Switching between MF & AF effects correct light metering on 1Ds-Mk3

Started May 9, 2008 | Discussions thread
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astirusty
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Switching between MF & AF effects correct light metering on 1Ds-Mk3
May 9, 2008

Due to all the AF discussions, I decided to experiment with my ability to focus the camera via my "old eyes" vs. the Camera's AF system using single center AF point. That testing got side tracked when I ran into a strange problem with light metering.

Setting: Camera on a tripod, static indoor scene, 50mm 1.4 lens

Camera: ISO 1600, Manual Mode (1/200 & f1.4), Evaluative Metering, Only Center AF point selected for use with autofocus.

With the lens set for AF -- Viewfinder: Shows Exposure Indicator at 0 (middle) -- Results correctly exposed image

With the lens set for MF -- Viewfinder: Setting Exposure Indicator to 0 (middle) for a supposedly correct exposure requires 1/640 shutter speed (keeping f1.4) -- Results very under-exposed image

With the lens set for MF -- Viewfinder: Shows Exposure Indicator at +2 (6 bars up) after setting shutter back to 1/200th (keeping f1.4) -- Results correctly exposed image

I have seen similar results in the same scene with ISO 800 and using Shutter priority. Switching repeatedly between MF & AF yields the same results. The camera does have the latest firmware installed. The AF/MF metering problem still occurs after clearing all customer functions. I have seen similar results in a different indoor scene, although the exposure difference was less (+1 or 3 bars up).

I have searched the manual for a possible reason and also contacted Canon Tech Support -- so far coming up with zip. Maybe its a forest for the trees thing?

Any ideas as to why changing between AF & MF while leaving everything else set the same would give an incorrect light meter reading via the Viewfinder Exposure Indicator?

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