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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)