Standing 2.5 m in front of a plane mirror with your camera, you decide to take a picture of yourself without turning the
问题描述：
Standing 2.5 m in front of a plane mirror with your camera, you decide to take a picture of yourself without turning the camera around. To what distance should the camera be focused to get a sharp image?
答
5m,the distance from the image in the plane mirror to the mirror equal the distance from you to the mirror.