Registered: Nov 18, 2002
Total Posts: 9376
Country: United States
Technically the challenge is recording a full tonal range. Let's say she is in black and white outfit. You want detail in both. To do that with a digital camera starting with a dark room you would want to:
1) place fill near camera flat lighting everything and raise is power until you see detail in the darkest parts of the black lingerie, then; 2) then place your key light off axis to create the desired 3D modeling and raise its power until the white accents on the outfit are just below clipping. If you want the 3D modeling to look "normal" you'll want the key light raised and hitting her at about a 45° downward angle — the average angle of natural light.
There are no rules of course, but there are cause and effect for any strategy. So try that even fill strategy, then leaving everything else the same just move your fill off axis. What you will find is that instead of evenly lifting all the shadows the fill will lift the ones it hits, but where the fill gets shaded you wind up with dark unfilled voids. You'll see this easier by turning off the key light and looking at the scene with just the off center fill. Everywhere you see a shadow from the fill you'll find a darker, harsher, less flattering shadow in the overall lighting pattern with the key light on. Once you understand the cause and effect of fill placement do what best matches your goal for the look of the shot.
I have a tutorial which shows how the four basic ingredients for studio lighting interact to create the illusion of 3D in a 2D photo — even frontal fill, frontal key light, accent lighting from behind to define overall shape, and background light to control foreground > background separation: http://photo.nova.org/FourLightExercise/
When you have less than four lights you need to find ways via the use of bouncing, reflectors, etc. to produce the same effects and modeling on the subject. For example you can create "kicker" accents by placing reflectors slighting behind the subject just out of camera range, using white foam core panels for a more diffuse glow and covering the other side with aluminum foil and using it when you want a more specular accents for a hard-edged look.
To get a rich, low-key look you'll need to control spill, which will not be easy to do with a shoot through umbrella bouncing light everywhere and lighting the space with spill fill like an overcast day. You may find it more effective to instead to make a foil "snoot" for your fill light and bounce it backwards to a cardboard box lined with white paper — a DIY SB. But if shooting on a white background all that from the shoot through spill will work in a good way to evenly light everything. You just need to start with a goal for the desired look of the lighting and the emotional reaction you want to create: soft and dream like, hard edged and sexual, or something in between.