I showed you how to adjust white balance in Chapter 3, using the 40D's built-in presets, white balance shift capabilities, setting exact color temperatures, and white balance bracketing (there's more on bracketing in Chapter 4, too).
In most cases, however, the EOS 40D will do a good job of calculating white balance for you, so Auto can be used as your choice most of the time. Use the preset values or set a custom white balance that matches the current shooting conditions when you need to. The only really problematic light sources are likely to be fluorescents. Vendors, such as GE and Sylvania, may actually provide a
The fluorescent lighting in the room where this historical re-enactor gave his performance added a distinct greenish cast to the image.
figure known as the color rendering index (or CRI), which is a measure of how accurately a particular light source represents standard colors, using a scale of 0 (some sodium-vapor lamps) to 100 (daylight and most incandescent lamps). Daylight fluorescents and deluxe cool white fluorescents might have a CRI of about 79 to 95, which is perfectly acceptable for most photographic applications. Warm white fluorescents might have a CRI of 55. White deluxe mercury vapor lights are less suitable with a CRI of 45, while low-pressure sodium lamps can vary from CRI 0-18.
Remember that if you shoot RAW or sRAW, you can specify the white balance of your image when you import it into Photoshop, Photoshop Elements, or another image editor using your preferred RAW converter. While color-balancing filters that fit on the front of the lens exist, they are primarily useful for film cameras, because film's color balance can't be tweaked as extensively as that of a sensor.
Until you delve into the situation deeply enough, it might appear that serious photographers have a love/hate relationship with electronic flash. You'll often hear that flash photography is less natural looking, and that the built-in flash in most cameras should never be used as the primary source of illumination because it provides a harsh, garish look. Indeed, most "pro" cameras like the Canon EOS 1D Mark III and IDs Mark III don't have a built-in flash at all. Available ("continuous") lighting is praised, and built-in flash photography seems to be roundly denounced.
In truth, however, the bias is against bad flash photography. Indeed, flash has become the studio light source of choice for pro photographers, because it's more intense (and its intensity can be varied to order by the photographer), freezes action, frees you from using a tripod (unless you want to use one to lock down a composition), and has a snappy, consistent light quality that matches daylight. (While color balance changes as the flash duration shortens, some Canon flash units can communicate to the camera the exact white balance provided for that shot.) And even pros will cede that the built-in flash of the Canon EOS 40D has some important uses as an adjunct to existing light, particularly to fill in dark shadows.
But electronic flash isn't as inherently easy to use as continuous lighting. As I noted earlier, electronic flash units are more expensive, don't show you exactly what the lighting effect will be (unless you use a second source called a modeling light for a preview), and the exposure of electronic flash units is more difficult to calculate accurately.
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