Why does my flash flash-on by itself

Here's what I'm trying to describe. My flash will be on, usually in ETTL. I'm not touching any buttons on the camera or the flash (or at least so I think) and all of the sudden, my 580 will start strobing very quickly (almost like a constant on) for a 1-2 second burst.

Can someone help me understand hy is it doing this and what triggered it?

Thanks.

is it in slave mode? master mode? try one or the other to see if it stops.

Are you hitting the flash button by the lens.

Have you read the manual? I'm quite sure low-light flash focus assist is covered.

I would bet you are pushing the DOF preview button by accident.

tkbslc wrote in post #11809851
I would bet you are pushing the DOF preview button by accident.

+1 You are hitting the modeling light button which tends to be the same as the DOF button.

By chance is there a wireless trigger close to the 580exii? My 580exii will set off my Quantum Radio slaves and do exactly what you're describing. It would even set my strobe off by just bringing the 580exii close to the sender with nothing attached to the 580exii.

tkbslc wrote in post #11809851
I would bet you are pushing the DOF preview button by accident.

This.

Thanks, everyone. I didn't think I was hitting the DOF field button, but next time the flash goes off like this, I'll take special notice. I appreciate the insights.

Probably DoF Preview button, but on the off chance that it's not maybe your flash isn't seated in the hot shoe properly.