Minor 50L Discovery

I was contemplating the 50L fiasco today and had an idea. I wondered if enabling the expanded AF area on my 5D would have any affect on the focusing anomaly. I casually set up the focusing chart and enabled the expanded AF points (custom function 17) while in one shot focusing mode and center focusing point selected. As you might expect no difference.
Then I put the camera in AI servo mode (still with center focusing point selected) and shot a frame without enabling cf 17 then several with cf 17 engaged. To my surprise the shots with cf 17 enabled were consistantly better on the focusing chart.

Now Iam not saying this solves the problem. It only improves the shift slightly on my camera on the focusing chart. I have not had a chance to try it in real world shooting. I was hoping some of you would try to duplicate the findings and maybe try this in some real world shots if you have not already.

This post contains a typical cropped shot from my 5D/50L at f/2.8 AI servo without cf-17 engaged.

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These are typical shots with cf-17 engaged at f/2.8

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Damn it. I KNEW I needed a 5D! So for all of us 50L 1.2 users, Canon should automatically mail us a free 5D for our troubles...

ADDITIONAL INFO: (for all you silently interested 50L lovers...:oops Setting cf-17 to on only seems to change performance on the focus chart when the camera is held vertically. When I hold the camera horizontally cf-17 appears to make no difference.

It may have something to do with the orientation of the extended focus points and the markings on the focus chart.

EDIT: Looked at 5D viewfinder with AF points on Canon site. If you look at the picture (borrowed from the Canon site) of the horizontal viewfinder and superimpose that on the focus chart target, you can see that the AF assist points will be above and below the target line. However, if you flip the viewfinder vertical the AF assist points will then intersect the focus chart target line and presumably aid the focus.

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It makes sense that the expanded points have an effect in AI Servo mode because they don't function in one shot. Glad you discovered this workaround!

Got your PM. Thanks. I might have missed this thread otherwise as I've been a bit busy. It makes sense you'd might get some help from the extra AF points though the correction doesn't seem as significant as when using the points further out. It might be just enough to get an eye sharp though. Perhaps that is because they aren't offset very much from the center of the lens.

Here are a couple of crops from some test shots I did a few weeks back. Nothing fancy as I was really testing the field curvature of the lens but decided to take a few quick snaps with various AF points with the same set up. For these shots I used AF on a black strip for either the center AF point or the far right AF point. These crops are at f/2.8 and about 2 ft.

center AF point

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Wow,
The outer point almost brought the DOF up too far! I saw that a few times when I shot with the camera horizontal and allowed the hidden assist points to catch part of the target.
This lens certainly has some interesting issues!