Jim I can\'t say for the 85 as I don\'t have a ZF-85 ( I know complete the collection) but here is some tests results I did on the Zeiss lens I have. Its not fully scientific so there is room for error.
Aperture with filter when a hot spot starts to show - LifePixel is on IR only camera that was modified for IR, the other two were filters on lens.
Zeiss ZF 21
LifePixel 715 - 5.6
B+W 093 850 -unable to filter
Heliopan 1000 - unable to filter
Zeiss ZF 50 (1.4) IR
LifePixel 715 -None
B+W 093 850 - None
Heliopan 1000 - None
* There was one set of tests that had the 850 and 1000 show a hot spot at F8, but I haven\'t been able to duplicate it.
