Siemens Star charts are use to adjust BF on pro video cameras.
SG6 your point is well understood.
ZL4PLM I think your right, that makes sense.
I was just looking for better daylight method to tweak BF after setting. After putting together the adapers, spacers, and EFW...adding the filter space 1/3 you still will have a 'stacking error' usually making the BF slightly too long. So you end up taking sample pictures looking at the corners for flaring and shimming back and forth to get the final adjustment.
It seems to me there was a post here on making a device to check and adjust (tweak) BF but I can't find it now.