Imaging Sensor Size

Imaging Sensor Size is just like aperture:  size matters!  All standards and guidelines for forensic digital imaging, regardless of discipline, require a “full frame imaging sensor”.  In other words, the imaging sensor in the camera must be 36 mm horizontal x 24 mm vertical, which is the standard size of a 35 mm film frame.

Unfortunately, FAR too many law enforcement agencies buy less expensive digital camera that use a much smaller APS-C imaging sensor.  The Canon APS-C standard is smaller (22.3 x 14.9 mm) than Nikon, Sony, et al (23.6 x 15 mm).  For comparison, a “full-frame” imaging sensor is 2.5 times LARGER than an APS-C imaging sensor. 

There are two significant issues caused by APS-C imaging sensors in forensic photography.  First, due to the size difference, there is a function known as “focal length” that must be considered.  For example, a Nikon camera with a 60 mm macro lens (required for latent print capture) and APS-C imaging sensor has a focal length of 1.5.  In layman’s terms, this means the camera body must be 1.5 times further away from a latent impression than a Nikon camera with a 60 mm macro lens and a full-frame imaging sensor.  This distance can affect the quality (clarity) of the impression being photographed.

Also, there are a significant number of advantages when using a full-frame imaging sensor:

• Improved low light performance: a full-frame imaging sensor can capture more light, which allows a sharper focus.
• Higher ISO performance: there are hundreds of articles that provide details about the noise introduced into an image because of smaller photoreceptors on the imaging sensor.  Using a full-frame imaging sensor with larger photoreceptors is crucially important when photographing evidence using an alternate light source!
• Greater control over depth of field: This is crucially important when photographing latent prints (or when using macro photography in general), especially when the impression is on a curved or textured surface.  You can get the camera much closer to the object with a larger imaging sensor, which causes the depth of field to become smaller. 
• Improved dynamic range and color: a full-frame sensor captures more tonal range details in shadows (dark side of the histogram aka underexposed) and highlights (light side of the histogram aka overexposed).  The amount of visible detail and color accuracy are significantly better at both ends of the histogram.

When viewing the EXIF details in the Photoshop history in Adobe Photoshop, the lens will appear as a 60 mm macro lens, but it also documents that the lens has the effective range of a 90 mm macro lens (i.e., 60 mm x 1.5 = 90 mm).

To help overcome some of the noise and focal length issues, a 40 mm macro lens may be used on digital cameras with the smaller ASP-C imaging sensor because 40 mm x 1.5 = 60 mm.

For detailed specifications about different makes and models of digital cameras, please refer to https://www.dpreview.com/.  This website contains a database of all digital cameras developed worldwide since the 1980s.  Dpreview.com provides the most accurate, complete and reliable detailed list of specifications than any other website.  Moreover, they publish details that you cannot find even on the manufacturer’s website.