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Hi Daniel,
I have made two filters for my 8" SCT and one filter for my 12" Newtonian with a sheet of the Baader film.
I used cardboard purchased from a newsagent to make them. The cardboard is about 1mm thick. I need one sheet of the cardboard to make a filter for my 8" SCT, 3 sheets for the 12" Newtonian.
I cut strips of the cardboard 5cm wide along the long side of the cardboard. I use 5 strips for an 8" and 8 for a 12". I then use packing tape (that ugly brown stuff) to join the strips together into one long strip 5cm wide.
I then wrap this tightly around end of the telescope where it is going to fit and join the end with the packing tape. Then I remove the ring of cardboard and wrap tape around it in about 8 places to hold the coiled cardboard ring together.
I then put it back on the telescope to make sure it is a good fit. I like it to be so tight that it is quite hard to get it on and off.
Now you measure the outer diameter of the cardboard ring while it is attached to the tube and draw two circles of that diameter on the remaining cardboard. At this time I mark off six points around the perimeter of each circle with the compass. At each of these six points on both circles I roughly draw a tab about 3cm long and 2cm wide to secure the disks to the ring.
For a full-apeture filter I now use a compass to draw circles for the apeture of the filter material. I leave about 2cm around the edge. I then cut these out with a knife and cutting board.
Next I cut out the two disks each with 6 tabs. I use a stanley knife.
If making an off-axis filter, I now line up the two discs so that the 12 tabs are evenly spaced around. Now mark the centre of the off-axis filter circle with a pin that you push through the top disk and into the second disk. Also place some matchmarks so you can line the discs up in this position again later. Draw the circles for the off-axis filter on the two discs and cut them out with a knife.
I then put double sided tape in strips around the filter apeture and secure a piece of the filter material to the disc then cut away the excess. The material should look relaxed, not streched. I try to get the material flat, place the disk on top and press down around the edges to secure the tape.
Now put more double sided tape on the other disc in order to secure the two disks together. Using the match marks made eariler line up the disks and press them together.
Finally, I secure the disc to the ring with packing tape.
I also find a box to keep it in.
Anyway, thats how I do it.
Hope this helps.
Have fun,
Doug
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