If you have a pressure pad with a shining chrome bar or anything in the picture area that is light colored, the light will pass through the film and reflect forward and be photographed. Remember you will need Bell and Howell perfs l866 on both sides which is the standard perfs used in most of the world. Reflex viewing on the camera will, therefore, do you no good. This filter is available from Harrison and Harrison. Shoot a test to determine the look and exposure you're after .
Infrared light is a different wave length than normal lenses have their back focus adjusted to.
Most still lenses have either a red dot or some sort of a red mark near the normal witness mark and with these you should focus by eye to the normal mark and then shift the position you have focused to the red mark. If you focus by tape measure, use the red mark to set the engraved distance on the lens. A lens technician, using a collimator, could put red marks on your lenses by comparing a still lens that has the red mark with the same focal length cine-lens and, using the collimator, mark the red mark using the same back focus offset for the same focal length still lens. I would not use zoom lenses. Even though I have not tested them with infrared, I would be surprised if there wasn't focus problems.