Underexposure when 550Ex used with 10D

[Soumitra]

Respected everyone,
I have experienced this problem with 550EX with 10D 1.5 stops to 2 stops under exposure with Tv, Av, Manual, P, Full auto. Used Centerweighted Metering, Partial & evaluative metering , Tried all possible combinations still negative result, Very balanced result with EOS 7E & 3 bodies, Kindly advice
Regards
soumitra pendse
Bombay, India

[MooseDawg1970]

Hello,

Are you using an off camera shoe cord? Ck the connections with that. I would also ck the flash exposure compensation on the camera and on the flash.

Hope this helps,
Dave

[scottbergerphoto]

Turn off the Automatic Reduction Of Fill Flash in the custom functions. In addition, you may find it helpful to switch to manual focus on the lens, or use Cfn, 4-1 to separate focus from exposure, and release the * button before you shoot. The reason is that ETTL1 emphasizes the active AF point(s). When you switch to MF, it forces the camera to average the flash over all the flash metering segments.
Canon changed this with the introduction of ETTL2 with the Mark II. In ETTL2 flash metering is totally independent of the active AF points.
Scott

[dpanicc1]

"When you switch to MF, it forces the camera to average the flash over all the flash metering segments"

Is that for sure? I thought the 10D uses center-weighted when you switch to manual focus?

Back to the original poster:

I believe any camera metering system yields exposure calculations that produce midtone results, but problems result if you use evaluative metering because you don't know what the "evaluative algorithum" does to the exposure; therefore, exposure compensation is not recommended when using evaluative metering. If you use center weighted--and the circle is covering the specific area you want to properly expose--you need to add or subtract a stop or two depending on the subject's tone with respect to midtone; all other tones will fall into place. So in the case of a white dress, for example, if you go with the camera's suggested exposure values, the dress will turn out darker--or midtone; you have to intervene and open up 1 to 2 stops so the dress appears white. I am fairly confident the flash metering system shoots for medium tone results too necessitating the need for flash compensation based on the main subject's darkness or lightness.

This is more a question in the form of a statement so please feel free to correct, add, etc.

//Dan

[scottbergerphoto]

"When you switch to MF, it forces the camera to average the flash over all the flash metering segments"

Is that for sure? I thought the 10D uses center-weighted when you switch to manual focus?

//Dan
Your mixing apples and oranges. Changing from AF to MF chages the way the camera evaluates the pre flash, not the metering of the ambient light. In ETTL1 (10D), the camera biases flash exposure to the active AF points regardless of the metering you have set for ambient light(CW, Partial, Eval). When you go to MF, you force the camera to average the metering of the pre flash. This is not the case eith ETTL2 (1D Mark II). In ETTL2, the flash metering is totally independent of the AF points regardlss of AF/MF status.
Scott

[dpanicc1]

Scott, You're right: thanks for clearing that up. //Dan