Yeah the trial and error method is a little annoying, but if you remember to mark your starting point its not that bad.
What i normally do is record a fjew seconds, then turn lens a little, wave hand in front of lens and then record a little again, this i repeat 3-4-5 times.
Reviewing the footage on computer let me count my ajustments ( wave of hand in front of lens ) and then if i have gotten too far i can backtrack X notches till i am closer to the sweet spot.
You might have to do this a fjew times to make sure you are there, its mot much of lens turn between perfect and a total blur.