forensic microscopy i
TRANSCRIPT
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Chapter 7
Forensic microscopy
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Terms
Virtual image
Real image
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Physical properties of light
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Compound
microscopes
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Compound microscope terminology
Transmitted illumination (below)
Reflected illumination (above)
Condenser
Iris diaphragm Parfocal
Monocular
Binocular Depth of focus
Field of view
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Compound microscope
40-450x magnification (up to 1000x)
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Comparison
microscope
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Stereoscopic microscope
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Stereoscopic microscope
Most frequently used in
forensics
10-125x range Large working distance
Good for bulky artifacts
Wide field of view & great
depth of focus (3-D images) Trace evidence on artifacts
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Polarizing microscopy
Polarized light
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Polarizing microscope
Polarizer Analyzer
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Polarizing microscopy
Analyzer out of path =
plane polarized light;
gives specimens true
color Analyzer in path =
crossed polars; gives
specimens
interference color Polyester,plane-polarizedlight
Polyester,under crossed polars
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Polarizing microscopy
Improves specimen contrast
Stained plant fibers, left stained; right polarized
light
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Polarizing microscopy
Birefringence
Calcite produces two images when it is placed over the blue pencil. One of the
images appears normally as when viewing an object through clear glass. Theother pencil image appears displaced, due to the nature of doubly-refracted light.
When anisotropic crystals refract light, the resulting rays are polarized and travel
at different velocities. One of the rays travels with the same velocity in every
direction through the crystal and is termed the ordinary ray. The other ray travels
with a velocity that is dependent upon the structural properties of the crystal
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Polarizing microscopy
Many crystalline
substances are
birefringent Forensic analysis of
soil components
Many synthetic
fibers arebirefringent
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Microspectrophotometer
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Principles of spectroscopy
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Principles of spectroscopy
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Microspectrophotometer
Infrared spectromicroscopy
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Scanning electron microscopy
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Scanning electron microscopy
High magnification (up to 100,000x)
Excellent focal depth (3-D)
Used with X-ray analyzer (Fig 7-12), canidentify elemental composition of a
specimen Has a suspect fired a gun?
Pollen identification
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Online microscopy resources
Molecular expressions
Olympus Microscopy Resource Center
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For next class
Read chapter 7 Read chap. 7 Case Reading
Reading #1 (reading pack)