Peter Osman writes: > I once saw an electron micrograph of a CDRom, it was covered with > indentations tens of microns wide by 100's of microns long, so I guess its > acting something like a diffraction gating combined with a diffuse > reflector. > > Has anyone actually had any success using a CD Rom as a signalling mirror > over realistic distances? > One afternoon last summer I was playing with a CD-ROM, seeing how far I could reflect the image of the sun on a distant surface. I was very surprised to see that the reflected solar image 100' away still showed the image of the disk- round with a hole in it! This was completely unexpected, and suggested to me that perhaps these could be used as signaling mirrors. (This would be useful for the paddlers and campers in my office as a number of us have towers many feet high of discarded disks). I wonder if the diffraction grating surface has something to do with this? Perhaps a physicist in the group could reflect on this. -- mike ------------------------- Michael Edelman mje_at_spamcop.net http://www.foldingkayaks.org http://www.findascope.com *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
> > I once saw an electron micrograph of a CDRom, it was covered with > > indentations tens of microns wide by 100's of microns long, so I guess its > > acting something like a diffraction gating combined with a diffuse > > reflector. > > Has anyone actually had any success using a CD Rom as a signalling mirror > > over realistic distances? > >This would be useful for the paddlers and campers in > my office as a number of us have towers many feet high of discarded > disks). > I wonder if the diffraction grating surface has something to do with > this? Perhaps a physicist in the group could reflect on this. > Mike Probably the diffraction effect had much to do with the colors Peter Osman mentioned. We've also tried them out around here in NJ. They could be spotted from hilltop to hilltop; if so, then probably by an airplane as well. Two keys to make them work: One is that you don't want a steady light -- a flash is much more of an attention getter. The other is that you have to be relatively sure that that flash of light is aimed where you want it. That's why signal mirrors have a hole in them. I've found it helpful to stick my hand out in front and line up my fingertips with the target. Then illuminate my fingers with the light as I sight through the hole while holding the CDRom at my face. Then wiggle it a little..... Joe P. *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
<snips> > > Has anyone actually had any success using a CD Rom as a signalling mirror over realistic distances? I will be chaperoning a group of Boy Scouts in the Chiricahua Mountains in July and I have packed a number of handheld optical wireless signaling devices. I figure they can't hurt and in an emergency just might me helpful. I will try to determine how far they can practicably be used. I also wonder whether they could be used to send simple Morse code messages between advance and rear guard hikers (think 18 hikers strung out over high desert terrain). Tom Joyce ------------------------------------------ The information contained in this e-mail message may be privileged, confidential, and protected from disclosure. If you are not the intended recipient, any further disclosure or use, dissemination, distribution, or copying of this message or any attachment is strictly prohibited. If you think that you have received this e-mail message in error, please delete it and notify the sender. *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
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