Chapter 7 The Microscope

Introduction THE MICROSCOPE Optical instrument Lens or combination of lenses Magnify, resolve fine details Earliest methods for examining physical evidence Magnified image = virtual image Image viewed directly = real image. THE MICROSCOPE

The Compound Microscope

The Compound Microscope Schematic diagram of stereoscopic microscope Two separate monocular microscopes Each has own set of lenses except for the lowest Objective lens common to both microscopes

The Compound Microscope The Mechanical System Base: the support. Arm: the C-shaped upright structure Stage: the plate on which the specimens are placed Body Tube: the hollow tube on which the objectives and eyepiece lenses are mounted THE MICROSCOPE

The Compound Microscope The Mechanical System Coarse Adjustment: the knob used to focus the microscope lenses by moving the body tube Fine Adjustment: the knob also used to focus the lenses by moving the body tube, but by a much smaller magnitude THE MICROSCOPE

The Compound Microscope The Optical System Illuminator: artificial light, usually supplied by a light bulb, to illuminate the specimen. Transmitted Illumination: when the light is directed up through the specimen from the base. Vertical or Reflected Illumination: when the light comes from above and reflects off the specimen. THE MICROSCOPE

The Comparison Microscope Two independent objective lenses joined together by an optical bridge to a common eyepiece lens. The objects under investigation are observed side-by-side in a circular field that is equally divided into two parts Modern firearms examination Began with the introduction of the comparison microscope Ability to give the firearms examiner a side-by-side magnified view of bullets THE MICROSCOPE

The Stereoscopic Microscope Two monocular compound microscopes Three-dimensional image of a specimen Use both eyepiece lenses Evidence not requiring very high magnification (10x–125x) Large working distance Microscopic examination of big, bulky items THE MICROSCOPE

Polarizing Microscopy Plane-polarized Light that is confined to a single plane of vibration Polarizing microscope Examination of the interaction of plane-polarized light with matter THE MICROSCOPE

Polarizing Microscopy Wide applications for the study of birefringent materials Materials that split a beam of light in two Each with its own refractive index value Determination of these refractive index data Provides information that helps to identify minerals present in a soil sample or the identity of a man-made fiber. THE MICROSCOPE

The Microspectrophotometer Spectrophotometer coupled with a light microscope. Can simultaneously obtain the visible absorption spectrum or IR spectrum of the material being observed Trace evidence, paint, fiber, and ink evidence. THE MICROSCOPE

The Microspectrophotometer

The Microspectrophotometer

The Scanning Electron Microscope (SEM) bombards a specimen with a beam of electrons instead of light Produces a highly magnified image from 100x to 100,0000 Depth of focus 300X better than optical systems at similar magnification Bombardment of the specimen’s surface with electrons Produces x-ray emissions Characterize elements present in the material under investigation THE MICROSCOPE

Dental Plaque

Bread Mold Aspergillus sp.)

Penecillium sp.

SEM: Hair and Hair follocles

SEM: hafnium nitride interface coating on carbon fibers

Dust Mite Family Reunion