However, the most important thing is to MA at the distance you will most normally shoot at....or at least 25-50x, it that is shorter.
I agree with John. The reason for the 25-50x focal length is to make sure that the target that one uses, can
not be fully resolved by the sensors due to magnification factor. When the target is not sharp, and if you shoot it from too close, the image of the target will still be a little fuzzy and the MA will not be able to find a good optimum. At a larger distance the smaller magnification will create a better challenge.
Also, many lenses are supposedly designed with an optimum performance at roughly 10 metres or 30 feet, so that they will do best from say half that distance to infiinity. If that is the case for a particular design, then calibrating it for too short or too far a distance will perhaps not allow to achieve its optimum.
But in practice, I usually calibrate at the most commonly used distance, or at something like 3 - 4 metres (also easier to achieve indoors), and then I verify if it auto-focuses well when aimed at a distant (or very close, if that's more common) subject.
Cheers,
Bart
