POLICE PHOTOGRAPHY
Mr. Bayani H. Salamanca
Dean, College of Criminology
Araullo University
PHINMA Education Network
POLICE PHOTOGRAPHY
is an art or science that deals with
the study of the principles of
photography, the preparation of the
photographic evidence, and its
application to police work.
PHOTOGRAPHY IN CRIMINAL
INVESTIGATION
Photography is an essential tool for the
law-enforcement investigator. As a tool, it
enables him to record the visible and in
many cases, the invisible evidences of a
crime. Special techniques employing
infrared, ultra-violet, and X-ray radiation
enable him to record evidence, which is
not visible. The photographic evidence can
then be stored indefinitely and retrieved
when needed. There is no other process,
which can ferret, record, remember and
recall criminal evidence as well as
photography.
Photographs are also a means of
communication. It is a language
sometimes defined as the “most
universal of all languages”.
Photography has an advantage as a
language because it does not rely
upon abstract symbols-words.
Photography thus is more direct and
less subject to misunderstanding.
A. FUNCTIONS OF PHOTOGRAPHY IN
INVESTIGATIVE WORK
Identification
–
–
–
–
Criminal
Missing Person
Lost or stolen property
Civilian
Communication and Microfilm files
– Transmission of photos (wire and radio
photos)
– Investigative report files
Evidence
–
Recording and preserving
Crime scenes
Vehicular accidents
Homicide or murder
Robbery cases
Fires or arson
Object of evidence
Evidential traces
–
Discovering and proving
By contrast control
By magnification
By invisible radiation
Action of offenders (Recording)
–
–
–
–
Surveillance
Burglary traps
Confessions
Re-enactment
Court Exhibits
–
–
–
–
Demonstration enlargement
Individual photos
Projection slides
Motion Pictures
Crime Prevention
–
Security clearance
–
Prepared training films (Police tactics,
investigation techniques)
Traffic studies
Documentations (riots and mob control,
disaster, prison disorders)
Public Relation
Police Training
–
–
Reproduction and copying
–
–
Photographs
Official records
B. PHOTOGRAPHY DEFINED
It is an art or science which
deals with the reproduction of
images through the action of
light, upon sensitized materials
(film or paper) with the aid of a
camera and accessories and the
chemical
processes
involved
therein.
PRINCIPLES OF PHOTOGRAPHY
Photograph is both the mechanical
and chemical result of photography.
To produce a photograph, light is
needed aside from sensitized
materials (film or paper). Light
radiated or reflected by the subject
must reach the film while all other
lights are exclude by placing the film
inside a light tight box (camera).
PHOTOGRAPH
From the Greek word which means:
- photo means light
- graph means to draw
The effect of light on the film is not visible
in the formation of images of objects. To
make it visible, we need or required a
chemical processing of the exposed film
called development.
The visual effect of light on the film
after development varies with the quantity
or quality of light that reached the
emulsion of the film. Too great in the
amount of light will produce an opaque or
very black shade after development. Too
little will produce a transparent or white
shade after development.
The amount of light reaching the film
is dependent upon several factors
like lightning condition, lens opening
used, shutter speed used, filter used,
etc..
HOW DOES THE LIGHT
TRAVELS?
C. DIFFERENT PHOTOGRAPHIC
RAYS
X-ray – radiation having a wavelength
between .01 to .30 nanometer or millimicrons. They are produced by passing
an electric current through a special type
of vacuum tube.
Ultra-violet rays – radiation having a
wavelength from 30 to 400 milli-microns.
It is used to photograph fingerprints on
multi-colored background, documents
that are altered chemically or over
writings and detection of secret writings.
Visible light rays or White light –
rays having a wavelength of 400 to
700 milli-microns.
Infra-red rays radiation having a
wavelength of 700 to 1000 millimicrons. It is used in taking
photographs of obliterated writing,
burnt or dirty documents or
blackout photography.
