ETTL

Yesterday I was shooting at a party with 20D and 580EX flash with 24-70, 2.8L lens. All the time I was shooting in P mode and flash set at ETTL. For some reason, in the middle of the party, my flash settings went into TTL.
I could not change back to ETTL. My shutter speed was too low for that, and pictures were shaky. I tried in camera settigns to set at evaluative mode and tried other things. Tried flash settings as well. I could switch back to ETTL. What may have caused this and why could not I set it back. Mind boggling. For this reasong, I had to switch to M mode both in camera and in flash and got pictures OK. Can some one help me to understand this. Thank you.

Maybe you should have your flash looked at by Canon repair services. The 580EX TTL/ETTL mode is changed via a custom function so if you weren't fiddling with the custom functions, there might have been a glitch or a defect in the 580EX that made it switch to TTL al by itself.

Were you using an off camera cord?

Terry

TTL (without the 'E') would've given full manual flash on the 20D. Meaning full flash output every time. Either something's wrong with the flash, or there's a loose contact somewhere.

Are you sure about that, Rene? I know it would for the 1D series but I'm not so sure with the 20D, though. But you could be right.

IIRC any camera needing E-TTL will only fire TTL flashes at full power.

Aren't the EZ models TTL flashes? If so, my 10D wll not fire it in TTL mode although my 1D2 does. And the same goes for the 20D according to the 20D manual unless the TTL flash has the manual flash feature and is set to manual mode.

Yes. Rene said "full manual flash on the 20D"; you asked if he was sure; I affirmed that he was correct.

Whoa PacAce, come again? Your 540EZ fires in TTL mode on a 1D2? Should *not* be the case, since the 540EZ is (A)TTL, not ETTL, and the 1D2 is *only* ETTL(2). The 540 should flash at full output.

OK, I guess it was just a matter of differences in the interpretation. I assumed that Rene was talking about the flash firing in full output mode with the flash in TTL mode, not in Manual mode, otherwise, for the 580EX, it would have been a moot point to mention it since we already know that the 580EX works with the 20D in manual mode.

Check page 99 of the 1D2 manual. And I've confirmed this with my own EZ-compatible flash and the 1D2.

[Edit: Oops. I just reread your post. Looks like we got our wires crossed. I didn't mean to imply that the flash will fire with the camera controlling the output of the flash. I meant that the flash will fire, at full output, with the flash set to TTL mode. Didn't mean to imply that the camera was working in TTL mode.]

OK, I just tried some test with my 580EX set to TTL mode (C.Fn-3=1):

10D with flash in TTL mode -> flash does not fire (I assume that the 20D will behave the same way)
10D with flash in M mode-> flash fires

1D2 with flash in TTL mode -> flash fires at full power
1D2 with flash in M mode -> flash fires