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InvisiblelIllIIIllIlIIlIlIIllIllIIl
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Registered: 12/16/04
Posts: 11,123
Loc: Texas
a flat magnifying glass
    #7790494 - 12/22/07 08:55 PM (16 years, 1 month ago)

when i was a kid i had this flat magnifying glass

i'll describe it:

-it was a square sheet of flexible clear plastic
-it was uniform thickness
-it had a pattern in it like concentric rings

any idea how this worked? it was great for starting fires... it seemed to work because of the rings in it, which were an engraved pattern of growing circles starting from a point in the center of the sheet

i think it was the same size as a letter sized paper with holes to fit in a binder

it really wasn't very thick, maybe 1 mm thick


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OfflineToTheSummit
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Re: a flat magnifying glass [Re: lIllIIIllIlIIlIlIIllIllIIl]
    #7790509 - 12/22/07 09:01 PM (16 years, 1 month ago)

Its called a 'fresnel lens' I think.


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InvisiblelIllIIIllIlIIlIlIIllIllIIl
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Registered: 12/16/04
Posts: 11,123
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Re: a flat magnifying glass [Re: ToTheSummit]
    #7790556 - 12/22/07 09:23 PM (16 years, 1 month ago)

ahh thanks



that is sort of how it looked only the rings were much smaller

it must work on the same principle

Quote:

A solar forge is a device that uses the power of the sun to melt materials, such as asphalt. A large Fresnel lens, usually rectangular and several feet long on each side, is positioned as a lid of a hollow standing cylinder. The lens focuses the sun's radiation to a point inside the cylinder, where the material to be melted is placed. The effect is the same as a magnifying glass used to burn a dry leaf, except that the heat achieved is much greater.

Solar forges work best in desert areas where there is plenty of sunlight. They are dangerous to approach because of the great heat and light generated. A safe way to handle the danger is to cover the lens when not in use. Solar forges are easy to build, because they consist of only two parts. Other optional parts are: a cover, a pollution-control device (for the smoke), a vent, a temperature gauge, protective fire-proof clothing, and gas masks. Solar forges have the benefit of cheap construction and no fuel cost, unlike other forges. However, they cannot achieve the higher temperatures that other forges can. They are good for melting materials with low melting points.




http://en.wikipedia.org/wiki/Solar_forge

neat


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Invisibledaussaulit
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Registered: 08/06/02
Posts: 2,894
Loc: Earth
Re: a flat magnifying glass [Re: ToTheSummit]
    #7790630 - 12/22/07 09:50 PM (16 years, 1 month ago)



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OfflineSeussA
Error: divide byzero


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Re: a flat magnifying glass [Re: daussaulit]
    #7791371 - 12/23/07 01:53 AM (16 years, 1 month ago)

Lots of fun.  I had a huge one when I was a kid.  Got it off an OLD television magnifier. (The original large screen TV :grin:)  Used to be able to melt copper pennies, start wood on fire in a second or two, explode concrete, and melt asphalt.


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