Question: what is the ae af lock button nikon?
Answer: Set to the right of the viewfinder, the AE-L/AF-L button on your Nikon D3400 enables you to lock focus and exposure when you shoot in autoexposure and autofocus modes. By default, the button is set to lock autofocus and autoexposure together and to keep them locked as long as you keep your finger on the button.