Today I woke up, saw the sun, and knew that I needed to set my camera to 1/200, ISO 100 at f/8 and flash at 5.6 feet, 1/8 power, with subject in open shade to overexpose the background by one stop and get -1 illumination on the subject. I literally woke up thinking about it and then went out and did it, and you can see it below. Everything you see in this article was done using full manual everything, no metering, no checking, no histograms, no blinkies. Just knowledge.
Even though the background was overexposed one stop at f/8, I still needed f/8 from the flash because aperture governs flash power as well as ambient exposure. Correct illumination from the flash requires light that matches the f-stop set in the camera, regardless of what the background exposure is. However, for testing purposes, I put out f/5.6 of light from the flash, rendering the subject -1.
Then (below) I put the subject in full sun between me and the sun and, using only distance and power, knew the subject would be even with the background. One shot, everything in manual, no metering. Why manual? Look at the subject: white shirt, dark hair, dark background. The camera and flash won't know what to do. Moreover, I don't want the camera controlling the image and making decisions. And notice the background. Even at f/8 it's out of focus. Why? Because my subject-to-background distance relative to subject-to-lens distance and telephoto perspective throw it out of focus.
How's that for fast manual flash? I'm not talking about the lighting pattern. Obviously this isn't a client portrait. But look at the illumination, the rim light, the exposure of the background, and catchlights in the eyes. Without flash, the subject would be in dull shade, and without knowledge, you'd be struggling to get a good picture.
Let's take another look. Below is just the background, overexposed about one stop. It may not look overexposed, but it is. One stop is not a huge difference when you're making something very dark a bit brighter.
Now below is the subject in shade with the background overexposed about one stop but no flash on the subject.
Now below is the same shot but with proper flash illumination from camera left.
If you want to learn how to do this, please contact me for workshop information. I do small workshops and presentations throughout the year when I'm not shooting. It could be a 1-hour seminar with demonstrations or a full-day workshop. If you'd like to schedule a program, please contact me. I'm happy to share my knowledge and skills to help others improve their photography.