Back Button AF and Priority Settings

Started Apr 30, 2020 | Discussions thread
Erik Baumgartner Senior Member • Posts: 3,548
Back Button Focus and Focus Settings in General

I wrote a thing about BBF a while ago and saved it. It also describes how my AF-C settings are configured which may help you to get the most out of your X-H1, so I’m just gonna save some time and paste it below. Everybody has their own way of doing things and there are a million different ways to set up your camera. This may or may not work for you, but however you end up configuring everything, you may glean some usefully tidbits here...

BBF (Back Button Focus) is usually used to decouple the AF function from the shutter button so you can continuously maintain AF on a moving subject independently with your thumb and shoot with your index finger on the shutter button, or focus on a static subject with a momentary touch of your thumb and then you recompose and shoot without the shutter button reinitiating AF. You can set your Fuji up this way too - I did, and while it works, it doesn’t work all that well. The Fuji AF-C (at least on the X-Trans III models - X-T2, X-T20, X-H1 etc) works FAR better when it first initilizes and locks on - if you use continuous BBF or engage AF-C using the shutter button using a half-press (with AF not decoupled from the shutter button), the AF system seems to get lazy, less responsive, and less accurate. I get far better results (with Focus Priority switched on) just following the subject with the focus box (single point or sometimes zone) prepositioned where I want my subject to appear in the frame and fully mashing the shutter button down - no half press and track first (an initial quick half-press is a good idea to get a slow lens in the ballpark, though). I get tack sharp results nearly every time with this method with the 16-55, 50-140 and even using the older slowpoke 35 and 56mm lenses (though they can be slower to track initially.

Also, unlike AF-S, AF-C works at shooting aperture only, so you'll definitely want a larger aperture (f/2 - f/2.8 minimum in very low light). ...and don't use the smallest focus box (Single Point) for AF-C - ever, it just doesn't work well, the dimmer the light, the bigger the focus box needs to be. The zone box seems to be the way to go for distant and/or isolated objects like birds in flight (or maybe race cars etc.), but I find that single point tends lock on a closer subject where I want it to, while zone will miss the target and pick a peripheral feature instead. YMMV.

For the fastest, most responsive AF try custom AF-C setting #6: Tracking Sensitivity: 0, Speed Tracking Sensitivity: 2, Zone Area Switching: FRONT (CENTER might work better if the subject isn’t coming right at you). I find that of the factory presets, #4 has the snappiest response time - I use it with my X-T20 which doesn’t have a mode #6 option. This also works very well in continuous shooting mode - I recommend CL mode, 5 fps or less unless you have lots of light and a contrasty subject. Use a slower speed with slower, older lenses. Again, YMMV. I do have BBF set up to work in M mode so I can easily focus, recompose and shoot with static subjects. In S mode I use the shutter button half-press and recompose method (with release priority). It sounds complicated, but it’s super simple once you get your head around it.

So with just moving the front AF switch, I get:

M mode - either manual focus or BBF single point (automatically decoupled from the shutter button in M mode)

C mode - fast, accurate focus for moving subjects with a full press of the shutter button, or continuous tracking with a half-press (which can work quite well in some situations if you switch to Wide Tracking AF).

S mode - full button press if the focus box is on your subject, or half-press and recompose if it isn’t.

Lots of options for almost any situation just by rotating the little front switch. I use this on my X-T2 and X-T20 but it should be adaptable to any of the X-Trans III or IV cameras (although the newest cameras MIGHT work better with the DSLR method of continuous tracking). I use the rear command dial for AF On). I hope some of that makes sense.


 Erik Baumgartner's gear list:Erik Baumgartner's gear list
Fujifilm X100V Fujifilm X-T2 Fujifilm X-T20 Fujifilm XF 35mm F1.4 R Fujifilm XF 56mm F1.2 R +2 more
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