I turned a beat up Isolette into a pinhole --- The entire front of the camera-- bellows, lens, door, everything ends up being removed-- the front of the camera is covered with foamcore and a pinhole--- the size of the hole was f128, and covers 6x6 fine. I have a filter ring epoxyed to foamcore to put a lenscap on the outside and a brass pinhole in the center

--- You will need to do your own measurements and calculations on your own specific camera and construction job. Use sites like www.mrpinhole.com/ to help you with you calculations. There is no reason to need the red window to go away.