Recomposing using back button focus issue

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Scotland Rocks

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Hi folks, first time posting. Newbie to BBF. I have a Nikon D7500 and I've set up BBF using Steve's instructions. Not convinced it's working correctly though. I understood it that when you focus on a specific object, release the back button (AE-L / AF-L) it locks focus on the object allowing you to move the camera to recompose. The item you locked focus on should remain in focus and not the position that you move to when you press the shutter button. When I take my thumb off the bb and move the camera, press the shutter the focus point seems to be on wherever I've moved the point to. I've verified this by checking the focus point in the playback and it shows the red square on the area that I recomposed on. It doesn't appear to be locked on chosen subject. Hope the above makes sense. What am I doing wrong??
 
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Not sure you can do this with the 7500 as I haven't used one, but on the higher end bodies there is a setting in the menu that turns off AF for the shutter button. Should be in Custom Settings, bank a. It's in a8 on a D850......looks like maybe a6:

a6: AF Activation

onlinemanual.nikonimglib.com onlinemanual.nikonimglib.com
 
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Like Warren, I'm not sure how on the 7500, but on my D500 it's function a8, "AF activation". You need to change from "Shutter/AF-ON" to "AF-ON only". That changes your shutter button to meter on and shutter trip only, and the back AF-ON to activate autofocus.
 
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Scotland Rocks said:
Hi folks, first time posting. Newbie to BBF. I have a Nikon D7500 and I've set up BBF using Steve's instructions. Not convinced it's working correctly though. I understood it that when you focus on a specific object, release the back button (AE-L / AF-L) it locks focus on the object allowing you to move the camera to recompose. The item you locked focus on should remain in focus and not the position that you move to when you press the shutter button. When I take my thumb off the bb and move the camera, press the shutter the focus point seems to be on wherever I've moved the point to. I've verified this by checking the focus point in the playback and it shows the red square on the area that I recomposed on. It doesn't appear to be locked on chosen subject. Hope the above makes sense. What am I doing wrong??
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Scotland Rocks said:
When I take my thumb off the bb and move the camera, press the shutter the focus point seems to be on wherever I've moved the point to. I've verified this by checking the focus point in the playback and it shows the red square on the area that I recomposed on.
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If you're just talking about which focus point shows in the viewfinder and what you see in your image playback then yes the camera is working fine. If you're saying the actual focusing changes when you depress the shutter release then the advice above is on target.

But it sounds to me like you're saying the focus point indicator in the viewfinder moves when you recompose and the playback info on focus point selected moves as well. That is perfectly normal. BBAF and recomposing doesn't make the focus point stay up on the target (e.g. the eyes) as in many cases that would require the focus point to be outside the range of possible focus point locations on the D850. When you recompose the focus point will move as you change the framing but that's not important as long as you've already locked the actual lens focusing on your desired target. The key thing is that the AF system does not re-engage when you depress the shutter and change the actual focusing of the lens, where the focus point selection box appears in the viewfinder or the playback isn't important.
 
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Steve said:
Yup, you have to turn off A6 or it'll still focus with the shutter release.
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DRwyoming said:
If you're just talking about which focus point shows in the viewfinder and what you see in your image playback then yes the camera is working fine. If you're saying the actual focusing changes when you depress the shutter release then the advice above is on target.

