I was reading some articles recently about digital cameras and there is a known issue with purple around the edges of pictures if you blow them up beyond a certain resolution,check out this web site and look up your model,it might have it in there as a known issue http://www.imaging-resource.com/
Thanks for that.
Looks like the problem alright but my model (F401) isn't amongst the ones they recalled.
I'll email them and see if other models were later discovered to be faulty too