Compound microscopes are key tools for scientific research and education around the world and in many fields. They vary widely in price, allowing students, scientists and hobbyists of all income levels to all utilize various models. In the last 400 years, especially prior to the 1900s and the development of alternate models of microscopes, compound microscopes have redefined the understanding of a vast array of phenomena. From the analysis of cork cells to the study of bacteria, these devices have been central to scientific exploration.
The light from the light source passes through the specimen, resulting in an image that your naked eye would ordinarily see if looking at the slide. The image is then magnified by the lower (objective) lens.
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.
Types of Lenses
A compound microscope is essentially a frame that holds a series of magnifying lenses. There are two main categories of lenses: the eyepiece, which is the lens closest to the eye, and the objective lens, which is the lens (or series of lenses) close to the object.
The eyepiece is usually near 10x in strength. Most compound microscopes have three to four objective lenses on a turning plate called the nosepiece that often range from 4x to 100x in power. The longer lenses are more powerful. To determine the strength of the total magnification, multiply the two numbers together (a 10x nosepiece and a 40x objective lens would result in 400x magnification).
40x magnification is primarily for dissections and the viewing of whole, three-dimensional objects. This is especially good for children since it doesn't require the preparation of a slide. 400x magnification is commonly used in biological sciences. Above 400x, a special condenser lens is useful to focus the light and improve the image resolution.
Microscopes can be monocular, binocular or trinocular. This refers to the number of eyepieces (one, two, or two and a camera).
Other Parts and Their Functions
The tube connects the eyepiece to the objective lens.
The arm connects the tube to the base.
The nosepiece is the rotating plate that holds the objective lens. This allows for quick switching between magnification levels.
The stage is the flat platform beneath the objective lens that holds the slides. It often can be adjusted to allow for better viewing of the sample.
The rack stop adjusts how closely the objective lens can approach the specimen. This is a factory setting usually only adjusted when dealing with very thin slides at high magnification.
The light source is either a bulb or a mirror that reflects light from another source through the bottom of the stage. This illuminates the specimen.
The iris is a disk beneath the stage that allows for adjustment of the amount of light that hits the specimen.
Compound microscopes are used most commonly to magnify thin sections of specimens placed on slides. The 400x compound microscope is used by almost every college level biology student.
Almost every scientific field has found use, at some point, for magnifying small objects. Microscopes are probably used most often in biological and chemistry related fields. They are routinely used in hospitals for diagnosis and research, and are common at police analysis labs. Compound microscopes have assisted in the discovery of the cell, the understanding of cell division, the study of bacteria and the study of molecules.
Compound microscopes are limited by the abilities of light and glass, so alternative 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 the electron microscope, acoustic microscopes, which act similarly to sonar to scan surfaces.