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Well...tweaking those 3 screws are sure fun for the past day and a half. Depending on how far you turn the screw (clockwise for back focusing and counter clockwise for front focusing), you could have different focus points showing either front or back focusing....
My both edge focus points, left and right, can exhibit a slight back focusing at f2.8..while using the focusing points closer to the middle circle would get tack sharp images... Fortunately, I never use the extreme edge focus points for compositions. Why is this way I can't explain..hehehehe...
I wish I have a more precise method to test it but so far...the focus is in the acceptable range..maybe either 1mm to 2mm off the target, front or back. That can be the result of focus shift due to the loose tolerance of my 50g f1.8. In the real world, it won't matter.