Experiment 2: Microscopy & Simple Staining september 30, 2013 General microbiology laboratory The invention of the microscope has opened up a whole new dimension in science. By using microscopes scientists were able to discover the existence of microorganisms, study the structure of cells, and see the smallest parts of plants, animals, and fungi. Today, the microscope is still a commonly used tool to diagnose illness in hospitals and clinics all over the world (1).
The three well-known branches of microscopy are: light microscopy, electron microscopy and scanning probe microscopy (2). There are many types of light microscopes the most commonly used are bright- field, dark field, fluorescence and confocal microscopes. The bright-field microscope is the simplest of all and is commonly used in microbiology labs, where it can be employed to examine both stained and unstained specimens.
It’s called the bright field microscope because it forms a dark image against a bright background ( 3). It has two lenses the objective and the ocular and they create the image by working together. Light pass through the specimen by a light source which is located on the base and is focused by the objective lens which can magnify from 4 to 100 imes, then the ocular lens further magnifies the image by 10 times.
The total magnification is calculated by multiplying the objective and the eyepiece magnification together (3). When a ray of light passes from one medium to another, retraction occurs that’s the ray is bent at intertace (3). The retraction index is a measure of the bending of a ray of light when passing from one medium into another (4). Lenses act like a collection of prisms, when a light is distant so that parallel rays of light strike the lens, a convex lens focus their rays at a specific point, the focal point.
The most important part of the microscope is the objective lens, which must produce a clear image, not Just a magnified one, thus the resolution is extremely important and it’s defined as the ability of a lens to separate or distinguish between small objects that are closed together (3). To increase the resolution of the light microscope the oil immersion can be used, oil immersion is a technique used to increase the resolution of a microscope. This is achieved by immersing both the objective lens and the specimen in a transparent oil of high refractive index, thereby increasing the numerical aperture of the objective lens (5).