1. Chapter 7 Forensic microscopy

2. Terms Virtual image Real image

3. Physical properties of light

4. Compound microscopes

5. Compound microscope terminology Transmitted illumination (below) Reflected illumination (above) Condenser Iris diaphragm Parfocal Monocular Binocular Depth of focus Field of view

6. Compound microscope 40-450x magnification (up to 1000x)

7. Comparison microscope

8. Stereoscopic microscope

9. 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

10. Polarizing microscopy Polarized light

11. Polarizing microscope Polarizer Analyzer

12. Polarizing microscopy Analyzer out of path = plane polarized light; gives specimen’s “true color” Analyzer in path = crossed polars; gives specimen’s interference color Polyester, plane-polarized light Polyester, under crossed polars

13. Polarizing microscopy Improves specimen contrast Stained plant fibers, left – stained; right – polarized light

14. 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. The other 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

15. Polarizing microscopy Many crystalline substances are birefringent birefringent –Forensic analysis of soil components Many synthetic fibers are birefringent

16. Microspectrophotometer

17. Principles of spectroscopy

19. Microspectrophotometer Infrared spectromicroscopy

20. Scanning electron microscopy

21. High magnification (up to 100,000x) Excellent focal depth (3-D) Used with X-ray analyzer (Fig 7-12), can identify elemental composition of a specimen –Has a suspect fired a gun? Pollen identificationPollen

22. Online microscopy resources Molecular expressions Olympus Microscopy Resource Center

23. For next class Read chapter 7 –Read chap. 7 Case Reading Reading #1 (reading pack)