So thanks for your answers!
I made a little animation (with horrible compressionartifacts) of how I think it could look like.
Zoom has a scala of 1 - 3.5 and Amount 0 - 4.8
Maybe in the end the Zoom doesnt behave so linear to the Amount. But we will see when its running.
@hulmanen so if I understand you right you just put 0 in the middle of the scala (-2.5 - 0 - +2.5) and use positive and negative values.
I had this thought too but didnt know how to pull it of.
@sozap I am afraid I need something else.
I want to set keyframes on one slider, and the other one should then automatically behave reverse, but in the given scala of his own.
If the oneclickhoster should make troubles, I am open for other ones. This is what DuckDuckGo gave me.