Using Your Flash in Manual Mode
The off camera flash is one of the most versatile pieces of equipment in our camera bags. It can serve as our main light source, an accent light, or be used to simply fill in shadow areas of a high contrast scene. Recently I have been experimenting using the flash to illuminate foreground subjects in the landscape. I first came up with the idea when photographing a lava beach in Hawaii.
As I was shooting the waves rushing in and out over the lava, I noticed a slight warm glow on the water in the foreground. At first I was confused as to the source of light, but as I looked around I noticed a nearby hotel had turned on its flood lights. I was just out of range of the full force of the lights, but it was enough to slightly illuminate the water in my foreground. The effect was very subtle, so I decided to enhance the brightness using my Canon 580EX II Flash. The result, was the warm color of the flood lights gave an interesting contrast to the blue sky and water, so I taped an amber Rosco Gel from their Swatchbook over the front of the flash to warm up the otherwise neutral color of the flash.
Long Exposure, Multiple Flash Firing
It was nearly dark so my exposure was very long-30 seconds @ F/5.6. This allowed me time to pop my flash 4 times while the shutter was open. Using a cable release I began my exposure and stepped to the right and forward of my camera. Pointing the flash to the center of the photograph, I manually fired my flash by pressing the test button on its back. As soon as the flash recycled, I moved a litte further forward and fired again. I then walked behind my camera to the left part of the scene and repeated the process. The resulting photograph glows as if the light is emanating from the center.
Creating images like this is actually much easier than you might imagine, especially with the ability to check your exposure using the camera’s histogram and LCD. To simplify the process, think of the flash exposure and the ambient exposure as two separate problems to solve.
Getting the Exposure Correct
The first step in the process is getting your ambient (existing light) exposure correct. My exposure for the first shot was 30 seconds @ F/5.6. This combination of shutter and aperture gave me the desired exposure for the sky and the ocean but left my foreground too dark. The second step is setting your flash exposure to match or compliment the ambient exposure of the scene. Too much flash looks fake and not enough is ineffective. The balance is not difficult to achieve but is quite subjective.
I use my on-camera flash off of the camera in the manual mode which can be found on middle to high end flashes. Manual Mode (as opposed to TTL) results in the flash outputting a predetermined amount of light when triggered that I've dialed in. The camera no longer turns the flash on and off to get a correct exposure. Flash output in Manual Mode is controlled by reducing or increasing the power setting of the flash. The 1/1 power setting will output the full power of the flash. The 1/2 power setting will output half the power of the flash and so on. Flash Meters are handy for obtaining a proper manual setting but if you don’t have one, time, and a little experimentation will suffice. This gets better with experience and a little bit of experimentation. Getting your hands dirty with this stuff is the best part!
The camera’s settings will also have an affect on the flash exposure. While both the aperture and shutter speed influence the ambient exposure, the aperture is the primary control that affects the brightness of the flash. The smaller the aperture (F/22, F/16) the less effective the flash. The larger the aperture (F/4, F/5.6), the more effective the flash.
The shutter controls ambient light (continuous sources such as the sun or light bulbs, etc.) by lasting longer to gather more light, or shorter to collect less light. The duration of the flash is so short (typically 1/1000 of a second or shorter) that the shutter does not affect its brightness. The flash easily reaches full brightness and shuts down long before the shutter is closed. This remains true as long as you are shooting below the cameras sync speed. You can see the note at the end of the posting for more info on sync speed.
The point illustrated: Lets take an example where your scene is properly illuminated but you need more depth-of-field. Your flash is set to 1/8 power in manual mode and your camera is set to 15 seconds @ F/5.6. In order to increase depth-of-field with the same ambient exposure, you will need to change your aperture to F/8 and your shutter speed to 30 seconds. By closing down your aperture to f/8 you have increased depth of field, but decreased the amount of flash hitting your sensor. Compensate for this by increasing the power of the flash one stop to 1/4 power. The resulting image will have the same brightness as the initial image but with more depth-of-field.
So the steps are straightforward:
- Find your composition
- Get your ambient exposure correct through your F stop and shutter speed settings.
- Set your flash to manual mode and set the power to 1/1
- Use a colored gel to alter the color of the flash if desired
- If you have a flash meter you can use it to find out how much light the flash is outputting. For example; your meter reads 15 seconds at F/22 with the flash at 1/1. You, however want to shoot at F/8. This means you have to decrease the power of the flash to 1/8 (F/22-F/8=3stops, 1/1-1/8=3 stops).
- If you don’t have a meter, experiment by setting your flash power to 1/4 power. Make a test exposure. If the flash is too bright, lower the setting. Too dark? Raise the setting.
In the following example I used the above steps to add drama to this rock structure in Zion National Park after the sun went down. In this case I used an orange gel to match the natural color of the rocks at sunset. The exposure was 30 seconds @ F/8, ISO 100. The flash was set manually to 1/2 power.
Experimenting with your shoe-mount flash in manual mode is a great way to add drama to your photographs and extend your shooting day! Good luck and have fun!
The shutter speed does not affect the flash brightness as long as your shutter is set to the cameras sync speed or slower (typically from 1/60-1/500). The shutter on your camera consists of two curtains, which move up and down across the frame to expose the sensor. During longer exposures, say 2 seconds, the first curtain quickly opens to expose the sensor. After 2 seconds has elapsed, the other curtain quickly closes to stop the exposure. It is during this time, when the shutter is completely open, that the flash fires. This works the same all the way up to the maximum sync speed. At speeds faster than the maximum sync, the curtains aren’t fast enough to fully open and then close. At high shutter speeds, the second curtain begins to close before the first curtain fully opens. The effect, then, is a gap in the shutter that scans across the frame allowing a shorter shutter speed. When using standard flash mode, the burst of flash is unable to illuminate the entire scene. Instead it simply illuminates the part of the scene that is open to the “gap” in the shutter. Look to your flash manual to see if your flash has High Speed Flash capabilities.
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