copy from general thread as these questions are mostly macro-related:
2 questions regarding which measurements to use to determine macro distance and focal length:
1) Is the minimal macro focusing distance measured from the object to front lens element or from the object to the sensor plane? Is this the same for all brands?
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?