I've recently been photographing seabirds and have noticed what I would term a 'halo' effect which is especialy noticeable on white feathers against a blue sky as seen below around the birds white breast. It also shows up but less noticeable with dark feathers. Does anyone have an explanation? Might the UV filter be at fault? Camera is a 400D and lens a 300mm f/4L with 1.4x TC.[img]/cfs-file.ashx/__key/CommunityServer.Components.UserFiles/00.00.00.23.16/Razorbill-4.jpg[/img]