1. Forensic Science Ms. Urling
Microscopy (Chapter 5)
Forensic Science
Ms. Urling
SEM of Bed Bug

2. Types of Microscopes Magnifying Glass Compound Microscope
Comparison Microscope
Stereo Microscope
Polarized Light Microscope
Microspectrophotometer
Electron Microscope

3. Magnifying Glass: Simple Convex Lens
Wider in the middle
Bend (refract) light rays as they pass through the lens
Virtual Image (and larger image) forms on other side of the lens (further away from actual object)
Can only magnify up to about 50X
Used to observe fingerprints, soil, tool marks, etc.

4. Compound Lens Uses two convex lenses
If the first lens magnifies 10X and the second magnifies 40X, then the total magnification is 400X.
Virtual image is upside down

5. Compound Microscope Microscope made from two convex lenses
Used to observe dust, fibers, glass, hair, paint, etc.

6. Characteristics of Compound Microscopes
Magnification: # of times an object is magnified (10x, 20x, 400x, 10,000x, etc.)
Resolution: crispness (details) of an image
Field of View: amount of the object that is being viewed (inversely proportional to the magnification)
Depth of Focus: how far inside the object the image will be in focus

7. How to Use a Compound Microscope

8. Comparison Microscope
Consists of two compound microscopes mounted side by side
Allows two pieces of evidence to be compared side by side.
Evidence from crime scenes can be matched to suspects.
Can be used to match bullets, hairs, fibers, etc.

9. Stereo Microscope Also known as a dissecting microscope
Low magnification (25X – 50X)
Objects can easily be manipulated while viewing them (with forceps, needles, etc.)
Objects can be seen in three dimensions
Used to view marijuana, tools, etc.

10. Scanning Electron Microscope (SEM)
Lenses distort light and limit resolution to around 1000x.
Electrons (rather than light) can magnify images up to 200,000x.
Pollen SEM

11. The World’s Most Powerful Microscope