What can be done with this lens?

[Ed Norman]

I saw this in a catalog I got and have been trying to find a way to use it to heat water. If it melts pennies it should heat water, but might not be controllable.

The Mother Of All Fresnel Lenses

It came from either outer space, or a projection TV. Our largest Fresnel lens measures 49-1/8" x 37-1/8" x 1/16" or 1/8" thick, with a 42" focal length. Build your own lighthouse or projection TV, teach optical properties to students, or just turn your 21-inch model into one with a tavern-size picture. Held in the sun, the lens will concentrate rays enough to cook eggs or torch lumber. And, under adult supervision in the parking lot, employees of a certain un-named scientific and surplus purveyor actually melted pennies in seconds. Extremely cool and done strictly, we assure you, to determine the lens's focal length. Do not, we shouldn't have to remind you, store this puppy in direct sunlight. Or let the underage or under-mature sneak it into the sunlight.

http://www.sciplus.com/category.cfm/subsection/21

[wy_white_wolf]

You could build a larger version of this

Yes they can be used to heat water. Work good to heat a small volume to high temperature.

The main problem is they need a tracker to keep them focused.

[Harry Chickpea]

You do realize you can get this same lens for free if you take an old 50" rear screen projection tv and remove the screen from it? That is undoubtedly where they are getting theirs.

Simply put, it is not suitable for heating water. You would need too much supporting tech to make it work.

[cowboy joe]

Yeah, may not be usable for heating a large volume of water but it's really cool. Sadly I fall into the under-mature category so I won't be able to have one.

How about a solar cooker? Here's a link to a site where they built one using a similiar lens.

http://www.solarcooker-at-cantinawes...lar-grill.html

[Ed Norman]

Originally Posted by Harry Chickpea

You do realize you can get this same lens for free if you take an old 50" rear screen projection tv and remove the screen from it? That is undoubtedly where they are getting theirs.

Simply put, it is not suitable for heating water. You would need too much supporting tech to make it work.

Old 50" projection TVs aren't exactly growing on trees around here. I've never even seen one and wouldn't know where to find one. But if I ever do see one at the dump, I will own the fresnel lens from it.

Originally Posted by cowboy joe

Yeah, may not be usable for heating a large volume of water but it's really cool. Sadly I fall into the under-mature category so I won't be able to have one.

How about a solar cooker? Here's a link to a site where they built one using a similiar lens.

http://www.solarcooker-at-cantinawes...lar-grill.html

Are you under-mature because of age or because you would have to try and melt everything you found, like I would?

The cooker looks interesting, but the thought of burning my hand off at the wrist while reaching to flip a burger is off-putting.

Maybe run some water lines through some kind of heat-resistant material and let the rays focus on that to heat the pipes inside. That would hold down the chance of burning a hole in the pipe if it ever had an empty spot, and would also give more mass to transfer the heat.

[Roadking]

take a look at http://www.builditsolar.com/index.htm It has many DIY projects using Fresnel type lenses, magnifying sheets, etc. Plus, we all remember using a magnifying glass to wreak havoc on the unsuspecting ant hill. A lot of fun available, and some practical uses as well. I have built several solar thermo-siphon heaters from plans from this site.
Matt

[cowboy joe]

Originally Posted by Ed Norman

Are you under-mature because of age or because you would have to try and melt everything you found, like I would?

Definately the later...I been known to run with scissors too!