I once read that Leonardo da Vinci had an interesting technique for lighting subjects for his paintings and portrait studies. He had studio with a big center courtyard and he would place his model in the courtyard and then cover the open space above with white cloth. A huge diffusion modifier placed up and over his subject, covering them completely in soft light from above.
After reading this I started to see variations of this technique used in expansive street scenes in movies. One afternoon I had a friend (above) come by and help me with a few lighting experiments. I was constrained by weather, etc. to shoot indoors and that also played into my need for finding repeatable methods.
I placed a six foot by six foot diffusion panel on an aluminum frame directly above the model. the rear of the panels ended just behind her head. This allowed for almost all of the six feet of soft light to fall in front of her. Habit moves us to center things and centering the diffusion above her would have wasted half the value of the light.
I got my tallest light stand and extended it as far up as I could with the light pointing down toward the diffusion surface. My goal was, more or less, complete and even coverage of the scrim but without much spill into the background. My mistake with this particular example was my chickening out about contrast and putting a fill card to bounce light back under her chin, just out of frame. Had I forgone the fill card I think a stronger shadow under the model's nose and chin would have made the portrait much more interesting. This is how I learn though. If everything turned out just right on every try this would be a pretty boring avocation.
I included a favorite portrait below which was done in my favorite, "go-to" lighting. It shows me the importance of shadow and highlight differentiation. Somehow, this is the way I think portraits look best. But my interest in "Da Vinci" lighting has resurfaced and I'm looking for another model to test out some fine-tuning upon. It's easier to experiment with digital. I don't have to wait for the film to come back to see what I should have done better....