Snapping with a Canon EOS 600D in narrow DOF situations (for example with low f-stop numbers at long focal lenght), I get ghosting artefacts on the parts of the photograph which are out of focus.
These artefacts consist of the same light-reflecting object showing up not just blurred, but multiple times.
This is an example of such artefacts:
The nature of the artefacts (objects showing up multiple times) suggest a defect (or a quirk) of the optics, where adjacent inbound rays take diverging paths and end up in multiple places on the sensor; however, I have never seen the phenomenon before and I'm not sure of the aforementioned explanation. Has anyone observed this? What could it be?