Consider a point at the focal point of a convex lens. Another convex lens of short focal length is placed on the other side. Then the nature of wavefront emerging from the final image.

Explanation

Consider the ray diagram shown below

The point image `I_(1)`, due to `L_(1)` is at the focal point. Now, due to the converging lense `L_(2)`, let final image formed is I which is point image, hence the wavefront for this image will be of spherical symmetry.