Forensic Photography Exam 1

Primary subject

single object; close up photograph of evidence; small area of crime scene; midrange photo showing relative distance between an evidence item and fixed object; is evidence, fixed object and distance between them

Primary subject with large area

multiple items; overall photo to show crime scene in relation to area immediately around it; helps acclimate others to general surroundings of the scene; select few objects to help the viewer understand relationships

Composition

intentional choosing of image elements; deliberate, purposeful composition is necessary for all crime scenes

Four composition issues

1. determine primary subject and composition that best captures it

2. determine proper exposure

3. select optimal focusing technique

4. determine optimal lighting to use

Cardinal rule 1

fill the frame

cardinal rule 2

maximize depth of field

cardinal rule 3

keep the film plane parallel

fill the frame

same for single item or area of scene; put as many of sensor's digital pixels as possible over primary subject; get closer to eliminate unwanted areas

midrange photos

don't include too much space; focus in as much as possible

large areas

show the distance between the gun and fixed object in scene

object sizes

if primary subject is longer than it is wide, use appropriate horizontal or vertical viewpoint; if longer from near to far, use vertical; don't get so close that edges of primary subject are cut off in print

in the background

its assumed that if its included, you wanted it there; circle around primary subject until background has fewer or no distracting elements; tilt camera down more

in the foreground

its assumed that if its included, you wanted it there; circle around primary subject until background has fewer or no distracting elements; tilt camera up more

areas left to right

it is assumed that if it's included, it's because you wanted it there; Use the same considerations as for the background & foreground; if you want it, include it. If not, eliminate it somehow; Fill the frame with the subject

shadow control: sunlight

avoid having shadows; if its impossible, and scene and object allow, reposition so your shadow completely covers photographed areas; try to have entire scene shadow-free or completely covered in shadow

shadow control: electronic flash

Hold yourself responsible for this shadow, even if you couldn't see it when the photograph was taken; You should begin to "pre visualize" your flash shadows; Change the position of the flash head to minimize or control shadows; Use a detachable flash head to better control where the shadows are

hard shadows

very dark shadows that hide detail beneath it; sometimes it doesn't matter when it falls outside of evidence nothing is covered; sometimes it does matter when it falls within evidence (shoe or tire print)

Soft shadows

use bound card/reflector to add light to shadow area, creating this; allows you to see detail within shadow

lens flare

sunlight directly enters the lens and creates images on the lens' optical elements & aperture opening; colorful circles that distract the viewer; may or may not be visualized through the viewfinder; if possible avoid taking photographs with sun in front of you; objects that are important tend to be backlit and underexposed

lens hood

extends from front of lens and prevents light from directly entering; can also use your hand to block out some of the sun

macro lenses

take photographs with lens close to object than with other lenses; make small objects much larger; decreases focal distance as compared to other lens; crop and enlarge objects with better clarity; puts more pixels over evidence, increasing resolution

pixel importance

more pixels on image means better resolution when enlarged

maximize depth of field

DOF is variable range of what appears in focus; includes both foreground and background; try to have everything in focus

Reciprocal exposure

for DOF; uses smallest aperture; combination of shutter speed and aperture; various combinations of f/stops and shutter speed result in same exposure; You must change both to keep the exposure; If you increase (let more light in) one variable by 1 stop, decrease (let less light in) the other by 1 stop; With a smaller aperture, you will need a longer shutter speed to get the same amount of light

hyperfocal focus

when background is infinity; uses DOF scab with camera's distance scale

Zone focus

when infinity is not the background; focus by rule of thirds if lens doesn't have DOF scale; prefocus camera with macro lenses; put camera at its closest focusing position by rotating the lens' focus ring to shortest distance; set up camera at distance where object is in focus

Keep the Film Plane Parallel

keep front of lens parallel to subject

overall photo

shows larger view of an area, relationships between multiple items

midrange photo

shows smaller view of an area, relationship between few items; arrange subject and fixed feature so that both are same distance from you; film plane parallel to imaginary line connecting the two; need to show accurate distances between objects; diagonal photos make this impossible

close-up photo

shows one object in detail; most photos will include a scale; allows image to enlarged to actual size, or zoom in while keeping original size in mind; scale must be on same plane as evidence; film plane must be parallel to evidence and scale

Building facades

diagonal views have part of wall closer to camera and part away from the camera; everything needs to be the same size; Diagonal views create a distance issue between the foreground & background; Depth of field becomes an issue; Diagonal views prevent an electronic flash from equally illuminating the entire scene; Part will appear overexposed, and other parts underexposed

