Back Button Auto Focus on the SL Bodies

[Luke_Miller]

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Warning - A long winded and arcane post.

I'm a long time Nikon DSLR shooter and early on adopted the technique of back button auto focus. That method involves separating auto focus from the shutter release and adding initiation of AF-C auto focus to the Nikon's AF-On button. That enables one to press and release AF-On while focusing on a static subject which effectively acts like focusing in AF-S mode. The focus is locked, allowing focus and re-compose or waiting for the decisive moment. With a moving subject one holds down AF-On and autofocus operates in AF-C, tracking the subject. This setup gives me either AF-S mode or AF-C mode depending on whether I press and release or hold down the AF-On button. I’ve probably taken over 60 thousand images this way, so the muscle memory is really ingrained.

When I added the SL and SL2 I wanted to set them up the same way with the Joystick serving the function of the AF-On button. While this can be done the results are different. When the Joystick is configured to initiate AF-C auto focus and I press and release it on a static subject I see the focus point indicator turn green and the focus aids confirm focus. But when I release the shutter the resulting image will be soft or significantly out of focus about half the time. It appears the focus did not lock and drifted slightly before the shutter was released. If I keep the Joystick depressed while the shutter is released the camera focuses continuously and I get a sharp image on a static subject. If instead I have AF-S assigned to the Joystick I get the same results as with my DSLRs on static subjects and can recompose or wait before releasing the shutter.

The is an observation, not a complaint. My hope was to capitalize on my hard-earned muscle memory when shooting with my SL bodies. At this point I think the best solution is to have one set of User Settings with AF-S assigned to the Joystick and another with AF-C assigned. Putting User Settings on a FN Button will let me change between them quickly. Not perfect, but workable.

Another approach is to have the camera in AF-C mode (shutter initiates auto focus) and assign AF Lock to the Joystick. Pressing and holding the Joystick initiates and locks focus. Depressing the shutter does not re-focus. For moving subjects I would not depress the Joystick, but instead half-press and hold the shutter button, engaging AF-C. This works for both static and moving subjects without having to shift between User Settings. But it is different enough from how I shoot with my Nikons to potentially cause problems when I use them.

I love my SL bodies and my sense of them is they were designed by people who are also photographers. So having to adapt to them is worth the effort.

[JeffWright]

Are you setting up focus to be manual and assigning the joy stick button to do either AF-C or AF-S? This decouples AF from the shutter release.

 

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[Photoworks]

I have noticed the Green box to came up even if it still in the focusing process.

I never use AF-c because it is to busy focusing all the time, and the EVF become a lowres images.

I use the back Botton focus in AF-s in video often to get me started and then follow up with M focus on the lens.

[Luke_Miller]

2 hours ago, JeffWright said:

Are you setting up focus to be manual and assigning the joy stick button to do either AF-C or AF-S? This decouples AF from the shutter release.

Yes.  My settings decouple auto focus from the shutter release.  The issue is in AF-C releasing the Joystick results in a slight (or sometimes significant) defocus of the lens before I take the shot.

[trickness]

1 hour ago, Luke_Miller said:

Yes.  My settings decouple auto focus from the shutter release.  The issue is in AF-C releasing the Joystick results in a slight (or sometimes significant) defocus of the lens before I take the shot.

I think I've had this in a couple of shots recently and was equally perplexed. Was using manual focus mode, getting spot focus with the crosshair/back button and tripping shutter. A couple of shots had very soft focus and I was holding the camera quite steadily. Not sure what is going on here, it's pretty random. This was with the 35 SL Summicron

[Luke_Miller]

I see it with both the SL and SL2 and the 35 Summicon SL and 24-90 Vario-Elmar.  So it is apparently the nature of the beast.  I just have to work around it.

Edited September 27, 2022 by Luke_Miller

[matted]

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I have my SL2-S set up in a similar fashion and have noticed the same thing, however I have just attributed it to the contrast detect AF and some minuscule "hunting" it does when in AF-C to ensure it is in focus. I think the AF can't believe that the subject is not moving and needs to reassure itself every now and then by reacquiring focus, so if you release the joystick button at the wrong moment you could be left with your subject out of focus.

My old Nikon SLRs rarely if ever hunted while using AF-C on static subjects so if you released the AF-ON button you could be sure it would still be focused on whatever it was focused on while the button was depressed. However, I have found that other cameras that I have tried to use in the same fashion (Fuji mirrorless and now SL2-S) were rarely locked on 100% to static subjects in AF-C the way that my Nikon bodies were, and would occasionally hunt a bit to reacquire focus, although they have become a lot better since the XT1 was released.

