Is anyone experience "back button focus" issue like this?

Started 3 months ago | Questions thread
WayneDST
OP WayneDST Forum Member • Posts: 52
Re: Is anyone experience "back button focus" issue like this?

Erik Baumgartner wrote:

WayneDST wrote:

Hi Erik, I have tried BBF with MF mode. It works fine. What do you mean it doesnt work?

There is one issue I observed, when I set BBF+MF mode. When I hold the BBF buttoj, the AF+MF overwrite willnot works. I mean you cna't use the focus ring to change the focal distance. It eill be locked.

BBF is just for momentary use in MF mode, often followed by fine tuning with the ring with magnified Focus Check on.

I wrote a thing about my experience with Fuji BBF a while ago and saved it. It also describes AF-C settings and other possibly useful tidbits you might find helpful so I’m just gonna save some time and paste it. ...

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 Boost mode and Focus Priority switched on) just following the subject with the focus box (usually single point, but occasionally 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 slowpoke 35 and 56 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 subjects like birds in flight (or maybe race cars etc.), but I find that single point tends to lock on a closer subject where I want it to, while zone will miss the target and pick a peripheral feature instead (or the wrong feature on the subject),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 (focus is 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 the subject, or half-press and recompose if it isn’t.

Lots of options for almost any situation just by rotating the little front switch (which can be done easily on the fly as the moment requires with your eye in the EVF). 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, and the AFL button for Focus Check, I hope some of that makes sense.

Hi Erik, Thanks for your explanation in details. It really helps a lot. Especially the AF-C mode, it seems works quite well. Because most of my lens are old and slow, I didn't use AFC that often. After firmware update, I will try more.

As to AF-S, I set the BBF on the AE-L button (I feel more confirortable and stable with AE-L than AF-L). And using rear command dial for Focus check (I feel this command dial button is harder than other button). So far this setup works quite well. I

I am trying M mode + BBF today. It shuld be kind of "focus jump" check this link: https://drive.google.com/file/d/1CEpgbOS3-W_2gR3ZRB8rkinAgXVRZrPZ/view?usp=drivesdk

The "focus jump" happens, when using BBF+M mode on my xt3+56.2. There will be no jump when fully manual focus by roating the focus ring.

My guess is the BBF is assigned by the firmware. Maybe this issue could be solve by the firmware update.

 WayneDST's gear list:WayneDST's gear list
Nikon D3S Fujifilm X-T3 Nikon AF Nikkor 50mm f/1.8D Fujifilm XF 18-55mm F2.8-4 R LM OIS Fujifilm XF 56mm F1.2 R +3 more
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