Forensic (prelim)

• Photography


  The art or science that deals with the reproduction of images through the action of light, upon sensitized materials, with the aid of a camera and its accessories, and the chemical processes involving therein
• Literal definition of photography

  Derived from the Greek words "phos" meaning "light" and "graphia" meaning "write", therefore photography best translates to "write with light"
• Modern definition of photography

  An art or science that deals with the reproduction of images through the action of light, upon sensitized materials, with the aid of a camera and its accessories, and the chemical processes involving therein
• Technical/Legal definition of photography

  Modern photography may be defined as any means for the initial thermal, electrical or electronic recording of the images of the scenes or objects formed by some type of radiant energy, including gamma rays, X-rays, ultra-violet rays, visible light and infrared rays
• Police photography


  An art or science which deals with the study of the principles of photography, the preparation of the photographic evidence, and its application to police work
• Forensic photography


  The art or science of photographically documenting a crime scene and evidence for laboratory examination and analysis for purposes of court trial
• Principles of photography

  • A photograph is a mechanical and chemical result of photography
  • To produce a photograph, light is needed aside from sensitized materials
  • Lights reflected or radiated by a subject must reach the sensitized materials while all other lights must be excluded
  • The exclusion of all unwanted and unnecessary lights is achieved by placing the sensitized material inside a camera
  • The amount of light on the sensitized material after exposure is not immediately visible to the eyes
  • To make the formed image visible, it must undergo the development process
  • The visual effect that results from chemical processing is dependent on the quality and quantity of the exposing light
  • More light will yield an opaque or black shade on the sensitized material after development
  • Too little will produce a transparent or white shade
• Light


  A radiant electromagnetic energy which travels in wave motion and can be seen by the naked eye
• Photographic rays

  • X-rays (1-30 nanometers)
  • Ultraviolet rays (30-400 nanometers)
  • Visible light (400-700 nanometers)
  • Infrared rays (700-1000 nanometers)
• Primary colors of light

  Blue, green, red
• Secondary colors of light

  Cyan, magenta, yellow
• Additive color mixture

  Using three beams of primary colors of light resulting in secondary colors, cyan, magenta and yellow
• White


  Presence of all colors
• Black


  Absence of all colors or absence of light
• Subtractive color mixture


  Using three beams of secondary colors to know which is complementary with each other
• Reflection


  The deflection or bouncing back of light when it hits a surface
• Refraction


  The bending of light when passing from one medium to another
• Diffraction


  The bending of light when it hits a sharp edge of an opaque object
• Hagen-Fresnel's principle


  The width of the diffracting obstacle is not very largely compared to the wavelength
• Types of objects based on how they behave to light

  • Transparent objects
  • Translucent objects
  • Opaque objects
• Sources of light

  • Natural light source
  • Artificial light source
• Natural light sources

  • Bright sunlight
  • Hazy sunlight
  • Dull sunlight
  • Cloudy bright
  • Cloudy dull
• Artificial light sources

  • Continuous radiation (fluorescent lamp, incandescent lamps, carbon arc lamp, photoflood lamp, gas lamp, etc.)
  • Short duration (flash unit)
• Camera


  A light tight box with a lens to form an image, a shutter and diaphragm to control the entry of light, a means of holding film to record the image, and a viewfinder to show the photographer what the image is
• Instamatic (point and shoot) camera


  The simplest type of camera because it is fixed focus, also known as box type camera
• SLR (single lens reflex) camera


  The most ideal camera type to use in forensic photography, light in weight, compact and versatile, with interchangeable lenses and attachable accessories
• Methods of image formation

  • Pinhole method
  • Shadow method
  • Lens method
• Lens


  A transparent medium which either converges or diverges light rays passing through it to form an image
• Types of lenses


  • Convergent (positive, convex) lens
  • Divergent (negative, concave) lens
• Inherent lens defects or aberrations

  • Spherical aberration
  • Coma
  • Curvature of field
  • Distortion
  • Chromatic aberration
  • Astigmatism
  • Chromatic difference of magnification
• Types of lenses according to degree of correction

  • Achromatic lens
  • Rapid-rectilinear lens
  • Anastigmat lens
  • Apochromat lens
• Types of lenses according to focal length

  • Wide angle lens
  • Normal lens
  • Telephoto lens
  • Zoom lens
• Lens diaphragm


  A device found in between the lens components of a camera which can be expanded or constricted by moving a turning ring on the lens barrel, controlling the size of the opening that represents the ratio of the focal length and diameter of the opening
• Diaphragm as controller of speed


  The diaphragm controls the amount of light reaching the film, thereby controlling the exposure time or shutter speed
• Diaphragm as controller of depth of field


  The diaphragm controls the depth of field, which is the distance between the nearest and farthest objects in a scene that appear acceptably sharp in the image
• Diaphragm as controller of definition


  The diaphragm controls the definition or sharpness of the image by controlling the amount of light reaching the film
• Wide Angle Lens


  A lens with a focal length of less than the diagonal of its negative material. This lens has a wide area of coverage but produces a small image size.
• Normal Lens


  A lens with a focal length approximately equal or more but not more than twice the diagonal of its negative material. Its coverage corresponds to nearly the coverage of the human eye.
• Telephoto Lens


  A lens with focal length of more than twice the diagonal of its negative material. Produces bigger image of objects at far distance but area of coverage is smaller.
• Zoom Lens


  A lens with variable focal length.