I understand from my classes that, when looking to calculate the electric field of a charge we can use the electric field measured in its rest frame to find its electric field in the lab frame (where the charge is moving). The gamma factor changes the value for the component electric field if it is perpendicular to the direction of the charge's motion. I don't understand why it is not also for the parallel part: if length contraction and charge conservation are at play, then in the lab's frame, there would be "more" charges per metre along the axis where the charges is moving? And so the electric field increases by superposition of "extra" electric fields? And how does is discriminate between the direction of motion and the direction perpendicular? Thanks for reading!