I tend to agree with Alex here, Martin. If your eyepieces or Barlow's are not up to scratch optically, their faults will manifest in resulting aberrations like this. Best way to remove it would be to use the defringing action in Registax. It will create a soft mask around the perimeter of the planet and help disguise the CA. Good on you for getting out there so early while Jupiter is quite low in the sky. It's still a nice result.