COLORS IN PHOTOGRAPHY
THE PRIMARY COLORS
THE SECONDARY COLORS
D. TYPES OF LIGHTNING CONDITION
Natural (Sunlight)
a. Bright- object in open space casts a
deep and uniform shadow
b. Hazy – object in open space casts a
transparent shadow
c. Dull – object in open space casts no
shadow
Artificial
– Continuous radiation – incandescent
lamps, fluorescent lamps, photoflood
lamps, etc.
– Short duration – chemical flash (Flash
bulb), electronic flash.
E. TYPES OF FILM ACCORDING TO
SPECTRAL SENSITIVITY
Perhaps the most important
characteristics of a film is its
variation in response to
the
different wavelength of light source
which is called spectral sensitivity.
Blue sensitive – sensitive to ultra-violet
rays and blue color only.
Orthochromatic – sensitive to ultra-violet
rays, to blue and green color. It is not
sensitive to red color.
Panchromatic – sensitive to ultra-violet
rays, to blue, green and red color.
Infra-red – sensitive to ultra-violet rays,
to all the colors, and also infra-red rays.
F. EMULSION SPEED
The extent to which an emulsion is
sensitive to light is referred to its
emulsion speed.
Emulsion Colors
Emulsions are thin, gelatinous, light-sensitive coatings
on film that react chemically to capture the color and
shadings of a scene. The four layers pictured here show
the same image as it would appear on different
emulsions in photographic film after the first stage of
developing. For black-and-white photographs, only one
emulsion is required, because it is the amount of light,
not the color, that activates the chemical reaction. Color
film requires three layers of emulsions, each of which is
sensitive to only one of the primary colors of light: blue,
green, or red. As light passes through the layers, each
emulsion records areas where its particular color
appears in the scene. When developed, the emulsion
releases dye that is the complementary color of the
light recorded: blue light activates yellow dye, green
light is magenta, and red light is cyan (bluish-green).
Complementary colors are used because they produce
the original color of the scene when the film is
processed.
Microsoft ® Encarta ® Reference Library 2004. ©
1993-2003 Microsoft Corporation. All rights reserved.
The two general types of speed ratings are:
ASA (American Standards Association)
- This is expressed in arithmetical value
system. The speeds in numbers are
directly proportional to the sensitivity of
the material. A film with an arithmetical
value of 400 is four times as fast as one
with a speed of 100.
DIN (Deutche Industri Normen) Rating
- This is expressed in logarithmic value
system. In this system an increase of 3
degrees double the sensitivity.
ISO Rating (combination of ASA and DIN
rating)
G. CHARACTERISTICS OF
PHOTOGRAPHIC PAPER
According to chemical contents –
chloride papers, bromide papers,
chloro-bromide papers.
According to contrast #0, #1, #2,
#3
According to physical characteristics
– weight (single, double) surface
(glossy, semi-matte, matte) color
(white, cream).
H. CAMERA
A camera is basically nothing more than a
light tight box with a pinhole or a lens,
shutter at one end and a holder of
sensitized material at the other. While
there are various kinds of camera from
the simplest construction (Box-type) to
the most complicated, all operate on the
same principles. The exposure of the
sensitized material to light is controlled by
the lens and its aperture, and the shutter
through its speed in opening and closing
of lens to light.
The essential parts of a camera are:
a light tight box, a lens, a shutter, a
holder of sensitized material, and
viewfinder. All other accouterment of
any camera merely make picture
taking easier, faster, and convenient
for the operator and are called
accessories.
Body or Light Tight Box
- suggest an enclosure devoid or light. An
enclosure, which would prevent light from
exposing the sensitized material inside the
camera. This does not necessarily mean that
the box or enclosure to always light tight at all
the times because if it does, then no light could
reach the sensitized material during exposure.
It means that before and after the extraneous
light, which is not necessary to form the final
images.
Lens
– the function of the lens is to
focus the light coming from the
subject. It is chiefly responsible for
the sharpness of the image formed
through which light passes during
the exposure.
