Just successfully tuned my 50/1.8 & 85/1.8 with this dot-tune method with my 5d2.
There is no question in my mind that horshack's new MFA method works and works consistently.
Thanks for sharing this brilliant idea horshack!
To get a consistent result in my 50/1.8, I had to gaffer tape the focus ring of the 50/1.8
so it doesn't move right after manual focusing (x10) in LV.
Getting the AFMA value for 85/1.8 was easy as it was in range: -18 to -1, meaning a AFMA value of -10.
However, it was a bit more tricky for the 50/1.8 as the dot remains red at -20 and the upper range was -4.
-4 should be credible but -20 is questionable and it could be -21, -22, -23 etc but the scale doesn't show it.
So I was guessing horshack's "detuning method" and detuned the focus a bit.
I did so by first setting AFMA to +5 (guessing) and turn the focus ring manual until I get a beep (red dot).
So now I know +5 is within range. Based on this detuned focus, using the dot-tune method gives me a range
of -9 to +9. So I know the half range is 9. Based on the credible upper value of -4 and subtracting
9 (half range) from it gave me a final value of -13.
Using the obtained AFMA values gave me much sharper images at f1.8 at the distance I performed the calibration. (distance suitable for a full-length shot)
So in my mind, the dot-tune method is solid. What is questionable to me is the
implementation of AFMA, as it seems subject distance dependent.
For example, my 85/1.8 with AFMA of -10 works great with full length portraits but I will get soft images at a distance of 10 feet and closer. The 50/1.8 seemed to work well with AFMA of -13 at all distance with the calibration target and lighting. However, it doesn't work very well with somce other subjects and lighting. So I just have to turn off AFMA in case of doubt.
I feel this kind of AFMA is a bandage solution anyway and I am hoping Canon will incorporate their factory lens
calibration routine into EOS Utility and I will be laughing! No more "bad copies" of lens... sigh...
Note the competition already has "USB lens dock" for factory strength lens calibration LOL!