As a rule, you use a Telephoto lens when you can’t get as close to your subject as you would like. Fro example, when you’re video recording & photographing a sports game the Statue of Liberty in New York, or a chalet perched on a distant hillside. You can’t climb into a cage at the zoo to get a close up of a lion of stand in the middle of a Hudson River to get a close up of luxury yacht, but a SAD-N728 7x telephoto lens can produce a big image & movie of such subjects by bringing them closer to you optically.