I read a few remarks on the web saying that you could see it with the naked eye but I'm having no luck. Well, naked as in no magnification but I do have a #10 and a #5 welder's lens sandwich, taped on the edges. The best info I can com up with is that the sum minus one gives you the protection number.

I put 2 eights together for one of my clients, two of the 4x5 inch or so size. The sun is plainly visible through them, no discomfort. He's 40 miles away, has some small binnoculars and a telescope but says he's afraid to use them. Best I can find is that when placed between the sun and the scope, the #14 filter is safe. Between scope and eye is not safe, of course.

__________________
Te futueo et caballum tuum

1986 300SDL, 362K
1984 300D, 138K