The document provides an overview of microscopes, including: 1) The history of microscopes from early compound microscopes developed in the 1590s to improvements made by Antony van Leeuwenhoek and Robert Hooke that increased magnification. 2) How microscopes work using convex lenses, with light being focused and magnified through an objective lens and further magnified through an ocular lens. 3) Different types of microscopes including brightfield, darkfield, phase contrast, and fluorescent microscopes and how they produce images.

1. MICROBIOLOGY
TOPIC :MICROSCOPE
PRESENTED BY:MISS TASMIA ZEB

2. THE HISTORY
 Many people experimented with making
microscopes
 Was the microscope originally made by
accident? (Most people were creating
telescopes)
 The first microscope was 6 feet long!!!
 The Greeks & Romans used “lenses” to
magnify objects over 1000 years ago.
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3. THE HISTORY
Hans and Zacharias Janssen of Holland
in the 1590’s created the “first”
compound microscope
Anthony van Leeuwenhoek and Robert
Hooke made improvements by working
on the lenses
Anthony van Leeuwenhoek
1632-1723
Robert Hooke
1635-1703
Hooke Microscope
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4. ANTIONI VAN LEEUWENHOEK
• Leeuwenhoek is
called "the inventor
of the microscope"
• Created a “simple”
microscope that could
magnify to about 275x, and
published drawings of
microorganisms in 1683
• Could reach magnification
of over 200x with simple
ground lenses
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5. HOW A MICROSCOPE WORKS
Convex Lenses are
curved glass used to
make microscopes
(and glasses etc.)
Convex Lenses bend
light and focus it in
one spot.
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6. HOW A MICROSCOPE WORKS WITH..
Ocular Lens
(Magnifies Image)
Objective Lens
(Gathers Light,
Magnifies
And Focuses Image
Inside Body Tube)Body Tube
(Image Focuses)
•Bending Light: The objective (bottom) convex lens
magnifies and focuses (bends) the image inside the
body tube and the ocular convex (top) lens of a
microscope magnifies it (again). 6

7. INTRODUCTION
A microscope is an optical instrument that
uses a lens or a combination of lenses to
magnify and resolve the fine details of an
object.
The magnified image seen by looking
through a lens is known as a virtual image,
whereas an image viewed directly is known
as a real image.
The object to be magnified is placed under
the lower lens, called the objective and
viewed through the upper lens, called the
eyepiece. 7

8. DEFINITIONS
 Absorption
When light passes through an object the intensity is reduced
depending upon the color absorbed. Thus the selective absorption of
white light produces colored light.
 Refraction
Direction change of a ray of light passing from one transparent
medium to another with different optical density. A ray from less to
more dense medium is bent perpendicular to the surface, with
greater deviation for shorter wavelengths
 Diffraction
Light rays bend around edges - new wavefronts are generated at
sharp edges - the smaller the aperture the lower the definition
 Dispersion
Separation of light into its constituent wavelengths when entering a
transparent medium - the change of refractive index with
wavelength, such as the spectrum produced by a prism or a rainbow
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9. REFRACTION
Light is “bent” and the resultant colors separate (dispersio
Red is least refracted, violet most refracted.
Short wavelengths are
“bent” more than long
wavelengths
dispersion
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10. REFRACTION & DISPERSION
Light is “bent” and the resultant colors separate (dispersion).
Red is least refracted, violet most refracted.
dispersion
Short wavelengths are “bent”
more than long wavelengths
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11. BECAUSE OF REFRACTION WE CANNOT
SOMETHING IN WATER
SHOOT
.
But it is really here!!
He sees the
fish here….
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12. LENSES AND THE BENDING
OF LIGHT
light is refracted (bent) when passing
from one medium to another
refractive index
a measure of how greatly a substance
slows the velocity of light
direction and magnitude of bending is
determined by the refractive indexes of
the two media forming the interface 12

13. LENSES
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 focus light rays at a
specific place called
the focal point
 distance between
center of lens and focal
point is the focal length
 strength of lens related
to focal length
short focal length
more magnification

