02-08-2015, 12:39 AM
Popo may be correct and this may be spurious resolution.
What happens if you stop the lens down or change the focus slightly? If it disappears -> spurious resolution/interference pattern. If not -> probably an instance of total internal reflection inside the lens.
What happens if you stop the lens down or change the focus slightly? If it disappears -> spurious resolution/interference pattern. If not -> probably an instance of total internal reflection inside the lens.