Forensic Archiving I. [1] [1] American Heritage College Dictionary Third Edition, Houghton Mifflin...
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Transcript of Forensic Archiving I. [1] [1] American Heritage College Dictionary Third Edition, Houghton Mifflin...
Forensic Archiving I
[1] American Heritage College Dictionary Third Edition, Houghton Mifflin Company, 1993. [2] http://www.pcmag.com/encyclopedia_term/0,2542,t=active+archiving&i=37447,00.asp#. Accessed 3/20/2009.
Forensic Archiving Documentation:
A current standard no longer reflects current practice
Times change as does a profession’s lexicon
Archiving:Preserving the scene’s recordEncompasses more than simply photography,
sketching, or imagingModern relationship with a digital world
Archiving Essentials Critical responsibility of the crime scene unit
Preserve the scene as found Impossible to predict when another pair of eyes will need to review the
“original” scene
No single archiving method is sufficient Taking notes Videography Photography Sketches 3D archiving systems CAD Writing reports
Each method has attributes and deficiencies
Crime Scene Archive Traditionally stored in
filing cabinet or storage boxes
Contemporary investigations employ a form of digital media Computer hard drive
or a CD backup
Forensic PhotographyAn Essential Skill
Telling The Scene’s Story
The Purpose of Forensic Photography
To archive the scene
Record as found
Show the relative position of evidence
Establish the relative dimensions of evidence
Complement other archiving techniques
Active vs. Passive Archiving
Active archiving: Process of combining the “rote,” the passive aspect of archiving, with an engaged brain
Thinking critically about relationship of evidence to the scene
Passive Archiving: Overview photographs and snapping photographs without considering what is being captured
Need to think about Forensic perspective or how different items at the
scene relate to each other
Photography: Is Integral Part of Scene
Search Photography is an integral part of searching the scene
Visible investigation Active investigation
Not artistic photograph but forensic photograph The artist is trying to be creative
Artist allows the landscape to guide the artistic process
Forensic investigations capture the best perspectives in order to capture the scene’s story Forensic photographer allows the scene to guide the continuum of
photographs from relevant evidence to relevant evidence
Paradoxically: forensic photographer must capture EVERYTHING
Single Lens Reflex (SLR) Cameras
Why SLR’s?Lenses can be changed
The investigator sees exactly what the lens “sees” Unless camera is modified for IR photography
Large image sensors
Near-zero lag time
Managing Your CameraCamera Function
Result
Aperture Priority You set the aperture (f/stop) and the camera sets the shutter speed
Shutter Priority You set the shutter speed and the camera sets the aperture
Manual Priority You set the aperture and the shutter speed
http://www.mir.com.my/rb/photography/fototech/apershutter/aperture.htm
Managing Your Camera Exposure control ring –
various setting may be represented by a few symbols/letters "P" is for programmed AE ”S" is for shutter priority “A” is for aperture
priority “M” refers to manual
mode
Newer autofocus SLR cameras set aperture via the lens aperture ring Instead of the thumb wheel
Shutter Speed (B)
Aperture (A)
[1] Kelby, Scott – Chapter 1 – Pro Tips for Getting Really Sharp Photos. In The Digital Photography Book, Volume 1. Peachpit Press 2006, page 1.
