Ian, I agree with Malcolm, I believe your problem is seeing and not collimation.
The seeing of late here at Cambroon has been dreadfull and I would say looking at your image that is your problem as well.
Saturn may look sharper as it is smaller and so will have a sharper contrast,but if you looked it at high mag you would see it is just as soft as Jupiter.
Observing in caloundra not far from the sea and heat from the buildings etc would definitely not help in any way what so ever.
Cheers
