Is there a way of replicating the action of the AF-On button, which is lacking on our latest D7100 and D750 cameras? Joan & Ronnie Hall, via email

Jason says... This useful button, which is often favoured by action sports and wildlife photographers, is omitted on many cameras, including your D750 and D7100. The good news is that if you open the Custom Setting menu and go to the Controls section, you’ll find options for assigning various functions to the AE-L/AF-L button, one of which is AF-On. Naturally, you lose the ability to lock exposure settings with the rear button but, if you want to keep this facility, you can assign the locking function to another button, again using the Custom Settings menu.

For panning shots, it can feel a lot more natural and intuitive to assign autofocus to a dedicated button, rather than relying on a half-press of the shutter release