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Thread: Back Button AF - How and Why.

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    Other side of the hill ... WhoDo's Avatar
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    Back Button AF - How and Why.

    Thought our members might enjoy this short video on Back Button AF. Examples are Nikon-based but principles apply equally to Canon (and maybe also Pentax or Sony ). Enjoy!

    Waz
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    Who let the rabble in? Lance B's Avatar
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    I have always used the "back-button" technique. I find it the best method as you can focus recompose and for BIF it is a must, IMO. When you become used to it, it just works so much better.

    Thank you for the link, Waz.

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    Ausphotography Addict Lplates's Avatar
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    Interesting presentation. I've been using it since reading about it here some time last year. I really like it, but my husband, who uses his left eye on the viewfinder, isn't such a fan.

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    That's a great explanation.
    Cheers

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    Quote Originally Posted by Lance B View Post
    I have always used the "back-button" technique. I find it the best method as you can focus recompose and for BIF it is a must, IMO. When you become used to it, it just works so much better.
    I've been using AF-C almost exclusively, Lance, but the problem is that once that's selected you have no control over composition. AF-S means easily missing focus if you aren't quick enough to recompose... and I'm usually pretty slow. Seems like this might be the answer for me so I'm going to give it a serious try to see how much I can improve my BIF keepers and my faster moving waterbirds. Thanks for commenting, mate.

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    The reason why I like back button focusing is because it removes the need to change focusing mode - just leave it on AF-C and your finger takes care of both modes.

    Only issue is when you give the camera to someone else to use - they don't know how to focus (or want to know)!
    Cheers, Troy

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    Interesting I have been trying B/B/F for a while but wasn't aware of having the AF-C function activated and if necessary just went straight to the AE/AF in the main menu and activated there so have switched on AF-C then AF-L and see if it's different in the way it perfoms
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    Who let the rabble in? Lance B's Avatar
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    Quote Originally Posted by WhoDo View Post
    I've been using AF-C almost exclusively, Lance, but the problem is that once that's selected you have no control over composition. AF-S means easily missing focus if you aren't quick enough to recompose... and I'm usually pretty slow. Seems like this might be the answer for me so I'm going to give it a serious try to see how much I can improve my BIF keepers and my faster moving waterbirds. Thanks for commenting, mate.
    I use AF-C mostly as well and especially for BIF or other fast moving subject matter. However, when using AF-C for non fast moving subject matter, when you are not going to focus recompose, it is also useful using the Back Button Focus Method as you keep your thumb on the Back Focus Button it will keep adjusting your focus right up until you push the shutter button so as you're assured that you get optimum focus if the subject moves slightly or you move slightly (like in or out). If you are going to focus recompose, then you need to remove your thumb from the Back Focus Button when you recompose otherwise it will focus on something else. I don't know whether you saw my thread entitled "Wanna see some detail":

    http://www.ausphotography.net.au/for...ee-some-detail

    as I used the Back Button Focus and AF-C on that photo and I obtained optimal focus due to the fact that I kept my thumb on the Focus Button right through when I pressed the shutter. This means that if I was swaying in or out or the bird slightly moved, the focus would have been perfect, which it was. The DOF was micro small as I was using my 300 f2.8 VRII @ f4 and at or near minimum focus of about 2.51mts (according to EXIF) which means a DOF of 14.7mm!!! So, any slight movement back or forth would have meant that the eye, which I focused on, may have meant missing the exact focus. I like to use wide apertures to get beautiful out of focus areas, good subject isolation and best bokeh - that's just my preference.
    Last edited by Lance B; 28-01-2014 at 5:51pm.

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    keen learner of new tricks.
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    thanks Waz and Lance too for that explanation. I have tried it on several occasions but I have never realised about holding the button down like shown in the video. Must try it.
    Graeme
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    Quote Originally Posted by WhoDo View Post
    I've been using AF-C almost exclusively, Lance, but the problem is that once that's selected you have no control over composition. ......
    Waz!!

    (and others who's camera is capable of this feature)

    Your camera(most Nikon's except for the D3xxx and lower series) should have the ability to set the AE-L/AF-L button to do the AF-On work.
    If you don't use AE-L/AF-L(which I never have), and set AF-C mode, you can still maintain AF and recompose in the one action.

    The AF area mode to try is called 3D tracking, which basically tracks the colour and shape of the initial point of focus acquisition.

    So(eg, in bird photography) ... you set the camera up as I describe(using the AE-L button as AF-On) set AF-C and focus point mode as 3D tracking.
    3D tracking is not the same as the standard Auto focus point mode!!! Look for the 3D mode.

    This still gives you only a single point mode for focus selection, but the trick is that as long as you press the AF-On button, the focus point moves in sync as you recompose.
    So for example: you start af 'tracking' the bird at it's head using the central focus point, and as you pan with the bird in flight, but slightly recompose to give the bird more lead in space, the af point will try to stay on the birds head. Your af point changes position from the original central point.
    This obviously works better as the area of focus point coverage is greater in the vf too, as it gives better composition flexibility.

    one thing to note about this mode.
    Earlier cameras(say D300 generation) were not as reliable for actually tracking the original AF acquisition point.
    Haven't tried it in say a D7000 series camera to compare, but the D800 is miles ahead in terms of tracking reliability when compared to the D300(which it and the D3 were the initial implementations of the system).

    I don't use it all that much to be honest, so can't give an overall impression of how good it is in everyday usage, but in those times when I have used it it seems to work well .. and the main ingredient to successful operation is in using it with the AF-On button.
    That is, if it suddenly begins tracking the wrong area, to know when to stop AF, recompose to start the tracking sequence again and give it a chance to work.

