And is that comment based on your experience Richard?
Yes. I have bought about a dozen lenses in recent years. Mainly Canon, but also Sigma, and an old Tamron superzoom.
In use, I have never detected a significant focus error that was down to the camera or lens. But out of curiosity I have done a few focus tests, including the infamous A4 sheet of paper shot at 45 degs. That is where many people go wrong, and it is the bane of camera service centres everywhere.
While in theory that test should work, it is mega critical beyond necessity and in practise it is unreliable for several reasons, and also prone to user error. I can see how easy it is for this test to lead people to believe they have a problem when in fact they haven't. The result is that they send their camera back for calibration, it is checked by the manufacturer to be fine, and returned with an invoice.
This is not a good situation for anybody, and I believe that the micro-focus user adjustment feature is there largely to address this particular issue. So that people can do it for themselves, without any cost, and put it back if they need to. Of course this is not always the case, and some cameras and/or lenses are not as good as they should be from the factory. But this is very much the exception.
Because I am interested in this sort of thing, I have devised my own test which is much more real world relevant. It works fine, and so do my cameras and lenses.
All I would say is, unless you have noticed a problem in actual picture taking, why are you testing it? But if you're just curious, make sure your test is relevant and bear in mind that these are analogue devices, and adjusted to operate within an acceptable tolerance range.
