Issue with YN622's

I just received a pair of YN-622's and immediately noticed a large discrepancy in exposure when using them vs. on-camera speedlight. First off, I'm using my trusty old Sigma EF-500 DG ST, so is it possible there's a compatibility issue with that? (I have a YN-568 on order, my plan is to experiment with using one speedlight on camera and one off).

For these quick and dirty tests I'm using the built in diffuser on the speedlight and bouncing off a textured white ceiling. For the off-camera exposures I held the flash in as close proximity as possible to the position it was in for the on-camera exposures, so I'd expect them to come out pretty darned close to each other. Here's what I got (All exposures were with my XSi, ISO 200, 1/60 sec, f2.8, evaluative metering):


edit to add: I wouldn't be surprised for an instant if I'm missing something in the setup (certainly wouldn't be the first time).

ON CAMERA, 0 FEC:

HTTP response: 404 | MIME changed to 'image/gif' | Byte size: ZERO | PHOTOBUCKET ERROR IMAGE

HTTP response: 404 | MIME changed to 'image/gif' | Byte size: ZERO | PHOTOBUCKET ERROR IMAGE

HTTP response: 404 | MIME changed to 'image/gif' | Byte size: ZERO | PHOTOBUCKET ERROR IMAGE

HTTP response: 404 | MIME changed to 'image/gif' | Byte size: ZERO | PHOTOBUCKET ERROR IMAGE

HTTP response: 404 | MIME changed to 'image/gif' | Byte size: ZERO | PHOTOBUCKET ERROR IMAGE

HTTP response: 404 | MIME changed to 'image/gif' | Byte size: ZERO | PHOTOBUCKET ERROR IMAGE

The 622s won't do ettl with your flash.

I did a lot of experimenting tonight, found that if I put the Sigma speedlight in group C then turn the compensation for group C down by -2 that it seems to work ok. Walked all over the room, turned the FEC up and down, and it seemed to give me the expected results. So all is not lost.

Now I just wish my YN568 would hurry up and get here so I can figure out if I can make it play nice with the older Sigma.

And I'll give a plug to "The Other YN-622C User Guide" https://docs.google.co​m/open?id=0B77...FpqNk​pBYXBHajA . It's proving to be a great help.

(edited to fix link)

Thanks for the promo, groundloop. But that is version 1 -very old. Try version 3.20 -see TOYUG link in my signature.

Interesting - when I put my YN-565 on the camera (E-TTL) I have to dial the EC down by about 1.5 stops. Using it with a YN-622 and E-TTL gives me very close to the desired exposure with no EC. Using two YN-622 / YN-565s also seems to work as expected.

I'd really like to understand how the YN-622 handles TTL. I'd have thought that it was purely a 'conduit' for digital commands between the camera and flash, much like a wired off-camera flash, but apparently there's more going on than that.