Create stunning images using high-speed sync.
The most common question I get is: How do you use speedlights outside in the full sun? It’s a question that is best answered in a full-day seminar, but following are a few basic tips on my outdoor and location lighting technique using speedlights and high-speed sync, as excerpted in part from my book Shoot to Thrill.
Understanding TTL Metering and Exposures
At the center of my outdoor lighting technique is an understanding of how the flash and the camera interact using the TTL (through the lens) metering system. Once you have this understanding, you can more readily achieve the lighting effects you desire. For example, I often purposely make creative and technical decisions to under-expose midday skies in order to render the skies a deeper blue. I do that by understanding the camera’s TTL meter reading and by knowing how to override my camera’s automated exposure settings.
Turning Everything Gray
Your camera’s built in reflective metering system has one job and one job only: it wants to turn everything it “sees” into middle gray. Taking a portrait of a polar bear on a snowfield? Your camera’s metering system will want to turn it gray. Taking a portrait of a black panther on a black velvet rug? Your camera’s metering system will want to turn it gray. Understand that you meter does not know what the subject matter is; it merely wants to create an average exposure (note that I did not say “correct exposure) by pushing the exposure towards the middle tones of a histogram. Thus, the polar bear (or white wedding dress) turns gray as the white tones are recorded as middle gray.
How Flash Interacts with TTL
I’ve just described how your camera’s TTL system reacts to the ambient light it “sees”. But how does it account for and incorporate TTL flash? The default system is as follows:
- Ambient Light. The camera’s meter first reads the ambient light in the scene and calculates an average exposure balancing it towards middle gray.
- Camera Settings. The camera then takes into account any settings you have made that affect the exposure. These include the shooting mode—whether your camera is set to manual, aperture-priority (Av), shutter priority (Tv), or program. If you have selected the program mode, go sit in the corner and ponder your poor life choices.
- Exposure Compensation. Next the camera takes into account whether you have dialed in any exposure compensation (EC). The exposure compensation setting allows you to override the camera’s built in metering system to make the desired exposure adjustments. Remember our polar bear on the snowfield example? If you dialed in an exposure compensation setting of + 1 1/3 EV, the camera would record the white of the scene properly. You are telling the camera to ignore what it “sees” and not to underexpose to make the white subject gray.
- Flash Output. Next if you have a speedlight on-camera, turned on, and set to TTL, the camera senses that and will fire a preflash to illuminate the scene at 1/32 power. It reads the reflection of this flash, mixes it in with the exposure already determined for the ambient-light scene, and then sends a command to the flash to fire it at the power level appropriate for a balanced exposure according to all of the settings and adjustments above in points #2 and #3.
- Flash Exposure Compensation. One sidetrack to this combined exposure is if you have separately set any flash exposure compensation (FEC) on your flash or in your camera. If this is the case, the camera then adds to or subtracts from the flash exposure based on this override.
- Making the Exposure. Finally the shutter opens and your camera records the exposure.
This complex scenario all happens in a fraction of a second as you start to depress your shutter button. As professionals, we need to be smart enough to understand what the camera is “seeing” and know when to override and adjust the flash/camera settings based on what we want the camera to record from our own creative and technical point of view.
Now let’s apply this knowledge to an example: a bride out in the midday sun. For a shallow depth of field portrait, my preferred camera settings are aperture-priority mode, ISO 100, and f/4.
As my camera reads the ambient light in the scene, it sees a lot of bright blue sky and a white dress. Because its job is to achieve a balanced exposure and to render everything to 18 percent gray, it will automatically underexpose the scene slightly. Still, I will typically dial in – 1/3 EV exposure compensation to further underexpose the ambient light and deepen the sky (but I am also darkening the white dress even further, which I will compensate for in the next step).
The camera will provide the appropriate corresponding shutter speed—which, in this case, is 1/2000 second. Holy cats! That’s a fast shutter speed right? This is the major reason I default to the aperture-priority mode for this type of portrait; once the shutter speed climbs above 1/500 second, I really no longer care how high it goes. It won’t affect my ability to hand-hold the camera or to stop average motion.
But wait a minute. How can the flash handle a shutter speed that fast? Isn’t the camera’s maximum flash-sync speed around 1/200 second? Read on to learn how we can resolve this issue.
Maximum Flash-Sync Speed
You will need to know your camera’s maximum sync speed. You will find that information in your camera manual. The maximum flash-sync speed (called the X-sync speed) is around 1/200 second, depending on the camera model. If you exceed this shutter speed, one or both of the shutter curtains will block the flash’s light from reaching the sensor, resulting in a dark bar or under exposed area at the edge of the frame.
So what are we to do in a situation this this? Well, if you set the flash to HSS (Canon) or the camera to FP (Nikon), something magical happens: the flash no longer fires one quick burst of light. Instead it pulses to time the very narrow gap between the front and rear curtains of the shutter as it passes in front of the sensor. This creates an even flash exposure across the entire scene.
Best of all, it allows you to use a wide-open aperture (and a very short shutter speed that correspond) in order to achieve shallow depth of field. The trade-off is the HHS pulsing robs a lot of power from the flash, so you may need to double up speedlights in order to compensate for the loss of power. This is the option I choose.
In practice, I fire a quick test shot with an image like this and then adjust the exposure compensation and the flash exposure compensation to taste. As a general rule, I try not to turn down the exposure compensation to more than -1 1/3 EV. Once I go beyond that point, the ambient light seems just to “disappear”.
Want to learn more? Pick up my new book Shoot to Thrill where I cover all of this and much, much more and include 60 practical examples of speedlight portraiture.