Enter my new macro lens. Now, please note, what is to follow is only an example and the photos are simply crops of larger photos but I think they serve to prove my theory. I recently purchased the Canon 100mm 2.8L Macro Lens. This purchase got me thinking about macro photos and histograms ... and that led me to my current exposure process.
My theory was that I would be able to expose for a subject's skin by taking a photo that encompasses the highlights to shadows of the subjects face and then look at the histogram to determine if the exposure was correct. I quickly realized that the histogram changed depending on the lighting ratios/setup and the intended mood of the image. I found that a flat lighting setup gave a histogram that spread from the "bottom" (shadows) 1/3 to the top (highlights) 2/3s of the histogram. Now, this is not always true for every lighting setup, or every photographer. You will need to determine your ideal histogram shape and spread.
I start by taking a photo of the subject (a forehead) as you see below. Note, that you do not need a macro lens to do this as you can take the same photo, out of focus, and achieve that same result.
After that, I look at the histogram and adjust settings until I get a histogram that spreads from the lower (left) 1/3 to upper (right) 2/3s of the histogram (see below). I've found that I tend to like the look that is shifted slightly to the right.
I then step back and begin shooting. and get images that, I have fond, require little adjustment for skin exposure in post. Now, this does not include a explanation of determining background exposure. That is another beast for another post, and I would be happy to explain that process if there is interest. In any case, below is an example the overall histograms and photos that I have been getting out of camera.
As always, comments, opinions or other methods of exposing for skin are very, very welcome. Take care everyone!