
Focal length is ever the same, change the field of view (focal angle).
Usually the calculation is focal angle / 1.65.
Or if you are more confortabile with focal lenght you can calculate focal lenght * 1.65 (since).
Anyway is a concept, not a real value.
There is many aps-c, s35, ff sensor size, the value 1.65 is only a roughy reference to know how is the crop. For example I had 3 different size of sensor s35 from Ursa Mini Pro, pocket6k, Bmpc4k against aps-c of my Fuji x-t4.
From many years I learned to put lens on mount for what I like to see, then check if my space in front of subject allow me to work correctly
Inviato dal mio iPhone utilizzando Tapatalk