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5D Mark III - Exposure locked to AF point

Sam Puri , Jun 25, 2012; 10:47 p.m.

I have recently bought 5D Mark-III (with 24-105 L) and still trying to make sense of menu options and its usage.
Instead of locking exposure using center focus point and then recomposing the shot I wanted to have the ability to lock the exposure to selected AF point in manual mode.
To achive above, (after reading the manual) I did the following:
1. Put metering mode to Evaluative Metering.
2. Selected - Single Point AF.
3. Selected - Single Shot mode.
But I still couldn't achieve exposure locked to manually selected AF point, and keep on getting under exposed images in case of backlit subjects.

Any ideas what else I need to do to get the desired results?

Thanks for your help.


Marcus Ian , Jun 26, 2012; 08:35 a.m.

Buy a 1D. The 5D3 doesn't support the changing AF point linked metering.
The 1Dx, 1Dmk4, 1Ds3, 1Ds2, 1Dmk3 are the only bodies which support the feature.

Larry West , Jun 26, 2012; 08:37 a.m.

Evaluative Metering does not lock the exposure to a single AF point in a similar way like "spot" metering does for the center point. It will add slightly more weight to the area around the selected AF point, and progressively less in all directions away from the selected point, but it still is evaluating the entire scene. If your subject is harshly backlit, and/or a relatively small part of the scene, Evaluative Metering won't help a lot, in contrast to spot metering which uses only that one central part of the scene.

Here's an image from Canon that shows what the different modes do: Metering Zones. It's for the 40D, but the same applies for other cameras, just more metering zones and AF points to deal with.

Marcus Ian , Jun 26, 2012; 09:24 a.m.

Any ideas what else I need to do to get the desired results?

I'm sorry, forgot, there is a simple way to get the desired results (w/ your current eqp). Set metering to spot, Use the center AF point, focus/meter on your subject, lock the exposure with the AE lock button, then recompose, and shoot.
If you are using extremely narrow DOF, you may have trouble w/ precise focal point (as focus/recompose moves the focal plane behind the subject slightly) placement.

Puppy Face , Jun 26, 2012; 01:58 p.m.

The last prosumer camera I recall that could to link spot metering to the active AF point was the 1998 EOS 3. It even had spot meter averaging. But for most cameras, save the 1D series, you need to do what Marcus wrote. I rarely bother with AE lock or spot metering anymore. I learned to estimate how much EC to dial in for any given situation (backlighting, dark clothing, light clothing, etc.) as metering behavior is very predictable.

Keith Reeder , Jun 26, 2012; 04:11 p.m.

The 7D has something like metering linked to AF point - in Evaluative mode, the metering algorithm gives highest weight to the exposure under the selected AF point.

Having once used Nikon bodies with metering linked to AF spot, I can confirm that the end result is pretty similar.

I also understand that the 5D Mk III does not work the same way.

Sam Puri , Jun 26, 2012; 09:50 p.m.

Hi All,
Thank you very much for your inputs.
I read the user manual again. On the bottom of Pg 171 of manual (pdf copy), under the section - AE Lock Effects, it is mentioned that with Evaluative metering, AE lock is applied to the selected AF point. Whereas in other metering modes, AE lock is applied at the center AF point.
So I assumed that while normal usage also (and not just AE lock mode) camera will use selected AF point for metering. (which was the case with Nikon D700). Which is probably not true in the case of 5D Mark III.
I didn't get much time to play with the camera yet, but this morning when I changed the Single Point AF to Single Point SPOT AF (smaller area to focus) with Evaluative metering, it gave me much better metering, and resultant pic was what I was expecting.
So, I guess, I need to play a little more with this camera to confirm my findings.
Thanks again friends for all your time and patience. I will look forward to your feedback to enhance my understanding on this wonderful camera.
(By the way: I cannot be happier with the IQ of this camera and improved focusing over Mark II). :)

Larry West , Jun 28, 2012; 03:50 p.m.

The 7D has something like metering linked to AF point - in Evaluative mode, the metering algorithm gives highest weight to the exposure under the selected AF point.

That is true, but it is not nearly the same effect as when using the center focusing point and spot metering. More weight is given to the AF point selected, but not all the weight.

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