Working with Ambient Light and Flash Photography
We have two sources of light to take into account when doing flash photography. The first is the ambient light, which is the light emitted from any light sources that aren’t the flash, such as LED’s, spotlights, fluorescent light or the sun. The second light source is the flash itself. Unlike the ambient light sources, which are continuously shining light, flash emits its light in one short burst.
Calculating the best exposure for flash photography involves finding a balance between these two sources of light. In TTL mode, the flash handles how bright it should be, which leaves the photographer to decide how much ambient light they wish to record.
In event environments, exposure comes down to some personal taste and it isn’t uncommon for photographers to have different approaches to choosing their settings. Here are suggestions are a good place for beginners to start:
Turn off your flash and take a test shot. Work out how you want to expose the ambient light
Set your camera’s shutter speed to 1/100 of a second. This gives you an indication to either reduce the brightness of the background by one stop (1/200 sec) or to increase the brightness by one stop (1/50 sec)
Set your aperture to taste and based on how much depth of field you want
Choose the ISO you need to give you the desired exposure
Turn your flash on and set it to TTL
Manual camera exposure will work best for getting consistent looking photos as long as the environment you are shooting in remains similar. Normally, the lighting in one space (either inside or outside) will be relatively consistent across the entirety of the space, so you can dial in your manual settings when you start and leave them. When you move to a new room perform a new meter reading and adjust to taste. Manual exposure on your camera will work with Manual or TTL flash, and combined with TTL gives a good compromise between versatility and control for unfamiliar flash shooters.
We recommend leaving the flash in TTL, regardless of whether you are bouncing flash off walls, ceilings, using modifiers or pointing directly at your subject. As you change your distance between you and your subjects the flash will automatically make power adjustments. Use flash compensation to fine tune the power of the flash from if you notice it is consistently under or over exposing.
The ambient light in the image above is not lighting the subject directly. Because the subject is lit from behind, the ambient light is creating rim-lighting on the subject which helps to define the form of the subject. The subject is lit from the front with the flash.
Keep in mind that when we’re mixing ambient light and flash, the shutter speed will only affects the brightness of the ambient light—not the light from the flash. This means we can use shutter speed to make the background brighter or darker without affecting the brightness of the subject. However this can be an issue in different shooting situations, see Shutter Speed on the following page.