Nice round stars Simon, but it doesn't look very sharp. How are you focussing? Is it cropped from a wider field image, or is this more or less the whole image. For some reason there doesn't seem to be as much detail as one would expect from 25 mins of exposure. What ISO were you using?
raymo
Can you post a single frame from this set Simon? It might show whether
the softness is caused during the stacking process. It would also be interesting to see how much detail is visible in a single frame.
raymo