cgardner
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 p.1 #6 · Outdoor with just 2 flashes? | |
Outdoors if you put the back of the subject to the sun you have the equivalent of a four light set-up indoors: The sun provides back-rim (i.e. hair) light directly, and the light reflecting from the sky illuminates the background and contributes to main and fill.
With back to the sun and front of the face and body entirely in the shade, the shady side is about - 3 stops below the sunny side (Sunny 16 /Shady 5.6). Without flash what we'd typically do is use the "Shady 5.6" exposure to get the face correctly exposed and then minimize the fact the highlights are clipping by finding a dark background and lettting the hair go "nuclear" and other less important areas clip.
When using flash it is possible to fit the scene to the sensor and not blow any highlights. Start the same way with back to the sun, front entirely in shade, then add flash until the two balance. But the important thing to realize when adding the first flash to a backlight scenario is that IT IS NOT FILL!
The shady side is already filled, somewhat inadequately, by the "shady" sky the person is facing. When flash is added on top of that fill it creates a HIGHLIGHT PATTERN on top of the key fill. So what is happening is the flash becomes the KEY light, on top of the fill and the sun becomes the ACCENT/HAIR light. The shadows on the front not hit by the flash remain lit by the sky FILL.
The mistake many make with single flash in that situation is not positioning it like a KEY light should be, above the eye-line of the subject. What makes lighting patterns look "natural" is the angle of the light relative to the face. Natural light outdoors comes from overhead, both directly from the sun and indirectly from the sky, so when using single flash outdoors it should be raised, ideally directly over the lens...
The shot above was taken with a 580ex flash and diffuser on bracket. Raising the light creates a "butterfly" pattern of highlight on the face which defines the 3D shape with contrast. The contrast comes from the fact the shadows are illuminated by the sky.
Let's stop and consider the lighting ratio in that scenario. The shady side is - 3 stops which is an incident ratio of 8:1. The ambient exposure is controlled to keep the hair and white top below clipping. The flash has added highlights to a point just below the "paper white" value of around 250 retained in the clothing because and exact match would result in a fake flat look. So the resulting ratio between highlights and shadows on the face is probably around 6:1 or so; quite dark and harsh. But that ratio works OK in a full face pose with the centered lighting strategy because the pattern and the angle of face to camera are both symmetrical and the dark shadow actually work to define and slim the face in the normally least flattering full-face view.
If the flash, acting as KEY light was moved 45 from the nose, shortlighting the face, the tone of the shadows would be the same, but because more of the face that is seen would be in shadow the lighting would look much harsher perceptually. Its not just the lighting ratio that affects perception, its also the relative amounts of highlight and shadow seen on the face.
The solution to the problem of the sky fill alone being to dark for flattering lighting with and off axis key light is to add a second flash from the direction of slightly over the camera, or where the first flash is already in the full face scenario above. The second flash supplements the fill. Why over the camera? To duplicate the direction and angle of the natural fill.
The brighter card affects perception of the face, so here it is with the card covered:
During a discussion of modifiers outdoors I dragged the in-house model out of the garden for the shot above to illlustrate the effect of the sky when combined with direct, unmodified flash and a neutral fill strategy. The sky is God's own softbox which wraps completely around the face. Any modifier put on a flash will be puny and ineffective by comparison. In the two flash + backlight scenario the sky is actually providing the most of the light. The flash simply kicks it up a notch:
Break it down on a cause and effect level:
Sunny highlights on hair and clothing are kept below clipping. I shot that in Av mode and had to dial in - 2 EC to keep the hair and shoulder from clipping.
Without flash the face was - 3 stops with sky fill. The flash on the bracket in the role of supplemental fill added about 1.5 stops, making the shadows on the face lighter. Then the flash off axis, 45 degrees from the nose to the right, worked just like it would indoors, overlapping the combined sky/flash fill with about 1 stop more light. The net result? Lighter shadows with highlights which are 2x brighter: a 2+1:1 or 3:1 ratio.
I used Canon wireless in ETTL mode for that shot at FEC=0. The evaluative metering was able to sorted out the exposure correctly because I didn't blow the ambient lit highlights.
The common denominator in both the single flash / full-face and dual-flash/oblique strategies is my knowing how to create a natural pattern of contrast on the face with the light. The highlights create a "mask" which define the face and make it easy to recognize even if blurred:
Outdoors you need situational awareness of the ambient light. Even in open shade the eyes will be darker than the cheeks because the brows still shade it. The solution is not to add flash, but simply to raise the eyes into the same light that is hitting the brighter cheek. Raise the face an bring a step ladder along so you can raise the camera angle by the same amount, keeping the relationship of face and camera the same as eye level.
When canoeing you can go with the flow, or fight the current. With lighting outdoors you can put the sun to the back of the subject and get the full benefit of the wonderfully soft light from the sky - so soft you don't need much if any modification on the flash you add to it. Or you can choose to "paddle upstream" and fight the direct sun on the front of the subject, which takes much more equipment and winds up looking harsher unless scrims are used to diffuse the direct sun.
I'm not advocating using just direct flash. That was just to show a baseline of what direct flash will produce, which on the face is rather smooth transitions. If you were to duplicate that set-up starting with direct flash, then add progressively larger modifiers you'll find that the character of the light changes more in the highlights. Direct flash creates specular highlights. As the modifer size increases the highlight transitions will become smoother and the catchlights in the eyes larger
All lighting solutions need to balance results with logistics. Its possible to get pleasing results outdoors with just a single flash - if one knows how to use it with the ambient light effectively. The results will certainly be better as modifer size is increased, but that complicates the logistics outdoors on a windy day if working alone. If you test starting with two direct lights, then add larger modifers, you will be able to find the point where the logistics of the modifers become more work that the difference in results warrant. That will be different for everyone, and the only way to find out is to experiment.
Chuck
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