[Laser] Large TV Projection Lens

[C. Turner]

Hi Bernie,

> Clint, where did you obtain this lens?  I purchased one about a decade
> ago that sounds much like what you have from a mail-order electronics
> surplus company.  Did it arrive rolled up with a thin sheet of foam to
> prevent scratching?
>    

To answer your questions:

- Unleashing a search on my email archive revealed the the lens was 
bought from the Electronic Goldmine in 2006.  It was P/N G13994 ($49.95) 
- an item that they no longer have in stock.  I haven't any idea what 
the currently-available lenses are like.
- Yes, it did - and in its very own long and skinny box.

> I have also found this lens to be unwieldy, but made a frame from PVC
> pipe and elbows and small bungee cord loops with clamps attached.  The
> lens is "pulled" by the elastic-corded clamps to be centered withing
> its frame, but it's still an unwieldy sail.  But it can melt asphalt
> on a sunny day.
>    

That sounds like a reasonable way to do it.  I'd have no problem with 
drilling a few holes in it for attachment points, but I also know that 
in order to "hold on point" for an optical communications system (e.g. 
to within a 10th of a degree or better) I'd need to have a frame that 
was a lot more rigid than PVC:  Think 2x4 or some sort of truss arrangement!

I've put a divot in asphalt with mine, too (with two people holding it, 
unfurled) as well as exploded a rock and piece of concrete.  With much 
smaller lenses I've demonstrated the vitrification of sand on numerous 
occasions - and if anyone is curious, the red sand from southern Utah 
that I scraped off my Jeep makes green, glass glassy blobs!

Frankly, Fresnel lenses - even those "page magnifier" types - scare the 
hell out of me when they are in the sun:  It would take only and instant 
to get a "4th degree" burn if you put your hand in the wrong place - and 
this is one reason why all of my optical transceivers are "intrinsically 
safe" (e.g. Fresnels covered) when they are stowed.  Even a small lens 
will instantly incinerate any organic substance that falls at the focus 
under anything resembling full sun!  Walking around with such a lens in 
the daylight is, in some ways, like carrying a lit blowtorch around - 
but they are still great fun!

73,

Clint
KA7OEI
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