In the last couple of exercises, we looked at what are generally considered the two most pressing technical issues in exposing, for a digital photograph, highlight clipping and noise. They are at opposite ends of the tonal scale, and they define what is known as the ‘Dynamic Range’ of a camera. In earlier days, the range between dark and bright was often called the contrast range, however, it is now known as dynamic range, as this is more accurate.
There are several ways of measuring the dynamic range, however, the most easiest for a photographer is in the form of F-stops. The dynamic range of a scene, is therefore the number of F-stops between the brightest highlight, and the darkest shadow. The dynamic range of a camera is the number of F-stops it can capture in one exposed frame. If the dynamic range of your camera is greater than the scene you are about to photograph, all is well and there should be no problem capturing the visible detail. If, on the other hand, the camera’s range is less than that of the scene, something has to be lost. This is the cause of most exposure problems.
As the dynamic range is between darkest and brightest that can be captured, we need to find the end points. The easier of the two is the brightest. Using the highlight clipping warning, we are able to find the exposure which captures the brightest point. Noise determines the darkest tone that can be captured. If you look in the very dark shadows of an image, where most of the noise is, there is a point at which it is impossible to distinguish between noise and real detail. In order to see this clearly, it is necessary to lighten the image temporarily in Photoshop. There are however, disagreements over this, which explains why different dynamic ranges appear for the same camera, depending on who is deciding.