The art of grinding lenses is developed in Italy and spectacles are made to improve eyesight. In the 13th century Salvino D'Armate from Italy, made the first eye glass, providing the wearer with an element of magnification to one eye. The earliest simple forms of magnification were magnifying glasses, usually about 6x - 10x and were used for inspecting tiny insects such as fleas, hence these early magnifiers called "flea glasses".
During the 1590's, two Dutch spectacle makers, Zacharias Jansen and his father Hans started experimenting with these lenses. They put several lenses in a tube and made a very important discovery. The object near the end of the tube appeared to be greatly enlarged, much larger than any simple magnifying glass could achieve by itself. Their first microscopes were more of a novelty than a scientific tool since maximum magnification was only around 9x and the images were somewhat blurry. Although no Jansen microscopes survived, an instrument made for Dutch royalty was described as being composed of "3 sliding tubes, measuring 18 inches long when fully extended, and two inches in diameter".
It was Anton van Leeuwenhoek (1632-1723), a Dutch draper and scientist, and one of the pioneers of microscopy who in the late 17th century became the first man to make and use a real microscope. Van Leeuwenhoek achieved greater success than his contemporaries by developing ways to make superior lenses, grinding and polishing five hundred and fifty lenses to make his new lens tube that had a magnifying power of 270x and could view objects one millionth of a meter (other microscopes of the time were lucky to achieve 50x magnification). Van Leeuwenhoek made many biological discoveries using his microscopes. He was the first to see and describe bacteria, yeast plants, the teeming life in a drop of water, and the circulation of blood corpuscles in capillaries. During a long life he used his lenses to make pioneer studies on an extraordinary variety of things, both living and non living, and reported his findings in over a hundred letters to the Royal Society of England and the French Academy.
Robert Hooke published Micrographia in 1665. It is his most famous work and is notable for the stunning illustrations, drawn by Hooke himself. Microphagia presents several accounts of Hooke's observations through the use of the microscope. He looked at all sorts of things (snow, a needle, a razor, etc.) with a primitive compound microscope, but his most significant observations were done on fleas and cork. He observed the fleas under the microscope and was able to observe the tiny hairs on the fleas' bodies. On the cork he saw pores. Upon examination of the pores, he decided to call them "cells"; however, he did not know he had just discovered plant cells. Despite these great achievements in microscopy, microscopes didn't change much over the next 200 years, even though there were imperfections when viewing an object due to the different refraction of light.
In the 1850s, German engineer Carl Zeiss began making refinements to the lenses he used in the microscopes he manufactured. In the 1880s, Zeiss hired glass specialist Otto Schott, who conducted research on optical glass, greatly contributing to the improvement of the optical quality of the microscope. We should also mention Ernst Abbe, who was hired by Zeiss to improve the manufacturing process of optical instruments, which back then was largely based on trial and error. In a long and fruitful collaboration, Abbe carried out theoretical studies of optical principles, improving the understanding of the optical quality of a microscope.
Richard Zsigmondy develops the ultra microscope and is able to study objects below the wavelength of light. Frits Zernike invents the phase-contrast microscope that allows the study of colorless and transparent biological materials. Ernst Ruska develops the electron microscope. The ability to use electrons in microscopy greatly improves the resolution and greatly expands the borders of exploration. Gerd Binnig and Heinrich Rohrer invent the scanning tunneling microscope that gives three-dimensional images of objects down to the atomic level.