So here’s an important concept in portrait photography: the sun isn’t great to work with. In fact, it's terrible.
If you try and shoot a portrait with the sun as a primary light you’ll wind up with seriously deep shadows. I know the next technique you’re considering. Run for cover, get into the shade of a tree. But I have issues with this. First this means I can’t choose where and when I’m shooting a portrait. I need to be in control of my process for both creative and practical purposes. What if my subject can only meet me at 2:00 in the afternoon. Am I going to turn down the shoot?
Next, there’s the white balance issue. If my subject is in shade and my background is bright, I have two different white balances. Shade is cool and sun is warm. So if I set my white balance to shade I have a background that looks like it’s on fire. If I set it for sunlight, my subject looks like a smurf. Obviously, this won’t work.
Lastly, I need to control for value contrast. The eye is drawn to the brightest part of the frame. Not only that, but some difference in the frame from the brightest area to the darkest adds a lot of interest to the shot. If my subject is the shade, then the background is brighter than the subject. This means the eye is drawn to the background, not the subject. By comparison, the subject will seem under-exposed. Even if, technically, she is not. If I step back into the sunlight my subject and background are lit the same, but I get those terrible shadows. If I try and shoot during cloud cover I’m not in control. I live in Denver: when will there be cloud cover? You tell me? And there’s not enough value contrast anyway.
Ideally, I want the subject to be the brightest part of the frame. Value contrast dictates if the subject is brighter than the background she will immediately be the most important aspect of the frame and will, actually, seem to separate from the background some. To get a subject brighter than a background I need to light the subject. Period.
So I’m trying to shoot this portrait. We’re outside. And the sun is just not a great light source. To get even light on the face I turned the subject away from the sun. Great. Now I have even light on the face. But she’s darker than the background. It's very flat lighting.
This is the perfect opportunity to use a single flash with an umbrella and light the subject. This accomplishes several things. First, I get the sun behind the subject (a placement that works for the sun). Second, I get the same white balance on the subject and background because flashes are set to about 5,000 degrees kelvin, close to sunlight. Third, I can light the subject with a larger light source than sunlight, creating more aesthetically pleasing shadows. Most importantly, I control this light and reproduce it anytime and anywhere.
Place the flash on the same side of the subject as the sun and the shadows will fall the same direction in foreground and background. Then set your ISO low (this was 50), set your shutter to about 1/125, and your aperture to something that darkens the sky just a touch. Then fire the flash in some kind of auto mode and you have an instant portrait. Shampoo, rinse, repeat.