Setting up Back button focus

Having a little issue setting up back button focus on my 5100.

I am following the instructions/video here:
- Nikon D5100 - Back Button Focus
- https://www.youtube.com/watch?v=FzqQskGoURE

I have:
- The A1 control on AF-C Priority/Release
- The F2 control on AF-ON, and
- AE Area-mode on Single Point AF

What's happening is:
Did I miss a key step somewhere??

I don't have a d5100 to play with, but it sounds like you are in a mode that will not allow af-c. To be sure, use A, S, or P mode for now. Auto mode or a scene mode could be a problem. On my d7100, Auto mode always takes me back to af-a, I can change it to af-c, but it will go right back to af-a if I change modes and go back. I'm not sure how live view behaves on your camera. My BBF setup seems to work when I switch to live view, but I don't think it stays in af-c mode. I'm not well versed in live view though. I only use it for some manual focus macro shots. So try A,S or P mode in viewfinder mode and see how that works.

What threw me it at first was that the video (using a D5000) was showing AF-C, yet my menu screen was not. But, yes, I had it in AUTO. When I switched to P,S or A, indeed the menu screen showed AF-C. I must have missed that part of the story in the 4 or 5 tutorials I read on this topic!. Mystery partly solved. But its still a bit weird as even with P,A or S, with AF-C on the menu screen, it displays as AF-S on the live screen when in Liveview.

Regardless, in all modes, the camera is now behaving very BBF-like – ie, in all modes the back button does the focussing and the shutter does no focussing, so that part is encouraging. …even if Auto.

I don’t know what is happening or not happening with auto exposure just yet- will need to experiment.

I have read some posts elsewhere that the D5100 could not be used with BBF – clearly not true - perhaps they were only referring to AUTO modes.

If BBF ends up only working in P,S or A, that’s perfectly fine by me, as thats where I plan to be nearly 100% of the time. Still “learning” the camera and “P” mode is where I will be for the next little while as is gives me lots of automation and flexibility. Also now shooting in RAW only (having recently discovered LightRoom). Also trying out Release mode on continuous (never used it before – quite nice)

Also looking forward to see how BBF works with my 105mm macro lens. I am okay with even a manual focus when super close up, but at a distance, the macro has been driving me nuts as I could never get it to focus correctly; it was always moving around. Perhaps I will have better luck with BBF.

I don't recall hearing that you can't do bbf on the d5100. I know on my d3100, there is no way to set release priority so I think that defeats most of the purpose of the technique on that camera. You need release priority so you can shoot in af-c mode, but still get a pseudo af-s mode by releasing the back button. This would be used for focus and recomposing. Push bb to focus, release bb, recompose, shoot. This won't work on the d3100 because there is no release priority, the camera must see focus to fire. After recomposing, the focus point could fall on blur and the camera won't fire.

I just looked in the d5100 manual. It looks like you only have af-s, af-f, and MF in Live View. I'm thinking you don't need af-c in that case. If you are in af-s, you push the back button and it should focus, release the button and it stays put. I think you will also be able to take the shot if you recompose even though the focus point may then fall on blur. Af-f focuses full time, so no need to hit back button at all. This is what I am seeing on my d7100. I'm not a live view guy though except for some video and some manual focusing for macro.

As for auto mode, you really won't be spending a lot of time there. It will still focus with the back button if you find yourself in auto. It might even let you focus and recompose. You won't be able to hold the button down and get continuous focus, but you wouldn't get that with the shutter button either.

As to liveview, I rarely use it as well, but took notice of what it was displaying to confirm how the camera was behaving with its BBF settings ; I felt a problem there might be indicative of a bigger problem - but you raised the valid point the liveview supports different modes than the viewfinder, so a restriction in one is not necessarily a restriction in the other.

Bottom line - sounds like the 5100 has a very workable BBF arrangement; I am looking forward to getting used to this type of focusing.

Thanks again for the insight.