Microscope1

Microscope1 - The
Microscope
...

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Unformatted text preview: The
Microscope
 What
is
a
microscope?
 •  Optical
instrument
the
uses
a
lens
or
combination
of
lenses
 to
magnify
and
resolve
the
fine
detail
of
an
object
 •  Many
different
types
 –  Magnifying
glass
(5‐10x)
 –  Stereoscopic
microscope
 –  Compound
microscope
 –  Comparison
microscope
 –  Polarizing
microscope
 –  Microspectrophotometer
 –  Scanning
electron
microscope
(SEM)
(100,000x)
 Microscope in Forensic Science •  •  •  •  Great
disparity
between
potential
and
actual
use
 Range
of
forensic
applications
is
broad
 Used
in
all
forensic
disciplines
 Extract
useful
information
from
a
variety
of
samples
 –  Physical
characteristics
 • Structural
information
 –  Chemical
characteristics
 • Identifications
 •  Cool
websites:
 –  http://www.ou.edu/research/electron/mirror
 –  http://www.microscopelab.com/microscope/
 Real
Image
 •  Formed
by
actual
convergence
of
light
 rays
on
a
screen
(or
film,
or
retina)
 •  Formed
on
opposite
side
of
lens
and
 inverted
 Virtual
Image
 • Image
that
cannot
be
seen
 directly
 • Seen
only
by
viewing
 through
lens


 • Image
is
not
inverted
 Anatomy
of
a

 Compound
Microscope
 Ocular or Eyepiece Arm Tube Objective Fine and coarse focus adjustment Stage Substage Condenser Illuminator Iris Diaphragm Field Diaphragm Base Illumination
 •  Transmitted
illumination:
light
passes
 through
specimen;
placed
below
specimen
 being
viewed
 •  Vertical
or
reflected
illumination:
light
is
 reflected
off
of
the
subject;
placed
above
the
 specimen
 –  Used
for
opaque
specimens
 Definitions
 •  Parfocal:
a
unique
microscope
that
when
an
 image
is
focused
with
one
objective
in
 position,
the
other
objective
can
be
rotated
 into
place
and
the
field
will
remain
in
focus.
 •  Monocular:
a
microscope
with
one
eye
piece
 •  Binocular:
a
microscope
with
two
eyepieces
 Definitions
 •  Total
magnification
 –  Ocular
x
Objective
=
Total
magnification
 •  Resolution
 –  The
ability
to
discern
fine
details
 –  Expressed
as
a
linear
dimension
 Resolution
 Numerical aperture (NA): the ability of an objective lens to resolve details into separate images is proportional to the value of the numeral aperture (the bigger the NA value; the shorter the distance required to resolve an image) Resolution
and

 Empty
Magnification
 •  Magnification
without
additional
detail
is
 considered
“empty
magnification”
 –  Minimum
useful
magnification
=
500
X
NA 


 obj –  Maximum
useful
magnification
=
1000
X
NA 

 obj Field
of
View
 •  The
area
of
specimen
that
can
be
seen
 after
it
is
magnified
 •  As
magnification
↑,
field
of
view
↓

 •  Start
with
low
magnification
 Depth
of
Focus
 •  The
thickness
of
a
specimen
entirely
in
focus
 •  As
magnification
↑,
depth
of
focus
↓
 Simple
Microscope
 •  Magnifying
lens
(5x
–
10x)
 •  Magnification
takes
place
 in
one
stage
or
step
 Stereoscopic
 Microscope
 •  Binocular
 •  Binobjective
 •  Most
frequently
used
in
 crime
labs
 •  Low
power:
 magnification
of
10X
‐
 125X
 Stereoscopic
Microscope
 •  Advantages:
 –  Presents
good
3‐dimensional
image
of
object
 –  Right‐side
up
image
(unlike
compound
which
 is
upside‐down
and
backwards)
 –  Wide
field
of
view.
Great
depth
of
field.
 –  Large
working
distance
(distance
between
 objective
lens
and
specimen).
Therefore
used
 to
find
trace
evidence
in
garments,
tools,
etc.
 The
Compound
Microscope
 •  Mechanical
System
 –  Base,
arm,
stage,
body
tube,
etc.
 •  Optical
System
 –  Light
source,
condenser,
objective
lens,
ocular
 lens,
etc.
 Image
Formation

