6.3: PHOTOGRAPHY

In this chapter, you will be learning about still photography, which means a photograph that is not moving as in a motion picture or video. Consider a motion picture that is made of many frames of individual photographs. The sequential movement of these frames provides for the seamless movement associated with a movie. The individual frame of the movie is called a still photograph. Although video cameras play a significant role in crime scene and forensic documentation, it is the still camera that provides the factual representation of the crime scene and the evidence located within the scene. Photography is the creation of an image of an object using the action of radiant light on a light-sensitive surface. Cameras record light. They do not record motion, unless we manipulate their functions in order to record motion; and by this, your author means to stop motion. Light is provided either by the sun or by electric lights or electronic flash. It is important to understand that every photograph taken at a crime scene is subject to discovery in courtroom proceedings. Therefore, no photographic image should ever be deleted. It also means that any photograph captured by any law enforcement official either in the crime scene or on the perimeter of the crime scene must provide that image to the court. It is essential that the only photographs of a crime scene must be captured by trained professionals who have the primary responsibility of processing the crime scene.

Depth of Field

Depth of field is likely the most important aspect of forensic photography because depth of field provides sharpness to the image being captured. Depth of field is the distance between the objects that are closest to camera’s lens and those that are furthest away. In other words, depth of field determines how much of the image is sharply in focus. Depth of field is controlled by the aperture of the camera, the focal length of the lens, and the distance between the lens and the object. The aperture of the camera can be found within the lens. Just like the human eye, the aperture of the camera widens or narrows to allow more or less light into the lens. The aperture is measured by focal lengths called F-stops. Here is where things get complicated. The higher the F-stop number, the narrower the aperture, and therefore the less light is being let in to reach the sensor. You might ask, wait a minute, if there is less light being allowed into the camera, how does this create a sharper image? The answer is shutter speed. When the shutter release button is pressed, the shutter opens for a specific amount of time to allow the light to enter the lens and to interact with the sensor. If the aperture is wide open, the speed at which the shutter must be left open must be very fast or too much light would come through the lens and the resulting image would be greatly over-exposed. If the aperture is very small, the shutter must remain open longer, and therefore more light is allowed to interact with the sensor. The drawback of a slow shutter speed is that the photographer likely would not be able to hold the camera steady enough to allow the image to remain in focus, and therefore the camera would need to be mounted on a stable platform like a tripod or copy stand. You will notice the importance of depth of field in the next series of photographs. You will also notice how important it is for fingerprint comparison purposes.

Figure \(\PageIndex{1}\): Aperture f4.2 - Shutter speed 1/10th of a second - Author's collection

Figure \(\PageIndex{2}\): Aperture f22 - Shutter speed 4/5th of a second - +0.03 exposure - Author's collection

Figure \(\PageIndex{3}\): Aperture f5.6 - Shutter speed 1/400th of a second - Author's collection

Figure \(\PageIndex{4}\): Aperture f22 - Shutter speed 1/25th of a second - Author's collection