If you made the mistake of buying any Cokin filters, believing they had decent optical properties, now is the time to put them to good use by taping them in place. You may be able to use your standard glass filters by taping them in place. I think it would be easier to hinge a plastic or gelatin filter to drop over the pinhole when you open the sliding "shutter" of the Zero Image cameras. I haven't tried it but it looks feasible.