I did in past big post about this - there is second problem with focal lengths in cctv world...
not only they are recalculated / virtual - but ranges in varifocals are totally FAKED for marketing / comparison purposes..
because all focal lengths data given by Dahua or HIK are not true..
the only data we always should check are FoV data = how big horizontal / vertical Field of View is..
this is the only true (or almost true) data about camera / lenses in cctv world...