What is a Light Microscope?

A light microscope, also called an optical microscope, is an instrument to observe small objects using visible light and lenses. It is a highly used and well-recognized microscope in the scientific community. The device can be used to view living or dead samples and can maximize these samples up to one thousand times (1,000x) their actual size. Light microscopes include almost all compound and stereo microscopes.

This type of microscope is composed of an objective lens, an ocular lens, a stage, a light source, a condenser, a tube, an arm to support the tube, and a focusing system. The specimen is set on the stage, a platform usually equipped with metal arms to hold the specimen or slide in place. The light bulb is situated beneath the stage so that the light shines up through the specimen. The tube focuses down on the stage so that the ocular lens, or eyepiece, is at the far end of the tube and the objective lens is at the end closer to the specimen.

The objective lens is a small, round piece of glass that collects the light from a small area of the specimen at a short focal length and directs the light into the tube. The image is then magnified by the ocular lens, which is put up to the eye. Because the objective lens is convex, it focuses and directs light into its center. By contrast, the concave shape of the ocular lens serves to spread out the light as it meets the eye, thereby making the image bigger. The condenser is a lens, often implanted into the stage or located just below it, that condenses the light rays from the light source onto the spot that is being examined on the specimen above.

A simple light microscope uses only one magnifying lens, but today, most microscopes use two or more lenses to magnify the image. Most microscopes today are compound microscopes that use more than one magnifying lens. The eyepiece typically magnifies to 2x, 4x, or 10x actual size and the ocular lens may magnify 4x, 5x, 10x, 20x, 40x, 50x and 100x. A microscope usually comes with three ocular lenses of different magnification levels set on a rotating nosepiece. There may also be a fourth lens used for oil immersion viewing of specimens, wherein a drop of oil is set on the slide to further refract light and the oil immersion lens is lowered until it touches the oil droplet.

The relationship of glass to magnification and the concept of lenses were discovered by the Romans in the first century, A.D. Lenses were eventually put to use at the end of the 1200s as spectacles. This may have set the stage for Zaccharias and Hans Jannsen, Dutch spectacle makers who, in the year 1590, are said to have invented the first compound microscope by experimenting with several lenses in a tube. The validity of the Jannsens’ claim to this invention, however, is highly disputed. Many historians credit Tuscan scientist Galileo Galilei with the development of the compound microscope and technologically similar telescopes in the early 1600s.

Later, a Dutch store apprentice named Anton Von Leeuwenhoek refined lens making to achieve a steep curvature on a small lens, allowing him to focus on much smaller specimens than ever before. He is often referred to as a father of microscopy as he introduced the microscope as a vital instrument to the field of biology. In addition to other discoveries, Anton Von Leeuwenhoek was the first to view bacteria, yeast, and the organisms in a drop of water.