The newer high-end Nikons, including the D500, let you assign different focus modes to different buttons. Why would you want such a thing? It’s all about fast reactions.
Many camera models and camera generations have of course allowed you to set the “focus mode selector” switch to auto-focus and then press the “AF-mode” button and spin the main command dial to AF-C for continuous auto-focus. Similarly, many models have the “AF-ON” button, or buttons that can be assigned this focus-on-demand feature. That’s only the beginning.
It’s silly to ever select AF-S mode instead of AF-C mode, since all you have to do is stop pressing the AF-ON button (while in AF-C mode) to stop focusing. A much more subtle focus requirement is to do something like ignore objects near your desired subject, or to ignore a branch in front of your subject.
As soon as you figure out how to select the desired number of focus points or how to set near-subject focus priority, something changes to spoil your shot. Now, you need to start all over again, because your camera insists on focusing on a near branch, or maybe you can’t keep that single focus point (single-point AF area mode) on your erratically-moving target.
The point is, the focus requirements never seem to stop changing and you just can’t keep up. You’re tired of missing those shots. What to do? The newer high-end Nikons let you at least triple your chances of getting the shot. Now, you can assign multiple buttons with auto-focus, and each button can have a totally different focus mode assignment.
The Nikon D500, for instance, will let you assign the “Pv”, “Fn1”, “Sub-selector” (joy stick), “AF-ON”, and your battery grip “AF-ON” buttons with different focus modes on each one of them!
On my D500, I presently have the following button assignments:
AF-ON = D25, thumb control, for ‘general-purpose’ focus.
Pv = Group Area, middle finger control, for near-subject priority.
Sub-selector = Single-point, thumb control, for precision focus.
Grip AF-ON = “=AF-ON” copies whatever the camera AF-ON has.
I don’t assign the “Fn1” button for focus, because I think its awkward to press it while my index finger is on the shutter release. More acrobatic users may not have this same issue. For me, I only want to use either my thumb or my middle finger to activate focus.
Unfortunately, the Sub-selector button is squirrelly, and I have to use the focus-selector lock lever to prevent the joy-stick from moving to different focus points instead of acting like an AF-ON button.
To assign these buttons on the D500, you go to the “Custom Settings” (pencil) menu, “f Controls”, and then “Custom Control Assignment”. For each of the desired buttons, you select “AF-area mode + AF-ON”. Each button sub-menu under this option lets you select “Single-Point”, “D-a AF 25, or D72, or D153”, “Group-Area AF”, or “Auto-Area AF”.
Auto-focus options for button assignment
Note that not every auto-focus option is available to these button assignments (e.g. 3-D tracking isn’t there). Because this is Nikon, different camera models offer a different set of AF assignment options. The Nikon D5, for instance, has the “D9” available, but the D500 starts at “D25”.
When you press your assigned button, the viewfinder will instantly change to show you the corresponding active focus-point pattern. This way, you get visual confirmation that you are using the focus mode that you intended.
Single-Point AF viewfinder view (center point selected)
25-Point Dynamic Area AF viewfinder view
Group-Area AF viewfinder view
The point I want to make here is that your choices aren’t set in stone. You can experiment with different modes assigned to different buttons until you feel comfortable with them. Don’t go overboard with changing the assignments all the time, however; it will totally mess up your muscle-memory.
Once you get used to using different buttons to get different focus modes, you’ll wonder how you ever got by without them. You can now react nearly instantly to changing conditions and get those shots that you used to miss. This is one of my absolute favorite things about using my D500.