# Parabolic mirrors and fresnel lenses



## Warwalk (May 25, 2011)

I'm sure that most of us have seen these devices at work, even if only in a video. They can start a fire almost instantaneously. They can flash-boil water in a jar in less than a minute (tho the container tends to shatter as a result of the high heat). Heck, people have even set up rigs where they can cook their bacon and eggs in times approaching a regular stovetop.

The only trouble with these devices as that they are very unweildy, very large, and ultimately very dangerous (one hand inadvertently swiped in front of the focal point could cause second degree burns).

Has anyone seen one of these harnessed in a manner to where they are somewhat safe? It would be interesting if someone were able to ~ either through mirrors or reflective shielding ~ create a commercially viable cooking device. Any thoughts? Have any of y'all not seen these things in action?


----------



## Bandit (Oct 5, 2008)

The only experience that I have had with a Fresnel Lens was the 4th Order Lens Fresnel lens that was in the lighthouse that I was Officer in Charge that We had to polish without slicing Our fingers off .
The lens produced 350,000 Candle Power and was visible for 14 miles . ( it was also pretty bright up in the lantern room ) LOL
Bandit


----------



## rsbhunter (Mar 25, 2012)

I have done alot of research on suppliers, and as such, have learned some...This method is used alot in undeveloped and underdeveloped countries. They work! But, as with anything not hooked up to 110/220 or gas, it does require alittle bit of effort and time....My honest belief is that , if one is gathering items to have in case of unfortunate times, these need to be on the list......Along with water filtration, etc....There are mirrors out there that are 36"-44" that are SERIOUS!!!!! I keep a plastic , roll up Fresnel lens in my backpack for firestarting in an emergency....There again, they do require moving to follow the sun for highest effieciency, but it's better than rubbing 2 sticks together!!!rsbhunter


----------



## ||Downhome|| (Jan 12, 2009)

I've got several from old rear projection TVs. 
Honestly all your doing is concentrating the solar energy.
if you built a solar cooker with the same collection area you would have the same cooking ability but easier to use. 
though solar cookers are not suitable to all cooking methods. 
I suppose if you positioned the focal point on a piece of plate steel you could then use it like a hotplate or heat rocks with it. lots of cultures used hot rocks for cooking.
you can also use only part of the "beam" as in closer to the lens so its not so concentrated like at the focal point.


----------



## rsbhunter (Mar 25, 2012)

The mirrors i'm talking about are made for cooking, etc...the focused beam reaches temps that will scare you...2251 degrees F (measured by an infared thermometer.!!!! DO NOT PLACE HAND AT THE FOCAL POINT!!! The place selling these suggest wearing welding goggles if you feel the need to look at the mirror while in the sun....These really are serious tools for cooking....rsbhunter


----------



## Warwalk (May 25, 2011)

I've wondered whether Pyrex (the clear glass type pots that are designed to stand up to intense heat) might be a good choice. I've seen applications where these devices are laid out flat on the ground ~ much like a contact lense might sit on one's counter if they dropped it ~ and then a pole is laid across the top, and a pot is hung from the pole (much as in the 1700's people would have a pot that could be swung over an open fire). @ Rsbhunter - where have you seen these for sale?


----------



## rsbhunter (Mar 25, 2012)

HUGE 35" PARABOLIC MIRROR

And pryex, to the best of my knowledge is not the best (clear) but cast iron, or any pot/kettle etc that is black....rsbhunter


----------



## solidwoods (Dec 23, 2005)

I'd say heat water with it and use the hot water.
jim


----------



## Jenn (Nov 9, 2004)

DH made one for fun from gluing silver mylar on an old sat dish. Burnt his fingers a bit, heated beans in a pot for us. Working on safe science expo for kids as a party trick.


----------

