Compound microscopes are a common tool found in classrooms and laboratories around the world. They range drastically in price, allowing hobbyists, scientists, students and kids all to learn and benefit from various models. Furthermore, microscopes have become a fundamental tool for research and learning in many scientific fields such as biology and chemistry. The ability to study an object with an amount of precision that well surpasses the abilities of the human eye has redefined our knowledge of everything from disease to the building blocks of elements.
Zacharias Janssen, a Dutch manufacturer of spectacles, is often cited as inventing the compound microscope in 1590. Sacharias Janssen, his father, and Hans Lippershey, the developer of the first true telescope, are two others commonly given credit for this discovery. Galileo developed a model in 1610 that Giovanni Faber first dubbed a microscope in 1625. In 1674, Anton van Leeuwenhoek developed new methods of manufacturing lenses that allowed for more a significant curve in the lens and thus an increased ability to magnify. During the 18th century microscopes gained popularity among scientists. In 1830, Joseph Jackson Lister discovered that by combining several weak lenses, he could reduce the halos of light caused by refraction. Ernst Abbe's Abbe Sine Condition formula, developed in 1972, allowed scientists to calculate the maximum possible resolution for microscopes. The 19th century brought the invention of the ultramicroscope, the phase-contrast microscope, the electron microscope and the scanning tunneling microscope, respectively. These microscopes allow scientists to study objects far smaller than a traditional lens microscope would allow
The most basic compound microscope is a tube with two convex lenses inside (the objective lens). This tube is often on a rotary plate (the nosepiece), which is attached to an observation tube with an eyepiece at the top. Microscopes can be monocular, binocular or trinocular. This refers to the number of eyepieces (one, two, or two and a camera). To determine the total magnification, multiply the power of the eyepieces by the power of the chosen objective lenses (a 10X eyepiece with a 40X objective lens would result in 400X magnification). Beneath the objective lens is a stage where the specimen is placed, which contains a window to allow a light source to illuminate the specimen. The light source can be adjusted via an iris beneath the stage.
The light from the light source reflects off the specimen, resulting in an image that your eye would ordinarily see in everyday circumstances. The image is then magnified by the objective lens. Many compound microscopes have multiple (often three) available objective lenses on a rotating nosepiece to allow for a quick change in magnification. The objective lens flips the image and magnifies it by bending the light. The light is bent as it passes through the convex surface on either side of the lens material. The eyepiece acts as a weaker version of the objective lens by flipping the image again and magnifying it further.
Compound microscopes are used for research in many disciplines of science. They have assisted in the discovery of the cell, the understanding of cell division, the study of bacteria, the study of molecules, and countless other endeavors.
The Future of Microscopy
While compound microscopes are limited by the abilities of light and glass, alternate forms of microscopes are under constant development. The scientific community is always looking for new, creative ways to view objects closer. As of May 2009, the scanning tunneling microscope, developed in 1986, is the most powerful microscope to date. It is useful for studying surfaces at an atomic scale. Other styles of microscopes include acoustic microscopes, which act similarly to sonar to scan surfaces.