Good Idea - Ask a National Geographic Photographer

Every month, National Geographic staff photographer Mark Thiessen answers your photography questions - and spills the secrets behind the shots.

Widely published in books and magazines, Thiessen has been on staff at National Geographic since 1997. He's covered subjects from the discovery of the U.S.S. Yorktown to the search for other Earths. He's also a certified wildland firefighter.

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