1. CHAPTER 7
THE MICROSCOPE

2. The microscope:
An optical instrument that uses a lens or a combination of lenses to magnify and resolve the fine details of an object.
An indispensable tool for the forensic scientist.
-One of the first tools used, yet still
used today.
Earliest & Simplest is a handheld magnifying glass. (5X – 10X)

3. What do you remember about a compound microscope?1) 2) 3) 4) 5) 6) 7) 8) 9)
10)
11)
12)
13) 1 13 12 5 10 11 9 4 2 8 3 7 6

4. What do you remember about a compound microscope?
1. ocular
2.Coarse adjustment knob
3. Fine adjustment knob
4. Stage clips
5. Arm
6. Base
7. Light source
8. Diaphragm
9. Stage
10. Low power objective
11. High power objective
12. Nosepiece
13. Body tube 1 13 12 5 10 11 9 4 2 8 3 7 6

5. Virtual image is not viewed directly but can only be observed when you look through the lens. A magnified or enlarged image.
Real image is seen directly, like the image that is projected onto a motion picture screen

6. The Compound Microscope
Utilizes transmitted light through a specimen – therefore specimens must be very thin.
Ocular lens is closest to the eye; Inscribed with its magnifying power (usually 10X)
Monocular: One eyepiece/ocular lens
Binocular: Two eyepieces/ocular lens

7. Total Magnification
Total magnification =
Mag. of objective lens X Mag. of ocular lens
What is the total magnification of the following microscopes?
10X ocular and 40X objective
= ____________
10X ocular and 10X objective

8. The area that is seen through the ocular of the microscope.
Field Of View
The area that is seen through the ocular of the microscope.
You can measure the field of view with a ruler if the area is big enough. If not, go by…
Low power = 2 mm
2000 um
High Power = 0.5 mm
500 um
(If different, values given)

9. Field of View Micrometers: 1/1000 of a millimeter
mm  um (micrometers/ microns) : mm x 1000
How big is the letter “e”?
The field of view is 2mm or 2000Um
There are 4 letter “e” in the field
Field of View/# of objects
Diameter “e” = 2000/4
500Um
2 mm

10. Field of View decreases as Magnification increases
Depth of Focus decreases As

11. Compound Microscope, cont.
Images appear enlarged, upside down and backwards (180 degree turn)
View under microscope view through lens
(not through lens)
Images move in opposite direction of the stage
A B.
To center the “e” you have to move the stage down in figure A. and to the left in figure B.

12. Comparison Microscope:
Two compound microscopes combined into one unit.
Two independent objective lenses joined by an optical bridge to a common eyepiece lens

13. Stereo/Dissecting Microscope
Utilizes reflected light
Can have magnification ranges from 10X – 125X
Produces a right-side-up
3-D image
Most frequently used and versatile microscope found in the crime laboratory.
-Wide field of view
-Great depth of focus

14. Stereo/Dissecting Microscope, cont.
Advantages…
*3-D image of an object that is right-side-up. (Unlike the compound microscope)
*Has a large working distance (the distance between the objective lens and the specimen)
*Useful for opaque objects, locating trace evidence.

15. Polarizing Microscope
Passes light through a polarizer which puts light waves in a single direction.
Polarized light passes through the specimen then through the analyzer, which sends it to the eyepiece.
This results in very vivid colors and contrasts that make a specimen very unique.
Is used on specimens that exhibit birefrigence as a physical property. Substances include…
*crystalline substances (minerals)
*synthetic fibers
*many plastics (cellophane)

17. Analyzer – a second polarizing crystal placed between a polarized beam
Polarizer – a device that permits the passage of light wave vibration in only one direction (plane).
Analyzer – a second polarizing crystal placed between a polarized beam
Analyzer is parallel to polarized beam =
light passes through
(when a specimen is observed)
Analyzer is perpendicular to polarized beam =
no light passes through
(this is when there’s no specimen)

19. Microspectrophotometer
Links a microscope to a computerized spectrophotometer
Allows the user to view a particle under the microscope while a beam of light is directed at the particle in order to obtain its absorption spectrum. take absorption and/or fluorescence measurements directly.

20. Uses: Paint, fiber and ink evidence
Comparison completed with the microscope, then the absorption spectra is determined at the same time.
Different inks/pigments will have a
different absorption pattern.
IR spectrophotometry will produce a unique ‘fingerprint’ for a substance (confirmation test).

21. Infrared absorption spectra

22. Scanning Electron Microscope (SEM)
SEM forms an image by aiming a beam of electrons, which is focused by means of magnets, onto the surface of a specimen.
This results in backscatter and the emission of secondary electrons from the surface elements of the specimen.
Has a magnifying range
From 10X to 100,000X.
Great depth of focus
(3-D)
Scanning Electron Microscope

23. Human hair (S.E.M.)

24. Head of a Termite (S.E.M.)

25. Spider (S.E.M.)

26. 146 X
S.E.M.
Sponge x400
392 X

27. Bacteria (T.E.M.)

28. Golgi Apparatus (T.E.M.)