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We've covered photography terms you should know about and highlighted why each is important.
Investigators and witnesses can describe crime scenes, sometimes in great detail. However, photographs can better tell the story better with objectivity. They freeze time and leave a permanent record of the scene. Despite its advantages, photography remains the least understood and least developed skill for arson and crime scene investigators. Below we’ve covered photography camera settings you should know about and highlighted why they’re important. All the settings interact with each other, and you can manipulate each one to capture the best image possible for your conditions. We’ve also covered a very useful technique for arson investigators, painting with light, which allows them to capture dark scenes where details and depth of field can be challenging.
First, your goal as an investigator is to capture a crisp, clean image with as much detail as possible. To do that, you’ll need to take the camera out of auto and set it to manual mode.
This is the size of the opening of the lens. It is expressed in f-numbers or f-stops (as in f/5.6). Smaller apertures let less light in and have a higher f-stop. Larger apertures (f/2.8–f/5.6) will allow more light into the camera, but the resulting photos will have a shallow depth of field (more on that later). Typically, you want to start with an aperture setting of f/8 to produce photos that are crisp from foreground to background.
A slower shutter speed will leave the shutter open longer and let in more light. A faster shutter speed lets in less light. A good rule of thumb is to take a picture using a shutter speed that is faster than the fastest thing in your scene. Additionally, cameras should be mounted on tripods, so if you set a long shutter speed, the image won’t be blurry because your hand or other elements caused the camera to shake.
The ISO is the sensitivity setting for the camera sensor. The higher the ISO, the more sensitive the camera sensor is to light. A higher ISO also diminishes the quality of your image, and it will become “grainy” or “noisy.” For arson and crime scene photographs, we want the ISO set at the lower end (100, 200, 400, 800).
The depth of field (DOF) is how much of the foreground to the background is in focus. A large DOF is best for arson and crime scene photography because it makes everything crisp. A good tip to remember: a small aperture setting, such as f/22, will produce photos with a large depth of field, while larger apertures like f/2.8 will produce photos with a shallow depth of field.
This technique is especially useful for arson investigators, because their scenes are typically dark with no natural light and often no other light sources available. To paint with light, use your flash or flashlight to shine light all around the scene so you can capture important details. You need a good tripod, your camera set in manual, and your camera flash or a flashlight.
To paint with light:
Always mount the camera on a tripod. Open the shutter for a long exposure. This will let in more light.
Choose a small aperture that will maximize your DOF.
Consider raising the ISO a little, making the camera sensor more sensitive to light.
Walk around the scene and use your flashlight or multiple flashes to paint the scene with light from all angles to capture more details.
In this extension activity, you will examine the importance of the camera angle and the distortion of fingerprint evidence.
Digital Camera or Cell Phone Camera
Piece of Card Stock or Index Card (4 x 6")
Ring Stand Clamp
Secure the developed fingerprint to the card stock or index card using a small piece of tape.
Tape only the bottom edge of the card to the table. This serves as a hinge.
Set up the ring stand and clamp so the camera or phone is 8 to 10 inches from the flat fingerprint.
Take a picture of the fingerprint. The fingerprint should be 90 degrees, or perpendicular, to the camera lens. Do not move the camera setup.
Use the protractor to raise the top edge of the card by 15 degrees. Take a picture.
Continue to raise the card in 15-degree increments and to take a picture until the card is upright—0 degrees, or in line with the camera.
Compare each picture with the original fingerprint. Which image looks the best?
Assume the role of a forensics expert testifying in a murder case and explain to the jury why photographing fingerprints is a critical step in gathering evidence.