Strobe And Sun

Strobe And Sun

A strobe-illuminated subject really pops off of an underexposed ambient background. In this case, a cloudy day and tall tree coverage helped bring the ambient down naturally, making it easier to overpower the daylight with a portable strobe.

Just because you’re working outdoors doesn’t mean you can’t take studio-style lighting control with you. Whether you’re working in bright sunlight or at the edges of the day, when it comes to mixing strobe with sunlight there are three fundamental approaches: flash as fill, flash as balanced key or flash overpowering the sun. For a guide to the essential lighting gear for outdoor photography, see Location Lighting, page 34

FILL FLASH

At its most basic level, combining strobe with sunlight most frequently happens by using a flash as a fill light. On-camera is the ideal placement for a fill flash, because from there it can subtly fill in any shadows that are visible to the lens, without creating new shadows.

A fine place to start with fill flash is to take advantage of TTL metering and let the flash automatically detect correct output. TTL stands for Through The Lens and refers to any flash that uses the camera’s internal metering to set exposure. Combining this technique with flash exposure compensation is an easy and effective way to work outdoors with on-camera flash in situations where the pace is fast and distances from camera to subject are constantly changing.

In “run and gun” situations like that, I find a manual flash setting can be a hindrance, because no doubt I’ll forget to change the power between a close-up and wide shot made moments apart. With the flash on TTL auto, you don’t have to remember to adjust the output. Better still, in bright daylight, smart flashes assume you want to use them solely as a fill, so they automatically dial back the output.

The challenge, of course, with auto anything is that sometimes the camera and flash work together to produce a fill light that is either too much or too little. This is especially true with scenes that appear particularly light or dark. One workaround here is to use the camera’s Flash Exposure Lock feature. To use it, simply aim the center point at an area of average brightness in the scene: a face, for instance, in an otherwise dark environment. With the center point on the average area, press the Flash Exposure Lock button to fire a test flash that the camera reads. Then recompose and fire away. The flash’s exposure will be based on the precise area of the scene you choose—immensely helpful when the center of interest is off-center.

A strobe balanced with natural daylight. Subtly overexposing the ambient background helps to make the strobe exposure look more natural too. As the background gets darker, the strobe becomes more obvious.
A strobe balanced with natural daylight. Subtly overexposing the ambient background helps to make the strobe exposure look more natural too. As the background gets darker, the strobe becomes more obvious.

This is a great technique to make the most of automatic flash exposure, but still, there’s only one way to ensure precision with the amount of fill light, and that’s to go manual and dial it in precisely from shot to shot. This becomes a challenge when you’re on the move and one shot may be six feet from a front-lit subject while the next may be 10 feet from a side-lit subject.

But with a stationary subject and a constant distance between flash and subject, you can dial in a manual output and fine-tune it shot by shot. If you have a handheld flash meter, you’re one step ahead of the game. With it, you can manually meter the flash’s output to balance it precisely with the sunlight key. For instance, with the basic daylight exposure of 1/125 at f/16 at ISO 100, I like to start with a fill flash exposure about a half-stop to a full stop underexposed, metering for about f/11. Then I simply add or subtract flash as needed based on the results I’m seeing on my LCD.

STROBE AS KEY, BALANCED WITH THE SUN

Strobe as key, balanced with the sun To use a flash as a key light, rather than just a subtle fill that brings up shadow detail, the process is the same whether you’re using an on-camera speedlight or a big, off-camera strobe. The look, however, is vastly different. And since on-camera flash is rarely ideal as a key light, by default I suggest using an off-camera strobe as the key.

Since the goal is to balance flash with ambient light, but to ensure the flash is the key rather than the sunlight, you first have to ensure the sunlight isn’t strongly illuminating the subject. (If it is, you’re in fill flash territory; revert to the aforementioned approach.) To keep the bright ambient sunlight off the subject, the use of shade is required. That means at minimum a silk, placed between subject and sunlight. Instead, you probably want stronger shade. This can be found on location in a variety of ways—everything from trees to buildings to making your own with a black flag or, in a pinch, a reflector between sun and subject.

Sunrise and sunset are both great times to combine flash with sun, not only because the natural light is beautiful but also because the lower light levels can be easier to work with.

Another great way to create shade on the subject and get a bonus hair light out of the deal is to place the sun at the subject’s back—i.e., shoot into the sun. Not only will the backlit subject’s face then be in shadow, ready for illumination via your strobe, but also the backlight from the sun acts as a natural hair light, adding depth and dimension and making it look as thoigh you used multiple light sources. Which you did—you just got one of them for free.

With the subject in shade (or, at least, the part of the subject the camera is pointing at), the next step is to determine the appropriate ambient exposure. We know what the exposure for a brightly illuminated background will be on a normal sunny day. But with the subject in shade, you’ve actually got a bit of wiggle room for what is an “appropriate” exposure for the background. Basic daylight exposure (1/ISO at f/16) might be, aesthetically, a bit darker than you’re hoping for. Instead, try opening up to f/11 or f/8 to bring up the background without, ideally, totally illuminating the subject. Often, shade is about two stops darker than sunlight, so you’ve got about that much room to work with.

In the examples here, you can see that a “normal” daylight exposure in the background can be balanced nicely with a strobe as key. But just because it’s normal, is it correct? Not to mention the fact that at f/11 or even f/8, a whole lot of that background is in focus. To make the depth of field shallower, you’ve got to open up the aperture nearer to its maximum, whether that’s f/4, f/2.8 or something even wider.

