I understand better. The "filters" I had in mind come in the form of a foil. The foil is micron thin, so there would be no reflection between the two sides of the filter, which is the main problem with glass filters. There may be reflections between the lens and the back side of the foil but, first, the coating of the lens should take care of that and, second, one could build a device to hold the foil at an angle to suppress these.
I found some foil which I had, but it is an old model. It dates back to the 1999 eclipse. I will try it, but I am not sure that present foils are the same.
Edit: the transmission curve of a popular astro foil is given
here and there is a problem: due to interference between the two very close layers, the spectrum exhibits a series of absorption rays. I don't think this will work...
Edit 2: about size of astro filters. They are usually available in 2 inches size and there are step-up rings from that size to common lens diameters.