Many users of flash feel quite comfortable with it in the studio. The studio makes things fairly straightforward. You expose to eliminate all the ambient light and then you add it back where you want it with your strobes or speedlights. But when many newer flash users struggle when they get out on location, where you can’t or don’t want to completely kill the ambient light, but need to add flash. In this video, Jay P Morgan at The Slanted Lens looks at how to mix strobes with the ambient light and how to balance them outdoors to achieve a good exposure.
Technically, the same rules apply indoors, too, but as mentioned above, typically we’ll kill the ambient light completely, removing it as a factor in our shot. But in all instances, you’re essentially working with two exposures simultaneously. One to put the ambient light where you want it, and another to add the flash.
It’s a fairly straightforward approach, once you become familiar with it, and Jay has put this process down into a set of easy to remember steps. The final rule only applies if you’re shooting below your camera’s sync speed. When you take a shot with a camera that has a mechanical shutter, it has two “curtains”. As the name suggests, these cover up the shutter – just like real curtains cover up your windows. There is a front curtain and a rear curtain. When an exposure begins after you hit the shutter button and you’re below the sync speed, the front curtain fully opens, exposing your sensor to the scene before it. At the end of the exposure, the rear curtain comes across your sensor to cover it back up again. But there comes a point where these mechanical curtains just aren’t fast enough. So, the rear curtain starts to close before the front curtain is fully open. The fastest speed at which the front curtain is fully open before the rear curtain starts to close is your maximum sync speed. In most cameras, this is typically somewhere between 1/160th of a second and 1/250th of a second. Check your camera manual or hit up Google to find out what the sync speed is for your own camera. Regardless of the speed, when your shutter speed is slower than your sync speed, the shutter speed doesn’t affect the flash exposure in your shot. Once you go past this speed, you’re into High Speed Sync territory, but that’s a whole different lighting conversation. The principle is still the same, but it’s just a little more difficult to meter unless you own a Sekonic L858 or you’re shooting TTL (in which case, metering doesn’t really matter anyway). For now, if you’re struggling with balancing flash and ambient light on location, whether it’s indoors or outdoors, day or night, Jay’s video should get you off to a good start.
