Ze strony:
http://www.prophotohome.com/forum/ca...ture-data.html


580EX transmission of color temperature data
There has been considerable interest in exactly how the "color temperature information" provided by the Canon Speedlite 580EX flash unit is utilized in optimizing the camera's white balance compensation process. It is fairly easy to imagine how this might work with the camera set to the "Flash" WB preset, more difficult to imagine with regard to the AWB choice (or any of the other presets, although information we have seen suggests it only applied to Flash and AWB WB choices).

Chuck Westfall, Director/Media & Customer Relationship, Camera Marketing Group/Canon U.S.A., Inc., today advised me as follows:

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The Speedlite 580EX's color temperature data transmission feature works on all EOS Digital SLRs introduced since the EOS-1D Mark II, including the 1D Mark II, 20D, 1Ds Mark II and Rebel XT. It does not work on earlier models.

The basic idea of the feature is to stabilize the color temperature of the images, especially during continuous flash photography in E-TTL II mode, which often requires significant variations in output level from shot to shot. The function is always "on" with compatible cameras when they are set to either AWB or Flash WB, and cannot be turned off by the user, except by selecting WB settings other than AWB or Flash.

How it works: The 580EX has a built-in look-up table that provides WB modification values based on the combination of flash duration and battery charge level. These values are always known prior to the actual exposure: in manual flash mode, the duration is based on the user's setting, whereas in E-TTL II mode, the duration is calculated from preflash data. Battery level is constantly monitored, and varies according to charge level and power source (internal, external, or both). When a compatible camera is set to either AWB or Flash WB, the 580EX WB modification value is applied to the camera's WB setting.

I am attaching a chart that shows how color temperature values vary according to battery level and flash duration for the 550EX. We have not received an equivalent chart for the 580EX, but I anticipate that the results will be similar, since both flash units operate on the same general principles. You may publish this chart on the Web as long as it is attributed to Canon via me.
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Here is a link to that chart:

http://doug.kerr.home.att.net/pumpki...EX_color_A.jpg

This explanation still left me baffled as to how the color temperature information from the flash unit would be utilized in the AWB mode. I mentioned this to Chuck. He replied with this further information:

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On all of the compatible cameras, AWB is calculated solely from the central portion of the image data, using an area that corresponds either to the spot metering circle on a 1D Mark II or 1Ds Mark II, or the partial metering circle in the case of the 20D or the Digital Rebel XT. (Same part of the picture that's used for custom white balance measurements.)The AWB calculation itself does not include the 580EX WB compensation factor. This factor, when available, is applied to the AWB calculation after it has been completed.