78 PART IV Digital Documentation
plates riveted together. Sandwiched between the plates was a small bi-convex
lens capable of magnifications ranging from 70× to over 250×, depending
upon the lens quality. The sample was placed on a pin that was moved with two
screws. With one screw Leeuwenhoek adjusted the distance between the sam-
ple and lens and with the other one he adjusted the height of the specimen. Looking
against the light, he was able to observe even tiny animals swimming about
in a drop of water.
Seeing Cells with the First Compound
Microscope
Robert Hooke built the first compound microscope, that is still preserved consisting
of an objective and an eyepiece. He used this microscope to study all
kind of nature, especially the world of fossils and geology. In 1665, he published
his famous book Micrographia, which shows impressive drawings of fleas
with proboscis, eyes and claws. He was also the first to visualize the structure
of cork. Since the structure reminded him of chambers in a monastery, he called
them »cells«.
Better Lenses – Better Quality
Being able to build microscopes with more than one lens and to produce lenses
at a better quality are leading to a higher image quality. Early microscopists were
hampered by optical aberration, blurred images, and poor lens design, which impeded
high-resolution observations until late in the 1800s. Chester Moor Hall
started to experiment with manual polished lenses of different glass types to increase
the microscopic image quality. In Germany, Joseph von Fraunhofer also
worked on these achromatic lenses. The quality of the microscope depended significantly
on the know-how of the polisher.
Light with different wavelengths and therefore different color is refracted
and distracted differently while passing through a lens. This
physical phenomenon results in chromatic aberrations on the edges
of observed objects. If you use systems with only one lens, this aberration
can be neglected. But if a microscope with more than one lens
is used, the aberration multiplies.