Here are a few articles that may be of help.
Just Google "long lens technique".
thanks for the links.... first link is like he describes me.
Judgment day comes when you get your first few rolls of slide film back from the lab and look at them with your loupe. "There must be something wrong with this lens - I had it on my tripod and the image looked sharp in the viewfinder but most of these photos are fuzzy!" This is an all too common occurrence.
by the way.
i know that i should rest my left hand on the lens barrel.
but to be honest i applied a bit of pressure. that´s wrong, right?
i should just lay it on the lens barrel and not apply a bit force (use my arm muscles) to press it down?