From observation, whenever I want to 'zoom in' in a camera, the lens expands outward. What is the reason behind this? My guess, 'zoom in' => greater magnification => object closer to the focal point of the lens (although greater than the focal lengths since otherwise the image would be virtual). The lens expand so that the object under investigation can be closer to the focal point of the lens in the camera so a greater magnification can be obtained. It links with the magnification formula M=-i/o where i is image distance and o is object distance. The lens being closer to the object => o is decreased and i might be increase => increase in M. The other things is that the lens distance is increased so that could increase magnification. i.e. the magnification for the compound microscope has a L term in it which is the distance between the two lens. which if increased will increase the magnification.