I am still getting used to the way the SL2-S focuses and have a fairly high hit rate, but every now and then I am disappointed by missed focus on static shots and also some double-image blur that I think may be related to OIS/IBIS but can't reproduce it consistently so who knows. My only AF lens is the 24-90 so all of my experiences are based on that.

[Luke_Miller]

24 minutes ago, matted said:

I have my SL2-S set up in a similar fashion and have noticed the same thing, however I have just attributed it to the contrast detect AF and some minuscule "hunting" it does when in AF-C to ensure it is in focus. I think the AF can't believe that the subject is not moving and needs to reassure itself every now and then by reacquiring focus, so if you release the joystick button at the wrong moment you could be left with your subject out of focus.

Thanks for your post.  I think that is exactly what is going on.  I notice that when I hold the Joystick down in AF-C and release the shutter I can hear the lens focus motor for a fraction of a second after the shutter fires. Since I don't get out of focus shots in AF-C when focusing using the shutter button (or holding down the Joystick) I wonder if the body waits a fraction of a second to release the shutter until the "hunting" brings the image image into in focus.

Haven't seen it yet with my SL bodies, but with my Nikons I would occasionally see some weird double image artifacts on static objects while the rest of the image is sharp. I also attribute it to the VR (OIS) function.

[matted]

1 hour ago, Luke_Miller said:

Thanks for your post.  I think that is exactly what is going on.  I notice that when I hold the Joystick down in AF-C and release the shutter I can hear the lens focus motor for a fraction of a second after the shutter fires. Since I don't get out of focus shots in AF-C when focusing using the shutter button (or holding down the Joystick) I wonder if the body waits a fraction of a second to release the shutter until the "hunting" brings the image image into in focus.

Haven't seen it yet with my SL bodies, but with my Nikons I would occasionally see some weird double image artifacts on static objects while the rest of the image is sharp. I also attribute it to the VR (OIS) function.

I was wondering if this was the case as well. Of course when I fiddle with focusing on static subjects around my house it seems to perform as expected, but my real world results would definitely suggest otherwise. It is for sure frustrating that as smart as the programming and processors are in today's cameras, they still can't replicate the AF performance of a 15 year old SLR body in some ways!

Interesting that you also experienced some double images with IS from other brands. I did have one little-used VR lens for a time many years ago but the SL2-S and 24-90 is my first real stabilized platform so I am still getting used to it. It definitely adds more than it subtracts, but I would definitely like to sort out if the double image thing I'm experiencing can be worked around somehow. Perhaps I'll start another thread so I don't derail this conversation further.

Edited September 27, 2022 by matted

[Virob]

I just switched to FW6.0, and noticed that when using back button focus and AFc, pressing the joystick AFc is activated and stays active. A second press is required to deactivate. In the previous version the joystick had to be continuously pressed for AFc. I haven’t checked, but this might help with maintaining focus on static subjects.

[SrMi]

1 hour ago, Virob said:

I just switched to FW6.0, and noticed that when using back button focus and AFc, pressing the joystick AFc is activated and stays active. A second press is required to deactivate. In the previous version the joystick had to be continuously pressed for AFc. I haven’t checked, but this might help with maintaining focus on static subjects.

If that is true, then that is a very bad idea!

[Virob]

53 minutes ago, SrMi said:

If that is true, then that is a very bad idea!

Can you elaborate? I can't decide whether it is good or bad since I almost never use AFc.

[SrMi]

1 hour ago, Virob said:

Can you elaborate? I can't decide whether it is good or bad since I almost never use AFc.

It is different than any other manufacturer's implementation, which means it will be confusing for those who are used to conventional BBF implementation, and there is no benefit.

Imagine if the shutter half-press would turn focusing on and off in AF-C.

(see my post below)

Edited December 10, 2023 by SrMi

[SrMi]

3 hours ago, Virob said:

I just switched to FW6.0, and noticed that when using back button focus and AFc, pressing the joystick AFc is activated and stays active. A second press is required to deactivate. In the previous version the joystick had to be continuously pressed for AFc. I haven’t checked, but this might help with maintaining focus on static subjects.

There is a new option, Button Lock. Change it to Press and Hold to regain the classic BBF functionality.

[LightedMoments]

Thank you for the post and replies.

i am also an old nikon shooter switched to leica sl2. Still have issues with back button focus with wildlife bird photography.

Anyone has idea to setup which will do a single press back button focus using AFs and another button that can turn on AFc including eye tracking? This would be very helpful when i track action of birds while shooting some static birds as well

[robb]

I just updated my 4 sl2 and sl2-s bodies to the latest 6.0 firmware.

thank you to the group for pointing out the new joystick setting in the menus for press and hold…

makes my life drama free.

Robb