cgardner
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Overall these are nicely posed and composed in the frame with flattering facial angles and good lighting strategies. However the lighting is all over the map exposure-wise and the fill flash is flat looking which are basic technical issues.
Exposure: To get correct exposure with fill flash, especially when using the Av / ETTL flash combination, its necessary to first get the ambient lit highlights exposed correctly. If you blow the ambient highlights, as on the coat in #1 if will confuse the flash metering. Digital must be correctly exposed for the highlights but judging when highlights are correctly exposed can be difficult in portraits because many subjects don't have textured white tones in them. I nail exposure every time in portraits by using a proxy for those highlights, a white terry towel held close to the face.
The concept is quite simple. Using the over-exposure warning of the playback as a guide I check the image of the towel and first adjust the ambient exposure until the sun-lit portions of the towel are correctly exposed, with detail such as in this high-speed flash test shot:
Perceptually that shot looks under-exposed and it is, but only on the shadow-side. But that's due to the fact the sensor can't handle the contrast range of the scene which pushes the middle-tones and shadows darker than normal; i.e., as typically perceived by eye in a similar situation with adaptable human eye sight. But getting the back-lit highlights right in Av mode in the technical sense of not blowing the highlights is necessary with Canon ETTL flash for the camera to get the flash fill portion correct. In the shot above it was necessary to dial in - 1-2/3 stops of EC. Once the ambient exposure was correct in the highlights I simply turned on the flash and let the evaluative metering do its thing with this result at FEC = 0:
With the ambient set correctly, retaining detail in the white textured highlights, the camera was able to add frontal fill in sufficient amounts to exactly match the backlighting. Perceptually this result may look over-exposed in the foreground because if seeing that same thing by eye we'd perceive the shadow side as being darker. But technically, the foreground is reproduced, in the abstract, perfectly as FEC =0 should expose it when just the target is evaluated:
If shooting a portrait I would have dialed in minus 2/3 - 1 stop FEC to make the foreground a bit darker, biasing the foreground from being correctly exposed in the technical sense to make it look more realistic perceptually.
So the points I'm trying to make here are that you need to get ambient exposure correct in the technical sense of not blowing any highlight detail for automatic flash exposure to work correctly by evaluation of just the highlights because your perception of the overall scene by eye will seem underexposed: trust the feedback from the towel and OEW. Then when you add the fill flash, adjust its power perceptually by eye until you get the desired balance of correctly exposed sun-lit highlights on the subject and how bright the face in the shadows looks.
Fill flash position:
Using flash outdoors in backlight is the same as using a single flash indoors with respect to how the light hits a face. To get flattering modeling on a face with a single light the most effective strategy is to raise it directly above the lens of the camera which does two very important things which model and flatter the face:
1) It hides distracting shadows: Its the shadows, not just highlights which define shape, which is way flash near the camera axis produces such flat 2D rendering. But as flash is moved off axis the nose creates a shadow. That shadow can either perfectly define the shape of the nose by perfectly covering half of it, or hang off the nose sideways into the opposite cheek and eye becoming a distraction. It's necessary to move a flash about 45 degrees to either side to get the perfect 1/2 nose shadow (i.e. short lighting) which just can't be done with flash on camera from the distance needed for portraits. Besides even if the single flash was placed out at 45 degrees, without a second flash on camera for fill the shadows would be dark and distracting. A more effective and flattering lighting strategy with a single flash is to raise it vertically, in the same direction the nose is on the face, so the nose shadow -- the biggest potential distraction -- falls down under the nose where it is not noticed.
2) It creates a natural "mask" pattern on the face: Ever consider how the brain figures out a pattern of highlight and shadow contrat on a screen or print represents a 3D face? It's done with pattern recognition. Your brain sub-consciously matched the pattern with memories of faces and 3D objects you have seen in person. Because its subconscious you don't realize it is happening, but to effectively light a face it is very helpful to understand the how it works and use it to your advantage.
Most natural and artificial light sources are overhead. So that means a "natural" lighting pattern is created by light from above the head. Light from above the head hits the raised parts of the face such as the forehead, ridge of nose, tops of cheeks, protruding mouth and skin and also creates shadows down and to the side opposite the direction of the light. That "mask" of highlight and shadow is what helps the brain recognize there is a face in the photo, even if the photo is blurred as in this example:
That diamond shaped pattern of highlights on forehead, cheeks and chin, surrounded by shadows, are like the landing lights of an airport runway telling the brain of the viewer "Here's the face".
The simple expedient of raising your fill flash on a bracket will created that very desirable and flattering downward pattern for the fill flash in a backlit situation with sunlight or when a second flash is used behind the subject for rim light:
Flash raised on a bracket with a diffuser is also quite flattering indoors with single flash for the same reasons: no harsh shadows on the face and downward 3D modeling via the mask pattern:
So when I recommend you use a camera-flip bracket for your fill that's why: you will get much more flattering fill flash... 
In terms of exposure control, in a backlight situation I would control exposure manually by first selecting the aperture desired for DOF then using the towel test target to find the shutter speed needed for correct exposure of the highlights. Since your subject-camera distance will change when shooting I'd stick to ETTL and evaluative flash metering, which keys off the highlights. Once you dial in the amount of FEC needed for the desired perceptual level of frontal fill the camera should keep the exposure consistent shot-to-shot in the foreground, but if you radically change the amount of ambient light hitting the front of the subject by changing the pose it will affect fill flash exposure and you'll need to re-adjust FEC to the new scene. FEC is an inter-active process, not something you can set and forget.
Chuck
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