Ok other than the bolts in the tube, this seems like a very plausible explanation.
It would seem to me that this really matches up with another anomaly with the tube that I have noticed and thought nothing of it. The heavily linearly stretched image attached shows an uneven illumination of the field that I have noticed throughout all of the images. Would this correlate to the mirror droop? It was another thing that I was going to look at fixing once the diffraction spikes are finished, but if it is our real problem then that would be two birds with one stone!
Also with the full resolution image you can see the diffraction spike problem on that mag 6 star.
Thanks
Dan
