Originally posted by falconeye
So, I evebtually think that Christine's camera wasn't different but that she just didn't hit the intermediate region where the AF assist beam engages only once.
Falk,
Interesting theory re the AF focus light being triggered by the AF sensor - I'm inclined to think it is plausible.
However, my camera does behave differently from your theory. Once the AF light engages, it will engage until the completion of focus (even in EV2-3).
It's very hard to get the AF assist to come on, even in very dim light. I usually force it by cupping my hands in front of the lens, which then forces the AF assist light to fire.
Once that happens, the AF assist light has a "tendency" to continue to be engaged for subsequent shots, even when I raise the ambient light to as high as EV3.
To get the AF asist light to stop engaging, I have to raise the ambient light to EV4-5 at which point it will stop working, and continue not to work even if I lower the light back to EV1-2.
Interesting behaviour, and implies the camera has some control over the AF assist light, and it's not driven purely by the AF sensor readings.