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I read that the canon 600ex rt has some face detect eTTL magic. Has anyone found this to provide real improvements? I'm shopping for a second flash and want to know if this is worth taking into consideration.

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Perhaps you could provide a link to where you read this? –  Michael Clark Sep 1 '13 at 15:03
    
What's with the downvotes? Seems like a valid question to me. As they answers show the assumption is false but that is why he asked. (A link to where he read this could be nice, though) –  Unapiedra Sep 1 '13 at 18:57
    
A quick Google finds this page on Canon's New Zealand site - see the penultimate paragraph. –  Philip Kendall Sep 1 '13 at 19:29
    
Hi everyone, yeah as Philip Kendall said, it's on that page. I wanted to put a link in but I couldn't find one in time. There's a few Canon websites where the face detect isn't mentioned and a some where it is. –  Peter pete Sep 1 '13 at 22:40
    
Interesting that the 600EX user manual doesn't mention this feature when discussing Manual External Flash Metering on pages 36-37 of the user manual. –  Michael Clark Sep 1 '13 at 23:03

2 Answers 2

Face detection has to do with focusing and is performed by the camera, not the flash. Whatever face detection features your camera body are capable of will determine the performance of the camera/flash system in this regard. With most bodies this would require using Live View to use the facial detection features. The EOS 1D X has an advanced metering system with RGB exposure meters rather than the usual monochrome metering sensor. This metering system can distinguish different colors/tones, detect typical flesh tones, and adjust exposure accordingly based on metering via the viewfinder as well as by using Live View Face Detection. The EOS 1D X uses this system to recognize skin tones when using PD AF so it is quite possible that when coupled with the 1D X the 600EX RT can adjust exposure to match skin tones without shooting in Live View (see the fourth bullet point here: http://learn.usa.canon.com/resources/products/eos_1d_x/eos_1d_x.shtml).

Once the camera has selected the point of focus it does communicate distance information to the flash for use in figuring the needed amount of flash power. Although the primary factor in figuring the power is the amount of reflected light from the pre-flash recorded by the area of the camera's metering sensor associated with the selected point of focus (which may have been selected by the camera using the facial recognition feature), the distance information is also used to allow compensation for highly reflective surfaces that would otherwise fool the metering system during the pre-flash measurement.

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Hi. Yep, I thought that the facedetect AF may communicate light reflectance from the preflash to the camera. But then it's a pretty useless feature on the 600ex-RT since it won't work for phase focus but only contrast/70d liveview focus. Phase focus doesn't face-detect –  Peter pete Sep 1 '13 at 22:43
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The 1D X does have an advanced metering system with RGB exposure meters rather than the typical monochrome and can distinguish different colors/tones and adjust exposure. The 1D X also uses this system to do facial recognition in PD AF so it is quite possible that when coupled with the 1D X the 600EX RT can adjust exposure to match skin tones without shooting in Live View. –  Michael Clark Sep 1 '13 at 22:53
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Oooooh. This is an interesting thing. I didn't know 1dx did face-detect in PD. I did know about its RGB metering. Maybe this is when it works. –  Peter pete Sep 2 '13 at 9:23

The camera body handles metering, not the flash. The 600EX-RT has no face detection feature as it doesn't even do exposure calculations. When using E-TTL, the camera triggers a pre-flash, meters the result of the pre-flash and calculates the flash power based on that metering. What could be possible is that your camera itself may meter based on where it detects faces, but that would be a camera body feature.

The only other thing I could think of that you might be thinking of is that the 600EX-RT has an IR illuminator that projects a near-IR focusing grid that can help focus while in dark environments. This might also help the face detect feature of some cameras that support it possibly since it projects a known pattern on to the subjects.

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Howdy. Yep, I know all you just said, but: "Exposure metering has also been improved. The unit's stable E-TTL metering function uses a face detection algorithm that detects face colour and then optimises flash output to optimise the exposure for the subject." is said on tinyurl.com/lxl9j9p second last paragraph –  Peter pete Sep 1 '13 at 22:42
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@Peterpete - I can only assume that they have some model of camera that incorporates this into the E-TTL processing, but that processing is handled in the camera body, so I don't see how it could possibly be added by the flash. I also can't find any mention of the behavior in the flash documentation and have never noticed it acting differently as a result of something like this. (I have the 600EX-RT and a 5d mark iii body that I use it with.) –  AJ Henderson Sep 1 '13 at 23:00
    
Thanks for the "not in the documentation" mention. Maybe i'll email Canon and try to find out. –  Peter pete Sep 2 '13 at 9:22
    
@Peterpete - yeah, that's probably the best bet. Be sure to post back here with your results if they get back to you about it. I'd certainly be interested in knowing for sure. –  AJ Henderson Sep 2 '13 at 16:28

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