Forensics Unit 4 Part 2 Notes

FORENSIC PHOTOGRAPHY LAB GUIDE

Why is photographic documentation of physical evidence is necessary?

• A dispassionate and accurate description of the scene must be available to investigators for future analysis.
• Biological evidence must be documented in its original condition for presentation in court, as evidence is often altered during testing.
• Physical evidence must be presented in context which it was found.
• The adage that “a picture is worth a thousand words” is especially true in forensic science.
• EXPOSURE
  • The amount of light allowed into the camera. The amount of light is controlled by: APERTURE SIZE and SHUTTER SPEED and ISO
• APERTURE SIZE
  • This describes the width of the whole lens, and controls the amount of light sent through the lens to the sensor. 
  • The measure of aperture diameter is expressed as a fraction (f/number) of the aperture relative to the focal length.
  • A SMALLER APERTURE  INCREASES THE DEPTH OF FIELD.
• SHUTTER SPEED
  • The amount of time the shutter is open. 
  • Measured in seconds or fraction of seconds. 
  • If your camera has this feature, manual shutter speed can be set to 2, 1, ¼, 1/8, 1/250, and 1/500 seconds. 
  • Longer shutter speeds may require a tripod.
• ISO
  • The film speed
  • This will also affect the exposure of your photo 
  • A low ISO has more pixels than a higher one
• EXPOSURE COMPENSATION (BRACKETING)
  • The term bracketing usually refers to exposure bracketing: the photographer chooses to take one picture at a given exposure, one or more brighter, and one or more darker, in order to select the most satisfactory image. Technically, this can be accomplished by changing either the shutter speed or the aperture, or, with digital cameras, the ISO speed, or combinations thereof.
• FOCAL LENGTH
  • The distance from the lens to the image formed inside the camera.
  • The focal length will change not only the focal point in your photo, but also the depth of field and area of view. 
  • You can control this by choosing a predetermined mode.
• Depth of field:
  • The thickness or portion of the photograph in sharp focus.
  • This is controlled with the aperture. 
  • A smaller aperture gives a greater depth of field.
• ANGLE OF VIEW
  • In photography, angle of view (or field of view) describes the angular extent of a given scene that is imaged by the camera.
• Close-Up (a few inches away) MACRO LENS 50-200mm
• Portrait (3-20 ft.) NORMAL LENS 50 mm
• Scenery WIDE ANGLE LENS 20-30mm
• LENSES
  • You may not notice a huge difference in your photos without getting special lenses.
• Good Composition
  • 2 scales 
  • Scales border photo 
  • Scales are in the same plane as the subject 
  • Object fills the field of view 
  • At 90 degrees 
  • No hot spots 
  • Contrasting background
• OBLIQUE LIGHTING
  • Using a second light source held at an angle to create shadows and increase resolution and decrease contrast in a photo. 
  • It is also used when an image is shiny and produces a hotspot on the image from light bouncing back into the camera from the flash
• CONTRAST
  • The relative difference between light and dark. 
  • LOW CONTRAST - many shades of gray =  HIGH RESOLUTION
  • HIGH CONTRAST - black and white =  LOW RESOLUTION 
  • Depending on what you are interested in inspecting, either could be better. 
• RESOLUTION
  • The quality of the image in terms of fine detail or pixilation.
• ISO or  FILM SPEED
  • 100 slow - more granulation, higher resolution 
  • 800 fast - less granulation, lower resolution
• COLOR TEMPERATURE and WHITE BALANCE
  • White light is a mixture of other colors of light, so depending on the source of lighting in your picture the colors may change.
  • Our brains adjust for the color difference so we do not notice the difference, but in photography the camera records what it sees so the colors may require adjustment.
  • The color temperature of a light source is the temperature of an ideal black-body radiator that radiates light of comparable hue to that of the light source. A black-body radiator is any object which fully absorbs all frequencies of light, just as a white body is any object which fully reflects all frequencies of light. It is measured in K
• WHITE BALANCE
  • White balance is a feature many digital cameras and video cameras use to accurately balance color. It defines what the color white looks like in specific lighting conditions, which also affects the hue of all other colors.
  • In auto mode, your camera will choose a middle range. 
  • For best results, select the actual light setting in the room. 
  • If the light source is on the blue end, it will warm the colors. 
  • If the light source is on the red end, it will cool the colors.
• BLACK & WHITE FILM PHOTOGRAPHY
  • Different color wavelengths of light have different energies and will produce different shades of gray.
• COLOR FILTERS and BLACK & WHITE PHOTOGRAPHY
  • Color filters can be used to darken colors or lighten colors in a photo to increase contrast. 
  • For example, a red filter will allow red light through and lighten that object in the photo while absorbing its complement and darkening that
  • TO LIGHTEN A COLOR : Choose the same color 
  • TO DARKEN A COLOR : Choose the compliment color
• THE POINT REFERENCE METHOD
  • Take individual photos that overlap and piece together. 
  • Photograph 360 degrees. 
  • Include entry and exit points. 
  • Used to establish location
  • The point reference method is preferred over using the panorama function which often distorts the image.