Forensic Photography Final Exam Review

The Magnifications ratio for a typical 50mm lens is about…

1:7

A built-in flash will typically “accentuate” surface details, while an oblique flash will typically “flatten” the light. True or False?

False

When photographing through the “envelope” of a bulb to capture the condition of the filament, the following lighting technique will probably work best

Backlighting

 “Tire impressions” are relational dimensions between two or more tires and can be used to determine the wheelbase of the vehicle, True or False?

False

The following is (are) true about tire “scuff” marks?

They’re also known as “critical speed yaw” marks, they exhibit stria diagonal to the outside edge of the tire mark, they're made while the tire is still rotating

An aperture of f/8 allows twice as much light as f/16 to enter the camera. T or F?

False

Which filter is recommended for all camera lenses

1A, skylight, or UV

Which value is one stop less light than provided by an aperture f/8

f/11

Which camera has gotten rid of its mirror and uses an electronic viewfinder

A DSLM

 For crime scene photographs to be admissible in court, they…

Must be true and accurate representations of the scene

The person who first introduced crime scene photography techniques is

Alphonse Bertillion

When is the processing history required for a processed digital image…

For digital images classified as category 2 photographs

 Digital images stored using a JPG file format are recompressed each time the image file is opened and closed, T or F?

False

The visual perception of lines (pattern) that is caused by a digital camera when the “lines” of the subject are running at an angle to the position of the photoreceptors in the imaging sensor, or when utilizing a “resampling” technique (during compression schemes) such as JPG, is known as…

A Moire pattern

 In nighttime environments, one may hand hold a camera effectively for up to 1s T or F?

False

If you're in a zone focusing situation, and your lens doesn't have a DOF scale, the quickest, most accurate method of focusing to maximize the DOF is to?

Focus at the distance that's midway between the top of the composed image and the bottom of the composed image

With telephoto lenses, their weakness is “Perspective distortion” in the form of foreground-to-background compression T or F?

True

When photographing 3D impressions with oblique illumination sometimes an impression will appear to have raised elements and sometimes the elements will appear to be depressed. This effect is known as?

Inversion Effect

The purpose of utilizing an attenuated light technique while photographing a bloody footwear print in total darkness, that is being treated with luminol, would be…?

To capture a conventional scale in the picture

 By adding a “¼ wave” retardation plate to a linear polarizer, you get circular polarized light, T or F?

True

 20% of light that reflects off the surface will “vibrate” parallel to that surface, T or F?

False

To determine max capture area for your camera that's the min image resolution compliant with NIST standards (for latent prints and palm prints), you simply divide the effective pixel resolution of your camera (both width and height measurements) by?

1000

 If you must photograph through a wire-fence structure, you can “minimize” the appearance of the wire mesh by using a shallow DOF and focusing on your subject, T or F?

True

When recording surfaces such as white-painted walls, what does the camera tend to do?

Underexposes the image

The minimum focusing distance for a typical 50mm lens is about…

18 Inches

In macrophotography work, we are usually trying to fill the frame with a magnification ratio of…

1:1

 Infrared photography can be used to “drop-out” the discoloration of decomposed human tissue to reveal a decedent's tattoo details T or F?

True

Infrared photography can be used to “drop-out” the color of a victim’s sweatshirt to reveal bullet holes, bullet wipe, and possible gunshot residue patterns, T or F?

True

 Telephoto lenses are best known for their ability to magnify distant objects. This effect can be determined by dividing the focal length of the telephoto lens by?

50mm

 In surveillance situations, to be confident magnification will be adequate to recognize either a subject’s face or to read a vehicle's license plate, you should use a lens that has a focal length of how many mm?

2mm of lens per foot of distance between the camera and the subject

The technique to maximize DOF when infinity is composed in the background is known as…

Hyperfocal Focusing

 With wide-angle lenses, their weakness is “perspective distortion” in the form of foreground-to-background elongation. T or F?

True

What is the purpose of using a scale that has a circle printed on its surface, at a crime scene?

It's used to calculate the angle of the film plane by measuring the major and minor axes of the circle

When an external flash is held very low to the ground causing the light to be reflected off of any dust particles and into the camera lens, this lighting technique is known as?

Oblique Lighting

When making examination quality photographs of impression evidence, is the following true about your lighting technique?

Attach a flash and hold approximately 5 ft away from the impression

Generally, there are 3 kinds of polarized light: linear, circular, and elliptical, T or F?

True

A polarizing filter can be used in photos to reduce glare from surfaces, such as glass T or F?

True

“Right-Handed” circular polarized light remains “right-handed” after it reflects off of a surface, T or F?

False

Which of the following makes this photograph shown above (the only one taken at the crime scene) a poor example of good crime scene documentation?

The film plane angle, not an examination quality photograph, no scale in the picture, possible cross-contamination of trace evidence

Typically, you should not use flash in rainy or snowy conditions T or F?

True

When photographing ”shiny” or “polished” objects or “small” crime scenes, the following technique should be done to avoid creating “hotspots”?

