Light microscope

introduction history detail of light microscope and its different types with their working pronciple

1. Light microscope Presented by: syeda jaweria rehman

2. Components of a light microscope

3. Working principle

4. Main types of light microscope Followings are the basic types of light microscope: Dark field microscope Bright field microscope Phase contrast microscope Flourescence microscope

5. Dark field microscopy It is used to improve the contrast of unstained and transparent speciman Light scattered by the specimen enters the objective lens to produce a bright image against the dark back ground It has low resolution Used in microbiology and many other fields Many variation are availeble for better results

6. BRIGHT FIELD Brightfield microscopy  is the most elementary form of microscope illumination techniques and is generally used with compound microscopes. The name " brightfield " is derived from the fact that the specimen is dark and contrasted by the surrounding bright viewing field. Simple light microscopes are sometimes referred to as brightfield microscopes

7. Working principle In brightfield microscopy a specimen is placed on the stage of the microscope and incandescent light from the microscope’s light source is aimed at a lens beneath the specimen. This lens is called a condenser . The condenser usually contains an aperture diaphragm to control and focus light on the specimen; light passes through the specimen and then is collected by an objective lens situated in a turret above the stage . The objective magnifies the light and transmits it to an oracular lens or eyepiece and into the user’s eyes. Some of the light is absorbed by stains, pigmentation, or dense areas of the sample and this contrast allows you to see the specimen. For good results with this microscopic technique, the microscope should have a light source that can provide intense illumination necessary at high magnifications and lower light levels for lower magnifications

8. Advantage Brightfield microscopy is very simple to use with fewer adjustments needed to be made to view specimens. Some specimens can be viewed without staining and the optics used in the brightfield technique don’t alter the color of the specimen It is adaptable with new technology and optional pieces of equipment can be implemented with brightfield illumination to give versatility in the tasks it can perform.

9. PHASE CONTRAST The basic principle to making phase changes visible in phase-contrast microscopy is to separate the illuminating (background) light from the specimen-scattered light (which makes up the foreground details) and to manipulate these differently. The ring-shaped illuminating light (green) that passes the  condenser  annulus is focused on the specimen by the condenser. Some of the illuminating light is  scattered  by the specimen (yellow). The remaining light is unaffected by the specimen and forms the background light (red). When observing an unstained biological specimen, the scattered light is weak and typically  phase-shifted  by −90° (due to both the typical thickness of specimens and the refractive index difference between biological tissue and the surrounding medium) relative to the background light. This leads to the foreground (blue vector) and background (red vector) having nearly the same intensity, resulting in low  image contrast .

10. Florescence microscope The specimen is illuminated with light of a specific  wavelength  (or wavelengths) which is absorbed by the  fluorophores , causing them to emit light of longer wavelengths (i.e., of a different color than the absorbed light). The illumination light is separated from the much weaker emitted fluorescence through the use of a spectral emission filter. The filters and the dichroic beamsplitter are chosen to match the spectral excitation and emission characteristics of the fluorophore used to label the specimen

11. Applications

12. A 40x magnification image of cells in a medical  smear test  taken through an optical microscope using a  wet mount  technique, placing the specimen on a glass slide and mixing with a salt solution Optical microscopy is used extensively in microelectronics, biotechnology, pharmaceutic research, mineralogy and microbiology. [ Optical microscopy is used for  medical diagnosis , the field being termed  histopathology  when dealing with tissues, or in  smear tests  on free cells or tissue fragments.

13. In industrial use, binocular microscopes are common. Aside from applications needing true  depth perception , the use of dual eyepieces reduces  eye strain  associated with long workdays at a microscopy station . Measuring microscopes are used for precision measurement

14. REFRENCES: The principles and practice of light microscopy ( cambridge university press) Classification of microscopes ( JR Blueford )

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