The problem, of course, is that as the aperture opens up the shutter speed must increase to keep from overexposing the scene.

In general, if you’re trying to open the aperture to f/2.8 in daylight, you’re going to be increasing your shutter speed to somewhere in the neighborhood of 1/1000th of a second. This is no bueno, since your camera doesn’t sync that fast. (Well, your DSLR anyway. Some medium format digital shooters have access to leaf shutters instead of the DSLR-style focal plane shutters, and leaf shutters can sync with flash at considerably faster shutter speeds.) The alternative is to use a flash with high-speed sync.

Assuming you’re not trying to shoot wide open on a sunny day, you may find the opportunity in lower light to open up slightly. Sunrise and sunset are both great times to combine flash with sun, not only because the natural light is beautiful but also because the lower light levels can be easier to work with. Whether at sunset or midday, adding strobe as a key is simply trial and error. I start with a no-flash ambient exposure to make sure the background looks as I want it to, and that the subject isn’t too exposed by the ambience. Next, I dial in the strobe power until it matches the ambient exposure. In practice, this means firing off a shot and checking the back of the LCD. Alternatively, I could use my handheld flash meter, and I do find that I’m more consistent when I take that extra step. But generally speaking, the “what you see is what you get” approach from looking at the LCD is pretty darn effective.

Bearing in mind that the shutter speed doesn’t affect the strobe exposure, the choices for modifying the strobe as key light boil down to turning up or down the power, or adjusting the aperture accordingly. When you adjust the aperture, though, the ambient exposure changes too. Since the flash fires way faster than even the relatively short duration of a 1/125th shutter speed, changing the shutter speed doesn’t affect the flash. The burst of light is still contained entirely within the duration that the shutter is open.

Another neat daylight (or low light) strobe effect is dragging the shutter. With this technique, a subject in ambient shadow with bright light behind will produce a silhouette to be illuminated by the strobe. With a slow shutter speed of, say, 1/15th of a second, any subtle movement by the camera or the subject will create a slightly bigger, slightly blurrier ambient silhouette. Then when the flash fires, it makes a tack-sharp exposure on the previously shadowed subject. It’s a neat effect that combines ambient, strobe and movement, and can almost look as if the photographer has drawn a shadowed outline around the subject.

OVERPOWER THE SUN WITH STROBE

Overpower the sun with strobe The principle outlined above—that shutter speed does not impact the flash exposure—is the linchpin of the third technique for combining strobe with daylight: overpowering the sun.

I know, the sun is a mass of incandescent gas, a gigantic nuclear furnace. But still, you can overpower it with your strobe. It helps to have a really big strobe, but it’s doable.

With the subject in shade, a normal exposure for this overcast day produces a dark subject and a normally exposed background. This is the perfect situation in which to add a strobe as key.
With the subject in shade, a normal exposure for this overcast day produces a dark subject and a normally exposed background. This is the perfect situation in which to add a strobe as key.

Shutter speed may not affect strobe exposure, but it does affect ambient exposure. So if the correct ambient exposure for a given situation is, say, 1/100th at f/11 at ISO 100, and you want to make the background two stops darker than normal, you can increase the shutter speed to 1/200th and decrease the aperture to f/16. Now all you need is a flash that’s powerful enough to provide you enough light for an f/16 exposure.

All you’re realwly doing with this technique is underexposing the ambient, by as much as you see fit. With strobes added to the mix, you’re then simply illuminating the subject with the strobe as you would in an otherwise darkened studio, and letting the shutter speed control the ambient, making it as dark as the situation will allow.

Without resorting to fancy high-tech flash settings (i.e., high speed sync), the premise is simple: with a powerful strobe you can overpower the sun. I find that a 1000-watt-second or 1200-watt-second strobe is typically enough, depending on the distance from the subject and the coverage area. If you want your flash at a greater distance, a 2000ws pack will facilitate that. If you’re pumping the strobe through diffusion, you’ve got to allow for the fact that you’ll need even more power. This shot, for instance, was from a 1200ws Broncolor Move pack providing barely half that, albeit on an overcast day where I only needed to get to f/11 to overpower the ambient. The lower the ambience to begin with, the easier it is to overpower with your flash. The ultimate display of power in blocking out the sun is the creation of a nearly black background in broad daylight. To do this, one must first take care to compose such that no bright blue sky is visible in the scene. (It’s always a dead giveaway because it’s particularly difficult to make bright sky turn black.) Then place the subject far from any background, and overpower the ambient exposure by at least four stops, preferably more. That means f/16 becomes f/22, 1/125th becomes 1/250th, ISO 100 becomes ISO 50 and we’re still in need of a stop or two. A polarizer or ND filter can cut the ambient even more, so you can keep your shutter speeds under the sync speed and still block out a lot of light to get the ambient down. Still, this is yet another hurdle for your strobe to overcome. A speedlight isn’t likely going to cut it. A 1000ws strobe positioned fairly close to the subject and with minimal diffusion, however, can definitely get you there.

Whether you’re overpowering the sun or balancing with it, one technique to consider is to position the flash at an angle that approximates what the sun is doing in the background. A low-angle sun from the left, for instance, may be ideally matched by a low-angle strobe from the same side, thus producing shadows on the subject that more naturally match the shadows in the ambient background.

Taking that technique one step further, a low-angle strobe with a CTO (color temperature orange) gel looks a whole lot like golden sunset light. In the middle of the day, even, you can overpower the sun to bring the ambience down, and then use an eye-level orange-gelled key to give the subject a golden glow and match the beautiful light that naturally occurs at the magic hour. 

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