EFS 17-55 USM corner blurriness: experts' opinion needed !

70d IF wrote:

I have a 70d with a Canon EFS 17-55 f/2.8 USM.

After a few months of use, I noticed that the bottom right corner of my image was unsharp in some situations. The issue was clearly visible at 55 mm f/2.8, less so at 17 mm f/2.8. At f/5.6 it was still visible, and at f/8 almost gone (or at least reduced to an acceptable level).

In addition I had the feeling that the AF was inaccurate, so I sent the body and the lens to Canon for servicing.

I got it back and now:
- The blurry corner is still there.
- The MFA has to be set to W:+12 T:+15 to get correct focus (instead of W:+6 T:+9 previously)
- The AF seems to be more accurate, i.e. focusing on the same target several times produces less focus variations.

I called the technician, who told me that he adjusted the body AF, but did nothing to the lens, as he tested it and concluded that it was "within Canon specifications".

that in comparison to the 24-105, this lens has three sharp edges vs. none. "What are you complaining about." But seriously...

He could also mean that the decentering here is not severe enough to mess with. To center it. you may end up with both sides noticeable soft although the right side will show improvement.

My first 24-70 II was soft 1/3 of the way into the frame from the right side. This is a decentering issue they can't ignore.

I had also a long discussion with him about the MFA value being higher than originally and thus all modes but M, P, Av, Tv and B being unusable, but this would deserve another topic. My main concern was and remains: corner blurriness.

My understanding of the situation is that the lens has an optical problem (a centering defect ?), however Canon will not fix it because it is within their manufacturing tolerances.

So my question is: are Canon testing criteria too low or my expectations too high ?

Please give me your opinion.

Here is an example illustrating the problem:

The orginal image is here: https://www.cloud.sfr.fr/?shareObject=489d7ce6-a84a-14e1-ad70-9e2f130135ce