Eos flash photography is a complex if not downright confusing art which makes Eos flash exposure errors a recurrent discussion topic. Lack of information from Canon would leave users in the dark if there was not PhotoNotes.org’s definitive reference for Eos flash photography. On the path to flash enlightement the photographer will often come back to it to refresh his knowledge at the source.

My most grievous Eos flash photography sin is the use of the “focus – recompose – shoot” drill with flash :

“The fact that the camera biases flash exposure to the nearest focus point [..] is important to keep in mind. If you’re in the habit of using the old “focus, lock AE and recompose image” technique, be sure not do this when taking flash photos.

Flash metering occurs after ambient light metering, so in this case you’re locking AE but not flash metering, and therefore recomposing messes up your flash metering. Instead, select the focus point that’s closest to your subject in order to bias flash exposure to that area”.

Flash exposure lock also provides a way to focus-recompose while metering flash on the right target, but the awkward ergonomics make it unusable in practice for photojournalist style photography.

ETTL-II introduced several improvements, but I had missed the most important from my point of view : a new evaluative metering algorithm. The rumor claims that ETTL-II ignores the AF point bias. Photonotes.org puts it much more mildly, but it looks like something that could potentially make the focus-recompose drill viable with flash.

The only drawback is that ETTL-II bodies are only ETTL-II. Only the 1D MkII has a custom function to switch between focus-point biased metering and evaluative metering.