Understanding E-TTL's metering...

Started Jun 23, 2012 | Discussions thread
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byawk Regular Member • Posts: 226
Understanding E-TTL's metering...

After years of just "winging it" with my on-camera flashes, I'm finally trying to learn the mechanics of how my Speedlite meters the scene so that I can get more accurate exposures.

I've read up on my 580 EX II, and my understanding is that, when in E-TTL, the flash will fire off a pre-flash to determine the reflectivity of the subject and it will also consider the distance of the subject from the lens. This makes sense to me, but what I don't understand is, what happens when I tilt or pan the flash head? I often like to bounce my flash off a wall or ceiling (or often even behind me a bit). In this case, how does the 580 EX II determine the flash exposure? The flash obviously doesn't know the geometry of my bounce, so I'm stumped as to what data it uses to determine what the flash exposure should be.

Any insights you have would be welcome! Thanks!

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