imp.part of microbiology laboratory for detecting the microorganism.

1. LIGHT MICROSCOPE
BY-: Abhishek Singh
Medical Microbiology

2. INTRODUCTION and history
The optical microscope, often referred to as the
"light microscope", is a type of microscope which
uses visible light and a system of lenses to magnify
images of small samples.
In 1590 F.H Janssen & Z.Janssen constructed the
first simple compound light microscope.
In 1665 Robert Hooke developed a first laboratory
compound microscope.
Later, Kepler and galileo developed a modern
classroom microscope.
In 1672 Leeuwenhoek developed a first simple
microscope with a magnification of 200x -300x.
He is called as Father of microscopy.
The term microscope was coined by Faber in
1623.

3. Light MICROSCOPE

4. Parts of light microscope
 Illuminator - This is the light source located below the specimen.
 Condenser - Focuses the ray of light through the specimen.
 Stage - The fixed stage is a horizontal platform that holds the specimen.
 Objective - The lens that is directly above the stage.
 Nosepiece - The portion of the body that holds the objectives over the stage.
 Iris diaphragm - Regulates the amount of light into the condenser.
 Base – Base supports the microscope which is horseshoe shaped.
 Coarse focusing knob - Used to make relatively wide focusing adjustments to the microscope.
 Fine focusing knob - Used to make relatively small adjustments to the microscope.
 Ocular eyepiece - Lens on the top of the body tube. It has a magnification of 10× normal vision.

5. Principle of light microscope
 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 eyepiece.
 The condenser is used to focus light on the specimen through an
opening in the stage.
 After passing through the specimen the light is displayed to the eye
with an apparent field that is much longer then the area of
illumination.

6. Light Microscope Resolution
 Ability of a lens to separate or distinguish small objects that are
close together
 Wavelength of light used is major factor in resolution
 Increase in size (greater magnification) without the ability to
distinguish structural details(greater resolution) is not beneficial
shorter wavelength  greater resolution

7. limits of resolution
 The resolving power of human eye is 0.25 mm
 The light microscope can separate dots that are 0.25µm apart.
 The electron microscope can separate dots that are 0.5nm apart.

8. Numerical aperture
The numerical aperture of a lens is the ratio of the diameter of the lens
to its focal length.
NA of a lens is an index of the resolving power.
NA can be decreased by decreasing the amount of light that passes
through a lens.
Diameter of the lens

9. magnification of light microscope
 It is the ratio of the size of an object seen under microscope to the
actual size observed with unaided eye.
 The total magnification of microscope is calculated by multiplying the
magnifying power of the objective lens by that of eye piece

10. The Concept of Magnification
Magnification of the Microscope
M Microscope = M Objective X M Eyepiece X M Intermediate Factor
M = Magnification
Example: Objective = 60 x
Eyepiece = 10 x
Intermediate Factor = 1 x
Overall M = 600 x

11. PROPERTY LOW POWER HIGH POWER OIL IMMERSION
Magnification of
objective
10x 40-45x 90-100x
Magnification of
eyepiece
10x 10x 10x
Total magnification 100x 450 – 450x 900 – 1000x

12. The effects of immersion oil on resolution

13. Images of light microscope
Baccili and cocci under light
microscope

14. Care of the microscope
 Hold a microscope firmly by the stand, only. Never grab it by the eyepiece holder.
 Hold the microscope by arm and stage.
 Since bulbs are expensive, and have a limited life, turn the illuminator off when you are
done.
 Always make sure the stage and lenses are clean before putting away the microscope.
 NEVER use a paper towel or any material other than good quality lens tissue or a cotton
swab (must be 100% natural cotton) to clean an optical surface.
 Use an appropriate lens cleaner or distilled water to help remove dried material. Organic
solvents may separate or damage the lens elements or coatings.
 Cover the instrument with a dust jacket when not in use.
 Focus smoothly; don't try to speed through the focusing process or force anything.