Two positive lens L1 and L2 has the same focal length f>0. The distance between them is f/2. L1 is placed to the left of L2.
(a) An object is placed to the left of L1 with a distance of 4f. Please determine the final image position after this lens system.
b) If we treat this lens system as a single lens, what will be the focal length of this entire system?
Hint: The focus of the combined lens system can be determined by sending parallel rays into this system and see where the light focused.