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Light Microscopy: Instrumentation and Principles

Author(s): David R. Caprette, PhD

Light Microscopy: Instrumentation and Principles

A light microscope is so named because it uses visible light to produce a magnified image. Compound light microscopes are indispensable to almost any teaching laboratory in biological science, yet many of us have a difficult time using them. Part of the problem is that with any light microscope, a user must select the right magnification, contrast and resolution, position, and focal plane, all at the same time. A second complication stems from the fact that most teaching lab microscopes are designed for bright field viewing only. A good bright field microscope can produce excellent high resolution images. However, many light microscopes are equipped with specialized optics that enhance contrast so that any specimen, living or preserved, can be imaged. 

For satisfactory contrast and resolution, some specimens are best examined using phase contrast or dark field optics. Polarized light provides the basis for differential interference contrast (D.I.C.), which produces three dimensional images. Specialized optics are usually necessary for imaging very small unstained living organisms, such as bacteria or the smallest protists. To maximize their capabilities, most research microscopes are equipped with some combination bright field and specialized optics.

Here, we will explore the features of compound microscopes, principles of imaging, magnification, contrast, and resolution. We also will look at the components of compound light microscopes and their functions.