Solar Eclipse Filter for Canon EF 100-400mm L IS ZOOM lens

This solar filter body has an ID (inner diameter) of 91mm so it fits snugly over the end of the outer rubber rings of the lens. For reference, 91mm is just over about 3.5 inches in diameter.
I printed the pieces separately to eliminate stringing between parts.

You will need the actual solar film to construct this, as the 3D printed parts are only the frame. I used Thousand Oaks Optical silver black polymer film.
https://thousandoaksoptical.com/shop/solar-filters/silver-black-polymer-sheets/

This is a threaded design and the solar film is held in place by pinching it in between the body and cap.  They are threaded with a ultra-fine thread.  This thread can be frustrating with 3D printed parts, but some patience is useful. Use a 0.4mm nozzle and very fine layer height for the threaded feature (0.07mm - 0.10mm layer height). I used variable height printing in PrusaSlicer, with the threaded region set at 0.07mm and 0.2mm above the threads. I used PLA+ for these and had good luck with the fine threads.  Work the threads in by twisting back and forth and then cleaning any plastic debris/dust and the then the threads should be relatively smooth. I scaled the solar film template disc to 91mm OD (outer diameter).  Use an X-acto knife to cut around it.  Finally, assemble the filter with the film.