According to both the Canon manual and the FoCal software, the recommended distance to the target when testing for microadjustment is 50X the focal length of the lens. My longest focal length currently would be 400mm (70-200 with 2x extender) which would mean a target distance of 65.6' according to the 50X rule.
I'm curious as to how you all have set up for these tests. I can't get that long of line-of-sight in my house. If you go outside, you have to worry about changing light, the wind blowing you target around (moving the target even very, very little between shots can mess up the analysis), not getting the target parallel to the plane of the sensor can cause problems, etc. Perhaps I'm being overly cautious about all of this. But I'm wondering how the rest of you have handled these longer focal length adjustments.
BTW, it doesn't apply to my situation, but when dealing with a crop camera do you take focal length x 50 x 1.6?