Focusing Tips for Wildlife Photography using Nikon D500 and D850 Cameras
Although these instructions apply to specific cameras they can be adapted for use with most semi pro cameras
Use Back Button Focusing
I would always recommend using Back Button Focusing. This is where the action of focusing with a half press of the shutter release is disabled and focusing is assigned to a function button on the camera.
There are many benefits of this technique and although it can take a bit of getting used to with practice it will become second nature.
One of the advantages of having the focus and release separated is that you are instantly able to focus manual without the camera overriding it when you press the shutter release.
Another advantage is that after you focus you can reframe your subject and still retain your original focus.
For Birds in flight. I find that it is often a benefit to be able to reset the focus after a burst of about three shots rather than rely totally on the camera to track as it can often get confused with long burst of rapid fire. I find that focus is also more accurate in these circumstances if I use the slower frame rate (marked CL on the release mode dial) and I have this set for 5 frames per second.
Use Two Buttons for Focusing
I have both of my Cameras set up to use two separate buttons for focusing.
I have the button on the back (marked AF-ON) set for group focus so that the camera will focus on the nearest focus point of a group of 5 in the centre of the frame. This can be easily changed as circumstances dictate but I rarely find this necessary.
I also reprogram the Preview Button (marked Pv) on the front of the camera so it will focus using only the single central focus point. This is useful for focusing on small subjects especially with obstructions in the foreground.
With my cameras set in this manner I can then use my thumb to activate group focus, my index finger to activate the shutter release and my middle finger to activate single point focusing. Although this might sound complicated you will find that after a short time you wont even think about what you are pressing because it becomes second nature.
Here is a link to a YouTube video that shows how to set up for focusing with the AF-ON and the Sub selector buttons but the principle is the same for using the PV button as I do. https://www.youtube.com/watch?v=a4EWvAaaJMM