Exception to cardinal rule 3

If the film plane is parallel to a window or mirror, you might see yourself or your flash as a reflection; Never include yourself or your equipment in your photographs; Use a slight diagonal viewpoint so you won't be seen; If you are using an electronic flash and the wall is very reflective, a parallel film plane will create a bright "hot spot" on the wall; Use a slightly diagonal viewpoint; Use a detachable flash and hold it far from the camera & diagonal to the wall; Use bounce flash; You may not be able to stand far enough away to maintain perspective with the film plane parallel to the wall; Use diagonal viewpoints when there is no alternative

avoid linear viewpoints

puts photographer and both objects along same line

Exposure

how much light is in the picture; appears normal or as we expect to see it

"stops"

used to express differences in exposure; changing stops either halves or doubles overall lighting from the original picture; A+1 doubles exposure' A-1 halves the exposure; properly exposed images are between -1 and +1

Variables the affect exposure

shutter speed; aperture, ISO, lighting

Shutter speed

located inside camera body in SLR cameras just in front of digital sensor; image viewed through viewfinder and the light striking the sensor both come from single lens; light coming from lens is reflected by mirrors; mirror is moved to take photos

Shutter speed pt. 2

when shutter is pressed, it opens for pre-determined amount of time; light enters lens and strikes sensor; indicated by whole numbers but are fractions; never use slower than 1/60

Shutter speed pt. 3

speeds longer than 1 second are indicated with "; "B" (bulb) used when shutter speeds are longer than those on camera are needed

Aperture

size of circular opening

Diaphragm

set of blades that forms circular opening

f/stop

fraction relating size of aperture to lens focal length' shown as whole numbers, but represent fractions; larger f/stop number=smaller aperture

ISO

camera film is rated for different film speeds; changing speed also results in 1-stop exposure differences; higher number=more sensitive to light (ISO 200 is twice as sensitive as ISO 100); lower number= more light is needed fro good exposure (3200 ISO good for outdoors at night)

ISO equivalents

faster ISO speeds can result in graininess, or digital noise; increases in contrast: lose mid-tones, image is made of light and dark sections; digital pixilation: underexposed, pixels "guess" what their color should be

Select exposure settings

1. ambient light conditions

2. select shutter speed (usually 60)

3. Assess reflective light meter

Ambient light conditions

what is already present at the scene

Bright: use slower ISO

Dim: use faster ISO

Rule of Thumb for ISO

1. outside, during middle of sunny day, use ISO 100

2. close-up photos, use ISO 100

3. all other times, start with ISO 400

ISO to shutter speed

use ISO as shutter speed, then pick setting closes to that speed and faster

Light and Color

different light sources have different effects on surroundings, you might not see but the camera will; for accurate color capture only use midday sun, electronic flash, or ensure white balance setting is correct

white balance

process of removing unrealistic colors

shade, cloudy, twilight

light color shifts toward blue; smaller aperture gives good DOF, but color will have bluish tint

sunrise, sunset

sun is tinted more red/orange than its usual yellow; correct using electronic flash

indoors

most light bulbs tungsten light creates an amber/yellowish tint; office spaces use fluorescent light creates greenish tint; correct with electronic flash

Outdoors

streetlight changes perceived colors of various objects; black objects appear brown, white objects depend on light

Digital white balance

can be used to eliminate blue tints on cloudy days

when in doubt

underexpose; cameras cannot capture all details in photos that contain both sun lit areas and deep shadow areas; take two pictures can be digitally altered to highlight both areas; underexposed pictures can be altered to show detail, overexposed cannot

photographer body movement

hold the camera securely & properly to limit movement; change shutter speed to help eliminate involuntary body movement; use shutter speed that is closest to focal length of lens, inverted into a fraction

subject motion

•1/125th will "freeze" a walker, enabling the face to be recognized.

•1/250th will "freeze" a jogger, or someone jumping.

•1/500th will "freeze" a bicyclist or a slow-moving vehicle (up to about 30 mph).

•1/1000th will "freeze" a vehicle going up to 60 mph.

•1/2000th will "freeze" an airplane powered by propellers

Rain & Snow

faster shutter speeds will freeze drops; slower shutter speed=more light; use lens filter to prevent overexposure; polarizing filters eliminate glare

Most crime scenes

should be captured with shutter speed 1/60 and either f/22, f/16, f/11, f/8

Reflective light meter

measures amount of light being reflected into camera; a "normal" scene is one in which 18% of light is reflected back

Snowy scenes

reflect more light than normal; results in underexposure

Darker scenes

reflect less light than normal; results in overexposure

non-normal scenes

predominantly light colored or dark colored; lots of sky in field of view; backlit scenes or have both bright lights and dark shadows

Predominantly light scenes

manually change recommendations set by meter; open aperture 1.5-2 stops wider than meter recommended

Predominantly dark scenes

manually change recommendations set by meter; close aperture 1.5-2 stops smaller than meter recommended

Large amounts of sky

sky reflects more light than normal toward camera; think outdoor overall photos, sky looks normal but building is underexposed; take meter reading with the sky not in view & use those settings

Backlit/high contrast scenes

use electronic flash to fill in the dark areas and keep proper exposure for light areas

