In the first half of the last century we have achieved a true technical perfection, and imagine what couldn't Galileo and Leeuwenhoek do. However, the capabilities of light microscopes are limited if we speak of the wave properties of light - as light is made of electromagnetic waves, by means of which we are receiving it, as a radio tuner, in high and short lengths. The wavelength is approximately 0.5 microns, is about 500 times thinner than a human hair. The light waves freely bend around smaller objects, just like radio waves bend around tall buildings without encountering any resistance .
Despite the apparent simplicity and historical completeness, light microscopes are constantly being improved. Moreover, improving is not only in structural elements, there is a theoretical basis for a fundamentally new development. Thus, more recently, in 2006, some German scientists have developed an optical microscope which allows obtaining images of objects with the wavelength of light comparable to that of an electron microscope.
Light microscopes differ according to the "contrast type" - there is the concept of "white box" and "black box". The most common school microscope, as a rule, is a "white box", ie the lens receives the light passed through the sample or reflected from it. For this reason, the object being studied would be perceived as dark on a white background.
The human eye is more accustomed of course to the opposite situation. In addition, many objects of study are transparent, and they may be visible only on a dark background. To achieve this effect, they apply a special, sometimes a very complex lens and condensers, placed under a glass slide. Condensers darken the central part, which allows you to see the object under study "in the black box."
Many microorganisms do not have any color and are almost completely transparent. In order to see them, an light microscope uses a special polarized system. This one is a practically new device, called a polarizing microscope, making it possible to see transparent objects with our eyes as dark gray on light gray background.