Back Button Focus.

Discussion in 'Beyond the Basics' started by stapo49, Feb 16, 2020.

  1. Braineack

    Braineack Been spending a lot of time on here!

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    It's all I use. How could it be redundant? It's simply disconnecting the focus acquisition from the shutter release.

    There's very little drawback to it, but tons of pros.


     
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  2. wfooshee

    wfooshee No longer a newbie, moving up!

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    My own take is that I don't see the point unless you have to separate focusing from shutter release, i.e. aim, focus at a specific point, then recompose and shoot at leisure. BBF ensures that no focus changes occur while you recompose. That's much easier than holding the half-press! I never saw any need to use BBF otherwise. With 3D continuous AF I miss very few shots on moving subjects. By very few, I mean maybe 1 in a couple of thousand at an air show, for example.
     
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  3. Braineack

    Braineack Been spending a lot of time on here!

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    The ability to focus and recompose easily is a HUGE benefit. It's much easier and faster to do than programming any AF-L. Even more so when you have to take a second recomposed shot -- you just shoot. Otherwise you must refocus and recompose.

    Just off the top of my head:

    What about shooting in the studio, focusing once and never having to worry about it again. If you setup some scene, you can easily move focus around when using on-shutter-press AF.

    Or shooting moving things, you can keep your AF set to AF-C and always track the subject and take a shot at will. Need AF-S, just press the focus button and release it.

    It's much easier to require focus on your subject when lining up a shot, or shoot through obstacles with just releasing your thumb.

    If your lens is manual override, you can focus it manually without changing any settings.

    Shutter will always fire -- I'd rather have slightly off focus, than no shot at all -- this is huge for event photography.

    Able to more precise with the shutter timings.


    All my cameras are setup for AF-ON and AF-C 100% of the time. It's extremely rare I miss focus in any situation. I can pick up any of my cameras and shoot; simply worrying about exposure settings and not if I need to track the subject or not.
     
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  4. wfooshee

    wfooshee No longer a newbie, moving up!

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    BBF in action shooting means holding a button while working the shutter. Goofy, to me. Yeah, it can be done, but why require the second button?

    The advantage is in focus-then-compose, and it's great for that. Only that. I have spoken. :allteeth:
     
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  5. Braineack

    Braineack Been spending a lot of time on here!

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    it's literally the same thing as half-pressing a button while working the shutter, but less fatigue on your finger and better control over the shutter itself...
     
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  6. Overread

    Overread has a hat around here somewhere Staff Member Supporting Member

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    For action there's several benefits:

    1) If you're using VR or IS or any other anti-shake you can enable the anti-shake (half press the shutter) without engaging auto focus. This might be good for enabling the anti-shake before the subject will appear in the frame. So there's nothing to focus on, but you still want the lens ready and working and countering shake for when the subject does appear. If your focus is already in the right ballpark position you don't want it hunting back and forth or focusing way off into the distance when the subject appears

    2) You can pre-focus at a specific spot you know the subject/action will be at, but you're also then able to turn the AF on after that point and track movement right after. Eg an animal jumping a showjump you can pre-focus on the jump itself- get the shot as they go over; then enable AF with the backbutton and track the subject as it moves off the jump and away to somewhere else.
    Backbutton is far faster at this than trying to find the right switch on the lens barrel for AF/MF switching. Especially as on some lenses the switch can be a long way from where you naturally hold the lens.

    3) You can half press to engage metering and meter the scene. The light might be shifting and changing so being able to doublecheck before the action starts, but without losing your focusing point lets you make quick checks even near to action moments.
     
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  7. Braineack

    Braineack Been spending a lot of time on here!

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    Yep. Three things I forgot. I've used all three.
     
  8. zulu42

    zulu42 Been spending a lot of time on here!

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    You guys are making sense but I'm still not convinced. I don't really understand the advantage of BBF over AF-L for pre-focus or focus and recompose situations.
    For manual override of focus, I can see that benefit.
    for metering without changing focus, AF-L...
    Finger fatigue? Get outta here.
     
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  9. Derrel

    Derrel Mr. Rain Cloud

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    Finger fatigue...that one left me at the border town called Credulity...AF-L has served quite well for two decades for me.leaves the right thum free to grip, select focus points withe the D- pad. Run the shutter speed selector.

    With a large and heavy lens on the camera the thumb serves a pretty important part of gripping the camera. when you add on a 7 lb 200 or 300mm lens, the thumb as a gripping point is not to be compromised.
     
  10. TWX

    TWX No longer a newbie, moving up!

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    I tried it in-part because I have a lens whose AF/MF switch is busted and I left it in the AF-mode, so BBAF allowed me to selective use AF.

    I found that the traditional BBAF with the shutter-button not doing any AF simply didn't work well for me on my 77D. I've been slowly retraining myself to use my right eye, but I've traditionally been a left-eye shooter, and that makes it harder to reach the AF-ON button. Likewise, even when I use my right eye, the 77D body, like the Rebels, is small enough that my face still makes it awkward to reach the BBAF button.

    What I instead do is use the AF-ON button as an AF-OFF button. This allows me to use the shutter button to achieve focus, then hold down AF-OFF when I don't want subsequent shots to use AF while pressing the shutter button. This has the advantage of allowing a novice like my wife be able to use the camera with traditional half-press AF as well.
     
  11. JBPhotog

    JBPhotog No longer a newbie, moving up!

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    I guess one might want to ask from a R&D perspective, if there was no value to BBAF then why do manufacturers design cameras with them? The answer is rather simple, it is the preferred method of focusing by the majority of professional (i.e. working) photographers. As Steve Perry says in his eBook mentioned earlier, "BBAF once again separates AF from the shutter release - the way the camera gods intended." And for those who have been around before AF was invented, these two functions where separated, the shutter did its job, the focus ring did its job the two were not married to each other.

    Here's a great video explaining BBAF.

     
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  12. TWX

    TWX No longer a newbie, moving up!

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    I wish that the lock switch on my camera would allow me to enable or disable AF on the shutter button. If that could be configured in that fashion that would make it a lot easier to just use BBAF or not at-will.
     

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