Gear Talk > Lighting

ETTL-II: on camera vs remote; evaluative vs averaging


First, thanks to everyone for helping me along my quest from old Leica/Film 283 flash to 5Dii/7D ETTL flash.

I ended up getting a pair of YN-568EXii flashes.  Had problems with both battery doors, fixed those.  There are threads on both of that.

Here's my question.

I know the differences between ETTL-II evaluative vs averaging metering, with evaluative comparing the preflash vs ambient on some of the central metering areas (not tied to focusing point) along with distance feedback, if available.  Averaging... just considering the preflash over the central metering areas.  That I've got down.

What I'm having a hard time with, is two things:

a.  Why off camera flash, using the YN622's are seemingly the same as averaging even though the camera is set to evaluative.  Its behaving like averaging for some reason.   For instance - same scene, on camera, evaluative is 2/3 stops underexposed as compared to averaging, however off camera flash is the same, regardless of averaging vs evaluative.
b. Why zooming seems to show that evaluative, only when on camera, is underexposed at certain focal lengths (24-105 and 16-35ii) but is good to go at all focal lengths when used remotely with the YN622 - again, it seems that no matter what it says, you're getting averaging not evaluative when the YN622 is ues.

Any thoughts?


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