How to Use Your Flash Effectively by Matthew L Kees, guest to the MCP Actions Blog
Matthew Kees, Director of MLKstudios.com Online Photography Course [MOPC]
Outdoor TTL Flash (“everything and the sync…”)
Outdoors, in daylight, you are using the flash as a fill light and not the main light or key like you do indoors.
Your exposure should always be based on the brightness of your key light (in this instance the sun), so you’ll need to first set the exposure for it. Also, you need to be aware of your camera’s “sync” speed. For most Canon cameras it is 1/200 or 1/250. For Nikon it can go as high as 1/500. If you don’t know what your camera’s sync speed is, you’ll need to look up X-sync in your camera’s owner’s manual, or online.
The sync speed is simply the fastest shutter speed you can use with a normal flash pulse. There is another flash mode that allows you to go above sync described below.
Since the shutter speed is a limiting factor to the exposure, you need to be thinking in Shutter Speed priority mode (even though you will be shooting with your camera in Manual exposure mode). To keep the shutter speed at, or below sync in bright light, use the lowest ISO setting your camera has — typically 100 or 200. This will give you an exposure with the largest aperture that is possible. If needed you can lower the shutter speed, which will require a smaller aperture, to get more depth of field. But in normal flash mode, never go above the camera’s “sync”.
Your steps so far are:
1. Choose the lowest ISO setting
2. Set the shutter speed to the camera’s sync speed (1/200 to 1/500 depending on camera make and model)
3. Adjust the aperture for the light (use normal in-camera metering)
4. If more Depth of Field is required, lower the shutter speed and reset the ap
Then you simply turn on the flash to add a fill. In TTL mode you adjust the flash output to taste by using the flash’s EV control — plus for more and minus for less. When you have plenty of light in the scene, it is a good time to use Nikon’s TTL-BL setting (BL stands for Balanced Lighting). It tries to blend the fill with the available light, and hence, it lowers the flash output. With Canon cameras you simply need to lower the EV.
Once you have that down, you can now control the two exposures separately. The built-in meter gives you the background exposure and the flash setting gives you the foreground exposure. So, try darkening the background by slightly underexposing, and adjusting the foreground light (the flash exposure or FEC) up and down as well.
With practice, you will have complete control of how much fill you want plus how light or dark you like the background.
In low exterior light, you simply turn the flash on and let the flash in TTL mode handle the exposure for you. It again becomes the key light, and you use a slow shutter to grab some ambient light the same as you learned using the flash indoors.
In bright light when you really need a shallow Depth of Field and are using flash for “fill”, you will have to use High Speed sync mode. Nikon and Olympus call it Focal Plane (FP) sync mode, because it allows the use of a “focal plane” shutter found in Single Lens Reflex (SLR) type cameras. If you have a modern digital camera, like the Canon XSi or XTi, or a Nikon D90, it’s often called a DSLR for Digital Single Lens Reflex.
In HS or FP sync mode the flash produces a series of very quick blinks of light to mimic daylight. It accomplishes this by eating up your battery power. Also, it is only useful when used close-in since no single bright burst of light is produced. FP sync mode was another Olympus invention made available on their OM-2 camera and flash system.
You are probably now wondering what would happen if you set your camera above the sync speed in normal flash “pulse” mode. Well, it won’t harm the camera. But, you’ll see a dark edge in an indoor studio shoot, and in bright light outdoors using flash as a fill, the fill light won’t cover the entire frame. Technically, at any shutter speed above sync the two curtains that open and close to let the light reach the sensor, are never completely open. The second curtain trails the first as it moves across the sensor.
There are many ways to use a flash to make interesting lighting. Again, this is but a simplified quick start tutorial of certain things you need to consider when shooting outdoors with a flash.