Inconsistent focus with Sigma 8-16/f4.5-5.6 DC HSM lens

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MisterBG Veteran Member • Posts: 6,393
Inconsistent focus with Sigma 8-16/f4.5-5.6 DC HSM lens

I normally use manufacturer lenses, but as a wide angle fan, I recently had the chance to buy a Sigma 8-16/f4.5-5.6 DC HSM lens, which gives coverage which is not provided by native Canon lenses.
Initial testing with this lens on my Canon 80D has proved a little disappointing.
The results are not as sharp as I was expecting, but the lens also seems to have an AF problem.
I've been using single shot AF with a single centre focus point, which is the way I work most of the time.
Despite getting a focus confirmation "beep" the image is simply not sharp, both in the viewfinder and the recorded image.
One thing I have noticed is that looking at the focus scale on the lens barrel, the focus indicator is frequently well beyond the "Infinity" mark, even on relatively close subjects. I also set the camera on a tripod and repeatedly pressing the pre-focus button resulted in the lens refocussing at a different point on the same static subject.
Another thing that is puzzling is that viewing the EXIF data, the "focus point" is given as 3.53 metres on almost every image.
I don't know how the EXIF is generated, but it's strange to see the focus distance reported as exactly 3.53 metres on 30+ images, all of different subjects, especially as the focus point is obviously different between them all.
On shots taken with a different (Canon) lens, the focus distance is different in each shot, as I would expect.

The lens was purchased from a leading UK dealer and I decided to return it (they still have real stores staffed by humans.)
I was given the option of a refund, or they could send it to Sigma UK for repair. (A replacement item was not available from stock.)
I decided on the repair option, so it will be interesting to see what Sigma say about the lens.

 MisterBG's gear list:MisterBG's gear list
Sony RX100 Canon EOS 6D Sony a6000 Canon EOS 80D Canon EOS 5D Mark IV +11 more
Canon EOS 80D Sigma 8-16mm F4.5-5.6 DC HSM
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