I think he meant that at certain focal length, the auto-focus does not focus well enough because the fact that it is third party lens.
So this renders recalibration to make sure at all focal lengths, auto-focus does not give you this problem.
But again, I am not sure if that's what he meant.
Thanks
I think TS was referring to the back/front focusing issues that plague some lenses from 3rd party manufacturers like Tamron and Sigma.
Nothing to do with focusing ability at certain focal length. 3rd party lenses are capable of auto focusing at all focal lengths. Inability to do so is a serious flaw that no recalibration can fix.
And I have already given a response to his question if you read more carefully here.
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