Ars Technica: "As many of you know, I am a bit obsessed with imaging techniques. It is not just that I love pretty pictures; I believe that images are absolutely the best way to start understanding something. This is particularly true when that something is complicated, like a living cell.
One of the challenges of imaging live cells (or, in fact, most sorts of organic materials) is contrast. More to the point, there is no contrast. If you take a typical cell, the vast majority of it is water mixed up with oily bits and proteins. These things are all pretty much transparent to visible light and have similar refractive indexes, meaning that the interfaces between the oily and watery bits don't reflect much light either."