Question

In which situation focal length equal to value of image distance
Please answer and explain how

Answer 1

Explanation:

As the object distance gets very large (compared to the focal length) the image distance approaches the focal length. For instance, if the object is a mile away, the image distance equals the focal length for all practical purposes.

Answer 2

The focal length of a lens determines the magnification at which it images distant objects. It is equal to the distance between the image plane and a pinhole that images distant objects the same size as the lens in question.