Sigma Flash EF500 DG Super Produces Inconsistent Results?

[dr_who]

I have not used a Canon flash yet, so I don't know if this is a sigma problem or just due to my setup. When I shoot stage performance, about 10~40 feet from stage, with camera set to Tv of 1/100th, eval metering, flash exposure set to -1 on camera, ETTL on flash, I get very inconsistent behavior (1/3 shots over exposed, 1/3 under exposed, 1/3 ok). I'm using 350D

What could be wrong?

[Curtis N]

A few sample images would help greatly.

E-TTL metering can be fussy. Most likely it's the camera's metering system causing the inconsistency, not the flash unit. If you post a few problem shots, we might be able to help.

[Jere Lee]

Are you using a zoom lens?

[dr_who]

I will post some after I get home. I've heard story that Sigma reverse engineered Canon's flash control protocol, and was wondering if that could be the problem causing the inconsistence. But I guess if no one here knows about it, it's probably just set up.

The strange thing is, the shots are shot very close to each other, same background/foreground. I'm wondering why the vast exposure difference.

A few sample images would help greatly.

E-TTL metering can be fussy. Most likely it's the camera's metering system causing the inconsistency, not the flash unit. If you post a few problem shots, we might be able to help.

[dr_who]

Yes, 70-200mm. Also the shots with same zoom factor has quit different exposure...
Are you using a zoom lens?

[Livinthalife]

Are you using a zoom lens?

this is a bit vague.

I think what Jere Lee means,

If you are using a zoom (which I assume you are since that's in your sig) that when you zoom, this will change the amount of light you camera is metering (generally), so this could be the cause.

If you are on a tripod, fixed focal length, and getting inconsistencies, then there is def a problem

[Jere Lee]

Is it possible to try your 433? This won't solve your Sigma problem but it might get you by until you do. I'm sure the results would be much better. Hell Canon can't even make ettl work in a lot of situations. Curtis might be able to help you further if you could give him the info he needs to do so. I just bought a new Sigma 530 dg Super and I could use some tips from him myself.

[kevie]

Well if you shooting in TV mode then your aperture will be changing as your shooting and that would possibly give you different exposures each time.... right?

[Curtis N]

Well if you shooting in TV mode then your aperture will be changing as your shooting and that would possibly give you different exposures each time.... right?Theoretically the flash system is designed to account for the aperture to keep things consistent.

Theoretically. ;)

[digadv]

Might be as simple is not allowing the flash to fully charge between shots. Just something to check.