Solar Filter Mount for Small Telescope (<120mm or 4.7") with Protective Case

Design Considerations

I recently purchased a SkyWatcher Star Travel 102mm refracting telescope and wanted to DIY a solar filter for sun observations. I was inspired by several different designs but none I saw were adaptable for my specific scope so I set out to create my own. I designed for ease of printing and assembly using just 4 M3 bolts and nuts plus the solar film and double sided tape. The STL files included are for a mount that can attach to a tube with an outer diameter of about 116mm (the diameter of the dew shield on my scope). I include Fusion and STEP files for easy modification for other telescope dimensions.

Insert the CRITICAL safety precautions about never looking at the sun directly, and making sure that the filter is intact and properly installed before making any observations of the sun through the telescope. YOU CAN LOSE YOUR EYESIGHT FROM IMPROPER VIEWING OF THE SUN!!

Printing Notes:

As the solar filter will get heated up by direct sun exposure, the use of more heat tolerant PETG is recommended over PLA. In Orcaslicer I used concentric top and bottom shells for a nice symmetrical appearance. You may need to use fine grain sandpaper to smooth out any blemishes on the two surfaces that will clamp the film, to reduce risk of tearing the fragile solar film.

Materials Used:

Baader AstroSolar Safety Film (optical density 5.0)
(I purchased the A4 200x290mm size and sized my holder design to be 145mm square which allows making two filters from one sheet)
Double-sided tape
4 M3 8mm bolts
4 M3 nuts

Assembly Instructions:

1. After printing, test fit all the parts before installing the film. Different filaments and printer settings may result in shrinkage and dimensional changes, and the tolerances I included in this design are pretty tight. Make sure that the Mount Base fits securely over your OTA or dew shield. It must be tight enough to not fall off or get accidentally knocked off during observations. You can use masking tape on the inside of the Base cylinder to get a tighter fit over your telescope tube.

2. Use very fine grain sandpaper to smooth the two faces of the Base and Cover that will be in contact with the solar film, to reduce risk of tearing the fragile film.

3. Use a sharp blade to cut the solar film to a rectangle or square with 145mm sides. If you are using the A4 Baader solar film, you would cut the sheet exactly in half.

4. To attach the solar film, put an even ring of double sided tape on the top flat surface of the holder Base. Baader states that the film must not be pulled taut when mounted, so what I did was place the solar film on a clean flat table (with the protective sheet on the bottom) and lined up one edge of the Base along the edge of the film, and then gently laid the Base down over the film. I then pressed down on the edges and corners of the base to make sure that the film was nicely sticking to the double sided tape. Then I used the sharp knife to cut off the excess solar film around the Base. The film should be flat but not taut; it should have some give if you blow on it.

5. Before attaching the Cover, use the sharp knife or a needle to poke some holes in the film through the screw holes. You don't want the film to rip when you put the bolts through the holes, so make sure there is enough clearance for the bolts to slide easily into the hole. Then attach the Holder Cover and use the M3 bolts and nuts to tighten the cover down over the base to clamp the film in place.

6. Solar filter film is very fragile, so that's why I designed a case to go with the mount.

Clear skies and happy observing!