Taking it outside, as it turns out, using a flash outside to fill shadows, cross-light, and create stunning sunset portraits isn't much different from balancing flash with ambient indoors. The secret: expose for the background, light the subject.
|Flash used to fill shadows from mid-day sun. 1/200th f10 ISO 100|
My last lighting exercise was spent in the living room walking the shutter speed back from my D7000's max-sync speed to a full ambient exposure, firing the flash for each frame.
By the time I got within two stops of the correct ambient-only exposure, I was making good photos that balanced my flash with the ambient light in the room. In fact, it was pretty easy to see exactly what was happening with the light by doing this exercise. But does that hold true when you're working outdoors?
As it turns out, yes!
Let's start with the lede photo. The thing to remember about working outside with a speedlight is that compared to the sun, you don't have a whole lot of power, so often times the sun is going to serve as your key light and the flash will be used as a fill.
For the above shot, I started by taking a meter reading from my subject's face then closed the aperture down a stop to make that blue sky stay a nice rich blue. I also wanted more depth of field, so at f10 and ISO 100 I needed 1/200th of a second to get a proper background exposure. But there was a problem.
You should be able to tell where the sun is coming from in this picture. If not, it's to camera left, at about a 45 degree angle from the model and hanging pretty high in the sky. The problem here is that with that light alone, the shadows on her face, and the side of her face opposite the sun were going pretty dark. Especially so since I'd under-exposed the image by a stop.
The solution: Set up a flash at camera right a couple of feet away from me and about 5 feet from the model, up above her head slightly, and set to 1/2 power.