Spot metering, EC

Started Jan 2, 2013 | Questions thread
MOD elfroggio Senior Member • Posts: 2,796
Re: Spot metering, EC

Severian The Lame wrote:

The evaluative metering takes the whole scene into account and tries to strike a balance between the brightness of the subject matter and the rest of the scene. Of course the camera is just guessing as to what the subject is and how the "typical" photographer would judge the scene should be exposed. It does this based on: 1) The AF point(s) that you are using for focus (it assumes, not unreasonably, that that is where the subject is). 2) The distribution of light at the other metering zones. 3) A large database of "correctly" exposed photos and how the brightness is distributed in them. And 4) some super secret proprietary algorithm cooked up by Canon engineers. It gets it right more often than not, but not always. It can guess wrong or you could want an exposure that it doesn't consider right. Moreover, based on (what it guesses is) the subject, it could have already built in some exposure compensation, and if you then add EC you actually make the exposure worse.

Technical clarification of Canon's evaluative metering:

The screen is divided in 63 zones for the purpose of metering. In evaluative metering the 7D use the zone underneath the AF points that in focus + metering zones of the points that are almost in focus + the adjacent zones to the point that are in focus and the points that are almost in focus.

It does this over 2 layers: one for the blue/green light and the other one for the red/green light.

Perfect metering? Far from it, but there is never a perfect metering, which is why Steve McCurry, the ex-National Geographic/Afghan Girl photographer always uses bracketing.

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