Hello,

I'm usinga two flash setup with a 580EX on camera (30D) and a EF-500 as a slave. This works well normally, however I'd like to set ratios between them.

Setting the Sigma to Group 2 and telling the 580EX to enable ratios results in the Sigma firing at full power always. Setting the Sigma to another group doesn't affect the flash ratio in the picture.

Can anyone help me? Neither manual gives instructions on how this can be done with only one slave flash.

Thanks

TMz06 wrote: Yes - It can be done with 1 slave!

The ratio is controlled from the Master flash (i.e. whichever is mounted on the camera). In your case it's the 580EX -> group 2 is group B in Canon, select ratio on the 580EX with A:B then dial in your ratio...

Thanks for your reply, but I still can't get it to work - the Sigma keeps overexposing badly whatever the ratio and flash exposure compensation I dial in :?

Several questions:

1. Is the 580EX set to Master mode?
2. Did you dial-in the ratio on the Master (i.e. the 580EX) only and left the Sigma on ETTL with one set of 'lightning' on the rear LCD (i.e. slave mode)?
-> You can confirm the above by pressing FEL (or the lens stop-down lever) - In one case they will preflash (and the other the modeling lights will pulse rapidly)


3. Was the Sigma changed to Group 3 (i.e. Group C)? The flash exposure compensation do not work on Group 2 (i.e. Group B) - Check the Canon manual:
-> Group C is unique and the only group that the exposure compensation can work on in the Canon system (if you have left it in Group 2(B) the exposure compensation has no effect!) - Ditto with Group 1 or A, it won't work there either

-> Also the front of the slave(s) flash has to face the camera (the head can be pointed anywhere), it need to get the commands from the Master which is sitting on the camera

Yes, the switch is in the Master position


Yes, both of them function, although the lightning bolt flash indicator in the viewfinder blinks when I use FEL with ratio on.

I didn't know that - thanks for the info! It still overexposes when set to Group 3 but not as much as when set to Group 2, very odd. Playing with the AB and C ratios gives some pretty unpredictable exposures and at no point did the green correct flash exposure lamp come on the 580EX when ratios was on. :sad:


I try to keep the slave flash pointing towards the camera, and I am indoors so communcation between the flashes should be okay.

Can you just select just A:B alone?
AB and C let you do exposure compensation so you can varies all 3 groups independently form one another (i.e. A:B&C together and then C can be varied with the exposure compensation)

You really don't need to use exposure compensation at all...
A:B alone should work if you set the Sigma on group 2 - I've used it many times in this configuration

-> If all else fail you can also use the Sigma as the Master (all the controls will be set from the Sigma then) and the 580EX set on Slave - This configuration works for me as well...

Thanks for all your help NHL. It seems like everything works when I puttheslavein a channel other than 1; flash exposure confirmation, ratios, the lot. :|

Only thing is, 1:1 ratio doesn't give the same exposure as ratios off (the slave flash is much brighter in the shot) - is that what's supposed to happen? Sorry, I'm new to TTL wireless flashes.

Thanks again for your help

I've never try that but I guess that it could happen

In 1:1 the camera meter A and then B and then adjust both output to approximately the same level...
Whereas when the ratio is off the camera exposes A correctly for the scene, and then it exposes B independently of A for the same scene - This just my guess, but may be this would help: http://eosseries.ifrance.com/eosseri...ork_ssfil.html