There is a trend that I see in the portrait work of many photographers that I think is counterproductive or at least blandly homogenizing... It's the tendency to light everything with very flat, omni-directional light sources. It could be a big beauty dish or softbox right above camera with gratuitous fill light coming from below camera and it could be as goofy and aesthetically flat as two big soft boxes; one on either side of the camera, giving a 1:1 lighting ratio.
What light like that does is to wipe out any real dimensional modeling on a human face and takes with it any interesting photographic sensibility in the photograph. The way one of these flatly lit documentations gets help to finally appeal to consumers is with tons of make-up or metric tons of post production work. I may be a rank traditionalist but I like a sense of depth in a photography and one way to achieve that is to create lighting that shows off the true contours of the face with light that comes from one main source. And though it is ubiquitous advice, the other tenet is to move your light away from the camera axis if you want it to be interesting.
I cringe when I see the work of a (self-proclaimed) famous headshot photographer who lights every one who comes into his studio with the same triangular assemblage of ultra soft fluorescent light sources. He uses them to wrap the light from top to bottom and side to side, as evenly as possible. All the heavy lifting to add any sort of three dimensional interest to the sitters' faces is done by a make-up artist. The flatly lit image giving the stylist a more or less blank canvas on which to paint. It certainly is an effective way to automate one's approach to making portraits but it rarely serves the final recipient as anything more than mundane documentation. Even the expressions the photographer coaxes from his customers are boringly the same and hopelessly contrived.
But maybe when we talk about a feeling of depth there is a