Liquid lens

I knew about oil immersion and microscopes--I'd watched my mother put a dab of oil on the bottom lens when she needed extra magnification. (She was typically looking for worm eggs.) The amount of magnification wasn't exactly reproducible, but it suited the purpose well enough.

Apparently one can now use a liquid lens. An electronically controlled iris lets you adjust the focus extremely rapidly. As the circumference shrinks, the drop's curvature changes, and therefore the focal length of the device.

Clever. Of course the lens will perform best when it is looking down (or up) at the object--otherwise the curvature will vary from one side to the other. Maybe not much--that depends on the surface tension of the liquid.