The code below makes it only zoom as mouse3 is held;
on mouse3 letgo, it goes back
alias +zoom "crosshair 15;fov 50;sensitivity 2.6"
alias -zoom "crosshair 9;fov 100;sensitivity 4.8"
bind mouse3 +zoom
The code below zooms in when mouse3 is clicked;
and goes back when mouse3 is clicked again. (I prefer this one)
alias +zoom "crosshair 15;fov 50;sensitivity 2.6;bind mouse3 -zoom"
alias -zoom "crosshair 9;fov 100;sensitivity 4.8;bind mouse3 +zoom"
bind mouse3 +zoom