Wildlife videos with Nikon D500 + Nikon 200-500/5.6

RudyPohl wrote:

• I never try to focus on birds in flight, either manually or with the back button - I have made many attempts over the last year at doing this and all have been failures. Instead, I intentionally plan to record birds that are mostly flying side to side so they remain in my focal plain as long as possible.
  So in the case of my video posted above with the flying Canada Geese I positioned myself on the bank of the river so I could capture the geese flying from my far right to my far left. I make my initial focus when the geese are still sitting on the water using the back button focus and checking it in my external monitor with focus peaking. Then once they take off all I do is track them with my camera, I never touch the focus ring or back button. All my flights are done in 1080p 60fps and slowed down in post.
  I usually use very small aperture settings, typically between f11 - f22, depending on the brightness of the day. This deals with two issues: One I have no ND filter for 200-500mm lens, plus this gives my the widest depth of field possible. Here it's important to be far enough away from the birds so that you have as wide a depth of field as possible.
  Lastly, when doing side to side bif recording it's crucial to have your tripod perfectly leveled or your horizon will progressively either rise or fall as your video proceeds and it's almost impossible to fix in post.

With the above method, that is, keeping distant from the birds and having a huge depth of field via small aperture, you are able to even record birds that are flying towards and away from you. I do this and I simply cut the clip once the birds that are coming towards me are unacceptably out of focus. As seen in the video below.
Hope this helps,
Cheers,
Rudy

That's what I have been doing wrong !! Trying to focus on flying birds and making a mess of the clip. Thanks so much. I'll give this a try.
What's the external monitor you use? I am feeling the need for one but, having never used it, I have no idea how to begin looking for one. One that is suitable for my D500.