Light microscopy:
Microscopy started with light microscopes using visible light to illuminate the objects, the most used and familiar microscope is called compound light microscope. Its simplest form it consists of two optical lenses, one at each of a hollow tube. The lens closer to the object is called objective and the one closer to the observer eyes is called eyepiece. The object, mounted upon a glass slide, which is put upon a centrally perforated satge under the objective, is illuminated by light , a mirror is fitted below the stage to focus light on to the object, a third lens system ,called condenser may be fitted between the mirror and the stage to concentrate the light. The limit of the resolving power of best compound light microscopes is about 0.2 achieving a magnification of about 2000 times the size of the objects. Thus these microscopes can resolve even most of the bacteria, but they cannot reveal the internal details of bacterial cells.
Use of ground glasses as optical lenses to magnify objects was presumably realized several centuries ago. The first name on record is of Conrad Gesner who used magnifying lenses to observe certain foraminifera's. Next Zacharias Janssen (Dutch 1590) constructed, together with his father, Hans Janssen the first compound light microscope to study insects which could magnify objects 10 to 30 times. Galileo constructed microscope with greater magnifying powers and studied the arrangement of facets in the compound eyes of insects. Marcello Malpighi (1628-1694) microscopically studied animal and plant tissues in thin slices of several organs, earning the title of the father of microscopic anatomy, Robert Hooke (English 1665) designed a compound light microscope either a magnifying power of about 42 times and studied amongst other object thin slice of cork discovering cells. Antony van Leeuwenhoek (Dutch 1676) designed single lens microscopes with magnifications approaching 300 times and become the first to observe sperms, blood cells muscle fibres, lenses of eyes, hydrae yeast cells and microscopic organisms in water like bacteria, protozoan's rotifers tec. Earning the little of the father of microbiology so commonly used these days by students in schools and collages all over the world , was developed from Hooke model by Wilson (1970).
Zigmondy (1900) designed an ultra microscope using ultraviolet rays in place of ordinary light and quartz lenses in place of ordinary glass lenses, achieving a resolving power of0.1 and magnification of about 4000 times.