But it sounds to me like you're saying the focus point indicator in the viewfinder moves when you recompose and the playback info on focus point selected moves as well. That is perfectly normal. BBAF and recomposing doesn't make the focus point stay up on the target (e.g. the eyes) as in many cases that would require the focus point to be outside the range of possible focus point locations on the D850. When you recompose the focus point will move as you change the framing but that's not important as long as you've already locked the actual lens focusing on your desired target. The key thing is that the AF system does not re-engage when you depress the shutter and change the actual focusing of the lens, where the focus point selection box appears in the viewfinder or the playback isn't important.
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I think you've understood what I was saying however now I'm even more confused. I've followed the setting BBF to the letter using Steve's guidelines so I'm pretty sure I've done it right. My AE-L/AF-L is showing as AF-ON & my AF activation has AF-ON ONLY selected so my shutter should be disconnected, saying that when I press just my shutter button the red box turns black and the white dot shows in the viewfinder as if its acquiring focus, surely this shouldn't happen???. Also when I use BBF release my thumb even without recomposing I then press the shutter button and it goes from red to black square and white dot appears. To me that says shutter is still connected. Getting really frustrated. When I look through the viewfinder and press the bb on the subject (I tend to us the central focus point as that's slightly better) it goes from red to black acquiring focus. I then take my thumb off and move the the camera to recompose. I understand that the focus point which is still black won't sit over my selected focal choice , that's fine. What I don't get is when I look at the playback it shows the red focus square which I believe is what the camera is telling me what it focussed on and that's not where I actually focussed on. That ties in with possibly the shutter still focussing. Also when I then look at the image and press the ok button which I've programmed using Steve's tip to zoom to the point where the focus square was it zooms to 100% on the recomposed area NOT the point that I locked focus on. Maybe that's just the way it is but I would have thought it would have zoomed to the locked focus point not the recomposed focus point. Getting to the point I want to give up. It's as if the shutter and the AE-L buttons are both focussing.
 
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Steve said:
Yup, you have to turn off A6 or it'll still focus with the shutter release.
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Steve I feel like my shutter button is still acquiring focus even though I've set up the BBF. Autofocus A1 AFC priority is set to RELEASE. F1 custom control assignment AE-L/AF-L says AF-ON. A6 Shutter Release button says AF-ON ONLY. However when I take my thumb of the bbf the black square disappears and then I press the shutter button the focus point reappears going from red to black and the white dot focus acquired point comes up in the viewfinder as if its focussing again. That ties in with the feeling that I'm not able to lock focus and recompose. Don't know how to sort it.
 
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Scotland Rocks said:
To me that says shutter is still connected
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The shutter is always connected to the AF Sensor activation but when set up for BBAF the AF system no longer sends controls to the lens. So yes, the AF detection system is still enabled when you press down on the shutter but if you've disabled focus on your shutter release the lens does not actually refocus. If your lens really is continuing to refocus you should be able to hear it when you depress the shutter or you can test it by prefocusing on something close or very far, recomposing so that everything in your viewfinder is completely out of focus and the depressing the shutter. If the captured image remains out of focus then the camera is not re-acquiring focus when you depress the shutter. If everything snaps back into focus then for some reason the AF has not been disassociated with the shutter release.

Also if there's a sufficiently in-focus image element under the selected focusing spot then the white focus confirmation dot will still appear as the AF sensing system is still enabled but that won't change the actual lens focusing once you've disassociated focusing from the shutter release.

The red focus square on playback simply tells you which focus point was selected in the viewfinder, it does not tell you the image element that you actually focused on before recomposing. IOW, that red square in playback should be the same square you selected when in Single Point or the center of the selected area in one of the Dynamic Area modes, the same as what you viewed through the viewfinder which of course won't be over your subject once you recompose before shooting. IOW, the camera isn't smart enough to know and save the portion of the image you focused on, it just shows which focus point was selected at the time the shutter was released regardless of where that sits in the frame and regardless of what you actually focused on before recomposing.

Does that make sense?

Bottom line, when you do focus and recompose shooting the red focus point square in playback doesn't tell you anything about where you actually focused the image prior to recomposing.
 
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FWIW, here's another way to think about what happens when you disassociate the AF function from the shutter release when using BBAF that might be simpler.

It's really the same as switching your lens into manual focus mode either via a switch on the lens or via a control switch on the body. When you do that and half or full press the shutter release the AF detection system still kicks in and you still see the focus direction arrows or white focus confirmation dot. And once you take the picture you still can still choose to see which AF point was selected during playback as a red square. This all happens when the camera or lens is set to manual focus mode and no AF is actually happening.

That's basically the same thing that happens when you set up your camera for BBAF. Focus detection still activates with a shutter press and you still see the focus assist and confirmation icons in the viewfinder but the lens doesn't actually re-focus as it's effectively in manual focus mode unless you hit that back button Focus-ON button. And when you playback an image you can still choose to view the red square showing which focus point was selected just as you can when using full manual focus.
 
