Sorry, I don't think I explained it properly. The photos that I attach are those that I have put when I have given up on not finding the reason why the circle does not coincide with the end of the focuser. I have previously tested the collimation with the tube on the mount, in vertical and horizontal position, with the camera attached to the focuser with an adapter first and then with the coma corrector, and with the focuser fixing screws tightened. I have also tried rotating the camera 360 degrees and the position of the circle remains, it does not change at all. But the result is always the same, the mismatch seen in the photos.