Forensic Photography definitions

manual

photographer controls all settings

automatic

camera controls all settings

aperture priority

camera controls shutter speed

photographer controls f/stop and ISO

shutter priority

camera controls f/stop and ISO

photographer controls shutter speed

programmed

camera controls shutter speed and f/stop

photographer controls ISO

UV light

emits __ radiation that causes fluorescence

best for bruising, bodily fluids, fibers, drug residues, and certain fingerprint reagents

IR light

materials absorb, reflect, or transmit __ light

best for GSR, ink differentiations, charred documents, and bloodstains

visible light fluorescence

creating fluorescence in the __ range

best for powders and developing chemicals, nonblood bodily fluids, fibers and drug residues

direct lighting

light fixtures pointed right at subject

oblique lighting

light fixture on same plane as subject, good for casting shadows (impressions)

bounce lighting

light fixture pointed towards camera, camera has white cardboard/paper positioned around the lens

axial lighting

light fixture parallel to subject, casting light through glass plane that is angled over the subject

diffused lighting

light fixture has plastic diffuser over it

manual flash

flash output power and aperture are set manually to control the desired exposure

standard i-TTL

flash output is adjusted to the correct exposure of the main subject regardless of background info

i-TTL balanced fill-in flash

flash output is adjusted to well-balanced exposure of the main subject and background

automatic (non-TTL)

flash measures the reflected flash and controls the flash output according to the reflected flash data

auto aperture (non-TTL)

flash measures the reflected flash and controls the flash output according to the reflected flash data and the lens and the camera information

inverse square law

2D = ¼ I

inverse square law 1

I = 1/D²

inverse square law 2

D(△) = √1/I

angle of view

angle represented by the area in the frame

field of view

distance represented by the area in the frame

wide angle lenses : focal length __ than normal

less

long lenses : focal length __ than normal

greater

circle of confusion

largest out-of-focus circle that appears to be in-focus

near DOF

distance from sensor to front of the depth of field

far DOF

distance from sensor to back of the depth of field

DOF in-front

range from front of the depth of field to the focus point

DOF behind

range from focus point to the back of the depth of field

total DOF

distance from the front of the depth of field to the back of the depth of field

DOF in-front + DOF behind

focus plane

middle of the depth of field

typically where the subject is

subject to camera distance

sensor to focus plane

near distance of acceptable sharpness

focus distance (HD - focal length) / HD + focus distance

far distance of acceptable sharpness

focus distance (HD - focal length) / HD - focus distance

infinity focusing

involves focusing on distant object (provides reasonable foreground sharpness)

hyperfocal focusing

useful for scenes involving a subject with both near and far components (closest focusing distance that will ensure objects near/far will be acceptably sharp)

zone focusing

focusing 1/3 into the scene (useful when a subject compromises a specific ‘zone’)

pre-focusing (best for close-up photographs w/tripod)

1) pre-focus to closest focusing distance 2) move camera toward subject until it is in focus

extension distortion (wide-angle lens)

items appear further away from each other, closer objects also appear larger

compression distortion (long lens)

items appear closer together, further away objects will appear larger

barrel distortions (wide angle)

straight lines appear to curve outward

pincushion distortion (longer lens)

straight lines appear to curve inward

resolution

spatial frequency measure in line pairs / reproduction of closely spaced object detail

acutance

ability to produce well-defined transitions at hard edges / edge contrast within an image

authenticity

a fair and accurate representation of the scene

relevance

material and probative

uncompressed

no compression applied (examiner quality)

lossy compression

some original data is permanently lost, cannot be reversed (JPEG)

lossless compression

all original data can be retrieved (examiner quality) (RAW)

mechanical shutter (physical pieces)

front and rear curtains physically move in front of the sensor

exposure recorded on the sensor

electronic front curtain shutter

front curtain is electronic, rear curtain is mechanical

exposure read line by line, typically top to bottom

standard electronic shutter

no mechanical parts present

exposure is read line-by-line

electronic global shutter

no mechanical parts present

reads whole sensor simultaneously

luminescence

ability of molecules to emit light from causes other than heat

fluorescence

emits light only while the surface is currently being stimulated (absorbed)

phosphorescence

emits light that is retained and will continue to be visualized after the stimulation has ended

chemiluminescence

emission of light as a result of some chemical reaction