Chapter 2 forensic Photography

Black

- is the absence of all colors or the absence of light

White

- is the presence of all color.

Light: Its Characteristics and Sources

1. Light is a form of energy, and to understand light we begin with the electromagnetic spectrum which is basically a grouping of all electromagnetic radiation arranged according to the amount of energy contained in the radiation. 2. Visible light is a part of this electromagnetic spectrum that creates the sensation of light when it falls on the human eye. 3. The properties of all electromagnetic radiation can be described by three inter - related terms. 4. These are wavelength, frequency and energy. Since light is a part of this spectrum, it too can be described by these terms. 5. Hence, it is important to understand these terms as a first step towards understanding light.

Magenta

400 nm

Blue

475 to 455 nm

Cyan

500 nm

Green

560 to 475 nm

Yellow

585 to 560 nm

Red

685 to 605 nm

Front Lighting

Distinct sun is used as front lighting when it comes from behind the photographer. It is a common belief that photographs taken at early in the morning or late in the afternoon is better compared to photos taken in any other time of day. The light, when the sun is low, is oftentimes described as magical. Colors are warm, shadows are long, and subject glow with razor sharp clarity

light

Electromagnetic radiation within the portion of the electromagnetic spectrum that can be perceived by the human eye

Radiation

If matter sheds its mass and travels with the speed of light

specular reflection

If the surface is so smooth and polished that the reflected rays are not scattered

hazy sunlight

It is a when the sun is covered by thin clouds but still clearly visible and it is illuminating your subject, it produces soft shadows and moderate highlight and contrast is also moderate, while rays are directional.

Ultraviolet light

It is used to photograph fingerprints on multi - colored background, documents that are altered chemically or over writings and detection of secret writings.

Moon and Stars

It is when the sun sets, day turns into night and it becomes dark. The night sky has the moon and innumerable stars. However, despite their brightness the moon and the stars can hardly keep the darkness away. The moon actually has no light of its own, it reflects the light. Natural light source

Violet

It ranges from 440 - 405 mμ

Indigo

It ranges from 455 - 440 mμ

Blue

It ranges from 475 - 455 mμ

Green

It ranges from 560 - 475 mμ

Yellow

It ranges from 585 - 560 mμ

Orange

It ranges from 605 - 585 mμ

Red

It ranges from 685 - 605 mμ

Artificial light sources

Light sources of this category are man-made and are divided into the continuous radiation and the short duration. Continuous radiation, those that can give illumination continuously, short Duration and it gives a brief flash of light produced by a burning metallic wire (flash bulb) or an electrical discharge through a gas - filled tube (electronic flash).

Dull Sunlight/Cloudy

Objects in open space cast no shadow. It is cloudy when the sun is shining bright but covered with thick moving clouds, other parts of the sky maybe clear, lighting is even throughout and not directional, it does not cast practical shadows on your subject and contrast is relatively fair.

Light

Radiant energy that makes things visible is classified by the wavelength into a system known as the electromagnetic spectrum.

Overcast Sky/Cloudy Bright

Sun is bright but not visible, light is soft and not directional, skies may be covered with stationary clouds and it provides no shadows and low contrast

Incident angle

The angle which it strikes

CD or DVD

The closely spaced tracks on a CD or DVD act as a diffraction grating to form the familiar rainbow pattern we see when looking at a disk;

wavelength

The distance between two consecutive peaks (or troughs) is called the _______, and is denoted by the Greek letter (lambda).

Invisible lights

The light that cannot be detected by the naked eye is the invisible spectrum. The left region of the visible light is called the ultra violet region. The right region of the visible light is called infrared region which are too long in wavelength to excite the retina of the eye. It is detected by the skin as heat. Invisible Radiation that are used in Modern Photography

Electromagnetic Spectrum

The light that we see is only a part of a tremendous range of energy. It is the whole range of radiant energy that includes radio waves, microwaves, infrared light, visible light, ultraviolet light, x rays and gamma rays.

Sunlight

The most popular and mostly used light source of photographers. It is free and no need to be transported. But it is not always there where we want it. It is uncontrollable but can be controlled using the camera controls (shutter speed & aperture opening).

tungsten lamp

This are incandescent, meaning that they work by burning a filament.

Fluorescence

This happens when molecules of the fluorescent material absorb energy at one wavelength and radiate it at another wavelength.

Electronic Flash Lamp

This is consisting of a slender glass tube filled with a gas (Xenon), a high voltage electrical discharge is passed through coiled tube, causing the gas to glow

Heavy Overcast/Cloudy Dull

This is practically the same as overcast sky but generally darker and light is dull. It provides very poor contrast and static cloud is so thick where one cannot tell the overhead position of the sun.

