Here is the issue,
Focus on moving, jumping, flight prone subjects examples birds insects etc.
They move to a non photo settings, behind leaves, branches etc.
Release shutter button, Ah! missed shot.
Re focus and lens racks all the way out and in or does not focus on subject, subject gone!
Happens even if you prefocus location.
Here is what I found to help fix this problem......
If your camera does not have focus lock (a100) but has DOF button.
After following subject press hold the DOF button and shutter locks along with lens focus settings.
Follow subject to new location and release DOF button after pressing shutter button down half way.
( this works even if you set camera down for hours).
Pick camera up and point to subject, press DOF button and then shutter half way.
The focus and setting pick up right where you left off.
Have not read about this technique any where. I did find it by accident.
This of course in lew of AF/MF button and you do not want to manual focus.
Any comments are always welcome.