Sarah Leen, the photographer and editor who changed National Geographic

▶ SUBSCRIBE ▶ If you want to give us a hand: She was the first director of photography for National Geographic magazine, a publication that, although it is not going through its best moments now, for many decades was the symbol of documentary and travel photography. That fact is just one line on the spectacular resume of Sarah Leen, a freelance photographer for 20 years, who published half a dozen covers in…