There is no one person who invented the microscope as several different inventors experimented with theories and ideas and developed different parts of the concept as they evolved to what is today microscopes. About 1590, two Dutch spectacles makers, Zacharias Janssen and his son Hans, experimented with a crude concept of a microscope which enlarged objects 10x to 30x. In 1609, Galileo improved on the principle of lenses and added a focusing device to improve somewhat on what the Janssens had done previously.
These rudimentary optical instrument did not change much until the 1670s. A Dutchman, Anton Leeuwenhoek, is considered the father of microscope because the advances he made in microscope design and use. He worked as an aprentice in dry goods store where magnifying lenses were used to count the threads in cloth. Anton was inspired by these glasses and taught himself new methods for grinding and polishing small lenses which magnified up to 270x. This led to the first practical microscopes. In 1674, Anton Leeuwenhoek was the first man to see and discribe bacteria, yeast, and plants in a drop of water.
There are two basic configurations of the conventional optical microscope, the simple (one lens) and compound (many lenses). A simple microscope is a microscope that uses only one lens for magnification, and is the original design of optical microscope. Van Leeuwenhoek's microscopes consisted of a small, single converging lens mounted on a brass plate, with a screw mechanism to hold the sample or specimen to be examined. A compound microscope is a microscope which uses multiple lenses to collect light from the sample and then a separate set of lenses to focus the light into the eye or camera. Compound microscopes are heavier, larger and more expensive than simple microscopes due to the increased number of lenses used in construction. The main advantages of multiple lenses are improved numerical aperture, reduced chromatic aberration and exchangeable objective lenses to adjust the magnification.