8)I can use IR ND mirror on any lens.
Where as some lenses have highly reflective coatings and may cause internal reflection off the filter. Use good lenses, such as Red, modern Cooke or Zeiss no problems there. Some old beaten glass may not have the type of optical quality (transparency) needed for compatibility with mirror-type filters. It is an important consideration when choosing a lens. In my experience, Arri-Zeiss Master Primes as well as Red 300mm prime are perfect for using mirror-type filters and I found no side effects even in the most difficult lighting conditions.
now i wonder what happens if i use the pancros on old lomo primes (spherical); will i get some pretty bad effect? maybe worse than the IR contamination i'd get without the pancros in the first place? or does it just limit the effectiveness of the IR filtering?