Shutter
– is used to allow light to enter
through the lens and reach the film
for a pre-determined interval of time,
which light is again blocked off from
the film
Holder of sensitized material
– located at the opposite side of
the lens. Its function is to hold
firmly the sensitized material in it’s
placed during exposure to prevent
the formation of a multiple or
blurred image of the subject.
View-finder
– it is a means of determining the
field of view of the camera or the
extent of the coverage of the lens.
I. INHERENT DEFECTS OF LENSES
Spherical Aberration
– photographic rays passing
through the edges of a lens are
bent or refracted more sharply than
those passing through the central
part of the lens, thus they coming
to a focus nearer the lens than
those of the central rays.
Coma
– sometimes known as lateral spherical
aberration. It concern with rays entering
the lens obliquely.
Curvature of the filed
– when the image formed by a lens
comes to a sharper focus on curved
surface than on a flat surface.
Distortion – outer parts of the
image produced by the lens will be
magnified either less or more than
the center image.
– Barrel distortion – diaphragm is placed
in front of the lens.
– Pincushion distortion – diaphragm is
placed behind the lens.
Chromatic Aberration
– inability of the lens to focus all the
colors in the same place.
Astigmatism
– inability of the lens to focus lines
running in different direction like for
example a cross.
Chromatic difference by magnification
– inability of the lens to produce image
sizes of objects with different colors.
Flares
a. optical
b. mechanical
J. TYPES OF LENSES AS ACCORDING
TO THEIR DEGREE OF CORRECTION
Achromatic lens – a lens corrected
for chromatic aberration.
Rapid Rectilinear – lens corrected
for distortion.
Anastigmat lens – lens corrected for
astigmatism.
Apochromat lens – lens corrected
for astigmatism but with a higher
correction of color.
K. LENS CHARACTERISTICS
Focal length – is the distance
measured from the optical center of
the lens to the film plane when the
lens is set of focused at infinity
position. As according to focal
length, lenses maybe classified as:
–
Wide-angle lens – a lens with a focal length
of less than the diagonal of its negative
material.
–
Normal lens – a lens with a focal length of
approximately equal or more but not more
than twice the diagonal of its negative
material.
–
Long or Telephoto lens – a lens with a focal
length of more than twice the diagonal of its
negative material.
Relative aperture – the light gathering
power of the lens is expressed in the Fnumber system. It is it is otherwise
called the relatives aperture.
It is an opening that changes in size to
admit more or less light (similar to the
iris of an eye). The numbers on the
aperture control are called F-stops and
referred to as F16, F11, F8, and so on.
By increasing or decreasing the Fnumber (F-stops) numerically, it is
possible to:
– control has the amount of light passing
through the lens
– control the depth of field
– control the degree of sharpness due to
the lens defects.
The aperture control may look something like this:
Here's how it works:
– The larger the F-stop number, the
smaller the opening.
– Each number higher lets in half as much
light as one number lower.
For example, F5.6 admits twice as much
light as F8, while F11 lets in only half as
much.
The aperture doesn't work alone,
however. The shutter speed is
responsible for exposure, too. It
controls the amount of time light is
allowed to reach the film.
Depth of field – is the distance
measured from the nearest to the
farthest object in apparent sharp
focus when the lens is set or focused
at a particular distance.
Hyper focal distance – is the nearest
distance at which a lens is focused
with a given particular diaphragm
opening which will give the
maximum depth of field.
Focusing – is the setting of the
proper distance in order to form a
sharp image a lens of a camera
except those fixed focused requires
focusing. A lens maybe focused by
any of the following.
- Focusing scale or scale bed – a scale is
usually found at the lens barrel
indicating pre-settled distance in feet or
in meters. To focus the lens of the
camera, the distance of the object to be
photographed is measured, estimated, or
calculated and the pointer or maker on
the lens barrel is adjusted to the
corresponding number on the scale.
Range-finders – is a mechanism
that measures the angle of the
convergence of light coming from a
subject as seen from two apertures.
There are two types of rangefinders:
- Split-image through the range finder, the
image of a straight line in the object appears to
be cut into halves and separated from each
other when the lens is not in focus. When the
images of the lines are aligned, the lens is in
focus.
