I recently upgraded from a D5500 to a D7500...and have spent some 3 nights tyring to figure out how to activate Back Button focusing. I am near positive that when I initially bought it, there was a line I believe (# 10) in the Custom Settings that actually said: Assign AFE/AFL button...?? or was there.?
I'm thinking this may have dissapeared (due to update 1.10 possibly), or I've just lost my mind...not quite sure which ..LOL.
While typing this up and about to ask the question, I finally figured it out..(f1 in Custom Control Assignment & a6 "AF Activation")...tis a bit of a weird way to do it.
Anyway..all good.
cheers.
Steakman
D5500
D7500
35mm DX f/1.8
50mm f/1.4 MF
18-70 DX
18-200 DX
Tokina 11-16 ATX Pro
...and a bunch of other junk (stuff actually).