Flash Metering

[btym3011]

hi all,
i'm using canon 450D with 430exii. assume i have my cam on manual mode and spot metering. when i hit FEL, will the camera calculate the correct power for my flash based on where my centre spot is?

 

[Dream Merchant]

For this, you'll need to try try and find out, or read the EOS Flash Bible.

It would likely be from your chosen AF spot, and not specifically only the center but I'm only guessing wildly. Seriously, your best bet is the bible.

All the best.

 

[theveed]

AFAIK, no, your camera's metering only meters for the ambient, the flash only has two metering modes, average and evaluative (check your manual and your camera's External Flash Function Setting window).

The 430EX II uses the E-TTL II autoflash (a preflash-evaluative exposure adjustment system). E-TTL II uses a reference exposure aperture, set either automatically or manually, and in just 0.002 seconds fires a weak pre-flash just before the exposure, detects the overall light conditions in the scene with the camera's multi-segment light sensor, instantly evaluates and determines the subject's position and the shooting conditions. It then calculates and stores the necessary flash power to make a natural-looking photo. It then immediately fires the main flash.

- http://www.canon.com/camera-museum/tech/report/200808/report.html

 

[Octarine]

hi all,
i'm using canon 450D with 430exii. assume i have my cam on manual mode and spot metering. when i hit FEL, will the camera calculate the correct power for my flash based on where my centre spot is?

AFAIK, the 450D can only measure on the centre AF point, so spot metering always refers to the centre of the image. Only higher end bodies can decouple AF point and spot metering. Your manual can tell you more details.
For everything else that the EOS flash system does or does not you can read here.