The post right above this one is right. the one suggesting 20 to 40 stops is way off base there. 6 to7 stops with an R72 filter correct. 6 to 9 stops with a R 89 is about right. Also it is now about too late in the year for much IR. You need to work mid day in bright sun around green leaves which will give you your best IR response. Once the leaves go dead and shift color, it is pretty much over till spring. Then we have to wait until May or June.