mawz

Photos does not yet have X-T4 support. You would need to use a RAW converter with X-T4 support, like Capture One Express for Fuji (which is a free download).

Lenses with floating elements, rear or front focusing groups or internal focusing (or many zoom designs for that matter, as zooms and IF lenses are essentially the same with regards to how they work) are notorious for not playing well with extension tubes, as the optical system is optimized for an assumed rear element to sensor geometry and extension tubes break that assumption. Teleconverters or front filters are the best solution there for improving magnification and/or reducing MFD. Fixed focusing unit lenses generally (but not always) play well with extension tubes, as they focus solely by adjusting the distance between the optical unit and the sensor and adding an extension tube is little more than extra focus helical extension for these lenses. They may or may not perform well, as the optical design is still optimized for a magnification or range of magnifications and the extension tube may take the optical design outside its designed magnification range with adverse results.

First step is to clean the electronic contacts on the lens. This sounds exactly like a case of dirty/worn contacts

I'll admit I'm a little amused by folks calling the relatively featherweight 100-400 a heavy lens. At 1375g it's actually the lightest 100-400 of its speed class, at 20g lighter than the Sony and over 250g lighter than the Canon. These are also reasonably fast lenses for the long end of their range, the only zooms that are faster at 400mm are the monster 180/200-400 f4's and the insanely huge Sigma 200-500 f2.8 (the Panasonic and Sigma mirrorless 100-400's are lighter at ~1-1.1Kg, but are also slower at the long end, being f4-6.3 for the PL and f5-6.3 for the Sigma) I'd definitely consider the 100-400 the go-to lens for the Fuji shooter who needs a telephoto. And at 2Kg or less when paired with a X-T body, it's not particularly heavy for the reach.

Only the single-digit X-T bodies support tethered shooting.

You've enabled a setting somewhere that only works in JPEG mode. There's a few of these available (IIRC some of the DRO settings, Auto & canned modes, etc)

Use your onboard or clip-on flash in manual mode, the SB-800 has a built-in optical trigger.

We saw a massive amount of updates on the older bodies for the simple reason that there were big jumps in capabilities across a similar hardware platform, as well as significant improvements in what could be done with the processor already present. You saw much less evolution on say the X-E2s (the last X-Trans II model) than the X-E2 or X-T1, because they were closer to the limits of the platform. The X-H1 was the last of the X-Trans III models and its changes flowed down to the earlier models, but there just wasn't that much they could add to the platform by the time the X-H1 came out that wasn't already included in the X-H1. That's why we've mostly just seen bug fixes and lens support updates. Today we have a fairly mature system on X-Trans IV, frankly I don't expect to see anywhere near the level of new feature adds via Kaizen updates as we saw early on with the X-Trans 1, II and III platforms

Depends on the ND filter and the light. If you're using a mild one to get wide apertures, no problem. A strong one for landscapes? Likely OK, but may not be depending on light levels. A very strong one for long-exposure cityscapes & such? Focus before adding the filter. Basic rule of thumb is that if you can handhold the shot, you can focus.

You'll get manual and auto flash with the SB-800 but not TTL or CLS. The electronics are low-voltage, so it's safe to use. The SB-800 was the last of the great Nikon 'use on everything' flashes.

The FD mount would be one of the least versatile. It's essentially FD/FL and M42 only in terms of adaptation, and the M42 adapter is rare. If you want versatility, go Canon EF, as most SLR mounts adapt well to EF mount. Canon FD and Minolta MD are the only significant exceptions to that.

Extension tubes reduce minimum focus distance and increase magnification, at the cost of losing infinity focus while mounted. So yes, it would have an effect. However a 16mm tube will not significantly increase magnification of a 70-300 lens due to the small amount of extension. You would need a significantly longer extension tube to have an effect (at 300mm, you need 150mm of extension to go from Infinity to 1:2 , or from 1:2 to 1:1). The MCEX-16 is best paired with a 35mm or shorter lens if a significant change in magnification is required. I'd suggest getting a used Micro-Nikkor 55mm f3.5 for pairing with your Nik-FX adapter to get up to 1:2 Macro (1:1 if paired with a PK-13 extension tube). They're available for as little as $35 from KEH.

No, only the models capable of tethering (except the X-T1) and the new X-A7 & X-T200 can be used as webcams

Honestly, I'd just get the XC35 new for 200 Euro I have one and it's welded to my X-E2. As a plus, it focuses noticably faster than the f1.4 version, and the X-E1 is slow to AF at the best of times.

