This jibes with my experience with the Rollei material. Somewhere I saw a graph of the HIE spectral sensitivity that showed it not only sensitive way farther into the IR spectrum, but also what looked to be a bit of a notch in the yellow green range. Thinking area-under-the-curve stuff I'd guess almost any red filter would skew HIE pretty well towards IR. The Rollei barely makes it into the IR range; I somewhat preferred the effect with a 760 filter over a 720, but that involves working so far down the spectral cut-off it takes a lot of extra exposure and seems a bit touchy for latitude.
Originally Posted by 2F/2F
Enh, experiment, experiment. And as pointed out, though the Rollei 400 is a nice pan film, the price of a roll would buy about three of Acros 100!