Bright sunlight or Distinct Sun

This is the direct sunlight striking the subject. It is the brightest of all, it is highly directional, images taken with distinct sun is characterized by extreme highlights and deep shadows and it provides the highest contrast in a picture.

Overhead Lighting

This normally occurs at noontime where sun is directly above your subject. This angle of lighting is generally not recommended for taking portraits. Strong dark shadows are cast at the subjects' eyes. However, it can be corrected with a fill - in flash

LASER

This refers to Light Amplification through Simulated Emission of Radiation. By illuminating certain items with LASER, they would fluoresce or could be made to stand out in sharp contrast from their background. This was especially significant in locating dried biological items

Incandescent

This refers to a conducting filament enclosed by a glass bulb heated by the electric current until emits lights.

Carbon Arc

This refers to a pair of carbon rods connected in series with a resistance across direct current.

Forensic Light Sources (FLS)

This refers to a wide variety of relatively inexpensive light sources which use filtered white light.

Soft light sources

This refers to cloudy and overcast sky, an open shade, direct flash bounced off an umbrella or direct flash whose light passed through a translucent fabric (soft box).

Hard light Sources

This refers to direct sunlight, direct flash, spotlight, flood lights, and light bulbs are among the light sources that produce hard lighting.

Alternative Light Source (ALS)

This refers to far more expensive alternative to forensic LASER. It uses a variety of band pass filters to provide a high intensity beam of non - coherent light.

Fluorescent Lamps

This refers to illumination in an electric discharge lamp of the mercury - vapor type. The coating fluoresces and sends out light of low brilliance with visible zone

Non - Directional Light

This refers to in outdoors, it is called Heavy Overcast. Light is dull from the sky that seems to envelope around. No obvious direction of light is evident in the surroundings. It casts very faint shadows underneath of subjects (like cars) or none at all on other subjects.

1.1. F - lamp

This refers to lamp that has effective flash duration of about 1/200 of a second.

1.3. M - lamp

This refers to lamp used for all shutter speeds provided the synchronizer level is on

Photoflood lamps

This refers to lamps that can be placed up very high producing deep shadows underneath protruding surfaces, if subject is a person standing, he will appear gloomy and sombre. These can be placed to shine from below giving mysterious and strange effects of frights to observers of the picture.

Ambient Light

This refers to light that is the existing in a room, in a coliseum, or in a covered basketball court. Lights can be directional or not, depending on the source. This type of light usually comes from lamps, ceiling droplights, light coming from windows or tainted glass, etc.

Chemical Flash Lamp

This refers to light that produces by the rapid burning of metal wire, foil or primer powders. To produce a rapid and complete burning, the bulb is charged with O2, the lamp flashed once

1.2. S - lamp

This refers to slow peak and their brilliance are about 30 milliseconds after the current is applied.

UV Lamp

This refers to some units are portable battery operated and are easily carried and can meet the rugged and rigorous demand for field work.

Filtration

This refers to the character of light to be altered from its colorless into visible state.

Interference

This refers to the color that can be produced by interference of light waves in thin film like soap bubbles or a film of oil floating in water.

Transmission

This refers to the light that passes through an object.

Rectilinear

This refers to the nature of light that normally travels in straight line.

Absorption

This refers to the nature of light to be absorbed in the process of dark surfaces.

Polarization

This refers to the process by which the vibration of light are confined to definite plane, the speed of light can be measured.

Side Lighting

This type of lighting happens mostly in the morning and afternoon when the sunlight hits the subject from either the right or left flank of the photographer. It brings out textures, patterns, and shapes of objects.

Back Lighting

This type of lighting happens when the sun strikes the subject from behind or when the sun is directly in front of the photographer. Light coming straight from the back of the subject in portrait produces a bright edged outlined around it. It also brings out shapes and good profile as well as silhouettes of your subjects.

visible light

This wavelength means a frequency range of roughly 430 - 750 terahertz (THz).

Infrared

Used in taking photographs of obliterated writing, burnt or dirty documents. Also known as "Blackout photography".

The RAT Law

When incident light hits a medium, three things might happen, the light maybe: ✓ Reflected ✓ Absorbed ✓ Transmitted

Incident light

When light strikes the surface and rebound it is said to be reflected

Diffused reflection

When reflect light is scattered by rough surface

X-ray

X - rays are electromagnetic energy having a wavelength that ranges between 10 - 30 millimicrons. ✓ Objects which are opaque as seen by the naked eye can be penetrated by x - rays. ✓ To produce a shadow photograph of an internal structure of solid objects, x - rays is suitable.

