I was experimenting with solar projection with my 8" scope. I first stopped up the aperture to about 3". All was well. Then I went for full aperture. The images were sharper.
But then the images went foggy. And I couldn't get them in focus. And smoke started coming out.
The lenses cleaned off fine with acetone. But I wonder how I can find a metal replacement spacer.
So, that's a warning for solar work: don't assume that just because the eyepiece tube is metal, the inside is metal, too.