MICROSCOPES

1. Microscopes

2. • Microscope meaning.
• Mikros=small.
• Skopein=to see/to look.

3. History of the Microscope
•1590 –first compound
microscope

4. History of the Microscope
•1655 – Robert Hooke used
a compound microscope
to observe pores in cork
–He called them “cells”

6. History of the Microscope
•Antoine van Leeuwenhoek
–1st to see single-celled
organisms in pond water

7. Microscope Vocabulary
• Magnification: increase of an
object’s apparent size
• Resolution: power to show details
clearly and separately
• Numerical aperture:light
gathering capacity of a lens.

8. 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

9. Numerical aperture(NA)
• Light gathering capacity of a lenses
with higher NA will be able to image
finer details than a lenses with lower
NA.
• This help to collect light
• Give bright image

11. Types of microscopes
Light
microscope
Bright field
microscope
1.Simple
microscope
Compound
light
microscope
Dark field
microscope
Fluorescence
microscope
Phase
contrast
microscope

12. Electron
microscope
Transmission
electron
microscope
Scanning
electron
microscope
Scanning
transmission
electron
microscope
Scanning tunnel
microscope

13. The Light Microscope
• many types
– bright-field microscope
– dark-field microscope
– phase-contrast microscope
– fluorescence microscopes

14. Simple microscope
• Used to distinguish extremely minute
objects less than 0.1 mm.
• Consist of simple convex lens .
• Magnification: only less than 3 times
the size of object.
• Due to distortion of colour ,form and
contrast.

16. Compound microscope
• Bright field microscope.
• Used to obtain both magnified and
resolved view of objects.
• Use visible light as a source of
illumination.
• Have mechanical & optical components.
• Mechanical components :-
• Strong base ,pillar, arm or limb,
indination joint, body tube, resolving
nose piece,drawtube

17. • Stage or platform,stageclip,iris
diaphram,corse adjustment,fine
adjustment.
• Optical components:-
• Source of light for illumination of
object,planoconcave mirror,substage
condencer lens,objective lens,ocular
lens or eye piece.

20. dark-field microscope/ultra
microscope
• produces a illuminated image against a dark
background.
• Used to improve the visibility and resolution .
• Used to observe transparent and semi
transparent objects which is not clearly visible
at bright background.
• Ordinary light microscope can transform to
dark field microscope by replacing condenser
with dark field or with an opaque object.

21. The Phase-Contrast Microscope
• enhances the contrast between
intracellular structures having slight
differences in refractive index
• excellent way to observe unstained
living cells
• 2 types namely dark or positive & light
or negative phase contrast.

22. • Principle:- small phase changes or
phase difference in light rays,induced
by difference in thickness and refractive
index of the different parts of an object
can be transformed to difference in
brightness of light indensity.

23. The Fluorescence Microscope
• exposes specimen to ultraviolet, violet,
or blue light
• specimens usually stained with
fluorochromes
• shows a bright image of the object
resulting from the fluorescent light
emitted by the specimen

24. • Work based on the phenomenon of
flouresence.
• Substance emmit flouresence is called
flurophore.
• The change in wave length to that of
visible light is called stoke’s effect.
• Useful in testing the chemical nature of
objects & also locating cellular
components based on chemical nature.

25. 2. Electron Microscope
–Used to observe VERY small
objects: viruses, DNA, parts
of cells
–Uses beams of electrons
rather than light
–Much more powerful

26. Electron Microscopy
• First EM made by knoll and ruska in
1928
• Used to examine objects less than 1mu
or below.
beams of electrons are used to produce
images
• wavelength of electron beam is much
shorter than light, resulting in much
higher resolution

27. • Magnification up to 50,00,000 times
and resolution up to 2 to 5 A.
• Two types of EM
• SEM, TEM
• SEM:-electrons are scattered or
reflacted back from the object.
• TEM:- electrons are transmitted through
the object

28. Types of Microscopes
•Transmission Electron
Microscope (TEM)
–Can magnify up to
250,000x

31. Types of Microscopes
•Scanning Electron
Microscope (SEM)
–Can magnify up to
100,000x

32. The Scanning Electron Microscope
• uses electrons reflected from the
surface of a specimen to create image
• produces a 3-dimensional image of
specimen’s surface features
• Image displaed on screen
• Image resembles image in hand lens
but it has much finer resolution

35. The Transmission Electron
Microscope
• electrons scatter when they pass
through thin sections of a specimen
• transmitted electrons (those that do not
scatter) are used to produce image
• denser regions in specimen, scatter
more electrons and appear darker
• The sourse of electron is cathod called
electron gun.

36. SCANNING TRANSMISSION
EM(STEM)
• Combination of stem and tem
• Specimen is scanned much as in sem using
secondary electrons
• Transmitted primary electrons used to produce
picture on flouresence screen or photograhic film of
tem.

37. SCANNING TUNNELING
MICROSCOPE (STM)
• Based on the principle of electtron
tunneling
• Enables visualisation of individual
atoms.
• Used to produce images of DNA
,proteins etc..
• Disadvantage:- the specimen must be
electron conducter ,or materials have to
be stained with heavy metals.

38. • atomic force microscope
• Modified version of STM
• High resolution scanning microscope
useful in molecular biology and
nanotechnology.
• Do not depend on current.
• Used to observe both electrical and non
electrical conducters
• Cannot be used to view biological
samples.