Question

You are trying to photograph a bird sitting on a tree branch, but a tall hedge 7.2 meters is blocking your view. However, as Figure shows, a plane mirror reflects light from the bird into your camera. For what distance must you set the focus of the camera lens in order to snap a sharp picture of the bird’* image?

Answer 1

The image of the bird is located into the mirror at the same distance the object is from the mirror, in this case 2.1 meters. This means the horizontal distance from the camera to the image is the 3.7 meters from the camera to the mirror and an additional 2.1 meters to the image, or 5.8 meters total. The vertical distance is still 4.3 meters. With the image on the other side, a right triangle is formed. By the Pythagorean theorem, the distance is

d = √((5.8)2 + (4.3)2) = 7.2201