Double-Process RAW For Better Tonality
Don't try to do it all in one step. Use the power of RAW to process two separate images optimized for different tonalities.
One problem photographers have always faced is the fact that no medium yet invented can capture the tonal range our eyes can see. Film can't get close to recording the brightness range of light that the human eye can perceive. This holds true for digital sensors as well. While some high-end sensors can record more tonal information than film, they still can't record all the tonal variations the eye can see.
The human eye can perceive a contrast ratio of 800:1; the best slide films, 30:1; and the best digital sensors, 40:1. So photography has always been about compromising. When shooting slide films, the old adage was "expose for the highlights, pray for the shadows." With digital, that has changed a bit, especially with RAW files.
You can process the RAW file two (or more) different ways and combine these images using an image-editing program to get the best of each exposure. When shooting with a digital camera in the RAW format, you have the capability of processing your image specifically for different exposure values, highlights, midtones and shadows. You can use this flexibility of the RAW format to your advantage when photographing scenes with a high dynamic range of light.
Is it best to slightly underexpose or overexpose RAW images? When you lighten a dark RAW image, you risk adding a lot of noise to the shadow areas. When you darken a light RAW image, you might not have good highlight detail. I find when shooting under contrasty light that it helps to slightly overexpose the image and then process it twice—once to have more shadow detail and once to bring back the highlight detail.