Forensic Photography midterm

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Name the f/stops we need to know

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f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32

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Name the shutter speeds we need to know

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30, 15, 8, 4, 2, 1, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000

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FIS 335

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71 Terms

1
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Name the f/stops we need to know

f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32

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Name the shutter speeds we need to know

30, 15, 8, 4, 2, 1, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000

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Name the ISO values we need to know

100, 200, 400, 800, 1600, 3200, 6400, 12800, 25600, 51200

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Name the flash powers we need to know

1/1, 1/2, 1/4, 1/8, 1/16, 1/32, 1/64, 1/128

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When moving from f/8 —> f/11, what happens?

Less light, narrower aperture, more DOF

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When moving from f/11 —> f/8, what happens?

More light, wider aperture, less DOF

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What happens when you move from 30 sec —> 1/30 sec?

Faster/shorter shutter speed, less light

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What happens when you move from 1/30 sec —> 30 sec?

Slower/longer shutter speed, more light

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  1. f/8, 1/30 sec, 200

  2. f/16, 1/8 sec, 400

What is the change between the two photos (stops and amount of light)?

f/8 —> f/16 is -2 stops

1/30 sec —> 1/8 sec is +2 stops

200 —> 400 is +1 stop

-2+2+1 = +1 stops or 2x the amount of light in photo 2

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If a histogram is a perfect bell curve what does that mean?

the picture was properly exposed

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If a bell curve is more/curved towards the left side more, what does this mean?

The photo is underexposed, has more shadows

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If a bell curve is more/curved towards the right side more, what does this mean?

The photo is overexposed, has more highlights

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What does “clipped off left or right side” mean?

those parts of the photograph were taken outside of the camera’s dynamic range

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Dynamic Range

The minimum and maximum intensities from the darkest it can capture to the brightest it can capture

does NOT capture pure black or white but instead captures a range between them

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Can clipped parts of photos be recovered?

Some may be able to be recovered in post-processing but not always

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Assume the graph is normal and White at “0”, what would the photograph look like?

The photo would be underexposed and would push left towards the mid tones (18% middle gray)

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Assume the graph is normal and Black at “0”, what would the photograph look like?

The photo would be overexposed and would push right towards the mid tones (18% middle gray)

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Example: underexposed scene, how would you get it to be properly exposed?

f/stop- lower f/number, increased/wider aperture, less depth of field

shutter speed- slower/longer shutter speed, decrease shutter speed

ISO- increase/higher number

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Example: overexposed scene, how would you get it to be properly exposed?

f/stop- narrower aperture, larger f/number, more depth of field

shutter speed- faster/shorter, smaller number

ISO- decrease/smaller number

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what are the types of stops we use on our camera?

1/3 stops

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— I I I I I I I I 0 I I I I I I +

what stop is this?

If I’m at f/11 how would I need to move this to get to 0?

If I’m at 1/30 sec how would I need to move this to get to 0?

  • +1 1/3 stops

  • + 1 stop would be f/16, need to go higher so go to f/22

  • + 1 stop would be 1/60 sec, need to go higher so go to 1/125 sec

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How do you find the aperture diameter?

find the aperture diameter using f/11 and 35 mm focal length

A.D. = focal length/ f number

A.D. = 35 mm/ 11 = 3.18 mm

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Shutter Priority mode

ex. settings- f/16, 1/60 sec, 400; adjust exposure comp to -2

I control the shutter speed and ISO

camera controls the aperture

the camera changes f/number from f/16 to f/32

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Aperture priority mode

ex. settings- f/16, 1/60 sec, 400; adjust exposure comp to -2

I control the aperture and ISO

camera controls the shutter speed

the camera would change shutter speed from 1/60 sec to 1/250 sec

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Programmed mode

I control ISO

camera controls shutter speed and aperture

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Manual mode

photographer controls everything

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Which has more data/info, RAW or JPEG?

RAW has more data/info. Use this setting is you need to post-process something

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f/4 represents what?

Think ¼ of a focal length, if you have 100 mm, then it would be 100/4 = 25 mm

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Focal length 1: 35 mm

Focal length 2: 50 mm

Which has a higher Angle of view? Field of view?

35 mm has a higher angle and field of view

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You are using a 35 mm focal length and a Nikon APS-C crop sensor, your friend is using a full-frame camera at 35 mm. What focal length do you need to use on APS-C to achieve that?

divide 35 mm by 1.5 (Nikon crop factor), 35/1.5 = 23.3 mm

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What setting should you use if you want to expose a really small section of a scene like the underneath of a car?

Spot metering

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What does matrix metering mode do?

sections, zones, grids, and then it takes each of those and combines them through an algorithm, and comes up with what it believes to be the best exposure for the scene

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f/5.6, ¼ sec, 200

If ISO is changed by -1 stop, what would the new variable be and what would f/stop or shutter speed have to do to keep proper exposure?

New ISO- 100

Shutter speed or aperture would have to increase by one-stop

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SNR

which do we prefer, a higher or lower SNR?

give an example

Signal to Noise ratio

we prefer a higher signal so that there is less noise

ISO 400 to 800= less light, lower SNR, more noise controlling images (bad)

ISO 800 to 400= more light, higher SNR, less noise controlling images (good)

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What ISO setting is SNR the highest?

ISO 100

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What tones does Incandescent add to a scene?

adds cool tones to a warm scene

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140 mm, 35 mm, and 18 mm

which is a wide-angle lens, normal, and long?