- Co-incident image – through the eyepiece, a
single image is seen double when the subject
is out of focus. Make the image concede and
the lens is in focus.
. Ground Glass – is focused by
directly observing the image formed
at the ground glass, screen placed
behind the taking lens. If the image
formed is blurred, fuzzy, or not clear,
the lens is out of focus. Make the
image sharp, the lens is in focus.
Zone – this is possible in wide angle
lenses only. There are only three
settings for focusing. One for close
distance (approximately 3-6 ft)
another for the medium distance
(approximately 6-15 ft) and finally
for distance objects (approximately
15 infinity).
L. Shutter
– A contraption or device used to block
the path of light passing through the
lens and exposing the sensitized
material.
- is a device that opens and closes at
varying speeds to determine the
amount of time the light entering the
aperture is allowed to reach the film.
Shutter speed is measured in fractions of
a second. 125 means 1/125 of a second,
60 means 1/60. Typical shutter speeds
range from 1 second to 1/1000. A shutter
speed setting for a bright, sunny day using an aperture of F11 - might be 1/125
second. A cloudy day might use 1/60
second with the same aperture, exposing
the film to light for a longer period of
time.
The settings for a good exposure are
determined by a light meter. (Most 35mm
cameras have a built-in light meter that
shows you the appropriate settings, or
automatically controls them.)
Aperture and shutter settings work
together. Because the shutter (like the
aperture) approximately halves or doubles
the light reaching the film with each
change in setting, a number of different
combinations of settings can result in the
same exposure.
Aperture
F22 F16 F11
Shutter
1/3
0
F8
F5.6
1/6 1/12 1/25 1/50
0
5
0
0
Any of the combinations shown above would
result in approximately the same exposure.
- Generally there are two types of
shutters:
Central Shutters – one that is located near
the lens (usually between the element of
the lens). It is made of metal leaves and
its action starts from the center toward
the side then closes back to the center.
Focal Plane Shutter – is located near the
focal place or the sensitized material. It is
usually made of cloth curtain. Its action
starts on one side and closes on the
opposite sides.
M. Exposure
– is the product of illumination and time.
Exposure is computed by any of the following
methods.
1. Use of light or exposure meter. The
amount of light coming form a source or
the amount of light being reflected by
the subject is measured by the light
meter. Proper adjustment therefore
becomes simplified.
2.
By taking into consideration
exposure factors like;
emulsion
speed or film sensitivity, lightning
condition, kind of subject.
Example :
When using a film with an ASA
rating of 100, for a normal subject, set
the shutter speed at 1/25 of a second
and adjust the diaphragm opening in
accordance with the following lightning
conditions.
Bright sunlight – f-11
Hazy sunlight – f-8
Dull sunlight – f-5.6
Exposure errors affects:
a. detail
b. tone reproduction
c. contrast
Aperture
F22
F16
F11
F8
F5.6
Shutter
1/30 1/60 1/125 1/250 1/500
N. CHEMICAL PROCESSING
Development – is the process of reduction.
Expose silver halides are reduced into metallic
silver. There is a separate developer for film (D76) and another for paper (Dektol). The factors
that affect developing time are: agitation,
temperature, concentration of chemicals and
exposure.
Stop-Bath – an intermediate bath between the
developer and the fixer. It is usually a
combination of water plus acetic acid or just
plain water. Primarily, its function is to prevent
the contamination of two chemical solutions.
Fixation – the process of removing
unexposed silver halide remaining in the
emulsion after the first stage of the
development of the latest image. The
usual composition of an acid fixing
solution are solvent silver halide known
as hypo, an anti-staining agent like
acetic acid, preservative like sodium
sulfite, and a hardening agent like
potassium alum.