14. THE LIGHT MICROSCOPE
many types
bright-field microscope
dark-field microscope
phase-contrast microscope
fluorescence microscopes
 compound microscopes
image formed by action of 2
lenses
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15. COMPOUND MICROSCOPES
In compound
microscopes
image formed
by action of
2 lenses

16. THE COMPOUND MICROSCOPE
The Optical System
Objective Lens: the lens closest to the specimen;
usually several objectives are mounted on a
revolving nosepiece.
Parafocal: when the microscope is focused with one
objective in place, another objective can be rotated into
place and the specimen remains very nearly in correct
focus.
Eyepiece or Ocular Lens: the lens closest to the
eye.
Monocular: a microscope having only one eyepiece
Binocular: a microscope having two eyepieces.
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17. DARK FIELD MICROSCOPE

18. PRINCIPLES OF PHASE CONTRAST
MICROSCOPE

19. FLUORESCENT MICROSCOPE
Dichroic Filter
Objective
Arc Lamp
Emission Filter
Excitation Diaphragm
Excitation Filter
Ocular
EPI-Illumination
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20. THE BRIGHT-FIELD MICROSCOPE
produces a dark image against a
brighter background
has several objective lenses
parfocal microscopes remain in
focus when objectives are changed
total magnification
product of the magnifications of the
ocular lens and the objective lens
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21. Eyepiece
Body Tube
Revolving Nosepiece
Objective Lens
Arm
Stage
Coarse Focus
Fine Focus
Stage
Clips
Diaphragm
Light
Base
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22. BINOCULAR MICROSCOPE
 Schematic diagram of
a stereoscopic
microscope. This
microscope is
actually two separate
monocular
microscopes, each
with its own set of
lenses except for the
lowest objective lens,
which is common to
both microscopes.

23. 31
The principle of the compound microscope. The passage of light through two
lenses forms the virtual image of the object seen by the eye.

24. MAGNIFICATION
 An object can be focused generally no closer
than 250 mm from the eye (depending upon
how old you are!)
 this is considered to be the normal viewing
distance for 1x magnification
 Young people may be able to focus as close
as 125 mm so they can magnify as much as
2x because the image covers a larger part of
the retina - that is it is “magnified” at the place
where the image is formed
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25. MAGNIFICATION
 To determine your magnification…you just multiply
the ocular lens by the objective lens
 Ocular 10x Objective 40x:10 x 40 = 400
Ocular lenses usually magnifies by 10x
So the object is 400 times “larger”
Objective Lens have
their magnification
written on them.
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26. 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
shorter wavelength
greater resolution

27. OBJECTIVES
Limit for smallest
resolvable distance d
between 2 points is
(Rayleigh criterion):
d = 1.22
This defines a “resel” or “resolution element”
Thus high NUMERICALAPERTUREis
critical for high magnification
In a medium of refractive index n the
wavelength gets shorter: n
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28. NUMERICAL APERTURE
 Resolving power is directly related to numerical
aperture.
 The higher the NA the greater the resolution
 Resolving power:
The ability of an objective to resolve two distinct lines very
close together
NA = n sin u
(n=the lowest refractive index between the object and first
objective element) (hopefully 1)
u is 1/2 the angular aperture of the objective 38

29. NUMERICAL APERTURE
A
Light cone
NA=n(sin )
(n=refractive index)
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30. OIL IMMERSION INCREASES
MAGNIFICATION
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31. CARING FOR A MICROSCOPE
 Clean only with a soft
cloth/tissue
 Make sure it’s on a flat
surface
 Don’t bang it
 Carry it with 2
HANDS…one on the
arm and the other on
the base

32. CARRY A MICROSCOPE
CORRECTLY
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33. USING A MICROSCOPE
Start on the lowest magnification
Don’t use the coarse adjustment knob
on high magnification…you’ll break the
slide!!!
Place slide on stage and lock clips
Adjust light source (if it’s a
mirror…don’t stand in front of it!)
Use fine adjustment to focus
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34. THANK YOU