flash experts, need your help

[dave.richards]

So I was playing around a bit with the built-in wireless capabilities of the 580EX's and ran into a couple of problems.

1. I was under the impression that when changing FEC on the master unit it would affect the lighting output of the slave unit as well. This is not the case with mine. What am I doing wrong? Both units are set to ETTL

2. In the manual it says that you can disable the master unit from firing, but allow the slave unit to still fire. When I set the master unit to "oFF", it still fires anyways. Any ideas??
Just got a thought about this...maybe I am seeing the pre-flash? EDIT after more testing it is not the pre-flash I see. I shot into a mirror and can see the flash in the picture.

[dave.richards]

another thought....I am using CF.4-1....would that make any difference?

[Titus213]

Not sure about #1 but I'll bet what you see in #2 is the communications flash. I believe that's how they set the units.

[dave.richards]

Hmm interesting.....so this may be a very low power flash I am seeing that is used to transmit the data?

[René Damkot]

I allways set the 'overall' FEC on camera.
But: from the 580 manual: 'Any flash exposure compensation amount, high-speed sync (FP flash), FE lock, FEB amount, manual flash, and stroboscopic flash settings set with the master unit will all be automatically transmitted to the slave units'.
So no idea there.... Try setting FEC on camera.

The flash you see with 'Master flash off' is the flash used to trigger the slave.
I've read on POTN before that it can be visible in the shot in some scenarios (like the mirror example)

[Titus213]

CF4-1 should not make a difference. What is the issue with photos taken with this system? Over exposed, under exposed or wrong ratios for what is set? Perhaps a sample image with a problem would help figure it out.

[dave.richards]

Well, just to test it, I took a picture of my subject at -3 FEC, then changed to +3 FEC on the master unit, shot again, and the picture looked identical to the previous one.

[Titus213]

What was the shutter speed, f-stop, camera mode? Can you post an example with exif?

[dave.richards]

ISO 400, f/4, 1/60th, manual mode. I can post an example later when I get home.

[PacAce]

And you said that you're setting the FEC on the flash unit itself, right, and not on the camera?

[dave.richards]

Yes, on the master flash unit itself

[Titus213]

Got me, something's just not right. But I think you already knew that...:lol:

Page 36 of the 580EX manual does have a footnote indicating that the master will flash even when off if it's in a wireless environment...

[dave.richards]

Yea I saw that, thanks. I am going to try again tonight with a different subject. Maybe the subject I was using (a candle on my coffee table) was too small to be able to notice the difference in light output. But FEC -3 should totally be noticable compared to FEC +3 no matter what the subject is, right?

[Curtis N]

FEC -3 should totally be noticable compared to FEC +3 no matter what the subject is, right?It should be one heluva difference, as long as your primary light source is flash, not ambient light.

It might help if you posted a few sample images with EXIF info.