A few people have asked me about the solar filter used on my Mewlon 180 F12 ‘scope, so here are some details.
The full aperture solar filter that I use on my telescope for high magnification astrophotography is made from
Baader AstroSolar ™ Photo Film which has an Optical Density of OD = 3.8. The Baader website writes that:
“AstroSolar™ PhotoFilm is not intended for visual observation. PhotoFilm is only for use with telescopes for high magnification photographic work. Do not use it for producing solar eclipse viewers, do not mount it onto DSLR camera lenses.”
For visual use, Baader also produce AstroSolar ™ Safety Film which has an Optical Density of OD = 5.
WARNING: Never look at the Sun through an optical instrument without a specialised, full aperture, astronomy filter – otherwise you will destroy your eyes.
To make my filter cell, I used high density, closed cell foam. This is the tough stuff that is hard to compress, not the soft, floppy stuff which offers little support.
The following photos provide some details on how I made the filter and importantly, how I secure it to the front end of the telescope so that a gust of wind will not blow it off.
- After cutting the correct length of foam strip, I joined the ends of the strip to form the cell body, using contact adhesive, staples and gaffer tape. I used contact adhesive to glue the solar film onto the cell body and contact adhesive for gluing the foam ring to the solar film at the top of the cell.
- I drilled 1/8 inch pilot holes spaced at 120 degree intervals around the circumference of the cell body and fitted x3 off ¼-20” nylon bolts (trimmed to length) to act as retaining lugs for a rubber retaining band.
- The large rubber retaining band was purchased from Bunning’s in their electrical cable section – I removed a plastic slider so the band fits nicely around my OTA.
The Finderscope filter was made using the visual use Baader AstroSolar ™ Safety Film which has an Optical Density of OD = 5.
- I used 1 inch thick closed cell foam and glued the Safety Film to the foam using contact adhesive.
- My finder is close to the OTA so I had to cut a flat side on the finder scope filter cell, to fit it to the finder scope – it is a tight fit and will not blow off.
If you do not know what you are doing, do not risk your precious sight – purchase an approved, ready made filter suitable for your particular ‘scope.
Cheers
Dennis