A **bright field microscope** is a type of compound light microscope that illuminates the background against a stained specimen ¹². It is commonly used in practical labs to study organisms' behavior and characteristics such as size, shape, and arrangement ². The microscope uses light rays to produce a dark image against a bright background ¹. It is specially designed with magnifying glasses known as lenses that modify the specimen to produce an image seen through the eyepiece ¹. The bright field microscope is made up of various parts, including the eyepiece, objective lenses, focusing knobs, and stage ¹. I hope this helps! Source: Conversation with Bing, 7/11/2023 (1) Brightfield Microscope (Compound Light Microscope)- Definition .... https://microbenotes.com/brightfield-microscope/. (2) Bright Field Microscopy - Biology Reader. https://biologyreader.com/bright-field-microscopy.html. (3) Bright-field microscopy - Wikipedia. https://en.wikipedia.org/wiki/Bright-field_microscopy. (4) Bright Field Microscope: Definition, Parts, Working Principle, Application. https://microbiologynote.com/bright-field-microscope-definition-parts-working-principle-application/.

1. Topic: PRINCIPLE AND APPLICATIONS OF
BRIGHT FIELD MICROSCOPE
BY
AHALYA.S
M.Sc(Ag)Microbiology

2. MICROSCOPE
MICROSCOPE :
Microscope is an optical instrument that uses a lens or a combination of
lenses to produce highly magnified images of small specimens especially which are too
small to be seen by the naked eye.
Light source is either mirror(natural light) or lamps.
MICROSCOPY:
Microscopy is the technical field of using microscope or investigation by a
microscope.

3. HISTORY OF MICROSCOPE
● Hans and zacharias Janssen - 1590
First compound microscope (2 lenses),tube
with lenses at each end.
● Anton van Leeuwenhoek -1670
Simple microscope(1 lenses)
Father of microbiology
● Robert Hooke - 1667
Compound microscope improvement with
2 lenses - objective & ocular lenses.

4. CLASSIFICATION OF MICROSCOPE
MICROSCOPE
SIMPLE MICROSCOPE COMPOUND MICROSCOPE
LIGHT MICROSCOPE ELECTRON MICROSCOPE
BRIGHT FIELD DARK FIELD FLUORESCENCE PHASE CONFOCAL SCANNING TRANSMISSION
MICROSCOPE MICROSCOPE MICROSCOPE CONTRAST MICROSCOPE ELECTRON ELECTRON
MICROSCOPE MICROSCOPE MICROSCOPE

5. PARTS OF MICROSCOPE

6. PARTS OF MICROSCOPE
OPTICAL COMPONENTS :
o Eyepiece or Ocular Lenses is what you look through at the top of the microscope.
Typically, standard eyepieces have a magnifying power of 10x. Optional eyepieces of
varying powers are available, typically from 5x-30x.
o Objective Lenses are the primary optical lenses on a microscope. They range from
4x-100x and typically, include, three, four or five on lens on most microscopes.
Objective lenses can be forward or rear-facing. Standard objectives include 10x, 40x
and 100x although different power objectives are available.
o Condenser Lens is used to collect and focus the light from the illuminator on to the
specimen. It is located under the stage often in conjunction with an iris diaphragm.

7. PARTS OF MICROSCOPE
MECHANICAL COMPONENTS:
● Head/Body - houses the optical parts in the upper part of the microscope.
● Base - supports the microscope and houses the illuminator.
● Arm - connects to the base and supports the microscope head. It is also used to carry
the microscope.
● Eyepiece Tube holds the eyepieces in place above the objective lens.
● Nosepiece houses the objective lenses.. The objectives are exposed and are mounted
on a rotating turret so that different objectives can be conveniently selected.

8. PARTS OF MICROSCOPE
● Coarse (wide focus) and Fine Focus knobs (sharp & fine focus) are used to
focus the microscope.
● Specimen Stage is where the specimen to be viewed is placed. A mechanical
stage is used when working at higher magnifications where delicate movements
of the specimen slide are required.
● Stage Clips are used when there is no mechanical stage. The viewer is required
to move the slide manually to view different sections of the specimen.
● Aperture is the hole in the stage through which the base (transmitted) light reaches
the stage.

9. PARTS OF MICROSCOPE
● Illuminator is the light source for a microscope, typically located in the base of the
microscope. Most light microscopes use low voltage, halogen bulbs with continuous
variable lighting control located within the base.
● Iris Diaphragm controls the amount of light reaching the specimen. It is located
above the condenser and below the stage.
● Light Switch present at bottom of right side of microscope to switch on/off the
light source(illuminator).
● Brightness Adjustment helps to adjust the brightness of light that comes out from
the illuminator.

10. SIMPLE MICROSCOPE. COMPOUND MICROSCOPE

11. SIMPLE MICROSCOPE. COMPOUND MICROSCOPE
● Invented by Anton van Leeuwenhoek
in 1670.
● Structure : Stand is small, hollow
cylindrical attached to base is used to
hold the microscope.
● Contain single eyepiece. Total
magnification is limited to ocular lens
magnification.
● Light source is natural light.
● Mirror - concave which helps in
reflection of light.
● No condenser lenses.
● Magnification power up to 300x.
● adjustment of magnification is not
available.
● Used for study of microscopic
fungi,algae.
● Invented by Hans and Zacharias
Janssen in 1590.
● Structure : arm is curved used to hold
the microscope.
● Contains either single or double
eyepiece - ocular lens & objective lens.
● Total magnification is eyepiece*obj lens.
● Light source - natural light or
illuminator.
● Mirror - plane at one side & concave at
other side.
● Condenser lens present which adjust the
intensity of light
● Magnification power up to 2000x.
● Adjustment of magnification by 3 obj
lenses 10x,40x,100x.
● Used for study of morphology of
bacteria & other microbes.

