# Flash: Please explain ETTL-II Metering



## StudentOfLight (Mar 15, 2015)

Can anyone please provide links or a comprehensive explanation of the difference between Average and Evaluative ETTL-II metering:

On the 5D-III you can access the settings via the following menu structure follows:
MENU > SHOOT1 > External Speedlight control > ETTL-II Meter. > Evaluative
MENU > SHOOT1 > External Speedlight control > ETTL-II Meter. > Average

What exactly is the camera/flash combination doing with either of these setting?
When would one choose one setting over the other?


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## Lawliet (Mar 19, 2015)

Average takes the overall reflected light from the center of the frame with a gradual falloff towards the borders. Basically akin to autoflash, but through the lens so focal length doesn't play a role.

Evaluative puts more emphasis on the area around the active AF point. How that is affected by focus and recompose is...predictably random.

And then we have the II, which incorporates distance information to avoid mishaps from image content that deviates to much from a neutral gray subject. At least while the flash is on camera and locked straight forward. Can cause surprises when used with an off camera cord.


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## Marsu42 (Mar 19, 2015)

Lawliet said:


> Evaluative puts more emphasis on the area around the active AF point. How that is affected by focus and recompose is...predictably random.



Indeed, it's basically like eval camera metering - that's why cameras have both exposure lock and flash exposure lock. It's the mode I use, but it's a hassle with a center-point only camera like the 6d that forces you to focus & recompose all the time :-\


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## Lawliet (Mar 19, 2015)

Well, flash exposure lock works technically - but the human component can be a problem. In social situations most subjects will mistake the preflash for the real thing. Full body ETTL-induced lazy eye effect. :-X


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