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

Rays emerging from the point source, which is kept at the focal point of the first convergent lens, will became parallel after refraction through the lens. Now, when another lens is placed in the path of these parallel rays, the rays will again come to focus at the focal point of second lens. So, a real point image is finally. The wavefront emerging from the final image is spherical.