1. Microscopes
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2. What is a microscope
Microscopes are instruments designed to produce magnified visual or photographic images of small objects. The microscope must accomplish three tasks:
produce a magnified image of the specimen
separate the details in the image
render the details visible to the human eye or camera
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3. Visualizing Cells

4. The history of the microscope
Light Microscopes have been used for four centuries. The word was first used for magnifying instruments in 1625
Many people experimented with making microscopes
The Greeks & Romans used “lenses” to magnify objects over 1000 years ago.
Hans and Zacharias Janssen of Holland in the 1590’s created the “first” compound microscope
Light microscopes can now magnify up to 1000x
The “First” Microscope
Zacharias Jansen
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5. History of the Microscope
Antoine van Leeuwenhoek
1st to see single-celled organisms in pond water
He called them “wee beasties”

6. History of the Microscope
1655 – Robert Hooke used a compound microscope to observe pores in cork
He called them “cells” because they reminded him of the monastery cubicles where the monks lived

7. The history of the microscope
Anthony van Leeuwenhoek and Robert Hooke made improvements by working on the lenses
Anthony van Leeuwenhoek
Robert Hooke
Robert Hooke published his microscope drawings in a book called Micrographia
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8. The history of the microscope
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9. A light microscope is also known as an optical microscope
Types of Microscopes
Light (Compound) Microscope
First type of microscope
Most widely used
Use reflected or transmitted light which is detected by the eye, or sometimes a camera.
Light passes through lenses to produce image
Lower magnifying power. Can magnify up to 2000x
A light microscope is also known as an optical microscope
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10. Types of Microscopes Stereoscopic Microscope
Gives a three dimensional view of an object. (Examples: insects and leaves)
Used for dissections
Used for viewing whole specimens
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11. Types of Microscopes Confocal Laser Scanning Microscope (CLSM)
A laser beam is used to illuminate spots on the specimen
A computer compiles images created from each point to generate a 3-dimensional image
Used on specimens that are too thick for a light microscope
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12. Types of Microscopes Electron Microscope
A beam of electrons passes through lenses to produce image
Detectors sense the interactions which create images of the sample
High magnifying power Used to observe VERY small objects: viruses, DNA, parts of cells.
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13. Introduction to Electron Microscopy
Electron Microscopes were not developed until the Twentieth Century
The first Transmission Electron Microscope (TEM) was built in 1932
An electron beam is directed at a very thin slice of specimen stained with metal ions
The heavily stained material absorbs electrons, but the lightly stained material allows the electrons to pass through
These electrons strike a fluorescent screen and create an image
Can magnify up to 250,000x
Transmission Electron Microscope

14. Introduction to Electron Microscopy
The first Scanning Electron Microscope (SEM) was built in 1942
The electron beam is focused on a specimen coated with a very thin layer of metal
The electrons that bounce off the specimen form an image on a fluorescent screen
The SEM shows three dimensional images of the surface
Can magnify up to 100,000x

15. Electron Micrographs Scanning electron microscope (SEM)
Transmission electron microscope (TEM)
Figure 4.1B

16. Electron Micrographs Scanning electron microscope (SEM)
Transmission electron microscope (TEM)
Figure 4.1B

17. Introduction to Electron Microscopy
The Scanning-Tunneling Microscope was developed in 1982.
A needle-like probe is used to measure differences in voltage caused by electrons that leak, or tunnel, from the surface of the object being viewed
A computer tracks the movement of the probe
The computer generates a three-dimensional image of the specimen’s surface
Objects as small as individual atoms can be viewed
Can be used to study living organisms

18. Light vs Electrons Electrons can be focussed using magnetic lenses
Shorter wavelength than visible light

19. The advantages of using electrons
Large depth of field
More of the sample is in focus at one time
Higher resolution
Smaller features can be imaged
Analysis
The electron beam interacts with the sample enabling information on composition to be collected using additional detectors

20. Parts of a compound microscope

21. How a Light Microscope Works
Convex Lenses are
curved glass used to make microscopes and glasses etc.
Convex Lenses bend
light and focus it in
one spot.

22. How the Microscope works Important Terms
Field of view - area of the specimen that can be seen through the microscope with a given objective lens
Magnification - product of the magnifying powers of the objective and eyepiece lenses. Increases the size
Resolution - the closest two objects can be before they're no longer detected as separate objects (usually measured in nanometers) The power to show detail
In the 1870s, a man named Ernst Abbe explained why the resolution of a microscope is limited. He said that since the microscope uses visible light and visible light has a set range of wavelengths. The microscope can't produce the image of an object that is smaller than the length of the light wave.
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23. RESOLUTION
The minimum distance two points can be apart and still be distinguished as two separate points

24. Depth of Field Focal Plane
Depth of field - vertical distance, from above to below the focal plane, that yields an acceptable image
Focal Plane
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25. Image quality
When you look at a specimen using a microscope, the quality of the image you see is assessed by the following:
Brightness - How light or dark is the image?
Focus - Is the image blurry or well-defined?
Resolution - How close can two points in the image be before they are no longer seen as two separate points?
Contrast - What is the difference in lighting between adjacent areas of the specimen?
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26. Brightness
Focus
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27. Resolution
Contrast
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28. Parts of a microscope

29. Ocular Lens Eyepiece Arm Base
Used to support the microscope when carried. Holds the body tube, nose piece and objective lenses
Base
Magnifies the specimen image
Supports the microscope

30. Objective Lenses Nose Piece Body Tube
The body tube holds the objective lenses and the ocular lens at the proper distance
The Nose Piece holds the objective lenses and can be turned to change the lens
The Objective Lenses increase magnification (usually from 10x to 40x)

31. Diaphragm Light Source Turn to let more light in or to make dimmer.
Projects light upwards through the diaphragm, the specimen and the lenses
Some have lights, others have mirrors where you must move the mirror to reflect light
Diaphragm
Turn to let more light in or to make dimmer.
Light Source
The Diaphragm controls the amount of light on the slide/specimen

32. Stage Coarse Adjustment Knob FINE ADJUSTMENT KNOB
Moves the stage up and down (quickly) for focusing your image
Supports the slide/specimen
FINE ADJUSTMENT KNOB
This knob moves the stage SLIGHTLY to sharpen the image

33. Magnification Ocular lenses usually magnifies by 10x
To determine your magnification…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.

34. 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

35. Carry a Microscope Correctly

36. 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

37. Electron Micrographs

38. The Scanning Electron Microscope
produces a 3-dimensional image of specimen’s surface features
spider
head of a butterfly

39. Transmission electron microscope
Chloroplast from a tobacco leaf
H1N1 virus

40. THE END