forensic microscopy

what are examples of trace evidence?

paints

soil

minerals

dusts

glass

polymers

hairs

fibers

papers

starches

wood

pollens

insulation

feathers

building materials

gunpowder residue

what is forensic microscopy used for?

tool mark comparison

firearms id and comparison

biological applications

drug chemistry

trace evidence

what is a microscope?

an optical instrument that uses a lens/lenses that magnifies and resolves details

magnifying glass is the simplest type

what is a virtual image?

an image that cannot be seen directly and can only be seen by a viewer looking through a lens

what is a real image?

an image formed by the actual convergence of light rays upon a screen

what are the types of microscopes used in a forensic lab?

magnifying glass

compound microscope

comparison microscope

stereoscopic microscope

polarizing microscope

microspectrophotometer

scanning electron microscope

what is the magnification of a magnifying glass?

5-10x

what is the magnification of a compound microscope?

combined power of both lenses can magnify up to 1500x

what is the magnification of a stereoscopic microscope?

10-125x

what is the magnification of a scanning electron microscope?

1millionx

what is parfocal?

a microscope having objective lenses that stay relatively in focus when changed from one objective to another

what is parcentric?

a microscope having objective lenses aligned in such a fashion as to allow a specimen to stay in the center of the field of view when changing from one objective to another

what are the details of a compound microscope?

2 lenses (objective and eyepiece)

produces a reverse image

what is working distance?

the distance between the front of the objective and the top of the cover glass on the slide

the higher the magnification, the smaller the working distance

what is field of view?

area of the specimen that can be seen

decreases as magnification increases

what is depth of focus?

defines the thickness of a specimen

decreases as magnification increases

what is numerical aperture?

ability of the objective lens to resolve fine structure detail in the specimen

resolution of a microscope objective is defined as the smallest distance between 2 points on a specimen that can still be distinguished as 2 seperate entities

the higher the numerical aperture of the total system, the better the resolution

what is empty magnification?

the max useful magnification of a compound microscope is approximately 1,000x the NA of the objective being used

ant attempt to increase the total magnification beyond this figure will yield no additional detail and is therefore referred to as empty magnification

what are the parts of microscope care?

hold a microscope firmly by the stand

hold plug when unplugging the illuminator

always make sure the stage and lenses are clean before putting away

never use anything but good quality lens tissue on any optical surface, with appropriate lens cleaner or distilled water

focus smoothly, do not try to spped through the focusing process or force anything

what is a stereoscopic (dissecting) microscope?

most utilized microscope in a forensic setting

right side up image

3d image

wide fov

great depth of focus

large working distance

what is a comparison microscope?

side by side comparison

2 '“matched” compound microscopes

optical bridge joins 2 objective lens into 1 binocular eye piece

split field

what is a polaring microscope?

re directs light waves to one plane

eliminates light glare

detect with second polarizer (analyzer)

analyze materials that polarize light (minerals, fibers)

what is a microspectrophotometer?

combines microscope with a spectrophotometer

analyzes trace materials like inks, paints, fibers and gunpowder

visible spectra, uv spectra or infrared spectra

what is a scanning electron microscope?

uses beam of electrons rather than a beam of light

viewed on crt screen - digital imagery today

depth of focus 300x better than compound light microscope

combines with an x ray analyzer to identify elemental compositions

what is forensic palynology?

collection and examination of pollen and spores connected with crime scenes, illegal activities or terrorism

microscopy is the main tool utilized by the forensic palynologist

what is microscopy?

analytical approach in which a microscope plays a central role in maximizing the extraction of useful info from a variety of samples

what is the objective lens?

closest to specimen

parfocal and parcentric

what is the ocular lens (eyepiece)?

monocular and binocular