question back-button auto focus

deepakaa · Jul 6, 2017

2 questions pls :

i use Nikon D7200

1)
if the back button auto focus is enabled...does it matter if the autofocus mode is selected to be af-s or af-c ??

2)
what is the difference between af-c d51 and af-c 3d ? which setting is better for shooting kids playing around, especially if am using classing way of focusing by half pressing shutter button ?
and does this matter while using back button auto focus ?

Thanks

benhasajeep · Jul 7, 2017

To use a back button AF first you turn off the shutter button AF function. The camera has to be in AF-c mode to use back button. On my D800 I have an af on button. On my D600 I do not have that button. So my AE-L / AF-L button is assigned.

D51 AF is the camera will use any of the 51 AF focus points while in continuous auto focusing. So if your trying to take pictures of your kids and lose focus. The camera will pic a new AF point from the 51 (normally the point closest to camera). And example would be bird in flight and you have your initial focus point on the eye. You don't pan good and lose focus. The camera will use any of the 51 points to regain focus. Most likely chosing an AF point on the wing tip closest to you (if its crossing your frame). 3d af uses color for focus tracking.

I have my cameras set for back button and single point af. Occasionally I will use d9 area AF for things moving thats hard to keep a single AF point on the target. I don't think I have ever tried D21 or D51.

Why back button AF? Back button AF is basically a way to use AF-S and AF-C without stopping what your doing to make a setting change. For example when your in single AF-s you can depress the shutter make focus and recompose the frame, then press rest of the way to take the picture. Good for static / no motion pictures. But if your in AF-c you do this when you recompose the camera will try to focus continuously. But if your taking pictures of something moving you may miss focus in AF-s. You want AF-C for moving subjects. Well back button allows you to do both without taking time to make a change in camera.

The camera will only focus when the button is pressed. If you have a static object you press the button and it focuses, you let it go and the camera will stay focused at that distance. If something is moving as long as you hold the af On or the assigned button the camera will continuously AF while it's held.

deepakaa · Jul 8, 2017

hello
Thanks a lot for your feedback.
Do you mean to say it using BBF, it doesn't matter if the camera setting is on af-c or af-s ?

i am also confused on the use of focal point while shooting running kids..but i will post the question separately. Thanks again.

benhasajeep · Jul 8, 2017

deepakaa said:
hello
Thanks a lot for your feedback.
Do you mean to say it using BBF, it doesn't matter if the camera setting is on af-c or af-s ?

i am also confused on the use of focal point while shooting running kids..but i will post the question separately. Thanks again.

The camera must be in AF-C to use back button focus.

Casey08 · Aug 21, 2017

Continuous-Servo AF (AF-C)
Use this mode should if your subject is moving. If you hold the shutter button half-pressed, the D7000 will continually evaluate focus distance, useful if the subject is moving nearer or further away from you. You then choose the appropriate AF area mode according to how much lateral movement you need to track, and if you want to control the focus point or let the camera do it (Auto-Area AF). I recommend you don’t select Auto-Area AF.
If your subject is hard to follow or moving laterally (left or right), set the AF-Area Mode to one of the Dynamic modes or 3D-Tracking. Use a higher number dynamic mode if there is greater lateral movement. Place your focus point over your subject and half-press the shutter, the DSLR will then follow the movement continually re-focusing.
This mode is ideal for sports, action, children/pets playing, motorsports etc.