avdbrandt wrote in post #17582881
So you take 41 images (-20 till +20) and compare them in lightroom or DPP (DPP shows the MFA value I found out).
did try something similar but did not see very little difference, I think I used the wrong subject (traffic sign) to do this test.
Do you see much difference IQ wise between 500mm and 600mm?
anyway thanks for your help, this weekend I try again.
It's not easy. I found the same as you - many times the shots show little change...
What I did do was take Live View images as well, and compare them against that - the LV image should be correctly focused as it requires no MFA.
So the LV image was my benchmark.
Then I took images at the extremes +/-20, then +/-15, then +/-10, and so on until I narrowed it in...