Processing Method – negative-positive
method, reversal method
Developing Film
Developing photographic film requires a series of
chemical baths that cause the latent image on the
exposed film to become visible as a negative. The
process begins with the developer (1), which causes
metallic silver to form where the film has been exposed
to light, in densities that depend on the amount of
exposure. To stop the action of the developer, film goes
into a stop bath (2). After a rinse in water, the film goes
into a fixer (3) to removes any silver salts not converted
to metallic silver. After a short rinse, the film is
submerged in fixer remover (4) to clear any remaining
fixer from the film. The final bath (5) is a thorough rinse
in water. The developed negative is then allowed to dry.
Printing Photographs
Producing a photographic print from a developed
negative also requires a series of chemical baths. The
process begins by projecting light from an enlarger
through the negative and onto a piece of photographic
paper (paper treated with a light-sensitive coating). A
developer bath (1) makes the positive image visible on
the paper; a stop bath (2) stops the action of the
developer so the print won't continue to darken; and a
fixer bath (3) and a thorough rinse in water (4) remove
any remaining reactive chemicals. The finished print
then dries.
CHEMICAL COMPOSITION OF
DEVELOPER
Reducers or developing agents –
Elon, Hydroquinone
Preservative – sodium sulfite
Accelerator – sodium carbonate
Restrainer or fog preventer –
potassium bromide
CHEMICAL COMPOSITION OF A FIXER
Dissolving agent – Hypo or sodium
thiosulfate
Preservative – sodium sulfite
Neutralizer – boric acid, acetic acid
Hardener – potassium alum
FACTORS THAT AFFECTING
DEVELOPING TIME
Characteristic of negative material
Strength and composition of the
developer
Temperature of the developing
solution
Agitation or stirring during
development
O. ENLARGING TECHNIQUES
After processing an exposed film into a
negative, the next step would be to turn
the negative into a positive print or copy.
This could be done by either contact
printing or projection printing. For contact
printing, a contact printer is used while in
projection printing an enlarger is needed.
FOUR ESSENTIAL PARTS OF AN
ENLARGER
1.
2.
3.
4.
a
a
a
a
base and stand
lamp house
condenser or diffuser
lens
ACCESSORIES OF THE
ENLARGER
1. a negative holder
2. easel (Paper holder)
STEPS IN ENLARGING
Preparation of the darkroom, chemicals
and the enlarger.
Put off white light, switch on red light.
Place the negative in the negative holder
with the dull side of the negative facing
down.
Insert the negative holder into the
enlarger.
Switch on the enlarger’s light.
Adjust the easel to the desired size of
the photograph.
Focus the lens of the enlarger. Focusing
is done by first opening the lens
diaphragm fully. After the image has
been focused, and the density of the
negative permits, the lens of the
enlarger must be stop down a little bit.
Switch off the light of the enlarger.
Insert the photographic paper in the
easel with the shinny side facing up.
Make the exposure.
Immerse the exposed photographic
paper in the developer. The usual
developing time for a normally exposed
paper is about 1 to 1½ minutes.
Transfer the developed print in the stop
bath for about 30 seconds.
Place the prints in the acid fixer. The
fixing time is about 30 minutes.
Wash the prints in running water for
about 20 to 30 minutes.
Drying
Mounting
REMEDYING CHEMICAL
DEFECTS IN NEGATIVES
– Underdeveloped -Intensifier
– Overdeveloped – reducer
– Stains – Stain remover
FREQUENT FAULTS IN PRINTING
Blurred exhibits
Muddy and mottled exhibits
Yellowish exhibits
Dark exhibits
Light exhibits
Harsh exhibits
Flat exhibits
Fogged exhibits
Blemishes on prints
Distorted prints
P. CRIME SCENE PHOTOGRAPHY
PHOTOGRAPHIC PROCEDURES
The camera should be mounted on a sturdy
tripod whenever to prevent camera
movement.
The camera should be leveled whenever
commensurate with the particular
photograph to be taken.
Crime scene views include three general
classes.
– Long views, showing general location and
conditions.
– Medium views, pinpointing a specific object of
evidence or significant segment of the crime
scene.
– Close-up views, recording position and details.
