by: David Tong
Different light sources have different color wavelengths, as you probably realized, sunsets give you an orangy light, while twilight and dawn gives you a bluish light. With artificial lights, the same thing occurs, tungsten/incandescent/halogen lights are warmer (more red) in color while fluorescent is bluer.
The incredible human eyes does not see a significant color shift in lighting and we’re not that affected by it. Camera sensors and film, however are designed for a certain color temperature, especially with film. Digital sensors allow you to change the color temperature on the fly with white balance settings, which is a lot more convenient that film days where a filter has to be screwed on with each light shift.
Correcting white balance means that you’re making sure what’s white should be white in the scene, unless intentionally altered by a colored light source (like a colored stage light, for example).
Why did I specifically include the word “flash” in the topic, then?
Like what I’ve mentioned in the flash articles previously, the camera and flash are separate entities that tries to work together when it comes to color and exposure.
Your flash’s color temperature matches daylight’s color temperature, in general. If you’re shooting under the sun, your flash and camera’s daylight/auto white balance presets will give you an image with consistent color in both ambient and subject. However, when you introduce a significantly cooler or warmer ambient color, such as shooting during sunset, indoors with incandescent, you can only alter the white balance in your camera, not in your flash as flash guns don’t have white balance presets.
If you changed your camera’s white balance to match the ambient’s warmer tone, for example, your flash will still remain in “daylight” color temperature. Your ambient will be orangy while your subject will become blue due to the color temperature differences.
This is where color correction filters come in.
The gels you see above are free swatch samples from Lee Filters. Conveniently, their swatches fit most flash head’s Fresnel lens so I’m using these.
Note that the ambient (stalls at the back) has the correct white balance of “tungsten” but as soon as the pop-up flash fired, the subjects are lit with a cooler color light source (the flash).
By holding an orange gel in front of the flash, the ambient and the flash-lit subjects now receive a better matched color temperature. The colors could still be improved with additional color gelling but for this illustration, it’s clear that even a half-CTO gel resulted to a much better image than the first. If I need to alter the white balance further, both the subject and ambient will receive the same color shift.
Pictures will illustrate this practice better:
Photo # 1) Auto WB + No Flash
This is our reference image, shot with auto white balance and no flash. The light source is a tungsten-colored fluorescent tube.
Photo #2) Tungsten WB setting, no flash
With the correct ambient white balance chosen, the image looks true to the scene. Without flash, however, I was forced to use a slow shutter speed of 1/8sec @ f/4 @ ISO1600, let’s use flash then.
Photo #3: Tungsten WB + Flash (No CTO)
Whoa! What happened here!? With the flash fired directly at Buzz, the blue light source overpowers the ambient and turned everything blue! Star Command will not like this.
Photo #4: Tungsten WB + Flash with full CTO gel applied.
The resulting image is much better. The cement is grey as it should be, and Buzz’s colors are accurate. I was now able to use 1/60sec @ f4 instead of 1/8sec as well, minimizing camera shake in the process.
Photo #5: Photo #4 + White Balance changed to “Shade” + bounced flash.
I found the previous image a bit too sterile, since our overall scene has the same white balance, thanks to the CTO and camera’s WB combination, I can then change my white balance during post-processing to a warmer hue. I don’t have to worry about differences in color temp between the ambient and subject anymore. In addition, Buzz doesn’t like direct, frontal lighting, so I bounced the flash over my right shoulder where a small, beige wall was behind me. The result is a much more pleasing image with soft shadows, warm tone, and balanced exposure.
Hope that Buzz was able to help you out.