Managing Contrast
One day or another every photographer is challenged by the contrast in his scene. Either too low, or worse, too high. Choices have to be made. Will the highlights be clipped or do we lose the detail in the shadows. Maybe a bit of both. Either way the picture will not look nice.
The “Zone System”
In the old days of black and white film we could, and still can, influence our dynamic range by manipulating the exposure and development.
Perfected by Ansel Adams in his “Zone System” one can measure the dynamic range in a scene and act accordingly. When executed well, you would end up with perfect negatives which could be enlarged without too much hassle in the darkroom.
In short the Zone System says: “expose for the shadows and develop for the highlights”. Basically, a high contrast scene will be overexposed and underdeveloped. A low contrast scene will be underexposed and over developed. The problem of course here is that a normal roll of film has 36 exposures. For Ansel Adams there was no problem because he used single sheets of 4×5 or 8×10 inch film which CAN be individually developed.
How about Digital?
Okay, nice that you can do all this with film but I’m certainly not going to use film – I hear you say. How about digital?
Digital acts very much like slide film. First of all it’s a positive process, there is no negative intermediate and similar to digital the dynamic range is limited. Dynamic range is the amount of contrast a medium can capture. For slide film that is limited to 3 to 5 stops exposure. Digital capture is better then that but still not nearly as good as negative B&W or colour negative film. So, on a nice summer day with loads of sun the contrast of the scene will easily be higher then even the best digital sensor can handle.
Important to know about digital sensors is that anything that is really overexposed, also called clipped, is gone forever. There is no info in there, it’s just plain white. But in the shadows there might be quite some details hidden but not seen at first sight. Especially with the new sensors, a shot at low ISO can easily retrieve 3 stops in the shadows without showing noise.
Because the digital sensor is a positive process, contrary to the B&W analogue process, we should “Expose for the highlights and develop for the shadows”. Where develop here is meant as post processing in Lightroom, Photohsop or any other photo manipulation program. In practice this means you’ll expose to make sure there is still detail in your important highlights. Then in post processing the shadows can be lifted. But only when using low ISOs where the noise is very low. On higher ISOs the shadows will be getting too noisy. What this means in practice is that you can use spot metering to measure the highlights and overexpose them by 1 to 1,5 stops. Or use matrix metering and underexpose the whole scene by 1 to 1,5 stops.
Of course you’re shooting in RAW to get the most out of your sensor and have the biggest leeway in your processing. Also your highlight clipping warning and histogram on the back of your camera is of great use for this technique. If you can assess your histogram before shooting, as on most high end P&S and mirror-less cameras it’s even easier.
Too much contrast in this scene to be captured by the sensor.
Same scene but 2 stops underexposed.
Shadows lightened.