I've been searching for some confirmation regarding the difference in DEFINITION of Focal length between:

1. Physics/Optics(Which in the simplest case uses a classical thin lens to define the focal length as the distance from the lens to the focal point/convergence point)

vs

2. Photography(Which defines it as the distance from focal point/convergence point to the sensor).

Now I understand that a camera is actually a complex assembly of multiple lens elements and I believe this is where I'm getting mixed up.

Is it that since there are multiple lenses we really can't define it in a classical physics thin lens definition way since which lens element are we calculating the distance from?? Thus, instead we calculate from the final convergence point(since there can even be multiple convergence points along the way) to the sensor?? Would I be right in saying this??