2) When converting viewing angles to obtain the focal length; do you measure the angle between between the extremities of the object and the front lens element or the angle between the object extremities and the sensor plane?
Neither. It is the angle at the nodal point of the lens.
|Drano by Kukla|
from Colorful Abstract
|Contemplating by Eyefull Tour|
|Chanuka by RivkiLocker|
from Happy Holidays