EOS 10D - 550EX flash exposures inconsistent

[kip4fast]

Hello,
Maybe somebody here can help me out on this. Under the same conditions, from one shot to the next, I'm having wildly inconsistent flash exposures with the EOS 10D/550EX. I've posted examples, along with EXIF info at:
http://www-p.afsv.af.mil/NW/Eos/Eos.htm

Any advice greatly appreciated.
Thanks for your time,
Lee Schwabe

[slin100]

It looks like the camera was set to Auto Focus Point selection. Auto FP and flash is usually a recipe for disaster, as you have experienced. The problem with this combination is that flash exposure is heavily weighted around the selected focus point. If the camera automatically selects the FP, then the resulting exposure will essentially be a crap-shoot. If the focus point is on a dark area, the flash will overexpose. Conversely, if the FP is on a light area, the flash will underexpose.

The recommended practice when using flash is to manually select the focus point and place the focus point over a mid-toned subject. Do not recompose the image because the flash exposure is, by default, determined after the shutter is pressed.

If composition prevents you from doing placing the FP over a mid-toned subject, then there are alternatives.

1) Use FEL. This will fire the preflash. Exposure is based on the partial-metering area (e.g. the circle in the viewfinder). Aim the partial metering area at a mid-toned subject, press *, recompose and shoot.

2) Enable Custom Function 4-1 or 4-3. This remaps focusing to the * button. This forces flash exposure to be determined from an average weighting over most of the image instead of the selected focus point. There are conflicting reports over whether this works on a 10D, however. Experiment.

3) Switch to manual focus. This is guaranteed to force the flash to use average-weighting because there is no focus point.

Finally, there's the obligatory link to http://photonotes.org/articles/eos-flash/.

[Jim Larson]

2) Enable Custom Function 4-1 or 4-3. This remaps focusing to the * button. This forces flash exposure to be determined from an average weighting over most of the image instead of the selected focus point. There are conflicting reports over whether this works on a 10D, however. Experiment.

Finally, there's the obligatory link to http://photonotes.org/articles/eos-flash/.

The CF4-1 trick does work for the 10D. No one has reported one way or the other for the 300D. (I think it should work).

There was some question on the RG forums, but the person who was "doubting" was finally introduced to the appropriate Chuck Westfall posts.

[figment]

This post helped me understand the 550 a lot better. Thanks!

[yenoram]

Does anyone know if the "moving focus to the * button trick" works for the D60?

Thanks

[slin100]

Does anyone know if the "moving focus to the * button trick" works for the D60?
I believe it does not. But try it yourself. The manual focus trick should work.

[PacAce]

And if you still want the ability to do FE lock using a button after setting CF4 to 1, then set CF13 to 4. This will assign FEL to the Assist button (the one on the left of the * button. :)

[kip4fast]

Thanks for taking the time to look and offering suggestions. I guess the trick is to get my thought patterns to match the E-TTL thought process.

cheers,
Lee