I have an image that I need to open up the shadows, but using the fill light flatens out my image to much. So I want to create a mask for the shadows then process one file for the rest of the image and another file with the shadows. Is it best to just bump up the exposure to open up the shadows or should I use the fill light? What I have is a person in a black suite in a church. I am trying to figure out which way will open up the shadows but with out flatening out the suit to much.
PS I have been retouching for many years, so my question is specifically aimed at trying to determine the difference between open up shadow with expsure vs fill light when using a mask for the shadows.
Fill light is meant to work on only darker parts of the image. Those parts of the image that are in the left of the histogram. It should have almost no effect on the brighter parts of the image. Exposure adjustments effect the whole image. If your image has little detail in the upper part of the histogram, fill light and exposure might act the same. To my mind Fill light does make the image flatter as it reduces contrast. Another possible answer is to use curves and boost the darks there. I assume your trying to do as much retouching in camera raw as you can, but some problems are still best handled in Photoshop.
Here's the best technique I've found for accomplishing your goal. It's aimed at raw processing, but can be adapted for other.