6.2: The Camera

According to a 2024 Pew Research study, 98% of Americans own a cellular telephone. 91% of those telephones are smart phones with cameras. In effect, over 300 million people have a camera in their pockets or on their belts. Most of these cameras take great incidental photographs; however, these cameras are neither appropriate nor approved for forensic photography. The reason for this will be explored later in this chapter but is primarily a result of the way the cell phone camera artificially corrects depth of field and the manner in which the image is stored. For the better part of the 20th century, 35mm film cameras were the mainstays of the forensic technician. 35mm silver halide crystal film was cut into strips and loaded into a canister. The canister was easily loaded into the back of a camera, generally a single-lens reflex camera that allowed the photographer to view the image through the lens by a mirror and prism system, and either manually or automatically fed the film roll past a shutter arrangement. When the shutter was opened, a photon of light would react with the silver halide on the film strip forming a tiny speck of solid silver. The more light that interacted with the silver halide, the more specks of solid silver would be created. Of course, the image that was captured could not be observed by the human eye until after it had been developed. Since there were about 86,400,000,000 silver halide crystals on the film, the resulting photographic images were of great quality. This is the reason why most law enforcement agencies did not abandon their beloved 35mm cameras for digital cameras until the mid-2000’s or even later. Finally, photographs that did not need to be developed to be seen, having the ability to replay the photograph that was just taken, and the improvement of pixel quality of the captured images led to the adoption of digital single-lens reflex or DSLR cameras being the standard for law enforcement agencies.

Figure \(\PageIndex{1}\): 35mm Film Emulsion SLR Camera - Courtesy Brian A. DeLucia

Digital imaging utilizes a light-sensitive sensor to replace film to capture an image. The sensor is made of millions of minuscule photosites, which collect photons of light and converts them into electrical (digital) signals. These signals are gathered as numbers, which the camera’s processor uses to collect the information received by the sensor and to store it in its memory device. We rely on pixels or picture elements to visualize the data. Pixels are the smallest unit of a digital image, essentially one point of color or shade of grey. Your camera arranges pixels in a grid. Each position of a pixel on this grid corresponds with the location of that pixel on the digital image. The more pixels a digital camera can place on the grid, the higher the image resolution. Typically, digital cameras are inferior to the image resolution provided by silver halide film with one exception: full-frame digital cameras. The full-frame digital camera uses a sensor that is the same size as the 35mm film format. This provides for a higher quality image that more closely matches the quality of the 35mm film camera. It also provides better performance in low-light conditions than the smaller crop sensor found in the DSLR. The drawback of the full-frame camera is their price, which is generally outside of the means of anything but the largest police agencies. The current trend in digital imagery is the mirror-less digital camera, which replaces the prism and mirror arrangement of the SLR and DSLR with a sensor called an electric viewfinder or EVF. The benefits of the mirror-less camera is that by removing the prism and mirror arrangement, the cameras can be lighter, will have a fast-shooting speed, and may have better autofocusing properties. It should be noted that the best benefit of the DSLR camera is the ability to change lenses for the different responsibilities which with the forensic camera is tasked.

Figure \(\PageIndex{2}\): Your author's forensic camera

The reason cellular telephone cameras are not appropriate for forensic use is owing to the problem the camera has in dealing with depth of field, which is something you will learn about later in this chapter. Cellular telephone cameras lack the ability to physically adjust the aperture of the lens and lack the distance between the lens and the sensor, as in larger cameras. Therefore, in order to make corrections for depth of field, the cellular telephone camera uses software-based artificial adjustments to blur the background. This technique is called the bokeh effect. This makes the background appear as if it is further away from the principal subject of the photograph. This can also be accomplished using a process called depth map generation which uses depth-sensing technology, such as dual-pixel autofocus, to map the scene and artificially blur certain aspects to give the perception of depth. Another method used to correct depth of field problems is a process called multiple exposure whereby the camera takes two simultaneous photographs and layers the images on top of each other. Finally, most people leave their cellular telephone cameras set on portrait mode that require the camera to focus on the primary subject and to artificially create a shallow depth of field.