Why does the flagpole bend when I take a vertical shot of Tiananmen with an EOS camera?

Reason: Barrel distortion is a deformation phenomenon that occurs when a camera shoots an object. The main reason is the lens. It has nothing to do with the 400D body. It is a deformation phenomenon commonly seen when using wide-angle lenses. Characterized by the outward twisting of the middle portion of the straight line near the edge of the image field. The wider the angle, the more cylindrical the deformation is, so it is called cylindrical distortion. To avoid this phenomenon: 1. Place the flagpole in the center of the picture. 2. Back away and shoot with a longer focal length, such as 70MM or 50MM.