Question Detail
Question
A camera with a 80-mm focal length lens is used to photograph a tree 12 m tall. If a 32 mm high image of the tree on the film is required, what should be the distance between the tree and the camera?
Correct Answer
Option A is the correct answer.
Detailed Explanation
Magnification m = image height / object height = 32 mm / 12 m = 0.032 / 12 = 2.667 × 10⁻³. Also m = v/u. For a camera, the image distance v is approximately the focal length f (since the object is far away). So v ≈ f = 80 mm = 0.08 m. u = v/m = 0.08 / 2.667e-3 = 30 m.
Hint
Use magnification m = v/u = image height / object height. For a camera, v ≈ f.