This holder can be used with solar filter sheets, like Baader Astrosolar, and fits lens with 67mm threads. The back piece of the holder is wide to shade camera body from sun heat.

Cut a 70mmx70mm square from the solar filter sheet, put it between the two pieces of the printed holder and use few drops of glue to hold the two pieces together. Don't glue the sheet to the holder, use the glue just between pieces, so the thermal expansion doesn't stretch the sheet.