Photographs should be taken
progressively as the photographer enters
the building or room to avoid disturbing
something that might otherwise remain
unnoticed, and to maintain continuity.
Views should be taken to illustrate the
general location of the scene of the
crime. A large outdoors scene or a
matter involving several buildings may
call for any material view.
Definitely required is the view of exterior
of the building when the crime was
committed inside. It is well to include the
street number when this is possible.
7. Needed next is the complete
photographic coverage of the inferior
rooms within a crime area which show the
condition in general and relate the overall
scene to specific items and places.
8. Bodies of victims should be
photographed exactly as found from all
angles and especially from overhead when
this can be done for identification
purposes.
- Close-up photographs, one to one, if
possible, should be taken all wounds, bruises,
discolorations and abrasions-generally with
colors.
Measuring devices such as rulers, yardstick, and
tape measures can be used to show the relative
size of and distance between objects or the
degree of magnification of an enlargement. There
should obscure any important part of the
evidence. In photographing a document for
example, the ruler a six inches (or 15 centimeter)
is placed at the bottom or just below the object
will show the relative size of objects in a
photographing exhibit.
Field notes.
-Record the date and time of arrival at the crime
scene as well as the time of departure from the scene.
-Specifically record the location area, street number,
name of building, type of scene.
-Write down the names and badge numbers of all
investigative officers present during photographing.
-Total and record the number of exposures, which
necessitates the bad negatives and be saved for the
record.
-Record specific information on each exposure. This
should include the time of taking of each pictures, which
can be expressed either using AM or PM or on military
type 24 hour scales which 3:00 PM becomes 1500 hours.
Additionally:
pointed
-Direction of camera where it was
-General statement of what
has been photographed
-Exposure to ASA rating
-Kind of film
-The lighting, whether
available, flood lamps, flash
lamps, etc.
Problems in Fingerprint
Photography
–
–
–
–
–
–
Black fingerprint on colored background
White fingerprint on colored background
Fingerprint on multi-colored background
Fingerprint on glass
Fingerprint on Polished metal
Fingerprint on papers
PROBLEMS IN QUESTIONED
DOCUMENTS PHOTOGRAPHY
On handwritings
–
–
–
–
Sequence of crossed lines
Writing over folds
Differentiation of inks and pencils
Patching
On papers
–
–
–
–
–
–
–
Erasures
Watermarks
elimination of paper background
Faded writing
Restoring erased writing
Stamped out writing
burned papers
FILTERS
is a homogeneous medium which absorbs and
transmits differentially light rays passing through
it.
A color filter works in such a way that it
will transmit its own color and absorbs other
colors.
By using filters in combination of black
and white films, the photographer can control
tonal blues to get a technically correct condition
or to exaggerate, or suppress the tonal
differences for visibility, emphasis, and other
effects. With color films, filters are use to change
the color quality of the exposing lights to secure
proper color balance with film being used.
FILTER FACTORS
Because filter subtract some of the
light passing through the lens, and
increase in an exposure time or lens
opening is necessary. The number of
lines that the normal exposure must
be multiplied is called “filter factor”.
The filter factor value depends on
film type and light source in addition
to the absorption of the filter.
TYPES OF FILTERS IN BLACK AND
WHITE PHOTOGRAPHY
–
–
–
–
–
Correction filter- used to change the response of the
film so that all colors are recorded at approximately
the relative brightness value seen by the eye.
Contrast filter- used to change the relative brightness
values so that two colors which would otherwise be
recorded as nearly the same will have decidedly
different brightness in the picture.
Haze filter- used to illuminate or reduce the effect of
serial haze.
Neutrally density filter- used for reducing the amount
of light transmitted without changing the color values.
Polarizing filter- used to reduce or illuminate reflection
on highly reflective surfaces.
YOUR ACHIEVEMENT
IS OUR ACCOMPLISHMENT!!
SO…..
READ MORE….
LEARN MORE….
AND PASS THE BOARD!!!
THAT’S ALL FOLKS!!!
Descargar

POLICE PHOTOGRAPHY