Do you know the dynamic range of your digital camera—the tonal range of lights to darks it can usefully capture? It can guide the way you shoot; the smaller the dynamic range (DR), the more careful you must be that exposures don’t blow out highlights or fill in shadows. I’ve heard “experts” make conflicting blanket claims of anywhere from a four-stop to 12-stop DR for digital cameras, and manufacturer’s specs might be marketing hype—so why not just measure your DR for yourself? It’s easy to do; I’ll show you how. In the process you’ll learn at what exposure highlights saturate to pure white, and gain insight into how your camera assigns contrast.
You can determine the DR of your digital camera if it has manual expo- sure control, or exposure compensation that runs to ± 5 EV. You’ll need a computer with Photoshop or equivalent, two desk lamps, a sheet of 8.5×11-inch white paper, and a couple of hours. I’ll explain just what DR is for a digital camera; then I’ll describe how to set up and shoot the images you’ll need, and how to measure DR from your image files. Finally, I’ll show the results I got when I tested a Canon Powershot G6, a Nikon D2X, a Canon EOS 5D, and a Fuji S3 Pro.
What is digital dynamic range?
The dynamic range is the number of exposure stops between the lightest usable white and the darkest useable black. For digital cameras, determining the darkest useable black is a little tricky because of digital noise, a random speckle pattern produced by image sensors. A little bit of noise in bright tones isn’t noticeable, but it really stands out in dark tones. Noise limits the dark end of the DR: a camera may dutifully record extremely dark tones, but if noise makes the darkest tones virtually indistinguishable from each other, then, in practice, those tones can’t be used. (This is why I defined DR as extending down to the darkest useable black.)
Since noise sets the lower bound of the DR, measuring DR is a little subjective. A dark tone that’s too noisy for you may be just fine with me, and therefore we’d determine different DRs for the same camera. This subjectivity might be part of why expert opinion varies so widely.
It’s also helpful to know the exposure range the camera allows be- tween medium gray and pure white, which I call the “highlight latitude.” Greater highlight latitude decreases the chances of blown out highlights.