When we as professional portrait photographers look at a portrait we look to the eyes of the subject and the shadow pattern (if any) on the mask of the face to determine how the subject was lit.
As for the eyes I look for the position of the catch lights and the size and shape as well. The catch lights should not be dead center in the pupils and ideally they should be large and round—not square or rectangular (outside the studio) or worse yet hard-pinpoints (I call these Ice-Pick catchlights) most generally caused by speed lights.
Outside the studio we should make our lighting look as natural as possible. Centered catch lights meaning the key light is coming mainly from the front just washes out any shadows creating flat lighting. Without shadows you loose three dimensionality in your subject.
So, in my example portrait I first placed my subject in a spot that had nice back light for separation and visual interest. In addition, I have her placed near a large rock surrounded by trees just out of frame to camera left. The rock and trees are acting as Gobos—blocking light and creating a nice shadow on the left side of her face. This is called negative fill or subtractive lighting.
The key light is a large patch of open blue sky creating a nice soft, yet directional, lighting pattern on her face.
F4.5 @ 1/160 sec., ISO 400, lens @ 200mm
I typically use f4.5 to get the entire face sharp, yet still blur out the background nicely because my lens is at 200mm.
It’s that simple!! Feel free ask me anything about this type of lighting.
Author: Jerry W. Venz, PPA Master Photographer, Craftsman, Certified
Training site: http://www.LightAtTheEdge.com
Client site: http://www.TheStorytellersUsa.com