Chapter 30, Problem 25A

In terms of focal length, how far is the camera lens from the film or chip when very distant objects are being photographed?

To determine

The distance between camera lens and film in terms of focal length when distant objects are photographed.

Explanation of Solution

Introduction:

Rays from any distant object are rendered parallel to the principal axis on the lens.

Any distant object is supposed to be at infinite distance from the lens and the rays from object at infinite distance are assumed to be parallel beam of rays parallel to the principal axis. Now, a beam of rays incident parallel to the principal axis is converged at the focal point. Thus, the distance between the camera lens and film is equal to the focal length of the lens when the distant objects are photographed.

Conclusion:

The distance between the camera lens and the film is equal to the focal length of the lens when distant objects are photographed.