Chapter 33, Problem 1Q

Where must the film be placed if a camera lens is to make a sharp image of an object far away?

To determine

The position of the screen to obtain a sharp image of the far away object through a camera lens.

Answer to Problem 1Q

The screen should be placed behind the lens at the focus of the lens to obtain a sharp image of the far away object.

Explanation of Solution

The object kept far away from a lens means that it is at infinite distance from the lens or very far way. For such objects that are kept at a distance, the rays are considered to be travelling parallel to the axis of the lens.

For a lens either converging or diverging, the rays travelling parallel to the principal axis, get focused at the focus of the lens. A camera uses a converging lens and therefore, it converges the rays coming from a far object to the focus on the other side of the lens.

Therefore, in order to obtain a clear and sharp image of a far object, the screen should be placed at the focus of the lens on the other side of the lens or behind the lens.

Conclusion:

Thus, the screen should be placed behind the lens at the focus of the lens to obtain a sharp image of the far away object.