While pressing a button or touching - > set scale to lerp(a,b,c)
a = start point
b = destination point
c = "Transition's velocity"
For the c, use 1*dt,2*dt,3*dt, etc
Don't forget to always use dt (delta-time)
lerp(1,3,1*dt) ==> Went from scale 1 to 3.
Remember that you can always use expressions to get the current scale for the "a" and then use it again on "b" plus any number that you want to add ou subtract in order to zoom in and zoom out.