 Compound

 Microscope
 Compound
Microscope
Lens
System
 •  High
magnification
 with
short
working
 distances
 •  Two
stages
(places
 of
magnification)
 –  Objective
 –  Ocular
 Comparison
Microscope
 •  Two
compound
 microscopes
with
optical
 bridge
 •  Forensic
applications
 –  Hair
and
fibers
 • Transmitted
illumination
 –  Bullets
and
casings
 • Reflected
illumination
 Electro‐
 Magnetic

 Energy
 Visible
Light
Spectrum
 Polarization
of
Light
 •  Plane‐polarized
light
 –  Light
confined
to
a
single
plane
of
vibration
 •  Polarizer
 –  A
device
that
permits
the
passage
of
light
waves
 vibrating
in
only
one
plane
 Polarization
of
Light
 Crossed
Polars
 Anatomy
of
a

 Polarized
Light
Microscope
 Ocular or Eyepiece Intermediate tube with analyzer Tube Objective Fine and coarse Focus adjustment Rotating stage Substage Condenser Light source Iris Diaphragm Polarizer Field Diaphragm The
Polarizing
Microscope
 •  Used
to
study
materials
that
polarize
light
 –  crystalline
(birefringent)
minerals,
soils,
synthetic
 fibers,
drugs
 •  Light
passes
through
polarizer,
then
sample,
 then
“analyzer”
(another
polarizer
typically
 turned
90º
to
the
first)
 •  Polarizing
specimen
will
reorient
light
waves
so
 that
it
passes
by
analyzer
for
viewing,
usually
 producing
brilliant
colors
and
patterns.
 Birefringence
 Birefringence
 Polarization
Microscope
Images
 Polarized light photomicrographs of lunar rocks and lava Microspectrophotometer
 •  Microscope
linked
to
a
spectrophotometer
 •  Enables
forensic
scientist
to
view
a
particle
under
a
 microscope
while
at
the
same
time
take
an
IR
 (infra‐red)
or
visible
wavelength
absorption
 spectrum.
 •  Much
more
exact
determination
of
“color”
for
 instance.
 •  IR
spectral
determination
of
individual
fibers
and
 paint
chips.
 •  Visual
spectra
of
ink
on
suspected
counterfeit
 currency.
 Microspectrophotometer
 IR
Spectrum
 Scanning
Electron
Microscope
 (SEM)

 •  Advantages:

 –  high
magnification
(10X
‐
100,000X)
 –  high
resolution
 –  great
depth
of
focus
(300X
better
than
optical
 systems)
 •  Forensic
applications:
 –  gunshot
residue
analysis:
suspects
hand/arm
is
swiped
 • residue
particles
can
be
visualized
 • elemental
analysis:
lead,
barium,
and
antimony
are
 tell‐tale
signs
of
gunshot
residue
 Scanning
Electron
Microscope
 (SEM)

 •  All
previous
 microscopes
are
 considered
to
be
 “light
microscopes”
 •  Instead
of
light,
the
 SEM
aims
and
 focuses
a
beam
of
 electrons
onto
 specimen
by
means
 of
electromagnets
 Scanning
Electron
Microscope
 (SEM)

 •  Electron
beam
is
scanned
across
surface
of
 specimen
 •  Scattered
and
emitted
electrons
from
specimen
 are
translated
and
displayed
on
monitor
 •  Since
x‐rays
are
produced
in
the
process,
the
SEM
 can
include
an
x‐ray
analyzer
to
determine
 elemental
composition
 Scanning
Electron
Microscope
 (SEM)

 Scanning
Electron
Microscope
 (SEM)
and
EDS
 The
Lindbergh
Baby
Case
 •  Hopewell,
NJ,
March
1,
1932,
 baby
kidnapped
 –  2nd
floor

 •  Evidence
 –  Ransom
note,
ladder,
chisel
 The
Lindbergh
Baby
Case
 •  $50,000
ransom
paid
 •  Few
months
later,
babies
body
was
found
in
woods
 one
mile
away
 The
Lindbergh
Baby
Case
 •  Serial
numbers
from
ransom
bills
were
 being
looked
for
 •  1934,
Bruno
Richard
Hauptmann
used
a
 ransom
money
bill
to
purchase
gasoline
 The
Lindbergh
Baby
Case
 •  Ladder
and
ransom
note
became
a
focus
 of
the
investigation
 Convicted

 Death
Sentence
 ...
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This note was uploaded on 03/06/2011 for the course CHS 3501 taught by Professor Perr during the Spring '09 term at FIU.

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