I am wanting to give the internal filters a try on this lens shooting on a F35 but I am worried about far red contamination. I am looking at getting some Kodak Wratten 2 gel ND filters but I am concerned that I will get far red contamination, they appear to start transmitting again at 700nm and have no effect by 750nm. The F35 has an IR filter that begins at 700nm and full cuts by 750nm. I am also considering getting some 40 mm tiffen irnd glass filters and using them instead of gel. I know I will have to remove the filter housing to do so.
Do you have any idea if the wratten filters will work without the need of additional ir filtration? Would using glass filters instead of gel in the Cooke cause any problems like shifting backfocus, etc...?
Thanks in advance.