Let's say that there are three lenses A (all of which are semicircles: flat on one side, curved on the other). One lense is a short and curved D, another lense is a very elongated and narrow D (longer than the first lense), and the third lense is as long as the second lense but has a sharper curvature. How would you rank the focal lengths of these lenses? In other words, how is focal length of a lense related to its shape? More curved = shorter focal length? Longer lens = longer focal length?