Dealing with tough exposure situations in the field
Or why DR will become more important than MP in digital photography

Last revised: 3 Oct. 2005

Flatirons formation in morning mist, Boulder, CO. Fujichrome Velvia 50, Nikon F5, ND grad filter.

 As recently as 12 months ago, most of us photographers were anxiously awaiting the next great leap in imaging sensor technology—more megapixels.  The big deal in digital, it seemed, was squeezing more detail out of our sensors (we had to be "better" than film, you know).  With the arrival of the 12.4MP Nikon D2X, suddenly we found ourselves with imaging sensors that could potentially out-resolve our glass!  Certainly, the debate as to whether digital cameras could match or exceed 35mm film quality seems to be dying down. So what more could we possibly want from our cameras? Well, how about this forThe Next Great Thing: More Dynamic Range.

Dynamic range is a measure of the overall amount of light in a scene.  When the dynamic range of a scene (expressed in total number of f/stops) exceeds the dynamic range of the detector (eye, film, digital sensor), then some of the information in that scene is clipped.  Values falling below the minimum detectable level will appear pure black, and intensity values above the maximum will appear pure white.  As anyone who has shot color slide film will understand, film (and digital sensors) do not capture the full range of detail that our eyes can discern.  In fact, most articles that I have read suggest that our eyes have a dynamic range of around 11 f-stops of light.  A good color slide film usually has about 5-stops of dynamic range: =/- 2.5 EV from the “metered value”.  Color print film generally has more dynamic range, or latitude, than slide film.  Digital sensors are certainly better than slide film, but probably not as forgiving as print (negative) film.  The sensor in Nikon’s D2X, based on my experience, is at least 6-stops, and more if you are willing to accept some noise in the image.  Noise, you see, starts creeping into the shadows as you make extreme levels adjustments to your image—it was always there, of course, but you don’t see it when things fade to black. So the next great improvement in digital sensors may not be more MP, instead it may be more DR. What do we do until then?

 Given that a bright daylight scene may have over 11-stops of DR, even with a good sensor, something is going to clip.  So what do we do when faced with a REALLY tough scene, where there is bright daylight in some of the frame and shadows in other parts of it? Sunrises and sunsets are notorious for having WAY too much DR. As a general rule with digital (and slide) photography, expose for the highlights.  You can then recover quite a bit of shadow detail later on using most post-processing software with levels or curves adjustments.  Exposing for the highlight detail is critical, however, because once you clip (blow) the highlights, you have lost the detail in that part of your image forever.  Psychologically, the mind is more forgiving of shadows being a little too dark, but bright areas are distracting and unpleasing to the eye.  But certainly by now you must be thinking that I wouldn’t be sitting here telling you this if that was all there was to it!  Let’s look at some techniques that we can use to improve the DR in our images.

Sunset, Merritt Island NWR, FL. Note the shadows are pure black (clipped). I did not have an ND grad filter for this photo. Sometimes, clipping shadows can be pleasing for silhouettes.

Page 2: Using graduated ND filters to balance exposure