1. The problem statement, all variables and given/known data A thin double convex lens of focal length f is broken down into two halves at the axis. The two haves are then combined, as shown in the figure. What will be the focal length for the arrangements? http://www.meritnation.com/app/webroot/img/shared/content_ck_images/images/Untitled(375).png [Broken] 2. Relevant equations 3. The attempt at a solution For (i), I think that the answer is infinite because any incident ray will either go undeviated or will be laterally displaced - but the combination will not be able to converge it. Is it right? And, about the second arrangement - I think it must be 2f, but in my book, f/2 has been given as the answer!