Proper exposure fir tricky scenes

Meter the camera on an 18% gray card, use those settings; The card must be in the same conditions as the scene (fully sunny, fully shady, etc.); Some photo identifier cards are also 18% gray cards; Meter the camera on green grass; It also reflects about 18% of light; Meter the camera on well-traveled asphalt; It also reflects about 18% of light; Meter your palm; Reflects about 36%, regardless of race; Open up 1 stop to avoid overexposure

Exposure modes

Manual, program, aperture priority, shutter priority

Manual exposure (M)

manually set f/stop and shutter speed for each photo and ISO; usually mode for crime scene photographers

Program exposure (P)

camera chooses f/stop and shutter speed based on what light meter detects; not good for crime scenes, can't manage DOF, motion; good for when arriving on scene and there is activity happening that you need to document quickly

Aperture Priority (A or AV)

you set f/stop; camera sets shutter speed based on available light and your f/stop

Shutter priority (S or Tv)

you set shutter speed; camera sets f/stop based on available light and shutter speed; does what M mode does but faster

Bracketing

taking same photo more than once, using different settings for different exposure

Manual exposure bracketing underexposure

If the minimum f/stop (f/22) has NOT been chosen, decrease aperture size; 1 stop dimmer, maximize depth of field; If the smallest aperture has already been chosen, use a faster shutter speed or ISO; 1 stop dimmer, can still hold the camera

Manual exposure bracketing overexposure

If not already using the slowest shutter speed (1/60), change shutter speed to slower time; If already using the slowest shutter speed (1/60 for 55 mm lens), can change f/stop or ISO; Remember that for smaller apertures, f/22, f/16, f/11, and f/8 are the best to use to maximize depth of field; Remember you don't want to go slower than 1/60 if holding the camera by hand

f/16 day

Midday, bright and sunny with crisp, defined shadows

•Use these settings:

•f/16

•Convert ISO to shutter speed

•ISO 100 (remember earlier we said this is best for sunny days)

•Shutter speed 1/125

•The reciprocal exposure provides better depth of field

•f/22 and shutter speed of 1/60

f/11 day

•Bright but hazy, shadows are indistinct (soft shadows)

•Use these settings:

•f/11

•Convert ISO to shutter speed

•ISO 100 (still good for bright days)

•Shutter speed 1/125

•The reciprocal exposure provides better depth of field

•f/16 and shutter speed of 1/60

f/8 day

•Bright and cloudy day, no shadows

•Use these settings:

•f/8

•Convert ISO to shutter speed

•ISO 100 (still good for bright days)

•Shutter speed 1/125

•The reciprocal exposure provides better depth of field

•f/11 and shutter speed of 1/60

f/5.6 day

•Many variations of the f/8 cloudy days, sometimes an f/5.6 is required

•Sunny day where the sun is blocked in a larger area

Polarizing filter

•When light reflects off a surface, it can become polarized in one direction and shows reflections

•Polarizing filters eliminate these reflections by blocking/filtering them

•Rotate the lens to block the light

•If not totally clear, lean to one side, or

move closer/farther away

focal length

the distance from the center of a lens to the focal point; tells us how much of scene will be captured and how large individual elements will be; longer the focal length, narrower angle of view and higher magnification; shorter focal length, wider the angle of view and lower the magnification

Focus

entire scene, and all its evidence should be in focus

resolution

ability of camera system to distinguish alternating line pairs as they get thinner and closer together

Acutance

camera's ability to render sharp edge of subject as sharp edge in the photograph; clear and precise distinction between edge of one object and beginning of surface that its on; crisp and defined edges

sharpness/being in focus

light enters camera and converges at sharp point on digital sensor; light becomes increasingly smaller circle until it converges at a point; light rays converging before or after digital sensor will always result in blurry image

circles of confusion

if light is a circle when it hits digital sensor, it will remain "confused" and out of focus;

Manual focusing

if just one object rotate focus ring; film plane parallel to top of object is important

Automatic focusing

press shutter halfway, can change main object in viewfinder; usually reason for poor crime scene photos

Zoom lenses

wide-angle lenses can cause barrel distortion; straight lines at sides appear bent outwards; can't be used for close ups

Depth of field

range in front of and behind plane of exact focus the also appears as being in focus; anything outside this appears out of focus because the circles of confusion are larger than resolution limit of eye

Hperfocal focusing

used to maximize DOF when background is infinity

3 general categories

Large scenes when background is infinity

Medium distances where background is not infinity

Small areas/close up images of single evidence items

Zone focusing

used to maximize DOF when background is not infinity

Rule of thirds

•The DoF usually extends 1/3 in front of the point of exact focus and 2/3 behind the point of exact focus

•Not always exact and not always correct (think hyperfocalfocusing), but a good place to start

•Focus at the distance that is midway between the top and bottom of the composed image in the viewfinder

minimize DOF

daytime surveillance and latent prints on glass

Aperture and DOF

wider apertures create very short DOF ranges (F/2, f/8. f/4); one object is very clear, others are very blurry; focus on 1,2,3 with f/1.8, then with f/22

DOF variable

FLL/f/stop=DOD

FLL

focal length of lens