Hologram

a picture that changes when looked at from different angles

Infra-red

a wavelength emitted by the sun which cannot be seen, though we can feel it in our bodies as warmth or heat.

Role of Light in Photography

a. Light radiated or reflected by the subject must reach the film while all other lights are excluded by placing the film inside a light tight box. b. The effect of light on the film is not visible in the formation of images of objects. To make it visible, we need or require a chemical processing of the exposed film called development. c. 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.

Ultraviolet

another form of light we cannot see, but we know about it because it tans our skin in summer.

Cosmic rays

are high energy charged particles, originating in outer space, that travel at nearly the speed of light and strike the Earth from all directions. Most cosmic rays are the nuclei of atoms, ranging from the lightest to the heaviest elements in the periodic table.

Infrared light

are lights having wave length greater than 700 millimicrons. It wavelength ranges from 700 - 800 millimicrons.

Microwaves

excite the water molecules in food, heat them up, and pass the heat throughout the food. ✓ It can harm the body because it can heat the water molecules in deep tissues.

Ole Romer (Denmark)

he measured the speed of light in 1676. However, when light comes in contact with an object, it may be bended in the following manner.

Energy

man for the first time transmitted a substantial quantity of matter into light, heat sound and motion

Cosmic Rays

refers to galactic cosmic rays, which originate in sources outside the solar system, distributed throughout our Milky Way galaxy.

299,792,458 meters per second (approximately 186,000 miles per second)

speed of light to be exactly 299,792,458 meters per second (approximately 186,000 miles per second)

Visible light

usually defined as having wavelengths in the range of 400 - 700 nanometers (nm), or 4.00 × 10−7 to 7.00 × 10−7 m, between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths).

Quantum Theory

✓ A quantum of light is called photon, when photon strikes a light sensitive surface, it gives energy of electrons within the metal explain the photoelectric current.

Hertzian Waves

✓ An electromagnetic wave produced by the oscillation of electricity in a conductor (as a radio antenna) and of a length ranging from a few millimeters to many kilometers.

Refraction

✓ Bending of light when passing from one medium to another.

Translucent objects

✓ It allows light to pass, however diffuse it sufficiently that objects on the other side may not be clearly distinguished ✓ In some cases the objects on the other side may be recognizable but sharp detail and outlines are obscured. ✓ It transmits 50% or less of the incident light.

Transparent objects

✓ It allows sufficient visible light to pass through them that the object on the other side may be clearly seen. ✓ It transmits 90% or more of the incident light.

Diffraction

✓ It is also described as the bending of light when it hits a sharp edge of an opaque object.

Wavelength Theory

✓ It is best illustrated by the dropping of stone in a pond of still water.

Diffraction

✓ It is described as the apparent bending of waves around small obstacles and the spreading out of waves past small openings.

Opaque objects

✓ It is so greatly diffuse the light that recognizing the object on the other side is very difficult if not impossible. ✓ It divert or absorb light.

Refraction

✓ It is the change in direction of a wave due to a change in its speed. This is most commonly observed when a wave passes from one medium to another.

Quantum Theory

✓ It is used to explain X - radiation and photo - electricity.

Reflection

✓ It occurs whenever an object changes the direction of a light wave but does not allow the wave to pass through it. Reflected light maybe Specular or Diffused. ✓ When light strikes the surface and rebound it is said to be reflected, and it is called incident light. The angle which it strikes is called incident angle. ✓ If the surface is so smooth and polished that the reflected rays are not scattered, the term is specular reflection. ✓ Rays are reflected at the same angles as they strike. ✓ When reflect light is scattered by rough surface, it is called diffused. ✓ The reflected light rays are the one that affect the eyes. ✓ The object is seen as white when all of the various wavelength of the visible light were reflected. ✓ When there is no reflection of the object and all of the various wavelengths were absorbed, it will produce black or darkness.

Quantum Theory

✓ Max Plank theorized in 1900 that light might be made up of little bundles of energy named quanta

Quantum Theory

✓ The different energies in the electromagnetic spectrum are the following: cosmic rays, gamma rays, x - rays, UV rays, visible light, infra - red rays, heat rays, hertzian waves, and the alternating current oscillation.

Wavelength Theory

✓ The series of wave which travels outward from the center point are just like wave that travels in all direction from a source with equal velocity.

Wavelength Theory

✓ The wavelength of the light is the most pertinent, particularly in the design of lenses.

Radio Waves

✓ These light waves have the longest wavelength of all lights. ✓ Used for communicating through the modification and amplification of sound waves.

Wavelength Theory

✓ This theory maybe used to illustrate reflection, interference, refraction, diffraction and polarization.

Gamma rays

✓ Used in recording or photographing objects hidden by opaque mediums