Peter, if this is a problem for you, and you need something precisely
centred, you could drill and tap two more holes, and then you would have three equidistant screws to centre the focuser tube with. The camera and
the focuser tube normally sag as one entity, so the squareness would be retained.
If the connection between the camera and the focuser tube was sloppy,
so that you had camera sag only, the sensor would be out of square.
The malalignment would often be unnoticeable, unless the scope passed
the zenith, and then the camera would flop in a different direction,
ruining your pic.
raymo
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