Object always look bigger when they are closer. For example, if you want to check the fine details of a postage stamp, you tend to bring it closer to your eyes. Thus, as it comes nearer it looks larger. But there is a limit to how near you can bring it since if the stamp is too close, the eye can no longer focus on it, and the stamp looks blurred. In order for you to overcome this handicap, there is a need to add artificial lenses. This is the main job of the Microscope, to bring the objects as big as we want to.

Every one of us knows that there are two types of microscopes: The Simple and The Compound Microscope. How they differ with each other?

The simple microscope consists of a single lens, one that is thicker at the center than at the edges. This lens works by changing the direction of light passing through it so that it stops spreading out and converges again to form an image of the source. To understand how a lens can form an image, imagine this: a light wave from a distant source approaching the lens. The light wave could be likened to an ocean wave in the beach when a breaker rolls toward the shore. As the center of the wave starts to pass through the thick part of the lens, the two ends of the wave are still traveling through the air. Since light travels more slowly in glass than in air, the center of the wave slows down, while the two ends keep going at their original speed. What happens, then, is that the wave is bent around by the lens and emerges from the other side curved like the letter C. This newly shaped wave will form ever-tighter circles as it proceeds through the air, until it finally converges to a single point.

This point is what we call the focal point of lens. This is where the image forms. The distance from the lens to the focal point is called the focal length. Take note that the shorter the focal length, the greater the power of the lens to take a wave form and bend it around so that it will converge. There are instances though that the lens does not have enough power to converge the light. This usually happens when the source is very near to the lens. In that case the image formed by the lens does not appear on the viewers side but rather in back of the lens on the same side as its source. As you look through the lens you see the image on the far side, enlarged and more distant. The simple microscope works on this principle. By adjusting the position of the object with respect to the lens, you can get the largest image that you can see without straining your eyes.

The Compound Microscope

Now a day, most microscopes use two lenses for greater magnification. They are called compound microscopes. In fact, a microscope with a single lens, the one we called simple microscope is nothing more than a magnifying glass. Compound microscope features an upper lens —– the eyepiece, or ocular lens —– and a lower lens, at the opposite end of a tube —- the objective lens.

This type of microscope works by first the magnified image is formed by the objective lens, and projected up into the tube. This image is upside down. Next, the eyepiece takes over and enlarges the image once again, still leaving it upside down. As a result, what you always see in the microscope is always reversed. Take this example, when you move the object up, the image appears to move down. When you move it to the right, the image appears to move to the left.

The magnifying powers of the objective and the eyepiece are usually marked on the casing of the lenses. A typical medium power objective can magnifies the object 40 times, which means it has a magnification of about 40X. Usually, the eyepiece magnifies 12.5 times or has 12.5X magnification. You could usually figure out the total magnification of your microscope. Just remember that what you are looking at has been magnified twice, first by the objective and then by the eyepiece. To obtain the total, multiply the two magnifying powers. If the objective is marked 40X and the eyepiece 12.5X then the total magnification is 500X, or 40 X 12.5.