I've been doing some reading and this old thread seemed to be the most on-point for what I'm looking into. There are some points I'd like some clarification on...
The first is the required reduction in light, which seems there's two answers for. One is reduction for comfortable viewing, the other is for safety. I imagine if you were using a standard refractor with a full aperture solar filter and that filter fell off unexpectedly, I would assume you'd cook your retina before you had a chance to react. What is a ballpark reduction that the image would be even painfully bright but give you ample time to react without damage. I'll come back to this point.
I have a 105mm/1200mm uncoated primary and uncoated secondary. I may also have a prism that I could use inplace of the uncoated secondary if ghosting of the back surface proves to be a problem. I've seen DavidG's design, and I like the elegance of it, but I don't want a right angle after the focuser - just seems there'd be a lot of uncomfortable viewing angles. I was wondering if I could use an ND filter at the EP (post #9 in that thread suggests an ND 1.8 would be sufficient), stacked with half of a polarizing filter since the light reflecting off the secondary will be partially polarized I could spin the EP to tune brightness. Any reason this won't work?
One concern is safety as mentioned above. What if the filters fell off? The light at the EP after two reflections and no filtering will be ~0.16%. I'm sure you'd be seeing spots but is that attenuated enough to be able to react without pemanent damage?
Edited by Biff, 27 January 2023 - 10:58 PM.