Water Drop Lens

Water lens:  A drop of water on a transparency can act as a lens.  The ceiling lights may be imaged on white paper with little difficulty.  The size of a water drop determines the focal length and image size.  Large drops generally have larger focal lengths. The drop may be used to magnify print and objects. If you move the drop further than the focal length from print, it will invert as shown to the right.  If you keep moving away, there will be a shadow of the lens, because all the light going through the lens is bent to go to the sides.  I like to ask students how a clear object can make a shadow.