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DRwyoming said:
The shutter is always connected to the AF Sensor activation but when set up for BBAF the AF system no longer sends controls to the lens. So yes, the AF detection system is still enabled when you press down on the shutter but if you've disabled focus on your shutter release the lens does not actually refocus. If your lens really is continuing to refocus you should be able to hear it when you depress the shutter or you can test it by prefocusing on something close or very far, recomposing so that everything in your viewfinder is completely out of focus and the depressing the shutter. If the captured image remains out of focus then the camera is not re-acquiring focus when you depress the shutter. If everything snaps back into focus then for some reason the AF has not been disassociated with the shutter release.

Also if there's a sufficiently in-focus image element under the selected focusing spot then the white focus confirmation dot will still appear as the AF sensing system is still enabled but that won't change the actual lens focusing once you've disassociated focusing from the shutter release.

The red focus square on playback simply tells you which focus point was selected in the viewfinder, it does not tell you the image element that you actually focused on before recomposing. IOW, that red square in playback should be the same square you selected when in Single Point or the center of the selected area in one of the Dynamic Area modes, the same as what you viewed through the viewfinder which of course won't be over your subject once you recompose before shooting. IOW, the camera isn't smart enough to know and save the portion of the image you focused on, it just shows which focus point was selected at the time the shutter was released regardless of where that sits in the frame and regardless of what you actually focused on before recomposing.

Does that make sense?

Bottom line, when you do focus and recompose shooting the red focus point square in playback doesn't tell you anything about where you actually focused the image prior to recomposing.
Click to expand...

Thank you so much for such a detailed response. You obviously know what you're talking about. I've tried your suggested trial and pressing the shutter alone the camera doesn't seem to want to focus now. Not sure why it seemed to do it earlier. You explained the red focus square on the playback really clearly. I just had it in my head that it would show where the focus point was an in conjunction with zooming in and it landed on the same square just made me doubt everything I was doing. I hope I haven't wasted your time and I really appreciate taking the time to keep a newbie photographer on the right track. Thank you !!
 
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Scotland Rocks said:
Thank you so much for such a detailed response. You obviously know what you're talking about. I've tried your suggested trial and pressing the shutter alone the camera doesn't seem to want to focus now. Not sure why it seemed to do it earlier. You explained the red focus square on the playback really clearly. I just had it in my head that it would show where the focus point was an in conjunction with zooming in and it landed on the same square just made me doubt everything I was doing. I hope I haven't wasted your time and I really appreciate taking the time to keep a newbie photographer on the right track. Thank you !!
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You are free to ask the dumbest questions here, and we are all here to help and assist. Dave is our resident "STAR EXPERT" always ready not only to assist, but to also guide you correctly.
 
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Once again, I’ve pick up a few tidbits as well listening to this discussion. So , questions such as yours Scotland Rocks, are worthwhile and help others as well. Thanks guys.
 
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I
DRwyoming said:
FWIW, here's another way to think about what happens when you disassociate the AF function from the shutter release when using BBAF that might be simpler.

It's really the same as switching your lens into manual focus mode either via a switch on the lens or via a control switch on the body. When you do that and half or full press the shutter release the AF detection system still kicks in and you still see the focus direction arrows or white focus confirmation dot. And once you take the picture you still can still choose to see which AF point was selected during playback as a red square. This all happens when the camera or lens is set to manual focus mode and no AF is actually happening.

That's basically the same thing that happens when you set up your camera for BBAF. Focus detection still activates with a shutter press and you still see the focus assist and confirmation icons in the viewfinder but the lens doesn't actually re-focus as it's effectively in manual focus mode unless you hit that back button Focus-ON button. And when you playback an image you can still choose to view the red square showing which focus point was selected just as you can when using full manual focus.
Click to expand...
Dave’s explanations just got “Bookmarked” for future reference! I am building up my own Library of Key Topics. Taken pictures since 71’ in mostly Auto Mode. Since buying a D500 just over a year ago and getting introduced to Steve’s three books, plus now being introduced to the forum, a whole new world has opened up! Am so impressed how so many of you with a wealth of knowledge/experience are so patient and detailed in helping the rest of us out! Thanks!!
 
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