I want to shoot some IR with my Burnett combo (speed graphic 4x5 with 7" Aero Ektar lens). The lens came with an original yellow filter assembly, but I would prefer a no. 25 red filter for IR. The lens takes a 4.5" (115 mm) filter. If I could get plastic stock for a red filter I could cut it to fit into the yellow assembly, and be good to go. But I've been unable to find any red stock that large. 4"x4" seems to be about the max available.
Does anyone have any ideas?