“Bounce” Flash

Bracketing ones exposures (photos) refers to…

Recording multiple exposures of the same subject but in different ways

Will all else equal, which shutter speed is better able to stop motion?

1/400th of a second

An aperture of f/8 allows twice as much light as f/16 to enter the camera T or F?

False

Which ISO value is the most sensitive to light?

ISO 3200

 Zoom lenses…

Allow the photographer to capture images at a variety of focal lengths

What are the basic operating modes of the “typical” modern digital camera?

Program, Aperture priority, shutter (time) priority, and manual

Which filter is recommended for all camera lenses?

Average Density

Zooming in on the subject in question, reducing any extraneous background and thereby covering as much of the camera's image sensor as possible (gaining resolution) is known as?

Filling the Frame

What ISO setting should be used (at least in the “old” convention) for “examination quality” photographs?

ISO 100

To ensure crime scene photos are in proper focus, CSI investigators will try and use what f-stop settings?

f/11 or higher

What is a stop of light?

One-half or twice the next full value of light

 What is the rule of thumb regarding “handheld” photography?

The shutter speed should not be any slower than one over the lens’ focal length

As the distance light travels is doubled, its intensity?

Is quartered

Describe the resolution and archival Capabilities of the camera(s) assigned to you.

I have an 18 megapixel camera. It has two L settings, two M settings, two S1 settings, an S2 setting, an S3 setting, a RAW + L setting, and a RAW setting.

 Describe what the phrase “filling the frame” means to a photographer.

Filling the frame means using all the space in the photo to capture your subject. In other words, your subject should take up a majority of the image.

List at least three “camera care” guidelines to follow.

1. Use the carrying case to protect the camera and equipment

2. Use the camera strap

3. Protect the camera from harsh elements

 Describe what “ISO” settings are available on your camera(s). What ISO Setting Is Recommended for “Examination Quality” photographs?

My camera has ISO settings: Auto, 100, 200, 400, 800, 1600, 3200, and 6400. ISO setting 100 is recommended for examination quality photographs.

Describe what f-stops are available for your camera lens. Describe the relationship between f-stops and depth of field (DOF).

F-stops are available from 4.5 → 29. The lower the number (closer to 4.5), the larger the opening and the smaller depth of field. If the F-stop is closer to 29, the aperture is getting smaller and the depth of field is increasing.

With all else equal, which shutter speed is better able to stop motion?

1/400th

You accurately meter an exposure at ISO 200, f/5.6, for 1/500th of a second. You wish to bracket the exposure by adding one stop of light. What would be the new exposure values?

ISO 400, f/5.6, for 1/500th of a second  

OR

ISO 200, f/4.0, for 1/500th of a second  

OR

ISO 200, f/5.6, for 1/250th of a second

An aperture of f/8 allows twice as much light as f/16 to enter the camera.

False

Which ISO value is the most sensitive to light?

ISO 3200

Which value allows three more stops of light than the ISO setting 100?

ISO 800

Zoom lenses

d. Allow the photographer to capture images at a variety of focal lengths

A shutter speed of 1/250th of a second allows twice as much light as 1/500th of a second to enter the camera.

True

What are the basic operating modes of the ”typical” modern digital camera?

B. Program, Aperture Priority, Shutter (time) Priority, and Manual

Which filter is recommended for all camera lenses?

d. 1A, Skylight, or UV

Which filter(s) is most commonly used to reduce glare when photographing evidence behind glass?

c. Polarizer

Describe the relationship between DOF and f-stop?

Depth of field increases as the f-stop number increases. The aperture opening gets smaller and the DOF increases.

To ensure crime scene photos are in proper focus, CSI investigators will try and use what f-stop settings?

CSI investigators will try to use F11 or higher.

 If you have to photograph through a write-fence structure, what can be done to “minimize” the appearance of the wire mesh?

Change the depth of field to be further away. Therefore, the fence in the foreground won't be in focus and the subject past it will be.

Why should you try to avoid using the highest f-stop lens setting (f/22)?

Avoid F22 because then you start to get diffraction. Even though you have great depth of field you get slight distortion in the photo.

Describe the relationship between DOF and Focal length?

When you change the focal length it changes the size of the aperture opening. As you go up in focal length you go up in aperture size which means you go down in depth.

 What is the purpose of taking evidence photos with and without a scale?

Without a scale you take photos of how you find the scene when you arrive. That way no one can say that you tampered with the scene when you put the markers and scales down. With the scales you can tell the size and distance of objects.

With respect to photographs, what does the phrase “True and accurate representation” mean? Explain as if speaking to a jury.

It means that the objects and scenes are depicted in photos as accurately as possible in real life. The photos are not taken artfully with flare and filters. The photos are taken with the best light and of the best quality.

You are asked to determine the size of an item of evidence from a photo. Explain the process of doing this to a jury.

When you take photos at the scene you will also take photos of objects next to a scale of a size that makes sense for the object. Then they will be set to scale so they are at a one-to-one ratio with the real object in order to determine the size of the piece of evidence.

