Arthur Carlson wrote: > Tony Moss wrote: > > > >I found a couple of web sites on signal mirrors. > > >http://www.equipped.com/signal.htm#ReflectionsOfLight > > >describes how they work and how to use them. I also made a sketch of how > > >I think it works. The attached bit map file shows this. > > > > I understood the principle immediately from your diagram. 'One picture > > is worth 10000 words' > > Well, I'm sorry, but I haven't caught on yet. Bob refers twice to an image > of the sun, but I don't see from his diagram how or where any image of the > sun should be visible. The web site explains, "The fireball is produced by > retrodirective reflection from small metalized glass spheres adhered to a > mesh grid or cloth disk with a center hole." I could understand it if the > reflective material consisted of needles or flakes perpendicular to the > plane of the mirror, but spheres don't seem to be direction specific enough. > Wouldn't they look bright regardless of the orientation of the mirror? > Please try to share your insight! > > --Art Carlson
Art, The old mirror I have seems to have a steel mesh (about like window screen) with what looks like aluminum oxide abrasive grit on the wire. I don't think that it has to be a pure retro reflector. If it was too good it would blind the operator. I think the partial reflection on the glass surface closest to the eye attenuates the image of the sun. However the"fire ball" they talk about is kind of a fuzzy thing and is brightest in the direction of the reflected sun. "As I said before it also works away from the screen but not nearly so bright. I have always assumed that this scattering is due to surface defects of the glass but heck it is only my theory. I guess maybe I will consult an optical engineer we have tomorrow. I suppose if we really want to know maybe we should contact one of the manufacturers. This discussion reminds me of the CAR TALK letter that Tom and Ray received where the writer wondered if two people who don't know what they are talking about when combined know less than either by themselves. Bob
