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Thread started 27 Sep 2012 (Thursday) 17:49
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5D3: iFCL sensor and evaluative metering questions

46 posts
Joined Mar 2010
Sep 27, 2012 17:49 |  #1

(This topic also applies to the 7D and any other EOS with the iFCL sensor)

I tend to shoot a lot of low-light action. They are challenging conditions, so I'm trying to figure out the best settings for my camera to get the most keepers. For this thread, I'm limiting the discussion to the metering system.

A little background on the iFCL metering sensor of the 5D3 …settings/iFCL_m​ (external link)

Question 1: does this only apply when "Evaluative metering" is used (as opposed to Spot, Partial, and Average metering)? In other words, if I'm using Spot, Partial, or Average metering mode, is the iFCL sensor is completely irrelevant?

Question 2: It would seem to make sense that Evaluative metering mode is more complex than the others, hence, would using Evaluative metering potentially slow down my burst rate (say under difficult low light conditions)?

On the other hand, (question 3) would using Evaluative metering (and taking advantage of the iFCL sensor) result in more in-focus shots when I'm shooting fast, erratic subjects in low light? So would this be a trade off of continuous burst rate vs focus-accuracy? I mention this because the 5D3's overall AF system does incorporate the exposure system.

Does anyone have any real world experience regarding this? Any insight would be much appreciated

46 posts
Joined Mar 2010
Sep 27, 2012 22:47 |  #2


2,062 posts
Joined Nov 2010
Sep 28, 2012 01:17 |  #3

I'm probably wrong- but I'll give my two-cents.
1. Guess; I'd guess that it uses the appropriate part of the sensor to gauge the exposure.
2. Guess: Nope.. Dedicated processor and optimized coding- should be able to chew thru that data quickly and come up with a decision..
3. Nope.. It's for determining exposure- not focusing the lens.. According to your link- it's part kicks in after the focus has been determined- thus - it's done focusing and is in the process of determining exposure.. Of course, you could be using BBF- but reality- it's not the AF system.. Different piece.

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Sep 28, 2012 01:58 as a reply to  @ wayne.robbins's post |  #4

1. The clever algorithm which detects areas of interest in the image by checking what's in, or nearly in, focus applies to evaluative metering only.
The correction for color's impact on readings applies to all modes.

2. To take one example, a 7D has four CPUs on-board, one or two in the lens and may have a couple more in various accessories. There's enough distributed computing power to fix the evaluative metering on the fly. The only case where it slows down, but that applies to all modes (for some funny reason - it shouldn't really have to), is when it's very dark. Since exposure metering also implies focusing, and with all points, focusing has to be accomplished before metering. In low light focusing takes more time.
The 1DX has an even more complex metering system, the iTR, but then has a dedicated processor to do the work for that one.

3. Since it's focusing before metering, no.


46 posts
Joined Mar 2010
Sep 28, 2012 12:15 |  #5

Thanks, that makes sense now... it'd be pretty silly to have a sensor that's not being used for 3 of the 4 metering modes.

And as for metering comes after focusing, I guess what threw me off was something I read a while about about the AF system being tied to the metering, here let me find it (by Chuck Westfall):

http://www.arihazeghip​​nterview/ (external link)

CW: The AF sensor and AI Servo III tracking algorithms are identical for both cameras. However, the EOS 5D Mark III uses a 63-zone Dual Layer iFCL sensor for exposure metering whereas the EOS-1D X uses an approximately 100,000 pixel RGB sensor powered by a DIGIC 4 processor for exposure metering. As a result, the EOS-1D X supports EOS iTR AF (Intelligent Tracking and Recognition) that can apply face and color detection data from the 100,000 pixel sensor for improved subject tracking when the camera is set for automatic focusing point selection.

When I first read this, I thought Canon's metering system helps with AF-tracking. Now that I've re-read it, I guess this ONLY is true for the 1DX and its RGB sensor?

So the 5D3's iFCL sensor doesn't help with AF or tracking in any way?

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5D3: iFCL sensor and evaluative metering questions
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