1. Ch 7 – The Microscope Compound microscope.
Magnification, field of view, working distance, and depth of focus.
Comparison microscope.
Advantages of stereoscopic microscope.
Plane-polarized light and polarizing microscope.
Advantages of linking a microscope to a spectrophotometer.

2. Utilizing a microspectrophotometer for examining trace physical evidence.
Mechanism of image formation for light microscope Vs scanning electron microscope (SEM).
Advantages and applications of SEM in forensic science.

3. Virtual image: an image cannot be seen directly
Virtual image: an image cannot be seen directly. It can only be seen by a viewer looking through a lens.
Real image: an image formed by the actual convergence of light rays upon a screen
 Objective lens: the lower lens of a microscope that is positioned directly over the specimen
 Eyepiece lens: the lens of a microscope into which the viewer looks; same as the ocular lens

4. Transmitted illumination: light that passes up from the condenser and though the specimen
Vertical or reflected illumination: illumination of a specimen from above; in microscopy it is used to examine opaque specimens
 Condenser: lens system located under the microscope stage that focuses light onto the specimen

5. Parfocal: construction of a microscope such that when an image is focused with one objective in position, the other objective can be rotated into place and the field will remain in focus
 Monocular: a microscope with one eyepiece
 Binocular: a microscope with two eyepieces
 Field of view: the area of the specimen that can be seen after it is magnified

6. Depth of Focus: the thickness of a specimen entirely in focus under a microscope
Plane-Polarized light: light confined to a single place of vibration
 Polarizer: a device that permits the passage of light waves vibrating in only one plane
 Microspectrophotometer: an instrument that links a microscope to a spectrometer

7. Compound Microscope

8. Comparison Microscope

9. Polarizing Microscope

10. Stereoscopic Microscope
Cell division in a frog's egg.

11. Microspectrophotometer

12. Scanning Electron Microscope (SEM)

13. SEM Data Nanoscaled polyimide structures
Side-wall morphology of solar cell gridline

14. Viewing small Specimens
Ch. 7 - Microscopy
Viewing small Specimens

15. The Microscope Provides a direct image of a small object of interest
spectroscopy gives an abstract representation which must be interpreted on the basis of a model or some assumptions
A typical animal cell is nm in diameter
5x smaller than the smallest object that can be seen directly by the naked eye

16. The Microscope Produce a magnified image of a specimen
Separate the details in the image
Render the details visible to the human eye or camera

17. Lenses
Refraction of a light ray as it passes through a prism

18. Lenses
Light passing through two “identical” prisms stacked base to base would intersect at point I
produce a real image
converging lens

19. Focal Point & Focal Length
The point at which parallel rays are converged to an image is the focal point of the lens
The distance of this point from the lens is the focal length

20. Simple Magnifier Object O is placed close to the lens
rays converge but do not intersect
real image not formed
The observer’s eye follows rays back to the point of apparent origin (I)
I bigger than object

21. The Compound Microscope
Rays pass first through the objective lens forming a real, slightly enlarged, inverted image
The second lens (eyepiece) acts as a simple magnifier

22. Compound Microscope Both lenses produce magnification
Overall magnification is found by multiplying the two magnifications
Magnification determined mainly by objective

24. The Comparison Microscope
Two compound microscopes combined into one unit
When viewer looks through the eyepiece, a field divided into two equal parts is observed
specimen on left scope on left side of field
specimen on right scope on right side of field

25. The Comparison Microscope
Bullet comparisons
Hair & Fiber comparisons
Questioned documents

26. Test Fire Reference Gun

27. Use A Comparison Microscope

29. Striations match

30. Stereoscopic Microscope
Two separate monocular microscopes
Each has its own set of lenses

31. Stereoscopic Microscope
Using the Stereo Microscope
Using the Compound
Microscope

32. FT-IR Microspectrophotometer

33. Photocopier Toner Analysis
important for establishing corroborative evidence linking documents to specific locations in forensic investigations of corporate crime
Must be performed non-destructively
can’t remove toner from paper
physical size of specimen is very small
microscope to find sample
FT-IR to analyze the sample

34. Photocopier Toner Analysis

35. Limitations of Light Microscope
Radiation of a given wavelength can’t be used to probe structural details much smaller than its own wavelength
Light Microscope
limited to range of visible light
0.4 mm (violet) to 0.7 mm (deep red)
bacteria & nitochondria (~0.5mm wide) smallest objects that can be seen clearly

36. Range of Readily Resolvable Objects

37. Scanning Electron Microscope
This scanning electron microscope has a magnification range from 15x to 200,000x and a resolution of 5 nanometers

38. How the SEM Works

39. Conventional light microscopes use a series of glass lenses
to bend light waves and create a magnified image.

40. The Scanning Electron Microscope creates the magnified images by using electrons instead of light waves

41. The SEM shows very detailed 3-dimensional images at much higher magnifications than is possible with a light
microscope. The images created without light waves are rendered black and white

47. Samples have to be prepared carefully to withstand the vacuum inside the microscope

48. Biological specimens are dried in a special manner that prevents them from shriveling.
Because the SEM illuminates them with electrons, they also have to be made to conduct electricity

49. How do you make a mosquito conductive?
SEM samples are coated with a very thin layer of gold by a machine called a sputter coater

50. The specimen is now prepared

51. The sample is placed inside the microscope's vacuum column through an air-tight door

52. Air is pumped out of the column
An electron gun [at the top] emits a beam of high energy electrons.
travels downward through a series of magnetic lenses designed to focus the electrons to a very fine spot

53. Near the bottom, a set of scanning coils moves the focused beam back and forth across the specimen, row by row

54. As the electron beam hits each spot on the sample, secondary electrons are knocked loose from its surface.
A detector counts these electrons and sends the signals to an amplifier

55. The final image is built up from the number of electrons emitted from each spot on the sample

58. Fiber Analysis

59. Energy-Dispersive X-Ray Analysis (EDX)
Electron beam ~5,000-20,000eV
Atomic electrons are dislodged ionizing the sample
Resulting electron vacancy filled by an electron from a g=higher shell
X-ray is produced
x-ray energy characteristic of the parent atom

60. Gunshot Residue by EDX
Residue particle from the hand of a person who fired a .380 Browning automatic
The peaks of lead, barium & antimony together with the shape of the particle are quite specific & show that the subject had fired a weapon

61. I’m a louse fly of a wallglider (an alpine bird)
Who am I?
I’m a louse fly of a wallglider (an alpine bird)