Photographers using strobe and sun together have creative options at their disposal that aren’t available when working with other lighting tools. For that reason alone it’s unlikely that strobes will ever go away, no matter how good digital camera sensors get. Mixing strobes with sunlight is a magical lighting combination that unlocks creative controls otherwise unavailable to photographers. Here’s a look at four creative choices photographers have when choosing to mix flash with daylight in their photos.
Mixing Strobe And Sun: Fill Light
The first and most straightforward way to use strobe and sun is to use the flash as fill. This entails making the sun the key light—exposing for the daylight exposure—and then using the strobe to fill in dark shadows. Too much fill is unappealing, but just a bit—often a stop or more below the ambient exposure—is a great way to add a hint of detail to dark shadows without ruining the shape established by the key. Deep black shadows can be too dramatic for all sorts of things, but with a bit of frontal fill the colors and details come through in a more pleasing way. You can use a flash mounted atop the camera’s hot-shoe to add on-axis fill and detail to shadows visible to the lens, but you can also position an off-camera strobe nearby the camera for a similar effect. Be careful not to place the fill light too far opposite the key light, which can create dual shadows and an unnatural, unpleasing effect.
Mixing Strobe And Sun: Balanced Key
The next option for mixing strobe with daylight is to turn the strobe into the key light but use it “balanced” with the ambient. The easiest way to do this is to position the subject so that it’s largely in shadow while the remainder of the scene is fully illuminated. I often do this by shooting toward the sun such that the background is illuminated and the face of my subject is in shadow. Adding a frontal strobe becomes a new key to illuminate the shadowed subject. With portraits, this approach works really well as that sun from behind often manages to create a nice edge light on hair and shoulders, adding to the illusion of depth in the image. The trick to balancing the strobe evenly with the sun is to match the exposures. If the correct daylight exposure is, say, 1/125th at ƒ/11, you’ll want your strobe exposure to also approximate ƒ/11. This isn’t easily accomplished with small, underpowered flashes but can be more easily achieved with high-end speedlights and off-camera strobes.
Overpower The Sun
The third way to combine these light sources is to allow the strobe to overpower the sun—sometimes called a “day for night” effect. With a powerful enough strobe, the flash can be so bright that exposing for it correctly means that the daylight exposure from the sun is insufficient to provide a correct exposure. This is easiest when the subject isn‘t in full “sunny ƒ/16” kind of sun but rather in open shade or photographed on a slightly overcast day.
For example, instead of something like 1/125th at ƒ/11 for a sunlight exposure, shooting at ƒ/22 will render those daylight elements a full two stops underexposed. Put that subject in some open shade or on a cloudy day where the ambient exposure is only, say, 1/125th at ƒ/5.6, and now you’ve got four stops underexposure when used with a strobe at ƒ/22. This definitely takes a strong strobe, or at least a strobe positioned very close to the subject, in order to provide enough illumination to overpower the sun. But when it’s achieved, it’s a great way to create drama and allow the strobe to provide the scene’s illumination, eliminating some or all of the sunlight.
Motion Blur Magic
The final approach to blending daylight and strobe light is to take advantage of the unique properties of mixing a continuous ambient illumination (from the ambient daylight) with an instantaneous burst of bright light (from the strobe). With a subject largely shaded from direct sun and therefore primarily providing light on the background of a scene, without a strobe-as-key illumination a moving subject wouldn’t only be blurry but also underexposed. Add a strobe to the scene, however, and that brief flash of light serves to freeze movement and create a tack-sharp image element even when the rest of the scene—the parts illuminated only by the ambient light—show evidence of motion via blur.
Done deliberately, this technique is a great way to add a sense of motion in a still photograph. For example, a person riding a motorcycle down Las Vegas Blvd after dark might require, say, a half-second shutter speed to provide sufficient illumination. But someone in motion like that is sure to appear blurry in a half-second exposure. Instead, combine that half-second exposure for the motion-blurred background with a burst of strobe light and suddenly the moving subject is tack sharp. Used wisely, this technique provides a way for photographers to make pictures where important elements are sharp and precise, while other elements appear blurry in an effort to enhance the appearance of motion.