power 4dA convex lens of power + 6D is placed in contact with a concave lens of power – 4D. What is the nature and focal length of the combination. see full answer. Start JEE NEET FoundationTo find the focal length of the combination of two thin lenses in contact, we can follow these steps: Step 1: Identify the Powers of the Lenses We have two lenses: - Lens 1 has a power ( P1 = +4