MICROSCOPY, Light Microscopy, Magnification, Resolution, Contrast.pptx

*MICROSCOPY
*Light Microscopy (Principle of Light Microscopy, Application)
*Terms commonly used in Microscopy (Magnification, Resolution, Contrast)

1. MICROSCOPY

2. Microscopy includes techniques used to study the cell structure of all organisms by using microscopes. The unaided eye cannot comfortably distinguish two points <0.2mm apart The resolving power of eye is inadequate for the study of most cells. Therefore, magnification is essential to make them visible.

3. Light Microscopy The source of light microscope is simple light. A light microscope is a coordinated system of lenses which produces an enlarged, focusable image of a specimen. The organisms and biological structures are too small to be seen with the unaided eye. Therefore, biologists often use a light microscope to observe such specimens. A light microscope magnifies a specimen. It means that it increases its apparent size.

4. Principles of light microscopy Principle . The light microscope is an instrument for visualizing fine detail of an object. It does this by  creating a magnified image through the use of a series of glass lenses, which first focus a beam of light onto or through an object, and convex objective lenses to enlarge the image formed . In the majority of light microscopes, the image is viewed directly through binocular eyepieces that act as a secondary lens in the form of a magnifying glass to observe the projected image.

5. For light microscopy, visible light is passed through the specimen and then through a series of lenses that bend the light in a manner that results in magnification of the organisms present in the specimen

6. Application of Light Microscopy Light microscopes play an important role in many research laboratories. Biologists use microscopes to observe objects and details at a cellular level to learn more about the building blocks of all organisms. Microscopes are used when studying light and optics to learn how light refracts through converging lenses and how a combination of different lenses with varying focal lengths affects the properties of the image . Microscopes are used in schools as part of the technology section of the curriculum. Microscopes provide students with an understanding of real cells and their supporting structures.

7. Microscopes are used in forensics to help solve many crimes. Often times, there will be human evidences left on the crime scene. This allows forensic scientists to examine the evidence under a microscope and match the results with a database to find the culprit . Mineralogists also use light microscopy, typically with a special preparation of a sample called thin section. T hin sections are very thin slices of a rock. The sample needs to be thin enough for light to travel through from the light source to the user's eye. The thin section will allow the shape of different crystal grains to be seen.

8. Terms Commonly used in Microscopy Magnification Magnification is the capacity of an optical instrument to increase the size of an object than its original size . Magnification of a microscope is the product of multiplying the individual magnification of the ocular (eye piece) and objectives. Magnification power of a microscope = Objective magnification x ocular magnification E.g. If the eye piece is 10X and objective is 40X then the specimen image is magnified 400 times. i.e. 10X x 40X = 400X

9. 2. Resolution / Resolving power Effective magnification depends on the resolving power of a microscope. The resolving power is the ability to distinguish two adjacent objects as separate and distinct images rather than as a single blurred image. The minimum capacity of a lens to differentiate between two adjacent points is called resolution power of the lens. Resolution is the ability to distinguish two points as separate points. Our naked eye can distinguish two points. Such points have at least 0.1mm distance. Therefore, resolution of naked eye is 0.1mm.

10. 3. Contrast Contrast is the difference between the lightest and darkest parts of an image. The ability to distinguish detail also depends on contrast. Therefore, many specimens examined with a light microscope are stained with artificial dyes. These dyes increase the contrast and make the specimen more visible. Contrast refers to the darkness of the background relative to the specimen. Lighter specimens are easier to see on darker backgrounds.