Focus If not in focus, the rest doesn’t matter
Tack sharp or photographs in sharp focus
Digital Cameras: The LCD viewer allows for immediate inspection of
focus CAVEAT: LCD screen is small
Use the LCD as a guide of focus
Focus (2) Use tripod with a ballhead or at least a monopod
There are situations when hand-held is the only way to get the correct photograph
Pressing shutter moves the camera Cable release option Self timer function Infrared wireless remote Anti shake mechanisms
Vibration Reduction (Nikon) Image Stabilization (Canon)
Lock the camera’s mirror in the up position Move the mirror up manually
Exposure Delay Mode (Nikon) Mirror Lockup (Canon)
Focus (3)Lens’ sharpest aperture = about two full stops
smaller than wide open If the lens is f/2.8, the best apertures would be
f/5.6 and f/8 (two full stops down from 2.8)
Avoid high ISO’s On a tripod in dim light
Do not increase the ISO Keep the ISO at the lowest possible setting
Focus SummaryLCD on the camera back unreliable gauge
of focus
Out-of-camera image manipulation
Use a tripod when possible Hand-holding the camera increases the
likelihood of obtaining out-of-focus photographsUse the camera’s burst function Brace the camera against something sturdy
Avoid high ISOs
Photographic BasicsThe Essential Terms & Considerations
Aperture ShutterISO
Light Focal LengthDepth of FieldWhite Balance
ExposureImportant
Considerations
Understating Exposure
Exposure: Amount of light entering the camera
“the duration and amount of
light needed to create an image”
Stop: The basic unit of exposure One stop is the equivalent of doubling or halving
the amount of light entering the camera
Controlling exposure allows the photographer to obtain that perfect forensic perspective
http://www.cambridgeincolour.com/tutorials/camera-exposure.htm
Understating Exposure (2)
Correct exposure is a lot like collecting rain in a bucket
While the rate of rainfall is uncontrollable Three factors remain under your control:
The bucket's width
The duration you leave it in the rain
Quantity of rain you want to collect
You just need to ensure you don't collect too little ("underexposed"), or that you don't collect too much ("overexposed”)
There are many different combinations of width, time and quantity that will achieve this For example, for the same quantity of water, you can get away with less time in
the rain if you pick a bucket that's really wide
ApertureThe First & Most Critical Decision
About Exposure Begins with Aperture
http://en.wikipedia.org/wiki/Aperture
Aperture Aperture: Size of the hole through which light enters the
camera Covered by a mechanical shutter
Limits the time the digital sensor is exposed to the light
Terminology is f-stops or f/numbers Confusing and counterintuitive – a the larger the f/number,
say f/22, the smaller the hole and visa versa
Wide Aperture f/stop or aperture of f/2.8 is wide – hole is larger
Narrow Aperture f/stop of f/22 is a narrow opening – hole is small
f/4
f/11
f/8
f/5.6
DiaphragmLens opening
Stop Down1 Full Stop
½ Light
2x Light
Aperture - Basics
Telling the Scene’s Story
The Importance of Aperture
Aperture is one of the big three players in solving the correct forensic exposure puzzle
Aperture should be FIRST setting adjusted Aperture allows scene to tell its story
Each photograph has a specific forensic perspective the photographer must capture o What at the scene and what in this photograph should
be in focus? o What needs to be captured for the scene to tell its story
Depth of Field: What is in focus
Depth of FieldWhat is in Focus
Depth of Field (DOF)Depth of Field: The concept of what is
in focus in a photograph Photographer must consider the DOF because
it tells the scene’s story
Aperture & DOF are intimately associated Size of opening on camera controls what at
the scene is in focus in a photograph
Depth of Field Establishing (Overview) Shots
For maximum depth of field Focus about 1/3 of the distance into the scene
Doo
r
Knife
5ft
15ft28ft
Where to Focus at the Scene
Small focal length wide-angle lens …… 24mmFocus @ 10’ – just in front of the body
Strive for: Maximum depth of field1. Shorten focal length2. Smaller aperture opening (larger f/number)3. Greater distance to point of focus (evidence)
Window15ft
BloodPool
Shutter SpeedHow Long is the Exposure
Shutter Speed Shutter Speed: The speed the shutter closes
Closes the aperture Controls amount of light entering camera Regardless of size of the opening, if the digital sensor is
exposed too long, the resulting photograph will be over exposed and will not meet forensic or artistic standards
Typical Shutter Speeds
Typical shutter speeds
Older cameras: shutter speeds set to halve or
double light allowed in 1/500, 1/250, 1/125, 1/60, 1/30,
1/15, etc
Newer cameras 1/3rd steps
1/500, 1/400, 1/320, 1/250, 1/200, 1/160, 1/124, 1/100, 1/80, 1/60, etc
http://photographylife.com/what-is-shutter-speed-in-photography
SUGGESTED SHUTTER SPEEDS
TO FREEZE ACTION TO CAPTURE MOTION
Children – 1/250 – 1/1000 seconds
Amusement park rides: +/- one second
Moving water/waterfalls: 1/1000 seconds or more
Moving water/waterfalls: 4 or more seconds
Sporting event: 1/500 – 1/2000 seconds
Fireworks: 1/2 – 4 seconds
Birds in flight: 1/1000th a second and above
Moving cars at night: 8-10 seconds
Night photography – one or more seconds
When taking a photo of a moving subject, changing the shutter speed can change the look of an image.
