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

The focal point of a concave of a convergent lens is the position of the real image formed by the convergent lens, when object is situated at infinity.
When another converging lens of short focal length is placed on the other side of the first convergent lens, the combination will form a real point image at the combined focus of the two lenses. The wavefronts emerging from the final image will be spherical.