Question:
Consider a point at the focal point of a convergent lens. Another convergent lens of short focal length is placed on the other side. What is the nature of the wavefronts emerging from the final image?
Solution:
The orientation of wavefront and the ray are perpendicular to each other. In the above figure, L1 is the source of parallel rays, forming I2 at the focal length of the lens. The image formed acts as L2 through which the light rays get converged into L2 and the final image I is formed.