Message-Id: <l03110700b1f697ee4c4a@[192.174.2.173]>
In-Reply-To: <6FD1AD999BBED111854E00A0C99DBAEB0B5A52@mainex3.asu.edu>
Date: Tue, 11 Aug 1998 17:02:58 -0800
To: Steve Beeson <beeson@asu.edu>
From: Paul Doherty <pauld@exploratorium.edu>
Subject: Re: pinhole Rainbow maker
Hi Steve
The best science article on glass bead rainbows is
"Rainbow Dust" by Frank Crawford.
American Journal of Physics
vol 56 #11 p1006-1009 1988
The highway department retroreflective beads give a much better rainbow
than the sand blasting beads. (The sand blasting beads work well in
sunlight and work some in minimag light. The highway beads work great in
minimag light.)
The highway beads have an index of refraction of n = 1.51.
They are retroreflective but not perfectly so, they send the beam back in a
cone with a 22 degrees half-angle... the angular radius of the rainbow.
Each eye sees its own rainbow. Blink back and forth from one eye to the
other. Notice that the rainbow moves back and forth relative to the minimag
lightbulb, or other reference point. With both eyes open the brain fuses
the two images, one from each eye, into a rainbow with a particular
3-dimensional depth.
By the way remove the retroreflective head completely from the minimag and
leave the bare bulb for the best rainbows.
Paul Doherty