A solar filter made using a sheet of Baader AstroSolar Safety Film.
Important – Do not point a telescope or finder at the sun as this will result in permanent eye damage. When using the filter ensure caps are on the finder.
The film comes with instructions for making a solar filter which I modified slightly. Read the original instructions carefully especially the section about safety and damaging the thin film.
- Sheet of AstroSolar film
- A3 black foamboard modelling card
- A4 Foam Craft Sheets black EVA Sponge Paper 2mm
- Black Gaffa tape
- All purpose glue
- Craft knife
Cut the A4 Foam Craft sheets lengthwise into strips approximately 4cm wide. Use Gaffa tape strips to join a number of them end to end to make a long 4cm wide strip.
Wrap the connected strips around the top of the OTA so that it fits snugly against the black plastic top of the tube. The foam will give you some flex. I would make enough strips to encircle the aperture at least twice. Use the Gaffa tape to secure the final strip to the rest of the circle.
On two pieces of A3 foam board, use a compass to draw two circles each with an inner radius of 9mm and an outer radius of 12cm.
Cut these out with the knife to produce two rings that are 3cm wide.
Carefully place the film on its protective paper and move the top layer of protective paper. Hold one of the rings above the film to check that that the film will extend as close to the outer edge of the circle or beyond. Smear one side of the ring with glue and carefully place it on the film without creases or wrinkles.
Turn the circle and film over. Smear glue on the second rin and attach it to the other side of the film. Leave it to dry then cut off any excess film.
Use glue to fix the edge of the foam ring to edge of the filter and rings. Leave to dry. I also used small strips of Gaffa tape to secure the foam ring to the card ring.
Take a piece of A3 foam board and cut a rectangle 24cm long out of it so that it measures 24 x 23.6cm. Find the centre of the card and draw a 12cm radius circle. Cut out the ring with the knife and glue this to the rings and film to make a “handle” for the filter.