A History of the Optical Microscope

An optical microscope, also called a 'Light Microscope', is an instrument that is used to observe micro samples. It works by utilizing visible light and a number of lenses, which are strategically placed to enable a small sample to be magnified. Although there are many varieties of microscopes available today, optical microscopes are still the most common type, as well as the oldest.

Optical microscopes can be broadly categorized into two types, namely the simple microscope and the compound microscope. While the simple microscope uses a single lens, the compound microscope has more than one lens. Typically, a compound microscope that is used in biomedical technician schools today contains three objective lenses: a low power lens, a scanning lens, and a high power lens.

The birth of the optical microscope dates back to the year 1021, when Ibn al-Haytham, also known as Alhazen, mentioned it in his book The Book of Optics. It was only after the book was translated into Latin that European scientists began to develop eyeglasses. Although it is not clear who invented the optical microscope, there are a few names who contributed greatly to its development. Hans Janssen and his son Zacharias Janssen were Dutch spectacle-makers who are believed to be the inventors. Another contender is the astronomer Galileo Galilei. In 1609, he developed a compound microscope that contained both a convex and concave lens. In the late 17th century, another Dutchman by the name of Christiaan Huygens developed a microscope using a two-lens ocular system, which became known as the Huygens Ocular. This microscope, which continues to be used to this day, is achromatically corrected, which is viewed as its best feature.

In the 18th century, biologist Antony van Leeuwenhoek popularized the use of microscopes in biology and medical training. He used a single large lens instead of compound lenses to observe samples. Even though the microscope was not as easy to use, it provided magnification power which was unmatched by any other microscope of that time.

Some of the basic components in an optical microscope include the eyepiece, or ocular, which helps to bring a micro object to focus for the human eye; an objective lens that is composed of a cylinder and a few lenses that collect light from the sample, with standard objective values of x4,x10, x20, x40, x80 and x100; a stage which is a platform that supports the sample; and an illumination source that provides light to the sample being viewed. A mirror often acts as a simple illumination source, but high-end optical microscopes have a source of light as well as a condenser. This whole assembly is connected to a U-shaped base through an arm that can be pivoted. The controls for focusing the object are also mounted on the arm.

Digital microscopes are the latest development in microscopy, and they use a digital camera to magnify a sample. It is sometimes used in (medical training). It can offer high magnifications of up to x200, and it is comparatively very affordable. Some other popular varieties of optical microscope that are available at the moment and used by biomedical technician schools include the student microscope, the inverted microscope, research microscope, and the petrographic microscope.

Optical microscopes can be designed to be immensely powerful, capable of magnifying a sample up to x1000. However, there are a few inherent drawbacks such as the phenomenon of diffraction. This prevents it from providing a clear view of the fine details of a powerfully magnified sample. To overcome this problem, new microscopes like scanning electron microscope, transmission electron microscope, and the X-ray microscope have been developed.

In all optical microscopes, the eyes need to view a microscopic image at infinity. In reality, however, the eyes focus at a close distance and not at infinity, and it is for this reason that some people get a headache after prolonged use of an optical microscope.