 List and explain the three series of photographs, which should be taken to completely document a crime scene.

Overall photos are of the entire scene so you can get a general layout of where things occurred and where they are. Mid-range photos come after and should be slightly closer. They don’t show all the exact details of the objects but it shows where they are in relation to each other. Then closeup photos should be able to more accurately scale objects and show fine details.

 What are two considerations when utilizing a scale in your photographs?

The scale should be a similar color to the background so it doesn't get washed out but it should be distinguishable enough to read the numbers. A second consideration that should be taken when utilizing a scale in photographs is that the photo must not be taken on an angle so that the scale is not distorted.

When a bloodstain is found on a pair of blue jeans and the photographer wishes to increase the contrast of the image by making the red bloodstains darker in the photograph, which colored filter would be the best choice?

B. Blue

When a bloodstain is found on a pair on a section of green carpet and the photographer wishes to increase the contrast of the image by making the green carpet lighter in the photograph, which colored filter would be the best choice?

C. Green

Blood ______________ UV light.

B. Absorbs

Because light is additive, Luminol reactions are generally improved through longer exposures.

A. True

Describe how a polarizing filter works

A polarizing filter is used to absorb light vibrating in a particular direction. It reduces reflections and haze while increasing color saturation.

Why utilize a “fill-flash” technique?

Use built in flash for fill flash (to fill in shadows). Good to use in the forensic world when you need to get rid of things in the shadows. Used mainly during the day by photographers.

Why utilize a “bounce-flash” technique?

Bounce flashing helps prevent hot spots in the photos.

Why utilize an “external” flash opposed to the camera’s “built-in” flash?

Standard flash units aren't strong enough to use at night or very far away. “External” flash units are much more powerful and can get the light from different angles.

Why is it important to use a flash (from at least three different angles), when photographing a three-dimensional print?

It's important to use a flash from at least three different angles when photographing a three-dimensional print because it allows you to capture more detail. Checking the lighting and photographing from multiple angles allows you to have more options to choose from when you need to see details of a specific area of the photo.

Explain what is meant by “examination quality” photographs? Why is it important to take “examination quality” photographs of a footwear print (or fingerprint) prior to lifting or casting?

An “examination quality photograph is with a scale in the photo and with the film place of the camera, parallel to the impression. This allows for photographs to be taken that can be accurately compared to other impressions. Casting or lifting may ruin/destroy the original impression so photos must be taken first.

The rules of evidence (both the Federal Rules of Evidence as well as the rules of evidence adopted by many states) provide Two Primary legal principles for digital image processing. Processed (enhanced) digital images may be used if...?

Nothing material or essential has been added or removed from the original image

When using the Levels function to adjust the shadows and highlights of an image, what should you be careful of?

Be careful to ensure that you don't clip pixel values in the image when using the Levels function

Why is it sometimes necessary to “resize” or “calibrate images 1:1”, when doing comparison work?

You can photograph a “2” by “3” area or a “4” by “6” area. It makes no difference to the camera. Unfortunately, the camera has no idea how large the captured area is: it knows only that the area consists of a certain amount of horizontal and vertical pixels. So it may be necessary to resize or calibrate the image.

The “enhancement” process should be defined to allow only commonly accepted image processing techniques that improve the visualization (quality) of the image without adding or removing features (content) that were not present when the digital image was captured. Generally, is this statement True or False?

True

 With “Category 2” images, you should maintain the sequence of the steps used during the image enhancement process, and you should also record the settings and parameters used for each step. This information must be sufficiently detailed so that a person with comparable skills, training, expertise, and experience could repeat the process and achieve a comparable result. Generally, is this statement True or False?

True

 Why utilize a “tent” when photographing evidence close-up?

Utilizing a tent allows for the light to be more easily altered to the photographer's liking. It creates a controlled environment and gets rid of distractions in the background.

What should your “White Balance” setting be, while using the tent’s built-in lighting?

Your white balance setting should be set based on the lighting that each tent has. It may be fluorescent or natural or whatever.

What can you do to ensure your “White Balance'' is correct when photographing through a microscope?

You can use an 18% gray card and put it under the microscope on the stage. Once it is in place of the specimen you can adjust the diaphragm and other lights of the microscope until it looks right. This will ensure that when the specimen is put onto the stage after instead of the card, that the white balance is good.

What advantage is there to utilizing a “macro” lens when taking close-up photographs?

The advantage of utilizing a macro lens when taking close-up photos is reproducing a small subject at true size. You can focus at shorter distances so you can see many more details than with a normal lens.

List three types of Macro Photography accessories?

1. Macro lens

2. Extension tubes

3. Reversal Rings

 Why would it be a good idea to utilize a perspective grid in an overall crime scene photograph?

If there is a large number of measurements that need to be made at a scene. If there are poor weather conditions that could ruin the scene. If certain equipment or extra man power is not available. Or for minor scenes that could become major scenes.