HISTORY OF MICROSCOPE UP TO THE LATEST As humans go on with their lives they discover, and experiment something that is for nature in many dimensions. Most of them pass unnoticed by observation because their scale is too big or too small. In fact, we would have to be giants, to follow the path of clouds over continents. And who knows how big we should be, to be able to contemplate the majestic rotations of our galaxy! On the contrary, if we were as small as an ant, we could see the amazing miniature world where bizarre creatures like protists live. The microscope is an instrument that allows us to leave our dimension and explore the microcosm. A snowfall, a flower, a puddle seem normal things, without surprises. Yet, if you could see the beauty of a snowflake, the hidden shapes of flowers, the variety and the strangeness of tiny creatures that live in a puddle, you would surely be amazed. You will notice that you are surrounded by a fascinating and unknown world. The microscope is the right vehicle to conduct you in this amazing world.

Using this instrument you will be able to journey in the microcosm, while attempting to observe very small objects, we realize the impossibility of distinguishing details smaller than a tenth of millimeter by naked eye. Hopefully, man created instruments, like the microscope, that allowed him to overcome his natural limits. It is not really necessary to be a professional to use a simple but efficient instrument. As people in the past did, with passion and patience, we can try to penetrate into the microcosm, in search of what cannot be seen with only our eyes. That’s why they build a little or simple microscope by Anton van Leeuwenhoek in the XVIIth century, one of the first microscopes built. Like its illustrious ancestor, our microscope is based on a single but powerful lens. Leeuwenhoek was a simple fabric merchant. In his job, little glass pearls were regularly used to examine the textiles in detail. None of Leeuwenhoek’s colleagues had the idea of observing anything different to textiles, maybe because they did not think there was anything else worth looking at.

Leeuwenhoek, however, sparked by a natural and insatiable curiosity, began to observe everything around him. He examined saliva and blood, pond water, vinegar, beer and innumerable other things. Potentially every subject was good, but pond water or even water from a simple puddle the dirtier the better was the subject of most interest to examine. He discovered and described many microorganisms. He sent reports to the prestigious English Academy of Science, the Royal Society of London which widely distributed these documents. Leeuwenhoek’s first advance discovery was to move his attention from textiles to natural objects. To obtain ever-increasing magnifications, he worked on smaller and smaller lenses, finally reaching 1-2 mm diameter lenses. Such small and powerful lenses are difficult to handle and focus. To overcome these difficulties, Leeuwenhoek fixed them between two pierced brass sheets. He arranged the samples to be observed on the tip of a screw, so that he could regulate precisely the distance between them and the objective. The observer had to keep the instrument very close to his eye and look through the lens.

Essentially this instrument was composed of just one lens. Given the high curvature of its surfaces, this lens was very powerful and allowed magnifications of up to 300X, almost one third of the magnification of a modern compound microscope. In optics, this microscope is defined as simple, because it is formed by just one lens. In the same period of Leeuwenhoek’s studies, the English physicist Robert Hooke had already built a compound microscope, made up of two groups of lenses: objective and eyepiece but, the fabrication techniques of lenses were not developed enough and so this kind of instrument had serious optical defects. This rendered it less effective than a simple microscope. Only in the first half of the 1800’s were compound microscopes perfected. Leeuwenhoek built hundreds of microscopes. Some of these are still exist today and are conserved in museums essentially; this instrument was not easy to use and lacked an efficient illumination system.

Electron microscope- contains electric or magnetic lenses because standard glass lenses for light microscope. Microscope that uses electrons instead of visible light to produce highly magnified images of objects. Scientists use electron microscopes in many different fields of research, including biology, medicine, metallurgy, chemistry, entomology- the study of insects, and physics. Since its introduction in the 1930s, the electron microscope has revolutionized the study of microscopic structures and surfaces. Electron microscopes are able to obtain much higher powers of magnification than standard visible light microscopes because electrons have much shorter wavelengths associated with them than light waves. The highest magnification achievable with light microscopes is about 2,000X; modern electron microscopes can achieve magnifications approaching 1,000,000X.

Electron microscope has 2 main types, the transmission electron microscope TEM and the scanning electron microscope SEM. The TEM consists of an electron source, a number of LENSES, and a system that projects an image onto a fluorescent screen or photographic plate. The lenses must be electric or magnetic lenses because standard glass lenses for light microscopes will not focus a beam of electrons. The electron source is a filament of TUNGSTEN that releases electrons when heated. A high voltage electric field 50,000 to 100,000 VOLTS applied between a pair of metal plates accelerates the electrons, and electric or magnetic lenses condense the electrons into a narrow beam. The electron beam then passes through the specimen and individual electrons are scattered in various directions depending upon the density of the material they encounter. Denser material scatters the electrons more so that fewer of them reach the device used to detect the electrons. Once the electrons pass through the specimen, the objective lens focuses those using magnetic fields. Specimens must be sliced extremely thin for use in a TEM because only electrons that pass through the specimen are recorded. Modern TEMs are capable of magnifications of between 1,000X to about 1,000,000X. HOW SEM WORKS- SEM works by scanning a tightly focused electron beam over a sample. Electrons in the beam scatter off of the sample and onto a CATHODE RAY TUBE, or screen. Each point on the sample corresponds to a pixel or picture element on the screen. The more electrons that hit a particular element of the screen, the brighter the pixel appears. As the electron beam scans over the entire sample, a complete image of the sample is displayed on the monitor. SEMs have a range of magnification of between 20X to 200,000X.