Compound Light Microscope
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Microscopy is the science of using lenses to magnify small objects. An instrument in which the lenses and object are mounted along an optical path is called a microscope. The quality of a microscope is based on its ability to perform two specific tasks: 1) magnify, and 2) resolve detail. Magnification is the ability to produce enlarged images of objects. Resolution, or resolving power, is the ability to distinguish two separate points as being separate and distinct. The resolving power of a microscope determines the degree of detail that is visible.

Any microscope that uses light to illuminate the object is called an optical or light microscope. If the light microscope uses a single lens to magnify the image, it is called a simple light microscope. If the microscope uses more than one lens to magnify the image, it is called a compound light microscope. Compound light microscopes are the most common microscopes in use today.

Compound light microscopes use several different types of light illumination techniques to view magnified objects. The most common and simplest of the techniques is called bright field microscopy. In bright field microscopy, the sample is illuminated by white light focused on the specimen. This usually requires specialized stains to improve the contrast between object and background light and to make the object visible. A second type of relatively common illumination system is phase contrast microscopy. In phase contrast microscopy, contrast between object and background light is created by phase shifting the light scattered by the object. This eliminates the need to stain the object, allowing living cells to be viewed. Fluorescence microscopy is a third type of light illumination technique that utilizes a xenon or mercury lamp to illuminate a specimen stained with specialized stains called fluorophores.

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