A slow shutter speed captures movement. Fast shutter speed freezes action.
Shutter Speeds & a Variety of Subjects
ObjectPhoto’d
55-200mm18-55mm
12-24mm
Focal Length
Focal Length: The distance (mm) from the center of the lens to where the image comes into critical view
Distance from Object Photographed
Equivalent ExposuresEquivalent Exposures: Different camera settings that
allow the SAME amount of light to enter the camera Resulting photographs are subtly different
Examples of equivalent exposures f/8 – f-stop and ¼ second shutter speed f/11 – f-stop and ½ second shutter speed f/16 – f-stop and 1 second shutter speed
Aperture & Shutter SpeedEquivalent Exposures
http://irinaovery.com/wp-content/uploads/2012/03/2124175721_591714ec93.jpg
The combination f/2.8 and shutter speed 1/125 sec gives a cell with number 10.
If you do two stops on the right and towards the top of the chart, you will get the number 10 again.
80-400mm zoom lens @ 400mmf/32, 1/30sec
80-400mm zoom lens @ 400mmf/5.6, 1/1000sec
f/4, 1/500sec f/5.6, 1/250 sec
f/22, 1/15 sec
35-70mm zoom lens @ 35mm
Equivalent Exposures
f/4 – 800th sec – ISO 1250 f/5.6-500th sec - Iso1250
f/11 – 125th sec – ISO 1250 f/20 – 40th sec – ISO 1250
ISODigital Processor Sensitivity
International Organization of Standards
ISO ISO Rating: Measure of
the digital sensor’s sensitivity to light The higher the ISO
number, the more sensitive the sensor is to light
ISO settings affect exposure Change in ISO from 100 to
200 effectively doubles the light One full stop More light is not entering the
camera
ISO 100 ISO 3200
http://www.digital-photography-school.com/iso-settings
ISO Considerations Auto ISO Mode: The camera selects the appropriate ISO setting
depending upon the conditions It will try to keep the ISO as low as possible
Manual ISO Mode: Manually adjusting the ISO based on your aperture, shutter speed and conditions of the scene Overriding the camera impacts the aperture and shutter speed
If you bumped your ISO up from 100 to 400, you can shoot at higher shutter speeds and/or smaller apertures
Choosing the Correct ISO setting Light – Is the subject well lit? Grain – Do I want a grainy shot or one without noise? Tripod – Am I using a tripod? Moving Subject – Is my subject moving or stationary?
Always try to choose the lowest ISO setting possible If there is plenty of light AND need no grain in photo AND using a tripod AND
subject is stationary Use pretty low ISO rating If it’s dark AND want grain AND don’t have tripod AND subject is moving
Consider increasing the ISO - Can shoot with a faster shutter speed and still expose the shot well Trade off of increase in ISO is noisier (grainer) shots
When to use Higher ISO Settings
Indoor Sports Events – where your subject is moving fast yet you may have limited light available
Concerts – also low in light and often ‘no-flash’ zones
Art Galleries, Churches etc- many galleries have rules against using a flash and of course being indoors are not well lit
Birthday Parties – blowing out the candles in a dark room can give you a nice moody shot which would be ruined by a bright flash. Increasing the ISO can help capture the scene
Read more: http://www.digital-photography-school.com/iso-settings#ixzz1TKC5Zi00
http://www.digicamhelp.com/camera-features/advanced-settings/iso/
ISOBy the Numbers
AUTO ISO – digital camera automatically sets the ISO speed according the the brightness of the scene, increasing or decreasing the sensitivity. User has no control over which ISO number is used
ISO 80 – for taking photos in bright light; excellent for close-ups, landscape, and portraits. Produces fine detail and image quality
ISO 100 – for extra sensitivity with little, if any, reduced image quality
ISO 200 – cloudy and overcast days. Acceptable image quality, with some visible noise
ISO 400 – suitable for indoor photography whether or not a flash is used. Useful for “stop-action” and sports photographs. Most compact digital cameras produce high to very high image noise
ISO 800, 1600 and above – useful for taking photos in very low light, or outside in good light when increased shutter speeds are required. Results can be disappointing when shooting at these high numbers with compact digital cameras, so take test photos before photographing an important event
MeteringMeasuring Light
MeteringMetering: The actual light reflected
from an object being photographed• Cameras need to know how much light is
entering the cameraThus allowing the camera to choose a
starting point for an appropriate exposure
Modern digital cameras use TTL (through-the-lens) metering systems Cameras measure the amount of light reflected
from object to the digital sensor
Illumination Incident light: The actual light hitting the object
This is what should be measure Not reflected light
TTL system measures reflected light Approximation of the incident light, which is why cameras
don’t always get it right May force the camera into taking under or over exposed
photographs Backlit situation
Older cameras did not have built-in metering systems Photographer had to use hand-held meter to measure the
incident light hitting the object
ObjectPhotographed
External Meter Light Source
Incident Light
Reflected Light
TTL: Through-the-lensIn-Camera Metering
If all objects reflected the same percentage of incident light, the TTL would work just fine Real-world subjects vary greatly in their reflectance.
