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Peter
The 'star bloat' that you are seeing is due to chromatic abberation (CA) and is due to the inability of the lenses in your scope to bring all coours to the same focus. You may only see a small amount of blue by eye but when you do astrophotography and CA will become more prominent. The rest of your frame looks quite good, ie sharp stars except for the lower left hand side. This could be due to a slight mis-collimation issue ie the camera is not parallel to the optical axis, a fault due often to a misalignment caused by the focuser. Check that the camera is firmly held in the focuser and parallel to the face of the focuser.
The excessive CA you see in the shot MAY be tamed somewhat by 1) a fringe killer filter or semi-apo filter (expensive and mask your problem or 2) Noel Carnoni's actions for photoshop will reduce the (cheap $19.95).
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