18 mm is a wide-angle lens

35 mm is a normal lens

140 mm is a long lens

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What are 2 distortions of a long lens?

compression- makes objects appear closer together than they actually are

pincushion- the center pinches inwards

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what are 2 distortions of a wide-angle lens?

elongation- things appear farther apart than they actually are

barrel- the center bulges out

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Does f/5.6 have more or less DOF than f/16?

why?

less DOF

because the diameter of cone of light is wider than the diameter of the cone of light of f/16

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True or False:

As long as light converges/doesn’t converge at a distance equal to or smaller then the sensor of the Circle of Confusion, it’ll be in focus.

True

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True or False:

By raising the f/number (narrower aperture) the range represented by the CoC gets pushed further out from the sensor, increasing the DOF and what’s in focus to our eyes?

True

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Neutral Density Filter

Filter that blocks out a specific/certain number of stops

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Polarizer filter

eliminates reflections of glares, or at least reduces them. Can also increase color saturation

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Slower vs Faster shutter speeds

Slower- shutter curtains are farther apart from each other (don’t close at the same time)

Faster- shutter curtains are closer together, eventually will close so quickly after each other it’ll seem like they close at the same time

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What shutter speed (fast or slow) do you use to freeze motion blur?

Faster shutter speed like 1/100 s

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What are the 3 Cardinal Rules of photography?

  1. Fill the Frame

  2. Maximize DOF

  3. Keep the Digital sensor parallel

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What is flash sync speed?

the fastest shutter speed between the camera and the flash that can be handled. Allows the shutter to be open completely when the flash fires

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Macro lens vs Zoom lens

Zoom- the front element is curved. Zoom projects images curved along the digital sensor. DOF is really important with these lenses

Macro- the front element is flat. Closer minimum focusing distance than Zoom. Projects images flat along the digital sensor.

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What does “closer minimum focusing distance” mean?

The distance in which we are not able to achieve focus once we go past that distance

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What is focal length?

the distance (in mm) between the sensor and the optical center of lens when the camera is focused at infinity

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What accomplishes infinity optically speaking?

All the light rays running parallel from a particular point source are converging onto the center

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What is the max power/output from Flash?

1/1

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3 main factors that control DOF

  1. f/stop (larger f/number = more DOF)

  2. subject to camera distance (closer = less DOF)

  3. focal length (50 mm has more DOF than 24 mm)

55
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How does light behave when you’re looking through the viewfinder?

Remember- light does NOT get recorded onto the sensor until you press the shutter release button.

Before you press that button light is still coming through the lens through aperture coming back and reflecting off of a mirror. Some of that light goes through the mirror onto a secondary mirror and is reflected down into the autofocusing system. Most of that light forms the image you see through the viewfinder but it does that by having to go through a focusing screen, condensing lens, and a pentaprism first, then reaches the viewfinder.

56
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what does the mirror do whenever we take a photo?

flips up out of the way and the shutter opens

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What does light go through before it reaches the sensor?

The Bayer filter- a combination of how many green: reds: blues

2:1:1

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What ratio does a true macro lens achieve?

1:1 - life size on the sensor

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What does a 1:10 magnification ratio mean?

10x larger in real life than it is projected on the screen

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What can you use for shadow control?

  • bounce cards

  • reflectors

  • block the light by placing subject in full shadow

  • internal flash

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Bracketing

taking a series of photos using different exposures and the goal to accomplish the best exposure for the particular photo

example: -1,0,+1

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Higher EV (exposure variable) means the scene has ______ light?

more

+3 vs +5, +5 has more light

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General rule for handholding a camera

use the reciprocal of the focal length

70 mm focal length= 1/125 shutter speed (1/60mis below 70 so have to go to the next closest one)

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What is it called when the light is being shone directly up through the subject? What is it effective with?

transmitted

effective with- transparent or translucent subjects/evidence such as fingerprints on glass or watermarks on a paper

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What is it called when the light is being shone directly across from the subject? (*←— )(less than 45 degrees) What is it effective with?

oblique

effective with- impression evidence such as tool marks, fingerprints, footwear, and indented writing

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What is it called when the light is being shown at a 45-degree angle to the subject? What is this effective with?

Direct

effective with- general evidence where size and shape are important

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What is it called when a set-up uses a light that’s being bounced off a surface (generally white/neutral?) What is this effective with?

Bounce lighting

effective with- subjects that are concave or convex or other general photography when shadows are an issue

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What uses an item placed between the light source and the subject/evidence to soften the light and produce even illumination? What is it effective with?

Diffused lighting

Effective with- shiny or reflective subjects

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What uses a light source at 90 degrees from the axis of the lens with the subject located directly under the lens? A piece of glass is then positioned at a 45-degree angle in the axis of the lens. What is this effective with?

Axial lighting

effective with- subjects/evidence located on mirrors or inside hollow cavities/curved items like a cup

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What is it called when light is reflected directly off of the subject? (2 different 10-degree angles are formed, reflecting light at a 20-degree angle) What is it effective for?

Direct reflective lighting

Effective with- minimizing shadows formed within the subject/evidence and flat surfaces such as latent prints

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What is it called when the subject is surrounded by a cone-shaped tint using white paper or some other translucent material? The light source would be directed at the tint from one or both sides. What is this effective with?

Tint lighting

effective with- shiny and reflective surfaces