12. LIGHT MICROSCOPE
● A Llight microscope uses focused light and lenses to magnify a specimen, usually a
CellS, microorganisms.
● Also known as OPTICAL MICROSCOPE.
● Highest practical magnification is 4000x.
● best resolution 0.2 micrometer.
● Illuminating source: visible light wavelength of 450nm - 750nm.
ADVANTAGES:
● Easy to use.
● Low cost when compared to others.
● Live specimens can be studied.
● Shows true colours but sometimes stains required.

13. DISADVANTAGES :
● Low resolution due to shorter wavelength of light.
● Low magnification.
TYPES OF LIGHT MICROSCOPE
● Bright field microscope
● Dark field microscope
● Phase contrast microscope
● Fluorescence microscope
● Confocal microscope

14. MAGNIFICATION
● Magnification is the enlargement of the image.
● Light microscope in schools & colleges can magnify 400 times than actual
size.
● MMICROSCOPE = MOCULAR LENS * MOBJECTIVE LENS
MAGNIFICATION
OF OBJ LENS
MAGNIFICATION OF
OCULAR LENS
TOTAL
MAGNIFICATION
SCANNING 4x 10x 40x
LOW POWER 10x 10x 100x
HIGH POWER 40x 10x 400x
OIL IMMERSION 100x 10x 1000x

15. APPROPRIATE MAGNIFICATION
SAMPLE
 Stained – bacteria
 Thick tissue sections
 Blood smears
 Negative stained bacteria
 Algae and other microscope plant
material
MAGNIFICATION
 1000x
 100x , 400x
 400x , 1000x
 400x , 1000x
 40x , 100x , 400x

16. RESOLVING POWER
RESOLUTION / RESOLVING POWER :
● Resolution is the ability of lenses to distinguish fine detail and structure of the
specimens.(distance between two points as separate entities)
● Human eye resolution is 0.2 mm.
● Rmicroscope > Rhuman eye .
● d = wavelength of light(λ)
2×Numerical Aperture
● d = λ
2 n sinα
 Smaller the d, greater the Resolution.
 Shorter the wavelength of light(λ) used, greater the resolution.
 Lenses with higher numerical aperture(α) provide better resolving power.
 Greater the refractive index(n) , higher the resolution.

17. NUMERICAL APERTURE
● Number represents the angle of light produced by refraction & is the measure of
quantity of light gathered by lens.
● Mathematical constant derived from Physical structure of lenses.
● Each objective lens has fixed numerical aperture reading ranging from 0.1 in lowest
power lens(10x) to approximately 1.25 in highest power lens(100x).
WAVELENTGH :
● Wavelength is the actual distance between the two successive crests or troughs of a
wave.
● Visible light wavelength : VIBGYOR (300nm – 700nm).
REFRACTIVE INDEX :
● Refractive index of air = 1.003
● Refractive index of water = 1.33
● Refractive index of oil = 1.51(higher magnification)

18. BRIGHT FIELD MICROSCOPE
● Bright field microscope are named because the microscope field is bright
while the object being viewed is black (dark sample on a bright
background).
● Used to observe various stained specimens, naturally pigmented
specimens and to count microbes.
● In bright field microscopy, the sample illumination is transmitted white light
and contrast in sample is caused by absorbance of some of the transmitted
light in dense areas of the sample and this contrast allows us to see the
specimens.
● High contrast sample.

19. PRINCIPLE

20. PRINCIPLE
● It has a series of two lenses:
● The OBJECTIVES LENS close to the object to be observed
● The OCULAR LENS or EYEPIECE, through which the image is viewed by
eye.
● Light from the light source (electric lamp) passes through a thin transparent object.
● The objective lens produce a magnified “REAL IMAGE” (1st image) of the object.
This image is again magnified by the ocular lens ( eyepiece) to obtain a magnified
“VIRTUAL IMAGE” (final image), which can be seen by eye through the eyepiece.
● As light passes directly from the source to the eye through the two lenses, the field of
vision is brightly illuminated. That is why : it is a BRIGHT – FIELD
MICROSCOPE.

21. SPECIMENS

22. ADVANTAGES OF BRIGHT FIELD MICROSCOPE
 Shows the morphological as well as the internal structure of the specimen.
 Less expensive than dark field microscope.
 Stained, fixed and live specimens are observed.
 Specimen colour appears depending on the stain colour.
 Easy to use.
DISADVANTAGES:
 Does not allow us to observe the metal and minerals.
 Specimen preparation or staining is a complex and lengthy process. Takes too much
time.
 Opaque disc is absent.
 Does not resolve very small specimens, such as viruses.
 Requires a strong light source for high magnification applications and intense lighting
can produce heat that will damage specimens or kill living microorganisms.

23. APPLICATIONS
 Widely use in pathology to view fixed tissue sections or cell films/smears.
 Important for hematology, microbiology, Tb and malaria testing.
 Microscope magnifies the blood samples, so, the doctor can see the malaria
parasites attacking the red blood cells.
 Used in bacteriology, biology and medicine to examine minute objects such
as bacteria, other unicellular organisms and plant cell , animal cells and
tissues.
 Advances in fluorochrome stains and monoclonal antibody techniques
caused grow in use of analysis and cell biology.

24. APPLICATIONS