Question

A camera of 6 inches of focal length is used to photograph a distant scene. The distance from the lens to the image is approximately:

Options

A
0.5 ft
B
1 ft
C
2 ft
D
4 ft
E
6 ft

Explanation

The trick is that you are expected to interpret "distant scene” as an object distance of infinity, in which case the image would form exactly one focal length away on the image side (because that is actually the definition of focal length: rays coming from infinity come to a focus at the focal point). So the distance from the lens to the image would be (approximately) 6 inches.

6 inches= 0.5ft

So option A is correct

The focal length is the distance over which parallel light rays converge. For a distant scene, this is one focal length away, or 6 inches, which equals 0.5 ft.

This option suggests a longer distance than the focal length, which is incorrect for parallel rays from a distant scene.

2 ft is much longer than the focal length of the camera lens, which does not match the definition for parallel rays from infinity.

4 ft is not relevant to the focal length of 6 inches, which is the distance needed for converging parallel rays.

6 ft is a much longer distance than required for the defined focal length of 6 inches.