ludof:
Basically let's say I have to aim at something with the camera on the first position, do a specific motion and come back to the first position: I want to be able to come back to the first position as closely as possible.
I'm wondering if you could use some sort of re-positionable switch that would indicate to the Arduino that it has returned to the first position. Suppose you were able to slide a position block so that it clicks a switch on the camera mount and the lock the block in position. Then the mechanism moves the camera away from the block and when it later returns to the block it triggers the switch and the Arduino knows to stop and knows that it is back at the start of the movement. Something like that might give you the precision you need with the simplicity of a servo.
I know that is a poor description but my grey-cells seem to be at lunch-break.
...R