Fine-tuning lenses - what am I doing wrong?

'The first thing that comes to my mind is that you might have forgotten to defocus the lens manually between shots (e.g. focus to infinity).'

That's something I've not done. I had focus set to APS-C, middle point selected, on a tripod, lens doesn't have VR so no issue there, and I was using the infra-red remote with mirror-up.

But for the results, yes I really expected to see vast differences between -20 and +20 and wasn't. So maybe it's that step I'm missing along with getting the distance from camera to chart correct.

I shall try again when I get a chance.

As for WHY I'm doing it, well, y'know.... OCD 'n all that I would like to know if I have a good or bad lens - it does SEEM to be OK so I'm not overly concerned about it but it would be nice to at least make an effort to get it running it's best. As I'm still really an improving-amateur it would be nice to rule out any hardware related problems so that I really do know that the mistakes I make ARE all my own fault!!