I understand all that. But what I can never understand is how Danny in New Zealand can be so wonderful at BIF with his manual glass. sigh.
LOTS and LOTS of practice.
Back in the day when I started 35mm shooting, it was only manual focus lenses.
So you practice, and practice, and practice. And you gradually get better.
You find out what works and what doesn't work.
Study the subject.
In the case of BIF, a few factors are: behavior, the way they turn, flying pattern, etc.
If you can figure out some of this, you start to develop a "sixth sense" for their flying and can get more hits than me, with zero knowledge of the bird.
Same as you shooting pics of your daughter playing tennis. You know the game and her, and so can get better pics that I could.
The lens matters.
Some of the manual lenses, like Nikon, the focus ring is very light and smooth, so "follow focusing" is easier to do.
vs. some where the focus ring is stiff or sticky, and "follow focusing" is hard to do.
An old lens may need to be cleaned and relubed, if the old 30+ year old grease has dried out, as the focus ring will become stiff from the dried grease and lack of use.This is the same beef that I have with zoom rings on today's zooms.
A stiff/sticky zoom ring is hard for me to use for "follow zoom" when shooting action sports.
Which way do you turn the focus ring when the bird turns towards you?
If you have to think, it will be too late.
When you see the bird turn towards you, your hand has to turn the focus ring in the correct direction, WITHOUT your brain telling it turn left.
This is like driving a manual transmission car. If you have to think when to shirt from 1st gear to 2nd gear to 3rd gear, you can't drive well. The shifting has to be WITHOUT your brain actively telling your feet and hand to shift.
Finally, the old Hollywood saying, "no one sees what is on the cutting room floor."
You don't see how many frames Danny culled, to get his good shots.
When I shoot a high school game with the EM1-mk2, I will sometimes shoot over 2,000 frames. Shooting at 19fps results in a LOT of frames. But only about 100-150 get uploaded to the school's web site. No one sees the 90+% that got culled out.