Bright Field Microscope: Definition, Parts, Working Principle, Application.

Written by SouravBio · 4 minutes read >

Bright Field Microscope Definition

  • In bright field microscope, the specimen appears as dark against the bright background.
  • Bright-field microscope is a widely used microscope in laboratories and it also known as a compound or Light Microscope.
  • Stained, fixed and live specimens are observed under a bright field microscope.
  • A bright-field microscope is consists of A piece of apparatus, consisting of an eyepiece, an objective lens, a condenser lens, stage, and light source, which collects electromagnetic radiation in the visible range.

Working Principle of Bright Field Microscope

The specimen to be observed is placed on the stage of a  brightfield microscope. The light will transmit through the specimen from the source and then it will enter the objective lens where a magnified image of specimen will form. Then the light will enter an oracular lens or eyepiece, where the image will further magnify a then enter the into the user’s eyes. The viewers observe a dark image against a bright background.

In a bright-field microscope, only the scattered lights are able to enter the objective lens and transmitted lights or unscattered light rays are omitted, that’s why the viewer sees a dark image against the brightfield.

LightPath of Brightfield Microscope

  • A stained specimen or sample is placed over the specimen stage.
  • A condenser lens containing an aperture diaphragm is located under the stage, will focus the light ray on the sample or specimen.
  • The light rays will pass through the specimen sample and then it will be collected by an objective lens located over the stage.
  • The objective lens will form a magnified image of the specimen and then transmit it to the eyepiece, where viewers will observe a dark image against the brightfield.
  • During the transmission through the specimen, some of the light rays are absorbed by the stains, pigmentation, or dense areas of the specimen.

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Parts of Brightfield Microscope

Bright Field Microscope
Bright Field Microscope

A brightfield microscope is consists of these following parts (follow my previous notes, there I have already discussed all the parts with their functions);

  1. The top portion of brightfield microscope is known as the head.
  2. The holding portion of the microscope is known as Arm. Which we used to carry the microscope from one place to another. This portion provides support to the both optical and mechanical components.
  3. The bottom portion of the microscope, which holds the arm and other components is known as Base.
  4. Two lens were located at the top portion of a brightfield microscope, which are known as the eyepiece or ocular lens. Viewers observe the image through it.
  5. A long tube connected the both ocular lens and objective lens, called as body tube.
  6. An objective lens is located under the eyepiece. This lens helps to magnify the image. There are present different types of objective lenses, such as 40x, 10x, 100x, etc.
  7. A Nosepiece is located under the head. It contains different types of Objective lens.
  8. The Stage is located under the objective lens. The specimen is placed over the stage.
  9. The stage clips are located over the specimen stage. It holds the specimen slide.
  10. There are present different types of objective lenses, they vary based on their magnification power.
  11. A condenser lens is located under the stage. It focuses the light rays on the specimen.
  12. A hole is located over the stage, called the aperture. It pass the light rays. It also controls the density of light rays.
  13. Bright-fields microscope also contains two focusing knobs, called fine adjustment knob and the coarse adjustment knob. These knobs help to adjust the focus of objective lens.
  14. This microscope also contains a stage knob, which controls the stage.

Magnification of Bright-Field Microscope

The magnification power of a brightfield microscope can be calculated by ;

Total Magnification power = Magnification of the objective lens x Magnification of the eyepiece

Ex. The magnification power of an objective lens is 40x and 10x for the eyepiece, then the total magnification power of this bright-field microscope will be 40 x 10= 400x.

Application of Bright-Field Microscope

  1. Used in blood counting.
  2. Used to examine the bacterial cells.
  3. Used to examine the fungal cells.
  4. It also used in forensic laboratories.
  5. Used in agricultural laboratories.
  6. Used to study plant cells.

Advantages of Bright-Field Microscope

  1. It is easy to use.
  2. Low price.
  3. These are compact in size and easy to carry.
  4. Both stained and unstained specimens can be observed.

Disadvantages of Bright-Field Microscope

  1. Aperture diaphragm adds greater contrast which can create distortion.
  2. living specimens of bacteria can not be observed under a bright-fields Microscope.
  3. Most of the specimens required to be stained to visualize under this microscope, because of its low contrast.
  4. Distort images can be produced during the oil immersion.
  5. Specimens can be damaged by the uses of the coverslip.
  6. The bright-field microscope required a strong source of light to illuminate the specimen.

References

  • https://www.microscopemaster.com/brightfield-microscopy.html
  • https://en.wikipedia.org/wiki/Bright-field_microscopy
  • https://www.med.unc.edu/microscopy/files/2018/06/lm-ch-8-bright-field.pdf
  • https://www2.hawaii.edu/~johnb/micro/m140/syllabus/week/handouts/m140.2.4.html
  • https://www.rsc.org/publishing/journals/prospect/ontology.asp?id=CMO:0002529&MSID=C2LC21116E
  • https://science.umd.edu/CBMG/faculty/wolniak/wolniakmicro.html

Writer and Founder of Microbiologynote.com. I am from India and my main purpose is to provide you a strong understanding of Microbiology. Microbiologynote.com shares notes related to different branches of microbiology.

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