Can't get wireless ETTL on 2 sigma flash to work

[dr_who]

More trouble for you experts... Sorry that I have to constantly bother you guys. ETTL must be the most confusing part of photography.

I cannot seem to get ETTL wireless to work for 2 sigma flash. I set the one on camera to master, and not to fire. The off camera one set to ETTL slave, same channel, non FEC on both flash. I did not set flash ratio. Here are my problems:

1) the ISO number seemed not transfered over to the slave. If I change ISO on camera, I get nasty pictures.

2) the FEC on camera don't work reliably. Sometimes I change the FEC on camera body, the exposure doesn't seem to change at all. I made sure that a) ambient light is extremely low and does contribute b) used ISO 200 and F5.6, so flash distance is not too long or too short.

[PacAce]

Do you have any sample pictures with EXIF info you can show us? Also, what do you mean by "I get nasty pictures"? Are they too grainy? Over-exposed?

[dr_who]

Do you have any sample pictures with EXIF info you can show us? Also, what do you mean by "I get nasty pictures"? Are they too grainy? Over-exposed?

Thanks for the reply. I didn't post any picture since I'm not sure if EXIF will show the wireless flash info. I can try to post some after get home. Nasty picture means under/over exposed. I'm assuming if I shoot something, then only change the ISO, not the FEC, the next shot I take will be pretty much same exposure as before (ambient light is extremely low), but it was clearly not the case. I'm also assuming if I only change FEC, the exposure will change proportionally, which was also proved wrong. The final exposure is unpredictable.

[PacAce]

It depends on how much you changed the ISO. If you went from ISO 100 to ISO 1600, then there's a chance that you may overexpose the subject if your subject is very close, the aperture is wide open or both. And the reverse may be true if you went from ISO 1600 to ISO 100.