That happens when your imaging plane (the sensor) is not at right angles to the incoming light rays.
That, in turn, happens when your camera is not flush with the surface of the focuser (because the adapter is slightly smaller than the focuser tube, allowing some wiggle) or because the focuser itself is not mounted flush, or because the tube itself (including the focuser parts) sags.
Alex
That, in turn, happens when your camera is not flush with the surface of the focuser (because the adapter is slightly smaller than the focuser tube, allowing some wiggle) or because the focuser itself is not mounted flush, or because the tube itself (including the focuser parts) sags.
Alex
