Malcom, what you are seeing has to do with the process used in producing the filters. The older method sees the red spot around stars, & if I remember correctly, how much is seen depends on your eye placement or how square the filter is, even the EP being used - I can't remember which. Nothing wrong with the filters. I have a Lumicon DSF 1.25", & I see it too.
Newer filter production techniques have this thin film phenomenon eliminated. John Bambury I'm sure will be able to shed more light on this
