Originally Posted by
Steve Goldstein
If it happens with two different filters on the same lens then why do you say it's the filter? Do you get this effect using the same filter(s) on different lenses? How close together are the fringes? Is there any chance it's a pinhole light leak in a lensboard? This might not have much impact in normal use but with a 6-stops filter it could be significant.
It seems to me unlikely that it's light reflecting off the front of the lens and back off the filter. Uncoated glass reflects about 4%, and a multicoated filter less than 1%, so that would produce a reflection with at most about 0.04% of the intensity of the original source, about 11-1/3 stops down relative to the primary image-forming light after it's gone through the filter, and another stop down for a coated lens. I'd be surprised if this was it.
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