How can you locate the focus of a coverging lens?

The focus of a converging lens can be found located by moving the object(source) from a large distance and getting it closer to the lens.As we go closer the size of the image which is obtained on a screen placed behind the mirror increases.At a certain point the size of the image and that of the object are equal.This point is known as the center of curvature.The focus is the midpoint of the center of curvature and the optical point.In other Words the focal length is Radius of curvature/2