Saran's Learn Microbiology

  POLARIZING MICROSCOPE ·        A Polarizing microscope is a type of microscope that uses polarized light to view specimens. ·        Polarizing microscopes are conventional microscopes with additional features that permit observation under Polarized light. ·        Although the invention of the polarizing microscope is typically attributed to David Brewster around 1815, Brewster clearly acknowledges the priority of Henry Fox Talbot, who published his work in 1834. ·        Polarizing microscope is commonly used to observe minerals, crystals, and other transparent or semi-transparent materials. It is also used to analyze the structure and properties of the above given materials. Conversion of Unpolarized light to Polarized light ·        Light is an electromagnetic wave. Although light waves can vibrate in all directions, in general, they are described as vibrating in two directions at right angles to each other. ·        Any light which vibrates in more than one directi

  DIFFERENCE BETWEEN BRIGHT FIELD MICROSCOPE AND DARK FIELD MICROSCOPE BRIGHT FIELD MICROSCOPE DARK FIELD MICROSCOPE Formed a Dark image against Bright field. Formed a bright image against Dark background. Stained, fixed, and live specimens are observed. We can see the living and unstained cells. Specimen colour appears depending on the Stain colour. Specimen appears as Bright. Specimen background appears bright. Specimen background appears dark. Opaque disc is absent. Opaque disc is present. Specimen preparation or staining is a complex and lengthy process. Takes too much time. No need to stain. Shows the morphological as well as the internal structure of the specimen. Shows the External structure of specimen in great detail. Less expensive than Dark field microscope. More expensiv

  DARK FIELD MICROSCOPE ·        Dark field microscopes are named because the microscopic “field” is dark , while the object being viewed is bright . ·        Instead of the normal condenser, a dark field microscope uses a Dark field condenser that contains an Opaque disk . Principle ·        The Opaque disk blocks light that would enter the Objective lens directly. Only light that is reflected off (turned away from) the specimen enters the objective lens and reach the eye through Ocular lens or Eye piece . Because there is no direct background light, the specimen appears light against a black background-the dark field. Uses ·        Dark field microscope is used to examine live microorganisms that are ü   Invisible in the ordinary light microscope ü   Cannot be stained by standard methods, or are so distorted by staining that their characteristics then cannot be identified. ·        Dark field microscope is also

  BRIGHT FIELD MICROSCOPE ·        The bright field microscope is the most widely used type of Light microscope. ·        Bright field microscopes are named because the microscopic “field” is bright , while the object being viewed is dark . ·        Used to observe various Stained specimens and to Count microbes. ·        Does not resolve very small specimens, such as Viruses. Principle ·        Light from an incandescent source is aimed toward a Lens beneath the Stage called the Condenser , through the Specimen , through an Objective lens , and to the eye through a second magnifying lens, the Ocular or Eye piece . Uses To observe various stained specimens and to count microbes: does not resolve very small specimens, such as viruses.