The history of microscopy has focused on better and better resolution, as has been documented on these pages [e.g., J.-P Revel). As one can see in the first graph, the early improvement in resolution was agonizingly slow, as it was dependent on technological improvements in optics and methods for preparing specimens. Hans and Zacharias Jensenn are credited with being the first to put two lenses in the same optical path to create a primitive microscope in 1590 Nearly a century later Antoni van Leeuwenhoek was impaling specimens an needles. Whereas van Leeuwenhoek and other observers were able to make significant observations to change fundamental concepts of their day, microscopists such as Ernst Abbe, Hermann Ludwig Ferdinand von Helmholtz, Lord John Rayleigh and Carl Zeiss brougnt us to the brink of optimal performance of the light microscope.

No, Virginia, there is no objective lens in the Scanning Electron Microscope.

There is much confusion about the lenses in a scanning electron microscope (SEM). All of the lenses in a SEM are condenser lenses. The fact that some scanning electron microscope manufacturers have labelled the controls for the final condenser “objective lens” is misleading and this may have contributed to the confusion.

To get some perspective on this matter, observe your compound light microscope. Starting with the light source, the first lens encountered is the condenser lens (the lens that handles the light before it interacts with the specimen). Next the light interacts with the specimen on a microscope slide. Then the light enters the objective lens (the first lens the light enters after interacting with the specimen) and finally the light travels through the ocular lens and then it enters your eye.

Microscopists often recrystallize or precipitate compounds for purposes of identification. Almost as often, a few crystals form that are irresistibly beautiful and demand isolating for single-crystal x-ray diffraction, spindle stage, polarized IR absorption, or remounting in a crystal-rolling medium like Aroclor® 1260.

The isolation of one such crystal among hundreds from the center of a drop is not as difficult as it sounds. It is done at 50-100X under a stereomicroscope using a fine, usually a tungsten, needle. The needle may (rarely) need to be surface-treated by rubbing with a water-insoluble wax (then tissue-wiped “clean”) to prevent creeping of the solution up the needle and causing solution (and crystal) movement.

The needle is used to clear a path for the desired crystal by pushing the edge crust and other intervening crystals to one side. Complete clearance is not necessary. The desired crystal is then pushed with the needle along the slide to the edge and then well outside of the drop. A few smaller crystals and much solution may accompany it.