OK I was talking with a friend about generating electricity, and the subject came up of using lenses to create heat. Maby run a sterling engine with one.
He mentioned a friend had removed the parabolic lenses from inside of a television. The lenses acording to him are strong enough to burn a hole on cloth and other materials.
Well I have to have one. I am always in the need of new toys. I have a few questions before smashing up some tvs for fun.
Ok first of all is there such a lens inside a tv tude.
The burough land fill almost always has at least one tv hanging around and come christmas there will be plenty with all the flat screen upgrades. So the supply wont be a problem.
I have heard the dangers of latent electricity inside of a tv and the dangers even if it is off. I am aware of the dangers of the phosporus coating on the inside that is toxic. I am aware of the vacuume and resulting implosion/explosion if the tube is shattered. The air and resulting dust my be danerious as well.
I am still gonna get me some of the lenses though. If they are in there.
Has anyone here ever done this? Is there a way to get inside without damaging the lens? Do you have any good recomindations?
Also, if you want a large, cheap, rough-and-ready convex reflector, there are easier and less dangerous ways to make one; here’s one I’ve often wanted to try:
Get a rigid container with a large diameter
Run a bead of silicone sealant around the rim
Stretch a large sheet of aluminised Mylar across the top (like a drum skin)
Fold over the edges and secure them to the sides of the container
Evacuate some of the air from inside the ‘drum’ - the mylar skin should take up a convex shape.
I have no idea what you’re talking about – I don’t know of parabolic lenses or mirrors inside TV tubes.
If you just want to burn holes in things there’s no need to get a parabolic as opposed to a simple spherical mirror (or lens). And if the radius of curvature is large compared to the size of the item, you’re going to be hard-pressed to tell the difference anyway with optical testing.
Plenty of places sell large-area mirrors and lenses. Try Edmund Optics (formerly Edmund Scientific), or surplus houses.
If you’re really set on making a parabolic mirror, you can do what Robert Wood did a hundred years ago – rotate a big container full of mercury. (The idea was used in Raymond Z. Gallun’s SF story “Old Faithful” back in the 1930s. I note that there are several sites devoted to such liquid mirrors on the 'net). Except that people don’t like to be around mercury anymore.
I wonder if the OP’s friend is talking about the front glass of an old-fashioned ‘goldfish bowl’ TV - these were pretty uniformly convex, so the reverse side would make a fairly good concave mirror, if lined with foil or similar (assuming you could separate it cleanly from the rest of the tube without breaking it, or killing or injuring yourself.