Two photographers stand outside Badshahi Mosque at the same spot. One captures the entire courtyard in a single frame. The other fills the frame with one carved arch. Same camera, same distance, two completely different pictures. The difference sits in the number printed on the lens barrel. That number is the focal length, and it is measured in millimeters. It controls how much of a s... https://sigmaphoto.com.pk/what-is-focal-length-in-photography/