The microscope counts as one of the more remarkable inventions in the scientific world. Not only has it helped satisfy a great deal of basic human curiosity about things that are too small to see with the unaided eye, but it also has helped save countless lives. For example, a host of modern-day diagnostic procedures would be impossible without microscopes, which are absolutely vital in the microbiology world in visualizing bacteria, certain parasites, protozoans, fungi and viruses. And without being able to look at human and other animals cells and understand how they divide, the problem of deciding how to simply approach the various manifestations of cancer would remain a complete mystery. Life-giving advances such as in vitro fertilization ultimately owe their existence to the wonders of microscopy.
Like everything else in the world of medical and other technology, the microscopes of not so many years ago look like blunders and quaint relics when pitted against the best of the second decade of the 21st century – machines that one day will be snickered at in their own right for their obsolescence. The major players in microscopes are their lenses, for it is these, after all, that magnify images. It is therefore useful to know how the different kinds of lenses interact to form the often-surreal images that make their way into biology textbooks and onto the World Wide Web. Some of these images would be impossible to see without a special knickknack called a condenser.
History of the Microscope
The first known optical instrument that merits the designation of "microscope" was probably the device created by the Dutch youngster Zacharias Janssen, whose 1595 invention likely had considerable input from the lad's father. This microscope's magnifying power was anywhere from 3x to 9x. (With microscopes, "3x" simply means that the magnification achieved allows for visualization of the object at three times its actual size, and correspondingly for other numerical coefficients.) This was accomplished by essentially placing lenses at both ends of a hollow tube. As low-tech as this may seem, lenses themselves were not easy to come by in the 16th century.
In 1660, Robert Hooke, who is perhaps best known for his contribution to physics (in particular the physical properties of springs), produced a compound microscope sufficiently powerful to visualize what we now call cells, examining the cork in the bark of oak trees. In fact, Hooke is credited with coming up with the term "cell" in a biological context. Hooke later clarified how oxygen participates in human respiration and also dabbled in astrophysics; for such a true renaissance person, he is curiously underappreciated today compared to the likes of, say, Isaac Newton.
Anton van Leeuwenhoek, a contemporary of Hooke, made use of a simple microscope (that is, one with a single lens) rather than a compound microscope (a device with more than one lens). This was largely because he came from an unprivileged background and had to work at a humdrum job between making major contributions to science. Leeuwenhoek was the first human to describe bacteria and protozoans, and his findings helped prove that the circulation of blood throughout living tissues is a core process of life.
Types of Microscopes
First, microscopes can be classified based on the type of electromagnetic energy they use to visualize objects. The microscopes used in most settings, including middle and high school as well as most medical offices and hospitals, are light microscopes. These are exactly what they sound like and make use of ordinary light to view objects. More sophisticated instruments use beams of electrons to "illuminate" objects of interest. These electron microscopes use magnetic fields rather than glass lenses to focus the electromagnetic energy on the subjects under examination.
Light microscopes come in simple and compound varieties. A simple microscope has only one lens, and today such devices have very limited applications. The far more common type is the compound microscope, which uses one kind of lens