Forensic Microscopy Get ready for some short notes! Ch. 7 Quiz on Monday HW due Mon: Ch. 7 foldable and supplemental ?s If you were absent yesterday you.

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Presentation transcript:

Forensic Microscopy Get ready for some short notes! Ch. 7 Quiz on Monday HW due Mon: Ch. 7 foldable and supplemental ?s If you were absent yesterday you MUST make up your exam during 8 th or after school TODAY!

Forensic Microscopy Generally takes one of six forms depending on the type of evidence to be examined Light microscopes: –Compound microscope –Stereoscopic microscope –Comparison microscope –Polarizing microscope –Microspectrophotometer Electron microscopes –SEM – scanning e- microscope

Compound Microscopes The “classic” microscope Light is passed through object from beneath Image is upside down and backwards May possess a zoom magnification or multiple lenses of varying strength Monocular and binocular versions Generally up to 1000x magnification Higher magnification limitations –“Depth of focus” is decreased and creates focusing challenge –Cuts down on available light

Compound Microscopes Major Components –Eyepiece –Tube –Nosepiece –Objectives –Stage –Focus –Arm –Base

Compound Microscopes

Comparison Microscopes Essentially two compound or stereographic microscopes joined by a “bridge” Vital for side by side comparison of two pieces of evidence View can show either microscope or can be “split” to show both at the same time Especially useful in ballistics and hair/fiber cases

Comparison Microscopes

Stereographic Microscopes Most frequently used type of microscope in forensics Light is passed either through an object or from above Image is projected right side up and correct right to left Usually the only method for opaque forms of evidence Especially useful for soil analysis, entomology and macroscopic evidence Magnification generally ranges from 2x to 125x Often called “dissecting” microscopes

Stereographic Microscopes

Polarizing Microscopes A special microscope application that outfits a “normal” microscope with two devices (a polarizer and an analyzer) The polarizer is used to impact incoming light waves to reveal special properties of a material Affected light waves then pass through analyzer before hitting the eye Especially useful in soil analysis (minerals) and the identification of artificial fibers

Polarizing Microscopes

Polarizing microscope view a a thin slice of granite Blemish on an LCD screen visible in polarized light (right) but not in normal visible light (left)

Microspectrophotometer A beam of light is aimed at the object and its spectrum can be collected The specific spectrum will be unique to particular chemicals, fibers, etc. Spectral “fingerprints” can then be used to determine specific matches between different evidence samples

Microspectrophotometer

Electron Microscope Unique in that it uses a beam of electrons aimed at the object –Does not use light Extremely high magnification possible –Ranging from 10x – 100,000x Can also be used as a spectroscope in some applications Useful in gunshot residue cases Very expensive

Electron Microscope

Electron microscope