Background focus issues

[SRHayward]

I am having a problem with my Sigma 17-50mm F2.8 lens. It doesn't seem to be able to focus on distant backgrounds even when I tell it to focus on the background rather than foreground. So basically I can get sharp focused photos of objects near the camera but anything over maybe 10m away has soft focus at best regardless of f-stop or where the focus is set. I can't even focus stack to get a sharp photo from foreground to background. I have sent the lens into be tested and they said they couldn't find anything wrong.

Anyone else had this sort of problem?

 

[StewartR]

If you sent it you Sigma and they couldn't find anything wrong, then (in the politest sense) that indicates the possibility of user error. But we don't have enough information to work with. For starters, are we talking about autofocus, manual focus, or both?

 

[Sharky]

Does your body support MFA? May need tweaking if you have the option to adjust it at the wide and tele ends.

Also as Stewart said, what happens when you try and manual focus, both VF and LV?

 

[tijuana taxi]

Have a try at the wide end around f/11 focused at approx 3ft, should give you good detail front to back