A lot of welding filters (#12 shade, electric arc welding) were being sold at the Stellfane swap tables,
and while they worked great directly over the eyes, on a scope (extensively taped, lid taped well) 'moon-port',
the image came out quite blurry. I figured out the issue: the tempered glass has a lot of thickness and
strain variation, so the uneven surface is a blurry 'lens' over longer distances.
And....using it right over your eyepiece would likely bake and wreck your eyepiece...
So.....only good for a 1X over-the-eyes view, unfortunately.