A photograph of a landscape is captured by a drone camera at a height of 18 km. The size of the camera film is 2 cm 2 cm and the area of the landscape photographed is 400 km2. The focal length of the lens in the drone camera is :
- 2.8 cm
- 0.9 cm
- 2.5 cm
- 1.8 cm
Answer
(4) 1.8 cm
Solution
The ground is very far, so the film sits at the focal plane: v f.
[figure]
vu= 2 cm20 km v= 220 18=1.8 cm
f v=1.8 cm
Answer: (4)