I'm not sure if the X-E1 can do this. To get BBAF on the older 16MP bodies, go to Autofocus settings and set Instant AF to AF-S or AF-C (I'd suggest AF-S on the X-E1). Then set the camera to manual focus and press AF-L to focus. That said, I thought that Instant AF only came with the X-Trans II bodies (X-T1, X-E2 on later firmware, X-T10), not the X-Trans bodies (X-Pro1, X-E1)

The real question is do you want weather sealing or not? Because frankly from an landscape perspective there is VERY little reason to not shoot the inexpensive X-T200 for landscape if you don't need sealing. The base ISO IQ is on par with any of the other bodies and being a Bayer sensor camera, you don't have to be as particular about software as with the X-Trans (I still don't like LR with X-Trans although it is now usable, and stick to CaptureOne for that reason) The challenge there is there is only 1 UWA option that is sealed. If you need sealing, you're basically stuck with the 8-16, and your budget is basically an 8-16 and a X-T3 at best (maybe fitting the 16-80 kit lens in there, I'm not 100% sure of what UK pricing is). Otherwise you have the Laowa 9mm f2.8, at least 4 different 3rd party 12mm options, the 14/2.8 and the 10-24/4 OIS. Honestly on your budget I'd get the 10-24, 55-200 and whatever body you can fit in with the leftover. You should be able to fit up to an X-T3 into that budget. I'd look at the X-T3, X-T200 and used X-H1 or X-T2's, I don't think the X-T30 as good as the X-T200 for landscape use due to the screen setup (single-hinged on the X-T30, fully articulated on the X-T200. The X-T2/X-T3 double-hinged screen is the best for tripod stills use)

Also not a video shooter here. I think a lot of the push on video is just to get new features that justify an update, triggering sales from updaters. Fuji is one of the very few systems that has not seen a drop in sales as the overall ILC market imploded since 2012. Adding video adds sales from the video guys and serial updaters, as well as getting attention from the Youtube and IG influencers. It's simply a solid investment from the price/performance standpoint. And at the end of the day, where else are we going to go, Sony?

Sadly, the X-T1 is also the only tethering-capable body that isn't supported by the new app from Fuji either.

I'm purely a stills guy, so nothing I say applies to video. I used to be a real cheerleader for IBIS. These days I really don't pay much attention to its presence. I shoot a lot of low-light stuff, but since I'm often shooting non-static subjects (people or vehicles), IBIS adds nothing for me. I moved from an A7II to an X-T1 and have yet to notice the lack of IBIS. I can count on one hand the number of shots I have got because of IBIS. A couple really good ones, but it's very rare that I look at a missed shot with my Fuji's (or the Nikon's I've been shooting for most of the last 3-4 years) and thought 'I could have got that with IBIS'. And yes, OIS is equally effective on the lenses that have it. Don't get me wrong, if you shoot a lot of low-light static subjects IBIS is invaluable. The video guys love it because it makes their manual lenses a lot better for video. For long-lens work IBIS and OIS are practically a requirement to avoid silly shutter speeds.

The X-T30 is going to be faster. Better AF-C (AI Servo in Canon-speak), higher FPS, better video. For stills performance things are largely going to be similar in single-shot mode, you should see faster AF lockon and more usable face tracking on the X-T30, but other than than it's probably a wash. It's in video and continuous AF/Drive where the big changes between the 3rd & 4th gen bodies (X-E3 is 3rd gen, X-T30 is 4th gen) That said, right now it's VERY hard to beat the launch packages on the X-T30 with the f2 primes (23, 35 and 50 all are offered). That's going to be the best price/performance right now. You might look for the 35/2 package if that's what you are used to shooting with your Canon. DO be aware that 35/2 on Fuji is a tad wider than 35/2 on Canon, because Canon has a higher crop factor (1.6x vs 1.5x for Fuji). The X-E3 will likely slowly decrease in price until the X-E4 arrives (which will almost assuredly be the same featureset as the X-T30 in the X-E body). It's also worth noting that despite the looks, both bodies are very close in size. The X-T30 adds the viewfinder hump, pop-up flash and a flip-out screen for a pretty small size change.

Is your aperture ring set to A? That's a pre-requisite for any body control of aperture.

I'd expect WR. We haven't seen any new non-WR lenses arrive since the first WR ones shipped. The last all-new non-WR lenses were the 10-24 and the 56 and since then we've seen new 3 zooms and 2 new primes, all WR, and three variants of older non-WR lenses (the 56 APD and the XC zoom updates) which stayed non-WR.