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Back Button Focus

Discussion in 'Talking Pictures' started by EightBitTony, Jul 31, 2017.

  1. EightBitTony

    EightBitTony Well-Known Member

    I think this is the right place.

    So, people talk about Back Button Focus, and are often quite evangelical about it.

    I've tried it, and I'm clearly missing something.

    I tend to shoot in AI Autofocus on my 7dii, so when I want to take a shot, I focus on the subject (half hold the shutter down), and wait until the composition is just past what would have been good, and then I finish my click.

    If I'm in repeat-shot mode, I'll then just hold the shutter down and the camera follows the object in focus based on the relevant tracking options.

    What's different about back button focus (outside of when the exposure is measured)? It's one of those topics I've read up on, watched videos on, and tried, but I'm still not sure I understand what I'm missing.
     
  2. Benchista

    Benchista Which Tyler

    Big advantage for me is that it allows you to use manual focus much more easily, particularly if you wish to pre-focus, and then switch to AF when action reaches the spot.

    If I'm purely using AF, I don't use it.
     
  3. EightBitTony

    EightBitTony Well-Known Member

    Ah okay, so if the lens has full manual focus override (like many L series Canon lenses), you can leave the lens in AF, and because the shutter doesn't focus, it works like MF until you use the back button?
     
  4. Benchista

    Benchista Which Tyler

    Exactly.
     
  5. Terrywoodenpic

    Terrywoodenpic Well-Known Member

    It is very useful when using manual focus, and saves hanging on to half press when in AF.
    I use both AFL and AEL when doing hand held pans, I could also do With A colour balance lock button for doing them as well.
     
    Last edited: Jul 31, 2017
  6. Andrew Flannigan

    Andrew Flannigan Well-Known Member

    I'm another one that it doesn't work for. I'd rather use manual focus.
     
  7. EightBitTony

    EightBitTony Well-Known Member

    Thanks, that makes perfect sense.
     
  8. EightBitTony

    EightBitTony Well-Known Member

    I guess part of that is whether you come from a set of lenses which always have a manual override, not many EF-S lenses do, for example.
     
  9. Gezza

    Gezza Well-Known Member

    Or even simply seperating focus from exposure.
     
  10. EightBitTony

    EightBitTony Well-Known Member

    Yep, I mentioned that one in my first post - I'm aware of that feature of back button focus, and it's one of the uses I do get and understand :)
     
  11. PhotoEcosse

    PhotoEcosse Well-Known Member

    I don't claim that the way I use it makes much sense - but it is what I do.

    Sometimes I want to take my exposure reading from a different part of the frame to that I want to focus on. (Using both AE and AF). Typically I might want to expose for the foreground, excluding the sky, so I point the camera downwards so that only foreground is in the viewfinder and half-press the shutter release to lock the exposure. I then reframe the picture and, while doing that, use the back button to focus on the main subject.
     
  12. Terrywoodenpic

    Terrywoodenpic Well-Known Member

    Much easier when you have a separate AFL Button and an AEL button My Fuji XE2 is my first camera to have both under my thumb. and you do not even have to set manual focus.
     
  13. PeteRob

    PeteRob Well-Known Member


    It all depends on what your subject is. If you want to prefocus it is great. Ditto If your subject is moving behind obstructions (like a bird in reeds) where the AF will jump now matter how you can configure it. For a quickly moving subject I find one finger easier than two so I don't use it so much. I use it much more than I used to so there is an element of getting used to it.
     
  14. peterba

    peterba Well-Known Member

    I switched to BBF probably about six or seven years ago. Like you, I had read "evangelising" articles about it, and was intrigued by the idea, since I was frequently irritated by being let down by focus on the shutter button (half-press included). I set the camera up for BBF and started using it. There followed several days of under-the-breath swearing, but after about a week, I became comfortable with it, and never looked back. Now, if someone hands me a camera which ISN'T set for BBF, I find it really annoying.

    Focus and re-compose is just so easy with BBF, and also, foreground objects don't upset focus on a subject behind them (for example: tall reeds in front of birds on a lake). Having adapted to using BBF, I have absolutely no desire to switch back. :)
     
  15. PeteRob

    PeteRob Well-Known Member

    the superteles have a focus control button just off the focus ring too which is very ergonomic
     
  16. EightBitTony

    EightBitTony Well-Known Member

    I don't understand why though? How does back button focus improve that situation? It's a genuine question!
     
  17. EightBitTony

    EightBitTony Well-Known Member

    How? I still don't understand mechanically what the process does to achieve that, do you mean you focus on the object once, and then take your finger off the BBF, and then you can shoot to your heart's content without the reeds suddenly being in focus? If so, how do you focus on the birds which I presume are moving?
     
  18. Bazarchie

    Bazarchie Well-Known Member



    Have a look at this.

    You are correct in your second question above ie you can keep on shooting once you release your finger from the BBF button.

    Being able to quickly change from single point to af servo can be very useful when say photographing birds. However there are others ways to do this.

    I am yet to be convinced on BBF.
     
  19. EightBitTony

    EightBitTony Well-Known Member

    Thank you, that helps.
     
  20. PeteRob

    PeteRob Well-Known Member

    By separating focussing from the shutter release you can hold focus (prefocus) which can be useful. The bird in reeds is difficullt. You can't easily see the bird. Reeds move around a lot. With a long lens you wobble around a lot and depth of field is minimal. Focus will often hunt. You can forget tracking the bird movement. The only chance is if it is still fot a moment and not far in.

    For birds in flight I would use the shutter release for AF. Coordinating two buttons is too much.
     
    peterba likes this.

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