Microbiology Procedure

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Bright Field Light Microscopy

	Bright Field Light Microscopy This is the most familiar microscopy. The light microscope is a two lens system in which the lens nearest the object is known as the objective lens and that nearest the eye, is known as the ocular lens. Visible light rays are projected through a condenser that focuses them into a sharp cone, then sends them through the opening in the stage on which the slide rests.
The light passes through the slide, bounces off the object, then passes through the objective lens to form a magnified image darker than the background around it. This image is a real image that can be projected onto a screen. The image now becomes an object for the ocular lens and the light rays are magnified a second time creating a virtual image in space visible only to the observer.
The dual lens system is referred to as a compound microscope to distinguish it from a single lens system such as used by van Leeuwenhoek. In addition, a laboratory microscope usually has three objective lenses called the low power, high power, and oil-immersion lenses.
Generally, these magnify an object 10,40 and 100 diameters, respectively and the magnification is represented by multiplication symbol "X". The total magnification of the microscope is determined by multiplying the objective magnification by the magnification of the ocular lens. Thus, if the latter were to X, the total magnifications achieved would be 100X, 400X, and 1000 x, respectively.
	Resolving power in order for an object to be seen distinctly, the lens system must have good resolving power. This is the ability to transmit light without variation. If two objects are very close to each other, these must be distinguished clearly from each other as distinct, sharp objects. The resolving power (RP) of a lens system is a number (Le. the ability, represented numerically) used to determine the size of the smallest object that can be clearly seen.

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