Back button focus

[Dave442]

Going from manual focus SLR to a P&S I never really liked the focus being tied to the shutter release. When I started using a DSLR I found the BBF to work just how I wanted so I have stayed with it. I have tried it on the D7000 and don't really like using the AE-L button.

Derrel gives some good arguments for the focus points and dedicating the thumb to selecting focus points. I often focus and recompose, but I also use a focus point close to what I am focusing on. Just checking the example Derrel gave with 90.5" to subject, if I have a focus point to the right third of the frame (9 degrees from straight on with the 35mm lens) it is focused to 91.3" and if I then went to 13 degrees (half way to the edge of the frame) the focus distance is 92.7". So about the extreme that I would recompose off that 9 degrees from center would be halfway back to the center in one direction and over to 13 degrees in the other direction, further than that and I would probably select another focus point further out (and most cameras are limited to just how far out you can select a focus point at). If we go with the full difference from the 90.5" at 0 degrees and at 9 degrees of 91.3" we have a difference of 0.8" with subject being closer than focus point and from the 9 degrees to 13 degrees we have a subject 1.4" further away than the focus point. With a 35mm lens at f/1.4 focused to 90.5" we have 6.6" in front and 7.7" behind the subject appearing in focus per DOF chart (and I like to be more conservative that those numbers). For most subjects that works for me, especially if we do the lean.

With people I will often focus right on the eye and then fix the crop in post (I only have 11 focus points so can't always put the eye where I want it for the final composition).

I am excited about the new D500 and the focus point selector toggle next to the AF-ON button (as was introduced on the D4 in believe).

 

[Trever1t]

I seldom use back button focusing, but I do use the AF-Lock quite a bit. I know imagemaker46 does not use back-button focus, so it's not that one needs to use BBF, even to shoot action spots, or to be an accomplished shooter.

I personally think that linking the focusing operation to the trigger in AF-C, and having my right thumb free to move the AF point to the desired area trumps BBF.

This (and agreement with all else) is similar to how I work. I actually set my shutter release to lock AF and AE when depressed to half way in AF-S. In AF-C my shutter button only locks AE when not in Manual mode.

 

[imagemaker46]

Never used it, never found I needed or wanted to.

 

[jsecordphoto]

I switched a few years ago and haven't looked back. When I briefly had the 7200 I tried using the half pressing the shutter for AF and found it annoying. I would have focus locked on a bird and if I moved a tiny bit, sometimes when going back to shooting I'd press the shutter and focus would shift a bit. It's not for everyone, but I love having the AF and shutter on two different buttons, and the back button on the 750 is in a perfect spot, for me. When somebody hands me a camera now and it's not set to BBF it just seems weird to me now, though it took a few days to get used to at first

 

[Watchful]

I use BBF for most things, but especially for action and sports as it's so much faster than switching manually from center focus to continual focus when the action starts moving.

 

[pez]

I use it most of the time, and the assigned button on my K-3 is in a perfect spot ergonomically. I keep a User function slot programmed with shutter button focusing for a quick switch to conventional mode when I want, or if I hand my camera to someone else, for instance.