    One of the two major reasons I decided to go with a D800 over a D600 was due to the non existence of the AF-On button on the D600. I couldn't drive a camera without one.
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    Ausphotography Regular MissionMan's Avatar
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    Started using this a while back as it was one of the recommendations that Thom Hogan had in his guide to the D700. Extremely annoying to work with but after having used it for over a year now, I can't go back. As mentioned, you do have the minor issue of other people using your camera, but one of my custom settings is a point and shoot setting configured exactly for this reason.
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    Ausphotography irregular Mark L's Avatar
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    Now that I'm used to it, I can't believe it's not the default setting on DSLRs.
    As Lance mentioned, it gives you the ability to keep it pressed for constant focusing and then push the shutter button when needs be. Mich easier on the finger than half pressing the shutter button to keep adjusting focus. I used to get a tired finger and many photos I didn't want.
    'tis also good for landscape or still life. Back focus button locks the focus. You just have to then expose at your pleasure without the camera wanting tho refocus when you press the shutter button.

    For those new to photography, you may find some more useful (or not) comments in this thread ...... http://www.ausphotography.net.au/for...tton-focusing;)
    Last edited by Mark L; 28-01-2014 at 9:55pm.
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    Quote Originally Posted by Lance B View Post
    If you are going to focus recompose, then you need to remove your thumb from the Back Focus Button when you recompose otherwise it will focus on something else.
    Effectively using AF-S when you do this. I agree, this is a MUCH faster method than changing the AF mode manually.

    Quote Originally Posted by Lance B View Post
    I don't know whether you saw my thread entitled "Wanna see some detail":
    I did. Nice to know this is an example of what can be achieved using this mode.

    - - - Updated - - -

    Quote Originally Posted by arthurking83 View Post
    Waz!!
    ARFUR!!!!!

    Quote Originally Posted by arthurking83 View Post
    Your camera(most Nikon's except for the D3xxx and lower series) should have the ability to set the AE-L/AF-L button to do the AF-On work.
    If you don't use AE-L/AF-L(which I never have), and set AF-C mode, you can still maintain AF and recompose in the one action.

    The AF area mode to try is called 3D tracking, which basically tracks the colour and shape of the initial point of focus acquisition.

    So(eg, in bird photography) ... you set the camera up as I describe(using the AE-L button as AF-On) set AF-C and focus point mode as 3D tracking.
    3D tracking is not the same as the standard Auto focus point mode!!! Look for the 3D mode.
    I knew I had this feature but wasn't sure how it worked. I thought it simply indicated which part of the subject would be in focus rather than tracking the original selection. I'm not an avid experimenter so I just ignored it. Now I know what it does I'll definitely give it a try. Thanks for wising me up, Arfur!

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    A royal pain in the bum! arthurking83's Avatar
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    No problem Waz.

    Things to note about the 3D tracking.

    Always start with the central point. Experiment at home on various subjects and see how it works for you, using your lens/camera/operating technique.

    As an example of how well it can work, try it first on a subject with a lot of contrast(mainly colour contrast) first which will show you how effective is, look for say a red rose against an all green background(good colour contrast!).
    Set the focusing system up as I've described above holding down the **(what I call) AF-On button**, and maintaining the framing for a few moments. You MAY see the focus point flickering about one spot from the central point if you do this. This confirms that the system is working well! But what it should do is not stray to a nearby focus point and stay there for any longer an a split second.
    It may then settle down to the original af point again and stay there. I think this only means that the AF system is scanning all areas near the original AF point for confirmation of the initial subject.

    ** AF-On button = dedicated AF-On button or remapped AE-L/AF-L button!

    Then as you move the AF point moves across the screen for ya automagically
    If you move too fast, what I've also seen is that even tho the 3D system may not keep up properly, it can sometimes recover and then find the original subject you locked onto. This isn't always the case(and where the AF-On button comes into play.
    Release the af system quickly go back to your central position and try again.

    if it sounds convoluted, it's only in the reading. In actual use, it not only makes sense, but it feels like a natural action to perform.

    Note that I said the central point is generally the best to start off with, but this is mainly due to the cross type nature of that AF point. I think any af point with cross type sensor is also capable of the same result.

    Also! don't be too hard on the feature if it doesn't initially work too well. The conditions under which it works well have a huge influence on how well it works.

    scenes with very fussy backgrounds confuse the system easily, but even with that scenario, you can still get a good result if say your subject is static. Again the colour differences between subject and periphery plays an important role. In using the AF-On button, you need to control the system telling it when to go and stop and go again.

    A bird in flight against an all blue sky, will almost certainly work 99% effectively. the blue sky is the key here, and you may find that you simply need to activate the AF system continuously without any need for interruption.

    Anyhow, I'd be interested to hear how it works for 'ya(I can't even remember which camera you got

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    Ausphotography Regular MissionMan's Avatar
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    Tend to agree with Arthur on this one. I find very mixed results with 3D tracking and I tend to adjust my use accordingly. For sports, I tend to use 9 point or 21 point without 3D, with kids playing I find 3D tracking works better or locks onto the wrong object. This is in part due to the type of photography I do with sports (kiteboarding) where the 3D tracking gets confused with the water reflections. I don't use solely 3D for kids, I may use single point autofocus depending on the type of shot.

    Also remember there are focus lock on parameters which allow you to configure how long it should track a particular object if something happens. I.e. someone or something moves in front of the camera (like a pole) so should it now track the new focus point or the original target so it's worth experimenting to find the right option for your experience.

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