In principle, any red filter is fine, but the images may lack the typical IR look (Wood effect, etc.). Even with a #25 filter you may be disappointed. A #29 is, IMO, the very minimum, truly spectacular effects will result with #87, which is visually opaque. There are a couple of filters in between, which will still give good IR effects while being transparent enough for aiming the camera through them, for example an RG 665 (about #70, I believe).(posted 8405 days ago)Regards, Thomas Wollstein