There is a small difference between white light sunspot observing and a solar eclipse. During an eclipse, at the start of totality, the solar filter needs to be removed quickly and without applying any force to the optic that may shift it away from the sun, a few minutes later when totality ends, it needs to be replaced also without disturbing the optic. So anything that pushes on the
Baader Astrosolar film has four advantages over many other films and glass filters.
1. The Baader film is only 10 microns thick giving it a near perfect optical transmission quoted by
Baader as 96-98 Strehl.
2. The film is coated both sides so slight scratches or missing pinholes of coating won't affect the
eye safety of the coating
3. Being so thin, it doesn't alter the focus the way some glass filters or thicker black polymer filters do.
This means that as the solar crescent is thinning, I can focus on the filtered image and be ready and
focussed to capture the first fleeting phenomena of totality - Baily's Beads and the diamond ring
without wasting time refocussing.
4. It is relatively cheap. I purchased a 20in x 40in sheet 20 years ago and have made a variety of filters
for wide angle and telephoto lenses, small refractors, a 4"maksutov and my 8" cassegrain and I still
have plenty left.
In this article, I give detailed instructions how to securely attach a Baader Astrosolar film holder to your scope, or any other type of thin film to make a secure solar filter mounting that won't blow off but can be removed quickly. The film is recessed so that it doesn't get damaged if placed on a rough surface. I have made a number of flange pieces over the years for different telescopes but I am still using the same Astrosolar film in its recessed holder that I mounted in 2002.
The article describing the construction is here:
https://joe-cali.com/eclipses/EQUIPMENT ... lters.html