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I recently heard about a Fresnel lens to magnify infrared heat. Google search isn't cooperating with my grasp of the language - just getting bits and pieces. Anyone here know anything about this? So many possibilities, so little time. Bumpkin

I remember reading about it a while back. My search couldnt find it either. What I think it was was a holograghic prism that shifted each wave lenght into infrared. Hope that helps a little.

Thanks fullofhotair. Yeah, I might have heard about it in relation to motion sensors, and the thermal significance didn't occur to me until the source was gone. It would be neat if you could focus low-grade heat sources. Bumpkin

Bumpkin ;
The first sight is what is called an infrared Fresnel lens, I don’t think this what your looking for ,but maybe it is. The second sight is what I might have remembered. It isn’t an infrared lens but a hologram on the surface that can direct light from almost any angle, to one focal point. You don’t have to move the lens all day. Wouldn’t that be a good match up with an improved Fresnel?
http://www.edmundoptics.com/optics/opti ... enses/2042
http://thefraserdomain.typepad.com/ener ... c_sol.html
http://youtu.be/eZx4XRk6rI8
http://oilprice.com/Alternative-Energy/ ... Steam.html

fullofhotair, thanks for the links.
Here's another one:
http://en.wikipedia.org/wiki/Passive_infrared_sensor
The jist is that some translucent materials will transmit, and can be used to refract, energy in the infrared spectrum. The refraction, such as in a Fresnel lens, is used to magnify heat for thermal sensors. The energy harvesting implications of a very large lens of this type for focusing heat from any thermal mass, day or night, are obvious. So there must be some equally obvious hang-up I'm not seeing. I don't want to make my own lens, only wondering if such was available to focus the heat from one side of my woodstove onto a smaller area - just a passing distraction. Bumpkin

There are 2 types spot and linear I like linear as the heat is still good and multiple hot cylinders at once can be heated.

http://www.greenpowerscience.com/

Coog