While magnifying glasses and compound light microscopes perform the same basic function -- that is, making objects appear larger and easier for the eye to see -- there are numerous differences between the two tools. Furthermore, as technology has progressed, the functions of compound light microscopes have expanded as well, while magnifying glasses are still fairly limited in their abilities.
How a Magnifying Glass Works
A magnifying glass is a bi-convex lens, which means that it curves outward on each side to make a dome shape. Convex lenses make objects appear larger because light is bent by the shape of the lens, making the image appear larger to the eye even though it is not. The image is thus called a "virtual image." The power of magnification is determined by the optical quality of the lens and the distance it is held from the object being viewed. If the glass is held too far from the object, the object becomes blurry.
Compound Light Microscope Components
The key components of a compound light microscope are its objective lenses, ocular lens, stage, nose piece, focal adjusting knobs, and light source. There are typically three or four objective lenses on a microscope of this type, but there is only one ocular lens. The stage is where slides with objects to be viewed are placed. The nose piece is the rotating dial that holds the objective lenses in place. There are two adjustment knobs: the "coarse" adjustment knob and the "fine" adjustment knob. The light source in a compound light microscope is a steady, electric light that provides illumination up from the bottom of the scope. Older microscopes used mirrors to reflect light from an outside source.
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How a Compound Light Microscope Works
A compound light microscope uses a combination of lenses to magnify objects more than is possible with simple lenses such as magnifying glasses. The total magnification of a scope is determined by multiplying the power of the objective lens being used by the power of the ocular lens. Typically, the objective lenses are labeled with their relative magnification power, and the ocular lens is usually 10x. Objective lenses are usually 4x, 10x, 40x and 100x. The light shines through an aperture in the stage, illuminating the object from below. The adjustment knobs are used to attain proper focus. They control the amount of light coming through the aperture and the physical distance from the slide to the lens. The lower the magnification, the larger the distance, and when an object is being viewed at 100x it is nearly touching the slide on the stage. The image is magnified once by the objective lens, then that magnified image is seen through the ocular lens, which magnifies it again by 10x.
Magnifying glasses enlarge the image of an object. However, distortion occurs quickly. Improper distance can cause the object to appear smaller, and over-magnification can cause the image to lose quality and appear fuzzy and out of focus. Compound light microscopes eliminate the problem caused by the single bi-convex lens of a magnifying glass. The ocular lens on a microscope is essentially performing the same function as a magnifying glass, but it is viewing the image produced by the objective lens. The objective lens, when used in conjunction with the adjustment knobs on the scope, creates a magnified image and reflects it to the ocular lens so that there is no loss in fidelity.