GeezerGazer

Got it! Thanks all!!!

Stu, in re-reading your reply, I think I’m getting that the aperture should be cut off-center so that the vanes and the secondary are outside the aperture opening. Correct?

Thank you Stu.. My plan is to cut the desired aperture out of the heavy plastic 12" factory dust cap. The cap fits above the secondary (and vanes). I'll (very securely!) attach my solar film to the inside of the cap, covering the aperture. To protect the film I'll back it with plexiglass, glass, or clear acrylic. This will be behind the film to avoid direct sun exposure. I'll also paint the cap white or reflective silver for further heat reduction. Think this will work? Thanks again!

I'll be using my Orion SkyQuest goto dob (12" - F5) for casual solar observing. I read somewhere a while back that too much aperture can be harmful to the optics. If this is indeed the case, and as I am making a filter to fit the 12", I can easily choke the aperture down to any diameter. Any recommendations on how much aperture would be safe and effective would be greatly appreciated!