TTL on Fuji X-T2 - very reasonably priced, and a fully integrated system, so you can add units as you like to grow from a small start.
Buy from a credited reseller for 2 yr warranty - Adorama in the US for example.
I have shot with the small stuff - like the TT350F, as well as the large stuff like the AD600 units.
Both ends of the Godox spectrum, both worked well with the Fuji.
The TT350F is ok really close in, but is underpowered for any serious outdoor work
Here it is providing HSS TTL fill on the GFX (same as the X-T2)
- Fujifilm GFX 50S GF110mmF2 R LM WR
- ƒ/2.0
Larger speed light models with better guide numbers will give you more power/range and the same functionality. I don't own any but the TT685F would be the model to look at.
Note that you buy a specific hotshoe style for your camera, so to use the speed lights on various models, you'd need to buy a Nikon and a Fuji Version, or buy a Nikon and Fuji wireless Godox trigger, and trigger the one speed light model from there, giving you cross compatibility.
The triggers are the Godox XPro-F and Godox XPro-N - about $70 ea.
Godox also make a speed light with no hot shoe (for want of a better description) the Godox AD200. A stand mount speed light you can trigger wirelessly and fit with a range of accessory light modifiers. More powerful than speed light, less powerful than a strobe head. Priced accordingly.
The larger battery powered strobes like the AD600 are excellent - 600W, with the same wireless TTL and HSS capabilities. They can take a huge range of modifiers to allow you to grow the system. They are fully controllable from the Godox XPro-F.
Here with a mid sized Godox Octa on location, using the cheap remote head to allow me to keep the heavy strobe unit separate, low down on the stand to add stability:
Providing a result with the GFX like this:
- Fujifilm GFX 50S GF110mmF2 R LM WR
- ƒ/2.0
Again running TTL and HSS, same as it would with the X-T2.
You can scale up further by combining multiple AD600 units into a 1200W remote head, giving 1200W of TTL HSS power for studio or location, all at a very reasonable price.
Here driving an Elinchrom Litemotiv 190 deep octa with mount adapter:
Producing amazing controllable light for portrait work:
The point being you can start at $80, and go up from there, all with the same wireless and TTL/HSS integration.
Awesome system - it's replaced all my other flash units in the last year.
Hope that helps?
System components below:
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Your time is limited, so don't waste it arguing about camera features - go out and capture memories