In-camera metering is standardized based on the light reflected from an object appearing as middle gray If object is lighter or darker than middle gray
In-camera light meter will incorrectly calculate the amount of light The result is an under or over-exposed photograph
Hand-held light meter calculates the same exposure for any object under the same incident lighting
Canon PowerShot Metering Modes :
Evaluative, Center Weighted Average, Spot
LensesTelephoto
Capture images at long distances Long-range photography
of objects
Wide angle• Capture panorama
Establishing photography
Macro – Close-up lenses Allow close photography
Detailed evidence photography
Lenses Focus Light
http://en.wikipedia.org/wiki/Lens_%28optics%29
White Balance
White BalanceWhat is White
Color TemperatureDegrees Kelvin
1800 4000 5500 8000 12,000 16,000
Visible Color Red Yellow White Light Blue
Blue Dk. Blue
WB – set on “auto” WB – set on “fluorescent”
PhiladelphiaFlower Show
[1] Lezano, ibid, page 42.
White Balance (WB) White Balance: How the camera “interprets” white
Allows camera to produce accurate colors under a variety of lighting conditions
The camera relies on the photographer to tell it what the lighting condition is via the white balance setting
White balance can only be corrected using software Photograph must be taken in RAW format
Poor white balance signifies sloppy work Someone simply going through the motions of taking pictures
without paying attention to the business of forensic photography
Little or no thought about the consequences of selecting – or not selecting – the proper WB
Camera Option DescriptionAuto The camera sets the white balance.Incandescent The choice when the majority of the
lighting comes from incandescent light (common light bulbs)
Fluorescent The choice when the majority of the light comes from fluorescent lights.
Direct Sunlight The choice for subjects lit by sunlightFlash The choice when using the built-in flash –
mimics daylight.Cloudy The choice in daylight when the sky is
overcastShade The choice in daylight for subjects in the
shadeCustom Use a gray or white object at the scene as a
reference for the camera the WB
Camera White Balance Options
18% Gray card
Place gray card in scene oriented toward the direction of the incident light.
Take reading from it using a reflected light meter.
Assures photographer of consistent exposures across their photographs.
This technique is similar to using an incident meter, as it depends on the illuminance but not the reflectivity of the subject.
A gray card is only useful for setting or correcting the balance of neutral colors.
Use photograph of a Color Checker as a reference for color balance adjustments.
Gray & Color Checker Cards
FlashDrawback
Creates harsh light Washes out evidentiary
detail
Critical Uses Can Eliminate shadows Can Minimize glare Bounce light to provide
softer illumination
Flash BasicsFlash illumination is
dramatically affected by distance The inverse square law
The difference between a light at 2.8 feet & the same light at 4 feet is 1 stop
Same for 8 feet to 11 feet.
Same for 16 feet to 22 feet
http://photography-on-the.net/forum/showthread.php?t=171657
Cup @ 2.8 feet is 1 Stop Brighter than cup @ 4.0 feet
Takes 16x as much light to illuminateCup @ 11 Feet to = cup @ 2.8 feet
A Roadmap The Perfect Forensic Photograph
Set WB
CheckExposure
Set Shutter
BracketShots
Check WB & DOFOn Photo
Take PhotoSet Aperture
Readjust WB – DOF
Set CameraTo Manual
Close up EstablishingDOF
Choose Perspective
Observe &Smile
White Balance Light
General Illumination Glare
Forensic Perspective Relationship to other Evidence
Deceased? Weapons? Trail direction?
Name The Three Problems…