Or is PET film (Mylar?) necessary ?
NoAluminum foil is too thick to use as a solar filter: no light can get through itThe best solar filters are made by Baader using a specially developed film, significantly better optically than Mylar, called Astro-Solar filmThis is widely available from most astronomy stores, and mounted in excellent aluminum cells from Jim KendrickI have Kendrick filters for all my telescopes.
